Method for producing sk120 cold-rolled steel sheet

Abstract

The application discloses a production method of SK120 cold-rolled steel plate, which comprises the following steps: hot-rolling and pickling a steel coil, performing a water bath process, cold-rolling for the first time, spheroidizing annealing, cold-rolling for the second time, recrystallization annealing and skin passing, so as to obtain the SK120 cold-rolled steel plate. The method solves the problems of edge crack, brittle fracture and shape during uncoiling and cold-rolling, and improves the yield of the cold-rolled steel plate.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of cold-rolled steel plate rolling, and particularly relates to a production method of SK120 cold-rolled steel plate. BACKGROUND

[0002] The SK120 cold-rolled steel plate is an ultra-high carbon tool steel, the carbon content of which is 1.2%, and belongs to an extremely high-end product in steel materials, has high technical content and is difficult to produce.

[0003] The SK120 cold-rolled steel plate is currently basically supplied in the form of narrow strip steel, and the strip product is mainly applied to blades. The SK120 is a steel grade extremely prone to cracking and brittle fracture, especially in the cold rolling process.

[0004] The original characteristics of the steel grade and the increase of the width of the steel strip often cause the production of the cold-rolled plate to be unable to continue due to rolling edge cracks, rolling brittle fracture and shape problems, so that the existing yield of the steel grade is extremely low. SUMMARY

[0005] In view of this, the application provides a production method of SK120 cold-rolled steel plate, aiming to provide a production process with high yield and good product performance.

[0006] In a first aspect, the embodiments of the application provide a production method of SK120 cold-rolled steel plate, comprising:

[0007] hot-rolled and pickled steel coil, water bath process, first cold rolling, spheroidizing annealing, second cold rolling, recrystallization annealing and skin pass;

[0008] The steel coil comprises the following chemical components in mass percentage: C: 1.15% to 1.25%, Si: 0.15% to 0.35%, Mn: 0.35% to 0.50%, P: less than or equal to 0.018%, S: less than or equal to 0.010%, and the rest is Fe and inevitable impurities.

[0009] The water bath process comprises: hoisting the hot-rolled and pickled steel coil into a water bath pool at 50 to 60 DEG C, soaking for 2 to 4 hours and hoisting out, and sending the steel coil to a single-stand rolling mill for cold rolling within 10 minutes after hoisting out;

[0010] The first cold rolling comprises: adopting three passes, and the reduction rate of each pass is 8% to 10%, 8% to 10% and 8% to 10% respectively; the rolling speed of each pass is set to 80 to 150 m / min, the front tension of the strip unit is 0.10 to 0.20 KN / mm, and the rear tension of the strip unit is 0.15 to 0.30 KN / mm.

[0011] The spheroidizing annealing comprises: the steel coil is heated from room temperature to 200℃ freely; the heating process adopts the holding platform annealing, heated to 400℃ at a heating speed of 60℃ / h to 100℃ / h and held for 1 to 3 hours; then heated to 740℃ at a speed of 40℃ / h to 80℃ / h, held for 16 to 20 hours; after the second holding, the first cooling is performed to 80℃ to 100℃ for discharging;

[0012] The second cold rolling comprises: the total reduction rate is 10% to 50%; when the total reduction rate is greater than or equal to 20%, the three passes are adopted; the rolling speed of each pass is set to 200 to 300 m / min, the unit front tension of the strip is 0.08 to 0.15 KN / mm, and the unit back tension is 0.12 to 0.25 KN / mm;

[0013] The recrystallization annealing process comprises: the steel coil is heated from room temperature to 200℃ freely; the heating process adopts the holding platform annealing, heated to 400℃ at a heating speed of 60℃ / h to 100℃ / h and held for 1 to 3 hours; then heated to 700℃ at a speed of 40℃ / h to 80℃ / h, held for 16 to 20 hours; after the holding, the second cooling is performed to 80℃ to 100℃ for discharging;

[0014] The steel coil is subjected to the flattening and rewinding after the recrystallization annealing, and the flattening elongation is set to 1.0% to 3.0%.

