Cold-rolled boron-containing CH steel capable of resisting secondary machining brittleness and production method of cold-rolled boron-containing CH steel

Abstract

The invention relates to cold-rolled boron-containing CH steel capable of resisting secondary processing brittleness and a production method thereof. The steel comprises the following chemical components in percentage by weight: 0.10%-0.20% of C, 1.0%-2.0% of Mn, 0.1%-1.0% of Si, 0.6%-6.0% of Al, 0.02%-0.80% of Cr, 0.02%-0.80% of Mo, 0.0005%-0.02% of B, less than or equal to 0.01% of P, less than or equal to 0.01% of S, less than or equal to 0.005% of N, 0.005%-0.50% of Mg, 0.01%-0.50% of Ti and the balance of Fe and inevitable impurities, wherein Al / Si is more than or equal to 5 and less than or equal to 20; and the balance of Fe and inevitable impurities. The cold-rolled boron-containing CH steel capable of resisting secondary processing embrittlement has the characteristic of resisting secondary processing embrittlement while meeting basic performance indexes such as high strength and high formability of CH steel products, the yield strength of the cold-rolled boron-containing CH steel capable of resisting secondary processing embrittlement is larger than or equal to 600 MPa, the tensile strength is larger than or equal to 780 MPa, the A80 percentage elongation after fracture is larger than or equal to 10.0%, the hole expansion rate is larger than or equal to 60%, and the density is 6.5-7.5 g / cm < 3 >; and the secondary processing brittle transition temperature is less than or equal to-150 DEG C.

Description

Technical Field

[0001] The invention belongs to the technical field of cold-rolled steel, and in particular relates to a secondary processing brittle cold-rolled boron-containing CH steel and a production method thereof. Background Art

[0002] In recent years, as the automotive industry has increasingly higher requirements for material forming performance indicators, traditional dual-phase steels have been unable to meet the requirements of complex stamping parts for high drawability, and TRIP steels have been limited in their widespread use due to the high production costs caused by their high alloy content. CH steels, which emerged as the times require, introduce a certain amount of residual austenite into traditional dual-phase steels, and through the TRIP effect, the materials exhibit excellent forming properties, which can significantly overcome the shortcomings of DP steels and TRIP steels in the above-mentioned application processes. CH steels have become one of the current research hotspots in the field of automotive steel development.

[0003] Secondary processing brittleness (SWE) refers to the low-temperature brittleness characteristics of automotive cold-rolled steel sheets after stamping, which are manifested by their ability to withstand impact loads at low temperatures. When the secondary processing brittle transition temperature (SWET) is too high, it will pose a hidden danger to the safety of passenger cars, especially in areas with cold winter climates and large temperature differences between day and night. There is a great risk of automotive sheets being broken by low-temperature impact during use after stamping. How to effectively solve the secondary processing brittleness problem of automotive steel products has become a hot topic in the research and development of automotive steel products.

[0004] At the same time, under the background of "dual carbon", the steel industry is actively promoting energy conservation, environmental protection and green transformation and development. How to develop green, low-carbon and high-strength automotive products has become a research hotspot for major steel suppliers. Based on the above research status, it is urgent to solve the problems of poor forming performance and secondary processing brittleness of automotive high-strength steel, and at the same time adapt to the green and low-carbon product design of automotive high-strength steel under the background of dual carbon.

[0005] Patent document CN103160738A discloses a low-cost boron-containing steel and a manufacturing method thereof, wherein the main chemical components are: C: 0.05% to 0.08%, Si: 0.10% to 0.25%, Mn: 1.60% to 1.80%, Als: 0.03% to 0.045%, Ti: 0.032% to 0.045%, B: 0.0052% to 0.009%, P≤0.025%, S≤0.015%, O≤0.0015%, N≤0.0025%, and the rest is Fe and unavoidable impurities. The invention produces boron-containing steel with low cost characteristics, but the product of the invention is a hot-rolled product, and the secondary processing brittleness of the product is not considered.

