In recent years, China's rolling technology has rapidly advanced from being a follower to a parallel and then a leader. In terms of processes and equipment, China has achieved international leading levels in a series of innovations and applications, including multimode headless continuous casting and rolling technology, 5 600 mm wide-heavy plate rolling technology, 2 680 mm wide stainless steel hot continuous rolling production lines, six-stands six-high tandem unit for high-grade silicon steel, high-precision heat treatment processes and equipment for strip and plate, key production technologies for ultra-thin stainless steel sheets, and online microstructure and property control technology for hot-rolled seamless pipes. In steel products, China's advanced steel enterprises have essentially reached international leading standards in the quality of automotive steel, energy steel, engineering machinery steel, shipbuilding and offshore engineering steel, low-cost 2 000 MPa-level ultra-high-strength and ductile steel, and certain specialty steels. In terms of the "strength-plasticity-toughness" control mechanism for ultra-high-strength steel, innovative approaches such as the "dislocation engineering + TRIP effect" synergy mechanism and the "martensite topology design + metastable phase regulation" synergy plasticity enhancement mechanism have been proposed. Meanwhile, China has also reached international advanced levels in digital and intelligent empowerment for high-quality and stable rolling production.Overall, China has made significant progress in rolling processes, equipment, products, digitalization, and intelligent empowerment, but there remains a gap compared to international advanced standards in core rolling processes and equipment, large rolling mill control systems, and high-end, high-quality product technological innovation. Some core equipment and control systems still require imports.Considering the development trends of China's steel industry, key technological innovations and development directions to focus on include: core rolling process and equipment technology, high-end and high-quality product innovation, continuous and efficient key technologies integrated with upstream/downstream processes and the industrial chain, as well as digital and intelligent empowerment.

Flatness control technology for cold-rolled strip is one of the core control technologies in the iron and steel industry. Its control effectiveness directly determines the post-rolling flatness quality and influences subsequent downstream processes. Flatness actuators are the key technological means for achieving flatness control. Lower accuracy in the actuator models can impair the online correction capability for flatness deviations and easily lead to flatness defects. This paper comprehensively considers the influence patterns of key rolling parameters, such as rolling force and strip geometric dimensions, on strip flatness, as well as the coupling mechanisms among different flatness actuators. Based on this, a roll bending-roll tilting coordinated setup model incorporating quadratic influence coefficients is established. The concept of an "overspray coefficient" is introduced to construct a segmented cooling flow control model that accounts for the partial flow overlap characteristics between adjacent emulsion nozzles. To enhance the accuracy and computational efficiency of the setup model, an optimization strategy for setting the coefficients in the setup model is developed based on heuristic search theory. Industrial trials are conducted using a 1 450 mm UCM five-stand six-high tandem cold rolling mill as the application platform. The results indicate that the flatness actuator setup model and strategy developed in this paper can efficiently and accurately correct online flatness deviations. They reduce the setup complexity of the model and improve the hit rate of flatness root mean square error by approximately 8%.

The crown of cold-rolled non-oriented silicon steel strip is the result of the coupling effect of process parameters such as roll shifting, roll bending force and rolling force. It is difficult for traditional mechanistic models to predict and optimize the strip crown timely and accurately in production. To solve this problem, based on Deep Neural Network (DNN) and Whale Optimization Algorithm (WOA), this paper proposes a model for crown prediction and optimization of roll bending force and roll shifting in the cold rolling process of silicon steel. Taking variables such as the width and crown of incoming cold-rolled strip, roll shifting and roll bending force of each stand as inputs, the C₂₅ value of the cold-rolled outlet strip is predicted. Guided by the prediction results of the data-driven model, WOA is used to optimize roll bending force and roll shifting, and Latin Hypercube Sampling (LHS) is introduced to accelerate the optimization. The results show that the model can achieve high-precision prediction of C₂₅ crown of silicon steel strip, with a hit rate of 99.5% for errors within 0.5 μm. By optimizing roll bending force and roll shifting, the C₂₅ crown of cold-rolled silicon steel strip is reduced by 0.89 μm, and the slope of the edge drop region is decreased by 13.9% at the same time, solving the problem of excessive edge drop in cold-rolled silicon steel.

