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.

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”.

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.

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.

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.

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.

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.

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.

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.

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·%.

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.

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.

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.

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 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.

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.

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.

Aiming at the development of low-cost, high-performance DP780 hot rolled strip, the chemical composition of the optimized design is carried out to reduce the addition of expensive alloying elements Cr, Mo, V, etc., and the content design of C, Si, Mn is optimized. The designed chemical composition is as follows:w(C) =0.105%, w(Si) =1.15%, w(Mn) =1.7%, w(Ti) =0.01%. Combined with the integrated ultra-fast cooling system of front ultra-fast cooling + laminar cooling + rear ultra-fast cooling, a machine learning model of ultra-fast cooling heat transfer coefficient based on extreme learning machine was established, which effectively improved the control accuracy of the outlet temperature of front ultra-fast cooling and coiling temperature. Based on this, the effects of the front ultra-fast cooling outlet temperature and coiling temperature on the microstructure evolution and mechanical properties of DP780 hot rolled strip was investigated. The results show that the microstructure of DP780 hot rolled strip is ferrite and martensite when the coiling temperature is set at 190 ℃. The volume fraction of martensite decreases and the volume fraction of ferrite increases with the decrease of the front ultra-fast cooling outlet temperature. The microstructure of hot rolled strip is mainly ferrite, martensite and a small amount of bainite when the front ultra-fast cooling outlet temperature is set at 610 ℃ and the coiling temperature is 230 ℃. However, with the decrease of coiling temperature, the bainite in the microstructure gradually disappears, the volume fraction of martensite decreases, and the volume fraction of ferrite increases. The DP780 hot rolled strip with low cost and high performance was obtained by the integrated control process of hot rolling and ultra-fast cooling, with yield strength of 641 MPa, tensile strength of 1 068 MPa, elongation at break of 11.5% and strong plastic volume of 12 282 MPa·%.

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%.

With the continuous growth of energy demand in China, pipeline steel, as the core material for oil and gas pipeline construction, has seen rapid development in its production technology. The progress of pipeline steel production technology in China is summarized,and the development history of pipeline steel production in China is reviewed and sorted out, demonstrating the breakthroughs in pipeline steel production technology from early low-grade products to today's high-performance, high-grade pipeline steel. It high lights the key technologies in current pipeline steel production, including innovations in chemical composition design, rolling process, and microstructure control. Furthermore, it delves into the research progress of product characteristics and production control technologies for pipeline steel in terms of corrosion resistance, high strength, and low-temperature resistance. At the same time, it points out that the development of hydrogen storage and transportation, new oil pipelines and equipment, and the application of digitalization and artificial intelligence technologies in new energy are the research and development priorities for pipeline steel production technology in the future.

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.

A 304 stainless steel was rolled at different temperatures to explore the effect of rolling temperature on the microstructure evolution of metastable austenitic stainless steels and their mechanical property. The microstructure feature of deformed samples was observed via optical microscopy, scanning electron microscopy and transmission electron microscopy, and the corresponding mechanical properties were evaluated by Vickers hardness and quasi-static uniaxial tensile testing. The results showed that deformation-induced martensitic transformation occurred when the experimental steel was cold rolled at room temperature, leading to the formation of massive martensite. When warm rolled at 200 ℃, martensitic transformation was completely suppressed, the dominant deformation mechanism was twinning. Further increased the rolling temperature to 600 ℃, the formation of deformation twinning was also inhibited, and dislocation slip became the solely coordinated deformation mechanism. The increase of stacking fault energy caused by the increased rolling temperature is believed to be responsible for the transformation of deformation mechanism. Sample after cold rolling at room temperature, having about 84% volume fraction of martensite, possessed ultrahigh tensile strength of 1 710 MPa, and hardness of 473HV. As the rolling temperature increased, hardness and strength of the experimental steel decreased significantly, while the plasticity increased dramatically. All the warm-rolled steels showed a good combination of high strength and superior ductility,but Lüders strain accouted for more than 36% of the total elongation.

