In the last 40 years, rolling technology has undergone radical and significant changes, which has also driven and facilitated the metamorphosis of rolling theory from classical to modern. The computers have played a vital role in this metamorphosis. First, along with the great success of finite element method (FEM) numerical simulation, and the increasing capacity of computer storage and computation, a group of commercial software gradually added the function of solving rolling problems. Rolling steel theorists gradually mastered commercial software usage such as ANSYS, MARC, ABAQUS, etc. The emergence and development of crystal plasticity finite element method (CP-FEM) in recent years has pushed the reach of numerical simulation of forming processes into the microscopic realm.Secondly, the arrival of artificial intelligence (AI) in the field of rolling theory has inspired a shift in focus from the endless search for the deep laws of rolling theory to something that is actually happened, and to dig out regularities from data, models, and causal relationships, which helps people to indirectly grasp the essential features of the rolling process.Furthermore,classical rolling theory research has not stopped developing either. The traditional Karman equations meet a new problem and to take on a new form dealing with the new field of variable gauge rolling (VGR), and even the principle of equal second flow, which is the cornerstone of the kinematics of the rolling process, has been shaken up in VGR. We can see that several generations of Chinese steel rolling researchers after nearly 40 years of learning, accumulation, catching up, and now has entered the forefront of rolling theory development. Chinese scholars are capable and confidence to shoulder the responsibility of guiding rolling practice with rolling theory.

In recent years, the role of rare earth elements in steel has been discovered one by one. Through the investigation of the latest literature on rare earth steel, the mechanism and theoretical research methods of rare earth elements in steel are analyzed. The results show that the addition of rare earth elements in steel not only has the effects of purification, inclusion modification and microalloying, but also plays a positive role in catalyzing surface nitriding and inhibiting hydrogen diffusion. The application field of rare earth steel is gradually expanding. Of course, the development of rare earth steel is also restricted by many aspects, such as rare earth raw materials, rare earth addition technology, process smoothness and microstructure and performance control methods. Some advanced characterization methods can accurately capture the segregation position of rare earth elements in steel and accurately identify the phases such as rare earth compounds, but they cannot provide a detailed explanation for the mechanism of action of rare earth elements in steel and the evolution of related microstractures. Therefore, the advanced research concept based on atomic scale simulation is emphasized, and computer calculation and simulation technology is used to fill the lack of micro-mechanism of rare earth atoms, so as to accelerate the research and development of high-quality rare earth steel.

The visual imaging of the outer surface of steel pipes is prone to problems such as uneven grayscale and local overexposure, resulting in serious omissions and false alarms during surface defect detection using two-dimensional grayscale images. Therefore, a defect detection system based on 3D point cloud for the outer surface of steel pipes is designed. Multiple sets of 3D cameras are arranged around the tested steel pipes to obtain point clouds that represent the contour of the steel pipes. Samples are collected to construct a steel pipe defect dataset. PointNet++models are trained for point cloud segmentation, and a set of data points representing defects is output. The range covered by the dataset is the defect location, and the distance information between the data points relative to the calibration reference plane represents the depth of the defect. This system is applied to industrial sites to achieve depth quantification while completing defect detection. Its detection ability for outer surface defects of steel pipes is equivalent to that of a flaw detector, and it has a lower false alarm rate and lower equipment installation and maintenance costs. At the same time, the system can be extended to similar intelligent detection scenarios.

With the rapid development of the steel industry towards product high-end and high-quality, production high-efficiency, greenization and intelligentization, the hot rolled strip rolling technologies have also made tremendous progress, and many innovative achievements have emerged. The recent progress in advanced control models, specialized rolling technologies and the construction of intelligent steel factories for the production of hot rolled strip is reviewed. The focuses have been on the intelligent process control models of the heating furnace, the rapid calculation model of the rolls and strip, the mechanical property prediction model, the transverse thickness difference control technologies of silicon steel, the high-order shape control technologies of high-strength steel, the cooling shape control technologies of high-strength steel after rolling, the high-efficiency rolling technologies of conventional hot rolling production lines, the edge drop control technologies of endless rolling production lines, the shape control technologies of thin strip casting and rolling production lines, the quality control big data platform, the multi-dimensional information perception technologies of materials, the multi-regional centralized control technologies of hot rolling, and the multi-business collaboration technologies of hot rolling. The continuous innovation and application of these technologies have forged new quality productive forces in the production of hot rolled strip, improved the competitiveness of hot rolled strip products, and promoted the overall technological progress of the steel industry.

