In order to meet the demand of green and sustainable development in the transformation and upgrading of Chinese iron and steel industry, the serious problem of energy loss in the production of wiro rod and bar should be solved. The key technology of continuous casting and direct rolling of wire rod and bar was deeply studied. The process is a new type of process suitable for the production of ordinary wire rod and bar. By making full use of metallurgical heat energy of continuous casting billet, the heating process of billet can be completely eliminated, so as to achieve energy saving, emission reduction and burn loss reduction. The key technologies of wire rod and bar continuous casting and direct rolling process were studied and analyzed from four aspects: production capacity matching, temperature matching, rhythm matching and production management. The mathematical expressions of production capacity matching and rhythm matching were derived, and the variation law of casting billet temperature during the whole process from continuous casting to rolling was studied. The integrated production system of continuous casting and direct rolling process and the typical process layout scheme were given. The results show that wire rod and bar continuous casting and direct rolling is a green, environmentally friendly, low cost, high benefit and high efficiency production mode, which has good economic benefit and broad application prospect.

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 high-throughput computing technology in material genome engineering plays an important role in the research and development of steel products, which can help researchers gain a deeper understanding of the properties and behaviors of materials, such as composition design, phase diagram calculation, mechanical performance prediction, microstructure simulation, thermodynamic and kinetic analysis, etc. It accelerates the development process of new materials, improves the performance and quality of steel products, provids strong support for the sustainable development of the steel industry. On the basis of summarizing and analyzing the basic theories and methods, key technologies, and development status of high-throughput computing technology, the application ideas of high-throughput computing technology in the research and development of steel products was proposed. In the short term, high-throughput computing technology can shorten the research and development cycle while reducing costs. In the long term, it can also achieve on-demand design of steel products, enrich the steel material database, and provide methods and basis for subsequent material development.

The Sendzimir 20-high rolling mill is widely used in silicon steel, stainless steel and precision strip cold rolling. Its roll system configuration directly affects product accuracy and production cost. Excellent roll matching technology is the basis of efficient operation of the unit. For the Sendzimir 20-high rolling mill, the principle of roll matching and the requirement of grinding precision are put forward, the coordinate system is established to determine the initial position of each backing roll, and the center position of each roll is calculated during the working process, and the center coordinates of the middle roll and work roll are determined by coordinate method. By using the established equation, the relationship between the screw down stroke and the roll gap and the roll diameter compensation trajectory are analyzed, which is helpful to understand the control characteristics of the Sendzimir 20-high mill deeply and improve the field use efficiency.

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.

For traditional production process, the hot strip of austenitic stainless steel must be treated with off-line solution and annealing process before being delivered to the downstream user, which has a long production cycle and large energy consumption. On-line solution and annealing process can make full use of residual heat of hot strip after rolling for heat treatment, which has great advantages of energy saving and environmental protection. The key control techniques of on-line solution and annealing for hot strip of austenitic stainless steel were introduced. Based on 1 780 mm hot rolling line of GuangQing Metal Technology Co., Ltd., the industrial experiment of on-line solution and annealing was carried out. The hot rolled coil covered with “black skin” was obtained from the industrial experiment as raw material, and then was cold rolled after direct pickling without off-line solution and annealing treatment. The mechanical properties, resistance of intergranular corrosion and surface quality of the product were not significantly different from that of cold rolled coil produced with the conventional process, the feasibility of using the on-line heat treatment process instead of off-line solution and annealing process to produce high surface grade stainless steel cold rolled coil was fully proved.

In response to the problem of severe edge cracks in cold rolled strip caused by uneven transverse structure of high grade non-oriented silicon steel in hot rolling, the recrystallization degree was analyzed by thermal simulation testing machine at different temperatures and reduction rates. The results showed that the roughing rolling temperature dropped from 1 100 ℃ to 1 000 ℃, and the critical pressure rate of complete recrystallization increased from 30% to more than 40%. According to the results of thermal simulation, the hot rolling process was optimized by changing the roughing pass combination to 1+3, putting the edge heater setting 50 ℃ before finishing rolling, controlling the finishing rolling temperature according to the target upper limit of 865 ℃ + 20 ℃, and adopting post-cooling for laminar cooling. The transverse temperature difference, uniformity of microstructure and mechanical properties and dislocation of hot rolled strip before and after process optimization were analyzed by using the test results of thermal imager, metallographic microscope, tensile testing machine and transmission electron microscope. The results show that by increasing the rolling temperature, increasing the pass reduction rate, increasing the rolling speed and temperature compensation on the edge, the dislocation on the edge of the rolled piece quickly accumulated in large quantity at the grain boundary, and the dislocation density in some positions in the grain began to decrease, reaching a critical state and dynamic recrystallization occurred, which improved the transverse microstructure and property uniformity of the hot rolled strip. The correction rate of cold rolled products is reduced from about 25% to 5%.

