Design method for performance of low-cost automobile beam steel B510L product

Abstract

The invention relates to a low-cost automobile beam steel B510L product performance design method which comprises the following steps: step 1, component design, step 2, converter smelting of molten steel, tapping and entering a refining area, step 3, LF furnace refining of the molten steel, step 4, continuous casting of the refined molten steel to produce a plate blank, step 5, continuous casting of the plate blank, and step 6, casting of the plate blank to obtain the low-cost automobile beam steel B510L product performance. The method comprises the following steps of (1) heating a continuous casting slab, (2) carrying out rough rolling and finish rolling on the slab after heating, and (3) carrying out low-temperature coiling to enable titanium to form a solid solution in steel so as to achieve the purpose of stable performance.

Description

Technical Field

[0001] The invention relates to a design method, in particular to a design method for product performance of low-cost automobile beam steel B510L, belonging to the technical field of steelmaking. Background Art

[0002] B510L automobile beam steel is a conventional automobile structural steel product with relatively high demand in the current market. However, due to fierce homogeneous competition, its cost is forced to continuously reduce while maintaining the same quality requirements in order to occupy the market. Therefore, it is necessary to develop low-cost B510L automobile beam steel products.

[0003] The so-called low-cost automobile beam steel products refer to reducing the high-priced alloy manganese content, eliminating the high-priced niobium alloy, and increasing the cheap titanium alloy in large quantities. However, there is a problem with such automobile beam steel B510L products, that is, its performance fluctuates greatly (mainly the tensile strength performance index fluctuates greatly), fluctuating between 468-644MPa, and the fluctuation range exceeds the required range (510-630MPa), causing such low-cost automobile beam steel products to often fail to meet the performance requirements. The reason is that titanium alloys are elements with strong metallic activity and are easy to form titanium compounds in steel, such as titanium nitride and titanium carbide. When the coil is coiled, due to the high coiling temperature (540-600℃, target value 580℃) and uneven cooling of the coil, the size of the titanium compounds formed is different, which causes the performance of the steel to fluctuate greatly. Therefore, it is necessary to solve the problem of large fluctuations in tensile strength performance. The solution is to optimize the slab heating process and the coiling temperature of the hot-rolled coil so that titanium does not form titanium compounds in the steel, but is dissolved in the steel matrix. Since titanium compounds of different sizes are not formed, the uniformity of the steel structure is improved, thereby stabilizing the performance.

[0004] The existing technology achieves low cost as follows:

[0005] Patent No. CN201010181559.0, low niobium strengthening production process for automobile beam steel. The method is to increase the manganese content (Mn1.40%-1.55%), reduce the niobium content (0.008%-0.014%), and control the hot rolling reduction. The coiling temperature is controlled at (600~610±20℃) and 580~590±20℃ respectively due to different rolling thicknesses. These measures are different from this patent.

[0006] Patent No. CN201210511575.0, a method for producing hot-rolled steel plates for automobile beams at low cost. The method solves the problems of high cost of Nb and V micro-alloying and difficulty in controlling transverse cracks in the ingot during the steelmaking process by innovating the steelmaking and rolling processes. This is different from the problem of high cost and large performance fluctuations solved by this technology. Summary of the invention

[0007] The present invention aims at the problems existing in the prior art and provides a method for designing the performance of low-cost automobile beam steel B510L product. The technical solution makes full use of low-cost titanium alloy to replace manganese and eliminates niobium, so as to achieve the purpose of developing low-cost B510L automobile beam steel products.

[0008] In order to achieve the above object, the technical solution of the present invention is as follows: a design method for the performance of a low-cost automobile beam steel B510L product,

[0009] To achieve stable performance of this low-cost automobile beam steel product, its composition is as follows:

[0010] C: 0.05%-0.10%, Si: 0-0.35%, Mn: 0.7%-0.9%, P: ≤0.022%, S: ≤0.010%, Nb: 0, Alt: 0.01%-0.05%, Ti: 0.04%-0.08%, and the rest are unavoidable impurity elements. The reasons for the composition design are as follows:

[0011] Step 1: Design of ingredients.