[0015] According to the embodiment of one aspect of the present application, the first cooling and the second cooling respectively comprise: slow cooling to 550℃; then air cooling to 450℃; and then water cooling.

[0016] According to the embodiment of one aspect of the present application, the reduction rate of each pass in the first cold rolling is 10%, 10% and 10% in turn.

[0017] According to the embodiment of one aspect of the present application, the thickness of the SK120 hot-rolled and pickled steel coil is 1.8 to 3.0 mm.

[0018] According to the embodiment of one aspect of the present application, the thickness of the SK120 cold-rolled steel plate is 0.6 to 1.8 mm.

[0019] According to the embodiment of one aspect of the present application, the width of the SK120 cold-rolled steel plate is 900 to 1500 mm.

[0020] In a second aspect, the embodiment of the present application provides a SK120 cold-rolled steel plate, which is prepared by the production method of the first aspect.

[0021] The present application has at least the following advantageous effects:

[0022] The embodiment of the present application provides a production method, through reasonable water bath process, first cold rolling, spheroidizing annealing, second cold rolling, recrystallization annealing, leveling, preheating of the steel coil through the water bath process is utilized to avoid the significant brittleness of the ultrahigh carbon steel at low temperature, then through reasonable distribution of the cold rolling pass reduction rate of the first cold rolling and the second cold rolling, the over-hardening can be avoided, and certain heat of the steel strip is generated to improve the plasticity and toughness of the strip, and reasonable tension and rolling speed are set, so that the edge cracking and brittle fracture problems of the SK120 wide coil in the cold rolling process are avoided; the mechanical property uniformity of the strip is ensured through the reasonable annealing process, and under the condition that the edge cracking and strip breaking do not occur, the stable shape is ensured, the high-quality SK120 cold-rolled steel plate with a yield of more than 95% is produced; the rolling edge cracking, rolling brittle fracture and shape problems which are prone to occur in the uncoiling and cold rolling process are reduced, and the stable and smooth production problem of the SK120 ultrahigh carbon tool steel wide cold-rolled steel plate is solved. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required to be used in the embodiments of the present application will be briefly introduced, and other drawings can be obtained by those skilled in the art without creative labor on the premise that the drawings are not paid.

[0024] Figure 1 The rolling edge cracking appearance of the comparative example of the present application is shown.

[0025] Figure 2 The rolling brittle fracture appearance of the comparative example of the present application is shown.

[0026] Figure 3 The shape problem appearance of the comparative example of the present application is shown. DETAILED DESCRIPTION

[0027] In order to make the application purpose, technical solutions and beneficial technical effects of the present application more clear, the present application will be further described in detail in combination with the embodiments. It should be understood that the embodiments described in the specification are only for explaining the present application, and are not intended to limit the present application.

[0028] For simplicity, only some numerical ranges are explicitly recited herein. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with any other lower limit to form a range not explicitly recited, and likewise any upper limit can be combined with any other upper limit to form a range not explicitly recited. Further, although a range is recited, it is to be understood that every point or individual number within the range is also specifically disclosed. Thus, for example, every point or individual number within the range is to be considered as a separate embodiment.

[0029] In the description of the present application, it is to be noted that, unless otherwise stated, "above", "below", "under" and "on" are inclusive of the number itself, and "a plurality of" means two or more.

[0030] The foregoing summary of the application is not intended to describe every disclosed embodiment or implementation of the application. The following description more specifically illustrates example embodiments. Throughout this application, guidance is provided by a series of embodiments, which can be used in various combinations. In each instance, the recitation is merely representative of a group, and should not be interpreted as exhaustive.

