High-performance low-cost microalloyed steel for automobile I-shaped front axle and preparation method of microalloyed steel

Abstract

The invention relates to high-performance low-cost microalloyed steel for an automobile I-shaped front axle and a preparation method of the microalloyed steel, and belongs to the technical field of materials. The steel comprises the following chemical components in percentage by weight: 0.20 to 0.60 percent of C, 0.2 to 1.0 percent of Mn, 0.1 to 0.5 percent of Si, 0.6 to 1.2 percent of Cr, 0.01 to 0.10 percent of Nb, 0.01 to 0.06 percent of Mo and the balance of Plt, 0.01%, Slt; 0.01%, Olt; 0.0040%, and the balance being iron. According to the invention, the contents of Nb and C key alloy elements in the material are accurately controlled, so that Nb can be completely dissolved into a matrix in the smelting process, and the phenomenon of one-time NbC liquation is avoided. Heat treatment is directly carried out after smelting and casting, and the component control strategy is adopted, so that the precipitation of nano-sized dispersed NbC on an original austenite grain boundary is promoted, austenite grains are effectively pinned, and a microstructure with uniform and fine grain size is obtained; a martensitic structure is obtained through quenching, and uniform dispersion and precipitation of NbC carbide are realized in the martensitic structure through a subsequent tempering process, so that the strength and the toughness of the I-shaped front axle are ensured to reach the best match.

Description

Technical Field

[0001] The invention relates to high-performance and low-cost micro-alloy steel for an automobile I-shaped front axle and a preparation method thereof, belonging to the technical field of materials. Background Art

[0002] The I-shaped front axle of a car is an important part of the car chassis. It plays the role of bearing weight and connecting leaf springs, tires, etc. It also forms a steering system with tie rods, steering knuckles and other parts, which has a great impact on the safety and operational stability of the whole vehicle. In recent years, as the country has introduced many policies in many aspects such as energy conservation and energy saving and consumption reduction, it requires further weight reduction of automobile parts, especially the I-shaped front axle of the car, which requires a weight reduction of more than 20%. The energy consumption of a car mainly depends on the displacement of the engine and the total weight of the car. Research figures show that if the weight of the whole car is reduced by 10%, the fuel efficiency can be increased by 6% to 8%. Therefore, the lightweighting of the I-shaped front axle of the car is of great significance to the fuel economy of the whole vehicle.

[0003] 40Cr steel is a low-alloy high-strength structural steel. It has been widely used in various engineering structures because of its excellent comprehensive mechanical properties and good cutting performance. Especially in the automotive parts industry, 40Cr steel, as the key core material of the automobile I-shaped front axle, plays a vital role in the safe operation of the car. Fujian Tiechima Lightweight Axle Co., Ltd. mainly deals in automobile I-shaped front axles and other automobile parts. It is a traditional cast steel material industry. The company's annual sales reach more than 300,000 pieces, and its products account for more than 20% of the market share. The operating income reaches more than 100 million yuan, and it occupies an important position in the economic development of Fujian Province. The company adopts the traditional process of casting + heat treatment. The smelting and casting processes are backward, and the market competitiveness of the products is relatively weak. It can only rely on human resources and low material costs to maintain the market. However, due to the low mechanical properties of the automobile I-shaped front axle after heat treatment, it causes premature fracture failure during service, which limits the further development of the company. Therefore, it is very necessary to make targeted improvements to the current axle materials to further improve the comprehensive performance of 40Cr steel, especially the yield strength and tensile strength, so as to improve its fatigue performance, thereby extending its service life and enhancing safety, while reducing the weight of structural materials, enhancing the core competitiveness of products and avoiding being eliminated by the market.

