阅读说明：本技术 一种耐热高强度弹簧用钢及其生产方法 (Heat-resistant high-strength spring steel and production method thereof ) 是由 张晓瑞 汪开忠 尹德福 龚梦强 姜婷 于同仁 孙凯 郭湛 余良其 丁雷 吴建曦 于 2020-06-29 设计创作，主要内容包括：本发明公开了一种耐热高强度弹簧用钢及其生产方法,属于金属冶炼技术领域。本发明的一种耐热高强度弹簧用钢化学成份,按重量百分比为：C 0.55％～0.65％、Si 1.30％～2.00％、Mn 0.70％～0.90％、Cr 0.10％～0.30％、V 0.20％～0.40％、Mo 0.10％～0.30％、W 0.60％～1.20％、P痕量～0.015％、S痕量～0.010％、O≤0.0012％、N≤0.006％,其余为Fe和其它不可避免的杂质。化学成分配比需保证满足关系式：(1)W/(Mo+Co)≥1.5；(2)0.9C≤0.35W+0.70Mo+0.20Cr+V≤1.5C。本发明还提供了该钢的生产方法及热处理工艺。热处理后常温力学性能：抗拉强度≥1850MPa,断后伸长率≥10％,断面收缩率≥40％,疲劳强度≥860MPa；高温力学性能400℃抗拉强度≥900MPa,高温下应力变化率＜35％,具有良好的高温性能及高温抗松弛性能,满足高温环境中弹簧使用的要求。(The invention discloses heat-resistant high-strength spring steel and a production method thereof, belonging to the technical field of metal smelting. The invention relates to a heat-resistant high-strength spring steel which comprises the following chemical components in percentage by weight: 0.55 to 0.65 percent of C, 1.30 to 2.00 percent of Si, 0.70 to 0.90 percent of Mn, 0.10 to 0.30 percent of Cr, 0.20 to 0.40 percent of V, 0.10 to 0.30 percent of Mo, 0.60 to 1.20 percent of W, 0.015 percent of trace of P, 0.010 percent of trace of S, less than or equal to 0.0012 percent of O, less than or equal to 0.006 percent of N, and the balance of Fe and other inevitable impurities. The chemical component proportion needs to be ensured to satisfy the relation: (1) W/(Mo + Co) is more than or equal to 1.5; (2)0.9C is less than or equal to 0.35W, 0.70Mo, 0.20Cr and V is less than or equal to 1.5C. The invention also provides a production method and a heat treatment process of the steel. Mechanical properties at normal temperature after heat treatment: the tensile strength is more than or equal to 1850MPa, the elongation after fracture is more than or equal to 10 percent, the reduction of area is more than or equal to 40 percent, and the fatigue strength is more than or equal to 860 MPa; the tensile strength is more than or equal to 900MPa at the high-temperature mechanical property of 400 ℃, the stress change rate at the high temperature is less than 35 percent, and the high-temperature-resistant and anti-relaxation high-temperature-resistant rubber has good high-temperature performance and high-temperature-resistant relaxation performance and meets the requirement of using a spring in a high-temperature environment.)

1. A steel for heat-resistant high-strength springs, characterized in that: the spring steel comprises, by weight, 0.55-0.65% of C, 1.30-2.00% of Si, 0.70-0.90% of Mn, 0.10-0.30% of Cr, 0.20-0.40% of V, 0.10-0.30% of Mo, 0.60-1.20% of W, 0.015% of trace amount of P, 0.010% of trace amount of S, and the balance of Fe and other inevitable impurities.

2. The steel for heat-resistant high-strength springs as claimed in claim 1, wherein: the spring steel also contains element Co.

3. The steel for heat-resistant high-strength springs as claimed in claim 2, wherein: the content of the element Co is controlled to be 0.020-0.040% by weight percent.

4. The steel for heat-resistant high-strength springs as claimed in claim 3, wherein: the chemical composition proportion of the spring steel meets the formula that 0.9C is less than or equal to 0.35W, 0.70Mo, 0.20Cr and V are less than or equal to 1.5C.

5. The steel for heat-resistant high-strength springs as claimed in claim 4, wherein: the chemical composition distribution ratio of the spring steel also meets the formula W/(Mo + Co) being more than or equal to 1.5.

6. The steel for heat-resistant high-strength springs as claimed in claim 5, wherein: the content of impurity O in the spring steel is controlled to be less than or equal to 0.0012 percent, and the content of impurity N is controlled to be less than or equal to 0.006 percent.

7. Method for producing a spring steel according to any one of claims 1 to 6, characterized in that it comprises the steps of:

step one, smelting in an electric arc furnace;

step two, refining in an LF furnace;

step three, RH or VD vacuum degassing;

step four, round billet continuous casting;

step five, rolling the square billet;

step six, flaw detection and grinding;

heating the excellent rod in a heating furnace;

step eight, rolling and cooling control;

step nine, finishing the round steel;

step ten, quenching and tempering the round steel.

8. The method for producing a steel for a heat-resistant high-strength spring according to claim 7, characterized in that: in the seventh step, the heating temperature of the excellent rod heating furnace is 980-1070 ℃, and the furnace time of the square billet is less than or equal to 170 min.

