A method for producing low alloy high strength steel with a plate width of ≥1800mm

Abstract

A method for producing low-alloy high-strength steel with a plate width of ≥1800mm: conventional hot rolling and hot rolling plate surface convexity; pickling; cold rolling using five stands, refining the group spacing according to the thickness of the finished product and controlling the cold rolling reduction rate; continuous annealing; flattening. The present invention not only has a strip width of ≥1800mm, but also has a stable production process, the qualified rate can be increased from the current 40% to more than 80%, the tensile strength is ≥360MPa, and the performance meets the needs of users.

Description

Technical Field

[0001] The invention relates to a method for producing low-alloy high-strength steel, in particular to a method for producing low-alloy high-strength steel with a plate width of ≥1800mm. Background Art

[0002] With the in-depth development of the automobile market, the market requirements for automobile steel have shown a trend of differentiation and diversification. In order to improve the material utilization rate of steel plates, meet the overall forming requirements of parts, and reduce the welding cost of the original welded plates, some users require cold-rolled plates with larger plate widths.

[0003] Low alloy high strength steel is a kind of high strength steel that uses micro alloying elements to refine grains and dispersion strengthen to obtain high strength and good welding performance. Ultra-wide low alloy high strength steel is mainly used for structural parts and safety parts with high strength requirements such as inner longitudinal beams, rear longitudinal beams, and longitudinal beam covers of automobiles. Compared with conventional width materials, ultra-wide materials can significantly improve the material utilization rate of large-size parts, reduce the use of laser welded blanks, and reduce production costs and carbon emissions.

[0004] Because the width of ultra-wide low-alloy high-strength steel exceeds 1800mm, it is easy to scrape the furnace wall due to deviation during production in the continuous annealing furnace, which will lead to belt breakage and shutdown. It takes more than 20 hours to deal with the belt breakage and shutdown accident, which seriously affects the production rhythm and causes huge losses to the company. Therefore, reducing the deviation of ultra-wide low-alloy high-strength steel can effectively improve the production efficiency of the unit, and the most important thing to control the deviation is to control the shape of the steel plate. Secondly, low-alloy high-strength steel has a yield platform, which makes it easy for the plate to produce slip lines during the stamping process, which reduces the forming performance and cannot be processed again. Therefore, the yield platform needs to be reduced or even eliminated during the production process, and the excessive width of the plate makes it more difficult to eliminate the yield platform. The high-throughput, high-quality and high-performance requirements of the material have resulted in the inability of existing technologies to efficiently and stably manufacture ultra-wide low-alloy high-strength steel, and the production qualification rate is less than 40%.

[0005] The existing disclosed technologies only explain the production method, processing method or manufacturing method for a specific type of steel, such as patent application numbers CN201210574442.8, CN202010095552.0, CN201210205030.7, etc. There is no effective cold rolling process production control technology and technical solution for producing low-alloy high-strength steel with good stability and high pass rate with a width of ≥1800mm at home and abroad. Summary of the invention

[0006] The present invention aims to overcome the shortcomings of the prior art and provide a method for producing low-alloy high-strength steel with a plate width of ≥1800mm, which not only has a strip steel width of ≥1800mm, but also has stable production, a qualified rate of more than 80%, performance that meets user needs, and a tensile strength of ≥360MPa.

[0007] Technical measures to achieve the above objectives:

[0008] A method for producing low alloy high strength steel with a plate width of ≥1800 mm, characterized by the following steps:

[0009] 1) Perform conventional hot rolling and hot rolled plate surface convexity: the plate surface convexity value is controlled within 30 to 100 μm, wherein: when the thickness of the hot rolled plate is ≤2.8 mm, the plate surface convexity value is controlled not to exceed 90 μm; when the thickness of the hot rolled plate is >2.8 to 5 mm, the plate surface convexity value is controlled not to exceed 100 μm;

[0010] 2) Pickling: control the acid tank temperature at 70-90°C;

[0011] The free acid concentration in the three acid tanks is controlled as follows:

[0012] No. 1 acid tank is not less than 50g / l, No. 2 acid tank is not less than 70g / l, and No. 3 acid tank is not less than 130g / l; the pickling speed is controlled at no more than 180m / min;

