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.
In response to the high cost of X65M submarine acid resistant pipeline steel, a low-cost X65MOS hot-rolled strip that meets the mechanical properties, aging impact property, CTOD performance, HIC and SSCC resistance performance requirements of submarine acid resistant pipelines was developed using a reasonable TMCP process design without adding Mo, Cu, Ni elements in the chemical composition. Production practice has proven that under low-temperature rolling conditions, increasing the reduction rate of the final stand to 13%, and using ultra fast cooling and dense laminar cooling processes, the needle like ferrite grains of X65MOS strip were refined to a grain size of grade 12, significantly improving its mechanical properties. The results of the drop hammer experiment showed that the shear tear area of X65MOS strip reached 100% at -40 ℃, and the aging impact energy reached over 300 J at -60 ℃, with a CTOD value of+∞. Under the same HIC and SSCC test conditions, when there were many cracks in the X65M strip, there were no cracks in the X65MOS strip. The large number of dislocations in the microstructure of the X65MOS strip ensured its CTOD performance, HICand SSCC resistance performance in the absence of Mo, Cu, and Ni elements. The low-cost X65MOS strip developed has significantly better performance than X65M strip, which has important practical significance for enhancing product competitiveness and improving economic benefits.
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 key problem of how to realize the coupling matching of high yield strength and low yield ratio for high strength seismic building steel, based on the self-designed chemical composition, the microstructure and properties of the test steel were investigated by controlled rolling and controlled cooling process. The results show that under the process conditions of ' two-stage controlled rolling + water cooling (final cooling temperature 660 ℃) ', the microstructure of the test steel is a multiphase structure composed of ferrite, pearlite and bainite, which realizes a good match of strength, plasticity and low yield ratio. The average yield strength is about 660.0 MPa, the average tensile strength is about 1 196.7 MPa, the average elongation after fracture is about 14.8%, and the average yield ratio is as low as 0.55. The solid solution strengthening of Mn and Si elements in the test steel, as well as the fine grain strengthening and dislocation strengthening caused by bainite and pearlite structures are the main mechanisms for obtaining high strength and low yield ratio.
In order to study the influence of composition and structure of oxide scale on hot rolled strip on pickling time, ST12 steel, 45 steel and DP1180 steel were selected as experimental steels. The macro-morphology, cross-sectional micro-morphology, oxide layer thickness and main chemical composition of oxide scale on hot rolled strip surface of three steels were analyzed by SEM and XRD, and the pickling time was tested. The results showed that the oxide scales on the surface of ST12 steel and 45 steel hot rolled strip were composed of α-Fe, FeO, Fe3O4 and Fe2O3. There was no Fe2O3 in the oxide scale on the surface of DP1180 steel strip, but a certain amount of Fe2SiO4 was produced. The average thickness of oxide scale on the surface of ST12 steel, 45 steel and DP1180 steel strip were 10.88, 12.77 and 15.36 μm respectively, and the pickling time were 30.2, 23.8 and 16.2 s respectively. Compared with ST12 steel, the content of α-Fe in the oxide scale on the surface of 45 steel strip which was easy to react with acid solution was high, while the content of oxide which was difficult to react with acid solution was less, so its pickling efficiency was higher. The main reason for the shorter pickling time of DP1180 steel strip was that besides the high content of α-Fe in the oxide scale, there were more FeO in the threeoxides, and there were gaps between the oxide scale and the steel matrix, which could promote the diffusion and reaction of acid liquid in the oxide scale. Therefore, the pickling efficiency of oxide scale on the surface of hot rolled strip was mainly related to its composition and structure, and the thickness of oxide scale had little influence on it.
