阅读说明：本技术 一种精密冲压高速切割链锯片用冷轧钢板及其制造方法 (Cold-rolled steel plate for precision stamping high-speed cutting chain saw blade and manufacturing method thereof ) 是由 马植甄 于 2019-08-26 设计创作，主要内容包括：本发明公开了一种精密冲压高速切割链锯片用冷轧钢板及其制造方法,解决现有精密冲压高速切割链锯片用冷轧钢板的球化率低,热处理硬度低的技术问题。本发明提供的一种精密冲压高速切割链锯片用冷轧钢板,其化学成分重量百分比：C：0.64-0.70％,Si≤0.3％,Mn：0.3-0.5％,Cr：0.2-0.4％,Ni：0.2-0.4％,Mo：0.05-0.25％,P≤0.015％,S≤0.005％,其余为Fe和不可避免的杂质。冷轧钢板的屈服强度R_(P0.2)为330-400MPa,抗拉强度R_m为480-550MPa,断后伸长率A_(50mm)为24-32％。本发明冷轧钢板主要用于精密冲压高速切割链锯片的基板。(The inventionDiscloses a cold-rolled steel plate for a precision stamping high-speed cutting chain saw blade and a manufacturing method thereof, which solve the technical problems of low spheroidization rate and low heat treatment hardness of the existing cold-rolled steel plate for the precision stamping high-speed cutting chain saw blade. The invention provides a cold-rolled steel plate for a precise stamping high-speed cutting chain saw blade, which comprises the following chemical components in percentage by weight: c: 0.64-0.70%, Si is less than or equal to 0.3%, Mn: 0.3-0.5%, Cr: 0.2-0.4%, Ni: 0.2-0.4%, Mo: 0.05-0.25 percent, less than or equal to 0.015 percent of P, less than or equal to 0.005 percent of S, and the balance of Fe and inevitable impurities. Yield strength R of Cold rolled Steel sheet P0.2 330- m 480-550MPa, elongation after fracture A 50mm Is 24-32%. The cold-rolled steel sheet is mainly used for precisely stamping the substrate of the high-speed cutting chain saw blade.)

1. A cold-rolled steel plate for a precision stamping high-speed cutting chain saw blade comprises the following chemical components in percentage by weight: c: 0.64-0.70%, Si is less than or equal to 0.3%, Mn: 0.3-0.5%, Cr: 0.2-0.4%, Ni: 0.2-0.4%, Mo: 0.05-0.25 percent of Fe, less than or equal to 0.015 percent of P, less than or equal to 0.005 percent of S, and the balance of Fe and inevitable impurities; the metallographic structure of the cold-rolled steel plate is massive ferrite and granular pearlite, the grain size of the ferrite is I7.0-9.0 grade, and the nodularity is 90-95%.

2. The cold rolled steel sheet for a precision press high speed cutting chain saw blade as set forth in claim 1, wherein the yield strength R of the cold rolled steel sheet is 1.0-2.2mm thick_P0.2330-_m480-550MPa, the yield ratio of 0.64-0.72 and the elongation percentage A after fracture_50mm24-32%, and a Vickers hardness HV10 of 150-170.

3. The cold rolled steel sheet for a precision press high speed cutting chain saw blade according to claim 1, wherein the cold rolled steel sheet comprises the following chemical components by weight percent: c: 0.64-0.70%, Si is less than or equal to 0.3%, Mn: 0.35-0.45%, Cr: 0.25-0.40%, Ni: 0.2-0.4%, Mo: 0.05-0.25 percent, less than or equal to 0.015 percent of P, less than or equal to 0.005 percent of S, and the balance of Fe and inevitable impurities.

4. The cold rolled steel sheet for a precision press high speed cutting chain saw blade according to claim 1, wherein the cold rolled steel sheet comprises the following chemical components by weight percent: c: 0.64-0.70%, Si is less than or equal to 0.3%, Mn: 0.35-0.45%, Cr: 0.25-0.35%, Ni: 0.2-0.4%, Mo: 0.05-0.25 percent, less than or equal to 0.015 percent of P, less than or equal to 0.005 percent of S, and the balance of Fe and inevitable impurities.

5. The cold rolled steel sheet for a precision press high speed cutting chain saw blade according to claim 1, wherein the cold rolled steel sheet comprises the following chemical components by weight percent: c: 0.64-0.70%, Si is less than or equal to 0.3%, Mn: 0.35-0.45%, Cr: 0.25-0.35%, Ni: 0.20-0.35%, Mo: 0.05-0.25 percent, less than or equal to 0.015 percent of P, less than or equal to 0.005 percent of S, and the balance of Fe and inevitable impurities.