To address the low accuracy of traditional rolling force calculation methods, this paper proposes a PSO-LSSVM-AdaBoost model (Particle Swarm Optimization-Least Squares Support Vector Machine-Adaptive Boosting) based on machine learning to predict the rolling force of horizontal in hot rolling of H-beam. First, dimensional parameters of H-beams with various specifications, equipment parameters, and relevant rolling parameters were collected to create a multi-feature rolling force dataset. Outliers were removed using the Isolation Forest (IF) algorithm. Next, the Least Squares Support Vector Machine (LSSVM) parameters were optimized using the Particle Swarm Optimization (PSO) algorithm, while the weight assignment mechanism of the adaptive AdaBoost algorithm was employed to further enhance the model's predictive performance. Comparisons with traditional Support Vector Machine (SVM), Particle Swarm Optimization-Support Vector Machine(PSO-SVM), Least Squares Support Vector Machine(LSSVM), Particle Swarm Optimization-Least Squares Support Vector Machine(PSO-LSSVM), Least Squares Support Vector Machine-Adaptive Boosting(LSSVM-AdaBoost)models showed that the proposed model achieved greater accuracy and stability in predicting the horizontal rolling force of H-beam, can provide a reference for hot-rolled H-beam production.

Gearbox transmission systems typically operate at high speeds, rendering their key components susceptible to significant wear and impact damage. Given the inherent complexity of gearbox systems, simulation models often fail to accurately diagnose gearbox faults. To address this issue, this paper proposes a digital twin-based gearbox fault diagnosis method that combines physical modeling and data-driven approaches. First, by constructing two Boltzmann machines, features are extracted from the sensor data and the simulation data generated by the rigid-flexible coupled dynamic model. The information from these two data sources is mapped to a high-dimensional space to form a joint representation, which is then integrated with a multi-layer feed-forward neural network to create a multimodal information fusion model for real-time fault detection. However, during the practical application of digital twin-driven fault diagnosis methods, a discrepancy between the virtual space and the physical space often exists. Therefore, this paper develops an adaptive correction framework based on the multi-objective locust optimization algorithm to enhance the fidelity of the virtual space. Experimental results demonstrate that the proposed digital twin method reduces the information error between the physical space and the virtual space and significantly improves the accuracy of fault diagnosis of gearbox.

To address the insufficient corrosion resistance and high cost of stainless steel bipolar plates for hydrogen fuel cells, a novel austenitic stainless steel for PEMFC bipolar plates was developed by substituting nitrogen for molybdenum and increasing the chromium content. Compared with 316L stainless steel, the novel austenitic stainless steel exhibited a 0.208 V_MSE increase in corrosion potential and a three-order-of-magnitude decrease in corrosion current density, indicating significantly reduced corrosion susceptibility and reaction rates. Following 6 hours of potentiostatic polarization at 0.23 V_MSE (the cathode operating potential of PEMFC), the corrosion current density was 0.34 μA/cm², which meets the DOE 2025 target (below 1 μA/cm²). Furthermore, the polarization resistance (R_p) of the novel austenitic stainless steel reached 2.3×10⁶ Ω, approximately 41 times that of 316L stainless steel, substantially suppressing the corrosion reaction kinetics. Mott-Schottky analysis revealed that the passive film formed on the novel austenitic stainless steel possesses a lower oxygen vacancy concentration, which inhibits aggressive fluoride ion attack and thereby enhances corrosion resistance.