[0031] In a first aspect, the embodiments of the present application provide a production method of SK120 cold-rolled steel plate, comprising: hot-rolled pickled steel coil, water bath process, first cold rolling, spheroidizing annealing, second cold rolling, recrystallization annealing, skin pass, wherein the steel coil comprises the following chemical components in mass percentage: C: 1.15%~1.25%, Si: 0.15%~0.35%, Mn: 0.35%~0.50%, P≤0.018%, S≤0.010%; the rest is Fe and inevitable impurities.

[0032] According to the embodiments of the present application, the hot-rolled pickled steel plate with the above-mentioned components, by using suitable spheroidizing annealing process and suitable cold rolling process, the performance of the steel plate is changed, and the probability of edge cracking, brittle fracture and shape problem during rolling is reduced, and the yield of SK120 cold-rolled steel plate is improved.

[0033] In some optional embodiments, before the hot-rolled pickled steel plate is subjected to the first cold rolling treatment, the method further comprises:

[0034] The hot-rolled pickled steel plate is placed in a water bath pool at 50°C to 60°C for 2h to 4h, and the hot-rolled pickled steel plate is sent to a position for first cold rolling treatment within 10min.

[0035] According to the embodiments of the present application, the low-temperature preheating of the steel coil can avoid the significant brittleness of ultra-high carbon steel at low temperature, and reduce the probability of edge cracking and brittle fracture in the cold rolling process.

[0036] In some alternative embodiments, the water bath process comprises: hoisting the hot-rolled and pickled steel coil into a water bath pool at 50-60°C, soaking for 2-4 hours, and hoisting out; and sending the steel coil to a single-stand cold rolling mill within 10 minutes after hoisting out.

[0037] In some alternative embodiments, the first cold rolling comprises: adopting three passes, and the reduction rate of each pass is 8-10%, 8-10%, and 8-10% respectively; the rolling speed of each pass is set to 80-150 m / min, the unit front tension of the strip is 0.10-0.20 KN / mm, and the unit back tension of the strip is 0.15-0.30 KN / mm.

[0038] According to the embodiments of the present application, the rolling speed, the unit front tension of the strip, and the unit back tension of the strip in the first cold rolling process are key process parameters. Controlling the rolling speed, the unit front tension of the strip, and the unit back tension of the strip within the above ranges can change the deformation resistance and the microstructure of the strip while taking into account the production efficiency, thereby reducing the probability of edge cracking and brittle fracture during rolling, and improving the stability and thickness uniformity of the strip during rolling. In addition, the back tension affects the degree of deformation of the strip during cold rolling, thereby affecting the strength and hardness of the strip.

[0039] In the process of rolling the strip, the unit front tension of the strip (also known as the entry tension) is a very important parameter, which affects the rolling quality, the thickness control of the strip, and the stability of the rolling mill. The unit front tension of the strip usually refers to the tension per unit width.

[0040] In the process of rolling the strip, the unit back tension of the strip (also known as the exit tension) is also a key parameter. It plays an important role in controlling the quality of the rolled strip and ensuring the stability of the production process. The unit back tension of the strip usually refers to the tension per unit width.

[0041] In some alternative embodiments, the spheroidizing annealing comprises: freely heating the steel coil from room temperature to 200°C; adopting a holding platform annealing in the heating process, heating to 400°C at a heating speed of 60-100°C / h and performing first holding for 1-3 hours; then heating to 740°C at a heating speed of 40-80°C / h, and performing second holding for 16-20 hours; and after the second holding ends, performing first cooling to 80-100°C and discharging.

[0042] The above holding time can better ensure the uniformity of the temperature of the steel strip, thereby improving the uniformity of the microstructure of the steel plate.

[0043] In some alternative embodiments, the first cooling comprises: slow cooling to 550°C; then air cooling to 450°C; and then water cooling.

[0044] According to the embodiment of the present application, the cooling rate has a significant influence on the spheroidization degree and distribution of carbides and residual stress, thereby affecting the plasticity and toughness of the material. The above-mentioned cooling mode also affects the hardness and strength of the material, and slow cooling helps to improve the toughness and plasticity of the steel plate. Thus, the first cooling according to the embodiment of the present application can further reduce the probability of cold rolling edge cracking and cold rolling brittle fracture, and improve the yield.