[0013] 3) Use five stands for cold rolling, refine the group spacing and control the cold rolling reduction rate according to the thickness of the finished product:

[0014] When the finished product thickness is 0.6mm<≤0.7mm, the hot rolling raw material thickness is selected to be 2.2~≤2.4mm, and the total cold rolling reduction rate is controlled at 68~75%;

[0015] When 0.7mm<finished product thickness≤0.8mm, the hot rolling raw material thickness is selected to be 2.4~≤2.6mm, and the total cold rolling reduction rate is controlled at 67~73%;

[0016] When 0.8mm<finished product thickness≤0.9mm, the hot rolling raw material thickness is selected to be 2.7~≤2.9mm, and the total cold rolling reduction rate is controlled at 67~72%;

[0017] When the finished product thickness is 0.9mm<1.1mm, the hot rolling raw material thickness is selected to be 2.9~≤3.1mm, and the total cold rolling reduction rate is controlled at 62~71%;

[0018] When the finished product thickness is 1.1mm<1.4mm, the hot rolling raw material thickness is selected to be 3.4~≤3.6mm, and the total cold rolling reduction rate is controlled at 59~69%;

[0019] When the finished product thickness is 1.4mm<1.7mm, the hot rolling raw material thickness is selected to be 4.9~≤4.3mm, and the total cold rolling reduction rate is controlled at 59~67%;

[0020] When the finished product thickness is 1.7mm<≤2.0mm, the hot rolling raw material thickness is selected to be 4.1~≤5.1mm, and the total cold rolling reduction rate is controlled at 59~67%;

[0021] And control the emulsion temperature at 45-60°C, and the saponification value is not less than 170KOH / g;

[0022] The crown of the working rolls of each stand is controlled to be 20-40μm for the working rolls of the 1st to 4th stands, the crown of the working rolls of the 5th stand is not more than 10μm, and the inclination value of the 5th stand is controlled not to exceed 320μm. The absolute value of the tension difference on both sides of the strip at the mill exit is ≤5KN;

[0023] 4) Continuous annealing: before annealing the low alloy high strength steel with a plate width of ≥1800mm after cold rolling, first arrange 2 to 3 rolls of DC01 plain carbon steel coils with a width greater than the width of the low alloy high strength steel to be annealed, and the width greater than the value is not less than 5mm; DC01 steel and low alloy high strength steel use the same temperature and speed, and then enter the continuous annealing of the low alloy high strength steel with a plate width of ≥1800mm;

[0024] Each process operation is carried out as follows:

[0025] The annealing temperature of each section is controlled as follows:

[0026] The annealing temperature in the soaking section is 775~795℃.

[0027] The temperature of the slow cooling section is 630~660℃.

[0028] The temperature of the rapid cooling section is 400-430°C, and the rapid cooling rate is above 30°C / s.

[0029] The temperature of the over-aging stage is 360~400℃.

[0030] The temperature of the final cooling section is 170-180°C;

[0031] Control annealing speed according to strip thickness:

[0032] When the strip thickness is greater than 0.6 to 1.0 mm, the annealing speed is controlled at 160 to 220 m / min;

[0033] When the strip thickness is greater than 1.0 to 2.0 mm, the annealing speed is controlled at 130 to 180 m / min;

[0034] Control the tension of each segment:

[0035] Heating section:

[0036] The tension of the first heating section and the second heating section is controlled at 10-15KN, and the crown of the furnace roller is controlled at 0.25-0.35mm;

[0037] The tension of the third heating section is controlled at 8-12KN;

[0038] Soaking section:

[0039] The tension of this section is controlled at 6~10KN;

[0040] Slow cooling section and fast cooling section:

[0041] The tension of the two sections is controlled at 13-18KN;

[0042] Over-aging stage and final cooling stage:

[0043] The tension of the two sections is controlled at 8-13KN;

[0044] 5) Leveling, using a constant flow wet leveling mode, using a middle roller string roller, and controlling the leveling elongation at 1.5-2.0%;

[0045] Controlling the rolling force of the skin-pass mill:

[0046] When the strip thickness is greater than 1.0 mm, the temper rolling force shall not be less than 5000 KN;

[0047] When the strip thickness is ≤1.0mm, the temper rolling force shall not be less than 6500KN;

[0048] Control the front and rear tension of the leveler:

[0049] The tension before the leveling machine is controlled at 70~100KN, the tension after the leveling machine is controlled at 80~110KN, and the tension difference between the front and rear is controlled within 10KN.

