The development history of heavy plate production in China was sorted out, and the development of heavy plate in China was divided into five stages,i.e.initial stage, accumulation stage, development stage, maturity stage and optimization stage. The characteristics of each stage were analyzed from the aspects of mill specification, equipment level, capacity scale and so on; The technical progress and development of key processes and equipment for heavy plate, such as hot delivery and hot charging, reheating furnace, rolling mill and leveler were described; The development, application and advancement of typical heavy plate products, such as special shipbuilding steel and offshore engineering steel were elucidated; The future development of heavy plate in China was prospected and suggestions were put forward.

Automobile lightweight is an important means to achieve energy saving and carbon reduction. Hot-stamping steel with the advantages of high strength, light weight and high fatigue resistance is widely used in the automotive field. However, it is difficult to control the oxide scale stably during the rolling process of hot-stamping steel. In order to further improve the surface quality of hot-stamping, the oxidation behavior of 1 800 MPa hot-stamping steel under different coiling temperatures and environmental atmospheres was studied by means of SEM, EDS, LM spectrometer and thermal simulation testing machine. The results show that the outer oxide layer of experimental steel is mainly composed of Fe₃O₄, FeO and Fe-Si spinel layer; When the coiling temperature is less than 550 ℃, no internal oxide layer is found in the experimental steel under air or ambient environmental atmosphere conditions; As the coiling temperature increases, point-like internal oxidation occurs at the interface of the experimental steel matrix. When the ambient atmosphere is air, the thickness of the inner oxide layer increases from 2.5 μm to 5 μm; when the ambient atmosphere is argon, the thickness of the inner oxide layer is greater than that of the air atmosphere. When the cooling rate is 1.5 ℃/min, as the coiling temperature increases, the internal oxidation shows a tendency to increase.

The development history of heavy plate production in China was sorted out, and the development of heavy plate in China was divided into five stages, i.e, initial stage, accumulation stage, development stage, maturity stage and optimization stage, The characteristics of each stage were analyzed from the aspects of mill specification, equipment level, capacity scale and so on; The technical progress and development of key processes and equipment for heavy plate, such as hot delivery and hot charging, reheating furnace, rolling mill and leveler were described; The development, application and advancement of typical heavy plate products, such as special shipbuilding steel and offshore engineering steel were elucidated; The future development of heavy plate in China was prospected and suggestions were put forward.

The excessively high hardness of rolling-state 42CrMo steel bars significantly affects subsequent processing. Optimizing the rolling and cooling processes is crucial for reducing the hardness. Dynamic CCT curves of 42CrMo steel were drawn using the DIL805A phase transformation instrument and S60/58507 simultaneous thermal analyzer to investigate the effects of rolling and cooling processes on the microstructure transformation and hardness. The study reveals that during single-pass controlled rolling, ferrite preferentially nucleates at original austenite grain boundaries under various rolling parameters, followed by nucleation and growth within the grains. Lowering deformation temperature and increasing deformation degree significantly increase ferrite content and reduce hardness. In two-pass deformation and controlled cooling experiments, the ultra-fast cooling—slow cooling—air cooling process further raises ferrite content. At a slow cooling rate of 0.1 ℃/s, ferrite volume fraction reaches 41.79%, achieving rolling-state hardness well below the standard (≤241HV). A slow cooling rate slower than 0.2 ℃/s ensures hardness meet cold-forming requirements (≤220HV).

The development history of heavy plate production in China was sorted out, and the development of heavy plate in China was divided into five stages, i.e, initial stage, accumulation stage, development stage, maturity stage and optimization stage, The characteristics of each stage were analyzed from the aspects of mill specification, equipment level, capacity scale and so on; The technical progress and development of key processes and equipment for heavy plate, such as hot delivery and hot charging, reheating furnace, rolling mill and leveler were described; The development, application and advancement of typical heavy plate products, such as special shipbuilding steel and offshore engineering steel were elucidated; The future development of heavy plate in China was prospected and suggestions were put forward.

Marine engineering equipment faces significant challenges in achieving a coordinated design that integrates lightweight and properties with high strength and toughness under harsh service environments, such as those characterized by high salinity, high humidity, and impact loading. Traditional steel used in offshore platforms struggle to effectively balance the requirements of lightweight and mechanical properties. In contrast, Fe-Mn-Al-C lightweight high strength steels have emerged as highly promising alternative materials due to their lower density (10%-20% lighter than traditional steel), excellent strength and good weldability. Currently, under the "rolling + solution treatment" process route, the appropriate design of Al element content plays a crucial role in enhancing the properties of Fe-Mn-Al-C lightweight high strength steels. By employing characterization techniques, including optical microscopy(OM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD), the influence of Al element content on the microstructure and mechanical properties of the experimental steels during the staged preparation process was investigated. The results indicate that when the mass fractions of Al element are 5%, 8% and 12% respectively, the microstructure of the experimental steels after rolling treatment consists of austenite and ferrite phases. As the Al content increases, the morphology of austenite transitions from equiaxed to acicular, and the proportion of high-angle grain boundaries increases from 57% to 89%. When the Al element mass fraction is 8%, the rolled experimental steel exhibits the optimal strength-ductility balance, with a tensile strength of 747 MPa and an elongation of 28.3%. After solution treatment at 1 000 ℃, the comprehensive properties of the experimental steel with Al element mass fraction of 8% are further enhanced, achieving a tensile strength of 701 MPa, yield strength of 612 MPa, and elongation of 38.3%. Its fracture surface displays characteristic dimple patterns indicative of ductile fracture. Through optimization of Al element content and process control, precise design of the dual-phase microstructure in Fe-Mn-Al-C lightweight high strength steels have been realized, laying theoretical foundations for developing marine engineering steels.

To improve the low-temperature impact toughness of thick gauge offshore steel and achieve an excellent strength-toughness balance, the rolling and water cooling processes of 80 mm thick ness EH36 plates produced by a factory were studied. By regulating the microstructure through seven different processing schemes, the aim was to improve the strength-toughness match and low temperature impact toughness. Tensile tests, impact tests, and metallographic observations were conducted on the trial plates. The results indicate that with a low-carbon microalloyed chemical composition, by ensuring at least two passes with a reduction rate exceeding 10% during the roughing rolling stage, an intermediate slab thickness of over2h (where h is the thickness of the finished steel plate), controlling the finishing rolling temperature below 800 ℃, and the final cooling temperature below 300 ℃, a refined acicular ferrite and bainite microstructure can be obtained, resulting in a good strength-toughness match of plates. Further optimization was achieved by introducing a relaxation treatment before water quenching to 300 ℃, which promotes precipitation of proeutectoid ferrite and enhances microstructure uniformity. This dual-process strategy significantly improved the impact toughness of the plate.