[0045] In some optional embodiments, the second cold rolling includes: a total reduction rate of 10% to 50%; when the total reduction rate is greater than or equal to 20%, three passes of rolling are performed; the rolling speed of each pass is set to 200 to 300 m / min, the unit front tension of the strip is 0.08 to 0.15 KN / mm, and the unit back tension of the strip is 0.12 to 0.25 KN / mm.

[0046] According to the embodiment of the present application, the rolling speed, the unit front tension of the strip and the unit back tension of the strip in the second cold rolling process are key process parameters. Controlling the rolling speed, the unit front tension of the strip and the unit back tension of the strip within the above-mentioned ranges can change the deformation resistance and the microstructure of the strip on the basis of taking into account the production efficiency, thereby reducing the probability of edge cracking and brittle fracture during rolling and further improving the stability and thickness uniformity of the strip during the rolling process.

[0047] According to the embodiment of the present application, the total reduction rate is set to 10% to 50% to produce SK120 cold-rolled wide steel plates of different thickness specifications, and the thickness specifications are 0.6 to 1.8 mm.

[0048] In order to produce SK120 cold-rolled steel plates of target thickness, according to the thickness of the second cold-rolled plate, an appropriate total reduction rate is used to produce SK120 cold-rolled steel plates that meet the requirements on the premise of reducing the probability of edge cracking and brittle fracture in the cold rolling process.

[0049] In some optional embodiments, the recrystallization annealing process includes: the steel coil is heated from room temperature to 200℃ freely; during the heating process, the annealing is performed at a heating speed of 80℃ / h to 100℃ / h to 400℃ and is kept for 2 to 3 hours; then the heating is performed at a speed of 40℃ / h to 80℃ / h to 700℃, and is kept for 16 to 20 hours; after the keeping, the second cooling is performed to 80℃ to 100℃ for discharging.

[0050] In some optional embodiments, in order to improve the flatness and the shape of the steel coil, the steel coil is flattened and rewound after the recrystallization annealing, and the flattening elongation is set to 1.0% to 3.0%.

[0051] In some optional embodiments, the first cold rolling process adopts three passes of rolling, and the reduction rate of each pass is 10%, 10% and 10% respectively.

[0052] The above reduction ratio helps to maintain the plasticity and ductility of the steel plate, significantly improves the mechanical properties and microstructure of the steel plate after cold rolling, and significantly reduces the probability of edge cracking and brittle fracture of the steel plate during rolling, thereby improving the yield rate.

[0053] The first pass rolling adopts a low reduction of 10%, which can avoid excessive work hardening and make the steel strip produce a certain amount of heat to improve the temperature of the strip and improve its plasticity and toughness.

[0054] In some optional embodiments, the thickness of the SK120 hot-rolled and pickled steel coil is 1.8-3.0 mm.

[0055] In some optional embodiments, the thickness of the SK120 cold-rolled steel plate is 0.6-1.8 mm.

[0056] In some optional embodiments, the width of the SK120 cold-rolled steel plate is 900-1500 mm.

[0057] In some optional embodiments, in order to save costs and improve the uniformity of the steel coil heating and the uniformity of the steel coil performance, the second holding time is 16-20 h, which satisfies:

[0058] The weight of the steel coil is less than 16 tons for 16 h;

[0059] The weight of the steel coil is greater than 23 tons for 20 h;

[0060] The weight of the remaining steel coil is 18 h.