[0004] Fujian Tiechima Lightweight Axle Co., Ltd. and the Institute of Metal Research of the Chinese Academy of Sciences jointly tackled the problem of high-performance and low-cost materials for automobile I-axles. Through composition design and organizational regulation, a new type of high-performance material for automobile I-axles was developed, and the heat treatment process was optimized to solve the material problem that currently restricts the company's main product - automobile I-axles. The Institute of Metal Research of the Chinese Academy of Sciences has applied its scientific and technological achievements in 40Cr steel and developed a new type of micro-alloyed steel containing Nb for automobile I-axles. After optimized heat treatment, the comprehensive performance of the material has been further improved, especially the fatigue performance has been improved. It is expected to be used on automobile I-axles to achieve lightweight automobile I-axles. Summary of the invention

[0005] The purpose of the present invention is to provide a high-performance, low-cost microalloy steel for an automobile I-shaped front axle and a preparation method thereof. By precisely controlling the Nb element content in the invented material, the production of primary NbC is avoided, while ensuring the appropriate matching of Nb and C elements, ensuring that the Nb and C elements are completely dissolved into the matrix during the smelting process, avoiding the formation of large-sized primary NbC, and replacing forging with casting. In the 800-860°C solid solution heat treatment, NbC can effectively pin austenite grains and inhibit the movement of austenite grain boundaries, thereby obtaining finer grains and improving the mechanical properties of the material. In addition, by tempering at 480-530°C, tempered martensite structure and uniformly distributed NbC can be obtained, further improving the strength and toughness of the material, and finally obtaining the invented material with the best strength and plasticity matching, ensuring the fatigue performance of the material.

[0006] The technical solution of the present invention is:

[0007] The invention discloses a high-performance and low-cost micro-alloy steel for an automobile I-shaped front axle. The chemical composition thereof is, by weight percentage, as follows: C: 0.20-0.60%, Mn: 0.2-1.0%, Si: 0.1-0.5%, Cr: 0.6-1.2%, Nb: 0.01-0.10%, Mo: 0.01-0.06%, P<0.01%, S<0.01%, O<0.0040%, and the balance is iron.

[0008] The high-performance and low-cost microalloy steel for the automobile I-shaped front axle preferably has C: 0.35-0.45%, Nb: 0.040-0.60%, and the mass fraction product of C and Nb is controlled within (1.5-2.5)×10 -6 between.

[0009] The high-performance and low-cost micro-alloy steel for the automobile I-shaped front axle preferably contains 0.70-0.80% Mn, 0.80-1.0% Cr and 0.03-0.04% Mo.

[0010] The method for preparing high-performance and low-cost micro-alloy steel for automobile I-shaped front axle comprises the following steps:

[0011] (1) mixing the chemical components in proportion, smelting and casting to obtain an automobile I-shaped front axle ingot;

[0012] (2) The obtained automobile I-shaped front axle ingot is directly heat treated.

[0013] The method for preparing high-performance and low-cost microalloyed steel for automobile I-shaped front axles comprises the following steps: first, heat-treating the steel at 800-880°C for 30 minutes and then quenching the steel with water to room temperature; then heat-treating the steel at 450-550°C for 90 minutes and then cooling the steel with water to room temperature.

[0014] The preparation method of the high-performance and low-cost micro-alloyed steel for the automobile I-shaped front axle, the yield strength of the high-performance and low-cost micro-alloyed steel for the automobile I-shaped front axle after heat treatment reaches more than 950MPa, the tensile strength reaches more than 1050MPa, the elongation reaches more than 12%, the cross-sectional shrinkage reaches more than 40%, and the fatigue life B50 reaches more than 500,000 times.

[0015] The design concept of the present invention is as follows:

[0016] When a certain amount of Nb alloy element is added to 40Cr steel, Nb and C elements will form primary NbC carbides during the smelting process, which will lead to the appearance of larger NbC in the cast structure of the automobile I-shaped front axle. Since the automobile I-shaped front axle adopts the process of casting instead of forging, there is no process of thermal processing such as forging to break up the coarse carbides, and they cannot be effectively eliminated after subsequent heat treatment. Therefore, during the service of the automobile I-shaped front axle, the uneliminated primary carbides will become the initiation position of cracks, thereby reducing the comprehensive performance of the material, especially the fatigue performance of the material. Therefore, on the basis of 40Cr steel, how to regulate and optimize the Nb and C content in the steel to ensure that large particles of NbC are not formed becomes the key to the present invention.

