Spring steel and method for producing same, leaf spring

Abstract

This application discloses a spring steel and its preparation method, as well as a leaf spring. The spring steel, by mass percentage, comprises: 0.50%-0.60% C, 1.0%-1.6% Si, 0.9%-1.2% Mn, 0.9%-1.2% Cr, 0.15%-0.3% Ni, 0.01%-0.04% Nb, 0.12%-0.18% V, 0.001%-0.0035% B, less than or equal to 0.020% P, and less than or equal to 0.020% S. The metallographic structure of the spring steel comprises martensite. The spring steel proposed in this application has the aforementioned mass percentages of metallic elements, as well as Fe and other unavoidable impurities. The metallographic structure of the spring steel comprises martensite, exhibiting high hardness, strength, and elongation.

Description

Technical Field

[0001] This application relates to the field of steel materials, specifically to spring steel and its preparation methods, and leaf springs. Background Technology

[0002] The automotive industry is one of the important pillar industries of the national economy. With the improvement of the national economy, the performance requirements for automobiles are also constantly increasing, especially the requirements for safety and usability.

[0003] Leaf springs are a key component of vehicle suspension systems, ensuring ride comfort and vehicle stability by absorbing and releasing energy. During vehicle operation, leaf springs are subjected to repeated bending stresses, continuously absorbing and storing energy to reduce vibrations and impacts from the vehicle itself or external sources, thus playing a role in shock absorption and cushioning, maintaining a smooth ride and high safety and reliability. However, after long-term stress cycling, leaf springs may experience fatigue fracture and elastic relaxation, leading to spring breakage and serious accidents such as rollovers. The performance of leaf springs is limited by the properties of the spring steel used. Improving the durability and fatigue resistance of spring steel is an urgent technical problem to be solved in order to design and manufacture safer and more reliable automotive leaf springs and suspension systems to meet the needs of the modern automotive industry. Summary of the Invention

[0004] In a first aspect of this application, a spring steel is provided, comprising, by mass percentage: 0.50%-0.60% C, 1.0%-1.6% Si, 0.9%-1.2% Mn, 0.9%-1.2% Cr, 0.15%-0.3% Ni, 0.01%-0.04% Nb, 0.12%-0.18% V, 0.001%-0.0035% B, less than or equal to 0.020% P, and less than or equal to 0.020% S, wherein the metallographic structure of the spring steel comprises martensite.

[0005] The spring steel proposed in this application contains the aforementioned percentages of metallic elements, as well as Fe and other unavoidable impurities. The metallographic structure of the spring steel comprises a high proportion of martensite, resulting in high hardness, strength, and elongation.

[0006] In some embodiments, the spring steel comprises, by mass percentage: 0.50%-0.55% C, 1.4%-1.6% Si, 1%-1.2% Mn, 1%-1.2% Cr, 0.15%-0.3% Ni, 0.01%-0.04% Nb, 0.14%-0.18% V, 0.001%-0.0035% B, less than or equal to 0.020% P, and less than or equal to 0.020% S.

[0007] In some embodiments, the yield strength of the spring steel is greater than or equal to 1800 MPa, the tensile strength of the spring steel is greater than or equal to 2040 MPa, and the elongation after fracture is greater than or equal to 9%. Therefore, the spring steel has good resistance to plastic deformation and can withstand high tensile stress.

[0008] In some embodiments, the hardenability DI value of the spring steel is 270-280. Therefore, the spring steel has relatively uniform interfacial mechanical properties, which is beneficial for operation under heavy loads.

[0009] In some embodiments, the tempering hardness of the spring steel is 50HRC-52HRC. Therefore, the final performance of the spring steel achieves a high level of hardness.

[0010] In a second aspect of this application, a method for preparing spring steel is proposed, comprising: heat-treating the steel at a temperature of 920℃-960℃ for a time of 5 min-15 min; quenching the heat-treated steel at a temperature of 850℃-920℃; and tempering the quenched steel at a temperature of 400℃-450℃ for a time of 10 min-40 min, to obtain the spring steel.

[0011] In some embodiments, the quenching process includes oil quenching. This can improve the toughness and fatigue limit of the steel.

[0012] In some embodiments, after the tempering treatment, the cooling rate of the steel is greater than or equal to 2°C / s. This results in a martensitic microstructure.

[0013] In some embodiments, the thickness of the decarburized layer in the steel is less than or equal to 0.26 mm, and the hardness of the steel is less than or equal to 340 HBW. This reduces the impact of the decarburized layer in the steel on the hardness, strength, and other properties of the spring steel.

[0014] In some embodiments, the heat treatment temperature is 930°C-940°C, and the heat treatment time is 8 min-12 min. This allows the entire steel to reach the austenitizing temperature.

