Production method of secondary processing brittle coating boron-containing steel and coating boron-containing steel

Abstract

The invention relates to a production method of coating boron-containing steel capable of resisting secondary processing brittleness and the coating boron-containing steel. The steel comprises the following chemical components in percentage by weight: 0.005%-0.10% of C, 1.01%-2.0% of Mn, 0.01%-0.2% of Si, 0.02%-2.0% of Al, 0.0005%-0.02% of B, less than or equal to 0.005% of P, less than or equal to 0.005% of S, less than or equal to 0.005% of N, less than or equal to 0.10% of Nb, 0.002%-0.20% of Ti and the balance of Fe and inevitable impurities. The boron-containing steel plate has the characteristic of resisting secondary processing embrittlement while meeting basic performance indexes of products, the tensile strength of the boron-containing steel plate is larger than or equal to 270 MPa, the A80 percentage elongation after fracture is larger than or equal to 35.0%, the hole expansion rate is larger than or equal to 60%, and the density is 6.5-7.5 g / cm < 3 >; the secondary processing brittle transition temperature is less than or equal to-100 DEG C; and the personalized requirements of low cost and secondary processing brittleness resistance of the automobile are met.

Description

Technical Field

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

[0002] With the rapid development of automobile lightweighting, automobile manufacturers have gradually increased their requirements for the comprehensive performance of steel products. Among them, the secondary processing brittleness of automobile steel plates has been highly valued by automobile manufacturers and steel manufacturers. Secondary processing performance. Secondary processing brittleness (SWE) refers to the low-temperature brittleness characteristics of automobile cold-rolled steel plates 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 bring hidden dangers to the safety of passenger cars. Especially for areas with cold winter climates and large temperature differences between day and night, there is a great risk of automobile plates being broken by low-temperature impact during use after stamping. How to effectively solve the secondary processing brittleness problem of automobile steel products has become a hot spot in the research and development of automobile steel products. Studies have found that adding boron to steel can significantly improve its hardenability. Boron can easily combine with sulfides and oxides to organize their further growth, and make the shape of these inclusions tend to be small spherical and evenly distributed on the grain boundaries, which enhances the grain boundary energy and reduces the concentration of internal stress, thereby reducing the possibility of cracks. It can significantly improve the low-temperature toughness of steel materials. In addition, adding a small amount of boron to steel can save a large amount of precious elements. The country encourages the development of boron-containing steel and provides certain preferential treatment in export tax rebate policies.

[0003] In view of the above research status, this patent aims to develop a production method for a boron-containing steel with a coating that is resistant to secondary processing brittleness. The boron-containing steel with a coating that meets the basic performance indicators of the product also has the characteristics of resistance to secondary processing embrittlement. This invention technology can provide a reliable technical solution for steel companies and automobile manufacturers in solving the secondary processing embrittlement of automobile steel. Summary of the invention

[0004] The purpose of the present invention is to provide a production method of a secondary processing brittle coating boron-containing steel and a coated boron-containing steel, which not only meets the basic performance indicators of the product, but also has the characteristics of resisting secondary processing brittleness. The tensile strength of the boron-containing steel plate of the present invention is ≥270 MPa, A 80 Elongation after fracture ≥35.0%, hole expansion rate ≥60%, density 6.5~7.5g / cm 3 ; Secondary processing brittle transition temperature ≤ -100℃; Meet the personalized needs of low cost and resistance to secondary processing brittleness of automobiles.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A production method of secondary processing resistant brittle coated boron-containing steel comprises converter smelting, medium and thin slab continuous casting and rolling, pickling and cold rolling, coating process and skin pass, wherein the coating process is continuous hot-dip galvanizing or zinc-aluminum-magnesium process, or alloy hot-dip galvanizing process; the continuous hot-dip galvanizing or zinc-aluminum-magnesium process specifically comprises: the belt speed is controlled at 60-150 m / min, the annealing temperature is between 760-880° C., the dew point temperature is controlled between -20--10° C., the annealing time is between 30-300 s, the slow cooling outlet temperature is 680-750° C., the rapid cooling rate is greater than 40° C. / s, the rapid cooling outlet temperature is 150-250° C., the galvanizing temperature is 450-470° C., after the galvanizing is completed, the strip is firstly cooled to 400-420° C. by an air knife, and then cooled by air, and the temperature of the cooling tower top roller is controlled at 250-300° C.