Aiming at the cracking problem in the forming process of 700L beam steel for automobile, the causes of cracking were studied by means of macro-morphology and microstructure analysis and mechanical property test, and the corresponding improvement measures were put forward. The results show that there are cracks with a length of about 2 cm in the transverse and longitudinal directions of the bending position of the beam steel. There are inclusions dominated by Ti and N elements near the cracks, with an average size of about 13 μm and an area of about 44 μm². The difference of tensile strength and yield strength between the undeformed area and the bending deformation area of the beam steel is small, but the elongation of the tensile sample at the bending deformation area is 7.8%, while the elongation of the tensile sample at the undeformed area is 16.9%, and the crack arrest ability of the bending deformation position of the beam steel is reduced. The compound compounds of K, Na and other elements were found at the necking of the tensile fracture of the beam steel, which led to the increase of cracks, pores and other defects in the beam steel, the decrease of plasticity and toughness, and the increase of cracking probability. By optimizing the smelting process, the content of impurity elements such as K and Na can be reduced, and the aggregation of composite compounds such as K and Na can be avoided.Meanwhile, selecting the appropriate slab heating temperature and holding time in the process of rolling, the size, quantity and distribution of inclusions such as TiN can be controlled, the cracking risk of 700L beam can be reduced.

In order to benchmark the S355 steel of the European Union, GB/T 1591—2018 requires upgrading the original Q345 steel to Q355 steel. However, there is currently limited research on the mechanical properties of Q355 steel at high temperatures and after cooling both domestically and internationally. The reliability of Q355 steel in power fire scenarios is highly uncertain. Therefore, the mechanical properties and microstructure of Q355B steel under different heating temperatures, holding time and cooling methods were simulated and analyzed by means of high temperature confocal microscope and high temperature tensile test. The research results show that at the highest temperature of 1 100 ℃ in power fires, the microstructure of Q355B steel is austenite. With the increase of holding time, the grain aggregates and grows, and annealing twins appear. After holding at 1 100 ℃ for 45 minutes, the grain size does not change; In the range of 200-1 100 ℃, the yield strength and tensile strength of Q355B steel decrease significantly with the increase of heating temperature, and the plasticity increases continuously. At 1 100 ℃, the tensile strength and yield strength of Q355B steel are only 24.9 MPa and 11.4 MPa, and the holding time has little effect on its strength. When the heating temperature is less than 800 ℃, the cooling method has little effect on its mechanical properties. After the temperature exceeds 800 ℃, the water-cooled specimen has a mixed microstructure of ferrite, pearlite, and martensite, and as the temperature increases, the proportion of martensite gradually increases, leading to a sharp increase in strength. Based on the experimental results, mathematical models for the yield strength and tensile strength of Q355B steel under different cooling methods were established, providing reference basis for the application evaluation of Q355B steel in power fire accidents.

With the increasing demand for lightweight and safety in the automotive industry, the use of steel/aluminum/magnesium/aluminum/steel composite plates instead of pure steel plates can not only achieve weight reduction, but also utilize the property advantages of composite plates to meet the strength requirements of automobiles steel. Steel/aluminum/magnesium/aluminum/steel five-layer composite plates were successfully prepared by rolling process. The effects of rolling temperature (400 ℃, 450 ℃ and 500 ℃) on the interface microstructure, interface bonding strength, tensile properties, and fracture mechanism ofthe plate were studied by optical microscope (OM), scanning electron microscope (SEM) and tensile test machine. The results show that the composite plates prepared with a rolling reduction rate of 45% and a rolling temperature range of 400-500 ℃ can achieve good bonding effects. The steel/aluminum interface is flat and straight. The aluminum/magnesium interface is wavy, and the fluctuation degree increases with the increase of rolling temperature. As the rolling temperature increases, the grains in magnesium layer gradually undergo dynamic recrystallization and grow, and the precipitation content of silicides in the aluminum layer increases. The bonding strength of steel/aluminum interface increases, while the bonding strength and tensile properties of aluminum/magnesium interface show a trend of first increasing and then decreasing.At the rolling temperatures of 400 ℃、450 ℃ and 500 ℃,the bonding strength of aluminum/magnesium interface is 77.54 MPa, 88.63 MPa, and 81.14 MPa, respectively; the tensile strength is 310 MPa, 324 MPa, and 278 MPa, respectively; the elongation after fracture is 39.9%, 40.9%, and 22.3%, respectively. The comprehensive mechanical properties of the composite plate are optimal at a rolling temperature of 450 ℃.

Based on the application status of controlled rolling and controlled cooling process for hot rolled H-beams, combined with engineering examples, the application of controlled cooling technology in H-beam production was introduced in detail, including the layout of controlled cooling process, configuration of cooling modules, arrangement of cooling nozzles, and implementation plan of controlled cooling process. By combining the temperature model of cooling curve with the field measured data, it can effectively guide the implementation of H-beam controlled cooling process. This method significantly reduces the cooling non-uniformity of H-beams, ensures the dimensional and performance uniformity along the length direction of the products, avoids defects such as web waviness and cracks during cooling process, improves the comprehensive mechanical properties of H-beams, and reduces production costs. The research results can provide effective guidance for industrial production of H-beams.