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.

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.

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.

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 surface color difference problem of copper plated alloy welding wires was studied by SEM, EDS etc. It was found that for alloy welding wire steel with high Si content, such as ER70S-G, iron oxide scale with Fe₂SiO₄ and oxide cracks were prone to appear on the surface of the cast billet, which were difficult to remove. After rolling and wire rod drawing, they were inherited to the surface of the welding wire, causing poor copper plating and resulting in surface blackening. The relationship between Fe₂SiO₄, iron oxide scale, oxide cracks and the heating temperature, heating duration, and residual oxygen content was studied. When the heating temperature was above 1 150 ℃, the proportion of Fe₂SiO₄ in the iron oxide scale significantly increased.Under 1 100 ℃, oxidation reactions continued to occur and oxidation cracks significantly depened with the prolongation of heating duration. The higher the residual oxygen content in the furnace, the faster the oxidation rate of the billet. The oxidation rate of billets under a 10% residual oxygen content was four times that of a 2% residual oxygen content. To solve the color difference troubles, two retaining walls were added to the heating furnace and a special billet loading method is adopted. Thus the heating duration is cut down to be about 80-90 minutes. The temperature of furnace entrance is decreased to be less than 750 ℃. The first heating stage temperature is about 770-820 ℃, the second heating stage temperature is about 950-980 ℃, and the uniform heating stage temperature is about 1 050-1 100 ℃. This heating process solves the surface blackening problem of the high Si content welding wire products.

Aiming at the problem of bending cracks during the processing of 45Mn steel parts, the causes of bending cracks were analyzed and the production practice of improving the cold bending property of 45Mn steel through the slab hot spraying process was introduced. The results show that the presence of a fully decarburized layer and an intergranular oxide layer on the plate surface, along with the tensile stress on the outer surface during bending, lead to stress concentration at the interface of these layers, resulting in microcracks that serve as the initiation point for cracking. This is the primary cause of bending cracks during the processing of 45Mn steel parts. Under the condition of identical chemical composition and matrix microstructure, the intergranular oxidation on the surface of 45Mn steel is the main factor affecting its cold bending property. The application of a hot spraying anti-oxidation coating process on the slab before hot rolling can effectively inhibit the formation of intergranular oxidation on the plate surface, improving the cold bending property of 45Mn steel, enabling it to bend 180° without cracking, and there is no significant impact on its tensile strength, yield strength and elongation.

With the further improvement of forming efficiency and processing yield of enamel steel, the demand for wide and thin gauge deep-drawing enamel steel increases day by day. However, there are technical bottlenecks such as scale penetration, tail swing, wave shape and poor forming performance when using traditional hot rolling technology. Therefore, hot rolling pickling wide and thin gauge deep-drawing enamel steel is developed based on thin slab continuous casting and rolling line. The chemical composition design, production process, strip surface quality and mechanical property stability control process of deep-drawing enamel steel are introduced. The research and production practice show that the mechanical properties of finished products are uniform, and they have excellent formability, fish scale resistance and adhesion properties. The yield strength of the strip directly affects its deep drawing properties. The effective Ti content in steel, finishing rolling reduction distribution and finishing rolling temperature have significant effects on the yield strength of the strip. The coiling temperature has little effect on the yield strength of the strip. The main strengthening mechanism of deep-drawing enamel steel is solid solution strengthening and fine grain strengthening, and precipitation strengthening is weak. Based on the successful development of hot rolled pickling wide and thin gauge deep-drawing enamel steel in thin slab continuous casting and rolling line, the stable batch supply of 1.65 mm×1 500 mm extreme gauge deep-drawing enamel steel exceeds ten thousand tons, filling the market gap.