Relying on the less manned/unmanned operation and maintenance centralized control based on advanced inspection and intelligent equipment support, as well as multi-business collaborative digital business control based on the industrial Internet platform, it has formed a “dual intelligent control” structure for the construction of steel rolling intelligent factory. However, in the field of research and application, the concept of intelligent equipment has not yet established a clear and explicit positioning understanding.The description of specific technology modules and case studies are combined to discuss the effect and value of intelligent equipment on intelligent factories. Firstly, by relying on the whole process of surface inspection of surface quality digital control, integration of “platform + equipment + video AI + tracking” material tracking by branch, raw material warehouse and heating furnace area billet inspection and anomaly identification verification, intelligent visual inspection equipment to assist in operation and maintenance management, etc., an intelligent equipment construction model based on advanced inspection with enhanced perception to support digital business management and control is proposed. Secondly, by introducing the application of multiple types of industrial robots, asymmetric inspection and automatic deviation correction control in hot rolling operation, automatic steel transfer in medium plate mill, and intelligent transformation of heating furnace and direct rolling technology,the construction of “intelligent equipment for measurement and control integration” in collaboration with the control system of the equipment of the main production process and the development trend of improving the stability of product quality and the level of automation of production are demonstrated. Thirdly, it introduces the intelligent unmanned warehouse technology for long products and the less manned technology for bars in the post-rolling area, which puts forward the development mode of realizing the enhancement of key operation indexes such as production efficiency and product yield through the application of multiple types of intelligent equipments for the areas that are lack of automation control, intensive manual operation and harsh working environment. Finally, it looks forward to the development trend of intelligent equipment, that is, to integrate more closely with the main production equipment and key quality control, to realize the “intelligent mill” oriented to efficient and high-quality production, and to support the improvement of the digital business management and control applications, and to promote the continuous improvement of the construction level of the dual-intelligent control “intelligent steel mill”.

In view of the high-frequency thickness fluctuations at the head and tail of DP590 cold rolled coils in a factory, the causes were researched. The results indicate that the uneven property of the hot rolled coils along the longitudinal direction is a significant factor leading to process instability during cold rolling and thickness fluctuations of cold rolled coils. The fundamental reason for the uneven longitudinal property lies in the existence of mid-wave defects and residual cooling water during the pre-air cooling stage of hot rolled strip coiling. Therefore, it is proposed to control the shape of the strip, enhance the blow-off capability of the laminar cooling system, and adopt U-shaped cooling and other process optimization measures to ensure uniform cooling conditions along the longitudinal direction of the strip during the air cooling stage.The stability of thickness control during the cold rolling process can be significantly improved. The excessive thickness length of the cold rolled coils has been reduced from 41 meters to within 10 meters, and the first inspection failure rate has decreased from 31.8% to 1.6%. This effectively resolves the problem of thickness fluctuations at the head and tail of cold rolled coils, thereby improving the yield rate.

Aiming at the problem of shape defects due to overcooling at the edges during laminar cooling of Q235B hot rolled thin gauge strip at coiling temperatures between 660-680 ℃, a predictive model for the width S_Cof the low-temperature zone along the edges of a 2 250 mm hot rolling production line was developed, with a prediction error controlled within ±6 mm. A finite element model of laminar cooling for hot rolled thin gauge strip was established to compare and simulate the temperature field across the width of the strip, the proportion of phase transformation, and the distribution of residual stresses under conditions of laminar cooling and uniform edge shielding strategies. The results indicate that during laminar cooling, a temperature difference of 300 ℃ between the edges and the middle of the strip causes rapid cooling at low temperatures, leading to the formation of bainite structure with a volume fraction of approximately 33.48% at the edges, accompanied by the generation of tensile and compressive stresses. By applying uniform edge shielding, the temperature difference between the edges and the middle of the strip was controlled within ±15 ℃, eliminating edge bainite structure while reducing the difference in the volume fraction of ferrite phase transformation between the edge and middle from 18.6% to 5.11%, thereby making the phase transformation proportion and residual stress distribution more uniform, improving the cooling strip shape, and eliminating wave defects at the edges of the strip.

During the hot rolling process of steels, the microstructure evolution, surface oxidation, and rolling force energy load of the rolled piece interact with each other, forming a complex black box system. For a long time, analytical models have been used for separation and solution both domestically and internationally, resulting in only approximate analysis and inability to achieve accurate solutions, which has constrained the further improvement of product comprehensive quality. Nowadays, a big industrial model of hot rolling that integrates force, microstructure evolution, and interface has been developed by deeply mining experimental data and industry data, achieving comprehensive and accurate analysis of the main hot rolling process. The development process and latest development direction of the evolution of steel microstructure and mechanical property prediction technology in China are introduced,the direction for the digital transformation of the steel industry are pointed out.

The process and equipment of hot rolled strip production line have been relatively mature, but still need to be further optimized and improved.The selection of reheating furnace and the control of burning loss in typical hot rolled strip production line, the determination of the main motor speed of the roughing mill and the thickness control system of the finishing mill are taken as the research objects. Through the analysis of the influence of the furnace type on the output and the relationship between the amount of iron oxide scale and the heating temperature, the suggestion of selecting the walking beam reheating furnace is put forward to avoid the limitation of the output source. Through the calculation of rolling schedule, load simulation and the price comparison of motors with different speeds, how to determine the better speed of the main motor is introduced. Through the analysis of the influence of different thickness control system on the thickness, accuracy and shape of products in the finishing mill, the suggestions on the selection of thickness control system are put forward. After the optimization of the equipment selection and parameter determination, the production capacity of the hotrolled strip production line can be increased, the burning loss can be reduced, the consumption can be saved and the product quality can be improved.