In tandem cold rolling, strip thickness accuracy is one of the most important indicators to evaluate product quality and that downstream enterprises are concerned about. The existing methods for strip thickness prediction mainly focus on the hit rate of the strip head thickness, which cannot reflect the thickness accuracy and fluctuation of the whole coil. A continuous prediction model based on deep learning algorithm for the full length thickness of strip in tandem cold rolling is proposed, and the mapping from industrial data to strip thickness is realized. The data set is built by actual data of a five-stand tandem cold rolling production line. Random forest is used for feature selection to simplify the input features, and then genetic algorithm is used to optimize the initial weights and thresholds of DNN model for the further model performance improvement. The results show that the model can accurately and intuitively reflect the thickness accuracy and fluctuation of the whole coil with rolling time. In acceleration, deceleration and stable rolling stage, the relative errors of predicted results are controlled within ±0.5% and ±0.1%, which meet the actual production requirements. By using this model, the control system can improve the pre-setting accuracy and implement pre-adjustment at the corresponding time, so as to achieve the purpose of strip thickness accuracy improving.

Aiming at the key problem of how to realize the coupling matching of high yield strength and low yield ratio for high strength seismic building steel, based on the self-designed chemical composition, the microstructure and properties of the test steel were investigated by controlled rolling and controlled cooling process. The results show that under the process conditions of ' two-stage controlled rolling + water cooling (final cooling temperature 660 ℃) ', the microstructure of the test steel is a multiphase structure composed of ferrite, pearlite and bainite, which realizes a good match of strength, plasticity and low yield ratio. The average yield strength is about 660.0 MPa, the average tensile strength is about 1 196.7 MPa, the average elongation after fracture is about 14.8%, and the average yield ratio is as low as 0.55. The solid solution strengthening of Mn and Si elements in the test steel, as well as the fine grain strengthening and dislocation strengthening caused by bainite and pearlite structures are the main mechanisms for obtaining high strength and low yield ratio.

In order to study the influence of composition and structure of oxide scale on hot rolled strip on pickling time, ST12 steel, 45 steel and DP1180 steel were selected as experimental steels. The macro-morphology, cross-sectional micro-morphology, oxide layer thickness and main chemical composition of oxide scale on hot rolled strip surface of three steels were analyzed by SEM and XRD, and the pickling time was tested. The results showed that the oxide scales on the surface of ST12 steel and 45 steel hot rolled strip were composed of α-Fe, FeO, Fe₃O₄ and Fe₂O₃. There was no Fe₂O₃ in the oxide scale on the surface of DP1180 steel strip, but a certain amount of Fe₂SiO₄ was produced. The average thickness of oxide scale on the surface of ST12 steel, 45 steel and DP1180 steel strip were 10.88, 12.77 and 15.36 μm respectively, and the pickling time were 30.2, 23.8 and 16.2 s respectively. Compared with ST12 steel, the content of α-Fe in the oxide scale on the surface of 45 steel strip which was easy to react with acid solution was high, while the content of oxide which was difficult to react with acid solution was less, so its pickling efficiency was higher. The main reason for the shorter pickling time of DP1180 steel strip was that besides the high content of α-Fe in the oxide scale, there were more FeO in the threeoxides, and there were gaps between the oxide scale and the steel matrix, which could promote the diffusion and reaction of acid liquid in the oxide scale. Therefore, the pickling efficiency of oxide scale on the surface of hot rolled strip was mainly related to its composition and structure, and the thickness of oxide scale had little influence on it.

In response to the high cost of X65M submarine acid resistant pipeline steel, a low-cost X65MOS hot-rolled strip that meets the mechanical properties, aging impact property, CTOD performance, HIC and SSCC resistance performance requirements of submarine acid resistant pipelines was developed using a reasonable TMCP process design without adding Mo, Cu, Ni elements in the chemical composition. Production practice has proven that under low-temperature rolling conditions, increasing the reduction rate of the final stand to 13%, and using ultra fast cooling and dense laminar cooling processes, the needle like ferrite grains of X65MOS strip were refined to a grain size of grade 12, significantly improving its mechanical properties. The results of the drop hammer experiment showed that the shear tear area of X65MOS strip reached 100% at -40 ℃, and the aging impact energy reached over 300 J at -60 ℃, with a CTOD value of+∞. Under the same HIC and SSCC test conditions, when there were many cracks in the X65M strip, there were no cracks in the X65MOS strip. The large number of dislocations in the microstructure of the X65MOS strip ensured its CTOD performance, HICand SSCC resistance performance in the absence of Mo, Cu, and Ni elements. The low-cost X65MOS strip developed has significantly better performance than X65M strip, which has important practical significance for enhancing product competitiveness and improving economic benefits.

