A cold-rolled fine-blanking steel and a manufacturing method thereof

Abstract

The application discloses a cold-rolled fine-blanking steel and a manufacturing method thereof. By optimizing the chemical composition and microstructure of the cold-rolled fine-blanking steel, the C content is controlled to be 0.30%-0.47%, the strength and hardness after quenching can be ensured, the Mn content is controlled to be 1.0%-1.5%, the hardenability of the steel can be improved, the hot brittleness can be prevented, and the forgeability and plasticity of the steel are improved; meanwhile, the number ratio of the spheroidal carbide is controlled to be greater than or equal to 90%, the average diameter of the spheroidal carbide is adjusted to be 0.5-0.8 mu m, any spheroidal carbide particle A is selected in a 1000 times metallographic graph of a cross section of the steel, another spheroidal carbide particle B exists in a circular area with the particle A as a center and a radius of 2 mu m, a sector with a center angle of 30 degrees and symmetrically distributed along the thickness direction of the steel is taken in the circular area, and the particle B does not fall into the sector, so that the size of the spheroidal carbide is smaller and the distribution of the spheroidal carbide is more uniform, and therefore the semi-punching limit depth can be increased.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fine blanking steel, in particular to a cold-rolled fine blanking steel and a manufacturing method thereof. BACKGROUND

[0002] The metallographic structure of the cold-rolled fine blanking steel before stamping is mainly ferrite matrix, and the matrix has diffusely distributed cementite, wherein the proportion of spherical cementite in the total cementite is greater than 90%. After the fine blanking steel is prepared into fine blanking parts by stamping, the internal microstructure of the parts is usually changed into an organization close to all martensite by heat treatment, so as to obtain higher strength and hardness for use. In order to obtain higher strength and hardness after quenching, more alloying elements are usually added, but the addition of these alloying elements will make the fine blanking steel difficult to be formed by stamping, and in many cases, cracking will occur when the semi-stamping limit depth reaches about 20%. SUMMARY

[0003] Therefore, the primary purpose of the present application is to provide a cold-rolled fine blanking steel with a large semi-stamping limit depth and high hardness.

[0004] Another purpose of the present application is to provide a manufacturing method of a cold-rolled fine blanking steel with a large semi-stamping limit depth and high hardness.

[0005] According to the embodiments of the present application, in a first aspect, a cold-rolled fine blanking steel is provided, the chemical composition of the cold-rolled fine blanking steel includes Fe, C and Mn, and the content of C is 0.30% to 0.47% and the content of Mn is 1.0% to 1.5%, based on the mass of the cold-rolled fine blanking steel.

[0006] The cold-rolled fine blanking steel includes carbides, and the carbides include spherical carbides, and the proportion of the number of the spherical carbides is greater than or equal to 90%, based on the number of the carbides.

[0007] The average diameter of the spherical carbides is 0.5 μm to 0.8 μm.

[0008] In the metallographic graph of the cross section of the cold-rolled fine blanking steel, under a 1000 times field of view, an optional spherical carbide particle is recorded as particle A, and another spherical carbide particle is recorded as particle B in a circular area with a radius of 2 μm and the particle A as the center; and a sector with a central angle of 30° is taken in the circular area, the sector is symmetrically distributed along the thickness direction of the cold-rolled fine blanking steel, and the particle B does not fall into the sector.

[0009] It should be noted that the term "spherical carbide" in the present application refers to a carbide with an aspect ratio less than or equal to 2, and its appearance is spherical or spherical-like. The average diameter of the spherical carbide can be tested by the following method: using a digital metallographic microscope to take a cross section (i.e. perpendicular to the rolling direction) of the cold-rolled fine blanking steel, randomly selecting at least 5 fields of view, each field of view area is not less than 2500 µm 2 , more than 200 spherical carbides are taken, and then the equivalent circle diameter of each spherical carbide is fitted by using image analysis software , wherein A is the cross-sectional area of the spherical carbide; and finally taking the average value.

[0010] The "number ratio of spherical carbides" reflects the degree of spherical organization formed in the steel, and the higher the value, the more round and uniform the spherical organization, thereby significantly improving the strength, toughness and fatigue resistance of the material.