[0050] Furthermore: during continuous annealing, when the unit has an abnormality and needs to slow down, the heating furnace adopts a step-by-step speed reduction method, that is, the speed is reduced step by step, and the single speed reduction does not exceed 20m / min, and the minimum operating speed is controlled at not less than 60m / min.

[0051] Function and mechanism of the main process in the present invention

[0052] The reason why the present invention controls the plate convexity of the hot-rolled raw material is that the good plate shape mainly comes from the good hot-rolled raw material plate profile and the proportional extension in the width direction of the strip during the cold rolling process. The hot-rolled raw material plate profile has the most direct impact on the plate shape. The cold-rolled strip outlet convexity depends on the hot-rolled raw material convexity and the rolling mill roll gap convexity. The size of the difference between the two determines the size of the strip wave shape. In the plate shape control of ultra-wide low-alloy high-strength steel, because the plate width reaches the limit of the length of the rolling mill roll body, conventional plate shape control methods such as bending rolls and stringing rolls cannot achieve the best plate shape control effect. Therefore, appropriate hot-rolled raw material convexity can reduce the intermediate extension degree of strip rolling and improve the strip shape. Through a large number of experiments, it was found that when the hot-rolled raw material thickness of ultra-wide low-alloy high-strength steel is ≤2.8mm, the plate convexity value is 30-90μm; when the hot-rolled raw material thickness of ultra-wide low-alloy high-strength steel is >2.8-5mm, the plate convexity value is 30-100μm, and the cold-rolled plate shape control is better.

[0053] The present invention controls the temperature of the acid tank at 70-90° C.; controls the free acid concentration in the three acid tanks: the No. 1 acid tank is not less than 50 g / l, the No. 2 acid tank is not less than 70 g / l, and the No. 3 acid tank is not less than 130 g / l; and controls the pickling speed to not more than 180 m / min, in order to avoid over-pickling and under-pickling of the steel coil and improve the surface quality of the product.

[0054] The reason why the present invention controls the emulsion temperature at 45-60°C and the saponification value is not less than 170KOH / g is to control the plate shape of ultra-wide low-alloy high-strength steel and reduce residual oil and iron on the surface of the steel coil to improve the surface quality of the product.

[0055] The reason why the present invention refines the group spacing and controls the cold rolling reduction rate according to the finished product thickness is:

[0056] When the finished product thickness is 0.6mm<≤0.7mm, the hot rolling raw material thickness is selected to be 2.2~≤2.4mm, and the total cold rolling reduction rate is controlled at 68~75%;

[0057] When 0.7mm<finished product thickness≤0.8mm, the hot rolling raw material thickness is selected to be 2.4~≤2.6mm, and the total cold rolling reduction rate is controlled at 67~73%;

[0058] When 0.8mm<finished product thickness≤0.9mm, the hot rolling raw material thickness is selected to be 2.7~≤2.9mm, and the total cold rolling reduction rate is controlled at 67~72%;

[0059] When the finished product thickness is 0.9mm<1.1mm, the hot rolling raw material thickness is selected to be 2.9~≤3.1mm, and the total cold rolling reduction rate is controlled at 62~71%;

[0060] When the finished product thickness is 1.1mm<1.4mm, the hot rolling raw material thickness is selected to be 3.4~≤3.6mm, and the total cold rolling reduction rate is controlled at 59~69%;

[0061] When the finished product thickness is 1.4mm<1.7mm, the hot rolling raw material thickness is selected to be 4.9~≤4.3mm, and the total cold rolling reduction rate is controlled at 59~67%;

[0062] When the finished product thickness is 1.7mm<≤2.0mm, the hot rolling raw material thickness is selected to be 4.1~≤5.1mm, and the total cold rolling reduction rate is controlled at 59~67%;

[0063] And control the emulsion temperature at 45-60°C, and the saponification value is not less than 170KOH / g;