The traditional Cr-Mo gas cylinder steel production exhibits a significant strength-toughness inversion challenge, and current research both domestically and internationally indicates that its strength level is generally below 1 200 MPa, failing to meet the future requirements for lightweight and safety of high-pressure gas cylinders. In this study, by adding an appropriate amount of Ni element and small amounts of Nb and V elements to the traditional Cr-Mo seamless gas cylinder steel, the chemical composition (mass fraction) was designed as follows: w(C)=0.25%, w(Si)=0.35%, w(Mn)=1.0%, w(Cr)=1.0%, w(Mo)=0.8%, w(Nb)=0.04%, w(V)=0.20%, w(Ni)=1.5% for high-pressure seamless gas cylinder steel. After 8-pass hot rolling in the complete austenitization temperature range, the steel was directly water-quenched to room temperature. Two heat treatment processes, namely direct tempering and 870 ℃ quenching + tempering, were designed to investigate the microstructure and mechanical properties of the steel plates under different tempering processes. The results show that under the direct tempering process, the microstructure of the steel plate consists of flattened grains. After the 870 ℃ quenching process, uniform and fine equiaxed grains are obtained, with significant grain refinement from 5.4 μm to 2.6 μm, a refinement of approximately 51%. As the tempering temperature increases, the dislocation density gradually decreases. Under the direct tempering process, the dislocation density of the steel plate decreases from 6.511×10¹⁵ m^-2 to 2.019×10¹⁵ m^-2, with a faster dislocation recovery rate. When the 870 ℃ quenching + tempering process is adopted, the comprehensive mechanical properties of the steel plate are significantly better than those under the direct tempering process, and the transverse impact toughness at -50 ℃ is markedly improved. Particularly, under the process of quenching at 870 ℃ for 1 h + tempering at 590 ℃ for 2 h, the steel plate exhibits the best performance, with a tensile strength of 1 361 MPa, yield strength of 1 310 MPa, elongation of 12%. The transverse impact toughness is 90.1 J/cm²at room temperature and 86.3 J/cm² at -50 ℃ ylinders.

Appropriate processing technology can significantly improve the service performance of enameled steel sheets. In order to obtain enameled steel sheets with excellent properties, the effects of different annealing temperatures on the microstructure, mechanical properties and scale explosion resistance of enamel steel were investigated by laser confocal microscopy, scanning electron microscopy, electronic universal testing machine, double-cell hydrogen permeation device and other methods. The results show that the microstructure of the hot-rolled experimental steel consists of ferrite, a small amount of pearlite and lamellar cementite, with an average ferrite grain size of about 30.2 μm, yield strength of about 276 MPa, tensile strength of about 364 MPa, and elongation after fracture of about 38.3%. The microstructure of the cold-rolled and annealed experimental steel consists of ferrite, degenerated pearlite and granular cementite. When annealed at 620 ℃, the average ferrite grain size is about 10.4 μm, the yield strength of the annealed sheet is about 317 MPa, the tensile strength is 352 MPa, and the elongation after fracture is about 40.1%. With the increase of annealing temperature, the average ferrite grain size of the annealed sheet increases, while the strength decreases and the plasticity improves. The scale explosion resistance test shows that the scale explosion resistance sensitivity index T_H value of the annealed experimental steel sheet is about 16.4 min/mm², showing excellent scale explosion resistance, which is mainly attributed to the strong hydrogen trapping effect of second-phase particles such as Fe₃C, (Ti,Nb)(C,N) and TiC. With the increase of annealing temperature, grain coarsening and the growth of second-phase particles lead to the gradual reduction of interface area, the hydrogen trap density of the annealed sheet decreases gradually, and the T_H value decreases gradually, but the scale explosion resistance still remains at a high level.

Subsea pipeline steels operate under increasingly complex service conditions. In addition to requiring larger diameters, thicker walls, and higher pressure resistance, as well as excellent low-temperature drop-weight toughness, these steels must also possess resistance to sour environments. In this study, X70MS acid-resistant pipeline steel was selected as the research material. Based on the chemical composition of low-carbon acid-resistant steel, an alloy design strategy incorporating Nb addition was adopted. Thermomechanical controlled processing (TMCP) was employed to tailor the microstructure, aiming to achieve an optimal balance between high strength and excellent low-temperature toughness in X70MS. Subsequently, the influence of varying Nb content on the microstructure was investigated. Hydrogen permeation tests and hydrogen-charged slow strain rate tensile (SSRT) tests were conducted to characterize the effect of Nb content on hydrogen embrittlement susceptibility. The results indicate that increasing Nb content refines the microstructure, increases dislocation density, promotes the precipitation of (Nb,Ti)(C,N), and enhances strength. In Solution A, the hydrogen trapping capacity and crack initiation propensity of Nb carbonitrides were lower than those of oxides and sulfides. All experimental steels with varying Nb contents exhibited excellent resistance to hydrogen-induced cracking (HIC), with no hydrogen blistering observed on specimen surfaces. Following immersion testing, hydrogen-induced cracks were consistently found to be associated with inclusions containing oxygen and sulfur. Furthermore, the susceptibility to hydrogen embrittlement increased with rising Nb content. At hydrogen charging times of 5 h and 10 h, the elongation decreased significantly, while the strength was less affected. However, at a charging time of 20 h, both elongation and tensile strength declined sharply due to a significant increase in the content of trapped and free hydrogen.