[0011] "Fine blanking steel" refers to a steel suitable for fine blanking process. Fine blanking, also known as precision blanking, is a stamping method that can control the accuracy of the cross section, and can effectively avoid the generation of cross section tearing. Unlike ordinary stamping which can process almost any material, fine blanking process has high requirements for the material properties of fine blanking steel, which requires effective transmission of pressure stress between material crystals to suppress cracks, and also requires good plasticity, low yield ratio and high elongation of the material. At the same time, fine blanking parts usually also need high hardness and wear resistance.

[0012] The present application optimizes the chemical composition and microstructure of the cold-rolled fine blanking steel. On the one hand, the content of carbon (C) element is controlled in the range of 0.30%~0.47%, and the addition of appropriate amount of C plays a role in improving the strength of the steel, while also ensuring sufficient strength and hardness after quenching; on the other hand, the content of manganese (Mn) element is controlled in the range of 1.0%~1.5% to improve the hardenability of the steel, and Mn also has the effects of deoxidation and desulfurization, which can prevent thermal embrittlement and improve the forgeability and plasticity of the steel; thirdly, the morphology of carbide is controlled, so that the number ratio of carbide with an aspect ratio less than or equal to 2 (i.e. spherical carbide) is ≥90%, and the average diameter of the spherical carbide is fine adjusted in the range of 0.5 µm~0.8 µm to ensure that the size of the spherical carbide is smaller, and in the 1000 times metallographic image of the cross section of the cold-rolled fine blanking steel, a spherical carbide particle A is randomly selected, and another spherical carbide particle B exists in a circular area with particle A as the center and a radius of 2 µm, and a fan-shaped area with a central angle of 30° is symmetrically distributed along the thickness direction of the steel (such as Figure 1In other words, if the particle B does not fall into the sector, i.e. there is no spheroidal carbide C located in the sector, it can be ensured that the distribution of spheroidal carbides is more dispersed, more uniform and reasonable, and thus the semi-punching limit depth of the steel can be increased, so that the cold-rolled fine-punching steel of the present application has excellent mechanical strength and semi-punching limit depth, and the fine-punched parts obtained thereby also have high hardness.

[0013] The term "semi-punching limit depth" refers to the maximum pressing depth without cracks during the semi-punching process of the part. The greater the semi-punching limit depth, the less likely the steel material is to crack, thereby ensuring the dimensional accuracy and surface quality of the punched part, while improving the overall quality of the product and prolonging the service life of the die.

[0014] The present application researches and finds that if the content of C is lower than 0.30%, the strength and hardness after quenching cannot meet the use requirements, and if the content of C is higher than 0.47%, the size of spheroidal carbides will be affected, resulting in too high strength after quenching, which is not conducive to stamping forming. Mn plays a leading role in the kinetic diffusion mechanism of spheroidal carbide coarsening, and too much Mn will cause spheroidal carbide coarsening, leading to easy cracking during stamping and quenching process, and too high strength after quenching; and when the content of Mn is lower than 1.0%, the hardenability of the steel will be affected, resulting in a decrease in hardness, and the size of the formed spheroidal carbides is too small, which is easy to agglomerate, increases internal stress, and thus increases the risk of deformation and cracking. If the size of spheroidal carbides is too large, greater than 0.8 μm, there will be a large stress concentration at the carbide during the semi-punching process, resulting in a small semi-punching limit depth of the steel; and if the size of spheroidal carbides is too small, less than 0.5 μm, the spacing of spheroidal carbides cannot be controlled under the above chemical composition, which is easy to agglomerate, causing a sharp increase in internal stress, which also affects the semi-punching limit depth of the steel. Similarly, if the spacing of spheroidal carbides does not meet the rules, i.e. in the 1000 times metallographic graph of the cross section of the cold-rolled fine-punching steel, any spheroidal carbide particle A is selected, another spheroidal carbide particle B exists in a circular area with the particle A as the center and a radius of 2 μm, a sector with a central angle of 30° and symmetrically distributed along the thickness direction of the steel is taken in the circular area, and the particle B does not fall into the sector, resulting in a large stress concentration at the spheroidal carbide during the semi-punching process, and cracks are easy to occur at the junction between the region with more spheroidal carbides and the region with less spheroidal carbides, thereby not conducive to improving the semi-punching limit depth of the steel.

[0015] In some optional embodiments, the chemical composition of the cold-rolled fine-punching steel further comprises at least one of the following metal elements: Cr 0%~0.3%; Ni 0%~0.3%; Mo 0%~0.3%; Nb 0%~0.08%; Ti 0.%~0.04%.

