60si2mn spring steel cold rolled steel strip and method of making same

Abstract

This application discloses a cold-rolled steel strip of 60Si2Mn spring steel and its preparation method. The method includes: providing a hot-rolled pickled steel coil; the hot-rolled pickled steel coil contains the following chemical composition by weight percentage: C: 0.56wt.%~0.64wt.%, Si: 1.50wt.%~2.00wt.%, Mn: 0.70wt.%~1.00wt.%, Al: ≤0.020wt.%, P: ≤0.018wt.%, S: ≤0.004wt.%, Cr: ≤0.35wt.%, Cu: ≤0.25wt.%, Ni: ≤0.35wt.%; the remainder being Fe and unavoidable impurities. The hot-rolled pickled steel coils are subjected to multi-platform spheroidizing annealing to obtain annealed steel coils; the annealed steel coils are subjected to light-reduction cold rolling to obtain the first cold-rolled strip; the first cold-rolled strip is subjected to rapid spheroidizing annealing to obtain annealed cold-rolled strip; the annealed cold-rolled strip is subjected to high-reduction cold rolling to obtain the second cold-rolled strip; the second cold-rolled strip is subjected to recrystallization annealing to obtain the annealed third cold-rolled strip; the annealed third cold-rolled strip is subjected to low-reduction cold rolling to obtain 60Si2Mn spring steel cold-rolled strip.

Description

Technical Field

[0001] This application belongs to the field of cold-rolled spring steel manufacturing technology, and particularly relates to a cold-rolled steel strip of 60Si2Mn spring steel and its preparation method. Background Technology

[0002] 60Si2Mn is a classic high-carbon silicon-manganese spring steel. Due to its high strength, good resilience, and fatigue resistance, it is widely used in key components across various industries, including automotive and machinery. It is produced as a strip material, primarily used to manufacture disc springs, coil springs, and diaphragm springs for automobiles and machinery. Currently, this material is produced by cold rolling hot-rolled narrow strips with a width of less than 400mm. With technological advancements, cold rolling wide strips with a width of 900mm or more offers higher production efficiency and better product performance uniformity. Currently, there is a competitive effort in China to develop wide cold-rolled 60Si2Mn spring steel coils.

[0003] However, due to the relatively high C, Si, and Mn content in 60Si2Mn spring steel, the material itself is quite brittle, especially for strips thicker than 5mm. The grain size and carbide size are significantly larger than in thinner strips, making the brittleness more pronounced. Furthermore, the Ac1 to Ac3 phase transformation range in 60Si2Mn steel is very small, approximately 34℃. During bell-type annealing, temperature fluctuations can easily lead to full austenitization within the steel, resulting in the reformation of pearlite after annealing. Moreover, the pearlite clusters are larger and more brittle than before annealing. For these reasons, producing wide cold-rolled coils of 60Si2Mn spring steel, a high-end material, is technically very challenging. Strip breakage is highly likely during cold rolling, especially in wide hot-rolled coils thicker than 5mm, where the risk of breakage is 80%, making stable production virtually impossible. Summary of the Invention

[0004] This application provides a method for preparing 60Si2Mn spring steel cold-rolled strip, which solves the problem that the existing process of producing 60Si2Mn spring steel cold-rolled wide strip breaks during cold rolling, making it impossible to produce smoothly.

[0005] In a first aspect, this application provides a method for preparing cold-rolled steel strip of 60Si2Mn spring steel, comprising: Hot-rolled pickled steel coils are provided; by weight percentage, the hot-rolled pickled steel coils contain the following chemical composition: C: 0.56wt.%~0.64wt.%, Si: 1.50wt.%~2.00wt.%, Mn: 0.70wt.%~1.00wt.%, Al: ≤0.020wt.%, P: ≤0.018wt.%, S: ≤0.004wt.%, Cr: ≤0.35wt.%, Cu: ≤0.25wt.%, Ni: ≤0.35wt.%; the remainder is Fe and unavoidable impurities; Hot-rolled pickled steel coils are subjected to multi-platform spheroidizing annealing treatment to obtain annealed steel coils. The annealed steel coil is subjected to light-pressure cold rolling to obtain the first cold-rolled strip. The first cold-rolled strip was subjected to rapid spheroidizing annealing to obtain annealed cold-rolled strip. The annealed cold-rolled strip is subjected to a large reduction cold rolling process to obtain a second cold-rolled strip; The second cold-rolled strip is subjected to recrystallization annealing to obtain the annealed third cold-rolled strip. The annealed third cold-rolled strip was subjected to low-reduction cold rolling to obtain 60Si2Mn spring steel cold-rolled strip.

[0006] According to an embodiment of the first aspect of this application, the width of the hot-rolled pickled steel coil is 900mm to 1500mm, and the thickness of the hot-rolled pickled steel coil is 1.5mm to 6.5mm.

[0007] According to an embodiment of the first aspect of this application, a hot-rolled pickled steel coil is provided, comprising: The hot-rolled coils of 60Si2Mn spring steel were pickled at a rate of 10 m / min to 30 m / min.

[0008] According to an embodiment of the first aspect of this application, 60Si2Mn spring steel hot-rolled coils are pickled using hydrochloric acid aqueous solution, wherein the concentration of HCl in the hydrochloric acid aqueous solution is 150g / L to 240g / L.

[0009] According to an embodiment of the first aspect of this application, a multi-platform spheroidizing annealing treatment is performed on a hot-rolled pickled steel coil, comprising: performing a multi-platform spheroidizing annealing treatment on the hot-rolled pickled steel coil using a four-insulation platform.

[0010] According to an embodiment of the first aspect of this application, hot-rolled pickled steel coils undergo multi-platform spheroidizing annealing treatment using a four-insulation platform, including: The hot-rolled pickled steel coil is heated from room temperature to 200℃~220℃; The hot-rolled pickled steel coil is then heated from 200℃~220℃ to 400℃~420℃ at a heating rate of 50℃ / h~55℃ / h, and held at that temperature for 2 hours~3 hours. The hot-rolled pickled steel coil is then heated from 400℃~420℃ to 710℃~730℃ at a heating rate of 50℃ / h~60℃ / h, and held at that temperature for 2 hours~3 hours. The hot-rolled pickled steel coil is then heated from 710℃~730℃ at a heating rate of 20℃ / h~25℃ / h to Ac1+10℃ and held at that temperature for 2 hours~3 hours. The hot-rolled pickled steel coil is then cooled from Ac1+10℃ to Ac1-10℃ at a cooling rate of 20℃ / h~25℃ / h, and held at that temperature for 18 hours~20 hours. After the heat preservation is completed, the hot-rolled pickled steel coil is cooled from Ac1-10℃ to 620℃, then air-cooled to 400℃, and then water-cooled to 100℃ before being taken out of the furnace.

[0011] According to the embodiments of the first aspect of this application, the light reduction cold rolling process of the annealed hot-rolled pickled steel coil includes two-pass rolling using a single-stand mill, with a total reduction rate of 10% to 20%.

[0012] According to the embodiment of the first aspect of this application, in the step of performing light-reduction cold rolling on the annealed hot-rolled pickled steel coil, the reduction rate of each rolling pass is 5% to 10%, and the rolling speed of each pass is 100m / min to 150m / min.

[0013] According to an embodiment of the first aspect of this application, a rapid spheroidizing annealing treatment is performed on a first cold-rolled strip, including: The first cold-rolled strip steel was subjected to rapid spheroidizing annealing treatment using a four-insulation platform.

