Cold-rolled fine blanking steel and manufacturing method therefor

Abstract

Disclosed in the present invention is a cold-rolled fine blanking steel, comprising Fe and inevitable impurities. In addition, the cold-rolled fine blanking steel further comprises the following chemical elements in percentages by mass: 0.26-0.38% of C, 0.60-1.60% of Mn, 0.10-0.20% of Cr, 0.03-0.06% of Nb, 0.10-0.20% of Ni, 0.10-0.20% of Mo, and 0.001-0.005% of B; and the microstructure of the cold-rolled fine blanking steel after spheroidizing annealing is granular pearlite. Correspondingly, further disclosed in the present invention is a method for manufacturing the cold-rolled fine blanking steel, the method comprising the steps of: smelting and continuous casting; hot rolling: controlling the hot rolling coiling temperature to 550-650ºC; pickling and cold rolling: controlling the cooling reduction to be greater than or equal to 40%; spheroidizing annealing; and skin-pass rolling and fine blanking. The present invention can effectively avoid welding defects in fine blanking steel.

Description

A cold-rolled precision stamping steel and its manufacturing method Technical Field

[0001] This invention relates to a type of steel and a method for manufacturing the same, and more particularly to a cold-rolled precision stamping steel and a method for manufacturing the same. Background Technology

[0002] After cold-rolled fine-stamped steel is stamped into fine-stamped parts, it is usually heat-treated to obtain higher strength and hardness for use. As the application fields of fine-stamped products become wider, more and more fine-stamped parts need to be welded with other parts to form more complex parts assemblies.

[0003] For example, Chinese patent document CN116288002A, published on June 23, 2023, discloses a medium-high carbon alloy structural steel for fine stamping and its manufacturing method. The chemical composition and weight percentage content of the steel are as follows: C: 0.39-0.43%, Si: 0.17-0.3%, Mn: 0.7-0.8%, P≤0.015%, S≤0.003%, Alt: 0.02-0.05%, Mo: 0.15-0.25%, Cr: 0.9-1.1%, with the balance being Fe and unavoidable inclusions. This invention, through innovation in composition and process, develops a medium-high carbon alloy structural steel for fine stamping with a hardness of 150-175HV, a yield strength of 800-900MPa, a tensile strength of 900-1000MPa, an elongation of ≥15%, a D-type inclusion level ≤1, a DS-type inclusion level ≤0.5, a center segregation level ≤C0.5, a banded structure level ≤2, a spheroidization level of 3, and a spheroidization rate of ≥95%.

[0004] For example, Chinese patent document CN115478223A, published on December 16, 2022, discloses a cold-rolled precision-stamped steel strip and its preparation method, belonging to the field of high-carbon precision-stamped steel technology. The chemical composition of the cold-rolled precision-stamped steel strip includes: C, Si, Mn, P, S, Al, Cr, Nb, Fe, and impurities from the preparation of the cold-rolled precision-stamped steel strip; by mass fraction, the content of C element is 0.80% to 0.90%, and the content of Nb element is 0.02% to 0.12%. The cold-rolled precision-stamped steel strip has a yield strength of 400 to 500 MPa, a tensile strength of 600 to 700 MPa, an elongation after fracture (A50) of 20% to 30%, a hardness (HV5) of 165-180 HV, a spheroidization rate ≥95%, and an average diameter of spheroids of 0.8 to 1.5 μm.

[0005] However, during the welding process of fine-stamped steel, due to its high strength and the complex shape and varying thickness of the fine-stamped parts, welding defects or joint cracks often occur during the welding process. However, the aforementioned patent documents do not solve the problem of welding defects. Summary of the Invention

[0006] One of the objectives of this invention is to provide a cold-rolled precision stamping steel. By designing the composition and controlling the microstructure of the precision stamping steel, this invention can avoid the problem of weld joint cracking in the subsequent welding process.

[0007] To achieve the above objectives, the present invention provides a cold-rolled precision stamping steel containing Fe and unavoidable impurities, and further containing the following chemical elements in the following mass percentages:

[0008] C: 0.26~0.38%, Mn: 0.60~1.60%, Cr: 0.10~0.20%, Nb: 0.03~0.06%, Ni: 0.10~0.20%, Mo: 0.10~0.20%, B: 0.001~0.005%;

[0009] Its microstructure after spheroidizing annealing is granular pearlite.