Combined with the development trend of pipeline steel technology, in accordance with the latest requirements of domestic and foreign technical standards, and drawing on the development experience of large thick-walled X80 pipeline steel coil, the test research was carried out on the production of X90 pipeline steel coils for spiral welded pipes based on medium-thin slabs. The dynamic CCT curve of X90 pipeline steel was determined by the Gleeble-3800 thermal simulation tester, and the phase transformation law was obtained and the appropriate cooling rate was determined. On this basis, through the design of its chemical composition, and the fine control of smelting, continuous casting, rolling and cooling processes, the industrial trial production of 16.3 mm×1 550 mm gauge X90 pipeline steel coil was completed in 2 150 mm ASP medium thin slab continuous casting and rolling production of Angang. Its tensile properties are qualified, -20 ℃ impact energy is not less than 300 J, -20 ℃ impact shear area is not less than 90%, -20 ℃ DWTT shear area is not less than 90%, the microstructure is granular bainite, lath ferrite and dispersed M/A components, the property indicators meet the engineering requirements. The ø1 219 mm×16.3 mm steel pipe is made by spiral submerged arc welding, and the property indexes of the steel pipe are good. The successful trial production of X90 pipeline steel coil has achieved a major breakthrough in the production of ultra-high strength pipeline steel of using medium thin slab in China, which is of great significance for the development of ultra-large diameter, higher steel grade, and thicker walled pipeline steel coil.
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%.
Aiming at the problems of zigzag edges and burr defects that readily occur during the edge trimming process in the production of cold rolled ultra-low carbon strip, its edge trimming quality under different trimming process parameters, and different positions and shapes of the base strip were discussed. Based on analyses of mechanical properties, microstructure, and fracture morphology, the impact of base material characteristics and trimming processes on the edge trimming quality of the strips are clarified. Furthermore, a process control scheme is proposed to improve the edge trimming quality of base material for cold rolling. The analysis of the fracture morphology of the edge shear indicates that the fracture morphology of the strip edge after trimming can be divided into a trimming zone and a fracture zone along the thickness direction of the strip, and there are significant differences in the proportion of these two zones in the thickness direction under different strengths, trimming processes, and strip shapes. As the strength of the strip increases, the proportion of the trimming zone in the thickness direction significantly rises. The influence of the blade gap value on the edge trimming quality is significantly greater than that of the overlap between the upper and lower blades. As the bladegap value increases, the proportion of the trimming zone in the fracture morphology of the edge shear decreases significantly. The presence of wave shapes on the strip edge results in the appearance of oblique cutting zones and burr zones in the shear fracture, and the boundary between the trimming zone and the fracture zone fluctuates significantly, seriously affecting the edge trimming quality of the strip. By adjusting the blade gap value and overlap value, controlling the trimming and straightening lengths, and managing the wear degrees of the rubber sleeve and blades, the edge trimming quality of cold rolled ultra-low carbon strip has been improved.
The Sendzimir 20-high rolling mill is widely used in silicon steel, stainless steel and precision strip cold rolling. Its roll system configuration directly affects product accuracy and production cost. Excellent roll matching technology is the basis of efficient operation of the unit. For the Sendzimir 20-high rolling mill, the principle of roll matching and the requirement of grinding precision are put forward, the coordinate system is established to determine the initial position of each backing roll, and the center position of each roll is calculated during the working process, and the center coordinates of the middle roll and work roll are determined by coordinate method. By using the established equation, the relationship between the screw down stroke and the roll gap and the roll diameter compensation trajectory are analyzed, which is helpful to understand the control characteristics of the Sendzimir 20-high mill deeply and improve the field use efficiency.
With the development of metallurgical technology, the strength of high strength steel has increased significantly, which makes straighteners with a single-roll system have a very limited capacity to straighten high-strength plates. It is an effective way to improve equipment capacity by using roll system-replaceable straighteners with a double-roll system. For the straightening characteristics of the high strength plate, the roll system capacity characteristics were analyzed to conclude the roll system parameters of the double-roll system straighteners and the according straightening range. Firstly, the strengthening and reverse bending characteristics of high strength plates were analyzed, and the back bending conditions of high strength plates were established. Secondly, three roll system capacity characteristics of double-roll system straighteners were analyzed in terms of the back bending capacity, mechanical strength, and straightening accuracy. Finally, real examples were demonstrated based on the straightening characteristics of high strength plates. It provide a theoretical basis for the selection of roll systems parameters, and provides references for the development of high strength plate straightening schemes.
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.