[0064] The crown of the working rolls of each stand is controlled to be: the crown of the working rolls of the 1st to 4th stands is 20-40μm, the crown of the working rolls of the 5th stand is not more than 10μm and the inclination value of the 5th stand is controlled not to exceed 320μm, and the absolute value of the tension difference on both sides of the strip at the mill outlet is ≤5KN. This is because when the width exceeds 1800mm, the increase in deformation will cause a sharp increase in the rolling force of the mill, which greatly affects the adjustment effect of the bending roll and the shifting roll on the plate shape, and at the same time poses an extreme challenge to the cooling of the mill, causing the mill motor to overheat, which is more unfavorable for the stable control of the plate shape. With the increase in the rolling amount, the plate shape deteriorates further. Therefore, considering the plate shape comprehensively, the total reduction rate is appropriately reduced, the finished product thickness is ≤0.9mm, the reduction rate is controlled at 70-74%, the finished product thickness is greater than 0.9mm, and the reduction rate is controlled at 60-70%. The crown of the working rolls of the 1st to 5th stands: The crown of the working rolls of the 1st to 4th stands is 20-40μm, and the crown of the working rolls of the 5th stand is not more than 10μm; the inclination of the 5th stand is controlled, and the inclination value is controlled below 320μm to ensure that the absolute value of the tension difference on both sides of the strip at the mill outlet is ≤5KN. Reducing the tension difference on both sides of the strip can improve the quality of the plate shape, especially in the width direction, and can significantly reduce the risk of deviation of the continuous annealing unit.

[0065] The present invention controls that before annealing the low alloy high strength steel with a plate width of ≥1800mm after cold rolling, firstly arrange 2 to 3 rolls of DC01 plain carbon steel rolls with a width greater than the width of the low alloy high strength steel to be annealed, and the width greater than the width is not less than 5mm; the DC01 steel and the low alloy high strength steel adopt the same temperature and speed, and then enter the continuous annealing of the low alloy high strength steel with a plate width of ≥1800mm;

[0066] Each process operation is carried out as follows:

[0067] The annealing temperature of each section is controlled as follows:

[0068] The annealing temperature in the soaking section is 775~795℃.

[0069] The temperature of the slow cooling section is 630~660℃.

[0070] The temperature of the rapid cooling section is 400-430°C, and the rapid cooling rate is above 30°C / s.

[0071] The temperature of the over-aging stage is 360~400℃.

[0072] The temperature of the final cooling section is 170-180°C;

[0073] Control annealing speed according to strip thickness:

[0074] When the strip thickness is greater than 0.6 to 1.0 mm, the annealing speed is controlled at 160 to 220 m / min;

[0075] When the strip thickness is greater than 1.0 to 2.0 mm, the annealing speed is controlled at 130 to 180 m / min;

[0076] Control the tension of each segment:

[0077] Heating section:

[0078] The tension of the first heating section and the second heating section is controlled at 10-15KN, and the crown of the furnace roller is controlled at 0.25-0.35mm;

[0079] The tension of the third heating section is controlled at 8-12KN;

[0080] Soaking section:

[0081] The tension of this section is controlled at 6~10KN;

[0082] Slow cooling section and fast cooling section:

[0083] The tension of the two sections is controlled at 13-18KN;

[0084] Over-aging stage and final cooling stage:

[0085] The tension of the two sections is controlled at 8-13KN;

[0086] The reason why the present invention arranges 2 to 3 rolls of DC01 plain carbon steel is that the width of DC01 steel needs to be greater than the width of the ultra-wide low-alloy high-strength steel of the present invention. The leading material needs to be adjusted to the production process of ultra-wide low-alloy high-strength steel in advance, in order to ensure that the ultra-wide low-alloy high-strength steel can pass smoothly after entering the annealing furnace, reduce the uneven temperature difference between the strip and the furnace roller in the length direction, and reduce the thermal stress difference in the width direction of the strip. Therefore, a certain amount of leading material is arranged for hot rolling before production to reduce the probability of strip deviation.