[0007] The zinc plating solution contains 0.16wt% to 0.25wt% Al, the rest is Zn and unavoidable impurities, and the weight of the zinc layer per unit area is 60 to 200g / cm 2 The zinc-aluminum-magnesium plating solution contains 2.0wt% to 10.0wt% Al, 1.0wt% to 5.0wt% Mg, 0.001wt% to 0.1wt% Si, and the rest is Zn and unavoidable impurities. The weight of the zinc-aluminum-magnesium coating per unit area is 50 to 200g / cm 2 .

[0008] The alloying hot-dip galvanizing process specifically includes: the strip speed is controlled at 60-150 m / min, the annealing temperature is 770-870°C, the annealing time is between 30 and 300 s, the dew point is controlled at -20--10°C, the slow cooling outlet temperature is 680-750°C, the rapid cooling rate is greater than 40°C / s, the rapid cooling outlet temperature is between 150 and 250°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 470-530°C, and the alloying holding time is 5-60s.

[0009] The cold-rolled steel sheet of the present invention can be coated using three coating processes: continuous hot-dip galvanizing, continuous hot-dip galvanizing aluminum-magnesium and alloyed hot-dip galvanizing.

[0010] The converter smelting uses 40wt% to 80wt% scrap steel as raw material, and smelting is carried out in an electric furnace, with the temperature of the molten steel being between 1600 and 1750°C.

[0011] The medium-thin slab continuous casting and rolling comprises: using a special protective slag for high-aluminum steel (Li 2The casting process is carried out at a temperature of 1530-1600°C, a casting speed of 1.0-5.5 m / min, and a continuous casting billet thickness of 60-115 mm; the starting rolling temperature is between 1000-1150°C, the final rolling temperature is above 900°C, and the coiling temperature is between 600-700°C. The hot rolled coil thickness specification is 2.0-4.5 mm.

[0012] The hot rolled microstructure consists of 30% to 60% by volume of ferrite, 20% to 50% by volume of pearlite, 5% to 20% by volume of bainite, and 1% to 5% by volume of cementite; the total is 100%.

[0013] 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 sheet will decrease, and the thickness of the finished product after cold rolling is 1.0mm to 2.0mm.

[0014] The skin finishing process adopts rolling force control, the rolling force is controlled at 1000-3500 kN, and the rolling tension is 500-2000 kN.

[0015] A boron-containing steel with a brittle coating and resistance to secondary processing. The chemical components of the steel are as follows by weight: C: 0.005%-0.10%, Mn: 1.01%-2.0%, Si: 0.01%-0.2%, Al: 0.02%-2.0%, B: 0.0005%-0.02%, P≤0.005%, S≤0.005%, N≤0.005%, Nb≤0.10%, Ti: 0.002%-0.20%, and the balance is Fe and unavoidable impurities.

[0016] The reasons for the alloy design of the present invention are as follows:

[0017] 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 delayed fracture. Therefore, in the present invention, the content of C element is controlled to 0.005% to 0.10%.

[0018] 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 1.01% to 2.0%.

[0019] 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. If the Si content is too low, it will not play a strengthening role; if the Si content is too high, the surface quality and welding performance of the steel plate will be reduced. Therefore, in the present invention, the content of Si is controlled to 0.01% to 0.2%.

[0020] Al: Aluminum helps deoxidize molten steel. It can also inhibit the decomposition of residual austenite and the precipitation of carbides, and accelerate bainite transformation to improve the coordinated deformation ability. Too high Al content will not only increase production costs, but also cause difficulties in continuous casting production. Therefore, in the present invention, the Al content is controlled within the range of 0.02% to 2.0%.

[0021] B: Adding boron to steel can significantly improve its hardenability. 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 boundaries, thereby 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. 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%.

[0022] P: P is a harmful element in steel, which seriously reduces the plasticity and deformation performance of steel. The lower its content, the better. Considering the cost, the content of P in the present invention is controlled to P≤0.005%.

[0023] S: S is a harmful element in steel, which seriously affects the formability of steel. The lower its content, the better. Considering the cost, the content of S in the present invention is controlled to S≤0.005%.

[0024] N: N is a harmful element in steel, which seriously affects the comprehensive performance of steel. The lower its content, the better. Considering the cost, the content of N in the present invention is controlled to N≤0.005%.

[0025] Nb: The microalloying element Nb improves the comprehensive performance of the material by strengthening the grain size. No more than 0.1% Nb can be added as appropriate according to the actual situation. In order to control the production cost, Nb microalloying element may not be added.

[0026] Ti: A small amount of Ti element can refine the grain size, and the precipitates can pin dislocations to delay the expansion of crack sources at the weld and significantly improve the strength and toughness of the material. In the present invention, the Ti element content is controlled at 0.002% to 0.20%.