[0012] Carbon composition: 0.05%-0.10%. If it exceeds the upper limit of this range, although the strength performance can meet the requirements, the shaping and processing performance of the material cannot meet the requirements, and cracking and other problems are prone to occur. If it is lower than the lower limit of this range, although it is beneficial to improve the shaping and processing performance of the material, the strength performance cannot meet the requirements. Therefore, the carbon is determined within this range. The advantage is that it can meet the shaping and processing performance of the material. As for the strength of the material, in addition to carbon, alloys are also required to meet the strength requirements of the material.

[0013] Silicon composition: 0-0.35%. In this automotive beam steel product, silicon is a residual element, the less the better. However, if it exceeds 0.35%, the subsequent welding performance of the material will be reduced.

[0014] Manganese composition: 0.7%-0.9%. The design basis is to minimize the manganese content in order to achieve the low cost requirement. In addition, according to production experience, 0.1% manganese content can contribute 10MPa to the product strength (referring to tensile strength). If the contribution of manganese to the strength in automobile beam steel products is less than 70MPa, the required strength cannot be guaranteed. However, if the contribution of manganese to the strength exceeds 90MPa, the low composition requirement cannot be achieved. Therefore, it is appropriate to determine the manganese content at 0.7%-0.9%, so that the contribution of manganese to the strength is between 70-90MPa.

[0015] Alloy titanium: 0.04%-0.08%. Alloy titanium is not only cheap, but also contributes significantly to the strength of the material. However, according to production experiments, if the titanium content exceeds 0.08%, it is easy to burn during the steelmaking process, because titanium has strong metal activity and is easy to burn if the content is high. If it is less than 0.04%, it cannot achieve the effect of strengthening the material, so the titanium alloy content is determined to be within this range.

[0016] All aluminum: 0.01%-0.05%. It is a deoxidizing element and a necessary element in molten steel. The reason why all aluminum is controlled within this range is that a certain amount of aluminum is needed in molten steel, which can form aluminum nitride with nitrogen in the molten steel to improve the aging performance of the material.

[0017] Niobium: 0%. Niobium is an expensive alloy and is not required in the present automotive steel product.

[0018] Phosphorus: ≤0.022%. It is an impurity element, the less the better.

[0019] Sulfur: ≤0.010%. It is an impurity element, the less the better.

[0020] Step 2: Converter smelting molten steel, tapping, entering refining area. There is no content of the present invention in this process.

[0021] Step 3: LF furnace refining of molten steel. An unexpected effect was found in this process: it can simplify the steelmaking and refining process. It is no longer necessary to perform RH vacuum treatment on the converter molten steel after LF furnace refining as before the improvement. Only LF furnace refining treatment can meet the quality requirements of slag inclusion control level in molten steel. The mechanism is that titanium is an alloy with strong metal activity, which can be deoxidized in molten steel, reducing oxide slag inclusion. Then continuous casting is carried out to produce slabs.

[0022] Step 4: The refined molten steel is subjected to continuous casting to produce slabs.

[0023] Step 5: Heat the continuous casting slab. The principle of solid solution strengthening of titanium alloy by using high slab heating temperature is used to increase the heating temperature of the slab before hot rolling. After testing, in order to make the titanium alloy solid solution strengthened, two heating stages must be carried out. The first stage is to quickly heat the slab, the purpose of which is to improve the heating efficiency and not affect the production rhythm. The heating rate is controlled at 40℃ / h, and the temperature is raised to 1130℃ (experiments have shown that rising to this temperature basically does not delay the production rhythm). Then enter the slow heating stage, and the final temperature reaches 1230℃, the purpose of which is to make the titanium alloy in the steel fully dissolved in the steel matrix without forming titanium compounds. In order to balance production efficiency and ensure the solid solution of titanium alloy. The present invention stipulates the ratio of rapid heating time (T1) and slow heating time (T2): T1:T2=1:1. After experimental tracking, it was found that the slow heating time was more than 30 minutes, which could allow the titanium alloy in the steel to be completely dissolved.