Compared with ordinary galvanized sheets, zinc-aluminum-magnesium products have many advantages such as good corrosion resistance, automatic repair of cuts and excellent ammonia resistance. Aiming at the difficulties in the design and selection of continuous zinc-aluminum-magnesium coating line using hot rolled substrate strip, the classification and application of zinc-aluminum-magnesium coating products are introduced.Independent production line and continuous pickling & galvanizing line, gas heating and induction heating, vertical furnaces and horizontal furnaces are compared and analyzed respectively. At the same time, the selection of zinc pots, the design of post-galvanized strip cooling process and equipment, and the zinc ash defects and humidification problems in the furnace nose are technically introduced and selected, providing a reference for the design and selection of similar lines.

In order to further reduce the production cost of high strength low alloy steel(HSLA), the effects of different contents of Nb, Mn and annealing temperature on the microstructure and properties of HSLA steel were studied.The results show that the annealing temperature has no obvious effect on the ferrite grain size of HSLA steel, but the higher annealing temperature is not conducive to the formation of pearlite structure, resulting in a higher content of solid solution C in ferrite, a yield platform in stress-strain curve, and the coarsening behavior of NbC precipitates leads to a decrease in strength of the product. The formation of banded structure in HSLA steel is mainly related to the diffusion behavior of C element, and higher annealing temperature is beneficial to reduce the degree of banded structure. When the mass fraction of Nb increases from 0.014% to 0.021%, the effect of fine grain strengthening and precipitation strengthening is obviously enhanced, and the strength level of HSLA steel is obviously increased. Mn element mainly plays a solid solution strengthening effect in HSLA steel.

In order to refine the microstructure and improve corrosion resistance, the influence of cooling rate on the Zn-Al-Mg alloys with different rare earth contents were theoretically investigated. The solidified microstructures and corrosion resistance of the La and Ce-added Zn-1.7%Al-1.1%Mg alloys were studied under different cooling rates (air cooling, water cooling, furnace cooling) and varied rare earth contents, and thermodynamic calculations, scanning electron microscopy (SEM), X-ray diffraction method (XRD) and electrochemical test were carried out in the present work. The results show that the thermodynamic calculations can predict the precipitated phases and the related precipitation sequence of the Ce-added Zn-Al-Mg alloys during the solidification process. The LaZn₁₃/CeZn₁₁primary phases were initially precipitated from the La and Ce added Zn-Al-Mg molten alloys, and the Zn-rich phase, Mg₂Zn₁₁/MgZn₂ phases and Al-rich phase were solidified from the molten alloys, respectively. With the increase of the cooling rate, more fined microstructures were obtained and the Mg₂Zn₁₁phase would turn into MgZn₂ phase. The reason lies on that the metastable phase transition Mg₂Zn₁₁↔MgZn₂takes place in the Zn-Al-Mg system when the cooling rate increases. The results of Tafel polarization test and electrochemical impedance spectroscopy test (EIS) show that with the increase of rare earth contents, the corrosion resistance of the alloys elevates to a certain extent. When the cooling rate increases, the corrosion resistance of the Zn-Al-Mg alloys can be improved prominently. It can be concluded that refined microstructure benefits to the increase of corrosion resistance, thus cooling rate acts as the main controlling parameter of the alloy corrosion resistance of the alloy.

In recent years, the development of rolling technology and the demand for functional enhanced steel materials in green and intelligent social transformation in China have significantly boosted the rapid progress of steel roll-bonding technology. The recent advancements in steel roll-bonding technology in China is reviewed, focusing on the control of the microstructure and properties of roll-bonded clad steel products, as well as on the control of the microstructure and processing performance of both base and cladding layers. Typical roll-bonded clad steel products such as heavy plates, hot rolled strips and cold rolled sheets, are also introduced along with their demonstration applications.Meanwhile, further research is proposed on developing of full industry chain technology and standards for product design, preparation, processing, and installation in specific application scenarios. Considering the facts that most roll-bonded clad steel products are entirely new materials, these technologies and specifications are still incomplete. It is necessary to organize efforts for research and development.

Since the reform and opening up, the technological progress of non-oriented electrical steel in China has made important contributions to the development of the steel and electrical industries, as well as to the growth of the national economy.The entire production process of non-oriented electrical steel is analyzed, and the production process progress of key processes such as smelting, hot rolling, cold rolling, heat treatment, coating, etc. is systematically elaborated, combined with production technology and equipment upgrading. From the perspectives of texture control, magnetic performance enhancement, and silicon steel strengthening technology, a thorough analysis is conducted on the relevant material science and technology mechanisms that support the progress of production processes. The technological development trend of non-oriented silicon steel is described around the development goals of “high-efficiency, high-end, green, and intelligence”. Chinese non-oriented electrical steel has formed a good development pattern of mutual support between technological innovation, product progress, and technological mechanism research. It is expected that the technological level and product quality of Chinese non-oriented electrical steel will continue to lead the global development trend in the future.