[0016] The addition of chromium (Cr) element can improve the strength and hardness of the steel, and Cr is also an element with passivation tendency, and the presence of a certain amount of Cr can improve the corrosion resistance of the steel. However, when the content of Cr is too high (greater than 0.3%), it will increase the tendency of temper brittleness of the steel, resulting in cracking during subsequent heat treatment.

[0017] Nickel (Ni) element can exist in austenite and ferrite in the form of mutual solubility with iron (Fe) element, improving the strength and impact toughness of the steel, and Ni also has the effect of refining grains, and appropriate content of Ni can inhibit the precipitation of proeutectoid ferrite and is beneficial to the nucleation of acicular ferrite, which is beneficial to improving the impact toughness of the weld. However, too high content (greater than 0.3%) of Ni will result in too high strength and quenching cracking.

[0018] The addition of molybdenum (Mo) element can slow down the diffusion of carbon element in ferrite, inhibit the formation of proeutectoid ferrite, and is beneficial to the formation of acicular ferrite structure, which can improve the toughness of the weld while ensuring the strength of the weld. However, too high Mo content (greater than 0.3%) will cause carbon to be difficult to diffuse, resulting in the steel plate being difficult to pass the spheroidizing annealing to achieve a carbon carbide ratio of more than 90%, affecting the plasticity and toughness of the steel.

[0019] The addition of niobium (Nb) element can refine the grains, make the microstructure after quenching finer and more uniform, and also can improve the joint toughness and resist crack propagation. Therefore, the amount of addition needs to be 0.04-0.08wt%. However, too high Nb content (greater than 0.08%) will cause the precipitates to be coarse, and also will form a large amount of stable niobium carbide (NbC) by combining with carbon, consuming too much carbon element and reducing the hardness after quenching.

[0020] The addition of titanium (Ti) element can prevent slab cracking, and also can play the role of grain refinement as precipitates. However, too high Ti content (greater than 0.04%) will consume C element, causing the hardness to decrease after quenching.

[0021] More importantly, the present application research found that the presence of appropriate amount of Cr, Ni, Mo, Nb can also have a certain inhibitory effect on the diffusion of Mn, thereby forming a certain hysteresis effect around the spherical carbide, limiting the size of the spherical carbide. Only under the premise of uniform size distribution of the spherical carbide, can the spacing of the spherical carbide be more uniform.

[0022] It can be understood that the cold-rolled fine-blanking steel according to the present application also contains inevitable impurities, mainly sulfur (S) and phosphorus (P) elements. Among them, P can increase the cold brittleness of the steel and reduce the plasticity of the steel, therefore, the lower the content of impurity P is, the better, however, considering the smelting cost, the mass percentage of P can be controlled to be P≤0.015%. S is easy to form MnS with Mn in the steel, which deteriorates the mechanical properties, hole expansion properties and other forming properties, therefore, the lower the content of S is, the better, in the embodiments of the present application, the mass percentage of S can be controlled to be S≤0.005wt%.

[0023] In some optional embodiments, the chemical composition of the cold-rolled fine-blanking steel is: C 0.34%~0.45%, Mn 1.1%~1.4%, Cr 0.20%~0.25%, Ni 0.20%~0.25%, Mo 0.20%~0.25%, Nb 0.04%~0.06%, Ti 0.02%~0.03%, and the balance is Fe and inevitable impurities. In this way, the semi-punching limit depth of the steel can be further ensured to be large, the hardness is high, the corrosion resistance is good, and the steel also has appropriate plasticity, toughness and strength.

[0024] In the present application, the semi-punching limit depth of the cold-rolled fine-blanking steel is ≥40%.

[0025] Further, in some optional embodiments, the cold-rolled fine-blanking steel also satisfies at least one of the following conditions: the semi-punching limit depth is 60%~75%; the elongation is 21%~28%; the yield strength is 300MPa~400MPa; the tensile strength is 500MPa~600MPa.

[0026] Further, in some optional embodiments, a fine-blanking part is prepared after the cold-rolled fine-blanking steel is precisely stamped, and the surface hardness of the fine-blanking part after heat treatment is ≥45HRC.

[0027] According to the embodiments of the present application, in a second aspect, a manufacturing method of a cold-rolled fine-blanking steel is provided, including the following steps:

[0028] The hot-rolled steel is sequentially subjected to pickling, cold rolling and spheroidizing annealing treatment, wherein:

[0029] The reduction rate of the cold rolling is 40%~60%, and the temperature of the spheroidizing annealing is 680℃~750℃.