[0010] Furthermore, the present invention also provides a cold-rolled precision stamping steel, the chemical element mass percentage of which is:

[0011] C: 0.26–0.38%, Mn: 0.60–1.60%, Cr: 0.10–0.20%, Nb: 0.03–0.06%, Ni: 0.10–0.20%, Mo: 0.10–0.20%, B: 0.001–0.005%; balance Fe and unavoidable impurities.

[0012] In some embodiments, the present invention provides a cold-rolled, spheroidized annealed steel containing Fe and unavoidable impurities, and further containing the following chemical elements in the following mass percentages: C: 0.26–0.38%, Mn: 0.60–1.60%, Cr: 0.10–0.20%, Nb: 0.03–0.06%, Ni: 0.10–0.20%, Mo: 0.10–0.20%, B: 0.001–0.005%; its microstructure is granular pearlite. Further, the chemical element mass percentages of the cold-rolled, spheroidized annealed steel of the present invention are as follows: C: 0.26–0.38%, Mn: 0.60–1.60%, Cr: 0.10–0.20%, Nb: 0.03–0.06%, Ni: 0.10–0.20%, Mo: 0.10–0.20%, B: 0.001–0.005%; the balance being Fe and unavoidable impurities. In some embodiments, the spheroidization rate of the cold-rolled, spheroidized annealed steel is >90%. In some embodiments, the tensile strength of the cold-rolled, spheroidized annealed steel is 480–550 MPa, and the elongation is ≥25%.

[0013] In some embodiments, the present invention also provides a quenched steel containing Fe and unavoidable impurities, and further containing the following chemical elements in the following mass percentages: C: 0.26–0.38%, Mn: 0.60–1.60%, Cr: 0.10–0.20%, Nb: 0.03–0.06%, Ni: 0.10–0.20%, Mo: 0.10–0.20%, B: 0.001–0.005%. Further, the quenched steel of the present invention has the following chemical element mass percentages: C: 0.26–0.38%, Mn: 0.60–1.60%, Cr: 0.10–0.20%, Nb: 0.03–0.06%, Ni: 0.10–0.20%, Mo: 0.10–0.20%, B: 0.001–0.005%; the balance being Fe and unavoidable impurities. In some implementations, the tensile strength of the quenched steel is >1800MPa.

[0014] In this article, cold-rolled, spheroidized annealed steel refers to steel obtained after cold rolling and spheroidizing annealing; cold-rolled fine-blanking steel refers to steel obtained by leveling and fine-blanking of the cold-rolled, spheroidized annealed steel; and quenched steel refers to steel obtained by quenching the cold-rolled fine-blanking steel. It should be understood that leveling and fine-blanking do not change the microstructure of the steel. Therefore, the microstructure of the cold-rolled, spheroidized annealed steel of this invention is granular pearlite, and the microstructure of the cold-rolled fine-blanking steel obtained after leveling and fine-blanking is still granular pearlite. Although fine-blanking may cause some plastic deformation of the microstructure at some steps, the microstructure type remains granular pearlite. Furthermore, the properties of the steel do not change after leveling; fine-blanking is a stamping deformation process, and the properties of the unbent parts remain essentially unchanged, except for the properties of the bent parts, which may change.

[0015] In some embodiments, the present invention also provides a welded component comprising the hardened steel described in any embodiment herein, such as welded from the hardened steel described herein to other steels. In some embodiments, the welding is laser welding, as described herein. In some embodiments, the welded component is obtained by laser welding of two or more hardened steels described in any embodiment herein (as components to be welded); preferably, the welded component has the following characteristics: at a welding heat input of 50–150 KJ / m, its weld residual stress is less than 2700 MPa (e.g., between 2500 and 2690 MPa), and the average grain diameter of the weld is less than 5 μm (e.g., 3.0–5.0 μm); preferably, the weld of the welded component is free of cracks.