6. A cold-rolled steel plate for a precision stamping high-speed cutting chain saw blade is characterized by comprising the following steps:

after ladle refining and vacuum degassing treatment, molten steel is continuously poured to obtain a continuous casting slab, wherein the molten steel comprises the following components in percentage by weight: c: 0.64-0.70%, Si is less than or equal to 0.3%, Mn: 0.3-0.5%, Cr: 0.2-0.4%, Ni: 0.2-0.4%, Mo: 0.05-0.25 percent of Fe, less than or equal to 0.015 percent of P, less than or equal to 0.005 percent of S, and the balance of Fe and inevitable impurities;

the continuous casting plate blank is heated at 1180-1220 ℃ for 180-240min and then rolled, the hot rolling is a two-section rolling process, the rough rolling is 5-pass continuous rolling, and the rolling is carried out at the austenite recrystallization temperature or above; the finish rolling is 7-pass continuous rolling, the finish rolling temperature is 850-;

and uncoiling the hot-rolled steel coil again, then carrying out acid cleaning, cold rolling and annealing in a hood-type annealing furnace, coiling to obtain a finished cold-rolled steel sheet with the thickness of 1.0-2.2mm, wherein the cold rolling reduction rate is 40-50%, the cold-rolled hard strip steel is annealed in the hood-type annealing furnace, the temperature of the strip steel in a soaking section of the hood-type annealing furnace is 705-725 ℃, and the annealing time of the strip steel in the soaking section is 16-20 h.

7. The cold rolled steel sheet for a precision press high speed cutting chain saw blade according to claim 6, wherein the thickness of the hot rolled steel sheet is controlled to be 2.0 to 4.0mm after the finish hot rolling.

Technical Field

The invention relates to a cold-rolled steel plate for precision stamping, in particular to a cold-rolled steel plate for a precision stamping high-speed cutting chain saw blade and a manufacturing method thereof, belonging to the technical field of iron-based alloy.

Background

The chain saw blade has excellent cutting performance and wear resistance, and is widely applied to logging and wood processing. The steel for the chain saw blade is generally medium-high carbon high-quality steel, and after the material is processed and molded, high strength, hardness and wear resistance are obtained through heat treatment, so that high-speed cutting processing of lumbers and woods is guaranteed.

The common saw blade matrix of the chain saw is a medium carbon steel material such as 50 steel, 65Mn and the like, but the hardenability is poor, so that the hardness of the saw blade after heat treatment is low; the quenching degree is insufficient, so that the hardness of the part after quenching is low and uneven, the continuous casting and hot rolling of the plate blank are difficult, the defect sensitivity of the plate blank is high, the segregation of carbon and alloy elements is large, cracks and delamination are easy to generate, the strength of the rolled steel coil is high, and the cold machining and the heat treatment of materials are inconvenient for users.

The application publication number is CN105568170A, which discloses a high-quality strip steel for saw blades and a production process thereof, and the high-quality strip steel comprises the following chemical components: c: 0.50-0.55%; si: 0.20-0.30%; mn: 0.50-0.65%; p: less than or equal to 0.30 percent; s: less than or equal to 0.30 percent; cr: less than or equal to 0.20 percent; ni: less than or equal to 0.20 percent; cu: less than or equal to 0.20 percent, and the balance of iron and inevitable impurity elements. The patent adopts the traditional process of producing the hot-rolled narrow strip by square billet continuous casting, and the steel coil has low yield and poor tissue uniformity; meanwhile, the steel only contains conventional alloy elements such as C, Si, Mn and the like, and the hardness, the wear resistance and the like of the chain saw after heat treatment can not meet the use requirements.

The Chinese patent application with the application publication number of CN105018835A discloses a medium-high carbon strip steel with excellent fine blanking performance and a production and manufacturing method thereof, wherein the medium-high carbon strip steel comprises the following chemical components in percentage by weight: c: 0.50-0.65%, Si: 0.50-1.60%, Mn: 0.50-1.70%, Ca: 0.0030-0.0070%, B: 0.0008-0.0050%, Al: 0.015 to 0.030%, P: less than or equal to 0.015 percent, S: less than or equal to 0.008 percent; the balance of Fe and inevitable impurities. In the patent, Si element is used for improving the carbon atom activity, but the hardness of the material is improved and the blanking performance is deteriorated if the Si element is added in a large amount; meanwhile, the high silicon content generates a large amount of iron scale in the hot rolling process of the steel strip, and the surface quality of the steel strip is reduced.