[0017] The present invention ensures that NbC in the casting process can be completely dissolved into the matrix before heat treatment by accurately balancing the Nb and C contents in the invented material, while effectively avoiding excessively high solid solution temperature leading to coarsening of the material grains and deterioration of the material's comprehensive properties. The book "Second Phase in Iron and Steel Materials" gives the solid solubility product formula of NbC in austenite, as follows:

[0018]

[0019] Among them, γ is austenite, K NbCis the mass fraction product of Nb and C elements dissolved into austenite, T is temperature (℃), [wt%Mn], [wt%Cr], [wt%Mo] are the mass fractions of Mn, Cr, and Mo. In order to ensure that NbC can be completely dissolved and evenly integrated into the matrix during the casting process to avoid the formation of primary NbC, it is necessary to accurately control the Nb content to be optimized within 0.040-0.60%, and the C content to be optimized within 0.35-0.45%. In addition, the mass fraction product of Nb and C also needs to be controlled within (1.5-2.5)×10 -6 In the range of , at the same time, the content of Mn is optimized to be controlled at 0.70wt%~0.80wt%, the content of Cr is optimized to be controlled at 0.80wt%~1.0wt%, and the content of Mo is optimized to be controlled at 0.03wt%~0.04wt%. During the casting and cooling process of the front axle of the automobile I-beam, the Nb dissolved in the matrix will be uniformly precipitated as nano-sized NbC. NbC has high thermodynamic stability. During the solution treatment process, the NbC on the grain boundary can effectively hinder the migration of the grain boundary, thereby avoiding the growth of the grains and effectively controlling the grain size. Therefore, this characteristic distribution of NbC not only maintains the microstructural stability of 40Cr, but also significantly improves its strength and toughness.

[0020] The content ranges of the main elements in the present invention are described as follows:

[0021] C: C forms Fe3C and NbC carbides with Fe and Nb elements, which precipitate at interfaces such as original austenite grain boundaries and lath boundaries, pinning dislocations and hindering the movement of interfaces, playing a role of precipitation strengthening, and effectively improving the strength of the material. The increase in carbon content can improve the strength and hardness of the material, but too high a carbon content will reduce the plasticity and toughness of the material, and also increase the difficulty of welding. Therefore, the carbon content in the steel of the present invention is controlled to be 0.20wt% to 0.60wt%, and further optimized to be 0.35wt% to 0.45wt%.

[0022] Mn: Mn can enhance the strength and toughness of steel through solid solution strengthening mechanism. It replaces iron atoms in the steel lattice, causing distortion, thereby hindering the movement of dislocations and increasing the yield and tensile strength of the material. At the same time, it can significantly reduce the martensite formation temperature of steel. S point, improve the hardenability of alloy steel. However, the addition of manganese will affect the temperature at which NbC is completely dissolved into the matrix. Therefore, the manganese content in the steel of the present invention is controlled to be 0.2wt% to 1.0wt%, and further optimized to be controlled to be 0.70wt% to 0.80wt%.

[0023] Si: The Si element plays several key roles: First, as a deoxidizer, silicon helps remove oxygen from the molten steel and reacts with oxygen to form silicon dioxide (SiO2), thereby improving the purity and overall quality of the steel. Second, Si enhances the strength and hardness of the material through a solid solution strengthening mechanism, because Si atoms replace iron atoms in the steel lattice, introducing tiny distortions that make it more difficult for dislocations to move, thereby improving the mechanical properties of the steel. However, the silicon content needs to be carefully controlled, because too high a silicon content may affect the welding performance of 40Cr steel, mainly because a high silicon content may lead to the formation of pores in the weld metal, reducing the quality of the welded joint, so the silicon content in the present invention is controlled to be: 0.20wt% to 0.30wt%.

[0024] Cr: Chromium can reduce the concentration of carbon in pearlite and the limit concentration of carbon in austenite, slow down the decomposition rate of austenite, and improve the hardenability of steel. At the same time, it can form chromium carbide with carbon during tempering, significantly improving the strength of steel, while improving the wear resistance of steel, and easily obtaining a lower surface roughness. Therefore, the chromium content in the present invention is controlled to be: 0.60wt% ~ 1.20wt%, and further optimized to be controlled to be 0.8wt% ~ 1.0wt%.