[0030] The present application researches and finds that a suitable deformation (reduction of 40%~60%) in the cold rolling process is conducive to the refinement of the microstructure, and forms more uniform and dispersed distribution of spherical carbides after annealing, and the proportion of the number of spherical carbides is ≥90%. If the reduction is insufficient, less than 40%, it is difficult to ensure the high proportion of the number of spherical carbides and the appropriate size of the carbides, affecting the material strength and semi-punch limit depth; if the reduction exceeds 60%, the strength of the steel is too high due to work hardening, which makes it difficult to produce smoothly. Controlling the spheroidizing annealing temperature between 680℃~750℃ can make the carbides uniformly and dispersedly distributed, obtain a high proportion of the number of spherical carbides and uniform microstructure. If the annealing temperature is too high, it will lead to austenitization of the material, precipitate lamellar pearlite, resulting in insufficient proportion of the number of spherical carbides, and affecting the semi-punch limit depth, on the contrary, if the annealing temperature is too low, it will lead to the residual structure of hot rolling cannot be fully spheroidized, resulting in insufficient proportion of the number of spherical carbides, and affecting the semi-punch limit depth.

[0031] In some optional embodiments, the reduction of the cold rolling is 46%~55%, so that the semi-punch limit depth of the steel can be further improved while ensuring a high proportion of the number of spherical carbides and small and uniformly distributed spheroidized structure size.

[0032] In some optional embodiments, the spheroidizing annealing temperature is 690℃~720℃, so that the semi-punch limit depth of the steel can be further improved while ensuring a high proportion of the number of spherical carbides and small and uniformly distributed spheroidized structure size.

[0033] In some optional embodiments, after the spheroidizing annealing, the manufacturing method further includes a flattening treatment, and the flattening elongation is 1%~3%. A suitable flattening elongation can eliminate the yield strength platform, which is conducive to subsequent fine punching processing. If the flattening elongation is insufficient, the material strength will be reduced, but if the flattening elongation is greater than 3%, the strength of the steel will be too high, which will affect the semi-punch limit depth.

[0034] In some optional embodiments, the preparation method of the hot rolled steel includes heating the casting blank to 1230℃~1260℃ and then hot rolling. If the slab temperature is too high, it will cause the surface oxide layer to be too thick and produce surface defects, on the contrary, if the slab temperature is too low, it will cause rolling difficulty. After completing the hot rolling, the coiling is performed at 500℃~600℃. Controlling the coiling temperature after hot rolling in the range of 500℃~600℃ can ensure appropriate strength.

[0035] If the coiling temperature is lower than 500 DEG C, the strength of the steel strip is too high, brittle fracture is easy to occur, and the subsequent stable production is not conducive, and at this time the generated structure is mostly martensite, which is difficult to break during cold rolling, and the semi-punching limit depth is affected. If the coiling temperature is higher than 600 DEG C, serious surface decarburization and internal oxidation will occur, affecting the strength after quenching heat treatment, and at this time the hot rolling structure will form obvious banded morphology, affecting the semi-punching limit depth.

[0036] The technical scheme of the present application has the following advantages:

[0037] The cold rolling fine blanking steel provided by the present application optimizes the chemical composition and microstructure, on the one hand, the C content is controlled in the range of 0.30%~0.47%, the appropriate amount of C is added to improve the strength of the steel, and at the same time, enough strength and hardness after quenching can be ensured; on the other hand, the Mn content is controlled between 1.0%~1.5% to improve the hardenability of the steel, and Mn also has the effect of deoxidation and desulfurization, which can prevent hot brittleness and improve the forgeability and plasticity of the steel; thirdly, the morphology of carbide is controlled, the number ratio of carbide with aspect ratio less than or equal to 2 (i.e. spherical carbide) is greater than or equal to 90%, at the same time, the average diameter of spherical carbide is finely adjusted in the range of 0.5 μm~0.8 μm to ensure that the size of spherical carbide is smaller, and in the 1000 times metallographic graph of the cross section of the cold rolling fine blanking steel, any spherical carbide particle A is selected, another spherical carbide particle B exists in the circular area with particle A as the center and a radius of 2 μm, a sector with a central angle of 30° is taken in the circular area and symmetrically distributed along the thickness direction of the steel, and particle B does not fall into the sector, so that the distribution of spherical carbide is more dispersed and more uniform and reasonable, and the semi-punching limit depth of the steel can be increased, so that the cold rolling fine blanking steel of the present application has excellent mechanical strength and semi-punching limit depth, and the fine blanking part obtained thereby also has high hardness.