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.

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).

Aiming at the problems of zigzag edges and burr defects that readily occur during the edge trimming process in the production of cold rolled ultra-low carbon strip, its edge trimming quality under different trimming process parameters, and different positions and shapes of the base strip were discussed. Based on analyses of mechanical properties, microstructure, and fracture morphology, the impact of base material characteristics and trimming processes on the edge trimming quality of the strips are clarified. Furthermore, a process control scheme is proposed to improve the edge trimming quality of base material for cold rolling. The analysis of the fracture morphology of the edge shear indicates that the fracture morphology of the strip edge after trimming can be divided into a trimming zone and a fracture zone along the thickness direction of the strip, and there are significant differences in the proportion of these two zones in the thickness direction under different strengths, trimming processes, and strip shapes. As the strength of the strip increases, the proportion of the trimming zone in the thickness direction significantly rises. The influence of the blade gap value on the edge trimming quality is significantly greater than that of the overlap between the upper and lower blades. As the bladegap value increases, the proportion of the trimming zone in the fracture morphology of the edge shear decreases significantly. The presence of wave shapes on the strip edge results in the appearance of oblique cutting zones and burr zones in the shear fracture, and the boundary between the trimming zone and the fracture zone fluctuates significantly, seriously affecting the edge trimming quality of the strip. By adjusting the blade gap value and overlap value, controlling the trimming and straightening lengths, and managing the wear degrees of the rubber sleeve and blades, the edge trimming quality of cold rolled ultra-low carbon strip has been improved.

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.

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.

Cooling process and equipment design after coating are particularly important for continuous galvanized steel, galvanized aluminum, galvanized aluminum zinc, galvanized aluminum magnesium, galvanized aluminum zinc magnesium, galvanized aluminum silicon and other coating products. The principle of selecting cooling process after coating is proposed:only jet cooling can be used before the coating solidification, and the high magnesium coating that is prone to oxidation should be cooled by nitrogen; different cooling methods such as normal temperature air cooling, cooling air cooling, fine air mist cooling or spray solidification cooling can be chosen during the solidification process based on the required cooling speed of the product; the cooling of the coating after solidification can be selected according to the mechanical property requirements of the product and the temperature of the strip, such as jet cooling, air mist cooling, water cooling roll cooling, water spraying cooling, water quenching cooling and other forms; the form classification, application scenarios, process principles, technical requirements and design methods of the main cooling equipment of three cooling processes of jet cooling, air mist coolers and powder solidification cooling are introduced in detail. A new design principle of air jet cooling bellows based on zero pressure overflow of hot air and ensuring full contact between cold air and strip convection heat transfer is proposed, on this basis, a zero-pressure overflow channel, a slotted nozzle and an efficient and stable air jet cooling bellows with thin flow thickness are designed. The reference is provided for the selection and design of production line equipment of galvanized, galvanized aluminum, galvanized aluminum zinc, galvanized aluminum magnesium, galvanized aluminum zinc magnesium, galvanized aluminum silicon and other coating products.

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 ℃.

With the development of metallurgical technology, the strength of high strength steel has increased significantly, which makes straighteners with a single-roll system have a very limited capacity to straighten high-strength plates. It is an effective way to improve equipment capacity by using roll system-replaceable straighteners with a double-roll system. For the straightening characteristics of the high strength plate, the roll system capacity characteristics were analyzed to conclude the roll system parameters of the double-roll system straighteners and the according straightening range. Firstly, the strengthening and reverse bending characteristics of high strength plates were analyzed, and the back bending conditions of high strength plates were established. Secondly, three roll system capacity characteristics of double-roll system straighteners were analyzed in terms of the back bending capacity, mechanical strength, and straightening accuracy. Finally, real examples were demonstrated based on the straightening characteristics of high strength plates. It provide a theoretical basis for the selection of roll systems parameters, and provides references for the development of high strength plate straightening schemes.