[0015] In some embodiments, the quenching temperature is 860℃-890℃. This results in a martensitic metallographic structure with a non-equilibrium state.

[0016] In some embodiments, the tempering temperature is 420℃-440℃, and the tempering time is 15min-30min. This reduces the internal stress generated during the quenching process.

[0017] In a third aspect, this application proposes a leaf spring made of the spring steel disclosed in this application. Compared with leaf springs made of 51CV4 material under the same load, this leaf spring can reduce weight by more than 20% and significantly improve fatigue life. Attached Figure Description

[0018] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0019] Figure 1 This is a metallographic diagram of the heat-treated structure according to an embodiment of this application;

[0020] Figure 2 This is a metallographic diagram of the structure of a component of this application before heat treatment. Detailed Implementation

[0021] The embodiments of this application are described in detail below, with examples of these embodiments shown in the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0022] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit the application; unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0023] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are open-ended expressions, meaning they include what is specified in this application but do not exclude other aspects.

[0024] In the description of this application, all figures disclosed herein, whether or not the words "approximately" or "about" are used, are approximate values. Each figure may vary by less than 10% or by a difference that is considered reasonable by one of the art, such as 1%, 2%, 3%, 4%, or 5%.

[0025] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0026] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0027] Leaf springs are a crucial component in automobiles, significantly impacting vehicle safety and comfort. Based on the operating characteristics and failure modes of leaf springs, certain requirements are placed on the composition, properties, and processing characteristics of the spring steel used in their manufacture. Furthermore, the cost of the spring steel used to produce leaf springs also affects the overall vehicle manufacturing cost. Controlling the amount of modified precious metals added can thus control the production cost of the spring steel, facilitating its wider application.

[0028] To withstand continuous stress cycling, spring steel must possess high tensile strength, elastic limit, and fatigue strength to reduce the likelihood of fracture under high loads or repeated bending. Spring steel also needs good processing properties, including its performance during machining, forming, and heat treatment. Good processing properties improve the yield rate of leaf springs during manufacturing, making the material easier to process and less prone to defects.

[0029] The aforementioned performance requirements place high demands on the research and application of spring steel, necessitating both high performance and consideration of material costs and production processes. The spring steel proposed in this application possesses high yield strength and high tensile strength, while its processing method has a relatively short manufacturing cycle, facilitating large-scale promotion and application.

[0030] In a first aspect of this application, a spring steel is provided, comprising, by mass percentage: 0.50%-0.60% C, 1.0%-1.6% Si, 0.9%-1.2% Mn, 0.9%-1.2% Cr, 0.15%-0.3% Ni, 0.01%-0.04% Nb, 0.12%-0.18% V, 0.001%-0.0035% B, less than or equal to 0.020% P, and less than or equal to 0.020% S, wherein the metallographic structure of the spring steel comprises martensite.

[0031] The spring steel proposed in this application contains the aforementioned percentages of metallic elements, as well as Fe and other unavoidable impurities. The carbon content in the spring steel is 0.50%-0.60% by mass, making it a medium-carbon steel, which is beneficial for improving the steel's plasticity and reducing decarburization sensitivity. Cr element improves the hardenability of the spring steel, helps control carbide precipitation, and contributes to higher strength after quenching or tempering; it is an important alloying element in spring steel. Ni element improves the hardenability and corrosion resistance of the spring steel, inhibits corrosion in acidic environments, and helps improve the delayed fracture resistance of the spring steel. Appropriate addition of Nb element can refine the grains in the spring steel and enhance the stability of austenite grains in high-temperature regions. The addition of V element can improve the hardness and strength of the spring steel, and V element has a low solution temperature, effectively improving hardenability and recrystallization temperature during rolling. B element improves hardenability and inhibits the segregation of P and S elements to grain boundaries, thus improving grain boundary strength and the toughness of the spring steel. The carbon (C) content in the spring steel proposed in this application is within the aforementioned range, which is beneficial to the formation of martensite in the spring steel. The composition and combination of elements in the spring steel within the aforementioned range can affect the critical cooling temperature of the spring steel, thus favoring the formation of martensite. The metallographic structure of the spring steel includes a high proportion of martensite, as referenced... Figure 1 Martensitic structure can improve the strength and toughness of spring steel. Therefore, the spring steel has high yield strength, tensile strength and elongation.

[0032] In some embodiments, the spring steel comprises, by mass percentage: 0.50%-0.55% C, 1.4%-1.6% Si, 1%-1.2% Mn, 1%-1.2% Cr, 0.15%-0.3% Ni, 0.01%-0.04% Nb, 0.14%-0.18% V, 0.001%-0.0035% B, less than or equal to 0.020% P, less than or equal to 0.020% S, with the remainder being Fe and unavoidable impurities.