[0038] Additional aspects and advantages of the embodiments of the present application will be described and shown in part in the following description, or will be explained by the implementation of the embodiments of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0039] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings needed to be used in the specific embodiments or the description of the prior art. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0040] Figure 1 It is a schematic diagram of the distribution of spherical carbide in the cross section of the cold rolling fine blanking steel of the present application.

[0041] Figure 2Microstructure of the cold-rolled fine-blanking steel prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0042] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0043] The specific experimental steps or conditions not indicated in the following examples and comparative examples can be performed according to the conventional experimental steps described in the literature in the art or the operation or conditions. The reagents or instruments not indicated by the manufacturer are all conventional reagent products that can be obtained by purchase in the market.

[0044] Exemplarily, the cold-rolled fine-blanking steels with chemical compositions A1-A10 and the manufacturing methods B1-B15 of the cold-rolled fine-blanking steels as shown in Tables 1-2 are provided. It can be understood that, based on the cold-rolled fine-blanking steels with the above chemical compositions and the manufacturing methods thereof, those skilled in the art can obtain different embodiments by combining any one of the chemical compositions A1-A10 with any one of the manufacturing methods B1-B15 without creative work. For example, the cold-rolled fine-blanking steel with chemical composition A2 is manufactured by using the manufacturing method B1, or the cold-rolled fine-blanking steel with chemical composition A3 is manufactured by using the manufacturing method B1, or the cold-rolled fine-blanking steel with chemical composition A3 is manufactured by using the manufacturing method B2, etc.

[0045] Table 1 Chemical composition of the cold-rolled fine-blanking steel

[0046]

[0047] In Table 1, " / " indicates that the item does not exist.

[0048] Table 2 Manufacturing method of the cold-rolled fine-blanking steel

[0049]

[0050] The following examples and comparative examples are provided in the present application to more clearly illustrate the technical effects of the present application.

[0051] Example 1

[0052] The chemical composition of the cold-rolled fine-blanking steel in the present embodiment is: C 0.35%, Mn 1.3%, Cr 0.24%, Ni 0.22%, Nb 0.045%, Mo 0.23%, Ti 0.024%, P 0.004%, S 0.003%, and the balance is Fe.

[0053] The manufacturing method comprises the following steps in sequence:

[0054] Smelting and casting: smelting and casting into a blank according to the above-mentioned composition;

[0055] Hot rolling: heating the slab to 1240℃, and performing hot rolling out of the furnace, and coiling at 550℃ after completing the hot rolling;

[0056] Pickling;

[0057] Cold rolling: cold rolling the pickled hot-rolled steel strip, and controlling the reduction rate to be 50%;

[0058] Spheroidizing annealing: spheroidizing annealing is performed in a full-hydrogen cover furnace, and the annealing temperature is 695℃;

[0059] Skin passing: controlling the skin passing elongation to be 1%.

[0060] The chemical compositions of Examples 2-25 and Comparative Examples 1-8 are shown in Table 3. Among them, " / " indicates that the item does not exist.

[0061] The preparation methods of Examples 2-25 and Comparative Examples 1-8 are basically the same as those of Example 1, and the differences are shown in Table 4.

[0062] Table 3 Chemical compositions of cold-rolled fine-blanking steels in each example and comparative example

[0063]

[0064] Table 4 Manufacturing process parameters of cold-rolled fine-blanking steels in each example and comparative example

[0065]

[0066] It should be noted that the skin passing step in Example 25 uses a skin passing force of 2500KN.

[0067] Test example

[0068] 1. Microstructure test

[0069] After inlaying and polishing etching the sample, an electron microscope is used to scan and take pictures of the sample at 20000 times under the secondary electron mode.

[0070] Among them, the microstructure morphology of the cold-rolled fine-blanking steel prepared in Example 1 is as shown in Figure 2 .

[0071] 2. Yield strength, tensile strength and elongation test

[0072] According to GB / T 228.1-2021 test, the tensile specimen size is A80 specimen.