[0014] According to an embodiment of the first aspect of this application, a rapid spheroidizing annealing treatment is performed on a first cold-rolled strip using a four-insulation platform, including: The first cold-rolled strip steel is first heated from room temperature to 200℃~220℃; The first cold-rolled strip is then heated from 200℃~220℃ to 400℃~420℃ at a heating rate of 50℃ / h~55℃ / h, and held at that temperature for 2 hours~3 hours. The first cold-rolled strip is then heated from 400℃~420℃ to 600℃~620℃ at a heating rate of 50℃ / h~55℃ / h, and held at that temperature for 2 hours~3 hours. The first cold-rolled strip is then heated from 600℃~620℃ to 680℃~695℃ at a heating rate of 50℃ / h~55℃ / h, and held at that temperature for 2 hours~3 hours. Then, raise the temperature to 700℃~720℃ at a heating rate of 20℃ / h~25℃ and hold it for 14 hours~16 hours; Then, after the heat preservation is completed, the first cold-rolled strip is slowly cooled to 620°C, then air-cooled to 400°C, and then water-cooled to 100°C before being taken out of the furnace.

[0015] According to an embodiment of the first aspect of this application, a large-reduction cold rolling process is performed on annealed cold-rolled strip steel, including: A single-stand rolling mill is used for three-pass rolling, with a total reduction rate of 40% to 45%.

[0016] According to the embodiment of the first aspect of this application, in the step of performing large reduction cold rolling on the annealed cold-rolled strip, the reduction rate of each rolling pass is 10% to 15%, and the rolling speed of each pass is 300m / min to 500m / min.

[0017] According to an embodiment of the first aspect of this application, recrystallization annealing treatment is performed on a second cold-rolled strip, including: The second cold-rolled strip was subjected to recrystallization annealing treatment using two insulation platforms.

[0018] According to an embodiment of the first aspect of this application, a recrystallization annealing treatment of a second cold-rolled strip is performed using two heat-insulating platforms, including: The second cold-rolled strip is first heated from room temperature to 200℃~220℃; The second cold-rolled strip is then heated from 200℃~220℃ to 400℃~420℃ at a heating rate of 50℃ / h~55℃ / h, and held at that temperature for 2 hours~3 hours. The second cold-rolled strip is then heated from 400℃~420℃ to 600℃~620℃ at a heating rate of 50℃ / h~55℃ / h, and held at that temperature for 2 hours~3 hours. The second cold-rolled strip is then heated from 600℃~620℃ to 700℃~720℃ at a heating rate of 50℃ / h~55℃ / h, and held at that temperature for 14 hours~16 hours. Then, after the heat preservation is completed, the second cold-rolled strip is slowly cooled to 620°C, then air-cooled to 400°C, and then water-cooled to 100°C before being taken out of the furnace.

[0019] According to an embodiment of the first aspect of this application, the annealed third cold-rolled strip is subjected to low-reduction cold rolling, which includes: using a cold rolling leveling machine to perform low-reduction cold rolling on the annealed third cold-rolled strip.

[0020] According to an embodiment of the first aspect of this application, a cold rolling mill is used to perform low-reduction cold rolling on the annealed third cold-rolled strip, including: rolling on the cold rolling mill using an elongation mode, setting the leveling tension using a high-strength steel tension gauge, and controlling the elongation to 1.0 to 2.0%.

[0021] According to an embodiment of the first aspect of this application, the method for preparing 60Si2Mn spring steel cold-rolled strip further includes: finishing the 60Si2Mn spring steel cold-rolled strip to obtain the finished 60Si2Mn spring steel cold-rolled strip.

[0022] Secondly, this application provides a 60Si2Mn spring steel cold-rolled strip, prepared according to the preparation method of the 60Si2Mn spring steel cold-rolled strip provided in the first aspect embodiment; the 60Si2Mn spring steel cold-rolled strip comprises the following chemical composition by mass percentage: C: 0.56wt.%~0.64wt.%, Si: 1.50wt.%~2.00wt.%, Mn: 0.70wt.%~1.00wt.%, Al: ≤0.020wt.%, P: ≤0.018wt.%, S: ≤0.004wt.%, Cr: ≤0.35wt.%, Cu: ≤0.25wt.%, Ni: ≤0.35wt.%; the remainder being Fe and unavoidable impurities.

[0023] According to the embodiment of the first aspect of this application, the metallographic structure of the 60Si2Mn spring steel cold-rolled strip is a spheroidized pearlite structure with an average grain size of 5μm to 9μm.

[0024] The method for preparing 60Si2Mn spring steel cold-rolled strip according to the embodiments of this application, through six parts—multi-platform spheroidizing annealing process, single-stand light-pressure cold rolling process, first recrystallization annealing process, second cold rolling process, and second recrystallization annealing process—can solve the problem of strip breakage that is very likely to occur in the general cold rolling process of 60Si2Mn spring steel cold-rolled strip with a raw material thickness of 5mm or more and a thickness of 900mm or more. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic flowchart of the preparation method of 60Si2Mn spring steel cold-rolled strip provided in the embodiments of this application. Detailed Implementation

[0027] The features and exemplary embodiments of various aspects of this application will be described in detail below. To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain this application and not to limit it. For those skilled in the art, this application can be implemented without some of these specific details. The following description of the embodiments is merely to provide a better understanding of this application by illustrating examples.

[0028] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes said element.

[0029] To address the problems of the prior art, this application provides a cold-rolled 60Si2Mn spring steel strip and its preparation method. The preparation method of the 60Si2Mn spring steel cold-rolled strip provided in this application will be described below.

[0030] Figure 1 A schematic flowchart of the preparation method of 60Si2Mn spring steel cold-rolled strip provided in the embodiments of this application is shown.

[0031] like Figure 1 As shown, this application provides a method for preparing cold-rolled steel strip of 60Si2Mn spring steel, comprising: Hot-rolled pickled steel coils are provided; by weight percentage, the hot-rolled pickled steel coils contain the following chemical composition: C: 0.56wt.%~0.64wt.%, Si: 1.50wt.%~2.00wt.%, Mn: 0.70wt.%~1.00wt.%, Al: ≤0.020wt.%, P: ≤0.018wt.%, S: ≤0.004wt.%, Cr: ≤0.35wt.%, Cu: ≤0.25wt.%, Ni: ≤0.35wt.%; the remainder is Fe and unavoidable impurities; Hot-rolled pickled steel coils are subjected to multi-platform spheroidizing annealing treatment to obtain annealed steel coils. The annealed steel coil is subjected to light-pressure cold rolling to obtain the first cold-rolled strip. The first cold-rolled strip was subjected to rapid spheroidizing annealing to obtain annealed cold-rolled strip. The annealed cold-rolled strip is subjected to a large reduction cold rolling process to obtain a second cold-rolled strip; The second cold-rolled strip is subjected to recrystallization annealing to obtain the annealed third cold-rolled strip. The annealed third cold-rolled strip was subjected to low-reduction cold rolling to obtain 60Si2Mn spring steel cold-rolled strip.

[0032] As pointed out in the background section, when using general cold rolling processes to produce 60Si2Mn spring steel cold-rolled strip with a width of 900mm or more, cold rolling strip breakage is very likely to occur, resulting in a very low yield of less than 60%. In particular, when the thickness of the raw steel coil is 5mm or more, it is difficult to carry out normal production smoothly.