In response to the preparation requirements for non-oriented silicon steel used in new energy vehicle drive motors, this paper obtained normalized sheets with similar microstructures but different thicknesses by adjusting the normalization process. Subsequently, through cold rolling and annealing, non-oriented silicon steel sheets with a thickness of 0.25 mm were obtained. The effects of cold rolling reduction and annealing temperature on the microstructure, texture, magnetic properties, and mechanical properties of the non-oriented silicon steel sheets were investigated. The results showed that as the thickness of the hot-rolled non-oriented silicon steel sheets decreased (the cold rolling reduction decreased), the intensity of the unfavorable textures {223}<110> and {111}<110> in the cold-rolled sheets gradually decreased, ultimately improving the texture of the annealed sheets, with the texture factor gradually increasing by 0.14 to 0.63. The iron loss P_10/400 decreased by 0.2-1.3 W/kg, the magnetic induction intensity B₅₀ increased by 0.01-0.02 T, and the yield strength only decreased by 2-11 MPa. With an increase in annealing temperature, the P_10/400 of the annealed sheets with three different initial thicknesses decreased by 0.3-0.8 W/kg, and B₅₀first increased and then decreased (reaching a maximum value at an annealing temperature of 940 ℃), while the yield strength decreased by 3-13 MPa. Therefore, by thinning the initial hot-rolled steel sheets, the cold rolling reduction can be reduced, and combined with the optimization of the annealing process, the texture of the annealed sheets can be improved, enhancing the magnetic properties of the non-oriented silicon steel sheets.

Ultra-thin 321 stainless steel strips play a crucial role in electronic products and various precision instruments and equipment. In this study, a self-developed metal micro-forming rolling mill was adopted to investigate the variation laws of rolling force and finish rolling thickness during the asynchronous rolling of ultra-thin 321 stainless steel strips by adjusting the speed ratio and front-and-back tension. The results show that increasing the speed ratio can effectively reduce the rolling force and improve the thinning capacity of the rolling mill. Meanwhile, electrochemical experiments were conducted to analyze the effect of cold rolling reduction on the corrosion performance of ultra-thin 321 stainless steel strips. It is found that with the increase of rolling reduction, the corrosion rate of the ultra-thin strips accelerates and the corrosion resistance decreases. The analysis results of XRD patterns indicate that the austenite content of ultra-thin 321 stainless steel strips decreases and the martensite content increases with the increase of rolling reduction, which leads to the deterioration of its corrosion performance.

To improve the cut-edge quality produced by the crescent shear in a cold-rolling electrical steel production line at a steel enterprise and to reduce the incidence of strip breakage during rolling, this study carried out a targeted investigation on the optimization of crescent-shearing process parameters. The influence mechanisms of key shearing parameters on cutting quality were systematically examined. Guided by orthogonal experimental design, a series of numerical simulation cases with different parameter combinations were established. By varying the bite-in depth, shearing clearance, shearing speed, and strip thickness, the stress distribution in different regions of the sheet and the evolution of characteristic zones were analyzed as the parameters changed. The effects of shearing parameters on the edge cutting quality of electrical steel strips were quantified. Subsequently, response surface methodology (RSM) was employed to analyze and optimize the crescent shearing parameters for the head-tail regions of adjacent coils. The results indicate that a smaller bite-in depth leads to pronounced stress concentration at the crescent-tip region. Increasing the shearing clearance enlarges the maximum-stress region; however, when the clearance is below 0.2 mm, the fracture morphology becomes flatter and the shearing quality improves. shearing speed and strip thickness jointly affect the thickness and uniformity of the sheared zone on the cut surface. When the blade speed is smaller than 2 500 mm/s, the sheared-zone thickness accounts for a relatively high proportion of the cut-surface thickness (approximately 36.5%); as the speed increases further, the sheared-zone thickness gradually decreases. Increasing the strip thickness,the sheared-zone thickness increases, while its proportion decreases, suggesting that a thicker strip may improve shearing stability under certain conditions. Based on multi-factor coupling analysis via RSM, the optimal parameter set was identified as a bite-in depth of 8 mm and a shearing speed of 862 mm/s under a shearing clearance of 0.17 mm and a strip thickness of 2.3 mm. This optimized combination significantly enhances the quality stability of crescent shearing for high-grade electrical steel, providing effective theoretical support and practical guidance for industrial production.