[0006] Therefore, the present invention aims to develop a cold-rolled boron-containing CH steel that is resistant to secondary processing brittleness and a production method thereof. The invention realizes the low-carbon, green and lightweight design and development of automotive high-strength steel with a short-process, low-cost process path and an extremely cost-reducing alloy design, while taking into account the personalized needs of high-strength steel for resistance to secondary processing brittleness, high plasticity and high formability, providing a reliable technical solution for the majority of automobile manufacturers and steel companies. Summary of the invention

[0007] In view of the problems existing in the above prior art, the object of the present invention is to provide a cold-rolled boron-containing CH steel resistant to secondary processing brittleness and a production method thereof, which not only meets the basic performance indicators of CH steel products such as high strength and high formability, but also has the characteristics of resisting secondary processing brittleness. The cold-rolled boron-containing CH steel resistant to secondary processing brittleness of the present invention has a yield strength of ≥600MPa, a tensile strength of ≥780MPa, an A80 elongation after fracture of ≥10.0%, a hole expansion rate of ≥60%, and a density of 6.5-7.5g / cm 3 ; Secondary processing brittle transition temperature ≤-150℃.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] A secondary processing brittle cold-rolled boron-containing CH steel is provided. The chemical components of the steel are as follows by weight percentage: C: 0.10%-0.20%, Mn: 1.0%-2.0%, Si: 0.1%-1.0%, Al: 0.6%-6.0%, Cr: 0.02%-0.80%, Mo: 0.02%-0.80%, B: 0.0005%-0.02%, P≤0.01%, S≤0.01%, N≤0.005%, Mg: 0.005%-0.50%, Ti: 0.01%-0.50%, and 5≤Al / Si≤20; the balance is Fe and unavoidable impurities.

[0010] The reasons for the composition design of the present invention are as follows:

[0011] C: Carbon element ensures the strength requirement of steel through solid solution strengthening. A sufficient amount of carbon element helps stabilize austenite, thereby improving the formability of steel. If the content of C element is too low, the mechanical properties of the steel in the present invention cannot be obtained; if the content is too high, the steel will become brittle and there is a risk of hydrogen-induced delayed fracture. Therefore, in the present invention, the content of C element is controlled to 0.10% to 0.20%.

[0012] Mn: Manganese is an austenite stabilizing element in steel. It can expand the austenite phase area and reduce the critical quenching rate of steel. At the same time, it can also refine the grains, which helps to improve the strength by solid solution strengthening. If the Mn content is too low, the supercooled austenite is not stable enough, which reduces the processing properties such as plasticity and toughness of the steel plate; if the Mn content is too high, the welding performance of the steel plate will deteriorate and the production cost will increase, which is not conducive to industrial production. Therefore, in the present invention, the Mn content is controlled to 1.0% to 2.0%.

[0013] Si: Silicon has a certain solid solution strengthening effect in ferrite, ensuring that the steel has sufficient strength. At the same time, Si can also inhibit the decomposition of residual austenite and the precipitation of carbides, reducing inclusions in the steel. In the present invention, the Si element is used in combination with the Al element, and the design concept of replacing silicon with aluminum can significantly improve the surface quality of the steel. If the Si element content is too low, it will not play a strengthening role; if the Si element content is too high, it will reduce the surface quality and welding performance of the steel plate. Therefore, in the present invention, the content of the Si element is controlled to 0.1% to 1.0%.

[0014] Al: The density of aluminum is much lower than that of Fe. Adding an appropriate amount of Al to steel can significantly reduce the density of steel, which is conducive to the lightweight development of steel. At the same time, Al has an antioxidant effect. Adding it in combination with Si can effectively improve the surface quality of steel, which is conducive to the design of one steel for multiple uses. In addition, Al can also inhibit the decomposition of residual austenite and the precipitation of carbides, and accelerate the transformation of bainite to improve the coordinated deformation ability. In addition, aluminum can inhibit the decomposition of residual austenite and the precipitation of carbides, and accelerate the transformation of bainite to improve the coordinated deformation ability. If the Al content is too high, it will not only increase the production cost, but also cause difficulties in continuous casting production. When the aluminum content is too low, the low-density design of the material cannot be achieved. Therefore, in the present invention, the range of the Al content is controlled within 0.6% to 6.0%. The present invention adopts a design concept of partially replacing Si with Al, and realizes the synergistic effect of Al and Si by controlling the ratio of 5.0≤Al / Si≤20.0, which can expand the austenite phase transformation temperature range, accelerate the bainite transformation in the over-aging stage to improve the coordinated deformation ability of the product, and significantly inhibit the decomposition of residual austenite and the precipitation of carbides, thereby achieving the beneficial effect of significantly improving the ductility and formability of the CH steel plate.