With the development of the automotive industry, the application of advanced high strength steel has become more and more extensive. A low-carbon cold rolled complex-phase steel containing Cr-Mo-Nb-Ti was designed. Intercritical heating, slow cooling and overaging heat treatment process were adopted. By optical microscope (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and tensile testing machine, the microstructure and mechanical properties of experimental steel under different heat treatment processes were studied. The results show that the microstructure of the experimental steel is ferrite + bainite + martensite under different heat treatment processes. With the increase of annealing temperature, the degree of recrystallization of ferrite is higher, the dislocation density of ferrite decreases, thesuper-cooled austenite increases, and more bainite is formed in the overaging stage. At lower overaging temperature, martensite is partially tempered to form tempered martensite. Under the annealing temperature of 800 ℃ and overaging temperature of 350 ℃, the experimental steel has optimum recrystallization degree and bainite/martensite tempering state. The number of large angle grain boundaries accounts for 44.7%, the yield strength of the experimental steel is 613 MPa, the tensile strength is 799 MPa, the hole expansion rate is 67%,and the tensile fracture presents large and deep dimples.The excellent formability of the experimental steel has been obtained.

In the production process of hot strip rolling, the coiling temperature is one of the key process control indicators, and its control accuracy will directly affect the uniformity of the microstructure and the stability of mechanical properties of hot rolled strip coil. In order to solve the problem of low accuracy in controlling the coiling temperature hit rate of thick gauge strip, the heat transfer method after rolling,finishing rolling temperature control model, and production big data were organically combined and systematically analyzed. The results showed that the setting of threading speed and the control of ultra-fast cooling pressure under dry head mode were the main influencing factors for the coiling temperature deviation of thick gauge strip. Therefore, the method for collecting the inlet temperature of finishing rolling was optimized to improve the accuracy of threading speed setting. At the same time, an ultra-fast cooling pressure control program was developed under dry head mode, which improved the accuracy of ultra-fast cooling flow control and thus improved the accuracy of coiling temperature control. Through the above optimization measures, the coiling temperature hit rate of thick gauge (thicknees h>13 mm) strip has been increased by 7.24%, achieving good results.

It is of great significance to develop new types of shipbuilding steel with ultra-high strength, good toughness, and excellent welding performance to meet the development requirements of large-scale and lightweight ships, and to achieve efficient production. Scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy were used to study the effects of direct quenching (DQ) and reheat quenching (RQ) processes on the microstructure and properties of nanoscale Cu-NiAl co-precipitation strengthened ultra-high strength steel. The results show that the microstructures of both DQ and RQ steels consist of lath martensite. After 550 ℃ annealing, the DQT steel forms a finer lath martensite microstructure and higher dislocation density, providing more nucleation sites for the high-density precipitation of Cu-NiAl phase. Compared with RQ steel, DQ steel has higher annealing stability, retaining a higher density and a higher proportion of small angle grain boundaries after annealing. Therefore, under the combined action of more pronounced precipitation strengthening and fine grain strengthening, the DQ steel exhibits higher strength after annealing, with a yield strength that is 100 MPa higher than that of RQT steel, reaching 1 425 MPa.

There are some problems, such as difficulties in data fusion, imbalanced process development, low accuracy of key process control models and insufficient collaboration and sharing between internal and external enterprises, in the manufacturing process of Shandong Iron and Steel Group Co., Ltd. To address the above problems, a multi-source data collection and heterogeneous data processing platform was built in Shangang, and the automatic conversion, matching and spatiotemporal synchronization of heterogeneous data were carried out. A dynamic digital twin model using data-driven fusion mechanism was applied to address key control challenges in processes of smelting and hot rolling. Through the digital industrial chain/supply chain collaboration platform for the steel manufacturing process, future-oriented digital innovation applications and steel digital collaborative manufacturing have been achieved. After the application of relevant technologies, the accuracy of order delivery has reached over 96.56%, and the per capita steel production has reached over 1 710 tons.

The coiling temperature and cooling rate have a significant impact on the structure and pulverization performance of scale in the production of 700 MPa beam steel. However, adjusting the coiling temperature on a large scale can affect the microstructure refinement and Ti element precipitation of 700 MPa beam steel, which can easily cause fluctuations in the mechanical and stamping properties of theproduct,and the control methods for the cooling rate after coiling are relatively limited. Therefore, from the perspective of adding alloying elements, this article studies the improvement effect of adding trace amounts Cr element on the thickness and pulverization performance of scale on the surface of 700 MPa beam steel (700L steel) while ensuring the mechanical properties of 700 MPa beam steel. The effects of adding 0.2%Cr element on the oxidation characteristics, scale growth pattern and pulverization performance of 700L steel were systematically studied using differential thermal analysis, scanning electron microscopy, and cold bending tests. The results showed that after adding 0.2%Cr element, the oxidation resistance of 700L steel increased below 1 050 ℃.At 1 000 ℃, the weight decreased percent of 700L steel during isothermal oxidation can reach 26%, and an element enrichment layer with a thickness of nearly 6 μm is formed at the interface of the scale. Industrial production tests have shown that under the same hot rolling process conditions, the surface scale thickness of 700L hot-rolled plate decreases from 10-15 μm to 6-8 μm after adding 0.2%Cr element. The proportion of scale pulverization and peeling has decreased from 40% to about 7%.