[0033] The method for preparing 60Si2Mn spring steel cold-rolled strip provided in this application adopts the following steps: hot-rolled pickled steel coil—multi-platform spheroidizing annealing—single-stand light-reduction cold rolling—rapid spheroidizing annealing—single-stand high-reduction cold rolling—recrystallization annealing—single-stand low-reduction cold rolling. This method solves the problem of unstable production caused by strip breakage during the cold rolling process of 60Si2Mn spring steel cold-rolled wide strip produced by existing processes.

[0034] The method for preparing 60Si2Mn spring steel cold-rolled strip provided in this application is applicable to the cold rolling process of hot-rolled wide strip steel with a width of 900mm to 1500mm and a thickness of 1.5mm to 6.5mm. It effectively reduces the strip breakage rate and makes the yield of 60Si2Mn spring steel cold-rolled strip reach more than 95%.

[0035] In some embodiments, a hot-rolled pickled steel coil is provided, comprising: pickling a 60Si2Mn spring steel hot-rolled steel coil at a pickling rate of 10m / min to 30m / min to obtain a hot-rolled pickled steel coil.

[0036] The method for preparing 60Si2Mn spring steel cold-rolled strip provided in this application uses high-quality 60Si2Mn spring steel hot-rolled coil as raw material, and uses hydrochloric acid aqueous solution and the above-mentioned pickling process parameters to pickle the 60Si2Mn spring steel hot-rolled coil. While removing the iron oxide scale on the surface of the steel, it prevents the strip from breaking due to rapid deformation caused by excessively fast hydrochloric acid pickling rate.

[0037] In some embodiments, 60Si2Mn spring steel hot-rolled coils are pickled using hydrochloric acid aqueous solution, wherein the concentration of HCl in the hydrochloric acid aqueous solution is 150g / L to 240g / L.

[0038] The method for preparing 60Si2Mn spring steel cold-rolled strip provided in this application uses hydrochloric acid aqueous solution of the above concentration for pickling, which can effectively remove oxides from the surface of the steel coil.

[0039] In some embodiments, the hot-rolled pickled steel coil is subjected to multi-platform spheroidizing annealing treatment, which includes: performing multi-platform spheroidizing annealing treatment on the hot-rolled pickled steel coil using a four-insulation platform.

[0040] The method for preparing 60Si2Mn spring steel cold-rolled strip provided in this application adopts a four-insulation platform annealing process during the heating process of the steel coil, which better ensures the uniformity of the steel coil temperature and prevents the steel coil from austenitizing under large temperature fluctuations.

[0041] It should be noted that when a temperature is maintained at a certain temperature range for a period of time, that temperature range is called the holding plateau. Spheroidization in spheroidizing annealing refers to the transformation of lamellar pearlite structure in the hot-rolled state into spheroidized pearlite structure, that is, from lamellar to granular.

[0042] In some embodiments, hot-rolled pickled steel coils undergo multi-platform spheroidizing annealing treatment using a four-insulation platform, including: The hot-rolled pickled steel coil is heated from room temperature to 200℃~220℃; The hot-rolled pickled steel coil is then heated from 200℃~220℃ to 400℃~420℃ at a heating rate of 50℃ / h~55℃ / h, and held at that temperature for 2 hours~3 hours. The hot-rolled pickled steel coil is then heated from 400℃~420℃ to 710℃~730℃ at a heating rate of 50℃ / h~60℃ / h, and held at that temperature for 2 hours~3 hours. The hot-rolled pickled steel coil is then heated from 710℃~730℃ at a heating rate of 20℃ / h~25℃ / h to Ac1+10℃ and held at that temperature for 2 hours~3 hours. The hot-rolled pickled steel coil is then cooled from Ac1+10℃ to Ac1-10℃ at a cooling rate of 20℃ / h to 25℃ / h, and held at that temperature for 18 to 20 hours. After the heat preservation is completed, the hot-rolled pickled steel coil is cooled from Ac1-10℃ to 620℃, then air-cooled to 400℃, and then water-cooled to 100℃ before being taken out of the furnace.

[0043] The method for preparing 60Si2Mn spring steel cold-rolled strip provided in this application involves heating a hot-rolled pickled steel coil to 400℃~420℃ at a heating rate of 50℃ / h~55℃ / h and holding it at that temperature to remove grease, dirt, etc. from the surface of the strip and achieve uniform temperature of the steel coil. The hot-rolled pickled steel coil is then heated from 400℃~420℃ to 710℃~730℃ at a heating rate of 50℃ / h~60℃ / h and held at that temperature to obtain a steel coil with uniform temperature at a higher temperature. Finally, the hot-rolled pickled steel coil is heated from 710℃~730℃ to Ac1+10℃ at a heating rate of 20℃ / h~25℃ / h and held at that temperature to promote the partial dissolution of cementite into the ferrite matrix. The hot-rolled pickled steel coil is then cooled from Ac1+10℃ to Ac1-10℃ at a cooling rate of 20℃ / h to 25℃ / h and held at that temperature to spheroidize the remaining carbides and to precipitate the already dissolved carbides in spherical form. Therefore, in the preparation method of this application, the higher the degree of spheroidization of the carbides, the better, and the cementite is distributed inside the ferrite and at the grain boundaries.

[0044] It should be noted that after the heat preservation is completed, the power is first turned off to the heating hood of the bell-type annealing furnace, and the hot-rolled pickled steel coil is cooled naturally from Ac1-10℃ to 620℃. Then, the air-cooled hood is replaced for air cooling, and then the water-cooled hood is replaced for water cooling.

[0045] In some embodiments, the light reduction cold rolling process of the annealed hot-rolled pickled steel coil includes two-pass rolling using a single-stand mill, with a total reduction rate of 10% to 20%.

[0046] In some embodiments, in the step of performing light-reduction cold rolling on the annealed hot-rolled pickled steel coil, the reduction rate for each rolling pass is 5% to 10%, and the rolling speed for each pass is 100 m / min to 150 m / min.

[0047] The method for preparing 60Si2Mn spring steel cold-rolled strip provided in this application uses a small reduction rate for light-reduction cold rolling, which can prevent the steel strip from undergoing instantaneous brittle fracture due to the rapid increase in the work hardening index under rapid deformation conditions caused by the poor plasticity and toughness of 60Si2Mn spring steel. Slow rolling at the above-mentioned rolling rate can also allow the mechanical energy in the rolling process to be fully converted into the thermal energy of the steel strip, increase the temperature of the steel strip, and thus improve the plasticity and toughness of the steel strip.

[0048] In some embodiments, the rapid spheroidizing annealing treatment of the first cold-rolled strip includes: using a four-insulation platform to perform rapid spheroidizing annealing treatment on the first cold-rolled strip.

[0049] The method for preparing 60Si2Mn spring steel cold-rolled strip provided in this application involves rapid spheroidizing annealing of the first cold-rolled strip. The rapid spheroidizing annealing process is carried out using a four-insulation platform, which can better ensure the uniformity of the steel coil temperature, prevent the material from becoming fully austenitized due to fluctuations in the furnace temperature inside the bell-type annealing furnace, and form fine spheroidized pearlite structure inside the steel.