[0025] Nb: Niobium plays a role in grain refinement. NbC shows extremely high thermodynamic stability and is difficult to dissolve even at high temperatures. During the solution process, NbC tends to be distributed near the grain boundaries. This distribution effectively inhibits grain boundary migration, thereby maintaining the small grain size and significantly improving the strength and toughness of the material. However, when its content exceeds 0.10wt%, primary NbC particles will be formed, which will coarsen during subsequent hot working and reduce the mechanical properties of the material. Therefore, the Nb content in the steel of the present invention is controlled to be 0.01wt% to 0.10wt%, and is further optimized to be controlled to be 0.04wt% to 0.06wt%.

[0026] Mo: Molybdenum can promote solid solution strengthening and the formation of carbides. It replaces iron atoms in the steel lattice, produces distortion, thereby hindering the movement of dislocations, increasing the yield and tensile strength of the material, and dissolves in carbides to improve the stability of carbides. At the same time, during the tempering process, molybdenum and carbon form molybdenum carbide, which improves the strength of the steel. Therefore, the molybdenum content in the present invention is controlled to be: 0.01-0.06%, and further optimized to be controlled to be 0.03wt%-0.04wt%.

[0027] S, P: In the production of steel, phosphorus and sulfur are usually regarded as harmful impurities because they can significantly reduce the overall performance of steel. The presence of phosphorus increases the cold brittleness of steel, reduces the cohesion of grain boundaries, thereby reducing the toughness and plasticity of the material, and also affects the welding performance, causing welded joints to be prone to cracks. On the other hand, sulfur will increase the hot brittleness tendency of steel, especially during high-temperature processing. At the same time, excessive sulfur will also affect the mechanical processing quality of steel and reduce the strength and toughness of the material. Therefore, the content of sulfur and phosphorus in the steel of the present invention is extremely strictly controlled: S<0.01wt%, P<0.01wt%.

[0028] O: The control of oxygen content in steel is also crucial. When the oxygen content exceeds a certain limit, brittle oxide inclusions will form in the steel, which will significantly reduce its mechanical properties. Studies have shown that once the oxygen content in 40Cr steel exceeds 0.03wt%, its strength and plasticity will deteriorate. Since 40Cr steel is often subjected to heavy loads in the front axle of an automobile I-beam, its sensitivity to oxide inclusions cannot be ignored. Therefore, the oxygen content in the steel of the present invention is strictly controlled: O<0.004wt%.

[0029] The advantages and beneficial effects of the present invention are:

[0030] 1. The present invention creatively adds a certain amount of niobium to the high-performance and low-cost micro-alloy steel for the front axle of the automobile, and controls the product of the mass fractions of C and Nb to be (1.5-2.5)×10 -6 The niobium carbide is completely dissolved into the matrix within a certain range, thus avoiding the formation of large micron-sized primary niobium carbides. In the subsequent heat treatment stage, the niobium carbide is uniformly precipitated, thereby refining the grains and significantly improving the strength and toughness of the material.

[0031] 2. The present invention proposes a composition design idea for high-performance and low-cost micro-alloyed steel for automobile I-shaped front axles, and obtains a new preparation technology for high-performance and low-cost structural steel for automobile I-shaped front axles by adopting Nb micro-alloying. First, a trace amount of Nb element is added to 40Cr steel using the micro-alloying design idea. The addition of Nb helps to form fine NbC, and carbides can pin austenite grain boundaries during heat treatment, thereby achieving the purpose of grain refinement. The acquisition of these fine grains can effectively improve the strength of the material while maintaining good plasticity and toughness, thereby improving its fatigue performance.

[0032] 3. The present invention adopts a preparation process for a new low-cost material by microalloying Nb, and its comprehensive performance is greatly improved compared with that of traditional 40Cr steel. The yield strength is increased to 950MPa, the tensile strength is increased to 1050MPa, and especially the B50 fatigue life is increased to 500,000 times.