The hot working properties of superautenitic stainless steel exhibit sensitivity of variations in process parameters such as deformation temperature,strain,strain rate.In order to study the influence of deformation temperature and deformation rate on the hot working performance of S32654 super austenitic stainless steel, a hot tensile test was conducted. The temperature range for the hot tensile test was 1 050-1 200 ℃, and the strain rate ranged from 0.01 s^-1 to 10 s^-1. The fracture morphology and microstructure evolution of the super austenitic stainless steel under different deformation conditions were analyzed using XRD and EBSD. The results indicate that the S32654 super austenitic stainless steel exhibits good hot plasticity under the deformation conditions of 1 150 ℃ to 1 200 ℃ and 1 s^-1to 10 s^-1, while its hot plasticity is poor under the conditions of 1 050 ℃ to 1 100 ℃ and 0.01 s^-1to 0.1 s^-1. Under the deformation condition of 1 200 ℃ and 10 s^-1, the peak stress, maximum true strain and reduction of section are 269.5 MPa, 0.4 and 55.6%, respectively, showing the best thermoplastic property. Observation of the fracture morphology of samples reveals that the S32654 super austenitic stainless steel primarily exhibits intergranular brittle fracture in the low temperature and low strain rate regions, while it shows ductile fracture in the high temperature and high strain rate regions. EBSD microstructural analysis indicates that the occurrence of dynamic recrystallization at high temperatures and high strain rates hinders the formation and propagation of cracks. Additionally, a significant number of annealing twin boundaries are present in the recrystallized grain regions of the S32654 super austenitic stainless steel, which is related to its dynamic recrystallization mechanism being predominantly discontinuous dynamic recrystallization.

Aiming at the challenge of integrated control of key indicators such as shape, properties, and surface quality in the production of high-quality sheet and strip, the achievements of China in the integrated control technology of shape-property-surface for high-quality sheet and strip were introduced. The strip shape control technologies of multi-modal information fusion detection and multi-stand and multi-process coordination were briefly described from the aspects of straightness detection of hot rolled strip, intelligent prediction system of roll and strip shape state, comprehensive control model of roll bending and axial shifting, and strip shape feedforward control of cold and hot rolling process. The control technologies of hot rolling process and mechanical properties based on large model were briefly described from the aspects of microstructure parameters and mechanical properties control model of hot rollingprocess and pre-control of microstructure properties of hot continuous strip rolling. The intelligent simulation and control technology of high-quality strip surface characteristics was briefly described from the aspects of unsupervised classification detection algorithm for surface defects and comprehensive control of surface defects and characteristics. On this basis, the field applications of these technical achievements were described, and the development of comprehensive control of high-quality sheent and strip was prospected.

To formulate and optimize the hot working process for 18Ni (200) maraging steel, the hot deformation behavior of 18Ni(200) maraging steel was investigated using an MMS-200 thermal simulation testing machine. A hot processing map was established, and the microstructure evolution mechanism was analyzed. The results show that under the conditions of deformation temperatureT=850-1 100 ℃, strain rate=0.01-10 s^-1, and a maximum true strain ε=0.6, the flow stress of 18Ni (200) maraging steel decreases with increasing deformation temperature or decreasing strain rate, while the power dissipation efficiency gradually increases, leading to more complete dynamic recrystallization (DRX). When the true strain reaches 0.2, the area of flow instability zones is minimized. The flow instability zone is mainly distributed in the high temperature and high strain rate region. The complete recrystallization region of 18Ni (200) maraging steel was determined as follows deformation conditions:T=950 ℃、≤0.1 s^-1;T=1 000 ℃、≤10 s^-1;T=1 050 ℃、≤10 s^-1;T=1 100 ℃、≤10 s^-1.

With the development of automotive steel towards thin-gauge and high-strength, phosphorus is added to steel as a strengthening element to improve its strength. Compared with ordinary steel, the mechanical properties of phosphorus-containing steel are changed due to the addition of phosphorus element, and the rolling force is changed. In order to explore the effect of phosphorus content on the rolling force of phosphorus-containing steel, under the premise of fully considering the performance characteristics of phosphorus-containing steel, Zwick tensile machine was used to carry out tensile tests on phosphorus-containing steel with different phosphorus content under the same reduction amount, and a large number of actual production data were regression analyzed to obtain the calculation formula of carbon equivalent of DN0160E4 phosphorus-containing steel. The deformation resistance model and the relationship between phosphorus content and cold tandem rolling force were established. Finally, taking the first stand of 1 420 mm tandem cold rolling unit of a steel plant as an example, the actual rolling parameters are substituted into the model for calculation and analysis. The results show that the addition of phosphorus can increase the tensile strength and yield strength, and decrease the elongation of steel. The rolling force required by DN0160E4 phosphorous steel is larger than that of ordinary steel under the same reduction, and the rolling force increases linearly with the increase of phosphorus content in phosphorous-containing steel.

To further optimize the heating process of Ti-containing austenitic stainless steel, the influence of strain rate and deformation temperature on its high temperature deformation behavior was investigated by Gleeble 3800 thermal simulation testing machine. The influence of solution heat treatment process on the microstructure and mechanical properties of the plate was analyzed by metallographic microscope, scanning electron microscope, transmission electron microscope, ZWICK 600 tensile testing machine, ZBC 2602 impact testing machine and BRIN 400D hardness tester. The results show that the crack is most likely to occur in the center of the upper surface of the continuous casting billet during the heating process through the numerical simulation study of the temperature change law at different positions. The dynamic recrystallization behavior analysis shows that the deformation resistance and deformation temperature of Ti-containing austenitic stainless steel are approximately linear. Under the series solution heat treatment process of 1 080-1 150 ℃ and holding 15-120 min, the grain size of Ti-containing austenitic stainless steel is coarsened with the increase of solution temperature and holding time, and the average grain size has a power function relationship with holding time and an exponential function relationship with solid solution temperature. At the solution heat treatment process of 1 050 ℃ and 1 min/mm holding time, austenite grain size of Ti-containing austenitic stainless steel is 4-6 grade, and the comprehensive mechanical properties are excellent.

To solve the corrosion problem of steel used as mine hydraulic support due to the complex service environment, the microstructure, mechanical properties, corrosion behavior and mechanism of four commonly used steels(S890 steel and 30CrMnSi steel developed in China,andForeign Ⅰ、Foreign Ⅱ steels developed in foreign) for hydraulic support used the same heat treatment process were studied, and the suggestions for improving the corrosion resistance of S890 steel were put forward. The results show that the microstructure of S890 steel after quenching at 840 ℃ for 2 hours and tempering at 480 ℃ for 1 hour are tempered sorbite and martensite, and the yield strength, tensile strength and -20 ℃ impact energy are 855 MPa, 905 MPa and 195 J, respectively. The mechanical properties of S890 steel are better than that of similar materials developed at home and abroad. After total immersion corrosion (3%NaCl+5%HFAE solution, 3%NaCl and 5%HFAS solution), the annual corrosion rate of S890 steel in 5%HFAE emulsion is 0.36 mm, which is superior than 30CrMnSi steel and similar to that of the Foreign Ⅰ and Foreign Ⅱ steels. After analyzing the corrosion resistance of S890 steel it can be seen that the corrosion pits mainly occur in the CaS-Aloxide-MnS complex inclusions, which seriously accelerate the corrosion of the steel. Therefore, the content of S, P, Ca elements of S890 steel should be strictly controlled to reduce the quantity and density of composite inclusions. Meanwhile, the heat treatment process and the uniformity of the microstructure of S890 steel should be improved to increase its corrosion resistance.