[0087] The present invention controls the annealing temperature of different process sections, the temperature of the soaking section is 775-795°C, the temperature of the slow cooling section is 620-650°C, the temperature of the fast cooling section is 400-430°C, the fast cooling rate reaches more than 30°C / s, the temperature of the over-aging section is 360-400°C, and the temperature of the final cooling section is 170-180°C. Lowering the annealing temperature can effectively improve the product strength and eliminate the banded structure. Appropriately lowering the temperature of the cooling section can, on the one hand, reduce the temperature difference between the strip and the furnace roller and reduce the risk of cold buckling. On the other hand, matching the annealing speed can increase the cooling rate, which is conducive to increasing the supercooling degree during the phase transformation from austenite to pearlite, accelerating the nucleation of pearlite by austenite decomposition and reducing the eutectoid reaction temperature, thereby reducing the content of proeutectoid ferrite, increasing the amount of pearlite transformation, and improving the product strength. Turn on the electric heating device of the over-aging section to improve the temperature guarantee and stability of the aging section, reduce the change of the roller shape, and reduce the probability of surface defects such as cold buckling and scratches.

[0088] The reason why the present invention controls the annealing speed is that for strip thickness > 0.6 ~ 1.0mm, the annealing speed is 160-220m / min; for strip thickness > 1.0 ~ 2.0mm, the annealing speed is 130-180m / min. The cooling rate needs to reach above 35℃ / s to ensure that the product meets the requirements, so it is necessary to control a suitable speed to ensure the cooling rate. At the same time, in order to reduce the influence of the furnace roller shape on the wide strip, the operating speed of the annealing furnace needs to be increased, but the speed increase is likely to cause the strip to deviate, and in severe cases, cause strip breakage, and the low annealing speed is likely to cause the strip to bend. Set the minimum operating speed, that is, the safe operating speed of the plate. If the unit is lower than this speed, it is easy to cause serious buckling, thereby causing serious production accidents such as unit shutdown and strip breakage. In summary, the control of the annealing speed requires comprehensive consideration.

[0089] The reason why the present invention controls the tension of each process section is mainly to control the deviation of ultra-wide strip steel, buckling and reduce the fluctuation of the plate. In the first heating section and the second heating section, since the strip steel enters a higher temperature at a lower temperature, the internal stress of the strip steel is released, and the strip steel is prone to deviation. The ultra-wide low-alloy high-strength steel plate shape is not good or the tension difference on both sides of the strip steel is too large, which will aggravate the deviation of the strip steel. Therefore, the convexity of the furnace roller in this area should be improved and controlled at 0.25-0.35mm. At the same time, the tension of the first heating section and the second heating section needs to be increased and controlled at 10-15KN. In the third heating section, the probability of deviation is small. At the same time, since the strip steel is in a high temperature state and the steel is softer, the tension can be appropriately reduced and controlled at 8-12KN. In the equalization section, since the strip steel is kept at 775-795℃ for a period of time, the steel is softer, and the tension needs to be further reduced and controlled at 6-10KN. In the slow cooling section and the fast cooling section, lowering the temperature in the slow cooling section and the fast cooling section is conducive to reducing the temperature difference between the strip and the furnace roller, which can reduce the risk of cold buckling. However, the temperature reduction is achieved through the cooling bellows. The wind speed of the cooling bellows is high, which can easily cause the strip to shake and cause scratches. The ultra-wide strip shakes more, causing more serious scratches. Therefore, the tension needs to be larger and controlled at 13 to 18KN. In the over-aging section and the final cooling section, if the tension in this area is too large, the degree of cold buckling will be aggravated, and if it is too small, the degree of scratching will increase. Therefore, the setting of the tension value in this area needs to take into account both scratches and buckling, and be controlled at 8 to 13KN.

[0090] The reason why the flattening process of the present invention adopts a constant flow wet flattening mode and uses a string of intermediate rolls is mainly to ensure the consistency of rolling force in the width direction and ensure the plate shape of the ultra-wide low-alloy high-strength steel product. Before producing ultra-wide low-alloy high-strength steel, new working rolls are replaced to reduce the color difference of the strip edge caused by the transition from narrow specifications to wide specifications, ensuring the high surface quality of the finished product.