[0033] 4. The present invention provides an efficient and economical manufacturing method for high-performance and low-cost micro-alloy steel for automobile I-shaped front axles. By using casting instead of forging technology, the material cost can be greatly reduced while the comprehensive performance is guaranteed. The material of the present invention can better support the rapid development of my country's automobile industry. At the same time, it also provides a new idea for the development and application of low-cost and high-strength materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of the metallographic structure of Example 1 after heat treatment.

[0035] Figure 2 This is a schematic diagram of the SEM structure of Example 1 after heat treatment.

[0036] Figure 3 This is a schematic diagram of the TEM structure of niobium carbide in Example 5.

[0037] Figure 4 Schematic diagram of the metallographic structure of Comparative Example 1 after heat treatment.

[0038] Figure 5 This is a schematic diagram of the SEM structure of Comparative Example 1 after heat treatment.

[0039] Figure 6 This is a schematic diagram of the metallographic structure of primary carbide niobium in Comparative Example 2.

[0040] Figure 7 This is a schematic diagram of the TEM structure of primary niobium carbide in Comparative Example 3. DETAILED DESCRIPTION

[0041] In the specific implementation process, the present invention ensures that Nb can be completely dissolved into the matrix during the smelting process by accurately controlling the content of key alloy elements Nb and C in the material, thereby avoiding the occurrence of a single NbC liquid precipitation phenomenon. Heat treatment is directly carried out after smelting and casting. The above-mentioned component control strategy helps to promote the precipitation of nano-sized dispersed NbC on the original austenite grain boundaries, thereby effectively pinning the austenite grains and obtaining a microstructure with uniform and fine grain size; quenching is used to obtain a martensitic structure, and through the subsequent tempering process, the uniform dispersion and precipitation of NbC carbides are achieved in the martensitic structure, ensuring that the strength and toughness of the automobile I-shaped front axle are optimally matched. The automobile part adopts a casting-forging process, which saves mold and forging costs and achieves a low cost for the automobile I-shaped front axle.

[0042] The following examples and drawings will further illustrate the present invention, but are not intended to limit the present invention. The steel in the examples and the steel in the comparative examples are processed into standard tensile specimens after smelting and heat treatment to test the mechanical properties, and the fatigue performance is tested on a special test bench for the fatigue performance of an integral automobile I-shaped front axle B50 (3.5 times the load).

[0043] The preparation process of the high-performance and low-cost microalloy steel for the automobile I-shaped front axle of the present invention is: batching → smelting → casting → heat treatment. Examples 1 to 5 are all prepared by the following method, and the specific steps are as follows:

[0044] (1) mixing the chemical components according to the ratio, and obtaining an automobile I-shaped front axle ingot through smelting and casting;

[0045] (2) Heat treatment process after casting: first, keep at 800-880°C (Examples 1-5 are 800°C, 820°C, 840°C, 860°C and 880°C, respectively) for 30 min and then quench with water to room temperature. Then, keep at 450-550°C (Examples 1-5 are 450°C, 470°C, 500°C, 520°C and 550°C, respectively) for 90 min and then cool with water to room temperature.

[0046] Example 1

[0047] In this embodiment, the chemical composition of the high-performance, low-cost micro-alloy steel for the automobile I-shaped front axle is, by weight percentage, C: 0.38%, Mn: 0.72%, Si: 0.26%, Cr: 0.88%, Mo: 0.031%, Nb: 0.051%, S: 0.006%, P: 0.005%, O: 0.0029%, and the balance is iron.

[0048] Example 2

[0049] In this embodiment, the chemical composition of the high-performance, low-cost micro-alloy steel for the automobile I-shaped front axle is, by weight percentage, C: 0.36%, Mn: 0.78%, Si: 0.26%, Cr: 0.87%, Mo: 0.030%, Nb: 0.06%, S: 0.005%, P: 0.007%, O: 0.0039%, and the balance is iron.

[0050] Example 3

[0051] In this embodiment, the chemical composition of the high-performance, low-cost micro-alloy steel for the automobile I-shaped front axle is, by weight percentage, C: 0.40%, Mn: 0.76%, Si: 0.31%, Cr: 0.90%, Mo: 0.036%, Nb: 0.051%, S: 0.008%, P: 0.0065%, O: 0.0032%, and the balance is iron.