The type, amount, size, morphological characteristics and distribution of the second precipitate in offshore steel have a significant impact on its comprehensive performance. Based on the calculation of solid solution precipitation of composite precipitates and classical precipitation kinetics theory, the precipitation behavior of composite precipitates in austenite of E690 offshore steel were systematically studied, and the effect of deformation energy storage on the precipitation kinetics of composite precipitates in austenite were also discussed. The results showed that (Nb,Ti,Mo,V)C in E690 offshore steel would precipitate at 1184.5 ℃. In austenite phase region, the maximum precipitation mass fraction of MC carbides was 0.057 4%, and the maximum precipitation volume fraction was 0.000 727%, of which NbC and TiC accounted for the main part.The critical nucleation size of (Nb,Ti,Mo,V)C decreased with the decreasing temperature under different nucleation mechanisms, and the critical nucleation work for grain boundary nucleation was smaller than that for dislocation nucleation and uniform nucleation. (Nb,Ti,Mo,V)C preferentially undergone grain boundary nucleation, and the fastest precipitation temperatures for uniform nucleation, grain boundary nucleation and dislocation nucleation were 820.5 ℃, 908.7 ℃ and 818.3 ℃, respectively. With the increase of deformation energy storage, the relative nucleation rate of (Nb,Ti,Mo,V)C increased, the precipitation incubation period shortened, and the precipitation strengthening effect of composite precipitates improved.

In view of the problem of surface and internal cracks that were prone to occur when producing 304L austenitic stainless steel plate with high Cr and Ni content using continuous casting billets,effect of chemical composition and heating process on the microstructure and thermal plasticity of hot rolled 304L austenitic stainless steel plate was investigated. The results showed that with increasing of Ni element content, the ferrite transformation to austenite are more difficult of 304L austenitic stainless steel, and result in more large-sized ferrite phases distributed continuously at a certain angle to the rolling direction in the hot rolled plate, which deteriorated the bad thermal plasticity of the plate and formation internal cracks. With decreasing of Cr element content, the ferrite content is reduced, and result in the size and quantity of large-sized ferrite that is continuously distributed at a certain angle to the rolling direction in the plate and the thermal plasticity of the plate is improved further more. Higher heating temperature and holding time of the casting billets accelerated the transformation of residual ferrite to austenite during the hot rolling process, thereby the occurrence of large-sized ferrite that is continuously distributed at a certain angle to the rolling direction in the hot rolled plate is reduced, and the thermal plasticity of the plate is improved.

When the traditional 20-high rolling mill is used to expand the ultra-thin specifications during the rolling of silicon steel, the evaluation of equipment capacity and the selection of process parameters are based on experience and field trials. The lack of theoretical support leads to a high risk of equipment damage and high trial and error costs. At the same time, the product quality cannot be guaranteed after the specification expansion. In response to the above problems, fully considering the equipment and process characteristics of the 20-high rolling mill, combined with actual rolling data on site, and taking into account rolling stability and strip surface defect control, a 20-high rolling mill rolling capability evaluation model and technology was established and corresponding rolling ability accounting software was developed. This software can be used to accurately calculate rolling capacity of a 20-high rolling mill for silicon steel. It was applied to a cold rolling plant for silicon steel of a steel company. Through comparative analysis of the calculated minimum product thickness and the actual export product thickness, it was found that, under the premise of ensuring hourly output and considering rolling stability and defect control capabilities, the calculated minimum product thickness is smaller than the actual product thickness, and the product thickness specification has room for expansion in a thinner direction, which laid a theoretical foundation for the subsequent product quality control and rolling process development of high-grade non-oriented silicon steel and oriented silicon steel to expand to thinner specifications.

The 18-high single-stand mill is prone to produce diagonal wave defects when rolling high-strength and thin gauge strip. Analysis indicates that the mechanism behind the generation of diagonal waves is the existence of certain shear stress and uneven tensile stress in the strip, leading to uneven plastic deformation during rolling. To resolve the problem of diagonal wave shape defects, a three-dimensional elastoplastic simulation model of the rolling process of the 18-high mill was established using the finite element software ABAQUS. The shape control capabilities of intermediate roll bending and axial shifting were analyzed. The results show that as the strip width increases, the regulation effectiveness of intermediate roll bending and axial shifting on the secondary and quaternary crown of the loaded roll gap gradually increases in the 18-high mill. The regulation effectiveness of intermediate roll axial shifting is superior to that of conventional tandem cold rolling mills, while the regulation effectiveness of intermediate roll bending is weaker. The 18-high mill exhibits significantly higher adjustment capability for the quaternary crown of the loaded roll gap compared to conventional tandem cold rolling mills, but its adjustment capability for the secondary crown is weaker. When the strip deviates from the centerline during rolling, a rolling force deviation occurs on both sides of the mill, and the influence of strip deviation on the rolling force difference between the two sides of the 18-high mill is greater than that of conventional cold rolling mills. Therefore, compared to conventional tandem cold rolling, the 18-high single-stand mill is more prone to diagonal wave shape defects. To resolve the diagonal wave problem of strip produced by the 18-high mill, measures such as reducing the final pass rolling force (F＜5 000 kN) and increasing the forward and backward tension of the final pass (by 30%) were proposed, the diagonal wave defects was effectively controlled.