[0015] Cr: Chromium can increase the hardenability of steel to ensure the strength of steel and stabilize the retained austenite. Too low Cr content will affect the hardenability of steel, while too high Cr content will increase production costs. Therefore, the content of Cr in the present invention is controlled within the range of 0.02% to 0.80%.

[0016] Mo: Mo is a strengthening element in steel, which helps to stabilize the residual austenite and has a significant effect on improving the hardenability of steel. Mo and Ti can form a large number of TiMoC precipitates, which is conducive to making the diffuse hydrogen in the steel dispersed and reducing the aggregation of diffuse hydrogen, so that both high strength and hydrogen embrittlement resistance can be taken into account. The present invention controls the content of Mo element in the range of 0.02% to 0.80%.

[0017] B: Adding boron to steel can significantly improve its hardenability. Due to the small radius of boron atoms, it gathers in the grain boundary in the form of free state in steel, which has a good effect of strengthening the grain boundary, enhancing the grain boundary energy, reducing the concentration of internal stress, thereby reducing the possibility of cracks, and significantly improving the low-temperature toughness of steel materials. In addition, boron can easily combine with sulfides and oxides to organize their further growth, and make the shape of these inclusions tend to be fine spherical and evenly distributed on the grain boundary. When the boron content exceeds 0.02%, the hardenability decreases and the brittleness increases due to the presence of borides in the steel. Therefore, in the present invention, the content of B element is controlled within the range of 0.0005% to 0.02%.

[0018] P: P is a harmful element in steel, which is very easy to segregate to the grain boundary and seriously reduce the plasticity and deformation performance of the steel. The lower its content, the better. Considering the cost, the content of P in the present invention is controlled to P≤0.01%.

[0019] S: S is a harmful element in steel. Sulfur and manganese are easily combined to form MnS inclusions. After rolling and deformation, the transverse properties of the material will be significantly reduced, which seriously affects the formability of the steel. The lower the content, the better. Considering the cost, the content of S in the present invention is controlled to S≤0.01%.

[0020] N: N element easily reacts with Ti to precipitate large TiN particles, which act as crack sources during deformation and are detrimental to the anti-hydrogen embrittlement performance. Therefore, the N element content in the steel must be strictly controlled. The present invention controls the N content to N≤0.005%.

[0021] Mg: Magnesium is a good deoxidizer, desulfurizer and spheroidizer in steel. Mg can reduce the number of inclusions in steel, reduce their size, make their distribution uniform and improve their morphology. A small amount of magnesium can improve the carbide size and distribution of DH steel, promote the fine and uniform carbide particles, and also help to achieve low-density material design. In order to control production costs, the Mg content is controlled at 0.005% to 0.50% in the present invention.

[0022] Ti: A microalloying element forms compounds with carbon and nitrogen, which helps to delay the recrystallization of the material during hot rolling, refines the grain size, and significantly improves the strength and toughness of the material and inhibits crack propagation. In the present invention, the Ti element content is controlled at 0.01% to 0.50%.

[0023] The microstructure of the CH steel includes ferrite, bainite and retained austenite; the percentage by volume is: 40% to 60% ferrite, 30% to 50% bainite and 3% to 12% retained austenite; the retained austenite in the steel is in a film-like form, the grain size is between 0.05 and 0.50 μm, and the film-like retained austenite is mainly distributed between bainite laths.

[0024] The CH steel has a yield strength of ≥600 MPa, a tensile strength of ≥780 MPa, an A80 elongation after fracture of ≥10.0%, a hole expansion rate of ≥60%, and a density of 6.5-7.5 g / cm 3 ; Secondary processing brittle transition temperature ≤ -150℃; Meets the requirements of ultra-high strength automotive steel for resistance to secondary processing brittleness, high strength and high plasticity, and excellent forming performance.

[0025] A production method of secondary processing brittle cold-rolled boron-containing CH steel comprises converter smelting, medium-thin slab continuous casting and rolling, pickling cold rolling, continuous annealing or alloying hot-dip galvanizing.