[0016] This invention, through the controlled content of C, Mn, Cr, Ni, Mo, Nb, and B, ensures that the carbide precipitates in the steel, after spheroidizing annealing, are uniformly and diffusely distributed with a spheroidization rate >90%, facilitating subsequent fine blanking processes. The rational design of the composition guarantees the material's excellent uniform plastic deformation capacity and ensures good hardenability and quenching hardness during subsequent heat treatment. Simultaneously, it refines the grain structure of the welded joint and prevents post-weld cracking.

[0017] Specifically, the design principles of each chemical element in the steel of this invention are as follows:

[0018] C: In the steel described in this invention, carbon (C) is a crucial solid solution element. Appropriate C addition enhances the steel's strength and ensures sufficient strength and hardness after quenching. The C content in this invention is designed to be 0.26–0.38 wt%. This is because a C mass percentage below 0.26% cannot guarantee sufficient hardness and strength after annealing to meet the required specifications. A C mass percentage above 0.38% would result in excessively high steel strength and excessively high hardness during subsequent quenching, making welding cracking more likely. In some embodiments, the C content in this invention ranges from 0.30–0.38%.

[0019] Mn: In the steel described in this invention, increasing Mn can increase the strength and hardness of the steel. Mn has deoxidizing and desulfurizing effects by forming MnS. In addition, it can prevent hot brittleness. Therefore, Mn can improve the forgeability and plasticity of steel, eliminate the hot brittleness effects of sulfur and oxygen on steel, and improve weldability. However, too little Mn will lead to insufficient strength after final heat treatment, while too much Mn will lead to quenching cracking and is also prone to cracking of welded joints. Based on these considerations, this invention controls the amount of Mn added to be 0.6 to 1.6 wt%. In some embodiments, this invention controls the amount of Mn added to be 1.0 to 1.6 wt%.

[0020] Cr: In this invention, the addition of Cr can improve strength and hardness. Furthermore, Cr is an element with a passivating tendency; therefore, adding a certain amount of Cr to steel will give the steel a certain degree of corrosion resistance during subsequent processing and facilitate the formation of an oxide film on the steel surface. However, too little Cr will lead to insufficient strength after final heat treatment, while too much Cr can increase the steel's temper brittleness tendency, causing cracking during subsequent heat treatment. Based on these considerations, this invention controls the amount of Cr added to be 0.1–0.2 wt%.

[0021] Nb: The addition of Nb can refine the grains, resulting in a finer and more uniform microstructure after quenching. It can also precipitate fine NbC in the post-weld microstructure, further improving joint toughness and inhibiting crack propagation. However, in this invention, too little Nb will not refine the grains, while too much Nb will cause coarse precipitates, and excessive NbC will consume too much carbon, leading to insufficient strength of the steel after quenching heat treatment. Based on these considerations, the amount of Nb added in this invention is controlled at 0.03–0.06 wt%.

[0022] Ni: Ni can exist in austenite and ferrite in a miscible form with Fe, improving strength and impact toughness. Simultaneously, Ni also has a grain-refining effect, inhibiting the leaching of proeutectoid ferrite within a certain range and promoting the formation of acicular ferrite nucleation, which is beneficial for improving the impact toughness of welds. Furthermore, in this invention, too low a Ni content will not achieve the corresponding grain-refining and impact-toughness improvement effects, while too high a Ni content will lead to excessively high strength and quenching cracking. Based on these considerations, the Ni addition amount is controlled at 0.1–0.2 wt% in this invention.

[0023] Mo: In this invention, the addition of Mo can slow down the diffusion of carbon in ferrite, inhibit the formation of proeutectoid ferrite, and promote the formation of acicular ferrite structure, thereby improving the weld toughness while ensuring weld strength. Too low an addition will not achieve the above effects, but too high a Mo addition will hinder carbon diffusion, making it difficult for the steel to achieve a spheroidization rate of over 90% through spheroidizing annealing. Therefore, this invention controls the Mo addition amount to 0.1–0.2 wt%.

[0024] B: The addition of a small amount of element B can improve the hardenability of steel during quenching. In order to effectively improve hardenability, the B content in this invention must be above 0.001 wt%. However, when its content exceeds 0.005 wt%, the effect of improving hardenability reaches saturation. Therefore, the B content in this invention is controlled between 0.001 and 0.005 wt%.