In order to reveal the evolution law of the microstructure of complex phase steel with improved formalility during annealing, thermal simulation experimental machine and microstructure characterization methods such as electron probe microanalysis (EPMA), electron backscatter diffraction (EBSD), X-ray diffraction (XRD) were used to study the kinetics of bainite transformation in experimental steel. The influence of annealing process parameters such as soaking temperature, over aging temperature and over aging time on microstructure evolution was revealed. The results show that during the bainitic insulation phase transformation process, the bainitic phase transformation occurs when the over aging temperature is 350-400 ℃, and the completion time of the phase transformation is 84-131 s. When the over aging temperature is higher than 450 ℃, there is basically no bainitic transformation, and martensitic transformation occurs during the cooling process after the insulation is completed. During the simulated continuous annealing process, as the soaking temperature increases, the content of bainite in the experimental steel increases, while the content of ferrite and residual austenite gradually decreases. With the increase of over aging temperature, the content of bainite decreases, while the content of residual austenite first increases and then remains unchanged. The grain size ranges from 0 to 1.5 μm, mainly concentrated below 1 μm. As the over aging time increases, the bainite content in the experimental steel remains basically unchanged, while the residual austenite content increases. When the continuous annealing process is carried out at a soaking temperature of 880 ℃, over aging temperature of 400 ℃ and over aging time of 600 s, the maximum volume fraction of residual austenite in the experimental steel is 10.83%.

Aiming at the problems of long roll changing time and low reliability of roll changing device in the continuous cold rolling production line at present,the structure and principle of work roll changing device of 4-high skin pass mill were introduced. Through comprehensive analysis of work roll changing steps and time sequence, some of the series operation steps were optimized to parallel operation or lap operation. It was found that the key factor affecting the work roll changing time was the running speed of AGC cylinder, and then the servo hydraulic system was optimized with constant power pump characteristics to improve the running speed of AGC cylinder and greatly reduce the work roll changing time. In order to improve the reliability and stability of the work roll changing device, the structure design, the selection of detecting elements and the installation accuracy of the device were optimized and improved. After adopting above measures, the work roll changing time is greatly compressed from more than 120 s to less than 90 s, and the operation reliability and stability are significantly improved, which lays a foundation for the continuous and stable production of the cold rolling production line and the improvement of product quality.

Symmetric guides are widely used in the slant rolling piercing process of seamless steel pipes. However, due to the harsh service environment, the surfaces of the guide plates often suffer from nodules, steel adhesion, or partial melting, which in turn leads to defects such as spiral scratches on the outer surface and inner folds on the inner surface of the steel pipe products. Therefore, a novel asymmetric guide plate was designed by combining theoretical calculations with finite element simulations. The overall design concept of the asymmetric guide plate follows the basic principles of traditional symmetric guide plates, but the structure of the asymmetric guide plate not only has an asymmetric upper and lower structure but also has an adjusted geometric curve in the horizontal direction based on the symmetric guide plate. The improved asymmetric guide plate effectively increases the contact area between the guide plate and the rolled piece, reduces the contact stress, equivalent stress and force value, and plays a positive role in improving the quality of rolled products and the life of the guide plate. The industrial practice results show that the design and use of entrance cone structureof the asymmetric guide plate of cone shaped roll piercing mill have greatly reduced the impact and melting phenomena on the surface of the guide plate's entrance cone, thereby reducing the spiral outer fold defects caused by the guide plate's surface scratching the billet. The design and use of exit cone structureof the asymmetric guide plate have basically eliminated the inner folds and inner skin defects on the tail end of the steel pipe, and improved the small nodule defects of the guide plate's exit cone section, improved the appearance quality and circularization effect of the billet, and reduced the risk of jamming in the piercing process. The design and use of the asymmetric guide plate's upper and lower asymmetric difference structure have made the wear area of the guide plate in the center, solving the "crumbling edge" problem of the upper and lower surfaces of the guide plate, and at the same time improving the "fish tail" defects at the tail end of the billet.

In order to meet the demand of an enterprise reforming the continuous annealing unit to hot-dip galvalume unit, a reasonable technology reformation route and equipment transformation and integration plan are proposed base on reducing investment costs and maximizing the utilization of existing equipment capabilities. The key process technologies in the reformation and the main points of the equipment transformation of tension equipment, annealing furnace, zinc pot, post-cooling equipment, skin-pass mill and tension leveller are introduced. Production practice shows that the coating thickness of product in the galvalume line can reach up to 220 g/ , the yield strength can reach up to 650 MPa, and the tensile strength can reach up to 750 MPa, the maximum process speed is 180 m/min, and the maximum output is 79.5 t/h after reformation. The upgraded process design and equipment selection meet the production needs.

Aiming at the problem of stamping cracking of automobile steel, taking DP780 dual-phase steel strip with thickness of 1.5 mm as the research object, the causes of cracking during stamping forming were studied by means of metallographic microscope, scanning electron microscope, tensile testing machine and other equipment, and the improvement measures were put forward. The results show that when the shear clearance is 0.3 mm in the stamping process of DP780 dual-phase steel strip, the proportion of stamping bright band is 30%, the shear edge has no defects, and the stamping quality is the best. When the volume fraction ratio of ferrite and martensite is 7∶3, and the yield ratio of strip is not higher than 0.6, the synergistic deformation ability of ferrite+martensite dual phase is more favorable for forming. Increasing the annealing temperature can reduce the carbon concentration of austenite, increase the proportion of ferrite and reduce the strength of martensite. Increasing the overaging temperature can improve the recovery of dislocations in quenched martensite and reduces the hardness of martensite. When the annealing temperature is increased by 20 ℃ and the overaging temperature is increased by 40 ℃, the average yield strength of DP780 dual-phase steel strip is reduced by 30 MPa, the n value is increased by 0.02, and the r value is increased by 0.15. After adjusting the shear clearance and optimizing the annealing process, the quality of the shear surface of DP780 dual-phase steel stamping parts is significantly improved, no obvious tearing zone is found in the section, and no cracking of parts. The stamping yield is increased from 82% to more than 98%.

For weathering steel, the structure and nature of the dense surface rust is a key factor affecting the corrosion resistance of the material. In this paper, the effects of three alloying elements, Cr, Mn, and Cu, on the corrosion resistance of Fe₃O₄ were systematically analyzed using first-principle calculations. The results show that the addition of Cr, Mn and Cu elements can effectively protect the Fe atoms on the surface of Fe₃O₄, reduce the spacing between the surface atoms and the subsurface atoms, and impede the corrosion of the surface Fe atoms by external corrosive ions. Among them, the presence of Cu atoms can effectively reduce the surface energy of Fe₃O₄and increase the stability of the Fe₃O₄ structure; Cr and Mn atoms can promote the separation of H₂O molecules on the surface, resulting in the formation of FeOOH structure with good corrosion resistance. In addition, Cr, Mn and Cu can effectively reduce the effect of H₂O or Cl^-+H₂O corrosive environment on the chemical state of Fe atoms on the surface of weathering steel , reduce the adsorption of Fe₃O₄ on Cl^- and H₂O, and finally improve the corrosion resistance of Fe₃O₄.