Disclosure of Invention

The invention aims to provide a cold-rolled steel plate for a precision stamping high-speed cutting chain saw blade and a manufacturing method thereof, and solves the technical problems of low spheroidization rate and low heat treatment hardness of the existing cold-rolled steel plate for the precision stamping high-speed cutting chain saw blade.

According to the invention, the design of a component with higher carbon content is adopted, P, S harmful elements are further controlled, and a small amount of Cr, Ni and Mo alloy elements are added to meet the requirement of the heat treatment performance of parts; meanwhile, the temperature control in the hot rolling process is optimized, the cold rolling and spheroidizing annealing process is adopted, the spheroidizing effect of pearlite is improved, the strength and hardness of the material are obviously reduced, the elongation is improved, and the steel strip for the chain saw blade, which is used for fine blanking, is obtained.

The invention adopts the technical scheme that a cold-rolled steel plate for a precision stamping high-speed cutting chain saw blade comprises the following chemical components in percentage by weight: c: 0.64-0.70%, Si is less than or equal to 0.3%, Mn: 0.3-0.5%, Cr: 0.2-0.4%, Ni: 0.2-0.4%, Mo: 0.05-0.25 percent, less than or equal to 0.015 percent of P, less than or equal to 0.005 percent of S, and the balance of Fe and inevitable impurities.

The metallographic structure of the cold-rolled steel plate is massive ferrite and granular pearlite, the ferrite grain size is I7.0-9.0 grade, the nodularity is 90-95 percent, and the yield strength R of the cold-rolled steel plate with the thickness of 1.0-2.2mm_P0.2330-_m480-550MPa, the yield ratio of 0.64-0.72 and the elongation percentage A after fracture_50mm24-32%, and a Vickers hardness HV10 of 150-170.

The precision stamping high-speed cutting chain saw blade manufactured by adopting the cold-rolled steel plate as the substrate is mainly used for lumbering and wood processing.

The reason why the chemical composition of the cold rolled steel sheet for the precision press high speed cutting chain saw blade of the present invention is limited to the above range is as follows:

c: carbon is the main alloying element for pearlite formation and affects the hardness of the material after hot rolling, cold rolling, annealing and quenching of parts. The C content is too low, the pearlite content of the steel type is relatively low, and the final use requirement of parts cannot be met; if the content of C is too high, eutectoid steel is achieved, and the hardness is too high, so that the punch forming is not facilitated. The range of carbon addition in the present invention is 0.64-0.70%.

Si: silicon is used as a solid solution strengthening element, has a certain strengthening effect when being dissolved in a steel strip matrix, and plays a role in deoxidation and desulfurization as a deoxidizer during smelting. However, when the amount is large, the ferrite phase is hardened, and the workability is remarkably lowered. Si promotes the generation of the rust red iron oxide skin defect on the surface of the steel coil in the hot rolling process, and the appearance of a finished product is influenced; therefore, in the present invention, the material strength is reduced by reducing the Si content, and Si is limited to 0.3% or less.

Mn: manganese is a good deoxidizer and desulfurizer. The steel contains a certain amount of manganese, which can eliminate or reduce the hot brittleness of the steel caused by sulfur, thereby improving the hot workability of the steel. However, when the content is large, the solid solution strengthening effect is obvious, and the blanking processing performance is sharply reduced. Therefore, the invention reduces the material strength, improves the toughness and fine blanking performance by reducing the Mn content. In the present invention, Mn is limited to 0.3 to 0.5%.

P: phosphorus is an impurity element, segregates in a grain boundary to reduce the processing performance, and hopefully reduces the content of the phosphorus as much as possible to improve the forming performance; but considering the control capability of process equipment and dephosphorization cost, the invention limits P to be less than or equal to 0.015 percent.

S: sulfur is an impurity element, and forms inclusions such as MnS and the like in steel, thereby affecting fine blanking performance. It is desirable to reduce the content thereof as much as possible; considering the practical control capacity and desulfurization cost, the invention limits S to be less than or equal to 0.005 percent.

Cr: chromium increases the hardenability of steel and is a main alloy element for corrosion resistance and oxidation resistance. In the invention, the addition range of Cr is 0.2-0.4%, and the Cr is a main alloy element for improving the spheroidization of pearlite. The invention discovers that the pearlite structure of the hot rolled plate can be refined after the Cr element is added, thereby accelerating the fusing of the lamellar pearlite and the diffusion speed of C atoms and improving the spheroidization speed of the steel strip.