[0091] The reason why the flattening elongation of the present invention is controlled at 1.5-2.0% is that a large flattening elongation is conducive to eliminating the yield platform of the product, so that the product will not produce a slip line during the stamping process. The front and rear tensions of the leveling machine are controlled mainly because the flattening elongation of ultra-wide plates increases, which will make it more difficult to control the plate shape and easily produce edge waves at the edges. Therefore, it is necessary to control and stabilize the front and rear tensions of the leveling machine. The front tension is controlled at 70-100KN, the rear tension is controlled at 80-110KN, and the rear-front tension difference is controlled within 10KN. The rolling force of the leveling machine is controlled mainly to eliminate the yield platform of the product, especially for products with a strip thickness of ≤1.0mm. When the strip flattening elongation reaches 1.5-2.0%, the plate shape control is very poor and it is necessary to appropriately reduce the flattening elongation. At this time, it is necessary to ensure that the flattening rolling force reaches the required value.

[0092] Compared with the prior art, the present invention has not only a strip width of ≥1800mm, but also a stable production process, a qualified rate increased from the current 40% to more than 80%, a tensile strength of ≥360MPa, and performance that meets user needs. DETAILED DESCRIPTION

[0093] The present invention is described in detail below:

[0094] Table 1 is a list of main process parameters of various embodiments and comparative examples of the present invention;

[0095] Table 2 is a table of performance test results of various embodiments of the present invention and comparative examples.

[0096] Each embodiment of the present invention is produced according to the following steps

[0097] 1) Perform conventional hot rolling and hot rolled plate surface convexity: the plate surface convexity value is controlled within 30 to 100 μm, wherein: when the thickness of the hot rolled plate is ≤2.8 mm, the plate surface convexity value is controlled not to exceed 90 μm; when the thickness of the hot rolled plate is >2.8 to 5 mm, the plate surface convexity value is controlled not to exceed 100 μm;

[0098] 2) Pickling: control the acid tank temperature at 70-90°C;

[0099] The free acid concentration in the three acid tanks is controlled as follows:

[0100] No. 1 acid tank is not less than 50g / l, No. 2 acid tank is not less than 70g / l, and No. 3 acid tank is not less than 130g / l; the pickling speed is controlled at no more than 180m / min;

[0101] 3) Use five stands for cold rolling, refine the group spacing and control the cold rolling reduction rate according to the thickness of the finished product:

[0102] When the finished product thickness is 0.6mm<≤0.7mm, the hot rolling raw material thickness is selected to be 2.2~≤2.4mm, and the total cold rolling reduction rate is controlled at 68~75%;

[0103] When 0.7mm<finished product thickness≤0.8mm, the hot rolling raw material thickness is selected to be 2.4~≤2.6mm, and the total cold rolling reduction rate is controlled at 67~73%;

[0104] When 0.8mm<finished product thickness≤0.9mm, the hot rolling raw material thickness is selected to be 2.7~≤2.9mm, and the total cold rolling reduction rate is controlled at 67~72%;

[0105] When the finished product thickness is 0.9mm<1.1mm, the hot rolling raw material thickness is selected to be 2.9~≤3.1mm, and the total cold rolling reduction rate is controlled at 62~71%;

[0106] When the finished product thickness is 1.1mm<1.4mm, the hot rolling raw material thickness is selected to be 3.4~≤3.6mm, and the total cold rolling reduction rate is controlled at 59~69%;

[0107] When the finished product thickness is 1.4mm<1.7mm, the hot rolling raw material thickness is selected to be 4.9~≤4.3mm, and the total cold rolling reduction rate is controlled at 59~67%;

[0108] When the finished product thickness is 1.7mm<≤2.0mm, the hot rolling raw material thickness is selected to be 4.1~≤5.1mm, and the total cold rolling reduction rate is controlled at 59~67%;

[0109] And control the emulsion temperature at 45-60°C, and the saponification value is not less than 170KOH / g;

[0110] The crown of the working rolls of each stand is controlled to be 20-40μm for the working rolls of the 1st to 4th stands, the crown of the working rolls of the 5th stand is not more than 10μm, and the inclination value of the 5th stand is controlled not to exceed 320μm. The absolute value of the tension difference on both sides of the strip at the mill exit is ≤5KN;

[0111] 4) Continuous annealing: before annealing the low alloy high strength steel with a plate width of ≥1800mm after cold rolling, first arrange 2 to 3 rolls of DC01 plain carbon steel coils with a width greater than the width of the low alloy high strength steel to be annealed, and the width greater than the value is not less than 5mm; DC01 steel and low alloy high strength steel use the same temperature and speed, and then enter the continuous annealing of the low alloy high strength steel with a plate width of ≥1800mm;

[0112] Each process operation is carried out as follows:

[0113] The annealing temperature of each section is controlled as follows:

[0114] The annealing temperature in the soaking section is 775~795℃.