[0050] In some embodiments, a four-insulation platform is used to perform rapid spheroidizing annealing treatment on the first cold-rolled strip, including: The first cold-rolled strip steel is first heated from room temperature to 200℃~220℃; The first cold-rolled strip is then heated from 200℃~220℃ to 400℃~420℃ at a heating rate of 50℃ / h~55℃ / h, and held at that temperature for 2 hours~3 hours. The first cold-rolled strip is then heated from 400℃~420℃ to 600℃~620℃ at a heating rate of 50℃ / h~55℃ / h, and held at that temperature for 2 hours~3 hours. The first cold-rolled strip is then heated from 600℃~620℃ to 680℃~695℃ at a heating rate of 50℃ / h~55℃ / h, and held at that temperature for 2 hours~3 hours. Then, raise the temperature to 700℃~720℃ at a heating rate of 20℃ / h~25℃ and hold it for 14 hours~16 hours; Then, after the heat preservation is completed, the first cold-rolled strip is slowly cooled to 620°C, then air-cooled to 400°C, and then water-cooled to 100°C before being taken out of the furnace.

[0051] The method for preparing 60Si2Mn spring steel cold-rolled strip provided in this application involves rapid spheroidizing annealing of the first cold-rolled strip. The rapid spheroidizing annealing process utilizes a four-insulation platform, which better ensures the temperature uniformity of the steel coil and prevents full austenitization of the material due to temperature fluctuations in the bell-type annealing furnace. Both the air-cooled hood and water-cooled hood are components of the annealing furnace, allowing for rapid cooling in the low-temperature section. Switching to water cooling provides faster cooling and saves time.

[0052] In some embodiments, the annealed cold-rolled strip is subjected to a large reduction cold rolling process, including: three-pass rolling using a single-stand mill, with a total reduction rate of 40% to 45%.

[0053] The method for preparing 60Si2Mn spring steel cold-rolled strip provided in this application adopts a four-insulation platform.

[0054] In some embodiments, in the step of performing large-reduction cold rolling on the annealed cold-rolled strip, the reduction rate of each rolling pass is 10% to 15%, and the rolling speed of each pass is 300 m / min to 500 m / min.

[0055] The method for preparing 60Si2Mn spring steel cold-rolled strip provided in this application involves the above-mentioned high-reduction cold rolling process, that is, using a single-stand rolling mill to roll the returned cold-rolled strip in three passes, which can roll the cold-rolled steel strip to the required thickness.

[0056] In some embodiments, the second cold-rolled strip undergoes recrystallization annealing treatment, including: The second cold-rolled strip was subjected to recrystallization annealing treatment using a three-insulation platform.

[0057] In some embodiments, a recrystallization annealing treatment is performed on the second cold-rolled strip using a three-insulation platform, including: The second cold-rolled strip is first heated from room temperature to 200℃~220℃; The second cold-rolled strip is then heated from 200℃~220℃ to 400℃~420℃ at a heating rate of 50℃ / h~55℃ / h, and held at that temperature for 2 hours~3 hours. The second cold-rolled strip is then heated from 400℃~420℃ to 600℃~620℃ at a heating rate of 50℃ / h~55℃ / h, and held at that temperature for 2 hours~3 hours. The second cold-rolled strip is then heated from 600℃~620℃ to 700℃~720℃ at a heating rate of 50℃ / h~55℃ / h, and held at that temperature for 14 hours~16 hours. Then, after the heat preservation is completed, the second cold-rolled strip is slowly cooled to 620°C, then air-cooled to 400°C, and then water-cooled to 100°C before being taken out of the furnace.

[0058] The method for preparing 60Si2Mn spring steel cold-rolled strip provided in this application further performs rapid spheroidizing annealing treatment on the second cold-rolled strip through a three-insulation platform. The rapid spheroidizing annealing treatment using a three-insulation platform during the heating process can better ensure the uniformity of the steel coil temperature and prevent the material from becoming fully austenitic due to fluctuations in the furnace temperature of the bell-type annealing furnace.

[0059] In some embodiments, the annealed third cold-rolled strip is subjected to low-reduction cold rolling, which includes: using a cold rolling leveling machine to perform low-reduction cold rolling on the annealed third cold-rolled strip.

[0060] In some embodiments, a cold rolling mill is used to perform low-reduction cold rolling on the annealed third cold-rolled strip, including: rolling on the cold rolling mill using an elongation mode, setting the leveling tension using a high-strength steel tension gauge, and controlling the elongation to 1.0 to 2.0%.

[0061] The method for preparing 60Si2Mn spring steel cold-rolled strip provided in this application uses low-reduction cold rolling to achieve the final required thickness of the annealed third cold-rolled strip.

[0062] In some embodiments, the method for preparing 60Si2Mn spring steel cold-rolled strip further includes: finishing the 60Si2Mn spring steel cold-rolled strip to obtain the finished 60Si2Mn spring steel cold-rolled strip.

[0063] The method for preparing 60Si2Mn spring steel cold-rolled strip provided in this application involves finishing the 60Si2Mn spring steel cold-rolled strip to obtain a finished 60Si2Mn spring steel cold-rolled strip with good internal structure and good thickness dimensional tolerance.

[0064] The method for preparing 60Si2Mn spring steel cold-rolled strip provided in this application effectively prevents the formation of pearlite or other low-spheroidization microstructures in the strip caused by uneven heating of the strip or excessively high annealing temperature in the bell furnace. The multi-platform spheroidization annealing treatment can obtain a uniform and fine cementite structure with a spheroidization rate of over 90%. The multi-pass rolling process first employs a low reduction rate for cold-rolled steel strip production to prevent strip breakage. The second cold rolling process, namely high reduction cold rolling, is carried out after rapid spheroidizing annealing. Since the first cold-rolled strip already has good plasticity and toughness after rapid spheroidizing annealing, the high reduction rate cold rolling process fully flattens the microstructure of the annealed cold-rolled strip. Then, through the preceding rapid spheroidizing annealing and subsequent recrystallization annealing, the coarsening of the strip grains is controlled and refined, resulting in an extremely fine ferrite structure.

[0065] Secondly, this application provides a 60Si2Mn spring steel cold-rolled strip, which, by mass percentage, comprises the following chemical composition: C: 0.56wt.%~0.64wt.%, Si: 1.50wt.%~2.00wt.%, Mn: 0.70wt.%~1.00wt.%, Al: ≤0.020wt.%, P: ≤0.018wt.%, S: ≤0.004wt.%, Cr: ≤0.35wt.%, Cu: ≤0.25wt.%, Ni: ≤0.35wt.%; the remainder being Fe and unavoidable impurities.

[0066] In some embodiments, the metallographic structure of 60Si2Mn spring steel cold-rolled strip is spheroidized pearlite, and the average grain size of the metallographic structure is 5μm to 9μm.

[0067] The technical solutions and effects of this application will be further explained below through specific embodiments and comparative examples.