[0073] 3. Half-punch limit depth test

[0074] Prepare a circular blank with a diameter of 80 mm, place the circular blank on the fine-punch die of the press, adjust the pressing depth of the press, set the half-punch pressing depth h to 10%, 20%, 30%, 40%, 50%, 60%, 70%, and 80% of the plate thickness, respectively, take zero gap for the fine-punch die convex and concave dies, complete the half-punch forming operation through the fine-punch die, and obtain half-punch limit depth test samples with different half-punch depths. Observe the part where the crack first appears after the half-punch experiment is completed to determine the area that first fails. Take the maximum depth without cracks as the lower limit of the range of the half-punch limit depth. If the pressing depth is 50% and no cracks appear in the half-punch part, but cracks appear when the pressing depth is 60%, then the half-punch limit depth is between 50% and 60%. The area can be refined and repeated with the half-punch forming operation to determine the final refined half-punch limit depth.

[0075] 4. Surface hardness test

[0076] The test is performed according to the national standard GB / T 230.1-2018 “Metallic Materials - Rockwell Hardness Test - Part 1: Test Method”.

[0077] The test results are shown in Tables 5 and 6. The last column in Table 5 is described as “regular”. In the metallographic image of the cross section of the cold-rolled fine-punch steel, under a 1000x field of view, an optional spherical carbide particle is recorded as particle A. Within a circular area with a radius of 2 μm and the particle A as the center, there is another spherical carbide particle recorded as particle B. Within the circular area, a sector with a central angle of 30° is taken, and the sector is symmetrically distributed along the thickness direction of the cold-rolled fine-punch steel, and the particle B does not fall into the sector.

[0078] Table 5 Microstructure of cold-rolled fine-punch steel

[0079]

[0080] Table 6 Physical properties of cold-rolled fine-punch steel and fine-punch parts

[0081]

[0082] It can be seen from Tables 3-6 that by adjusting the C content in the range of 0.30% to 0.47%, the Mn content in the range of 1.0% to 1.5%, and the number of spheroidal carbides accounts for more than 90%, and by fine-tuning the average diameter of the spheroidal carbides in the range of 0.5 μm to 0.8 μm to ensure that the size of the spheroidal carbides is smaller, and the spacing of the spheroidal carbides meets the rule that in a 1000 times metallographic graph of the cross section of the cold-rolled fine blanking steel, any spheroidal carbide particle A, there is another spheroidal carbide particle B in a circular area with the particle A as the center and a radius of 2 μm, and the particle B does not fall into a sector with a central angle of 30° and symmetrically distributed along the thickness direction of the steel, the distribution of the spheroidal carbides is more dispersed and more uniform and reasonable, and thus the semi-punching limit depth of the steel can be increased, so that the cold-rolled fine blanking steel of the present application has excellent mechanical strength and semi-punching limit depth, and the fine blanking part obtained has high hardness.

[0083] Compared with Example 19, suitable amounts of Cr, Ni, Mo or Nb elements are added in Examples 20-23, which can limit the size of spheroidal carbides, thereby facilitating the increase of the semi-punching limit depth of the material. In Example 24, a suitable amount of Ti element is added, which is beneficial to improve the mechanical strength of the material.

[0084] Compared with Example 16, the chemical composition is the same but the preparation process parameters are different in Example 25, i.e. using the existing process, although a cold-rolled fine blanking steel with smaller spheroidal carbide size and more uniform distribution can also be obtained, but the yield strength is too high and the semi-punching limit depth is low. This shows that by using the preparation process provided by the present application, the semi-punching limit depth and the mechanical strength of the cold-rolled fine blanking steel can be further balanced.

[0085] Compared with Example 16, the C content is too high in Comparative Example 1 and the Mn content is too high in Comparative Example 4, which are beneficial to improve the hardness of the fine blanking part, but will cause the spheroidal carbide particles in the cold-rolled fine blanking steel to coarsen, affecting the semi-punching limit depth, and also leading to the strength of the cold-rolled fine blanking steel being too high, which is not conducive to processing; on the contrary, the C content is too low in Comparative Example 2, the spheroidal carbide particles are too fine, which is not conducive to the mechanical strength and semi-punching limit depth of the cold-rolled fine blanking steel, and also affects the hardness of the fine blanking part, the Mn content is too low in Comparative Example 3, the spheroidal carbide particles are too fine, affecting the elongation and semi-punching limit depth of the cold-rolled fine blanking steel, and the hardness of the fine blanking part also decreases. In Comparative Example 5, the cold-rolled reduction is too small, in Comparative Example 7, the annealing temperature is too low, and in Comparative Example 8, the annealing temperature is too high, which will cause the spheroidal carbide particles in the cold-rolled fine blanking steel to coarsen to varying degrees and the spacing to increase significantly, resulting in a sharp decrease in the semi-punching limit depth. In Comparative Example 6, the cold-rolled reduction is too large, causing the spheroidal carbide particles to be too fine, resulting in a decrease in the semi-punching limit depth, and also leading to the mechanical strength of the material being too high.