9. The method for producing a steel for a heat-resistant high-strength spring according to claim 8, characterized in that: and in the step eight, rolling and cooling control adopt KOCKS rolling and cooling control rolling, the initial rolling temperature is 880-945 ℃, and the final rolling temperature is 780-840 ℃.

10. The method for producing a steel for a heat-resistant high-strength spring according to claim 9, characterized in that: in the step ten, the quenching and tempering process comprises the steps of quenching, heating at 870 ℃ and oil cooling, wherein the temperature of a quenching medium is 15-35 ℃; then tempering, heating to 400 ℃ and air cooling to room temperature.

Technical Field

The invention relates to the technical field of metal smelting, in particular to heat-resistant high-strength spring steel and a production method thereof.

Background

The spring is a key basic part in the equipment manufacturing industry, has large quantity and wide variety, and is widely applied to various fields of national economy such as automobiles, railways, engineering machinery, electronic appliances and the like. The spring is widely used in various industries and plays an important role in the stability and safety of automobiles, airplanes and machinery, so that the requirement on the performance of the spring steel is extremely high.

Along with the lightweight of automobiles, the large-scale of major technical equipment and the limitation of parameters, increasingly high requirements are put forward on the variety and the performance of spring steel. According to the use requirements of different environments, spring steel products with a plurality of special properties, such as heat-resistant spring steel, are provided, and particularly, with the rapid development of domestic aviation industry, the spring steel needs to meet the requirements of high toughness of common springs and also needs to bear higher temperature and certain pressure during working, and the spring material is required to have good heat resistance. Spring steel is required to have good resistance to deformation due to its special use environment. The existing spring steel has poor deformation resistance at high temperature and is easy to deform, so that the existing spring steel cannot meet the use requirements of various occasions.

Through search, the Chinese patent CN107177782, publication date is: 2017, 9 and 19 months and discloses corrosion-resistant spring steel and a preparation method thereof, wherein the corrosion-resistant spring steel comprises the chemical components of 0.50-0.64% of C, 1.5-2.0% of Si, 0.70-1.0% of Mn, 0.05-0.09% of P, less than or equal to 0.015% of S, 0.75-1.10% of Cr, 0.12-0.50% of Cu, 0.01-0.05% of Nb and the balance of Fe and inevitable impurities. The spring steel has excellent mechanical property and corrosion resistance by adding a small amount of P, Cr, Cu, Nb and other spring steel components for microalloying and simply optimizing the production process, and the related production raw materials have low cost and simple production process, but the tensile strength is only 1700MPa and the spring steel does not have good heat resistance.

Chinese patent CN107747060A, published as: 3.2.2018, discloses a production method of a high-strength and high-fatigue life spring steel, which comprises the following chemical components in percentage by weight of 0.51-0.59% of carbon, 1.40-1.60% of silicon, 0.50-0.80% of manganese, less than or equal to 0.012% of phosphorus, less than or equal to 0.010% of sulfur, less than or equal to 0.02% of niobium, less than or equal to 0.005% of titanium, less than or equal to 0.005% of aluminum, 0.50-0.80% of chromium, and the balance of Fe and inevitable impurities. By adopting a series of new smelting and rolling technologies such as high alloying component design, LF + VD composite refining, casting blank flaw detection and coping, stelmor controlled rolling and cooling, the high-strength and high-fatigue-life wire spring steel with a sorbite structure as a matrix is produced, but the spring steel has low strength which is only 1000MPa and does not have good heat resistance and impact resistance.

Disclosure of Invention

1. Technical problem to be solved by the invention

In view of the problems that the performance requirements of the existing spring steel are higher and higher in many working occasions and the existing spring steel cannot meet the use requirements in the occasions, the invention provides the heat-resistant high-strength spring steel and the production method thereof, and the steel is added with a plurality of elements to change the performance of the steel so as to meet the use requirements of high performance.

2. Technical scheme

In order to achieve the purpose, the technical scheme provided by the invention is as follows:

the heat-resistant high-strength spring steel comprises, by weight, 0.55-0.65% of C, 1.30-2.00% of Si, 0.70-0.90% of Mn, 0.10-0.30% of Cr, 0.20-0.40% of V, 0.10-0.30% of Mo, 0.60-1.20% of W, 0.015% of trace of P, 0.010% of trace of S and the balance of Fe and other inevitable impurities.

Furthermore, the spring steel also comprises element Co.

Furthermore, the content of the element Co is controlled to be 0.020-0.040% by weight.

Furthermore, the chemical composition ratio of the spring steel meets the formula of 0.9C-0.35W +0.70Mo +0.20Cr + V-1.5C.

Furthermore, the chemical composition distribution ratio of the spring steel also meets the formula W/(Mo + Co) being more than or equal to 1.5.

Furthermore, the content of the impurity O in the spring steel is controlled to be less than or equal to 0.0012 percent, and the content of the impurity N is controlled to be less than or equal to 0.006 percent.