[0024] Step 6: After the slab is heated, rough rolling and finish rolling are performed. This process does not involve the content of the present invention.

[0025] Step 7: Use low-temperature coiling to form a solid solution of titanium in steel, so as to achieve the purpose of stabilizing performance. After the cost of the above B510L automobile beam steel alloy is designed at low cost, although the cost is reduced, the titanium content is increased and it becomes a high-titanium alloy steel, which has a problem of large performance fluctuations (tensile strength). The reason is that titanium is an element with strong metal activity and is easy to form titanium compounds in steel, such as titanium nitride and titanium carbide. When the plate is coiled, due to the high coiling temperature (540-600℃, target value 580℃) and uneven cooling of the plate, the size of the titanium compounds formed is different, which causes a large fluctuation range of the performance of the steel. If low-temperature coiling is adopted, the low temperature is not conducive to the precipitation of titanium compounds, but a solid solution is formed in the steel grains. This can also achieve uniformity of steel performance. Experiments have shown that when the coiling temperature is reduced to 520-580°C (target value 550°C), the solid solubility rate of titanium in the steel matrix can reach 90%. Since most of the titanium is dissolved in the steel matrix, no titanium compounds of varying sizes are formed, thus solving the performance fluctuation problem caused by cost reduction of the B510L automobile beam steel.

[0026] Compared with the prior art, the present invention has the following advantages: 1. Fully utilizing low-cost titanium alloy to replace manganese and eliminate niobium, so as to achieve the purpose of developing low-cost B510L automobile beam steel products;

[0027] 2. After using titanium alloy to replace part of manganese and eliminating niobium alloy, it was found that the performance of the low-cost automobile beam steel product fluctuated greatly, and the performance (mainly tensile strength) was often unqualified. After testing, it was found that the method of high-temperature heating of the slab and low-temperature coiling of the hot coil can solve the problem of large performance fluctuations. In the experiment, the production rhythm was taken into consideration, and the heating of the slab was divided into two stages: rapid heating and slow heating. The time ratio of these two stages is the ratio of rapid heating time (T1) to slow heating time (T2): T1:T2=1:1;

[0028] 3. The problem of large performance fluctuations in low-cost automotive steel products is that titanium alloys form titanium compounds. By optimizing the slab heating time and heating temperature, and reducing the coiling temperature, the formation of titanium compounds can be prevented;

[0029] 4. After using titanium alloy to replace part of manganese and canceling niobium alloy, an unexpected effect was found: it can simplify the steelmaking and refining process. It is not necessary to perform RH vacuum treatment on the converter molten steel after LF furnace refining like the existing technology (i.e. before improvement). This technology only needs LF furnace refining treatment to meet the quality requirements of slag inclusion control level in molten steel. The mechanism is that titanium is an alloy with strong metal activity, which can be deoxidized in molten steel, reducing oxide slag inclusion. This further reduces the production cost of the B510L automobile beam steel. It reflects the characteristics of one measure producing multiple effects. The specific reduction of slag inclusion is shown in Table 1.

[0030] Table 1. Reduction of slag inclusion in molten steel after LF furnace refining

[0031] Example Average size of inclusions (um) Inclusion surface density (pcs / mm2) Existing technology (before improvement) 2.3 36 This technology 2.1 24

[0032] 5. Use low-temperature coiling to form a solid solution of titanium in the steel, thereby achieving the purpose of stabilizing performance. Tests have found that when the coiling temperature is reduced to 520-580°C (target value 550°C), the solid solution rate of titanium in the steel matrix can reach 90%. Since most of the titanium is solid-dissolved in the steel matrix, no titanium compounds of varying sizes are formed, thus solving the performance fluctuation problem caused by the cost reduction of the B510L automobile beam steel. Existing patents do not have such measures.