Ni: nickel is an austenite forming element in steel, stabilizes austenite in steel, reduces precipitation tendency of grain boundary carbide, remarkably reduces the number of intercrystalline carbide, reduces critical transformation temperature, reduces diffusion rate of each element, and improves hardenability. The nickel can also refine pearlite, improve the toughness of the material and improve the fatigue resistance. However, Ni is a precious alloy, the price is very high, and the addition range of Cr is limited to 0.2-0.4% in the invention in consideration of cost factors.

Mo: molybdenum has a certain solid solubility in steel and can form a compound with elements such as C, N in steel. In the quenching and cooling process, carbide is precipitated to increase the hardness and strength, improve the hardness and wear resistance of steel and simultaneously improve the hardenability and hardenability of the material. The addition of molybdenum enables the steel to be tempered at a higher temperature and maintain high hardness, and the tempering stability of the steel during heat treatment is improved. In order to achieve the effect, the content of molybdenum in the steel needs to be more than 0.05 percent; when the molybdenum content in the steel exceeds 0.30%, the hardness of the steel is sharply increased during hot rolling, which is disadvantageous for subsequent processing. The content of Mo is limited to 0.05-0.25%.

A method for manufacturing a cold-rolled steel plate for a precision stamping high-speed cutting chain saw blade comprises the following steps:

after ladle refining and vacuum degassing treatment, molten steel is continuously poured to obtain a continuous casting slab, wherein the molten steel comprises the following components in percentage by weight: c: 0.64-0.70%, Si is less than or equal to 0.3%, Mn: 0.3-0.5%, Cr: 0.2-0.4%, Ni: 0.2-0.4%, Mo: 0.05-0.25 percent of Fe, less than or equal to 0.015 percent of P, less than or equal to 0.005 percent of S, and the balance of Fe and inevitable impurities;

the continuous casting plate blank is heated at 1180-1220 ℃ for 180-240min and then rolled, the hot rolling is a two-section rolling process, the rough rolling is 5-pass continuous rolling, and the rolling is carried out at the austenite recrystallization temperature or above; the finish rolling is 7-pass continuous rolling, the finish rolling temperature is 850-890 ℃, the thickness of the steel plate after the finish rolling is 2.0-4.0mm, the laminar cooling is controlled by front-section cooling, the cooling speed is 25-40 ℃/S, and the coiling temperature is 580-620 ℃ to obtain a hot rolled steel coil;

and uncoiling the hot-rolled steel coil again, then carrying out acid cleaning, cold rolling and annealing in a hood-type annealing furnace, coiling to obtain a finished cold-rolled steel sheet with the thickness of 1.0-2.2mm, wherein the cold rolling reduction rate is 40-50%, the cold-rolled hard strip steel is annealed in the hood-type annealing furnace, the temperature of the strip steel in a soaking section of the hood-type annealing furnace is 705-725 ℃, and the annealing time of the strip steel in the soaking section is 16-20 h.

The hot rolling process and the control of the structure of the hot rolled steel sheet therein are one of the technical key points for realizing the present invention. By calculation, the component system A of the invention₃At 740.6 ℃ A₁The temperature was 735.7 ℃. The hot rolling process adopted by the invention is based on the composition system and the calculated phase change point.

The production process adopted by the invention has the following reasons:

1. setting of heating temperature and heating time of continuous casting slab

The heating temperature and time of the continuous casting slab are set to ensure that alloy elements such as C, Si, Mn, Cr, Ni, Mo and the like in the continuous casting slab are fully diffused and dissolved, and coarse carbide particles are dissolved and uniformly distributed in steel. Both too low a temperature and too short a heating time do not achieve the above objectives. The medium slab heating temperature is adopted, the target temperature is 1200 ℃, if the temperature is too high, the heating time is too long, and because the carbon content in steel is higher, the oxidation and decarburization of the slab surface are serious, the final performance and the surface quality of a steel strip are not facilitated, and energy is consumed at the same time. Therefore, the invention sets the heating temperature of the continuous casting slab to 1180-1220 ℃, and the heating time to 180-240 min.

2. Setting of finish Rolling finishing temperature

The finish rolling temperature of the invention is set to have two functions, on one hand, flat austenite grains with deformation zones inside are obtained by rolling the material in an austenite non-recrystallization area and are converted into fine ferrite grains in the subsequent laminar cooling process, thus playing the roles of refining the grains and reducing the zonal segregation; on the other hand, the high material strength and the low finishing temperature result in excessive rolling load and affect rolling stability. Therefore, the present invention sets the finish rolling finish temperature to 850-.