In recent years, low energy consumption and low cost CSP short-process technology has been rapidly developed in Chinese iron and steel industry. However, compared with the traditional hot rolling process, the yield strength of CSP products is higher, which is extremely unfavorable for the formability of steel used in stamping.Therefore, the dynamic recrystalization behavior and cooling phase transformation of austenite of DC04 cold-rolled deep-drawing steel were analized through thermal simulation experiments, and the dynamic recrystalization model was established, which was used to guide the production practice of CSP production line, and the cold-rolled deep-drawing steel sheet with rich {111}texture was successfully trial-produced. The experimental results show that the dynamic recrystallization model of DC04 cold-rolled deep-drawing steel in CSP production line isZ=ε·exp[295.21/(RT)]. The judgment conditions of dynamic recrystallization are Z=1.94×10¹⁰exp(61.34ε_c) and Z=2.57×10⁸exp(24.99ε_s).Based on the 3D dynamic recrystallization diagram, it is determined that the thermal deformation of the strip at F₃ stand in actual production is in the austenite part recrystallization region. In the trial production using F₃ stand bypassing scheme, the microstructure of the obtained strip is mostly equiaxed grain with low strength. However, the grains of the strips produced by the conventional rolling process of F₃ stand non-bypassing scheme,the grains contact with each other at sharp or right angles, and the strength is about 30 MPa higher than former. The F₁and F₂ stands of CSP production line adopt high temperature, high reduction rate and low deformation rate rolling, which can make the strip microstructure undergo complete dynamic recrystallization, complete the transformation of columnar crystal to equiaxed crystal, and avoid the generation of mixed crystal. The performance of cold-rolled sheets produced using a 70% cold rolling cumulative reduction, bell annealing at 710 ℃, and the F₃ stand by passing and non-bypassing schemes were compared. The cold-rolled sheets produced with the F₃ stand bypassing scheme showed little difference in strength compared to those produced with the conventional non-bypassing scheme, but exhibited higher elongation A₈₀ and r values reaching 45% and 2.1. Additionally, the proportion of the favorable texture component {111} was higher, resulting in excellent deep-drawing performance.

Medium-temperature copper-containing CGO silicon steel is widely used in the manufacture transformer core, and its performance improvement is of great significance for energy saving and emission reduction. Reducing strip thickness is an effective way to reduce iron loss, but with the increase of cold rolling reduction rate, the number of Goss grains in cold rolled strip is reduced, and the inhibitor ripening is accelerated, which brings challenges to the industrial upgrading of CGO silicon steel. The microstructure, texture and inhibitors of intermediate and high temperature annealing sheets of CGO silicon steel under different processes were characterized by EBSD and SEM. The results indicate that the conventional process, which controls the reduction rate of the second cold rolling at 55% to 60%, is no longer suitable for the requirements of thin gauge strip. Under the conventional process, the area fraction of Goss grains in the intermediate annealed plates is 2.81%. After primary recrystallization, the area fraction of Goss grains decreases to 0.742%, and the secondary recrystallization initiation temperature is 940 ℃. This leads to the abnormal growth of deviated Goss grains as well, resulting in a magnetic induction intensity B₈ of 1.682 T. By adjusting the reduction rates of the first and second cold rolling processes from 78% and 54% to 72% and 64%, respectively, the area fraction of Goss grains was significantly improved. The proportion of Goss grains in the intermediate annealed sheets increased to 3.84%, and after primary recrystallization, the proportion of Goss grains further rose to 1.47%. Under unchanged heat treatment parameters, this adjustment promoted more sufficient secondary recrystallization of Goss grains, resulting in an increase in the magnetic induction intensity B₈ of the finished sheets to 1.836 T. By utilizing the wide process window of the secondary cold rolling method, a nitriding process was introduced during the intermediate annealing stage. This addition did not affect the microstructure or texture of the CGO silicon steel but facilitated the precipitation of AlN particles during the secondary recrystallization process. As a result, the onset of secondary recrystallization was delayed, and the secondary recrystallization temperature was increased to 980 ℃. This ensured more accurate orientation of abnormally grown Goss grains, leading to a further improvement in the magnetic induction intensity B₈ of the finished sheet to 1.900 T. By regulating cold rolling parameters and introducing a nitriding process during intermediate annealing, high-performance medium-temperature copper-containing CGO silicon steel was successfully prepared. This achievement provides a new approach for enhancing the performance of CGO silicon steel while achieving energy savings and cost reductions.

Combining the calculation of resistance to deformation of rolled piece with the based finite element calculation of elastic deformation of roll system, the model of shape control in rollingsilicon steel thin-gauge strip with Sendzimir 20-high mill was established.By calculating the deformation resistance of the rolled piece based on the preset shape and iteratively calculating the elastic deformation between the roll system under the rolling force of the rolling mill, the influence laws of the support roll gap shape adjustment (ASU) and the taper change of the No.1 intermediate cone roll on the shape of the rolled piece were determined.The adjustment of ASU in the middle of the support roll mainly affects the area of 0.6 m at the center of the width of the rolled piece, and has almost no effect on the area of 0-0.2 m at the edge. The adjustment of ASU at both ends of the support roll has an impact on the edges of the rolled piece, and also on the middle part of the rolled piece. Increasing the taper of the intermediate roll has a significant effect on improving the strip crown at a distance of 0-0.15 m from the edge of the rolled piece. By optimizing the calculation of the ASU of the roll system and the axial shifting amount of the intermediate roll, the average difference of transverse of the same silicon steel thin-gauge strip rolled by Sendzmir 20-high is reduced by more than 25%,and the shape control of the 0.25 mm thickness strip reaches below 8 IU, effectively improving the shape control capability of the Sendzimir 20-high mill for silicon steel thin-gauge strip.