[0025] Furthermore, in the cold-rolled fine-stamped steel described in this invention, among unavoidable impurities, P ≤ 0.015% and S ≤ 0.01%.

[0026] The unavoidable impurities in this invention are mainly S and P, and their content should be as low as possible when the process conditions allow.

[0027] Phosphorus (P) increases the cold brittleness and reduces the plasticity of the steel strip, and also adversely affects its weldability. Therefore, in some embodiments, its content is controlled to be ≤0.015 wt%. In other embodiments, the content of P is controlled to be ≤0.010%.

[0028] Sulfur (S) in steel deteriorates mechanical properties, hole-expanding properties, and other formability properties; therefore, in some embodiments, its content can be controlled to ≤0.01 wt%. In some embodiments, the S content is controlled to ≤0.005%.

[0029] Furthermore, the spheroidization rate of the cold-rolled precision stamping steel described in this invention is ≥90%.

[0030] Furthermore, the cold-rolled precision stamping steel of the present invention has a tensile strength of 480-550 MPa and an elongation of ≥25% after spheroidizing annealing.

[0031] Furthermore, the tensile strength of the cold-rolled precision stamping steel described in this invention after quenching heat treatment is >1800MPa (e.g., 1850~2050MPa).

[0032] Furthermore, the cold-rolled precision stamping steel of the present invention, under the condition of welding heat input of 50 to 150 KJ / m, has a weld residual stress of less than 2700 MPa (e.g., between 2500 and 2690 MPa) and a weld grain average diameter of less than 5 μm (e.g., 3.0 to 5.0 μm).

[0033] Another object of the present invention is to provide a method for manufacturing cold-rolled precision stamping steel, which can be used to obtain the cold-rolled precision stamping steel described in the present invention.

[0034] To achieve the above objectives, the present invention provides a method for manufacturing cold-rolled precision stamping steel, comprising the following steps:

[0035] Smelting and continuous casting;

[0036] Hot rolling: Control the hot rolling coiling temperature to 550~650℃;

[0037] Pickling and cold rolling: Control the cold rolling reduction to ≥40%;

[0038] Spheroidizing annealing;

[0039] Leveling and fine blanking.

[0040] In the manufacturing method described in this invention, a coiling temperature of 550-650°C is used to match the steel composition. Since the steel composition contains a certain amount of Ni and Mo, if a coiling temperature below 550°C is used, the steel strip will have excessively high strength and be prone to brittle fracture; if the coiling temperature is above 650°C, severe surface decarburization will occur, affecting the strength after subsequent quenching heat treatment.

[0041] In the manufacturing method described in this invention, the cold rolling reduction rate is controlled to be ≥40% because a suitable deformation amount is beneficial for refining the microstructure and forming more uniformly dispersed carbides after annealing, ensuring a spheroidization rate >90%. If the reduction is less than 40%, it is difficult to guarantee a spheroidization rate >90%.

[0042] Furthermore, in the hot rolling step of the manufacturing method described in this invention, the slab heating temperature is controlled to be 1200–1250°C.

[0043] Furthermore, in the cold rolling step of the manufacturing method described in this invention, the cold rolling reduction can be further controlled to be 40-60%.

[0044] In these implementations, if the reduction exceeds 60%, the strip strength may become too high due to work hardening, which may increase production difficulty.

[0045] Furthermore, in the spheroidizing annealing step of the manufacturing method described in this invention, a full hydrogen bell-type furnace is used for heat preservation annealing, and the annealing temperature is 660-730°C.

[0046] Furthermore, in the leveling step of the manufacturing method described in this invention, the leveling elongation is controlled to be 1-4%.

[0047] In some embodiments of the present invention, when the flattening elongation is further limited to the above-mentioned range, it is considered that a suitable flattening elongation can eliminate the yield strength plateau, which is more beneficial to subsequent fine blanking. Insufficient flattening elongation may have poor effect, while excessive flattening elongation may lead to an increase in the strength of the strip.