In the process of producing strip in the cold rolling mill, unreasonable rolling process parameters will lead to serious plastic deformation of the strip product, resulting in cavity opening defects in the coiling of the produced strip. In order to prevent the serious loss caused by cavity opening defects, the tension system optimization model with the goal of preventing strip cavity opening defects was established by calculating the lubricating oil film thickness, friction factor and rolling force by fully combining the process flow and equipment characteristics of the cold rolling mill. By optimizing the tension between the stands of the cold rolling mill, the model reduces the rolling force as much as possible while ensuring the reduction rate, which effectively solves the problem of strip cavity opening in the rolling process of the cold rolling mill. After applying the optimization model in a domestic production site, the incidence of strip cavity opening defects decreased by about 6%, which significantly improved the product quality and production efficiency of strip manufacturers.

As a key part of the finishing process, the straightening process plays a non-negligible role in the quality control of medium and heavy plate shapes. The reasonable straightening process generally realizes the correction effect of the plate by setting the amount of reduction and the amount of bending roll. After on-site investigation, it was found that there were mainly one-dimensional bending defects and two-dimensional wave defects in straightening production. With the help of the ANSYS/APDL module, a three-dimensional finite element model of the dynamic straightening process was established with command flow, and the effects of different straightening methods on the flatness and shape of the straightened plate were simulated and studied. The results show that when the plate has a one-dimensional bending defect, the inlet and outlet reduction amount play a key role, and the residual stress of the straightened plate can be minimized by adjusting the reduction amount, which can significantly improve the flatness of the plate and achieve the expected straightening effect. When the plate has two-dimensional wave defects, due to the uneven longitudinal extension of different parts of the plate, in order to achieve the purpose of straightening, it is necessary to act together with the reduction amount and the amount of bending roll to evenly deform and extend. In addition, on the basis of simulation analysis, the relevant tests were carried out by using the straightening equipment at the production site of a company's wide and heavy plate factory, and the test data showed that the simulation conclusions were consistent with the test results, which provided a basis for the straightening methods of plates with different plate shape defects, and had certain guiding significance for actual production.

There are more than 20 heavy plate production lines with single stand rolling mill, accounting for about 30% of the total number ofheavy plate production lines in China. However, it is lack of research on batch rolling strategy and production equipment based on single stand rolling mills. To improve the production efficiency of single stand rolling mills, reduce the energy consumption and maximize the benefits of such production line, the multi-slab rolling strategy and the control logic of such technique are studied. Focusing on the process characteristics of large slab thickness and long waiting time under the condition of TMCP two-stage rolling process, the rolling strategy and control method of multi-slab rolling are discussed, and the core algorithm of such strategy is developed. According to the calculation results and production data of heating, rolling, cooling, straightening and other related process models, the AnyLogic process simulation software is used to build a rolling process simulation platform, and the production process of multi-slab rolling under different rolling processes is simulated and analyzed, the process is optimized, and the equipment utilization rate and rolling mill capacity are improved by optimizing the process layout and adding bypass roller tables, providing a reference for selecting the optimal rolling process and rolling strategy.

The development and changes of bar and wire rod production output and product structure in recent years in China were analyzed. For the process simplification of bar and wire rod production, starting from the rolling process, the technological advancement is introduced andsome new ideas are proposed from three aspects: simplifying the interface with the previous process, simplifying the rolling line itself and simplifying the interface with the subsequent process. Based on the above, the challenges and the development direction that bar and wire rod will face in the future in China at process simplification are discussed. It points out that innovation of process simplification is the top priority during the product structure optimizing and technological equipment upgrading for bar and wire rod, and is also the main technological direction that the entire industry chain needs to work together towards.

The Yongyang Boutique Light Rail Project in Hebei Province adopts semi-continuous rolling production technology, intelligent pre-bending and straightening processes, and fully automatic and efficient finishing lines, breaking the traditional light rail production process and creating a new mode of light rail production. A detailed introduction of the product plan, design difficulties, process flow of the new generation light rail production line, advanced technologies adopted, as well as the construction and operation of the production line is provided. At present, the production line has been running steadily, with high production efficiency and good product quality. Compared with traditional processes, the yield has increased by 3%, the comprehensive operation rate has increased by 5%, the electricity consumption per ton of steel has decreased by 5%, and personnel has been reduced by 25%. The comprehensive benefits and various indicators have reached the industry-leading level. It provides reference for equipment upgrading, product structure adjustment, and product quality improvement of other steel production enterprises, and also opens up new ideas for steel engineering design for engineering designers.