[0068] Example 1 A method for preparing cold-rolled steel strip of 60Si2Mn spring steel, comprising: The product is a hot-rolled pickled steel coil, comprising: pickling 60Si2Mn spring steel hot-rolled steel coil with hydrochloric acid aqueous solution, wherein the concentration of HCl in the hydrochloric acid aqueous solution is 230 g / L, and the pickling rate is 15 m / min, to obtain a hot-rolled pickled steel coil with a thickness of 6.5 mm, a width of 1450 mm, and a microstructure of grade 6; the hot-rolled pickled steel coil contains the following chemical composition by mass percentage: C: 0.58 wt.%, Si: 1.82 wt.%, Mn: 0.83 wt.%, Al: 0.011 wt.%, P: 0.012 wt.%, S: 0.001 wt.%, Cr: 0.21 wt.%, Cu: 0.04 wt.%, Ni: 0.08 wt.%; the remainder being Fe and unavoidable impurities; A multi-platform spheroidizing annealing treatment was performed on hot-rolled pickled steel coils using a four-platform heating system, including: freely heating the hot-rolled pickled steel coils from room temperature to 200℃; then heating the hot-rolled pickled steel coils from 200℃ to 400℃ at a heating rate of 50℃ / h and holding at that temperature for 2 hours; then heating the hot-rolled pickled steel coils from 400℃ to 710℃ at a heating rate of 50℃ / h and holding at that temperature for 2 hours; and finally heating the hot-rolled pickled steel coils from 710℃ to 710℃ at a heating rate of 20℃ / h. The hot-rolled pickled steel coil is heated to Ac1+10℃ (758℃) and held for 2 hours. Then, the hot-rolled pickled steel coil is cooled from 758℃ to Ac1-10℃ (738℃) at a cooling rate of 20℃ / h and held for 18 hours. After the holding period, the hot-rolled pickled steel coil is slowly cooled from Ac1-10℃ to 620℃, then cooled to 400℃ by air cooling, and then cooled to 100℃ by water cooling before being removed from the furnace to obtain the annealed hot-rolled pickled steel coil. The annealed hot-rolled pickled steel coils are subjected to light-reduction cold rolling treatment, including two-pass rolling using a single-stand mill, with a total reduction of 15%. The reduction of the first pass is 7%, and the rolling speed of the first pass is 100 m / min. The reduction of the second pass is 8%, and the rolling speed of the second pass is 120 m / min, to obtain the first cold-rolled strip. A rapid spheroidizing annealing treatment of the first cold-rolled strip was performed using a four-insulation platform, including: first, the first cold-rolled strip was freely heated from room temperature to 200℃; then, the first cold-rolled strip was heated from 200℃ to 400℃ at a heating rate of 50℃ / h and held for 2 hours; then, the first cold-rolled strip was heated from 400℃ to 600℃ at a heating rate of 50℃ / h and held for 2 hours; then, the first cold-rolled strip was heated from 600℃ to 680℃ at a heating rate of 50℃ / h and held for 2 hours; finally, the temperature was raised to 700℃ at a heating rate of 20℃ / h and held for 16 hours; after the holding period, the first cold-rolled strip was slowly cooled to 620℃, then cooled to 400℃ by air cooling, and then cooled to 100℃ by water cooling before being removed from the furnace, thus obtaining the annealed cold-rolled strip. Annealed cold-rolled strip was subjected to large-reduction cold rolling using a single-stand rolling mill, with a total reduction of 40%, including: a 10% reduction in the first pass at a rolling speed of 300 m / min; a 15% reduction in the second pass at a rolling speed of 500 m / min; and a 15% reduction in the third pass at a rolling speed of 400 m / min, resulting in a second cold-rolled strip with a thickness of 3.3 mm. The second cold-rolled strip steel was subjected to recrystallization annealing treatment using a three-insulation platform, including: first, freely heating the second cold-rolled strip steel from room temperature to 200℃; then heating the second cold-rolled strip steel from 200℃ to 400℃ at a heating rate of 50℃ / h and holding it at that temperature for 2 hours; then heating the second cold-rolled strip steel from 400℃ to 600℃ at a heating rate of 50℃ / h and holding it at that temperature for 2 hours; then heating the second cold-rolled strip steel from 600℃ to 700℃ at a heating rate of 50℃ / h and holding it at that temperature for 16 hours; then, after the holding period, slowly cooling the second cold-rolled strip steel to 620℃, then air cooling to 400℃, and finally water cooling to 100℃ before being removed from the furnace, to obtain the annealed third cold-rolled strip steel; The annealed third cold-rolled strip is subjected to low-reduction cold rolling, including: rolling on a cold rolling leveler using the elongation mode, setting the leveling tension using a high-strength steel tension gauge, controlling the elongation at 2.0%, to obtain 60Si2Mn spring steel cold-rolled strip. The 60Si2Mn spring steel cold-rolled strip was finished to obtain the finished 60Si2Mn spring steel cold-rolled strip with a microstructure grain size of grade 9 and a thickness tolerance of ±0.03mm.

[0069] Example 2 A method for preparing cold-rolled steel strip of 60Si2Mn spring steel, comprising: The product is a hot-rolled pickled steel coil, comprising: pickling a 60Si2Mn spring steel hot-rolled steel coil with a hydrochloric acid aqueous solution at a concentration of 200 g / L and a pickling rate of 20 m / min, to obtain a hot-rolled pickled steel coil with a thickness of 5.5 mm, a width of 1350 mm, and a microstructure of grade 7; the hot-rolled pickled steel coil contains the following chemical composition by mass percentage: C: 0.61 wt.%, Si: 1.84 wt.%, Mn: 0.80 wt.%, Al: 0.008 wt.%, P: 0.010 wt.%, S: 0.002 wt.%, Cr: 0.24 wt.%, Cu: 0.04 wt.%, Ni: 0.06 wt.%; the remainder being Fe and unavoidable impurities; A multi-platform spheroidizing annealing treatment was performed on hot-rolled pickled steel coils using a four-platform heating system, including: freely heating the hot-rolled pickled steel coils from room temperature to 200℃; then heating the hot-rolled pickled steel coils from 200℃ to 400℃ at a heating rate of 50℃ / h and holding at that temperature for 2 hours; then heating the hot-rolled pickled steel coils from 400℃ to 710℃ at a heating rate of 50℃ / h and holding at that temperature for 2 hours; and finally heating the hot-rolled pickled steel coils from 710℃ to 710℃ at a heating rate of 20℃ / h. The hot-rolled pickled steel coil is heated to Ac1+10℃ (758℃) and held for 2 hours. Then, the hot-rolled pickled steel coil is cooled from 758℃ to Ac1-10℃ (738℃) at a cooling rate of 20℃ / h and held for 18 hours. After the holding period, the hot-rolled pickled steel coil is slowly cooled from Ac1-10℃ to 620℃, then cooled to 400℃ by air cooling, and then cooled to 100℃ by water cooling before being removed from the furnace to obtain the annealed hot-rolled pickled steel coil. The annealed hot-rolled pickled steel coils are subjected to light-reduction cold rolling treatment, including two-pass rolling using a single-stand mill, with a total reduction of 20%. The reduction of the first pass is 8%, and the rolling speed of the first pass is 120 m / min. The reduction of the second pass is 12%, and the rolling speed of the second pass is 150 m / min, to obtain the first cold-rolled strip. A rapid spheroidizing annealing treatment of the first cold-rolled strip was performed using a four-insulation platform, including: first, the first cold-rolled strip was freely heated from room temperature to 200℃; then, the first cold-rolled strip was heated from 200℃ to 400℃ at a heating rate of 50℃ / h and held for 2 hours; then, the first cold-rolled strip was heated from 400℃ to 600℃ at a heating rate of 50℃ / h and held for 2 hours; then, the first cold-rolled strip was heated from 600℃ to 680℃ at a heating rate of 50℃ / h and held for 2 hours; finally, the temperature was raised to 700℃ at a heating rate of 20℃ / h and held for 16 hours; after the holding period, the first cold-rolled strip was slowly cooled to 620℃, then cooled to 400℃ by air cooling, and then cooled to 100℃ by water cooling before being removed from the furnace, thus obtaining the annealed cold-rolled strip. Annealed cold-rolled strip was subjected to high-reduction cold rolling using a single-stand rolling mill, with a total reduction of 45%, including: a 15% reduction in the first pass at a rolling speed of 300 m / min; a 15% reduction in the second pass at a rolling speed of 500 m / min; and a 15% reduction in the third pass at a rolling speed of 400 m / min, resulting in a second cold-rolled strip with a thickness of 2.4 mm. The second cold-rolled strip steel was subjected to recrystallization annealing treatment using a three-insulation platform, including: first, freely heating the second cold-rolled strip steel from room temperature to 200℃; then heating the second cold-rolled strip steel from 200℃ to 400℃ at a heating rate of 50℃ / h and holding it at that temperature for 2 hours; then heating the second cold-rolled strip steel from 400℃ to 600℃ at a heating rate of 50℃ / h and holding it at that temperature for 2 hours; then heating the second cold-rolled strip steel from 600℃ to 700℃ at a heating rate of 50℃ / h and holding it at that temperature for 14 hours; then, after the holding period, slowly cooling the second cold-rolled strip steel to 620℃, then using air cooling to lower the temperature to 400℃, and finally using water cooling to lower the temperature to 100℃ before being removed from the furnace, thus obtaining the annealed third cold-rolled strip steel; The annealed third cold-rolled strip is subjected to low-reduction cold rolling, including: rolling on a cold rolling leveler using the elongation mode, setting the leveling tension using a high-strength steel tension gauge, controlling the elongation at 1.8%, to obtain 60Si2Mn spring steel cold-rolled strip. The 60Si2Mn spring steel cold-rolled strip was finished to obtain the finished 60Si2Mn spring steel cold-rolled strip with a microstructure grain size of grade 10 and a thickness tolerance of ±0.03mm.