Cooling process and equipment design after coating are particularly important for continuous galvanized steel, galvanized aluminum, galvanized aluminum zinc, galvanized aluminum magnesium, galvanized aluminum zinc magnesium, galvanized aluminum silicon and other coating products. The principle of selecting cooling process after coating is proposed:only jet cooling can be used before the coating solidification, and the high magnesium coating that is prone to oxidation should be cooled by nitrogen; different cooling methods such as normal temperature air cooling, cooling air cooling, fine air mist cooling or spray solidification cooling can be chosen during the solidification process based on the required cooling speed of the product; the cooling of the coating after solidification can be selected according to the mechanical property requirements of the product and the temperature of the strip, such as jet cooling, air mist cooling, water cooling roll cooling, water spraying cooling, water quenching cooling and other forms; the form classification, application scenarios, process principles, technical requirements and design methods of the main cooling equipment of three cooling processes of jet cooling, air mist coolers and powder solidification cooling are introduced in detail. A new design principle of air jet cooling bellows based on zero pressure overflow of hot air and ensuring full contact between cold air and strip convection heat transfer is proposed, on this basis, a zero-pressure overflow channel, a slotted nozzle and an efficient and stable air jet cooling bellows with thin flow thickness are designed. The reference is provided for the selection and design of production line equipment of galvanized, galvanized aluminum, galvanized aluminum zinc, galvanized aluminum magnesium, galvanized aluminum zinc magnesium, galvanized aluminum silicon and other coating products.
In tandem cold rolling, strip thickness accuracy is one of the most important indicators to evaluate product quality and that downstream enterprises are concerned about. The existing methods for strip thickness prediction mainly focus on the hit rate of the strip head thickness, which cannot reflect the thickness accuracy and fluctuation of the whole coil. A continuous prediction model based on deep learning algorithm for the full length thickness of strip in tandem cold rolling is proposed, and the mapping from industrial data to strip thickness is realized. The data set is built by actual data of a five-stand tandem cold rolling production line. Random forest is used for feature selection to simplify the input features, and then genetic algorithm is used to optimize the initial weights and thresholds of DNN model for the further model performance improvement. The results show that the model can accurately and intuitively reflect the thickness accuracy and fluctuation of the whole coil with rolling time. In acceleration, deceleration and stable rolling stage, the relative errors of predicted results are controlled within ±0.5% and ±0.1%, which meet the actual production requirements. By using this model, the control system can improve the pre-setting accuracy and implement pre-adjustment at the corresponding time, so as to achieve the purpose of strip thickness accuracy improving.
Dual-phase steel has the advantages of high strength and strong extension, but it is difficult to process in cold rolling. Due to the characteristics of small diameter rolls and strong rolling ability, 18-high mill is gradually becoming the main mill for producing the strip hard to form. Compared with low carbon steel, the high strength of dual-phase steel makes it more challenging in cold rolling processing, so it becomes the technical research point of 18-high mill operation. Influenced by the strong deformation resistance of the material and the thickness difference fluctuation of the initial strip, the state of the rolling deformation zone is easy to fluctuate in the production process, which leads to the thickness difference fluctuation of the finished strip and affects the downstream industry and process. To solve these problems, the thickness fluctuation mechanism of the strip head and tail is analyzed, and its causes is traced. Based on the mill characteristic, structure characteristics and thickness control mechanism characteristics, the thickness control difficulties of dual-phase steel in 18-high mill are analyzed. The results show that a certain degree of phase transformation can also occur after the hot rolling coiling process of DP780 steel, which can be shown as the difference of bainite transformation degree at different target coiling temperatures, and can cause the mechanical properties of the cold rolling base material to fluctuate, and finally causes the thickness difference of the finished strip to fluctuate. Based on an 18-high single-stand rolling mill in a factory, the control characteristics and regulatory effectiveness of FF-AGC, FB-AGC, MF-AGC and BISRA-AGC are analyzed, the thickness difference combination control strategy of "FF+FB+Bisra" and the strip head thickness fluctuation control method using sine signal for interference control are proposed. The practical production show that this method can control the incoming material with thickness difference of up to 40 μm to the thickness differenceof ±10 μm, and achieve accurate control of the thickness difference of the full length,significantly improve the thickness pass rate of the finished strip, effectively improve the thickness control problem in the production of dual-phase steel in the 18-high mill, and provide a new idea and method for the production of high strength steel.