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 effect of controlled cooling process after hot rolling on the microstructure and mechanical properties of 75Cr1 steel after spheroidizing annealing was invesgated to meet the requirements of high strength, good toughness, corrosion resistance, high hardenability and thermal stability for saw blade steel. Electron probe microanalyzer (EPMA) and transmission electron microscopy (TEM) were utilized to characterize the microstructure of the experimental steel after hot rolling and spheroidizing annealing. The results revealed that different controlled cooling processes after rolling produced three types microstructure of hot rolled experimental plates with lamellar pearlite, pearlite+ferrite and pearlite+bainite microstructure. When the microstructure of the experimental plate after hot rolling was lamellar pearlite, the cementite particles were evenly distributed after spheroidization annealing, and the yield strength and tensile strength were 473 MPa and 556 MPa, respectively. When there was ferrite in the hot rolling microstructure, the spheroidized cementite particles aggregated, the grain size increased and the strength of the plates decreased. When the microstructure of the experimental plate after hot rolling was bainite, the diffusion distance of carbon atoms in the spheroidizing process was shortened, and a good spheroidized microstructure was obtained. The yield strength and tensile strength after spheroidization annealing were 553 MPa and 638 MPa, respectively. A comparative analysis was conducted on the spheroidization annealing effects of plates with different hot rolled microstructures. It was observed that controlling the final cooling temperature at about 510 ℃ during hot rolling resulted in a bainite microstructure whih facilitated obtaining a favorable spheroidized annealing microstructure compared to lamellar pearlite or ferrite+pearlite microstructures.

The various processes involved in strip rolling have reached a high level of control. However, the complexity of process coupling and operating conditions limit the improvement of product quality and production efficiency. Enhancing model accuracy and dynamic adaptability to complex operating conditions, as well as achieving coordinated optimization within and between processes, pose challenging issues in strip rolling. Digital techniques play a crucial role in improving product quality, enhancing production efficiency, reducing costs, and minimizing emissions. They are key drivers for the transformation and upgrading of steel enterprises, continuously enhancing competitiveness. Firstly, the characteristics of the strip rolling process and proposes solutions for digital upgrades were analyzed. An overall framework for the digital upgrading of the strip rolling process, which consists of industrial internet, intelligent perception and dynamic digital twins, whole-process multi-process coordinated optimization, and cyber physical system (CPS), was presented. Subsequently, the current development status of strip rolling process intelligence from four aspects, i.e. industrial internet, digital twin models, whole-process coordinated optimization, and CPS, were reviewed. Finally, based on the current status of digital development, prospects for the future development direction of digital technologies in strip rolling were provided.

Under the background of double carbon, the development of super wear-resistant steel products with higher strength and better wear resistance can further reduce the economic loss and resource waste caused by material wear. The ultra-high strength wear-resistant steel with tensile strength of 1.9 GPa was developed. Through reasonable chemical composition design and heat treatment process, the ultra-high strength wear-resistant steel with good comprehensive properties was trial-produced, and the effect of tempering temperature on its microstructure and mechanical properties was studied. The results showed that the excellent comprehensive mechanical properties of the trial plate were obtained by quenching at 880 ℃ and tempering at 180 ℃. The tensile strength was 1 951 MPa, the elongation was 14%, and the impact energy at -40 ℃ was 45.6 J. The microstructure of the plate was fine lath martensite, and there was a small amount of lamellar austenite between the laths, which increased the toughness of the plate. Among the various strength increment contributions, Ti(C,N) and Nb(C,N) nano-carbides produced by microalloying provide a precipitation strengthening increment of 243 MPa. After tempering at 180 ℃, high-density quenched dislocations were still retained, providing a dislocation strengthening increment of 828 MPa.

The progress of wide strip hot rolling technology in recent years is preliminarily summarized and introduced, including: production line and output development of hot rolled wide strip in China; high efficiency rolling, energy conservation, carbon reduction, TMCP and low cost control technology of hot wide strip production in conventional hot continuous rolling process; conventional rolling process, semi-endless and endless rolling process of thin slab continuous casting and rolling to produce high strength/ultra-high strength steel strip and ultra-thin strip rolling technology; predictive control of microstructure and properties, surface quality and strip thickness and shape control of hot wide strip; hot wide strip production digitalization, intelligent technology progress, etc. The statistical data show that whether it is the progress of conventional hot continuous rolling, thin slab continuous casting and rolling, endless rolling, thin strip casting and rolling production line equipment control technology, or hot wide strip rolling process, product development, microstructure,properties and quality control, as well as hot wide strip production digital, intelligent, green and other technical progress, have produced a development from quantity to quality. It has made an important contribution to promoting the progress of metallurgical science and technology and the national economic construction.

In order to solve the problem that the surface of galvannealed steel sheet is easy to appear the white spot color difference stripe defect in the actual production process, the morphology and composition of the normal part and the white spot defect part were compared and analyzed, the formation mechanism of white spot defect was revealed and the improvement measures were put forward. The results show that the white spot on the surface of the gray coating is normal dark gray on the edge and obvious white strip in the middle, and the white spot is actually an underalloying defect, the underalloying in the middle of strip is mainly caused by C-warpping in the head of strip, which results in the coating thickness on the upper and middle of strip being larger than that on the lower surface, and the Fe content on the upper surface is lower. By optimizing laminar cooling, strictly controlling the roll diameter of temper mill, increasing the tension of cooling section and reducing the pressure of correcting roll of zinc pot, the C-warping defect of strip was effectively improved, achieving good results.