[0061] According to the embodiments of the present application, the second holding time is controlled according to the weight of the first cold-rolled plate, which is beneficial to improve the uniformity of the internal temperature and microstructure of the steel plate, make the carbide spheroidization process consistent, and ensure the uniformity of the material performance; the second holding time is controlled according to the weight of the first cold-rolled plate, which is helpful to the uniform spheroidization of the carbide in the steel plate, directly improves the spheroidization degree of the carbide, reduces the hardness of the steel, improves the toughness and plasticity of the steel plate, and reduces the probability of cracking and embrittlement of the steel plate. The grain structure is refined, thereby improving the strength and toughness of the steel plate, and also reducing the probability of cold rolling edge cracking and cold rolling brittle fracture.

[0062] In some optional embodiments, the elongation of the tempering treatment is 1% to 3.0%.

[0063] In the embodiments of the present application, the tempering treatment can be followed by recoiling, and the tempering treatment can improve the plate shape.

[0064] In a second aspect, the embodiments of the present application provide a SK120 cold-rolled steel plate produced by the production method of the first aspect.

[0065] In some alternative embodiments, the mechanical properties of the SK120 cold-rolled steel sheet include a yield strength of 340-420 MPa, a tensile strength of 510-580 MPa, and an elongation of 20-28.5%. The yield of the SK120 cold-rolled steel sheet of the embodiments is between 95% and 97.6%.

[0066] Embodiments

[0067] The present disclosure is described in more detail by the following examples, which are merely illustrative and not limiting of the scope of the present disclosure, as various modifications and changes can be suggested by those skilled in the art. Unless otherwise stated, all proportions, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and used as received without further purification, and the instruments used in the examples are commercially available.

[0068] Example 1

[0069] The present embodiment provides a production method of a SK120 cold-rolled steel sheet, which includes:

[0070] A normal quality SK120 hot-rolled pickled steel coil is used as a raw material, and the mass percentage of the chemical composition of the hot-rolled steel coil is: C: 1.19%, Si: 0.25%, Mn: 0.41%, P: 0.012%, S: 0.003%; the rest is Fe and inevitable impurities. The specification of the hot-rolled steel coil is 1.8 mm x 1250 mm, and the coil weight is 18 tons.

[0071] Water bath process: the SK120 hot-rolled pickled steel coil is lifted into a 60°C water bath, soaked for 2h, and lifted out. The steel coil is sent to a single-stand rolling mill for cold rolling within 10 minutes after being lifted out.

[0072] First cold rolling process: three passes are adopted, and the reduction rate of each pass is 10%, 10%, and 10%, respectively. The rolling speed of each pass is set to 140 m / min, the front tension of the belt unit is 0.10 KN / mm, and the rear tension of the belt unit is 0.16 KN / mm.

[0073] The spheroidizing annealing process is: the steel coil is heated from room temperature to 200°C freely; the heating process adopts a holding platform annealing to better ensure the uniformity of the temperature of the steel coil, heated to 400°C at a heating speed of 100°C / h and held for 3h; then heated to 740°C at a heating speed of 80°C / h, and held for 18h according to the weight of the steel coil; after the holding is completed, the power is turned off and the steel coil is slowly cooled to 550°C; the air is replaced to cool to 450°C; the water is replaced to cool to 100°C and the furnace is discharged.

[0074] Second cold rolling process: the total reduction rate is set at 50%, and the rolling is carried out in three passes, and the reduction rate of the three passes is 15%, 15% and 20% respectively. The rolling speed of each pass is set at 280 m / min, the unit front tension of the strip is 0.09 KN / mm, and the unit back tension is 0.15 KN / mm.

[0075] Recrystallization annealing process: the steel coil is heated from room temperature to 200℃ freely; the heating process adopts holding platform annealing to better ensure the uniformity of the temperature of the steel coil, the heating speed is 100℃ / h to 400℃ and the temperature is kept for 3h; then the heating speed is 80℃ / h to 700℃, and the temperature is kept for 16h according to the weight of the steel coil; after the temperature keeping is finished, the power is stopped and the temperature is slowly cooled to 550℃; the air is replaced to cool to 450℃; the water is replaced to cool to 100℃ and the coil is discharged.

[0076] After the steel coil is annealed, flattening and recoiling are carried out to improve the flatness, and the flattening elongation is set at 1.0%.