The production of rectangular spring flat steel with dimensions of 56 mm × 75 mm is quite challenging and demands high quality standards. During the rolling process, it is prone to problems such as out-of-square deformation, torsion and steel stacking, making it difficult to control its dimensions, shape and quality. Therefore, the 56 mm × 75 mm rectangular 52CrMoV4 spring flat steel was developed based on existing round steel production equipment of Hunan Valin Xiangtan Iron and Steel Co., Ltd. By optimizing the heating, rolling and slow cooling processes, and designing specialized pass designs, namely K₆, K₄ and K₂, the stable production of 56 mm × 75 mm rectangular flat steel with resistance to torsion, stable dimensions and satisfactory quality had been achieved. The side wall inclinations and R-angles of the K₆, K₄ and K₂ pass designs were progressively reduced, enhancing roll utilization and reducing costs. Controlling the heating and slow cooling processes, the product obtained had a decarburized layer thickness of 0.21-0.24 mm and a hardness distribution between 320HB and 349HB, with all mechanical properties meeting customer requirements. The microstructure at the 1/4 width and the 1/2 width of the 56 mm× 75 mm rectangular 52CrMoV4 spring flat steel was predominantly bainite + pearlite + a small amount of ferrite + a trace of martensite.

Aiming at the problems of cold cracking, heat affected zone softening,toughness decreasing, and residual stress in the welding of high-strength steel for automobiles, the Q960E automobiles high-strength steel has been taken as the research object, the laser composite welding test method has been used to study the effects of different heat treatment parameters such as preheating temperature, quenching temperature, and tempering temperature on the microstructure and mechanical properties of the welded joint. The research results indicate that the welded joint of Q960E high-strength steel consists of a welding base material, a weld seam, a fusion zone, an overheated zone, and a normalized zone, at preheating temperature of 100 ℃, quenching temperature of 900 ℃, and tempering temperature of 400 ℃, the base material is tempered martensite, the weld seam is fine bainite, the fusion zone is fine bainite and coarse martensite, the overheated zone is coarse bainite, and the normalized zone is a recrystallized crystal composed of bainite and martensite. As the quenching temperature increases, the tensile strength and yield strength of the welded joint show a trend of first increasing and then decreasing, and the elongation at break shows a trend of first decreasing and then increasing. As the tempering temperature increases, the tensile strength and yield strength of the welded joint show a gradually decreasing trend, while the elongation at break shows a gradually increasing trend. When the preheating temperature is 100 ℃, the quenching temperature is 900 ℃, and the tempering temperature is 400 ℃, the tensile strength of the welded joint is 1 150 MPa, the yield strength is 1 075 MPa, and the elongation at break is 10.56%, the comprehensive performance is superior, and it is the best heat treatment processes for Q960E automotive high-strength steel.

Driven by the "dual-carbon" strategy, the transformation of 82B wire rod production processes from traditional long-process to electric furnace short-process has become inevitable. However, there is still a lack of systematic research on the causes of abnormal martensite structures near the core of wire rods produced by short-process technology. To address this, this study investigated the causes of abnormal martensite structures in 82B wire rods produced by recycled steel materials+electric furnace short-process through metallographic observation, quantitative analysis of macro/micro-segregation, and thermal simulation tests, combined with comparative analysis of 82B wire rod structures produced by traditional long-process technology. The results show that the segregation levels of Mn and Cr elements near the core of short-process 82B wire rods are more severe than those of long-process 82B wire rods. This segregation, along with the higher residual Ni content, shifts the C-curve of 82B steel to the right, reduces the critical cooling rate for martensite formation from 7 °C/s to 3 °C/s. As a result, the martensite content of short-process 82B wire rods under the same cooling rate is higher than that of long-process 82B wire rods. Based on experimental results, process adjustments were applied, including increasing the soaking temperature of billets from (1 120±10) ℃ to (1 160±10) °C and maintaining the heating and soaking holding times at 100-120 min. These adjustments significantly improved macro-segregation and suppressed the formation of abnormal martensite structures.

DP780 galvanized substrate strip is provided by an 18-high single stand mill in a production line, during the galvanizing process of DP780 steel, the problems such as strip tail swinged deviation, strip deviation in entry looper and preheating section often occur, leading to speed reduction or machine stoppage. These problems significantly impact production stability and result in substantial cost losses. Therefore, the deviation mechanism and stress state of strip on galvanized line are analyzed. A higher-order polynomial is employed to fit the strip flatness of the galvanized substrate strip, and the first-order coefficients after fitting is used as an indicator to characterize the deviation. The comparison between the first-order coefficient of the full-length flatness of DP780 galvanized substrate strip and the processing data of each continuous process controller (CPC) on the galvanizing line reveals that significant change of flatness first-order coefficients at the welding seam is the main factor causing strip running deviation. By using an asymmetric flatness target curve and textured roll at the final rolling pass, and establishing the criterion of cut length at the strip head and tail based on the strip flatness first-order coefficient, the cut loss rate of DP780 strip is reduced from 7.23% to 2.66% after cold rolling process optimization, which effectively improves the stability of DP780 galvanized production.

In the production of medium and heavy plates, the thickness of the intermediate billet significantly impacts the plate's performance. Establishing an accurate temperature drop model for the intermediate billet not only enhances the stability of the plate's performance but also optimizes the rolling rhythm, thereby improving production efficiency. Therefore, using industrial production data as the foundation, the Python method was adopted to investigate the effects of factors such as the thickness and width of the intermediate billet of controlled rolled plates, the initial waiting temperature, the final waiting temperature and the ambient temperature on the temperature drop rate of the intermediate billet. The results indicate that there is a strong positive correlation between the waiting time and the thickness of the intermediate billet, a moderately negative correlation with the final waiting temperature, a weak negative correlation with the initial waiting temperature, and an extremely weak correlation with both the width of the intermediate billet and the ambient temperature. Based on these findings, a prediction model for the temperature drop law of the intermediate billet was constructed using a machine learning approach. The determination coefficient R² of the model reached 0.901 3. Through testing and verification, the temperature drop model demonstrated high prediction accuracy, with the absolute deviation rate of the temperature waiting time prediction at -6%-6%. This model provides valuable guidance for formulating processes and optimizing the rolling rhythm of the production line.