Wear-resistant steel for construction machinery not only requires high wear resistance, but also should have good plasticity and toughness. Through the design of medium Mn alloy composition and annealing in two-phase region, the introduction of retained austenite (RA) in high Ti content martensitic wear-resistant steel can make the wear-resistant steel obtain good plastic toughness and wear resistance.The research results show that with the increase of annealing holding time in two-phase region at 630 ℃, the volume fraction of RA increased. After holding for 8 h, the volume fraction of RA of sample was 32.1%, and the elongation was 17%. During the tensile process, the work hardening rate curve of the samples annealed in the two-phase region first decreased and then increased slightly, then remained stable, and finally began to decrease until the sample breaks. The increase of the work hardening rate was related to the strain-induced martensitic transformation. High work hardening rate was beneficial to the increase of elongation of the steel. Compared with the rolled sample, the hardness of the sample annealed in the two-phase region for 8 h was reduced by 120HV, but the relative wear resistance was increased by 23%. The wear morphology of the sample annealed in the two-phase region was grooves and spalling pits, while the wear morphology of the rolled sample has more plastic deformation fatigue spalling in addition to grooves and spalling pits. Because of the low elongation, poor plasticity and fatigue resistance of the rolled sample, the experimental steel was prone to spalling due to plastic deformation fatigue during repeated deformation. In addition, during the wear process, the RA in the two-phase region annealed sample will undergo phase transformation, resulting in phase transformation induced plasticity effect and increasing the work hardening rate. The work hardening rate in the later stage of tensile had a great influence on the wear resistance. The higher the work hardening rate was, the better the wear resistance was. The X-ray results show that the volume fraction of retained austenite in the samples annealed in the two-phase region after wear will decrease by more than 50%.

Aiming at the problem of perforation crack in GCr15 bearing steel during break-down rolling, the causes were analyzed by the means of metallographic microscope, scanning electron microscope and FEI metal quality analyzer, and the improvement measures were put forward. The results showed that the perforation crack of GCr15 bearing steel originated from the core of the billet, and there were no inclusions or slag inclusions around the core crack. The microstructure was normal and there was no overheating and over burning phenomenon, indicating that the billet heating temperature was normal, while the obvious decarburization of the core crack indicated that it had expanded to the surface of the billet before leaving the heating furnace. Combined with the shot blasting test before the billet was put into the furnace, it was concluded that the core crack was generated during the heating process. Based on the macro-morphology of the section and microstructure of the defective billet, the perforation crack of GCr15 bearing steel is caused by supplementing gas supply when it cools down to below 1 000 ℃ and then heats up to 1 280 ℃ for rolling quickly. The billet is heated too fast, and the frequency of perforation crack greatly increase. And based on this, the heating process is optimized. For cooling problems such as insufficient gas supply of GCr15 bearing steel, it is necessary to wait for the heating furnace to regain its heating capacity. For the first heating, the temperature should be raised to over 1 000 ℃ according to the heating speed of 30-50 ℃/h in preheating stage, so that the billet can be fully austenitized. And then the billet can be heated rapidly. The adoption of this improved process can completely eliminate the problem of perforation crack during the hreak-down rolling process of GCr15 bearing steel.

Low density steel generally contains higher content of Al elements, which can reduce material density and achieve better lightweight effects, but it is easy to generate high temperature δ ferrite phase. This phase forms a coarse banded structure during the hot rolling process, which is difficult to eliminate through heat treatment, ultimately resulting in severe anisotropy of the steel. In response to the above issues, a low-density medium manganese steel with a chemical composition of 0.36%C-4.5%Al-7.6%Mn-0.31%V-0.31%Si-0.07%Ti was designed. Different rolling methods (hot rolling and warm rolling) and annealing process parameters (30 minutes insulation at 1 000 ℃, 1 100 ℃, and 1 200 ℃) were studied to reveal their influence on the evolution behavior of high temperature δ ferrite. The results indicate that with the increase of high temperature annealing temperature, the banded high temperature δ ferrite in the experimental steel gradually becomes short rod-shaped, the proportion of austenite content continuously decreases, and the size of high temperature δ ferrite continues to widen. The width of high temperature δ ferrite in the hot-rolled sample increases from 3 μm to 11 μm, while its width in the warm-rolled sample increases form 0.5 μm to 9 μm. As the annealing temperature increases, the large angle grain boundaries in banded high temperature δ ferrite increases and the entire coarse banded δ ferrite grain is segmented. When annealing at 1 200 ℃, the typical grain boundary orientation differences of high temperature δ ferrite obtained from the hot-rolled sample are 3.92°, 13.4°, and 35.6°, while the grain boundary orientation differences obtained from the warm-rolled sample are 42.2°, 54.2°, and 58.5°. Compared with the hot-rolled samples, the short rod-shaped high temperature δ ferrite can be obtained in the warm-rolled samples with a higher volume faction and finer size. The banded high temperature δ ferrites are basically all transformed into short rod-like shape in the warm-rolled sample annealed at 1 200 ℃ for 30 min, which indicates that the warm rolling process is more conducive to eliminating banded structures. In addition, directly cooled samples are prone to brittle fracture, and low-temperature tempering can improve the mechanical properties of low-density medium manganese steel in hot-rolled experimental state after high temperature annealing, significantly increasing the product of strength and elongation from 0.95 GPa·%to 29.36 GPa·%.