[0033] In some embodiments, the yield strength of the spring steel is greater than or equal to 1800 MPa, the tensile strength of the spring steel is greater than or equal to 2040 MPa, and the elongation after fracture of the spring steel is greater than or equal to 9%. Therefore, refer to... Figure 1 The spring steel has high strength because the martensite laths formed are relatively small, and the combination of fine grain strengthening and dislocation strengthening results in a small martensite lath group. Figure 1The high density of dislocations between the martensitic laths allows for greater slip along the lath boundaries with a longer mean free path, enhancing the plastic deformation capacity of the spring steel and thus improving its overall strength and ductility. Consequently, the yield strength, tensile strength, and elongation of the spring steel reach the aforementioned range.

[0034] In some embodiments, the hardenability DI value of the spring steel is 270-280. The formula for calculating the hardenability DI value is as follows:

[0035] DI(in)=25.4×0.54C×(0.7Si+1)×(3.3333Mn+1)×(2.16Cr+1)×(0.321+1.450Ni-0.612(Ni) 2 +0.125(Ni) 2 )×(1.73V+1), where each element is a mass percentage.

[0036] The spring steel of this application exhibits good hardenability, with its core quenching yielding over 80% martensite, resulting in high hardness and wear resistance, which helps improve its fatigue performance and impact resistance. Due to its good hardenability, steel components made from this spring steel possess relatively uniform mechanical properties across their cross-section, reducing deformation and cracking under stress.

[0037] In some embodiments, the tempering hardness of the spring steel is 50-52 HRC.

[0038] Tempering hardness is an important indicator for the final performance acceptance of spring steel. After tempering, the internal stress of the steel is reduced and the structure is stabilized, which causes the hardness and toughness of the steel to change again.

[0039] In a second aspect of this application, a method for preparing spring steel is proposed, comprising: heat-treating steel raw material at a temperature of 920℃-960℃ for a time of 5 min-15 min; quenching the heat-treated steel at a temperature of 850℃-920℃; and tempering the quenched steel at a temperature of 400℃-450℃ for a time of 10 min-40 min, to obtain the spring steel.

[0040] The method for preparing spring steel proposed in this application uses steel raw materials that, by mass percentage, include: 0.50%-0.60% C, 1.0%-1.6% Si, 0.9%-1.2% Mn, 0.9%-1.2% Cr, 0.15%-0.3% Ni, 0.01%-0.04% Nb, 0.12%-0.18% V, 0.001%-0.0035% B, less than or equal to 0.020% P, less than or equal to 0.020% S, and iron and other unavoidable impurities. (Reference) Figure 2 The metallographic structure consists mostly of pearlite and a small amount of ferrite. Using the method for preparing spring steel proposed in this application, the pearlite and ferrite in the steel raw material can be transformed into martensite, resulting in spring steel with higher tensile strength, yield strength, and elongation.

[0041] In some embodiments, the quenching treatment includes oil quenching. This is beneficial for refining the grain size of the martensitic structure. 。 The spring steel of this application has a suitable grain size. A suitable grain size can optimize the strength and toughness of the steel. Fine and uniform grains help to improve the fatigue resistance and toughness of the spring steel.

[0042] In some embodiments, after the tempering treatment, the cooling rate of the steel is greater than or equal to 2°C / s. Thus, the cooling rate reaches the critical cooling rate, and after tempering, the spring steel obtains a martensitic metallographic structure. Furthermore, tempering treatment gives the spring steel better surface quality and lower decarburization sensitivity, resulting in better corrosion resistance and wear resistance. Improved surface quality also helps extend the service life of the spring steel.

[0043] In some embodiments, the thickness of the decarburized layer in the steel is less than or equal to 0.26 mm, and the hardness of the steel is less than or equal to 340 HBW. Because the decarburized layer itself has low strength, limiting the thickness of the decarburized layer is beneficial to improving the strength of the steel.

[0044] In some embodiments, the heat treatment temperature is 930℃-940℃, and the heat treatment time is 8min-12min.

[0045] In some embodiments, the quenching temperature is 860℃-890℃. Within the aforementioned quenching temperature range, during the quenching process, some of the microalloying elements and their compounds present in the steel will pin to the grain boundaries, inhibiting the growth of austenite grains and facilitating the transformation of austenite to martensite. Simultaneously, some alloying elements in the steel play a role in solid solution strengthening and precipitation strengthening, thereby improving the strength and hardness of the steel.