[0026] The converter smelting comprises: the present invention selects 40wt% to 100wt% scrap steel as raw material, smelts through a converter, obtains molten steel that meets the following composition requirements by weight percentage: C: 0.10% to 0.20%, Mn: 1.0% to 2.0%, Si: 0.1% to 1.0%, Al: 0.6% to 6.0%, Cr: 0.02% to 0.80%, Mo: 0.02% to 0.80%, B: 0.0005% to 0.02%, P≤0.01%, S≤0.01%, N≤0.005%, Mg: 0.005% to 0.50%, Ti: 0.01% to 0.50%, and 5≤Al / Si≤20; the remainder is Fe and unavoidable impurities. The temperature of the molten steel is between 1600 and 1750°C.

[0027] The continuous casting and rolling of medium-thin slabs comprises: using a special protective slag for high-aluminum steel, preferably a Li 2 The mass percentage of O is 0.5% to 10.0%; the casting temperature is 1530 to 1600°C, the casting speed is 1.0 to 5.5 m / min, the continuous casting billet thickness is between 60 and 115 mm, the starting rolling temperature is between 1000 and 1150°C, the final rolling temperature is above 900°C, and the coiling temperature is between 600 and 700°C.

[0028] The thickness specification of the steel plate after hot rolling is 2.0~4.5mm. The microstructure of the hot rolled steel plate includes ferrite, pearlite, bainite, a small amount of cementite and impurities; the volume percentage of each microstructure is: ferrite 30%~60%, pearlite 20%~50%, bainite 5%~20%, cementite and impurities 1%~5%.

[0029] The pickling cold rolling: the hot rolled steel coil is subjected to acid solution to remove the surface iron oxide scale before cold rolling, and the cold rolling reduction rate is 45% to 70%. If the reduction rate is too high, the deformation resistance will be too large, and it will be difficult to roll to the target thickness; if the reduction rate is too low, the elongation of the cold rolled steel plate will decrease.

[0030] After pickling and cold rolling, the steel sheet is continuously annealed or alloyed and hot-dip galvanized.

[0031] The continuous annealing includes controlling the belt speed at 60-180 m / min, the furnace temperature of the soaking section is 760-880°C, the soaking time is 10-600s, the slow cooling outlet temperature is 700-760°C, the rapid cooling rate is between 15-30°C / s, the rapid cooling temperature is between 350-550°C, the aging temperature is 350-550°C, and the aging time is 60-1000s. The soaking temperature is 760-880°C. If the annealing temperature is too high, the ductility of the steel will be reduced due to the complete austenitization and insufficient ferrite ratio; if the annealing temperature is too low, the soft phase ferrite ratio of the final material is too high, which will greatly reduce the strength of the material. The soaking time is 10-600s. If the annealing time is too long, the steel plate will have coarse grains. If the annealing time is too short, the steel plate will not have time to complete the annealing and recrystallization process, resulting in a decrease in the elongation of the steel plate.

[0032] The alloying hot-dip galvanizing includes alloying hot-dip galvanizing: the strip speed is controlled at 60-180 m / min, the annealing temperature is 770-870°C, the annealing time is between 30-300s, the dew point is controlled at -20--10°C, the slow cooling outlet temperature is 680-760°C, the rapid cooling rate is between 15-30°C / s, the rapid cooling outlet temperature is between 480-600°C, the galvanizing temperature is 450-470°C, after the galvanizing is completed, the strip is first air-knife cooled to 400-420°C, and then alloying treatment is performed, the alloying temperature is 500-550°C, and the alloying holding time is 5-60s. The annealing temperature is 760-880°C. If the annealing temperature is too high, the ductility of the steel will be reduced due to the complete austenitization and insufficient ferrite ratio; if the annealing temperature is too low, the soft phase ferrite ratio of the final material is too high, which will greatly reduce the strength of the material. The annealing time is 30 to 300 seconds. If the annealing time is too long, the grains of the steel plate will be coarse. If the annealing time is too short, the steel plate will not have enough time to complete the annealing and recrystallization process, resulting in a decrease in the elongation of the steel plate.

[0033] It also includes skin finishing: the skin finishing process adopts rolling force control, the rolling force is controlled at 1000~3500kN, and the rolling tension is 500~2000kN.

[0034] The microstructure of the steel plate obtained after the above process includes ferrite, bainite and retained austenite; the volume percentages are: 40% to 60% ferrite, 30% to 50% bainite, and 3% to 12% retained austenite; the retained austenite is in a film-like form, with a grain size between 0.05 and 0.50 μm, and the film-like retained austenite is mainly distributed between the bainite laths.