Hot strip mills are prone to edge wraping defects in the later stages of the same-specification product continuous production, especially for wide-specification products. To solve this problem, the influence of different CVC roll contour parameters on the variation of the finishing work roll contour curve for hot rolled wide strip mills is analyzed, and the application of CVC roll contour+concave roll contour combination is studied. The results show that there is a negative correlation between the end roll diameter difference and the middle roll diameter difference of CVC roll, and an example of 2 050 mm hot rolling production line is given to illustrate this. This provides reference for the determination and optimization of CVC roll contour curves. The advantages and disadvantages of practical application of concave roll are introduced by analyzing the concave roll curve determining method and the axial shifting method of the concave roll, and the relationship between the bending change of the concave roll and the heat expansion value of the roll is analyzed theoretically, which shows that the CVC roll contour+concave roll contour combination can effectively solve the edge warping defect, extend the rolling kilometerage. Finally, the validity of its effectiveness is verified from the application angle by listing the changes in edge wraping of the same specification and steel grade after production.

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.

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.

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.

In view of the problems of high acid consumption and low recovery value of acid fume condensate in the current pickling process, the influence of exhaust pressure andFe^m+ concentration in the acid fume purification system on the concentration of hydrochloric acid was studied through theoretical calculations and experiments. The results showed that the concentration of hydrochloric acid solution obtained by the original 160 g/L hydrochloric acid solution under -60 kPa extraction pressure was 40.1 g/L, while the concentration of hydrochloric acid solution obtained by the same original 160 g/L hydrochloric acid under -5 kPa extraction pressure was only 10.9 g/L. In addition, the presence of Fe^m+ in the acid solution does not change the HCl content in the acid fume. To this end, corresponding improvement measures have been proposed: (1) separate the high and low concentration acid tanks for condensation, directly recycle the acid fume in the high concentration acid tank to the acid circulation system after condensation, and replace some of the rinsing waste water with condensed acid fume and transport it to the acid regeneration system for treatment. (2) improve the structure of the acid tank and exhaust system, reduce the amount of acid fume, and reuse some condensed hydrochloric acid solution to achieve acid fume reduction and green treatment.

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.

The chemical composition, microstructure, and fracture morphology of 45 steel hot rolled wire rods were studied to resolve the problem of drawing fracture. The reasons of the drawing fracture of 45 steel were analyzed, and process improvement measures were proposed. The results indicate that the uneven microstructure and mixed crystals on the surface of 45 steel hot rolled wire rod, as well as the high proportion of ferrite in the microstructure, are the main reasons for the drawing fracture of 45 steel wire rod. The carbon mass fraction of 45 steel was increased from 0.43%-0.45% to 0.46%-0.48%, the finishing rolling temperature was reduced from 945 ℃ to 915 ℃, the wire feeding temperature was reduced from 940 ℃ to 890 ℃, the number of fans was adjusted from 1^#-7^# to 1^#-9^#, and the starting roller speed of Stelmor air-cooled roller was increased from 0.70 m/s to 0.85 m/s (the speed of each subsequent roller section increased sequentially), effectively improving the microstructure of 45 steel hot rolled wire rod, significantly increasing the proportion of pearlite, and improving the drawing performance of 45 steel hot rolled wire rod.

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 problem of unqualified low-temperature impact performance of 50 mm thickness EH36 grade ship plate in actual production, the reasons were analyzed and the improvement measures were applied. The results show that the presence of MnS and CaO-Al₂O₃type inclusions in the microstructure of the 50 mm thickness EH36 ship plate sample, as well as coarse ferrite and pearlite at 1/4 thickness, are the main reasons for its poor low-temperature impact toughness. The cleanliness of molten steel was improved by optimizing the secondary refining process, the ferrite grains were refined by optimizing the controlled rolling and controlled cooling process, no MnS inclusions were found in 50 mm thickness EH36 ship plate, and the inclusion level of CaO-Al₂O₃ type was controlled below 1.0 grade. The microstructure were mainly fine-grained ferrite at 1/4 thickness of the plate. The average impact toughness level under -40 ℃ was increased to more than 200 J.The unqualified low temperature impact performance problem of 50 mm thickness EH36 ship plate has been effectively solved, and its low temperature impact toughness has been significantly improved.

In order to solve the problem of unstable impact toughness of 60 mm thickness Q690D plate under DQ process, the effects of casting billet thickness and single pass reduction of roughing rolling on impact toughness of the plate were analyzed. The results show that the good impact toughness ofthe plate needs to obtain a certain proportion of lath bainite, granular bainite and polygonal ferrite. The thickness of the casting billet should be increased as far as possible to ensure that the thickness of the casting billet is above 335 mm (compression ratio is above 5.5) and the reduction of the roughing rolling is above 40 mm for at least 1 pass.

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.