[0115] The temperature of the slow cooling section is 630~660℃.

[0116] The temperature of the rapid cooling section is 400-430°C, and the rapid cooling rate is above 30°C / s.

[0117] The temperature of the over-aging stage is 360~400℃.

[0118] The temperature of the final cooling section is 170-180°C;

[0119] Control annealing speed according to strip thickness:

[0120] When the strip thickness is greater than 0.6 to 1.0 mm, the annealing speed is controlled at 160 to 220 m / min;

[0121] When the strip thickness is greater than 1.0 to 2.0 mm, the annealing speed is controlled at 130 to 180 m / min;

[0122] Control the tension of each segment:

[0123] Heating section:

[0124] The tension of the first heating section and the second heating section is controlled at 10-15KN, and the crown of the furnace roller is controlled at 0.25-0.35mm;

[0125] The tension of the third heating section is controlled at 8-12KN;

[0126] Soaking section:

[0127] The tension of this section is controlled at 6~10KN;

[0128] Slow cooling section and fast cooling section:

[0129] The tension of the two sections is controlled at 13-18KN;

[0130] Over-aging stage and final cooling stage:

[0131] The tension of the two sections is controlled at 8-13KN;

[0132] 5) Leveling, using a constant flow wet leveling mode, using a middle roller string roller, and controlling the leveling elongation at 1.5-2.0%;

[0133] Controlling the rolling force of the skin-pass mill:

[0134] When the strip thickness is greater than 1.0 mm, the temper rolling force shall not be less than 5000 KN;

[0135] When the strip thickness is ≤1.0mm, the temper rolling force shall not be less than 6500KN;

[0136] Control the front and rear tension of the leveler:

[0137] The tension before the leveling machine is controlled at 70~100KN, the tension after the leveling machine is controlled at 80~110KN, and the tension difference between the front and rear is controlled within 10KN.

[0138] Table 1 List of main process parameters of various embodiments and comparative examples of the present invention

[0139]

[0140] Table 1

[0141]

[0142]

[0143] Table 2 Performance test results of various embodiments of the present invention and comparative examples

[0144]

[0145] As can be seen from Table 2, Examples 1-7, the ultra-wide low-alloy high-strength steel within the scope of the claims of the present invention, can not only be smoothly and high-quality plate-passed and produced, but also the surface quality and mechanical properties meet the requirements, and the performance indicators meet the technical indicators of HC300LA steel. The overall product qualification rate of Examples 1-7 reached 87%. In Comparative Example 1, due to the large difference in the strip tension at the exit of the rolling mill, the strip deviated in the annealing furnace, and the unit took emergency speed reduction measures, resulting in surface quality defects such as severe scratches on the surface of the strip. At the same time, the cooling rate was low, resulting in inconsistent product performance. In Comparative Example 2, due to the low flattening elongation and the flattening rolling force lower than 6500KN, the strip had a yield platform, and slip lines were easily generated during the stamping process, affecting customer use.

[0146] This specific implementation is only the best example and is not a restrictive implementation of the technical solution of the present invention.