[0048] Furthermore, in the manufacturing method described in this invention, a step quenching is included after the leveling and fine blanking steps. In some embodiments, the quenching step includes: heating the fine-blanked steel to above the material Ac3 temperature, holding it at that temperature for a period of time (e.g., 10–60 min), and then cooling it in air or oil at a rate >20°C / s (e.g., 25–100°C / s).

[0049] In some embodiments of the present invention, quenching heat treatment can further improve the strength of the fine-stamped parts obtained after the fine-stamping step.

[0050] Furthermore, in the manufacturing method described in this invention, a laser welding step is included after the quenching step.

[0051] Furthermore, in the manufacturing method described in this invention, during the laser welding step, at a welding speed of 20 to 80 mm / min, the oscillation amplitude of the laser beam in the weld width direction is 1.0 to 3.0 mm.

[0052] In the laser welding step of this invention, under the welding speed condition of 20-80 mm / min, the oscillation amplitude of the laser beam in the weld width direction is controlled to be 1.0-3.0 mm because: an appropriate oscillation amplitude can increase the weld width, play a certain role in stirring the weld, thereby refining the grains and reducing the residual stress of the weld, so that the residual stress of the weld is lower than 2700 MPa. If it is lower than the lower limit of the oscillation amplitude, it will cause heat input concentration and insufficient stirring effect, resulting in the residual stress of the weld being higher than 2700 MPa. If the oscillation amplitude of the welding exceeds 3 mm, it will cause insufficient welding heat input, and the weld is prone to defects such as incomplete penetration or bubbles.

[0053] In some implementations, the laser power in the laser welding is 3 to 10 kW.

[0054] The cold-rolled precision stamping steel and its manufacturing method described in this invention have the following beneficial effects:

[0055] The cold-rolled precision stamping steel of this invention, through the design of its composition and process, obtains a microstructure of granular pearlite with a spheroidization rate of ≥90%, thus avoiding weld joint cracking in subsequent welding processes.

[0056] In some embodiments, the cold-rolled fine-stamping steel of the present invention has a tensile strength of 480-550 MPa and an elongation of ≥25% after spheroidizing annealing.

[0057] In some embodiments, the tensile strength of the cold-rolled precision stamping steel described in this invention after quenching heat treatment is >1800MPa.

[0058] In some embodiments, the manufacturing method of the present invention, by controlling the laser welding process parameters, makes the residual stress of the weld less than 2700MPa, effectively avoiding weld cracking. Attached Figure Description

[0059] Figure 1 shows a schematic diagram of laser welding in the manufacturing method described in this invention.

[0060] Figure 2 shows a metallographic image of the weld obtained in Embodiment 1 of the present invention.

[0061] Figure 3 shows the metallographic image of the weld obtained in Comparative Example B1. Detailed Implementation

[0062] The following will provide further explanation and description of the cold-rolled precision stamping steel and its manufacturing method according to the present invention with reference to specific embodiments. However, such explanation and description do not constitute an improper limitation on the technical solution of the present invention.

[0063] The cold-rolled precision-stamped steels of Examples 1-6 and Comparative Examples B1-B6 of the present invention were all prepared using the following steps:

[0064] (1) Smelting and continuous casting.

[0065] (2) Hot rolling: First, heat the slab to 1200-1250℃, then take it out of the furnace for hot rolling, and after hot rolling, roll it at 550-650℃.

[0066] (3) Pickling and cold rolling: The reduction rate of cold rolling is controlled at 40%-60%.

[0067] (4) Spheroidizing annealing: All-hydrogen bell furnace is used for heat preservation annealing, and the annealing temperature range is 660-730℃.

[0068] (5) Leveling: Control the leveling elongation rate to 1-4%.

[0069] (6) Fine blanking to obtain fine blanked parts.

[0070] (7) Quenching: Heat the material to above Ac3 temperature and hold for 20 minutes, then cool it rapidly in air or oil at a rate of >20℃ / s.