[0052] Example 4

[0053] In this embodiment, the chemical composition of the high-performance, low-cost micro-alloy steel for the automobile I-shaped front axle is, by weight percentage, C: 0.42%, Mn: 0.77%, Si: 0.41%, Cr: 0.96%, Mo: 0.036%, Nb: 0.045%, S: 0.0045%, P: 0.0055%, O: 0.0035%, and the balance is iron.

[0054] Example 5

[0055] In this embodiment, the chemical composition of the high-performance, low-cost micro-alloy steel for the automobile I-shaped front axle is, by weight percentage, C: 0.45%, Mn: 0.79%, Si: 0.49%, Cr: 0.99%, Mo: 0.039%, Nb: 0.041%, S: 0.0052%, P: 0.0085%, O: 0.0026%, and the balance is iron.

[0056] Comparative Example 1

[0057] In this comparative example, by weight percentage, Nb in the high-performance, low-cost micro-alloyed steel for the front I-axle of an automobile is less than 0.01, and other chemical compositions and heat treatment processes are exactly the same as those in Example 1.

[0058] Comparative Example 2

[0059] In this comparative example, by weight percentage, the Nb content of the high-performance, low-cost micro-alloyed steel for automobile I-shaped front axles is 0.35%, and the other chemical compositions and heat treatment processes are exactly the same as those in Example 3.

[0060] Comparative Example 3

[0061] In this comparative example, by weight percentage, the Nb content of the high-performance, low-cost micro-alloyed steel for automobile I-shaped front axles is 0.06%, and the other components and heat treatment process are exactly the same as those in Example 5.

[0062] As shown in Table 1, the C and Nb mass products and mechanical properties in the examples and comparative examples.

[0063] Table 1

[0064]

[0065] As can be seen from Table 1, by adding a certain amount of Nb to the steel, the comprehensive performance of the material is significantly improved, the yield strength reaches more than 980 MPa, the tensile strength reaches more than 1066 MPa, and especially the B50 fatigue performance is improved by more than 45% compared with the comparative example 1 without Nb. This is mainly attributed to the grain refinement mechanism of Nb. During the solution process, NbC shows extremely high thermodynamic stability and is distributed near the grain boundary, which can effectively inhibit the grain boundary migration and prevent the grain growth, significantly improve the strength and toughness of the material, and obtain a martensitic matrix after water quenching; in the subsequent tempering process, dispersed and uniformly distributed carbides are obtained on the martensitic matrix, and the best combination of material strength and plasticity is obtained.

[0066] like Figure 1 As shown, it can be seen from the metallographic structure of Example 1 of the present invention that the steel matrix is ​​a martensitic lath structure, which is different from the metallographic structure of Comparative Example 1. Figure 4 In contrast, due to the optimization of Nb element content, the martensite laths and grains of the material are significantly refined.

[0067] like Figure 2 As shown, it can be seen from the secondary electron microscopic structure of Example 1 of the present invention that the SEM structure of Example 1 is different from that of Comparative Example 1. Figure 5 In contrast, after adding a certain amount of Nb, the size of the precipitated phase is refined and the distribution is more uniform.

[0068] like Figure 3 As shown in the figure, NbC in Example 5 is dispersed and evenly distributed at the martensite lath interface and inside the grains, and the size of the precipitated phase is between 20 and 50 nm. Compared with Comparative Example 3, it can be seen that the mass product of C and Nb is controlled at (1.5 to 2.5)×10 -6 The primary carbide precipitation can be avoided and the formation of nano-sized NbC can be ensured.

[0069] like Figure 4-Figure 5 As shown in the figure, in Comparative Example 1, Nb is not added, and although the matrix maintains the martensitic lath morphology, the martensitic lath is relatively Figure 1 and Figure 2 The grains are obviously widened, the grains are coarsened, and the sizes of the precipitated phases are different, not showing a dispersed and uniform distribution.

[0070] like Figure 6 As shown, in Comparative Example 2, the Nb content is as high as 0.35%, resulting in the existence of chain-shaped primary NbC in the matrix after solid solution, and the fatigue performance is the lowest, reaching 95,000 times.