[0033] 6. This technology is highly practical, low cost, simple process and pollution-free. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is the improved metallographic picture. DETAILED DESCRIPTION

[0035] In order to deepen the understanding of the present invention, the present embodiment is described in detail below with reference to the accompanying drawings.

[0036] Example 1: See Figure 1 , a design method for the performance of low-cost automobile beam steel B510L product, the method is implemented in the following steps:

[0037] To achieve stable performance of this low-cost automobile beam steel product, its composition is as follows:

[0038] C: 0.05%-0.10%, Si: 0-0.35%, Mn: 0.7%-0.9%, P: ≤0.022%, S: ≤0.010%, Nb: 0, Alt: 0.01%-0.05%, Ti: 0.04%-0.08%, and the rest are unavoidable impurity elements. The reasons for the composition design are as follows:

[0039] Step 1: Design of ingredients,

[0040] Carbon composition: 0.05%-0.10%. If it exceeds the upper limit of this range, although the strength performance can meet the requirements, the shaping and processing performance of the material cannot meet the requirements, and cracking and other problems are prone to occur. If it is lower than the lower limit of this range, although it is beneficial to improve the shaping and processing performance of the material, the strength performance cannot meet the requirements. Therefore, the carbon is determined within this range. The advantage is that it can meet the shaping and processing performance of the material. As for the strength of the material, in addition to carbon, alloys are also required to meet the strength requirements of the material.

[0041] Silicon content: 0-0.35%. In this automotive beam steel product, silicon is a residual element, the less the better. However, if it exceeds 0.35%, the subsequent welding performance of the material will be reduced.

[0042] Manganese composition: 0.7%-0.9%. The design basis is to minimize the manganese content in order to achieve the low cost requirement. In addition, according to production experience, 0.1% manganese content can contribute 10MPa to the product strength (referring to tensile strength). If the contribution of manganese to the strength in automobile beam steel products is less than 70MPa, the required strength cannot be guaranteed. However, if the contribution of manganese to the strength exceeds 90MPa, the low composition requirement cannot be achieved. Therefore, it is appropriate to determine the manganese content at 0.7%-0.9%, so that the contribution of manganese to the strength is between 70-90MPa.

[0043] Alloy titanium: 0.04%-0.08%. Alloy titanium is not only cheap, but also contributes significantly to the strength of the material. However, according to production experiments, if the titanium content exceeds 0.08%, it is easy to burn during the steelmaking process, because titanium has strong metal activity and is easy to burn if the content is high. If it is less than 0.04%, it cannot achieve the effect of strengthening the material, so the titanium alloy content is determined to be within this range.

[0044] All aluminum: 0.01%-0.05%. It is a deoxidizing element and a necessary element in molten steel. The reason why all aluminum is controlled within this range is that a certain amount of aluminum is needed in molten steel, which can form aluminum nitride with nitrogen in the molten steel to improve the aging performance of the material.

[0045] Niobium: 0%. Niobium is an expensive alloy and is not required in the present automotive steel product.

[0046] Phosphorus: ≤0.022%. It is an impurity element, the less the better.

[0047] Sulfur: ≤0.010%. It is an impurity element, the less the better.

[0048] Step 2: Converter smelting molten steel, tapping, entering refining area. There is no content of the present invention in this process.

[0049] Step 3: LF furnace refining of molten steel. An unexpected effect was found in this process: it can simplify the steelmaking and refining process. It is no longer necessary to perform RH vacuum treatment on the converter molten steel after LF furnace refining as before the improvement. Only LF furnace refining treatment can meet the quality requirements of slag inclusion control level in molten steel. The mechanism is that titanium is an alloy with strong metal activity, which can be deoxidized in molten steel, reducing oxide slag inclusion. Then continuous casting is carried out to produce slabs.