[0035] The above method can obtain a cold-rolled boron-containing CH steel resistant to secondary processing: yield strength ≥600MPa, tensile strength ≥780MPa, A80 elongation ≥10.0%, hole expansion rate ≥60%, density 6.5-7.5g / cm 3 ; Secondary processing brittle transition temperature ≤ -150℃; Meets the requirements of ultra-high strength automotive steel for resistance to secondary processing brittleness, high strength and high plasticity, and excellent forming performance.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1) The chemical composition of the steel material of the present invention mainly includes C, Mn, Al, Si and B as main elements, and the initial cost is relatively low.

[0038] 2) The present invention adopts a new short-process, low-cost production process of "large proportion of scrap steel + converter smelting + continuous casting and rolling of medium and thin slabs", which can greatly reduce carbon emissions and save energy consumption.

[0039] 3) The cold-rolled boron-containing CH steel resistant to secondary processing brittleness produced by the present invention is a conventional cold-rolled complex phase steel (CP) with a certain proportion of retained austenite added, and under the action of transformation induced plasticity (TRIP) effect, the characteristics of high strength, high plasticity and formability are achieved.

[0040] 4) The cold-rolled boron-containing CH steel produced by the present invention that resists secondary processing brittleness can add a large amount of aluminum elements to achieve low density of high-strength steel, and adding a large amount of boron elements can greatly improve the secondary processing brittleness of high-strength steel, meeting the personalized needs of automobile lightweight and service resistance;

[0041] 5) The cold-rolled boron-containing CH steel sheet produced by the present invention can realize a set of alloy systems to meet the two diversified product requirements of continuous annealing and alloyed hot-dip galvanizing due to the special design of composition and process, that is, one steel can be used for multiple purposes, which can significantly save product manufacturing costs;

[0042] 6) The cold-rolled boron-containing CH steel produced by the present invention can achieve a yield strength of ≥600MPa, a tensile strength of ≥780MPa, an A80 elongation after fracture of ≥10.0%, a hole expansion rate of ≥60%, and a density of 6.5-7.5g / cm 3 ; Excellent performance of secondary processing brittle transition temperature ≤-150℃. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is the engineering stress-strain curve diagram of Example 1-1. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the specific implementation methods of the present invention are further described below in conjunction with embodiments. The following embodiments are used to specifically illustrate the contents of the present invention. These embodiments are only general descriptions of the contents of the present invention and do not limit the contents of the present invention.

[0045] Table 1 lists the chemical composition of the example steel, Table 2 lists the continuous casting and rolling process parameters and hot rolling structure of the example steel, Table 3 lists the process parameters of continuous annealing of the example steel, Table 4 gives the process parameters of alloying hot-dip galvanizing of the example steel, and Table 5 gives the mechanical properties 2 of the example steel. Figure 1 It is the engineering stress-strain curve diagram of Example 1-1.

[0046] Table 1 Composition of steel according to the present invention (wt%)

[0047]

[0048]

[0049] Table 2 Main process parameters and hot rolling structure of steel smelting, continuous casting and rolling according to the embodiment of the present invention

[0050]

[0051] Table 3 Main process parameters of continuous annealing of steel in the embodiment of the present invention

[0052]

[0053] Table 4 Main process parameters of hot-dip galvanizing of steel in the embodiment of the present invention

[0054]

[0055]

[0056] Table 5 Properties of steel according to the present invention

[0057]

[0058] It can be seen from the above embodiments that the alloy composition, smelting, continuous casting and rolling, pickling cold rolling and continuous annealing process of the present invention can produce a secondary processing brittle cold-rolled boron-containing CH steel with a yield strength of ≥600MPa, a tensile strength of ≥780MPa, an A80 elongation after fracture of ≥10.0%, a hole expansion rate of ≥60%, and a density of 6.5-7.5g / cm3 ; Excellent performance of secondary processing brittle transition temperature ≤ -150℃; Meet the personalized needs of low cost, high hole expansion and resistance to secondary processing brittleness of automobiles.