Combined with the development trend of pipeline steel technology, in accordance with the latest requirements of domestic and foreign technical standards, and drawing on the development experience of large thick-walled X80 pipeline steel coil, the test research was carried out on the production of X90 pipeline steel coils for spiral welded pipes based on medium-thin slabs. The dynamic CCT curve of X90 pipeline steel was determined by the Gleeble-3800 thermal simulation tester, and the phase transformation law was obtained and the appropriate cooling rate was determined. On this basis, through the design of its chemical composition, and the fine control of smelting, continuous casting, rolling and cooling processes, the industrial trial production of 16.3 mm×1 550 mm gauge X90 pipeline steel coil was completed in 2 150 mm ASP medium thin slab continuous casting and rolling production of Angang. Its tensile properties are qualified, -20 ℃ impact energy is not less than 300 J, -20 ℃ impact shear area is not less than 90%, -20 ℃ DWTT shear area is not less than 90%, the microstructure is granular bainite, lath ferrite and dispersed M/A components, the property indicators meet the engineering requirements. The ø1 219 mm×16.3 mm steel pipe is made by spiral submerged arc welding, and the property indexes of the steel pipe are good. The successful trial production of X90 pipeline steel coil has achieved a major breakthrough in the production of ultra-high strength pipeline steel of using medium thin slab in China, which is of great significance for the development of ultra-large diameter, higher steel grade, and thicker walled pipeline steel coil.

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.

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.

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.

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%.

The causes of white spot defects that often occur at the edges of automotive sheets with a width of over 1 700 mm on the 2 250 mm production line at Hansteel Co. were analyzed which leading to product degradation. By using scanning electron microscopy to observe the microstructure of defects, it was found that there was a clear honeycomb like "sponge iron structure". energy spectrum analysis showed the presence of iron oxide, indicating that the residual edge oxide scale crushed and pressed in strip during hot rolling production was one of the reasons for the formation of defects. In addition, the thickness of the oxide scale on the edge of strip is also the main factor affecting its pickling effect, and the presence of edge waves also affects the straightening and pickling effect of cold rolling. The residual oxide scale forms white spot defects after annealing. Therefore, corresponding process improvement measures have been taken, including adding water curtains on both sides of the finishing mill outlet guide and sealing the edge nozzles to reduce cooling water splashing back at the edge of the work roll. Reduce the convexity of the strip, increase the coiling tension, accelerate the cooling of the coil, and reduce the thickness of the edge oxide scale. Optimize the calculation of thermal convexity and wear model of work roll of finishing rolling mills, control the timing of bending roll force, and increase the elongation of cold rolling straightening to improve strip shape and enhance the effect of straightening on scale breaking. Optimize the plan arrangement and eliminate reverse width rolling to avoid the serious impact of local wear of the work roll on the strip. After taking the above measures, the defect incidence rate was reduced to below 1%, greatly improving the surface quality of wide width automotive sheets.

Dual-phase steel has the advantages of high strength and strong extension, but it is difficult to process in cold rolling. Due to the characteristics of small diameter rolls and strong rolling ability, 18-high mill is gradually becoming the main mill for producing the strip hard to form. Compared with low carbon steel, the high strength of dual-phase steel makes it more challenging in cold rolling processing, so it becomes the technical research point of 18-high mill operation. Influenced by the strong deformation resistance of the material and the thickness difference fluctuation of the initial strip, the state of the rolling deformation zone is easy to fluctuate in the production process, which leads to the thickness difference fluctuation of the finished strip and affects the downstream industry and process. To solve these problems, the thickness fluctuation mechanism of the strip head and tail is analyzed, and its causes is traced. Based on the mill characteristic, structure characteristics and thickness control mechanism characteristics, the thickness control difficulties of dual-phase steel in 18-high mill are analyzed. The results show that a certain degree of phase transformation can also occur after the hot rolling coiling process of DP780 steel, which can be shown as the difference of bainite transformation degree at different target coiling temperatures, and can cause the mechanical properties of the cold rolling base material to fluctuate, and finally causes the thickness difference of the finished strip to fluctuate. Based on an 18-high single-stand rolling mill in a factory, the control characteristics and regulatory effectiveness of FF-AGC, FB-AGC, MF-AGC and BISRA-AGC are analyzed, the thickness difference combination control strategy of "FF+FB+Bisra" and the strip head thickness fluctuation control method using sine signal for interference control are proposed. The practical production show that this method can control the incoming material with thickness difference of up to 40 μm to the thickness differenceof ±10 μm, and achieve accurate control of the thickness difference of the full length,significantly improve the thickness pass rate of the finished strip, effectively improve the thickness control problem in the production of dual-phase steel in the 18-high mill, and provide a new idea and method for the production of high strength steel.

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.

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.