[0050] Step 4: The refined molten steel is subjected to continuous casting to produce slabs.

[0051] Step 5: Heat the continuous casting slab. The principle of solid solution strengthening of titanium alloy by using high slab heating temperature is used to increase the heating temperature of the slab before hot rolling. After testing, in order to make the titanium alloy solid solution strengthened, two heating stages must be carried out. The first stage is to quickly heat the slab, the purpose of which is to improve the heating efficiency and not affect the production rhythm. The heating rate is controlled at 40℃ / h, and the temperature is raised to 1130℃ (experiments have shown that rising to this temperature basically does not delay the production rhythm). Then enter the slow heating stage, and the final temperature reaches 1230℃, the purpose of which is to make the titanium alloy in the steel fully dissolved in the steel matrix without forming titanium compounds. In order to balance production efficiency and ensure the solid solution of titanium alloy. The present invention stipulates the ratio of rapid heating time (T1) and slow heating time (T2): T1:T2=1:1. After experimental tracking, it was found that the slow heating time was more than 30 minutes, which could allow the titanium alloy in the steel to be completely dissolved.

[0052] Step 6: After the slab is heated, rough rolling and finish rolling are performed. This process does not involve the content of the present invention.

[0053] Step 7: Use low-temperature coiling to form a solid solution of titanium in steel, so as to achieve the purpose of stabilizing performance. After the cost of the above B510L automobile beam steel alloy is designed at low cost, although the cost is reduced, the titanium content is increased and it becomes a high-titanium alloy steel, which has a problem of large performance fluctuations (tensile strength). The reason is that titanium is an element with strong metal activity and is easy to form titanium compounds in steel, such as titanium nitride and titanium carbide. When the plate is coiled, due to the high coiling temperature (540-600℃, target value 580℃) and uneven cooling of the plate, the size of the titanium compounds formed is different, which causes a large fluctuation range of the performance of the steel. If low-temperature coiling is adopted, the low temperature is not conducive to the precipitation of titanium compounds, but a solid solution is formed in the steel grains. This can also achieve uniformity of steel performance. Experiments have shown that when the coiling temperature is reduced to 520-580°C (target value 550°C), the solid solubility rate of titanium in the steel matrix can reach 90%. Since most of the titanium is dissolved in the steel matrix, no titanium compounds of varying sizes are formed, thus solving the performance fluctuation problem caused by cost reduction of the B510L automobile beam steel.

[0054] Example 2: See Figure 1 , a method for designing the performance of a low-cost automobile beam steel B510L product, the method comprising the following steps:

[0055] Step 1: Chemical composition examples, see Table 2.

[0056] Table 2. Chemical cost implementation

[0057] element C％ Si% Mn% P％ S％ Ti% Nb% Al％ The present invention 0.05-0.10 0-0.35 0.7-0.9 P:≤0.022 S:≤0.010 0.04-0.08 0 0.01-0.05 Example 1 0.0714 0.043 0.8310 0.0131 0.0007 0.0566 0.0015 0.0363 Example 2 0.0697 0.0218 0.7610 0.0108 0.0031 0.056 0.0012 0.0349 Example 3 0.0629 0.0239 0.7833 0.0163 0.0018 0.0567 0.0019 0.0351 Example 4 0.0675 0.039 0.7778 0.0125 0.0041 0.0564 0.0017 0.0299 Example 5 0.0714 0.0322 0.7806 0.0112 0.0043 0.0633 0.0016 0.0403

[0058] Step 2: The molten steel is refined in a LF furnace. Five embodiments are shown in Table 3.

[0059] Table 3. LF furnace refining example

[0060]

[0061] It can be seen from Table 3 that after simplifying the steelmaking refining process, the inclusion size and distribution density are significantly improved compared with the existing technology.

[0062] Step 3: Slab heating example, see Table 4.