[0077] The above method can produce high-quality SK120 wide cold-rolled plates with a thickness of 0.6mm.

[0078] Example 2

[0079] The embodiment of the application provides a production method of an SK120 cold-rolled steel plate, which comprises the following steps:

[0080] The hot-rolled pickled steel coil with normal quality is used as raw material, and the mass percentage of the chemical components of the hot-rolled steel coil is as follows: C: 1.22%, Si: 0.18%, Mn: 0.45%, P: 0.010, S: 0.002; the rest is Fe and inevitable impurities. The specification of the hot-rolled steel coil is 2.5mm*1250mm, and the coil weight is 23 tons.

[0081] Water bath process: the SK120 hot-rolled pickled steel coil is lifted into a 60℃ water bath pool, soaked for 2h and lifted out, and the steel coil is sent to the single-stand rolling mill for cold rolling within 10min after being lifted out.

[0082] First cold rolling process: three passes are adopted, and the reduction rate of each pass is 10%, 10% and 10% respectively. The rolling speed of each pass is set at 100m / min, the unit front tension of the strip is 0.16 KN / mm, and the unit back tension is 0.25 KN / mm.

[0083] Spheroidizing annealing process: the steel coil is heated from room temperature to 200℃ freely; the heating process adopts holding platform annealing, the heating speed is 100℃ / h to 400℃ and the temperature is kept for 3h; then the heating speed is 80℃ / h to 740℃, and the temperature is kept for 20h according to the weight of the steel coil; after the temperature keeping is finished, the power is stopped and the temperature is slowly cooled to 550℃; the air is replaced to cool to 450℃; the water is replaced to cool to 100℃ and the coil is discharged.

[0084] Second cold rolling process: the total reduction rate is set at 30%, and three passes are rolled, and the reduction rate of each pass is 10%, 10%, and 10% respectively. The rolling speed of each pass is set at 240 m / min, the unit front tension of the strip is 0.12 KN / mm, and the unit back tension is 0.20 KN / mm.

[0085] Recrystallization annealing process: the steel coil is heated from room temperature to 200℃ freely; the heating process adopts holding platform annealing, heated to 400℃ at a heating speed of 100℃ / h and kept for 3h; then heated to 700℃ at a heating speed of 80℃ / h, and kept for 20h according to the weight of the steel coil; after the keeping ends, power is stopped and slowly cooled to 550℃; air cooling to 450℃; water cooling to 100℃ and discharged.

[0086] After the steel coil is annealed, flattening and rewinding are carried out to improve the flatness, and the flattening elongation is set at 1.5%.

[0087] The above method can produce high-quality SK120 wide cold-rolled plates with a thickness of 1.2mm.

[0088] Example 3

[0089] The embodiment of the present application provides a production method of SK120 cold-rolled steel plates, which comprises the following steps:

[0090] The hot-rolled pickled steel coil with normal quality is used as raw material, and the mass percentage of the chemical components of the hot-rolled steel coil is as follows: C: 1.18%, Si: 0.28%, Mn: 0.39%, P: 0.009, S: 0.002; the rest is Fe and inevitable impurities. The specification of the hot-rolled steel coil is 3.0mm*1250mm, and the coil weight is 22 tons.

[0091] Water bath process: the SK120 hot-rolled pickled steel coil is lifted into a 60℃ water bath pool, soaked for 2h and lifted out, and the steel coil is sent to the single-stand rolling mill for cold rolling within 10min after being lifted out.

[0092] First cold rolling process: three passes are adopted, and the reduction rate of each pass is 10%, 10%, and 10% respectively. The rolling speed of each pass is set at 80m / min, the unit front tension of the strip is 0.20 KN / mm, and the unit back tension is 0.30 KN / mm.