3. Method of laminar cooling after finish rolling and setting of cooling rate

The laminar cooling after the finish rolling adopts a front-stage cooling process, can promote austenite in the material structure after the finish rolling to be quickly converted into ferrite, and has refined grains, uniform structure and cooling speed of 25-40 ℃/S.

4. Setting of coiling temperature in Hot Rolling

The hot rolling coiling temperature mainly influences the structure and the performance of the material and the subsequent spheroidizing annealing effect. And the lower coiling temperature is adopted, so that grains can be refined, and the downstream cold rolling processing and spheroidizing annealing are facilitated. If the hot rolling coiling temperature is too high, pearlite becomes too coarse, the brittleness of the material increases, and the structure uniformity is poor. Therefore, the invention sets the hot rolling coiling temperature to 580-620 ℃.

5. Setting of Cold Rolling reduction

The cold rolling deformation is an important means for improving the dimensional precision of the steel strip and meets the requirement of continuous fine blanking processing. Meanwhile, the increase of the cold rolling deformation can also promote the fracture of lamellar pearlite, so that the dislocation density in the material is greatly increased, and more energy is provided for spheroidization transformation of the pearlite. However, too high deformation will cause too large load on the cold rolling mill, increase the number of cold rolling passes, and greatly increase the cost of cold rolling. In view of the above, the preferred cold rolling reduction rate of the present invention is 40 to 50%.

6. Setting of annealing temperature and annealing time

The invention adopts the bell-type annealing furnace for annealing, and the spheroidization of flaky pearlite is promoted by considering the cold rolling deformation accumulation effect of the previous process, generally at A₁Annealing is performed below the point temperature. The too high annealing temperature can cause the ferrite grains to be coarse, and in order to improve the spheroidizing annealing effect, the annealing temperature of the steel strip in the soaking section of the hood-type annealing furnace is set to 705-725 ℃.

The heat preservation time of the soaking section is also very critical during annealing; if the heat preservation time is too short, the lamellar pearlite chains cannot be completely fused and disconnected; fine spherical particles cannot be generated, and the dispersion distribution is formed; if the heat preservation time is too long, the granular pearlite can grow up again and agglomerate together to form lamellar segregation, so that the toughness of the material is reduced, and the subsequent fine blanking processing is not facilitated. In order to improve the spheroidizing annealing effect, the time of the steel strip in the soaking section is 16-20 h.

The metallographic structure of the cold-rolled steel plate produced by the method is massive ferrite and granular pearlite, the grain size of the ferrite is I7.0-9.0 grade, the nodularity is 90-95 percent, and the yield strength R of the cold-rolled steel plate with the thickness of 1.0-2.2mm is_P0.2330-_m480-550MPa, the yield ratio of 0.64-0.72 and the elongation percentage A after fracture_50mm24-32%, and a Vickers hardness HV10 of 150-170.

Compared with the prior art, the invention has the following positive effects: 1. by adopting the design of higher carbon content, P, S harmful elements are further controlled, and a small amount of Cr, Ni and Mo alloy elements are added to meet the requirement of heat treatment performance of parts; meanwhile, the temperature control in the hot rolling process is optimized, the cold rolling and spheroidizing annealing process is adopted, the spheroidizing effect of pearlite is improved, the strength and hardness of the material are obviously reduced, the elongation is improved, and the steel strip for the chain saw blade, which is used for fine blanking, is obtained. 2. The invention exerts the functions of trace Cr, Mo and other alloy elements by controlling the hot rolling coiling temperature and the cooling process after rolling; obtaining the hot-rolled steel plate with moderately refined grains, wherein the metallographic structure of the hot-rolled steel plate is as follows: fine lamellar pearlite + a small amount of ferrite; the material has moderate hot rolling state strength and hardness, and is beneficial to subsequent cold rolling and annealing. 3. The invention adopts a reasonable annealing process to ensure that the lamellar pearlite in the structure of the annealed steel coil is fully spheroidized and the structure is uniformly distributed. The strength of the cold-rolled steel strip is greatly reduced, the toughness is excellent, the performance is uniform, and the requirement of precision stamping processing is met.

Drawings

FIG. 1 is a metallographic structure photograph of a cold-rolled annealed steel sheet according to example 3 of the present invention.