[0070] Example 3 A method for preparing cold-rolled steel strip of 60Si2Mn spring steel, comprising: The product is a hot-rolled pickled steel coil, comprising: pickling a 60Si2Mn spring steel hot-rolled steel coil with a hydrochloric acid aqueous solution at a concentration of 160 g / L and a pickling rate of 25 m / min, to obtain a hot-rolled pickled steel coil with a thickness of 5.0 mm, a width of 1350 mm, and a microstructure of grade 7; the hot-rolled pickled steel coil contains the following chemical composition by mass percentage: C: 0.62 wt.%, Si: 1.85 wt.%, Mn: 0.80 wt.%, Al: 0.012 wt.%, P: 0.009 wt.%, S: 0.001 wt.%, Cr: 0.26 wt.%, Cu: 0.05 wt.%, Ni: 0.03 wt.%; the remainder being Fe and unavoidable impurities; A multi-platform spheroidizing annealing treatment was performed on hot-rolled pickled steel coils using a four-platform heating system, including: freely heating the hot-rolled pickled steel coils from room temperature to 200℃; then heating the hot-rolled pickled steel coils from 200℃ to 400℃ at a heating rate of 50℃ / h and holding at that temperature for 2 hours; then heating the hot-rolled pickled steel coils from 400℃ to 710℃ at a heating rate of 50℃ / h and holding at that temperature for 2 hours; and finally heating the hot-rolled pickled steel coils from 710℃ to 710℃ at a heating rate of 20℃ / h. The hot-rolled pickled steel coil is heated to Ac1+10℃ (758℃) and held for 2 hours. Then, the hot-rolled pickled steel coil is cooled from 758℃ to Ac1-10℃ (738℃) at a cooling rate of 20℃ / h and held for 18 hours. After the holding period, the hot-rolled pickled steel coil is slowly cooled from Ac1-10℃ to 620℃, then cooled to 400℃ by air cooling, and then cooled to 100℃ by water cooling before being removed from the furnace to obtain the annealed hot-rolled pickled steel coil. The annealed hot-rolled pickled steel coils are subjected to light-reduction cold rolling treatment, including two-pass rolling using a single-stand mill, with a total reduction of 20%. The reduction of the first pass is 10%, and the rolling speed of the first pass is 150 m / min. The reduction of the second pass is 10%, and the rolling speed of the second pass is 150 m / min, to obtain the first cold-rolled strip. A rapid spheroidizing annealing treatment of the first cold-rolled strip was performed using a four-insulation platform, including: first, the first cold-rolled strip was freely heated from room temperature to 200℃; then, the first cold-rolled strip was heated from 200℃ to 400℃ at a heating rate of 50℃ / h and held for 2 hours; then, the first cold-rolled strip was heated from 400℃ to 600℃ at a heating rate of 50℃ / h and held for 2 hours; then, the first cold-rolled strip was heated from 600℃ to 680℃ at a heating rate of 50℃ / h and held for 2 hours; finally, the temperature was raised to 700℃ at a heating rate of 20℃ / h and held for 14 hours; after the holding period, the first cold-rolled strip was slowly cooled to 620℃, then cooled to 400℃ by air cooling, and then cooled to 100℃ by water cooling before being removed from the furnace, thus obtaining the annealed cold-rolled strip. Annealed cold-rolled strip was subjected to high-reduction cold rolling using a single-stand rolling mill, with a total reduction of 45%, including: a 15% reduction in the first pass at a rolling speed of 300 m / min; a 15% reduction in the second pass at a rolling speed of 500 m / min; and a 15% reduction in the third pass at a rolling speed of 500 m / min, resulting in a second cold-rolled strip with a thickness of 2.2 mm. The second cold-rolled strip steel was subjected to recrystallization annealing treatment using a three-insulation platform, including: first, freely heating the second cold-rolled strip steel from room temperature to 200℃; then heating the second cold-rolled strip steel from 200℃ to 400℃ at a heating rate of 50℃ / h and holding it at that temperature for 2 hours; then heating the second cold-rolled strip steel from 400℃ to 600℃ at a heating rate of 50℃ / h and holding it at that temperature for 2 hours; then heating the second cold-rolled strip steel from 600℃ to 700℃ at a heating rate of 50℃ / h and holding it at that temperature for 14 hours; then, after the holding period, slowly cooling the second cold-rolled strip steel to 620℃, then using air cooling to lower the temperature to 400℃, and finally using water cooling to lower the temperature to 100℃ before being removed from the furnace, thus obtaining the annealed third cold-rolled strip steel; The annealed third cold-rolled strip is subjected to low-reduction cold rolling, including: rolling on a cold rolling leveler using the elongation mode, setting the leveling tension using a high-strength steel tension gauge, controlling the elongation at 1.5%, to obtain 60Si2Mn spring steel cold-rolled strip. The 60Si2Mn spring steel cold-rolled strip was finished to obtain the finished 60Si2Mn spring steel cold-rolled strip with a microstructure grain size of grade 9 and a thickness tolerance of ±0.02mm.