[0093] Spheroidizing annealing process: the steel coil is heated from room temperature to 200℃ freely; the heating process adopts holding platform annealing, heated to 400℃ at a heating speed of 100℃ / h and kept for 3h; then heated to 740℃ at a heating speed of 80℃ / h, and kept for 18h according to the weight of the steel coil; after the keeping ends, power is stopped and slowly cooled to 550℃; air cooling to 450℃; water cooling to 100℃ and discharged.

[0094] Second cold rolling process: total reduction ratio set to 20%, according to single pass rolling. Each pass rolling speed set to 200 m / min, unit front tension of strip 0.12 KN / mm, unit back tension 0.24 KN / mm.

[0095] Recrystallization annealing process: steel coil from room temperature free heating to 200 °C; heating process using holding platform annealing, heating to 400 °C at a heating rate of 100 °C / h and holding for 3 h; then heating to 700 °C at a rate of 80 °C / h, holding for 18 h according to the weight of the coil; after holding, power off and slowly cool to 550 °C; air cooling to 450 °C; water cooling to 100 °C and discharge.

[0096] After annealing of the steel coil, flattening and re-coiling to improve the shape of the plate, flattening elongation set to 3.0%.

[0097] The above method can produce high-quality SK120 wide cold-rolled coil with a thickness of 1.8 mm.

[0098] Comparative Example 1 The difference between this comparative example and Example 1 is that there is no water bath process.

[0099] Comparative Example 2

[0100] The difference between this comparative example and Example 1 is that the first cold rolling process is different. The first cold rolling speed is set to 60 m / min, the unit front tension of the first cold rolling process is 0.08 KN / mm, and the unit back tension is 0.12 KN / mm; the first cold rolling process uses three passes, and the reduction ratio of each pass is greater than 15%.

[0101] Comparative Example 3 The difference between this comparative example and Example 1 is that the spheroidizing annealing process is different. The spheroidizing annealing includes using holding platform annealing for the first heating, then heating to 400 °C at a heating rate of 150 °C / h and holding for 3 h; then heating to 760 °C at a rate of 120 °C / h and performing a second holding, the second holding time is 14 h; after the second holding, first cooling to 100 °C.

[0102] Comparative Example 4

[0103] The difference between this comparative example and Example 1 is that the second cold rolling process is different. The second cold rolling speed is 350 m / min, the unit front tension of the second cold rolling process is 0.05 KN / mm, and the unit back tension is 0.10 KN / mm.

[0104] Comparative Example 5

[0105] This comparative example differs from Example 1 in the recrystallization annealing process. The coil was heated from room temperature to 200°C. During the heating process, it was annealed on a holding platform at a rate of 120°C / h to 400°C and held for 3 hours. It was then heated at a rate of 100°C / h to 700°C and held for 16 hours. After the holding period, the coil was cooled to 100°C and then removed from the furnace.

[0106] Comparative Example 6 The difference between this comparative example and Example 1 is that the steel coil is flattened and re-coiled after recrystallization annealing, and the flattening elongation is set to 0.8%.

[0107] Test section

[0108] The mechanical properties of the SK120 cold-rolled steel sheets of the examples and comparative examples were tested according to GB / T 228.1-2010 "Metallic Materials - Tensile Tests - Part 1: Room Temperature Test Methods." The test results are shown in the following table.

[0109] The yield rate is calculated as follows: the weight of each batch of qualified cold-rolled finished product coils ÷ the weight of the corresponding batch of cold-rolled raw material coils.

[0110] The test results are shown in the following table.

[0111] Table 1 Test results of SK120 cold-rolled steel sheets of the embodiment and comparative example

[0112]

[0113] The above measured performance parameters are averaged.

[0114] The test results in Table 1 show that the embodiment adopts a water bath process, a first cold rolling, a spheroidizing annealing, and a second cold rolling. The processes are matched with each other to produce a high-quality SK120 cold-rolled steel plate with a good plate shape and a low occurrence of edge cracks. As a result, the number of plates with trimmed edges is small, and thus the SK120 cold-rolled steel plate achieves a good yield.