In order to improve the plasticity of double-reduced tin plate,this paper studied the influence of α phase recrystallization annealing and α+γ phase intercritical annealing on the microstructure and mechanical properties of double-reduced tin plate, In this paper,the microstructures of the steel were detected by OM、SEM and TEM, the rockwell hardness and mechanical propertie of the material were tested respectively by rockwell hardness tester and tensile tester. The result showed that with the α phase recrystallization annealing process, the experimental steel′s microstructure were ferrite and cementite,the grain size of ferrite varied greatly and coarse cementite discretely distributed in ferrite grains and grain boundaries. With the α+γ phase intercritical annealing process, the experimental steel′s microstructure were ferrite and pearlite,the ferritic grains were equiaxed and distributed in uniform size,the pearlite island distributed in the ferrite grain boundary and the lamellar space of the pearlite reached about 150 nm.The rockwell hardness HR_30T of double-reduced tin plate with those two different annealing processes were both controlled between (73±4)HR30T.Compared with the double-reduced tin plate processed with α phase recrystallization annealing,the rockwell hardness of double-reduced tin plate processed with α+γ phase intercritical annealing increased by about 1.5 units,the yield strength R_p0.2 increased by about 25 MPa, the tensile strength R_m increased by about 30 MPa, and the elongation A₅₀ increased by about 4.0%.With the α+γ phase intercritical annealing process, the coarse cementite residued from the cold rolling redissolved sufficiently and thus formed equiaxed ferrite grains distributed in uniform size and pearlite with fine layer space during the subsequently cooling process after soaking heat, which led to the significant improvement of the material′s strength and plasticity.

The collaborative regulation of cementite and matrix in the microstructure of GCr15 bearing steel is a key technology to ensure the long-life, high-quality and stable service performance of bearings. The pre-treatment process is critical for controlling the morphology and distribution of the final carbides. In this paper, the synergistic evolution of the matrix microstructure and carbides in GCr15 steel under two pre-treatment processes,namely isothermal spheroidizing annealing (SA) and high temperature solid solution+isothermal quenching+high temperature tempering (HQT),were investigated. The results show that the SA-treated speciments exhibit distortion-free equiaxed ferrite grains and uniformly distributed carbides with high sphericity, while the microstructure of HQT-treated specimens consists of acicular martensite, fine bainite, and rod-like carbides.Although the carbide volume fraction is similar for both processes, the equivalent particle size of carbides in HQT is only about 1/4 of that in SA. Meamwhile, the densities of low-angle and high-angle grain boundaries, geometrically necessary dislocation density, and microhardness of HQT-treated specimens are much higher than those of the SA-treated specimens. Furthermore, the precipitation characteristics of carbides and elemental enrichment in carbides with different morphologies under HQT process are analyzed. This work provides a fundamental theoretical support for the precise control of heat treatment processes of GCr15 bearing steel and the development and manufacture of high-performance bearing products.

Aiming at the problems of large temperature differences between the head and tail of the billet in the soaking section of heating furnaces, low combustion quality and high energy consumption per ton of steel, a digital simulation platform for the entire steel process and a black box furnace temperature tracking test were used to study the billet reheating process and the uniformity of the heating temperature. Optimization measures for the furnace conditions were proposed. The results showed that the process parameters of the billet reheating were reasonable, and the temperature at the tail of the billet was 1 190 ℃ when the soaking section was close to the furnace, which was higher than the requirement of the process temperature of 1 160 ℃, and 50 ℃ higher than the temperature at the head of the billet. The main reason was that the burners on the north side of the heating furnace were blocked. To ensure heating capacity on the north side, the supply of gas was increased, which led to an enhanced heating capacity on the south side and consequently resulted in a higher temperature at the tail of the billet. After optimizing the northern burners, the temperature difference between head and tail of the billets is reduced to within 5 ℃, resulting in a decrease in gas consumption per ton of steel by 30 m³ and a reduction in carbon emissions by 8 254 t/a.