[0027] Through the above method, the tensile strength can be ≥270MPa, A 80 Elongation after fracture ≥35.0%, hole expansion rate ≥60%, density 6.5~7.5g / cm 3 ; Boron-containing steel with secondary processing brittle coating and secondary processing brittle transition temperature ≤ -100℃ meets the personalized needs of automobiles for low cost and resistance to secondary processing brittleness.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1) The boron-containing steel with secondary processing resistance brittle coating produced by the present invention is designed by optimizing the alloy composition, with C, Mn, Si, Al, and B as the main elements, without adding precious metal elements such as Cr, Mo, Nb, and V, and the alloy cost is very low.

[0030] 2) The boron-containing steel with brittle coating resistant to secondary processing produced by the present invention adopts the production process of converter smelting - medium-thin slab continuous casting and rolling - pickling and cold rolling - continuous hot-dip galvanizing, and the industrial production of boron-containing steel for automobiles can be realized on the traditional production line without adding new production equipment; however, in the present invention, the medium-thin slab continuous casting and rolling process is used to replace the original continuous casting-hot delivery and hot loading-heating-hot rolling-coiling process, which significantly shortens the process flow of boron-containing steel and stabilizes the production, and greatly reduces the product manufacturing cost.

[0031] 3) The boron-containing steel with secondary processing resistance brittle coating produced by the present invention can achieve low density of high-strength steel by adding a large amount of aluminum elements, and can greatly improve the secondary processing brittleness of high-strength steel by adding a large amount of boron elements, thereby meeting the personalized needs of automobile lightweight and service resistance.

[0032] 4) The boron-containing steel with secondary processing resistance brittle coating produced by the present invention can realize a set of alloy system to meet the three diversified product requirements of continuous hot-dip galvanizing, continuous hot-dip galvanized aluminum-magnesium and alloyed hot-dip galvanizing due to the special design of composition and process, that is, one steel has multiple uses, which can significantly save product manufacturing costs.

[0033] (5) The tensile strength of the boron-containing steel with brittle coating resistant to secondary processing produced by the present invention is ≥270MPa, A 80Elongation after fracture ≥35.0%, hole expansion rate ≥60%, density 6.5~7.5g / cm 3 The secondary processing brittle transition temperature is ≤-100℃, which ensures the short process and low cost of this product while taking into account the advantages of anti-secondary processing brittleness and high hole expansion. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a typical engineering stress-strain curve diagram of Example 1-1. DETAILED DESCRIPTION

[0035] 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.

[0036] Table 1 lists the chemical composition of the example steel; Table 2 lists the continuous casting and rolling process parameters of the example steel; Table 3 lists the main process parameters of continuous hot-dip galvanizing of the example steel of the present invention; Table 4 lists the main process parameters of continuous hot-dip galvanizing of aluminum-magnesium of the example steel of the present invention; Table 5 lists the main process parameters of alloying hot-dip galvanizing of the example steel of the present invention; Table 6 lists the properties of the example steel of the present invention; Figure 1 This is the engineering stress-strain curve of Example 1-1.

[0037] Table 1 Chemical composition of the example steel, wt%

[0038] Example C Mn Si Al B P S N Nb Ti 1 0.005 1.08 0.11 1.21 0.0018 0.005 0.001 0.001 0.011 0.032 2 0.008 1.63 0.09 0.54 0.0006 0.002 0.002 0.003 0.023 0.005 3 0.005 1.92 0.14 1.63 0.0017 0.003 0.003 0.001 0.039 0.023 4 0.006 1.25 0.16 0.55 0.0024 0.004 0.001 0.002 0.008 0.046 5 0.009 1.43 0.07 1.46 0.0013 0.003 0.002 0.003 0.041 0.014 6 0.007 1.19 0.14 0.37 0.0032 0.002 0.003 0.002 0.019 0.026

[0039] Table 2 Smelting and continuous casting and rolling process parameters and hot rolling structure of example steel

[0040]

[0041]

[0042] Table 3 Main process parameters of continuous hot-dip galvanizing of steel in the embodiment of the present invention

[0043]

[0044] Table 4 Main process parameters of continuous hot-dip galvanizing aluminum-magnesium steel in the embodiment of the present invention

[0045]

[0046] Table 5 Main process parameters of hot-dip galvanizing of steel in the embodiment of the present invention

[0047]

[0048] Table 6 Properties of steel according to the present invention

[0049]

[0050] It can be seen from the above embodiments that the alloy composition, smelting, continuous casting and rolling, pickling and cold rolling and continuous coating process of the present invention can produce a secondary processing brittle coating boron-containing steel with a tensile strength of ≥270MPa. 80 Elongation after fracture ≥35.0%, hole expansion rate ≥60%, density 6.5~7.5g / cm 3 ; Secondary processing brittle transition temperature ≤ -100℃; Meet the personalized needs of low cost, high hole expansion and resistance to secondary processing brittleness of automobiles.