[0086] Obviously, the above-mentioned embodiments are only examples for clearly illustrating the present application, but not limitation to the embodiments. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. Here, it is not necessary and also impossible to enumerate all the embodiments. The changes or variations derived from the above are still within the protection scope of the present application.

Claims

1. A cold-rolled fine-blanking steel, characterized in that, The chemical composition of the cold-rolled fine-blanking steel consists of Fe, C and Mn, wherein, based on the mass of the cold-rolled fine-blanking steel, C is 0.30% to 0.47%, and Mn is 1.0% to 1.5%; The cold-rolled fine-blanking steel includes carbides, and the carbides include spherical carbides with an aspect ratio less than or equal to 2; and, based on the number of the carbides, the number of the spherical carbides accounts for more than or equal to 90%. The average diameter of the spherical carbides is 0.5 μm to 0.8 μm. In a metallographic image of a cross section of the cold-rolled fine-blanking steel, under a 1000 times field of view, an optional spherical carbide particle is recorded as particle A, and another spherical carbide particle is recorded as particle B in a circular region with a radius of 2 μm and the particle A as the center; and, a sector with a central angle of 30° is taken in the circular region, the sector is symmetrically distributed along the thickness direction of the cold-rolled fine-blanking steel, and the particle B does not fall into the sector. The cold-rolled fine-blanking steel has a semi-punching limit depth of more than or equal to 40%.

2. The cold-rolled fine-blanking steel according to claim 1, characterized in that, The chemical composition of the cold-rolled fine-blanking steel further includes at least one of the following metal elements: Cr 0~0.3%； Ni 0 to 0.3%; Mo 0 to 0.3%; Nb 0 to 0.08%; Ti 0 to 0.04%.

3. The cold-rolled fine-blanking steel according to claim 2, characterized in that, The chemical composition of the cold-rolled fine-blanking steel is: C 0.34% to 0.45%, Mn 1.1% to 1.4%, Cr 0.20% to 0.25%, Ni 0.20% to 0.25%, Mo 0.20% to 0.25%, Nb 0.04% to 0.06%, Ti 0.02% to 0.03%, and the balance is Fe and unavoidable impurities.

4. A cold rolled and blanking steel according to any one of claims 1 to 3, characterized in that, The cold-rolled fine-blanking steel further satisfies at least one of the following conditions: The semi-punching limit depth is 60% to 75%; The elongation is 21% to 28%; The yield strength is 300 MPa to 400 MPa; The tensile strength is 500 MPa to 600 MPa.

5. A cold rolled and blanking steel according to any one of claims 1 to 3, characterized in that, The cold-rolled fine-blanking steel is subjected to fine-blanking to obtain a fine-blanking part, and the surface hardness of the fine-blanking part after heat treatment is more than or equal to 45 HRC.

6. A method of manufacturing a cold-rolled fine-blanking steel according to any one of claims 1 to 5, characterized in that, The manufacturing method includes the following steps: The hot-rolled steel is sequentially subjected to pickling, cold rolling and spheroidizing annealing treatment, wherein: The cold rolling reduction rate is 40% to 60%, and the spheroidizing annealing temperature is 680°C to 750°C.

7. The method of producing a cold-rolled fine-blanking steel according to claim 6, characterized by, The cold rolling reduction rate is 46% to 55%, and / or the spheroidizing annealing temperature is 690°C to 720°C.

8. The method of producing a cold-rolled fine-blanking steel according to claim 6 or 7, characterized in that, After the spheroidizing annealing, the manufacturing method further includes a flattening treatment, and the flattening elongation is 1% to 3%.

9. The method of producing a cold-rolled and fine-blanked steel sheet according to claim 6 or 7, characterized in that, The manufacturing method of the hot-rolled steel includes heating a casting blank to 1230°C to 1260°C and then hot-rolling, and coiling at 500°C to 600°C after the hot-rolling is completed.

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