Aiming at the problem of micro-cracks about 0.1-0.3 mm in length inside the low-carbon and low-alloy structural steel bars produced by a steel plant, the micro-cracks inside the steel bars were analyzed and studied through low power structure inspection, optical microscope and scanning electron microscope observation, and process improvement measures were proposed. The results show that after hot rolling, multiple micro-cracks with a length of about 0.1-0.3 mm, which were not connected to each other and no directionality, appear inside the steel bars. There were no metallurgical defects such as abnormal inclusions around the micro-cracks. The micro cracks propagated along the pearlite strip with a banded structure, and a mixed structure of bainite and martensite was distributed around the pearlite strip. Compositional segregation resulted in the formation of high-grade banded structures in steel bars, and mixed structures of bainite and martensite existed around the banded structures, which were more likely to produce micro cracks when large plastic deformation occurred. During continuous casting, the superheat was controlled at 20-30 ℃, the electromagnetic stirring parameters were set at 200 A and 2.0 Hz, the specific water content in the secondary cooling zone was reduced to 0.41 L/kg, and the casting speed was controlled at 1.2 m/min, which could reduce the banded structure from the source of the continuous casting billet. The composition segregation could be improved by appropriately prolonging the holding time of billet at high temperature of (1 180 ± 10) ℃ to 250-305 min. The slow cooling of the hot rolled steel bars into the pit could avoid the generation of bainite and martensite structures. After the process improvement, no internal crack defects were found in the non-destructive testing of hot rolled low-carbon low alloy steel bars, and the improvement effect was significant.

In recent years, in order to achieve the lightweight of automotive components, countries have continuously explored and developed low-cost high-strength metal materials. Q&P steel has gradually become the mainstream product of automotive high-strength steel with high strength, high ductility and easy weldability. In order to optimize the actual production process, the effect of the original microstructure on the phase transformation behavior of high-strength steel in the process of hot working was investigated. The austenitizing and grain growth of high-strength steel plates with different original microstructure and the phase transition during cooling were observed in situ by dynamic thermodynamic simulation tester, Confocal-Laser-Scanning-Microscopy (CLSM) and Axia Chemi tungsten filament scanning electron microscope (SEM). The results show that when the final cooling temperature is 350 ℃, 550 ℃ and 680 ℃, the original microstructure of the high-strength steel plate at the three final cooling temperatures is “martensite + ferrite” (M+F), “bainite + ferrite” (B+F) and “pearlite + ferrite” (P+F), respectively. It is found that the critical austenitic temperature (Ac₁) of the high-strength steel plate with the original microstructure of “P+F” is 647.9 ℃, which is 417 ℃ different from the critical temperature of austenite grain abnormal growth. The growth mode of austenite grains is grain boundary migration and small grain merger, and the average austenite grain size is 0.66 μm. The martensitic initial transition temperature (M_s) is 362 ℃, so there is a wide hot processing process window, which is conducive to the flexible control of Q&P heat treatment process in industrial production.

Surface decarburization of spring steel is the main reason for its fatigue life, for which many scholars have proposed various models to simulate its decarburization behavior. Considering the oxidation behavior in the decarburization process, a two-dimensional oxidation-decarburization synthetic model of spring steel billet based on finite volume method was proposed. Isothermal heating experiments were carried out on 55SiCr spring steel in air atmosphere. Under the conditions of 950-1 150 ℃ and 30-150 min isothermal heating, the thickness of the oxide layer changed with time in a parabolic trend. According to the experimental results, the calculation model of the oxide layer thickness of 55SiCr spring steel was established. According to Fick's second law, the two-dimensional decarburization mathematical model of 55SiCr spring steel was established. The two models were combined to obtain the two-dimensional oxidation-decarburization synthetic model of spring steel billet. The model can quantitatively describe the effects of heating temperature and holding time on the surface decarburization of spring steel. The prediction results of the decarburization model were compared with the experimental results, which verified the effectiveness of the model.

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.

In order to improve the stability of the strip shape in the rolling with long kilometers of ESP production line, and solve the quality problems such as ribbing of coils and serious wave shape in the middle and late period, a large number of field tracking tests, data analysis and research were carried out on the factors affecting the continuous casting kilometers, such as the drawing speed of continuous casting, the temperature difference of the slab section, the roll shape, the wear model, the matching of axial and transverse movement of rolls, the key process of the rolling line and the temperature control. A complete set of ESP long kilometer rolling technical scheme was formed, such as casting speed increase system, temperature difference control strategy of casting slab section, rolling process and thermal history control, roll shape design,load distribution optimization, wear and roll shifting coefficient adjustment, etc., and the ESP headless rolling production line was successfully realized with a single pouring time of 200 km long continuous rolling. The operation rate and yield rate of the mill are greatly improved, the rolling cost is effectively reduced, and the economic benefits are remarkable.