[0071] (8) Laser welding: Using a 5kW laser welding equipment, under the condition of a welding speed of 20 to 80 mm / min, as shown in Figure 1, the first fine blanking part 1 and the second fine blanking part 2 obtained based on the above steps (1)-(7) are laser welded together. The laser beam 3 travels along the length direction of the weld and swings in the width direction, so that it forms the path shown by the arrow in Figure 3. The swing amplitude of the laser beam 3 in the weld width W direction is 1.0 to 3.0 mm.

[0072] It should be noted that the chemical element composition and related process design of Examples 1-6 all meet the requirements of the design specifications of this invention, while the chemical element composition and related process design of Comparative Examples B1-B6 do not meet the requirements of the design specifications of this invention.

[0073] Table 1 lists the mass percentage of each chemical element in the cold-rolled fine-stamping steels prepared in Examples 1-6 and Comparative Examples B1-B6.

[0074] Table 1. (wt%, balance Fe and other unavoidable impurities besides P and S)

[0075] Table 2 lists the specific process parameters used in each step of Examples 1-6 and Comparative Examples B1-B6.

[0076] Table 2.

[0077] Samples were taken from each embodiment and comparative example after step (4) to prepare specimens. Metallographic analysis was performed on the cross-section of the specimens. The spheroidization rate was tested according to GB / T 38770-2020, and the test results are listed in Table 3.

[0078] In addition, samples were taken and test specimens were made for each embodiment and comparative example after step (8). The grain size of the weld structure was measured in accordance with GB 6394-2002, and the test results are listed in Table 3.

[0079] Table 3.

[0080] As can be seen from Table 3, the microstructure matrix of Examples 1-6 of the present invention is granular pearlite, and the spheroidization rate is ≥90%.

[0081] Samples were taken from Examples 1-6 and Comparative Examples B1-B6 after steps (4) and (7) respectively, and specimens were manufactured to test their relevant mechanical properties. The results of the mechanical property tests are listed in Table 4.

[0082] The relevant mechanical property testing methods are as follows:

[0083] Tensile test: The tensile strength and elongation of each embodiment and comparative example were tested at room temperature according to GB / T 228.1-2010 standard.

[0084] In addition, samples were taken from Examples 1-6 and Comparative Examples B1-B6 after step (8) and samples were manufactured to test their weld performance. The measured weld performance results are also listed in Table 4.

[0085] The weld performance testing method is as follows:

[0086] The tensile test method for welded joints shall be performed at room temperature in accordance with GB / T 2651.

[0087] Table 4.

[0088] As can be seen from Table 4, the residual stress of the welds in all embodiments of the present invention is below 2700 MPa, and no cracking occurs in the welds. In contrast, the residual stress of the welds in Comparative Examples B1-B6 is above 2700 MPa, and all welds crack.

[0089] Furthermore, Figure 2 shows a metallographic image of the weld obtained in Embodiment 1 of the present invention. As can be seen from Figure 2, the weld has excellent microstructure and no cracking has occurred.

[0090] Figure 3 shows the metallographic image of the weld obtained in Comparative Example B1. As can be seen from Figure 3, the weld has cracked.

[0091] It should be noted that the combination of the technical features in this case is not limited to the combination methods described in the claims of this case or the combination methods described in the specific embodiments. All technical features described in this case can be freely combined or combined in any way, unless they contradict each other.

[0092] It should also be noted that the embodiments listed above are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made thereto are those that can be directly derived or easily conceived by those skilled in the art from the content disclosed in the present invention, and should all fall within the protection scope of the present invention.

Claims

1. A cold-rolled precision stamping steel, containing Fe and unavoidable impurities, characterized in that, It also contains the following chemical elements in the following mass percentages: C: 0.26~0.38%, Mn: 0.60~1.60%, Cr: 0.10~0.20%, Nb: 0.03~0.06%, Ni: 0.10~0.20%, Mo: 0.10~0.20%, B: 0.001~0.005%; Its microstructure is granular pearlite.

2. The cold-rolled precision stamping steel as described in claim 1, characterized in that, Its chemical element mass percentage content is: C: 0.26–0.38%, Mn: 0.60–1.60%, Cr: 0.10–0.20%, Nb: 0.03–0.06%, Ni: 0.10–0.20%, Mo: 0.10–0.20%, B: 0.001–0.005%; balance Fe and unavoidable impurities.