Titanium/steel composite materials with high bonding strength have become key foundational materials in fields such as marine, chemical, and energy due to their strong corrosion resistance. Due to titanium being an active metal, the Fe-Ti brittleness phase during the preparation process is a common problem faced by the preparation of titanium/steel composite materials. Different composite interface structures are constructed through microstructure regulation and their formation mechanisms are explored. The results show that after modification and regulation of Ga elements, the Ti side near binding interface structure is composed of β-Ti transformed into α-Ti. At 850 ℃ and 900 ℃ hot rolling, the interface changes from discontinuous TiC and aggregated Fe₂Ti particles to a single uniform and continuous TiC layer. The bonding strength has been increased from 190 MPa to 290 MPa. When the difference in diffusion coefficient between D_C/γ-Fe and D_C/α-Ti is in the range of 5.94 × 10^-12-2.9 ×10^-12m²/s, the thickness of TiC layer is effectively regulated to 180-190 nm and the generation of Fe₂Ti and FeTi is significantly inhibited.

In the production process of hot rolling, the control accuracy of coiling temperature is one of the key parameters that determine the quality of the product. Based on the heat transfer mechanism model and comprehensive analysis of actual production data and process parameters, taking into account factors such as finlshing rolling temperature and strip thickness, it is deeply studied the impact of key factors such as strip speed, cooling water temperature, and seasonal variations on the coiling temperature model,and the model is revised and optimized. At the same time, the compensation model based on alloy composition was constructed using machine learning algorithms, and comparative analysis was conducted on different algorithms. The research results show that the random forest prediction model performs well in improving the control accuracy of coiling temperature. The research results were applied to actual production, resulting in an increase in the average qualification rate of coiling temperature for strip with thickness h≤6.0 mm, 6.0 mm <h≤13.0 mm, and h>13.0 mm by 3.07%, 3.82%, and 4.68% respectively, providing a new and effective way to further improve the control accuracy of coiling temperature.

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.

Aiming at the surface powder loss of pickling spring steel 60Si2Mn during cold rolling after annealing, the surface, cross-sectional morphology and composition of annealed and cold rolled samples were analyzed, and it was found that there was an obvious loose layer of about 10 μm on the surface of the annealed and cold rolled samples, with Fe as the main component, and the powdery substance that was rolled off was mainly Fe too. In order to further explore the correlation between the loose layer and the iron oxide scale, the hot rolled sample, incomplete pickling sample and complete pickling sample were annealed in the full hydrogen furnace, and the results showed that the surface iron oxide scale of hot rolled sample was completely reduced to a layer of dense metal iron, and the loose layer structure similar to rolling powder appeared on the surface of the incomplete pickling sample, and the surface of the complete pickling sample still retained the initial surface of pickling. In addition, it was also found that there was an inner oxide layer with a thickness of 8 μm under the iron oxide scale of 6 μm of 60Si2Mn hot rolled sample, but after incomplete pickling and annealing, the thickness of the loose layer of 8 μm was much larger than the thickness of the iron oxide scale of the hot rolled sample, and it obviously extended to the matrix to include the inner oxide layer. Through pickling experiments, it is found that the structure of 60Si2Mn iron oxide scale is very dense, and pickling mainly corrodes the oxide scale in the form of microcracks, because the pickling time required is about several times that of conventional high-carbon steel, therefore, at the same time as the corrosion of the iron oxide scale, the internal oxide layer undergoes obvious intergranular corrosion, which together with the residual iron oxide scale, forms a loose structure after annealing leading to powder loss problem during cold rolling. Therefore, for 60Si2Mn strip,in order to avoid the occurrence of such problems, on the one hand, it is necessary to try to pickle completely, on the other hand, controlling the thickness of the inner oxide layer is also an important factor.