Aiming at the problem that Q500MEZ35 heavy plateis difficult to quench through due to the insufficient on-line cooling capacity, the 40 mm thickness plate was developed for trial production. In the process of steel smelting, the inclusion size can be reduced by controlling the mass fraction of S element less than 0.002%, adding Ca line and rare earth element Ce, etc., so as to improve the Z-direction resistance to laminar-tear of plate. More and smaller (Ti,Nb,V)(C,N) second phase particles were precipitated by the finishing rolling process with low temperature and large deformation, which provided more nucleation sites for the subsequent ferritic transformation. Through different final cooling temperatures (580-350 ℃) tests, it is found that with the decrease of final cooling temperature, the long-range diffusion ability of C atom is weakened, the stability of residual austenite is reduced, and the size of M/A island is reduced. At the same time, the ferrite grains nucleate in shear mode and grow up due to the limitation of C diffusion, and finally form fine lath acicular ferrite. When the final cooling temperature is 350 ℃, the main microstructure of the plate is fine granular bainite and acicular ferrite, and the impact property is the best.

In the actual production process of the hot rolling production line, the intermediate billet is limited by the temperature of each pass, and it needs air cooling to wait for temperature, which has a certain impact on the rolling efficiency of the production line. Through the finite element simulation analysis, after the intermediate cooling process is put into use, the intermediate billet is rapidly cooled by the ultra-density header. Combined with the air cooling rewarming time of 20—50 s, the temperature inside and outside the intermediate billet tends to be uniform, and the maximum temperature difference in the thickness direction is less than 28 ℃, which can effectively improve the property stability of the slab, reduce the air cooling time of pendulum steel and improve the rolling rhythm. A medium-pressure water jet cooling header device with ultra-density layout was designed and developed, and the intermediate cooling equipment was put into the actual production application of wheel steel. The results show that compared with the actual production of conventional wheel steel, when the intermediate cooling equipment is put into operation, the average rolling time of each slab is shortened from 115 s to 102 s, the rolling rhythm time is shortened by 13 s, the number of coils per hour is increased by 4 coils/h, and the output per hour can be increased by 104 t. By comparing the number of different intermediate cooling water groups input and the microstructure and properties of the products, when the number of cooling water groups input by the intermediate cooling equipment increases, the banded structure of the wheel steel along the rolling direction is gradually broken completely, and the grain size in the center is smaller, and most of them are uniform equiaxed crystal. With the increase of the number of cooling water groups input by the intermediate cooling equipment, the yield strength fluctuation of wheel steel decreases by 42 MPa, and the elongation fluctuation after fracture decreases to 2%, and its properties tends to be more stable. At the same time, it also reduces the fluctuation of impact energy of wheel steel at low temperature.

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%.

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 order to explore the effect of trace rare earth elements on the phase transformation behavior of high strength steel for offshore platform, the phase transformation point and continuous cooling transformation (CCT) curve of undercooled austenite of FH460 steel with different rare earth Ce element content were measured by Formastor-FII automatic phase transformation instrument. The microstructure of FH460 steels under different cooling rates was observed and the microhardness was measured. The influence mechanism of rare earth Ce element on microstructure transformation of FH460 steel was analyzed by first-principles calculation. The results show that with the increase of rare earth Ce element content, the temperature Ac₃ ofFH460 steel increases, the temperature Ac₁ decreases, and the austenite zone is expanded. Compared with FH460 steel without Ce element, the CCT curve shape of FH460 steels with Ce element is basically unchanged, but the pearlite transformation zone and bainite transformation zone are expanded, and the Ce element inhibits the transformation of martensite. When the cooling rate is 30-90 ℃/h, the hardness of FH460 steel with rare earth Ce element is significantly higher than that of FH460 steel without Ce element. The addition of trace rare earth Ce element did not change the microstructure evolution of FH460 steel at different cooling rates. However, after adding trace rare earth Ce element, the pearlite was refined and the content was also significantly increased. At the same time, the transformation of bainite and the decrease of martensite lath spacing were promoted.

The first bright annealing unit of stainless steel strip in China was introduced, which integrated continuous bright annealing, double-stands leveling and stretch-bending straightening processes. The raw material strip gauges, production process flow, high-speed and intelligent control scheme were described as well as the technical parameters of main equipment. At the same time, the innovations of the design of the unit were introduced, which combined the double-stands leveling and tension-leveling process in the continuous annealing process of carbon steel strip to produce 200, 300 and 400 series high surface quality 2D, 2B and BA products. In addition, the inlet looper and outlet looper were designed by common rail technology, which greatly reduced the investment cost, improved the product quality and decreased the production energy consumption of the product.

Chinese technological progress in the fields of pickling, rolling, annealing, galvanizing & coating and core equipment, green and intelligent development of cold rolling was summarized.Some representative, global leading or global first or first technical achievements, methods or products in the field of cold rolling in China were described, such as high-grade silicon steel cold continuous rolling technology, cold continuous rolling technology for ultra-high strength steel, high magnetic induction oriented silicon steel and ultra-thin high-strength non-oriented silicon steel rolling technology, ultra-high strength steel production technology, development of high functionality and high corrosion resistance coating products, as well as the achievements in cold rolling green and intelligence.Through the efforts of Chinese cold rolling workers in recent years, the high-efficiency, high-end, green and intelligent achievements have made Chinese contribution to the development of cold rolling technology in the world.