[0071] Example 4 A method for preparing cold-rolled steel strip of 60Si2Mn spring steel, comprising: The product is a hot-rolled pickled steel coil, comprising: pickling a 60Si2Mn spring steel hot-rolled steel coil with a hydrochloric acid aqueous solution at a concentration of 150 g / L and a pickling rate of 25 m / min, to obtain a hot-rolled pickled steel coil with a thickness of 5.0 mm, a width of 1250 mm, and a microstructure of grade 7; the hot-rolled pickled steel coil contains the following chemical composition by mass percentage: C: 0.62 wt.%, Si: 1.85 wt.%, Mn: 0.80 wt.%, Al: 0.012 wt.%, P: 0.009 wt.%, S: 0.001 wt.%, Cr: 0.26 wt.%, Cu: 0.05 wt.%, Ni: 0.03 wt.%; the remainder being Fe and unavoidable impurities; A multi-platform spheroidizing annealing treatment was performed on hot-rolled pickled steel coils using a four-platform heating system, including: freely heating the hot-rolled pickled steel coils from room temperature to 200℃; then heating the hot-rolled pickled steel coils from 200℃ to 400℃ at a heating rate of 50℃ / h and holding at that temperature for 2 hours; then heating the hot-rolled pickled steel coils from 400℃ to 710℃ at a heating rate of 50℃ / h and holding at that temperature for 2 hours; and finally heating the hot-rolled pickled steel coils from 710℃ to 710℃ at a heating rate of 20℃ / h. The hot-rolled pickled steel coil is heated to Ac1+10℃ (758℃) and held for 2 hours. Then, the hot-rolled pickled steel coil is cooled from 758℃ to Ac1-10℃ (738℃) at a cooling rate of 20℃ / h and held for 18 hours. After the holding period, the hot-rolled pickled steel coil is slowly cooled from Ac1-10℃ to 620℃, then cooled to 400℃ by air cooling, and then cooled to 100℃ by water cooling before being removed from the furnace to obtain the annealed hot-rolled pickled steel coil. The annealed hot-rolled pickled steel coils are subjected to light-reduction cold rolling treatment, including two-pass rolling using a single-stand mill, with a total reduction of 20%. The reduction of the first pass is 10%, and the rolling speed of the first pass is 150 m / min. The reduction of the second pass is 10%, and the rolling speed of the second pass is 150 m / min, to obtain the first cold-rolled strip. A rapid spheroidizing annealing treatment of the first cold-rolled strip was performed using a four-insulation platform, including: first, the first cold-rolled strip was freely heated from room temperature to 200℃; then, the first cold-rolled strip was heated from 200℃ to 400℃ at a heating rate of 50℃ / h and held for 2 hours; then, the first cold-rolled strip was heated from 400℃ to 600℃ at a heating rate of 50℃ / h and held for 2 hours; then, the first cold-rolled strip was heated from 600℃ to 680℃ at a heating rate of 50℃ / h and held for 2 hours; finally, the temperature was raised to 700℃ at a heating rate of 20℃ / h and held for 14 hours; after the holding period, the first cold-rolled strip was slowly cooled to 620℃, then cooled to 400℃ by air cooling, and then cooled to 100℃ by water cooling before being removed from the furnace, thus obtaining the annealed cold-rolled strip. Annealed cold-rolled strip was subjected to high-reduction cold rolling using a single-stand rolling mill, with a total reduction of 45%, including: a 15% reduction in the first pass at a rolling speed of 300 m / min; a 15% reduction in the second pass at a rolling speed of 500 m / min; and a 15% reduction in the third pass at a rolling speed of 500 m / min, resulting in a second cold-rolled strip with a thickness of 2.2 mm. The second cold-rolled strip steel was subjected to recrystallization annealing treatment using a three-insulation platform, including: first, freely heating the second cold-rolled strip steel from room temperature to 200℃; then heating the second cold-rolled strip steel from 200℃ to 400℃ at a heating rate of 50℃ / h and holding it at that temperature for 2 hours; then heating the second cold-rolled strip steel from 400℃ to 600℃ at a heating rate of 50℃ / h and holding it at that temperature for 2 hours; then heating the second cold-rolled strip steel from 600℃ to 700℃ at a heating rate of 50℃ / h and holding it at that temperature for 14 hours; then, after the holding period, slowly cooling the second cold-rolled strip steel to 620℃, then using air cooling to lower the temperature to 400℃, and finally using water cooling to lower the temperature to 100℃ before being removed from the furnace, thus obtaining the annealed third cold-rolled strip steel; The annealed third cold-rolled strip is subjected to low-reduction cold rolling, including: rolling on a cold rolling leveler using the elongation mode, setting the leveling tension using a high-strength steel tension gauge, controlling the elongation at 1.5%, to obtain 60Si2Mn spring steel cold-rolled strip. The 60Si2Mn spring steel cold-rolled strip was finished to obtain the finished 60Si2Mn spring steel cold-rolled strip with a microstructure grain size of grade 9 and a thickness tolerance of ±0.02mm.

[0072] Comparative Example 1 A method for preparing cold-rolled steel strip of existing 60Si2Mn spring steel is basically the same as that in Example 1, except that the hot-rolled pickled steel coil is not annealed using a multi-platform annealing process, but is directly heated from 200°C to 760°C. The rest is the same as in Example 1.

[0073] The result was an abnormal microstructure, forming a ferrite + pearlite microstructure. The strip broke during the first cold rolling, and after three breakages, production could not continue.

[0074] Comparative Example 2 A method for preparing 60Si2Mn spring steel cold-rolled strip is basically the same as that in Example 1, except that the first cold rolling uses a large reduction of 30%, while the rest is the same as in Example 1.

[0075] The result was that three consecutive strip breaks occurred during the first cold rolling, making it impossible to continue production.

[0076] The performance and data of Examples 1-3 and Comparative Examples 1-2 are recorded in Table 1 below for comparison.

[0077] Table 1 Note: In Table 1, " / " indicates that the data for this item was not measured. Given the high number of strip breakages, it is no longer necessary to additionally measure the metallographic structure and the thickness tolerance of the strip after cold rolling.

[0078] As shown in Table 1, the preparation method of 60Si2Mn spring steel cold-rolled strip provided in this application embodiment can refine the grade of the metallographic grains, control the thickness tolerance of the finished 60Si2Mn spring steel cold-rolled strip to ≤±0.03mm, and effectively reduce the number of strip breaks of the finished 60Si2Mn spring steel cold-rolled strip.

[0079] The above description is merely a specific implementation of this application. Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working process described above can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here. It should be understood that the protection scope of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the protection scope of this application.

Claims

1. A method for preparing cold-rolled steel strip of 60Si2Mn spring steel, characterized in that, include: Hot-rolled pickled steel coils are provided; by weight percentage, the hot-rolled pickled steel coils contain the following chemical composition: C: 0.56wt.%~0.64wt.%, Si: 1.50wt.%~2.00wt.%, Mn: 0.70wt.%~1.00wt.%, Al: ≤0.020wt.%, P: ≤0.018wt.%, S: ≤0.004wt.%, Cr: ≤0.35wt.%, Cu: ≤0.25wt.%, Ni: ≤0.35wt.%; the remainder is Fe and unavoidable impurities; Hot-rolled pickled steel coils are subjected to multi-platform spheroidizing annealing treatment to obtain annealed steel coils. The annealed steel coil is subjected to light-pressure cold rolling to obtain the first cold-rolled strip. The first cold-rolled strip was subjected to rapid spheroidizing annealing to obtain annealed cold-rolled strip. The annealed cold-rolled strip is subjected to a large reduction cold rolling process to obtain a second cold-rolled strip; The second cold-rolled strip is subjected to recrystallization annealing to obtain the annealed third cold-rolled strip. The annealed third cold-rolled strip was subjected to low-reduction cold rolling to obtain 60Si2Mn spring steel cold-rolled strip.