Claims

1. A method for producing low alloy high strength steel with a plate width of ≥1800 mm, characterized in that Here are the steps: 1) Carry out conventional hot rolling and hot rolled plate surface convexity: the plate surface convexity value is controlled at 68-100μm, wherein: when the thickness of the hot rolled plate is ≤2.8mm, the plate surface convexity value is controlled at 81-90μm; when 2.8mm<hot rolled plate thickness≤5mm, the plate surface convexity value is controlled at 68-100μm; 2) Pickling: control the acid tank temperature at 70-90°C; The free acid concentration in the three acid tanks is controlled as follows: No. 1 acid tank is not less than 50g / L, No. 2 acid tank is not less than 70g / L, and No. 3 acid tank is not less than 130g / L; the pickling speed is controlled at no more than 180m / min; 3) Use five stands for cold rolling, refine the group spacing and control the cold rolling reduction rate according to the thickness of the finished product: When 0.6mm<finished product thickness≤0.7mm, the hot rolling raw material thickness is selected to be 2.2~≤2.4mm, and the total cold rolling reduction rate is controlled at 68~75%; When 0.7mm<finished product thickness≤0.8mm, the hot rolling raw material thickness is selected to be 2.4~≤2.6mm, and the total cold rolling reduction rate is controlled at 67~73%; When 0.8mm<finished product thickness≤0.9mm, the hot rolling raw material thickness is selected to be 2.7~≤2.9mm, and the total cold rolling reduction rate is controlled at 67~72%; When the finished product thickness is 0.9mm<≤1.1mm, the hot rolling raw material thickness is selected to be 2.9~≤3.1mm, and the total cold rolling reduction rate is controlled at 62~71%; When 1.1mm<finished product thickness≤1.4mm, the hot rolling raw material thickness is selected to be 3.4~≤3.6mm, and the total cold rolling reduction rate is controlled at 59~69%; When 1.4mm<finished product thickness≤1.7mm, the hot rolling raw material thickness is selected to be 4.9~≤4.3mm, and the total cold rolling reduction rate is controlled at 59~67%; When the finished product thickness is 1.7mm<≤2.0mm, the hot rolling raw material thickness is selected to be 4.1~≤5.1mm, and the total cold rolling reduction rate is controlled at 59~67%; And control the emulsion temperature at 45-60°C, and the saponification value is not less than 170KOH / g; The crown of the working rolls of each stand is controlled to be 20-40μm for the working rolls of the 1st to 4th stands, the crown of the working rolls of the 5th stand is not more than 10μm, and the inclination value of the 5th stand is controlled not to exceed 320μm. The absolute value of the tension difference on both sides of the strip at the mill exit is ≤5kN; 4) Continuous annealing: Before annealing the low alloy high strength steel with a plate width of ≥1800mm after cold rolling, first arrange 2 to 3 rolls of DC01 plain carbon steel coils with a width greater than the width of the low alloy high strength steel to be annealed, and the width greater than the value is not less than 5mm; DC01 steel and low alloy high strength steel use the same temperature and speed, and then enter the continuous annealing of the low alloy high strength steel with a plate width of ≥1800mm; Each process operation is carried out as follows: The annealing temperature of each section is controlled as follows: The annealing temperature in the soaking section is 775~795℃. The temperature of the slow cooling section is 630~660℃. The temperature of the rapid cooling section is 400-430°C, and the rapid cooling rate is above 30°C / s. The temperature of the over-aging stage is 360~400℃. The temperature of the final cooling section is 170-180°C; Control annealing speed according to strip thickness: When the strip thickness is 0.6mm<≤1.0mm, the annealing speed is controlled at 160~220m / min; When the strip thickness is 1.0mm<≤2.0mm, the annealing speed is controlled at 130~180m / min; Control the tension of each segment: Heating section: The tension of the first heating section and the second heating section is controlled at 10-15 kN, and the crown of the furnace roller is controlled at 0.25-0.35 mm; The tension of the third heating section is controlled at 8-12kN; Soaking section: The tension of this section is controlled at 6-10kN; Slow cooling section and fast cooling section: The tension of the two stages is controlled at 13-18 kN; Over-aging stage and final cooling stage: The tension of the two sections is controlled at 8-13kN; 5) For leveling, use a constant flow wet leveling mode, use an intermediate roller string roller, and control the leveling elongation at 1.5-2.0%; Controlling the rolling force of the skin-pass mill: When the strip thickness is greater than 1.0 mm, the temper rolling force shall not be less than 5000 kN; When the strip thickness is ≤1.0mm, the temper rolling force shall not be less than 6500kN; Control the front and rear tension of the leveler: The tension before the leveling machine is controlled at 70-100kN, the tension after the leveling machine is controlled at 80-110kN, and the tension difference between the front and rear is controlled Within 10kN.

2. A method for producing low alloy high strength steel with a plate width of ≥1800 mm as claimed in claim 1, characterized in that: During continuous annealing, when the unit has an abnormality and needs to slow down, the heating furnace adopts a step-by-step speed reduction method, that is, the speed is reduced step by step, and the single speed reduction does not exceed 20m / min. At the same time, the minimum operating speed is controlled at not less than 60m / min.

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