Hot strip mills are prone to edge wraping defects in the later stages of the same-specification product continuous production, especially for wide-specification products. To solve this problem, the influence of different CVC roll contour parameters on the variation of the finishing work roll contour curve for hot rolled wide strip mills is analyzed, and the application of CVC roll contour+concave roll contour combination is studied. The results show that there is a negative correlation between the end roll diameter difference and the middle roll diameter difference of CVC roll, and an example of 2 050 mm hot rolling production line is given to illustrate this. This provides reference for the determination and optimization of CVC roll contour curves. The advantages and disadvantages of practical application of concave roll are introduced by analyzing the concave roll curve determining method and the axial shifting method of the concave roll, and the relationship between the bending change of the concave roll and the heat expansion value of the roll is analyzed theoretically, which shows that the CVC roll contour+concave roll contour combination can effectively solve the edge warping defect, extend the rolling kilometerage. Finally, the validity of its effectiveness is verified from the application angle by listing the changes in edge wraping of the same specification and steel grade after production.
To solve the problem of difficult comprehensive production and poor properties of Q890D plates with a thickness of over 100 mm, a 130 mm thick gauge Q890D plate was developed through rational design of chemical composition, matching of clean steel smelting process, optimization of controlled rolling and controlled cooling, and quenching and tempering process. The test results show that the phase transformation temperature of the developed Q890D plate is Ac1=722 ℃, Ac3=869 ℃, Ms=424 ℃. When the cooling rate is higher than 10 ℃/s, the microstructure is fully martensitic. Within the quenching temperature range of 890-930 ℃, as the quenching temperature increases, the austenite grain size of Q890D plate coarsens, and its strength and ductility decrease. At a quenching temperature of 890 ℃, its original austenite grain size is 10.5 grade, and its comprehensive property is optimal. The 130 mm thick Q890D plate has achieved stable industrial production, with a yield strength of 892-927 MPa, a tensile strength of 974-1 015 MPa, an elongation of 13.0%-15.5%, an impact energy of 120-160 J at -20 ℃, and a Z-direction section shrinkage rate of 48%-62%. The internal ultrasonic testing of the plate has reached the quality level I in GB/T 2970—2016, and the all properties fully meet the requirements for supply and use. It has important reference significance for the development of thick ultra-high strength steel technology and industrial production.
In order to solve the problem of unstable impact toughness of 60 mm thickness Q690D plate under DQ process, the effects of casting billet thickness and single pass reduction of roughing rolling on impact toughness of the plate were analyzed. The results show that the good impact toughness ofthe plate needs to obtain a certain proportion of lath bainite, granular bainite and polygonal ferrite. The thickness of the casting billet should be increased as far as possible to ensure that the thickness of the casting billet is above 335 mm (compression ratio is above 5.5) and the reduction of the roughing rolling is above 40 mm for at least 1 pass.
Aiming at the problem of unqualified low-temperature impact performance of 50 mm thickness EH36 grade ship plate in actual production, the reasons were analyzed and the improvement measures were applied. The results show that the presence of MnS and CaO-Al2O3type inclusions in the microstructure of the 50 mm thickness EH36 ship plate sample, as well as coarse ferrite and pearlite at 1/4 thickness, are the main reasons for its poor low-temperature impact toughness. The cleanliness of molten steel was improved by optimizing the secondary refining process, the ferrite grains were refined by optimizing the controlled rolling and controlled cooling process, no MnS inclusions were found in 50 mm thickness EH36 ship plate, and the inclusion level of CaO-Al2O3 type was controlled below 1.0 grade. The microstructure were mainly fine-grained ferrite at 1/4 thickness of the plate. The average impact toughness level under -40 ℃ was increased to more than 200 J.The unqualified low temperature impact performance problem of 50 mm thickness EH36 ship plate has been effectively solved, and its low temperature impact toughness has been significantly improved.