[0046] In some embodiments, the tempering temperature is 420℃-440℃, and the tempering time is 15min-30min. Therefore, tempering the steel immediately after quenching can effectively reduce or eliminate the residual stress generated during quenching, which is beneficial for the formation of martensite, thereby improving the plasticity and toughness of the steel. Furthermore, the carbonitriding compounds precipitated during tempering also contribute to improving the strength and toughness of the steel.

[0047] In a third aspect, this application provides a leaf spring made of the spring steel disclosed in this application.

[0048] In some embodiments, the spring steel proposed in this application can also be made into air suspension guides or round steel as stabilizer bars and other components, so as to make full use of the advantages of springs such as high strength, high toughness, high hardenability, and lightweight.

[0049] The following specific embodiments illustrate the solution of this application. It should be noted that these embodiments are for illustrative purposes only and should not be considered as limiting the scope of this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0050] Examples 1-5

[0051] The steel raw material was heat-treated at a temperature of 930℃ for 10 minutes.

[0052] The heat-treated steel is then subjected to quenching treatment at a temperature of 870°C.

[0053] The quenched steel is then subjected to tempering treatment at a temperature of 400°C for 30 minutes, followed by a cooling rate of 30°C / s to obtain spring steel with a hardenability Di of 276.

[0054] Samples were taken from different parts of the spring steel as test samples for Examples 1-5.

[0055] The chemical composition (mass percentage) of the steel raw materials in Examples 1-5 is shown in Table 1.

[0056] Table 1

[0057]

[0058] Test method:

[0059] Tensile strength, yield strength, elongation, and reduction of area were tested in accordance with GB / T 228.1 Metallic materials - Tensile testing - Part 1: Test method at room temperature.

[0060] Test results: See Table 2.

[0061] Table 2

[0062]

[0063] As shown in Table 2, the spring steel samples obtained from different locations all had tensile strengths of 2040 MPa and above, yield strengths of 1800 MPa and above, and elongations of 9% and above.

[0064] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0065] In this application, the order in which the steps are written does not imply a strict execution order and does not limit the implementation process. The specific execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps in this application can be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0066] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A spring steel, characterized in that The spring steel comprises, by mass percentage: 0.50%-0.60% C, 1.0%-1.6% Si, 0.9%-1.2% Mn, 0.9%-1.2% Cr, 0.15%-0.3% Ni, 0.01%-0.04% Nb, 0.12%-0.18% V, 0.001%-0.0035% B, less than or equal to 0.020% P, and less than or equal to 0.020% S, wherein the metallographic structure of the spring steel comprises martensite.

2. Spring steel according to claim 1, characterized in that The spring steel comprises, by weight percentage: 0.50%-0.55% C, 1.4%-1.6% Si, 1%-1.2% Mn, 1%-1.2% Cr, 0.15%-0.3% Ni, 0.01%-0.04% Nb, 0.14%-0.18% V, 0.001%-0.0035% B, less than or equal to 0.020% P, and less than or equal to 0.020% S.

3. The spring steel according to claim 1, characterized in that, The yield strength of the spring steel is greater than or equal to 1800 MPa; and / or, the tensile strength of the spring steel is greater than or equal to 2040 MPa; and / or, the elongation after fracture of the spring steel is greater than or equal to 9%.

4. The spring steel according to any one of claims 1-3, characterized in that, The DI value of the spring steel is 270-280.

5. The spring steel according to any one of claims 1-3, characterized in that, The tempering hardness of the spring steel is 50HRC-52HRC.

6. A method for preparing the spring steel according to any one of claims 1-5, characterized in that, include: The steel is subjected to heat treatment at a temperature of 920℃-960℃ for a time of 5min-15min. The heat-treated steel is then subjected to quenching treatment at a temperature of 850℃-920℃. The quenched steel is then subjected to tempering treatment at a temperature of 400℃-450℃ for a duration of 10min-40min to obtain the spring steel.

7. The method according to claim 6, characterized in that, The quenching treatment includes oil quenching; and / or, After the tempering treatment, the cooling rate of the steel is greater than or equal to 2°C / s.

8. The method according to claim 6 or 7, characterized in that, The thickness of the decarburized layer in the steel is less than or equal to 0.26 mm; and / or the hardness of the steel is less than or equal to 340 HBW.

9. The method according to claim 6 or 7, characterized in that, The heat treatment temperature is 930℃-940℃, and the heat treatment time is 8min-12min; and / or, The quenching temperature is 860℃-890℃; and / or, The tempering temperature is 420℃-440℃, and the tempering time is 15min-30min.

10. A leaf spring, characterized in that, The leaf spring is made of the spring steel described in any one of claims 1-5.

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