2. The method for preparing 60Si2Mn spring steel cold-rolled strip according to claim 1, characterized in that, The width of the hot-rolled pickled steel coil is 900mm to 1500mm, and the thickness of the hot-rolled pickled steel coil is 1.5mm to 6.5mm. Optionally, the hot-rolled coil of 60Si2Mn spring steel is pickled at a rate of 10 m / min to 30 m / min. Optionally, the hot-rolled coils of 60Si2Mn spring steel are pickled with hydrochloric acid aqueous solution, wherein the concentration of HCl in the hydrochloric acid aqueous solution is 150g / L to 240g / L.

3. The method for preparing 60Si2Mn spring steel cold-rolled strip according to claim 1, characterized in that, Multi-platform spheroidizing annealing treatment is performed on hot-rolled pickled steel coils, including: multi-platform spheroidizing annealing treatment of hot-rolled pickled steel coils using four insulation platforms; Optionally, the hot-rolled pickled steel coils are subjected to multi-platform spheroidizing annealing treatment using a four-insulation platform, including: The hot-rolled pickled steel coil is heated from room temperature to 200℃~220℃; The hot-rolled pickled steel coil is then heated from 200℃~220℃ to 400℃~420℃ at a heating rate of 50℃ / h~55℃ / h, and held at that temperature for 2 hours~3 hours. The hot-rolled pickled steel coil is then heated from 400℃~420℃ to 710℃~730℃ at a heating rate of 50℃ / h~60℃ / h, and held at that temperature for 2 hours~3 hours. The hot-rolled pickled steel coil is then heated from 710℃~730℃ at a heating rate of 20℃ / h~25℃ / h to Ac1+10℃ and held at that temperature for 2 hours~3 hours. The hot-rolled pickled steel coil is then cooled from Ac1+10℃ to Ac1-10℃ at a cooling rate of 20℃ / h to 25℃ / h, and held at that temperature for 18 to 20 hours. After the heat preservation is completed, the hot-rolled pickled steel coil is cooled from Ac1-10℃ to 620℃, then air-cooled to 400℃, and then water-cooled to 100℃ before being taken out of the furnace.

4. The method for preparing 60Si2Mn spring steel cold-rolled strip according to claim 1, characterized in that, The annealed hot-rolled pickled steel coils are subjected to light-reduction cold rolling treatment, which includes two-pass rolling using a single-stand mill, with a total reduction rate of 10% to 20%. Optionally, in the step of performing light-reduction cold rolling on the annealed hot-rolled pickled steel coil, the reduction rate of each rolling pass is 5% to 10%, and the rolling speed of each pass is 100m / min to 150m / min.

5. The method for preparing 60Si2Mn spring steel cold-rolled strip according to claim 1, characterized in that, The first cold-rolled strip steel undergoes rapid spheroidizing annealing treatment, including: The first cold-rolled strip steel was subjected to rapid spheroidizing annealing treatment using a four-insulation platform. Optionally, a four-insulation platform is used to perform rapid spheroidizing annealing treatment on the first cold-rolled strip, including: The first cold-rolled strip steel is first heated from room temperature to 200℃~220℃; The first cold-rolled strip is then heated from 200℃~220℃ to 400℃~420℃ at a heating rate of 50℃ / h~55℃ / h, and held at that temperature for 2 hours~3 hours. The first cold-rolled strip is then heated from 400℃~420℃ to 600℃~620℃ at a heating rate of 50℃ / h~55℃ / h, and held at that temperature for 2 hours~3 hours. The first cold-rolled strip is then heated from 600℃~620℃ to 680℃~695℃ at a heating rate of 50℃ / h~55℃ / h, and held at that temperature for 2 hours~3 hours. Then, raise the temperature to 700℃~720℃ at a heating rate of 20℃ / h~25℃ and hold it for 14 hours~16 hours; Then, after the heat preservation is completed, the first cold-rolled strip is slowly cooled to 620°C, then air-cooled to 400°C, and then water-cooled to 100°C before being taken out of the furnace.

6. The method for preparing 60Si2Mn spring steel cold-rolled strip according to claim 1, characterized in that, The annealed cold-rolled strip undergoes a high-reduction cold rolling process, including: A single-stand rolling mill is used for three-pass rolling, with a total reduction rate of 40% to 45%. Optionally, in the step of performing large-reduction cold rolling on the annealed cold-rolled strip, the reduction rate of each rolling pass is 10% to 15%, and the rolling speed of each pass is 300 m / min to 500 m / min.

7. The method for preparing 60Si2Mn spring steel cold-rolled strip according to claim 1, characterized in that, The second cold-rolled strip undergoes recrystallization annealing treatment, including: The second cold-rolled strip was subjected to recrystallization annealing treatment using a triple-insulation platform. Optionally, the second cold-rolled strip is subjected to recrystallization annealing treatment using two insulation platforms, including: The second cold-rolled strip is first heated from room temperature to 200℃~220℃; The second cold-rolled strip is then heated from 200℃~220℃ to 400℃~420℃ at a heating rate of 50℃ / h~55℃ / h, and held at that temperature for 2 hours~3 hours. The second cold-rolled strip is then heated from 400℃~420℃ to 600℃~620℃ at a heating rate of 50℃ / h~55℃ / h, and held at that temperature for 2 hours~3 hours. The second cold-rolled strip is then heated from 600℃~620℃ to 700℃~720℃ at a heating rate of 50℃ / h~55℃ / h, and held at that temperature for 14 hours~16 hours. Then, after the heat preservation is completed, the second cold-rolled strip is slowly cooled to 620°C, then air-cooled to 400°C, and then water-cooled to 100°C before being taken out of the furnace.

8. The method for preparing 60Si2Mn spring steel cold-rolled strip according to claim 1, characterized in that, The annealed third cold-rolled strip is subjected to low-reduction cold rolling, including: using a cold rolling leveling machine to perform low-reduction cold rolling on the annealed third cold-rolled strip; Optionally, a cold rolling mill is used to perform low-reduction cold rolling on the annealed third cold-rolled strip, including: rolling on the cold rolling mill using an elongation mode, setting the leveling tension using a high-strength steel tension gauge, and controlling the elongation to 1.0–2.0%; Optionally, the preparation method of cold-rolled steel strip of 60Si2Mn spring steel also includes: The 60Si2Mn spring steel cold-rolled strip is finished to obtain the finished 60Si2Mn spring steel cold-rolled strip.

9. A cold-rolled steel strip of 60Si2Mn spring steel, characterized in that, The 60Si2Mn spring steel cold-rolled strip is prepared according to any one of claims 1-8. The 60Si2Mn spring steel cold-rolled strip comprises, by mass percentage, the following chemical composition: C: 0.56wt.%~0.64wt.%, Si: 1.50wt.%~2.00wt.%, Mn: 0.70wt.%~1.00wt.%, Al: ≤0.020wt.%, P: ≤0.018wt.%, S: ≤0.004wt.%, Cr: ≤0.35wt.%, Cu: ≤0.25wt.%, Ni: ≤0.35wt.%; the remainder being Fe and unavoidable impurities.

10. The 60Si2Mn spring steel cold-rolled strip according to claim 9, characterized in that, The metallographic structure of 60Si2Mn spring steel cold-rolled strip is spheroidized pearlite, with an average grain size of 5μm to 9μm.

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