[0071] like Figure 7 As shown in the figure, although the composition of Comparative Example 3 is within the scope of the invention, the C and Nb contents have reached the upper limit of the composition control, resulting in the mass product of C and Nb not being controlled within (1.5-2.5)×10 -6This causes the matrix to contain micron-sized primary carbides, which deteriorates the comprehensive properties of the material, especially its fatigue performance, which reaches 180,000 times, less than one-third of that in Example 5.

[0072] The results of the embodiment show that the high-performance and low-cost micro-alloy steel for the front axle of the automobile I-shaped shaft of the present invention is obtained by adding a certain amount of Nb element, using NbC to pin austenite grains, inhibiting the movement of austenite grain boundaries, obtaining fine grains, improving material strength and hardness, and combining the quenching + tempering heat treatment system to obtain tempered martensite structure and dispersed Fe3C and NbC carbides, while obtaining strength, ensuring the plasticity of the material. Finally, the yield strength reaches more than 980MPa, the tensile strength reaches more than 1066MPa, the elongation reaches more than 12.5%, the cross-sectional shrinkage reaches more than 40.5%, and the B50 fatigue performance reaches more than 560,000 times. High-performance and low-cost micro-alloy steel for the front axle of the automobile I-shaped shaft is obtained.

[0073] In particular, the optimized main chemical composition of the embodiment of the present invention is C: 0.35-0.45%, Nb: 0.04-0.06%, and the mass product of C and Nb is controlled within (1.5-2.5)×10 -6 Between, Mn: 0.70 ~ 0.80%, Cr: 0.80 ~ 1.0%, Mo: 0.03 ~ 0.04%; further adopted an optimized heat treatment process, the room temperature performance indicators of the obtained high-performance and low-cost micro-alloy steel for automobile I-shaped front axle are as follows: yield strength 980 ~ 1106MPa, tensile strength 1066 ~ 1240MPa, elongation 12.5 ~ 20.5%, cross-sectional reduction rate 40.5 ~ 55.0%, B50 fatigue life (life when the cumulative failure probability reaches 50%) 560,000 to 690,000 times.

[0074] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A high-performance, low-cost micro-alloy steel for automobile I-shaped front axles. It is characterized in that Its chemical composition, in weight percentage, is: C: 0.20-0.60%, Mn: 0.2-1.0%, Si: 0.1-0.5%, Cr: 0.6-1.2%, Nb: 0.01-0.10%, Mo: 0.01-0.06%, P<0.01%, S<0.01%, O<0.0040%, and the balance is iron.

2. The high-performance and low-cost micro-alloyed steel for the automotive I-shaped front axle according to claim 1, It is characterized in that Preferably, C: 0.35-0.45%, Nb: 0.040-0.60%, and the mass fraction product of C and Nb is controlled within (1.5-2.5)×10 -6 between.

3. The high-performance and low-cost micro-alloyed steel for the automotive I-shaped front axle according to claim 1, It is characterized in that Preferably, Mn: 0.70-0.80%, Cr: 0.80-1.0%, Mo: 0.03-0.04%.

4. A method for preparing a high-performance and low-cost micro-alloyed steel for an automobile I-shaped front axle according to any one of claims 1 to 3, It is characterized in that The steps include: (1) mixing the chemical components in proportion, smelting and casting to obtain an automobile I-shaped front axle ingot; (2) The obtained automobile I-shaped front axle ingot is directly heat treated.

5. The method for preparing high-performance and low-cost microalloyed steel for automobile I-shaped front axle according to claim 4, It is characterized in that In step (2), the heat treatment process is: first, keep the temperature at 800-880°C for 30 minutes, then quench with water to room temperature; then, keep the temperature at 450-550°C for 90 minutes, then cool with water to room temperature.

6. The method for preparing high-performance and low-cost microalloyed steel for automobile I-shaped front axle according to claim 4, It is characterized in that After heat treatment, the yield strength of high-performance and low-cost micro-alloy steel for automobile I-shaped front axles reaches over 950MPa, the tensile strength reaches over 1050MPa, the elongation reaches over 12%, the cross-sectional shrinkage reaches over 40%, and the fatigue life B50 reaches over 500,000 times.

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