[0115] Figure 1 The figure shows the appearance of the rolled cracked edge of comparative example 1 of the present application. Figure 2 The figure shows the appearance of the rolled brittle fracture of comparative example 1 of the present application. Figure 3 The figure shows the appearance of the plate shape problem of comparative example 1 of the present application. It shows that SK120 cold-rolled steel sheet is prone to rolling cracking, brittle fracture and plate shape problems. The occurrence of these problems reduces the yield rate of SK120 cold-rolled steel sheet and is not conducive to high-quality production of the production line.

[0116] The above are only specific embodiments of the present application, but the scope of protection of the present application is not limited thereto. Any familiarity with the present technology or replacement should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A method for producing SK120 cold-rolled steel sheet, characterized in that: include: Hot rolled pickled steel coil, water bath process, first cold rolling, spheroidizing annealing, second cold rolling, recrystallization annealing, and skin pass; The steel coil comprises the following chemical composition by mass percentage: C: 1.15% to 1.25%, Si: 0.15% to 0.35%, Mn: 0.35% to 0.50%, P≤0.018%, S≤0.010%; the remainder is Fe and unavoidable impurities; The water bath process includes: placing the hot-rolled pickled steel coil into a water bath at 50 to 60 degrees Celsius, soaking it for 2 to 4 hours, and then lifting it out. The steel coil is then sent to a single-stand rolling mill for cold rolling within 10 minutes after being lifted out. The first cold rolling comprises: three rolling passes, with reduction rates of 8% to 10%, 8% to 10%, and 8% to 10% for each pass respectively; the rolling speed for each pass is set at 80 to 150 m / min, the unit front tension of the strip is 0.10 to 0.20 kN / mm, and the unit rear tension is 0.15 to 0.30 kN / mm; Spheroidizing annealing includes: the steel coil is heated from room temperature to 200℃ freely; the heating process adopts holding platform annealing, heating to 400℃ at a heating rate of 60℃ / h to 100℃ / h and performing the first holding period of 1 to 3 hours; then heating to 740℃ at a heating rate of 40℃ / h to 80℃ / h and performing the second holding period of 16 to 20 hours; after the second holding period, the steel coil is cooled to 80℃ to 100℃ and then removed from the furnace; The second cold rolling includes: a total reduction rate of 10% to 50%; when the total reduction rate is ≥20%, rolling is performed in three passes; the rolling speed of each pass is set at 200 to 300 m / min, the unit front tension of the strip is 0.08 to 0.15 kN / mm, and the unit rear tension is 0.12 to 0.25 kN / mm; The recrystallization annealing process includes: the steel coil is heated from room temperature to 200°C; the temperature is raised by annealing on a holding platform, heating to 400°C at a heating rate of 60°C / h to 100°C / h and holding for 1 to 3 hours; then heating to 700°C at a rate of 40°C / h to 80°C / h and holding for 16 to 20 hours; after the holding period, the steel coil is cooled to 80°C to 100°C before being taken out of the furnace; After recrystallization annealing, the steel coil is flattened and re-coiled, and the flattening elongation is set to 1.0% to 3.0%.

2. The production method according to claim 1, characterized in that The first cooling and the second cooling respectively include: slowly cooling to 550° C.; then switching to air cooling to 450° C.; and then switching to water cooling.

3. The production method according to claim 1, characterized in that The reduction ratio of each pass in the first cold rolling is 10%, 10%, and 10% respectively.

4. The production method according to claim 1, characterized in that The thickness of SK120 hot rolled pickled steel coil is 1.8 to 3.0 mm.

5. The production method according to claim 1, characterized in that The thickness of SK120 cold-rolled steel plate is 0.6~1.8mm.

6. The production method according to claim 1, characterized in that The width of SK120 cold-rolled steel plate is 900~1500mm.

7. A SK120 cold-rolled steel plate, characterized in that: It is prepared by the production method according to any one of claims 1 to 6.

Images