In view of the problems of high acid consumption and low recovery value of acid fume condensate in the current pickling process, the influence of exhaust pressure andFem+ concentration in the acid fume purification system on the concentration of hydrochloric acid was studied through theoretical calculations and experiments. The results showed that the concentration of hydrochloric acid solution obtained by the original 160 g/L hydrochloric acid solution under -60 kPa extraction pressure was 40.1 g/L, while the concentration of hydrochloric acid solution obtained by the same original 160 g/L hydrochloric acid under -5 kPa extraction pressure was only 10.9 g/L. In addition, the presence of Fem+ in the acid solution does not change the HCl content in the acid fume. To this end, corresponding improvement measures have been proposed: (1) separate the high and low concentration acid tanks for condensation, directly recycle the acid fume in the high concentration acid tank to the acid circulation system after condensation, and replace some of the rinsing waste water with condensed acid fume and transport it to the acid regeneration system for treatment. (2) improve the structure of the acid tank and exhaust system, reduce the amount of acid fume, and reuse some condensed hydrochloric acid solution to achieve acid fume reduction and green treatment.
The causes of white spot defects that often occur at the edges of automotive sheets with a width of over 1 700 mm on the 2 250 mm production line at Hansteel Co. were analyzed which leading to product degradation. By using scanning electron microscopy to observe the microstructure of defects, it was found that there was a clear honeycomb like "sponge iron structure". energy spectrum analysis showed the presence of iron oxide, indicating that the residual edge oxide scale crushed and pressed in strip during hot rolling production was one of the reasons for the formation of defects. In addition, the thickness of the oxide scale on the edge of strip is also the main factor affecting its pickling effect, and the presence of edge waves also affects the straightening and pickling effect of cold rolling. The residual oxide scale forms white spot defects after annealing. Therefore, corresponding process improvement measures have been taken, including adding water curtains on both sides of the finishing mill outlet guide and sealing the edge nozzles to reduce cooling water splashing back at the edge of the work roll. Reduce the convexity of the strip, increase the coiling tension, accelerate the cooling of the coil, and reduce the thickness of the edge oxide scale. Optimize the calculation of thermal convexity and wear model of work roll of finishing rolling mills, control the timing of bending roll force, and increase the elongation of cold rolling straightening to improve strip shape and enhance the effect of straightening on scale breaking. Optimize the plan arrangement and eliminate reverse width rolling to avoid the serious impact of local wear of the work roll on the strip. After taking the above measures, the defect incidence rate was reduced to below 1%, greatly improving the surface quality of wide width automotive sheets.
The fundamental reason for the occurrence of pits and pitting defects in pure iron wire during the drawing process is the presence of local coarse grains on its surface. To explore the root cause of local coarse grain formation, a resistance constant temperature heating furnace was used to simulate the evolution of pure iron CH1T steel grains under different heating temperatures (900-1 200 ℃) and heating times (60-360 min), and the critical conditions for abnormal grain growth were obtained and controlled. The experimental results show that when the heating temperature is below 1 200 ℃, the grain size of pure iron CH1T steel will undergo three stages of rapid decrease, steady decrease, and further decrease with the increase of heating temperature and heating time. When the heating temperature is 1 200 ℃ and the heating time is extended to 360 minutes, local grain refinement will occur due to secondary recrystallization.
The chemical composition, microstructure, and fracture morphology of 45 steel hot rolled wire rods were studied to resolve the problem of drawing fracture. The reasons of the drawing fracture of 45 steel were analyzed, and process improvement measures were proposed. The results indicate that the uneven microstructure and mixed crystals on the surface of 45 steel hot rolled wire rod, as well as the high proportion of ferrite in the microstructure, are the main reasons for the drawing fracture of 45 steel wire rod. The carbon mass fraction of 45 steel was increased from 0.43%-0.45% to 0.46%-0.48%, the finishing rolling temperature was reduced from 945 ℃ to 915 ℃, the wire feeding temperature was reduced from 940 ℃ to 890 ℃, the number of fans was adjusted from 1#-7# to 1#-9#, and the starting roller speed of Stelmor air-cooled roller was increased from 0.70 m/s to 0.85 m/s (the speed of each subsequent roller section increased sequentially), effectively improving the microstructure of 45 steel hot rolled wire rod, significantly increasing the proportion of pearlite, and improving the drawing performance of 45 steel hot rolled wire rod.