[0063] Table 4. Implementation of the refined path

[0064]

[0065]

[0066] Step 4: Hot rolling and low temperature coiling example, see Table 5.

[0067] Table 5. Implementation of hot rolling and low temperature coiling

[0068] Example Coiling temperature℃ Performance (tensile strength) MPa Example 1 549 570 Example 2 557 580 Example 3 554 574 Example 4 558 580 Example 5 557 569 Existing technology (before improvement) 560-600 510-630

[0069] It can be seen from Table 5 that the performance is stable after improvement, the fluctuation range of the five embodiments is between 569-580 MPa, and the stability is good.

[0070] Step 5: Improved metallographic structure picture

[0071] The improved metallographic structure is shown in Figure 1 :

[0072] Depend on Figure 1 It can be seen that after the improvement, there are no titanium compound particles, and most of the titanium is dissolved in ferrite.

[0073] Step 5: Cost comparison before and after improvement. Before the improvement, the cost of hot-rolled products of B510L automobile beam steel was 3934.87 yuan / ton, and the cost after the improvement was 3720.92 yuan / ton. It can be seen that after the improvement, the cost has been greatly reduced.

[0074] It should be noted that the above embodiments are not intended to limit the protection scope of the present invention, and equivalent changes or substitutions made on the basis of the above technical solutions all fall within the protection scope of the claims of the present invention.

Claims

1. A design method for the performance of low-cost automobile beam steel B510L product, characterized in that: The method comprises the following steps: Step 1: Design of ingredients, Step 2: The converter smelts molten steel, taps the steel, and enters the refining area. Step 3: The molten steel is refined in LF furnace. Step 4: The refined molten steel is put into continuous casting process to produce slabs. Step 5: Heating the continuous casting slab. Step 6: After the slab is heated, it is subjected to rough rolling and finish rolling. Step 7: Use low-temperature coiling to allow titanium to form a solid solution in the steel, thereby achieving the purpose of stabilizing performance.

2. The method for designing product performance of low-cost automobile beam steel B510L according to claim 1 is characterized in that: Step 1: Design of ingredients, according to mass fraction, as follows: Its ingredients are as follows: C: 0.05%-0.10%, Si: 0-0.35%, Mn: 0.7%-0.9%, P: ≤0.022%, S: ≤0.010%, Nb: 0, Alt: 0.01%-0.05%, Ti: 0.04%-0.08%, and the rest are unavoidable impurity elements.

3. The method for designing product performance of low-cost automobile beam steel B510L according to claim 1 is characterized in that: Step 5: heating the continuous casting slab, as follows: using the principle of solid solution strengthening of titanium alloy by high slab heating temperature, increasing the heating temperature of the slab before hot rolling, in order to make the titanium alloy solid solution strengthened, two heating stages must be carried out, the first stage is to heat the slab quickly, its purpose is to improve the heating efficiency, not affecting the production rhythm, the heating rate is controlled at 40 ℃ / h, and the temperature is raised to 1130 ℃, and then enters the slow heating stage, the final temperature reaches 1230 ℃, its purpose is to make the titanium alloy in the steel fully dissolved in the steel matrix, without forming titanium compounds, in order to balance the production efficiency and ensure the solid solution of titanium alloy, the ratio of rapid heating time (T1) and slow heating time (T2) is specified: T1:T2 = 1:

1.

4. The method for designing product performance of low-cost automobile beam steel B510L according to claim 1 is characterized in that: Step 7: Use low-temperature coiling to allow titanium to form a solid solution in the steel, thereby achieving the purpose of stabilizing performance. The details are as follows: When the coiling temperature is reduced to 520-580°C, the solid solution rate of titanium in the steel matrix can reach 90%. Since most of the titanium is solid-dissolved in the steel matrix, no titanium compounds of varying sizes are formed, thereby solving the performance fluctuation problem caused by the cost reduction of the B510L automobile beam steel.

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