High-quality medium and high carbon steels, such as spring steel, impose stringent control requirements on the type and thickness of decarburized layers. In this work, isothermal oxidation and decarburization experiments were conducted on 28SiMnB spring flat steel within the temperature range of 700-1 000 ℃. The morphologies of oxide and decarburized layers were analyzed, and the coupling mechanism of oxidation and decarburization was investigated. The interface between the inner and outer scale layers was identified via Pt calibration, and EDS analysis confirmed that the inner scale consists of a multi-component oxide of Fe, Si and Cr, while the outer scale presents a three-layer structure composed of Fe₃O₄, FeO and a Fe₃O₄+FeO mixed phase. No decarburized layer was observed at the heating temperature of 700 ℃, whereas partial decarburized layers were detected in the specimens at 800 ℃, 900 ℃ and 1 000 ℃, with the thicknesses of 290 μm, 360 μm and 470 μm, respectively. However, a complete decarburized layer was not found, which may be attributed to the consumption of the decarburized layer by internal oxidation as well as the coupling effect of oxidation and decarburization.

To investigate the effects of controlled cooling processes on the microstructure, properties, and winter aging period of ø14 mm 82B wire rods for ultra-high strength prestressed steel strands, two controlled cooling processes were designed in this study. Process 1 adopted low roller speed and high fan power, with a slow cooling rate before phase transformation, and the controlled cooling curve did not exhibit a distinct phase transformation region. Process 2 employed high laying temperature, high roller speed, and high fan power, while reducing the roller speed in the insulation cover. The microstructure and mechanical properties of the wire rods were analyzed using scanning electron microscopy, EBSD, and tensile testing machines. The results showed that by adjusting the roller speed and fan power to increase the cooling rate before phase transformation from 5.2 ℃/s to 13.8 ℃/s, the pearlite interlamellar spacing of the wire rods was refined by 19.8%, and the pearlite colony size was refined by 21%. Consequently, the tensile strength of the wire rods increased from 1 180 MPa to 1 252 MPa, with the refinement of interlamellar spacing contributing 76% to the strength improvement. The diffusion of hydrogen in the wire rods caused the reduction of area to increase with aging time. By extending the residence time of the wire rods in the medium-to-low temperature section of the Stelmor air cooling line, the initial reduction of area was increased by 50%, and the winter aging period was shortened to approximately 10 days. This provides a new approach for optimizing the controlled cooling process of large-gauge 82B wire rods.

During the operation of a heavy plate rolling mill, the relevant parts dimensions of the roll system change due to equipment wear, assembly accuracy, and roll system adjustments. These changes affect the height of the rolling line and the normal operation of the roll system. This paper analyzes the influence of the roll system structure and its related dimensions on the rolling line, and accordingly adjusts the rolling line to meet the requirements of the rolling process. Meanwhile, in the control process of the existing roll gap set value, the transmission process of the set value calculated by the Level 2 system is optimized. The Level 2 pass schedule is received in advance and the roll gap is pre-calculated. The roll gap distribution between the upper and lower roll systems is also optimized, and the waiting and positioning time of the rolling mill is reduced. Through the research on the structure of the mill roll system and the optimization of roll gap timing control, the adverse effects of the rolling line on roll gap positioning and rolling process are avoided, and the rolling control level and rolling rhythm are further improved.

High-performance electrical sheet strip for new energy vehicles belongs to the thin-gauge, high grade non-oriented silicon steel. Due to its high silicon and aluminum content, it exhibits significant brittleness, leading to considerable production difficulty in cold rolling, high rates of strip breakage, and low yields. The causes of edge defects generated during normalizing and edge trimming were clarified in this paper by observing the shear section morphology and metallographic microstructure of the normalized sheets. Through mechanical property tests and rolling experiments at different temperatures and reduction rates, the relationships between the strip entry temperature, reduction ratio per pass, and exit temperature in the first cold rolling pass and strip breakage was established. Accordingly, production processes were improved as follows. The shear zone was controlled to be no less than 1/2 and no more than 3/4 of the strip thickness. The strip edge was heated (or kept) to 60 ℃ or above. Cemented carbide blades were adopted, with the disc shear blade clearance set at 10% of the strip thickness and the overlap at 1.5-2.0 mm. The temperature inside the normalizing furnace and the cooling mode of the strip after exiting the furnace were optimized to improve the temperature difference accuracy within the furnace and cooling uniformity. The strip temperature at the start of cold rolling should be set between 60 ℃ and 150 ℃. For production using a 20-high mill, due to its small diameter work rolls and rapid heat dissipation, the initial rolling temperature should be set between 75 ℃ and 125 ℃, and the reduction ratio of the first pass should be no less than 35%. With these process improvements, the strip breakage rate of silicon steel for new energy vehicle motors during cold rolling was reduced from the original 38.6% to 0.56%,and the yield increased by approximately 3%.