Detailed Description

The present invention is further illustrated below with reference to examples 1 to 5, which are shown in tables 1 to 4.

Table 1 shows the chemical composition (in weight%) of the steels of the examples of the invention, the balance being Fe and unavoidable impurities.

Table 1 chemical composition of the steels of the examples of the invention, in units: and (4) weight percentage.

Element(s)	C	Si	Mn	P	S	Cr	Ni	Mo
									The invention	0.64-0.70	≤0.3	0.3-0.5	≤0.015	≤0.005	0.2-0.4	0.2-0.4	0.05-0.25
Example 1	0.651	0.226	0.398	0.009	0.0007	0.274	0.246	0.101
									Example 2	0.676	0.181	0.364	0.012	0.0012	0.322	0.229	0.126
Example 3	0.669	0.243	0.415	0.008	0.0027	0.309	0.271	0.144
									Example 4	0.682	0.132	0.385	0.142	0.0021	0.266	0.239	0.203
Example 5	0.648	0.225	0.427	0.008	0.0028	0.335	0.311	0.118

Smelting the molten steel by a converter to obtain molten steel meeting the basic requirements of chemical components, carrying out deep desulfurization and fine adjustment of alloy components on the molten steel by an LF ladle refining furnace, carrying out vacuum cyclic degassing treatment on the molten steel by an RH furnace for more than 8 minutes, and finally pouring by a continuous casting machine to obtain a continuous casting slab; the thickness of the slab is 210-230mm, the width is 900-1300mm, and the length is 8500-11000 mm.

The fixed-length slab produced by steel making is directly sent to a heating furnace to be reheated, taken out of the furnace to be descaled and then sent to a hot continuous rolling mill set to be rolled. The rolling is controlled by a rough rolling and finish rolling continuous rolling unit, and the steel coil is coiled after laminar cooling, wherein the laminar cooling adopts a front-section cooling mode, the cooling speed is 25-40 ℃/S, and the hot rolled steel coil with the thickness of 2.0-4.0mm is produced. The hot rolling process control parameters are shown in Table 2.

TABLE 2 Hot Rolling Process control parameters of the inventive examples

The hot rolled steel coil is uncoiled again and then is pickled, and is cold-rolled on a reversible rolling mill after being stripped according to the width specification requirement, wherein the cold rolling reduction rate is 40-50%; annealing the cold-rolled hard steel coil in a bell-type furnace to obtain a finished cold-rolled steel strip with the thickness of 1.0-2.2mm, wherein the annealing process comprises the following steps: the annealing temperature of the steel coil in the bell-type furnace (soaking section) is 705-725 ℃, and the annealing time (soaking section) is 16-20 h. The control parameters of the cold rolling and annealing processes are shown in Table 3.

TABLE 3 control parameters of the cold rolling and annealing processes of the present invention

Cold rolling and annealing parameters	Cold rolling reduction/%)	Annealing temperature/. degree.C	Annealing time/h	Thickness/mm of cold-rolled steel sheet
					The invention	40-50	705-725	16-20	1.0-2.2
Example 1	43.3	715	18.5	1.7
					Example 2	45.5	710	17.0	1.2
Example 3	50.0	725	19.0	2.0
					Example 4	44.4	710	18.0	1.5
Example 5	48.5	720	16.5	1.8

Referring to fig. 1, the cold-rolled steel sheet obtained by the above method has a metallographic structure of bulk ferrite and granular pearlite, a ferrite grain size of I7.0-9.0 grade, a spheroidization rate of 90-95%, and a yield strength R of the cold-rolled steel sheet_P0.2330-_m480-550MPa, the yield ratio of 0.64-0.72 and the elongation percentage A after fracture_50mm24-32%, and a Vickers hardness HV10 of 150-170.

The cold-rolled steel strip obtained by the invention is subjected to tensile, microstructure and hardness detection according to a metal material tensile test method (GB/T228.1), a steel microstructure evaluation method (GB/T13299) and a metal material Vickers hardness test method (GB/T4340.1-2009), and the mechanical properties of the cold-rolled steel strip are shown in Table 4.

TABLE 4 Performance index of cold-rolled steel sheets according to examples of the present invention

The cold-rolled steel strip obtained by the invention has higher carbon and certain alloy content, lower strength, higher elongation and plasticity, fine and granular carbide and uniform distribution; meets the requirements of fine blanking and heat treatment.

In addition to the above embodiments, the present invention may have other embodiments; all technical solutions formed by adopting equivalent substitutions or equivalent transformations fall within the protection scope of the claims of the present invention.