Claims

1. A method for producing a boron-containing steel with a brittle coating resistant to secondary processing, characterized in that: It includes converter smelting, medium and thin slab continuous casting and rolling, pickling and cold rolling, coating process, and skin pass. The coating process is continuous hot-dip galvanizing or zinc-aluminum-magnesium process, or alloy hot-dip galvanizing process; the continuous hot-dip galvanizing or zinc-aluminum-magnesium process specifically includes: the belt speed is controlled at 60-150m / min, the annealing temperature is between 760-880℃, the dew point temperature is controlled between -20 and -10℃, the annealing time is between 30 and 300s, the slow cooling outlet temperature is 680-750℃, the rapid cooling rate is greater than 40℃ / s, the rapid cooling outlet temperature is 150-250℃, the galvanizing temperature is 450-470℃, after the galvanizing is completed, the strip is first cooled to 400-420℃ by air knife, and then cooled by air cooling, and the temperature of the cooling tower top roller is controlled at 250-300℃; The alloying hot-dip galvanizing process specifically includes: the strip speed is controlled at 60-150 m / min, the annealing temperature is 770-870°C, the annealing time is between 30 and 300 s, the dew point is controlled at -20--10°C, the slow cooling outlet temperature is 680-750°C, the rapid cooling rate is greater than 40°C / s, the rapid cooling outlet temperature is between 150 and 250°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 470-530°C, and the alloying holding time is 5-60s.

2. The method for producing a secondary processing resistant brittle coated boron-containing steel according to claim 1, characterized in that: The zinc plating solution contains 0.16wt% to 0.25wt% Al, the rest is Zn and unavoidable impurities, and the weight of the zinc layer per unit area is 60 to 200g / cm 2 The zinc-aluminum-magnesium plating solution contains 2.0wt% to 10.0wt% Al, 1.0wt% to 5.0wt% Mg, 0.001wt% to 0.1wt% Si, and the rest is Zn and unavoidable impurities. The weight of the zinc-aluminum-magnesium coating per unit area is 50 to 200g / cm 2 .

3. The method for producing a secondary processing resistant brittle coated boron-containing steel according to claim 1, characterized in that: The converter smelting uses 40wt% to 80wt% scrap steel as raw material, and the temperature of the molten steel is between 1600 and 1750°C.

4. The method for producing a secondary processing resistant brittle coated boron-containing steel according to claim 1, 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 1.0-5.5m / min, a continuous casting slab thickness of 60-115mm; 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.

5. The method for producing a secondary processing resistant brittle coated boron-containing steel according to claim 4, characterized in that: The hot rolled microstructure consists of 30% to 60% by volume of ferrite, 20% to 50% by volume of pearlite, 5% to 20% by volume of bainite, and 1% to 5% by volume of cementite; the total is 100%.

6. The method for producing a secondary processing resistant brittle coated boron-containing steel according to claim 1, characterized in that: The pickling cold rolling reduction rate is 45% to 70%.

7. The method for producing a secondary processing resistant brittle coated boron-containing steel according to claim 1, characterized in that: The skin-pass rolling force is controlled at 1000-3500 kN, and the rolling tension is 500-2000 kN.

8. A boron-containing steel with a brittle coating resistant to secondary processing produced by the method for producing boron-containing steel with a brittle coating resistant to secondary processing as claimed in any one of claims 1 to 7, characterized in that: The chemical composition of the steel by weight percentage is: C: 0.005% ~ 0.10%, Mn: 1.01% ~ 2.0%, Si: 0.01% ~ 0.2%, Al: 0.02% ~ 2.0%, B: 0.0005% ~ 0.02%, P ≤ 0.005%, S ≤ 0.005%, N ≤ 0.005%, Nb ≤ 0.10%, Ti: 0.002% ~ 0.20%, and the balance is Fe and unavoidable impurities.

9. The boron-containing steel with brittle coating resistant to secondary processing according to claim 8, characterized in that: The tensile strength of the boron-containing steel is ≥270MPa. 80 Elongation after fracture ≥35.0%, hole expansion rate ≥60%, density 6.5~7.5g / cm 3 ; Secondary processing brittle transition temperature ≤-100℃.

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