3. The cold-rolled precision stamping steel as described in claim 1 or 2, characterized in that, In unavoidable impurities, P ≤ 0.015%, S ≤ 0.01%.

4. The cold-rolled precision stamping steel as described in claim 1 or 2, characterized in that, Its spheroidization rate after spheroidizing annealing is ≥90%; and / or, its tensile strength after spheroidizing annealing is 480~550MPa, and its elongation is >25%.

5. The cold-rolled precision stamping steel as described in claim 1 or 2, characterized in that, Its tensile strength after quenching heat treatment is >1800MPa; and / or, under the condition of welding heat input of 50 to 150KJ / m, its weld residual stress is less than 2700MPa, and the average grain diameter of the weld is less than 5μm.

6. A cold-rolled, spheroidized annealed steel containing Fe and unavoidable impurities, and further containing the following chemical elements in the following mass percentages: C: 0.26–0.38%, Mn: 0.60–1.60%, Cr: 0.10–0.20%, Nb: 0.03–0.06%, Ni: 0.10–0.20%, Mo: 0.10–0.20%, B: 0.001–0.005%; its microstructure is granular pearlite; preferably, the chemical elements of the cold-rolled, spheroidized annealed steel are... The percentage content is: C: 0.26-0.38%, Mn: 0.60-1.60%, Cr: 0.10-0.20%, Nb: 0.03-0.06%, Ni: 0.10-0.20%, Mo: 0.10-0.20%, B: 0.001-0.005%; the balance is Fe and unavoidable impurities; preferably, the spheroidization rate of the cold-rolled, spheroidized annealed steel is >90%; preferably, the tensile strength of the cold-rolled, spheroidized annealed steel is 480-550 MPa, and the elongation is ≥25%.

7. A quenched steel, obtained by quenching cold-rolled fine-stamping steel according to any one of claims 1-5, wherein the tensile strength of the quenched steel is >1800MPa, preferably 1850-2050MPa.

8. A welded component comprising the quenched steel of claim 7; preferably, the welded component is made by laser welding of two or more quenched steels of claim 7; preferably, the welded component has the following characteristics: under a welding heat input of 50-150 KJ / m, its weld residual stress is less than 2700 MPa (e.g., between 2500-2690 MPa), and the average grain diameter of the weld is less than 5 μm (e.g., 3.0-5.0 μm); preferably, the weld of the welded component is free from cracking.

9. The method for manufacturing cold-rolled precision stamping steel according to any one of claims 1-5, characterized in that, It includes the following steps: Smelting and continuous casting; Hot rolling: Control the hot rolling coiling temperature to 550~650℃; Pickling and cold rolling: Control the cooling reduction to ≥40%; Spheroidizing annealing; Leveling and fine blanking.

10. The manufacturing method as described in claim 9, characterized in that, The method has one or more of the following characteristics: (1) In the hot rolling step, the slab heating temperature is controlled at 1200~1250℃; (2) In the cold rolling step, the cooling reduction is controlled to be 40-60%; (3) In the spheroidizing annealing step, a full-hydrogen bell-type furnace is used for heat preservation annealing, and the annealing temperature is 660–730℃; and (4) During the leveling step, the leveling elongation rate is controlled to be 1-4%.

11. The method for manufacturing quenched steel according to claim 7, characterized in that, The method includes the step of quenching the cold-rolled fine-stamping steel according to any one of claims 1-5.

12. The manufacturing method as described in claim 11, characterized in that, The quenching process includes: heating the cold-rolled fine-stamped steel to above the material Ac3 temperature, holding it at that temperature for a period of time (e.g., 10-60 min), and then cooling it in air or oil at a rate of >20℃ / s.

13. The method for manufacturing the welded component according to claim 8, characterized in that, The method includes the step of performing laser welding on two or more steel components for welding.

14. The manufacturing method as described in claim 13, characterized in that, In the laser welding process, the welding speed is 20-80 mm / min, and the oscillation amplitude of the laser beam in the weld width direction is 1.0-3.0 mm.

15. The manufacturing method as described in claim 13, characterized in that, In the laser welding step, the laser power is 3 to 10 kW.

Images