Claims

1. A cold-rolled boron-containing CH steel resistant to secondary processing brittleness, characterized in that: The chemical composition of the steel is calculated by weight percentage: C: 0.10% ~ 0.20%, Mn: 1.0% ~ 2.0%, Si: 0.1% ~ 1.0%, Al: 0.6% ~ 6.0%, Cr: 0.02 ~ 0.80%, Mo: 0.02 ~ 0.80%, B: 0.0005% ~ 0.02%, P ≤ 0.01%, S ≤ 0.01%, N ≤ 0.005%, Mg: 0.005% ~ 0.50%, Ti: 0.01% ~ 0.50%, and 5 ≤ Al / Si ≤ 20; the balance is Fe and unavoidable impurities.

2. The cold-rolled boron-containing CH steel resistant to secondary processing brittleness according to claim 1, characterized in that: The microstructure of the CH steel includes ferrite, bainite and retained austenite; the volume percentages are: 40% to 60% ferrite, 30% to 50% bainite and 3% to 12% retained austenite; the retained austenite is in a film-like form with a grain size between 0.05 and 0.50 μm, and the film-like retained austenite is mainly distributed between the bainite laths.

3. The cold-rolled boron-containing CH steel resistant to secondary processing brittleness according to claim 1, characterized in that: The CH steel has a yield strength of ≥600 MPa, a tensile strength of ≥780 MPa, an A80 elongation after fracture of ≥10.0%, a hole expansion rate of ≥60%, and a density of 6.5-7.5 g / cm 3 ; Secondary processing brittle transition temperature ≤-150℃.

4. A method for producing cold-rolled boron-containing CH steel resistant to secondary processing brittleness according to any one of claims 1 to 3, characterized in that: The process includes converter smelting, continuous casting and rolling of medium and thin slabs, pickling and cold rolling, continuous annealing or alloying hot-dip galvanizing. The continuous annealing includes a soaking section furnace temperature of 760-880°C, a soaking time of 10-600s, a slow cooling outlet temperature of 700-760°C, a rapid cooling rate of 15-30°C / s, a rapid cooling temperature of 350-550°C, an aging temperature of 350-550°C, and an aging time of 60-1000s.

5. The method for producing a cold-rolled boron-containing CH steel resistant to secondary processing brittleness according to claim 4, characterized in that: The alloyed hot-dip galvanizing includes alloyed hot-dip galvanizing: annealing temperature is 770-870°C, annealing time is between 30-300s, dew point is controlled at -20--10°C, slow cooling outlet temperature is 680-760°C, rapid cooling rate is between 15-30°C / s, rapid cooling outlet temperature is between 480-600°C, galvanizing temperature is 450-470°C, after galvanizing, the strip is first air-knife cooled to 400-420°C, and then alloying treatment is carried out, the alloying temperature is 500-550°C, and the alloying holding time is 5-60s.

6. The method for producing a cold-rolled boron-containing CH steel resistant to secondary processing brittleness according to claim 4, characterized in that: The continuous casting and rolling of medium-thin slabs includes: a casting temperature of 1530-1600°C, a casting machine pulling speed of 1.0-5.5 m / min, a continuous casting slab thickness of 60-115 mm, a starting rolling temperature of 1000-1150°C, a final rolling temperature of more than 900°C, and a coiling temperature of 600-700°C.

7. The method for producing a cold-rolled boron-containing CH steel resistant to secondary processing brittleness according to claim 6, characterized in that: The thickness specification of the steel plate after hot rolling is 2.0~4.5mm. The microstructure of the hot rolled steel plate includes ferrite, pearlite, bainite, a small amount of cementite and impurities; the volume percentage of each microstructure is: ferrite 30%~60%, pearlite 20%~50%, bainite 5%~20%, cementite and impurities 1%~5%.

8. The method for producing a cold-rolled boron-containing CH steel resistant to secondary processing brittleness according to claim 4, characterized in that: The converter smelting comprises: selecting 40wt% to 100wt% scrap steel as raw material, and the temperature of molten steel is between 1600 and 1750°C.

9. The method for producing a cold-rolled boron-containing CH steel resistant to secondary processing brittleness according to claim 4, characterized in that: The pickling cold rolling reduction rate is 45% to 70%.

10. The method for producing a cold-rolled boron-containing CH steel resistant to secondary processing brittleness according to claim 4, characterized in that: It also includes skin pass: the skin pass rolling force is controlled at 1000~3500kN, and the rolling tension is 500~2000kN.

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