Aiming at the problem of cross-folding defect occuring in boron-added low carbon cold-rolled strip produced by batch annealing process, the effect of chemical composition on this defectwas analyzed by microstructure characterization and tensile property testing. The results show that the atomic fraction ratio of nitrogen to boron (y(N)/y(B)) has a significant effect on the cross-folding defects of cold-rolled B-added mild steel, and the cross-folding defect problems are obviously improved with the increase of y(N)/y(B). The main mechanism is that with the increase of y(N)/y(B), the content of solid solution B in grain boundary aggregation decreases, and the content of solid solution carbon in the grain is correspondingly reduced. Therefore, the elongation at yield of the tensile curve of the test steel is reduced, and the yield effect is weakened, so as to avoid the occurrence of cross-folding defects.

In response to the issue of white spot defects appearing on the surface of hot-dip Al-Si IF steel strips during processing and use by customers in coastal areas, scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) were employed to analyze the surface and cross-sectional micromorphology and composition of the white spot defects and normal areas. The results indicated that the defective areas exhibited higher concentrations of O and C elements, along with the presence of Cl elements, which were absent in normal areas. The analysis suggests that the primary cause was excessive thickness of the passivation film on the strip coating surface, leading to the formation of cracks. In the salty and humid coastal climate, Cl^- diffused through these cracks, inducing electrochemical corrosion of the coating and resulting in white spot defects. Accordingly, corresponding improvement measures were proposed, including reducing the surface roughness of the strip, diluting the concentration of the passivation solution, and decreasing the passivation speed. These measures aimed to minimize residual passivation solution, hereby reducing the thickness of the passivation film to reduce cracks in the passivation film, and ultimately eliminate white spot defects on the coating surface.

In view of the problem that 30MnSi coil wire with a diameter of ø12 mm produced by a certain high-speed wire rod unit, when used for processing steel rods for prestressed concrete, some of the rods experienced cracking at the head during the head upsetting process, this paper analyzed the causes of the cracking and proposed corresponding measures by observing the crack morphology, analyzing inclusions, conducting microstructure and composition analysis on the cracked samples. The results showed that the cracking of the head of the steel rods for prestressed concrete was mainly due to the high content of phosphorus and sulfur in the billet, which formed segregation, and during the rolling process, ear defects were generated, causing the rolled products to form folds and loops, and during the drawing and twisting of the spiral ribs, the folds and loops expanded further due to the maximum shear stress, resulting in cracks. At the same time, corresponding improvement measures were proposed for key processes:strictly controlling the composition during the steelmaking and refining processes to minimize the content of phosphorus and sulfur, improving the purity of the molten steel and reducing composition segregation and fluctuations; following the process technical regulations for rolling, reasonably designing the rolls, accurately calculating the reduction and widening, precisely adjusting the roll grooves and guide vanes, reducing or eliminating defects such as ears, burrs, scratches, as well as surface defects such as loops, folds, peeling, and scabs on the finished products; using appropriate lubricants during the drawing process to reduce friction and heat generation, thereby reducing the risk of cracking; before the head upsetting process, the temperature of the end induction heating should be focused on, controlled at (900 ± 20)℃ for the best. After adopting the improvement measures, the cracking of the head of the steel rods for prestressed concrete was eliminated.

Hot-rolled equilateral angle steel is the main raw material for transmission towers. This paper lists the typical quality problems and insufficient standards of angle steel in the application of transmission towers, summarizes the application technology characteristics of angle steel for transmission towers, reviews the process of standard revision for hot-rolled angle steel products, analyzes the technological progress of angle steel smelting and hot rolling, summarizes the basis and principles for standard formulation and revision of hot-rolled angle steel for transmission towers at current stage. This paper focuses on the technical characteristics, practical achievements and engineering applications of the group standard T/TEC 352—2020 "hot-rolled equilateral angle steel for transmission line towers", and the positive impact on the industrial standardization of national standards for angle steel and section steel in China.