To address the automotive industry's demand for low-cost, high-performance, and lightweight wheel steels, an 800 MPa grade wheel steel has been developed. The chemical composition was designed utilizing a C-Mn-V-Nb-Cr alloy system, with an emphasis on optimizing vanadium utilization in Panzhihua-region resources. A thermo-mechanical controlled process (TMCP) was implemented, involving the following parameters: slab heating at 1 200 ℃ for 2 h holding; roughing rolling at 1 100-1 000 ℃ with three passes (compression ratio 2.5); finishing rolling at 860-830 ℃ with six passes (compression ratio 5.7); followed by 15 s air cooling to 750 ℃, then water quenching to 430 ℃, and final air cooling to room temperature. Microstructural characterization and mechanical testing revealed excellent properties of the developed steel which yield strength is 690-720 MPa, tensile strength is 860-870 MPa, yield-to-tensile ratio is 0.80-0.88, and elongation is 20%-22%. Notably, the impact energy at temperatures ranging from 20 ℃ to -60 ℃ consistently exceeded 140 J. Both cold bending and hole expansion capabilities meet the stand requirements for 800 MPa grade wheel steels.

In view of the problem of color difference defects on DH980 hot rolled strip after pickling, isothermal oxidation experiments were conducted to analyze the morphological characteristics of these defects and the formation mechanisms of intergranular oxidation, thereby identifying the root cause of the defect. The results indicate that the primary cause of color difference defects on pickled DH980 strips is intergranular oxidation within the hot-rolled coils. In following tension leveling, the bonding strength at intergranular oxidation sites decreases, leading to crack initiation. During the scale removal process in picking, pickling cracks appear at these intergranular oxidation regions, resulting in macroscopic color difference defects. Notably, slow cooling rates in the holding pit exacerbate intergranular oxidation depth. Isothermal oxidation experiments at 600-1 000 ℃ revealed that DH980 strip exhibits varying degrees of intergranular oxidation within the 700-1 000 ℃ range. Intergranular oxidation disappears at 600 ℃, with 800 ℃ identified as the critical temperature for maximum susceptibility. The depth of the intergranular oxide layer correlates closely with the competitive mechanism between internal and external oxidation. By optimizing coiling temperature and adjusting pickling parameters, the adverse effects of intergranular oxidation can be mitigated, effectively suppressing pickling color difference defects on DH980 hot rolled strips.

This cost-effective stainless steel composite plate integrates the excellent hydrogen resistance of stainless steel with the high strength and wear resistance of low-alloy steel. Such composites offer a promising approach for developing commercial materials with superior resistance to hydrogen. However, the influence of the cladding microstructure on the hydrogen resistance of stainless steel/carbon steel composite plates remains poorly characterized. Consequently, base materials exhibiting contrasting deformation resistance (Q235 vs. 700L) were employed to control the cladding microstructure. This work characterizes the microstructure of stainless steel and carbon layers in 316L/Q235 and 316L/700L composite plates and evaluates its impact on hydrogen resistance. Results show that the 316L cladding layer in the 316L/700L composite plate preferentially recrystallizes, reducing its hydrogen embrittlement susceptibility index from 9.8% of 316L/Q235 composite to 5.9%. Recrystallization control elevated ∑3 twin boundary density in 316L cladding (316L/700L) from 0.79% of 316L/Q235 composite to 19%. This microstructure simultaneously impedes hydrogen crack initiation through twin boundary resistance and suppresses propagation by disrupting random grain boundary networks, collectively enhancing hydrogen embrittlement resistance.

In order to develop ultra-high-strength prestressed steel strands with higher development intensity and superior comprehensive performance, using 87Mn wire rod as the raw material, the evolution of the microstructure and properties of the steel wire during the nine-pass drawing process were studied, revealing its strength-ductility mechanism. The results showed that the equiaxed pearlite structure was elongated and refined along the drawing direction with the drawing process, showing obvious directionality, and finally forming a typical fibrous drawing structure. The dislocation density inside the steel wire increases with the increase of drawing strain, and the growth rate is faster in the early drawing stage, from 2.35 × 10¹⁴ m^-2 to 4.59 × 10¹⁴ m^-2, and the growth rate of dislocation density gradually slows down in the middle and late drawing stages. After 9 passes of drawing, the tensile strength of 87Mn wire rod increases from 1 170 MPa to 2 085 MPa, and the elongation decreases from 12.56% to 7.20%. The change of mechanical properties during the drawing process is mainly divided into three stages:in the early stage of drawing, dislocation strengthening and boundary strengthening work together, and the strength contribution of dislocation strengthening growth is obvious, from 189 MPa to 460 MPa. At this stage, the strength of the steel wire increases with the increase of the drawing strain, and the plasticity decreases significantly. In the middle of drawing, dislocation strengthening and boundary strengthening work together. The strength contribution of boundary strengthening is significant, from 600 MPa to 806 MPa, and the growth rate of dislocation strengthening decreases. At this stage, the plastic decline trend of steel wire slows down and the strength continues to increase. In the late stage of drawing, a large number of cementite dissolved, and the strength contribution of solid solution strengthening was enhanced to 149 MPa. At this stage, the combined effects of boundary strengthening, dislocation strengthening and solid solution strengthening worked together. The strength growth rate of steel wire was obviously accelerated, and the plasticity decreased slightly.

A 700 MPa grade engineering machinery steel with Ti element mass fraction of 0.12% was prepared using a process route involving thermo-mechanical rolling and off-line tempering. Its microstructure and property regulation to determine the optimal tempering process were researched. The experimental steel billet was heated 1 220-1 250 ℃, followed by roughing and finishing rolling on a 2 250 mm hot rolling line, with the finishing rolling temperature controlled between 840 and 870 ℃. The hot-rolled strip was then subjected to laminar cooling and coiled at temperatures ranging from 580 to 610 ℃. After cooling, the coil was cross-cut and subjected to off-line tempering using a roller hearth open-flame furnace, with tempering temperatures controlled at 620, 650, and 680 ℃. The microstructure, precipitates, and mechanical properties of the plate after tempering were studied using optical microscopy, scanning electron microscopy, and transmission electron microscopy. The results showed that the tempering treatment led to the decomposition of M/A islands in the hot-rolled microstructure and a significant reduction in dislocation density within the grains. Additionally, a large number of fine, dispersed nano-scale precipitates were formed, resulting in an increase in yield strength by 105-139 MPa and tensile strength by 45-82 MPa compared to the hot-rolled state. As the tempering temperature increased, the internal stress in the plate was fully released, and the impact toughness was significantly improved. The experimental results indicated that the plate tempered at 650 ℃ exhibited the best comprehensive performance, effectively meeting the usage requirements for engineering machinery vehicles.