The invention relates to a production method of heat-resistant high-strength spring steel, which comprises the following steps:

step one, smelting in an electric arc furnace;

step two, refining in an LF furnace;

step three, RH or VD vacuum degassing;

step four, round billet continuous casting;

step five, rolling the square billet;

step six, flaw detection and grinding;

heating the excellent rod in a heating furnace;

step eight, rolling and cooling control;

step nine, finishing the round steel;

step ten, quenching and tempering the round steel.

Furthermore, in the seventh step, the heating temperature of the excellent rod heating furnace is 980-1070 ℃, and the furnace time of the square billet is less than or equal to 170 min.

Furthermore, in the eighth step, the controlled rolling and controlled cooling adopts KOCKS controlled rolling and controlled cooling rolling, the initial rolling temperature is 880-945 ℃, and the final rolling temperature is 780-840 ℃.

Further, in the tenth step, the quenching and tempering process comprises quenching, heating at 870 ℃ and oil cooling, wherein the temperature of a quenching medium is 15-35 ℃; then tempering, heating to 400 ℃ and air cooling to room temperature.

3. Advantageous effects

Compared with the prior art, the technical scheme provided by the invention has the following beneficial effects:

(1) according to the heat-resistant high-strength spring steel, elements such as W, Mo, Cr and V are added into the steel, and the components are matched with each other by adjusting the content of each component in the steel, so that the high-temperature performance of the spring steel is improved, the mechanical property of the spring steel at normal temperature is ensured, and meanwhile, the fatigue strength and the stress relaxation resistance of the spring steel at high temperature are improved, so that the use requirements of various industries are met.

(2) According to the heat-resistant high-strength spring steel, the V element is added, the grain size of the spring steel is refined, the toughness of the spring steel is not reduced while the strength is improved, and the wear resistance and the impact resistance of the spring steel can be improved by forming carbide with the C. By adding W, Mo, Cr, V and other elements, the element proportion satisfies the relation that 0.9C is less than or equal to 0.35W +0.70Mo +0.20Cr + V is less than or equal to 1.5C, and the elements form enough fine dispersed and stable carbides, so that the fatigue strength of the spring steel at high temperature is improved while the normal temperature performance of the spring steel is better, and meanwhile, the obtained spring steel has certain stress relaxation resistance, and the spring steel meets the use requirements under various conditions.

(3) According to the heat-resistant high-strength spring steel, the Co element is added into the steel, so that the precipitation of alloy carbide can be effectively promoted, the dispersity of the alloy carbide is increased, the secondary hardening effect is improved, the heat resistance and the heat stability are improved, and the corrosion resistance can be improved by a certain amount of Co. Co element is matched with W, M, and the three satisfy the relation: W/(Mo + Co) is not less than 1.5, and the hardenability, the heat resistance and the high-temperature tempering resistance of the spring steel are ensured while the red hardness of the spring steel is improved, so that the stress relaxation resistance of the spring steel at high temperature is further improved, and the high-temperature fatigue strength of the spring steel is further improved.

(4) The production method of the heat-resistant high-strength spring steel provided by the invention has the advantages that when the steel is subjected to heat treatment, in order to prevent overhigh temperature during quenching from easily causing excessive austenite grains to grow and decarbonize, the fatigue life of the spring steel is influenced, and the quenching heating temperature is controlled to be 850-950 ℃. Meanwhile, in order to prevent the precipitation of insufficient carbon at too low tempering temperature or excessive growth of carbides at too high temperature, the tempering temperature is controlled to be 370-470 ℃.

(5) According to the production method of the heat-resistant high-strength spring steel, the normal-temperature mechanical property of the obtained spring steel is superior to that of common spring steel after heat treatment; meanwhile, the high-temperature mechanical property and high-temperature stress relaxation resistance of the alloy are improved, and the alloy has good high-temperature property and high-temperature relaxation resistance and can meet the use requirements under various conditions.

Drawings

FIG. 1 is a table of chemical compositions used in examples of the present invention and comparative examples;

FIG. 2 is a table showing the mechanical properties at room temperature after heat treatment of steels obtained in examples of the present invention and comparative examples;

FIG. 3 is a table showing high-temperature mechanical properties of steels obtained in examples of the present invention and comparative examples after heat treatment;

FIG. 4 is a table showing high temperature stress relaxation properties of steels obtained in examples of the present invention and comparative examples.

Detailed Description

According to the heat-resistant high-strength spring steel, elements such as W, Mo, Cr and V are added into the steel, and the components are matched with each other by adjusting the content of each component in the steel, so that the high-temperature performance of the spring steel is improved, the mechanical property of the spring steel at normal temperature is ensured, and meanwhile, the fatigue strength and the stress relaxation resistance of the spring steel at high temperature are improved, so that the use requirements of various industries are met. By adding the V element, the grain size of the spring steel is refined, the ductility and toughness of the spring steel cannot be reduced while the strength is improved, and meanwhile, the V and the C form carbide, so that the wear resistance and the impact resistance of the spring steel can be improved. By adding W, Mo, Cr, V and other elements, the element proportion satisfies the relation that 0.9C is less than or equal to 0.35W +0.70Mo +0.20Cr + V is less than or equal to 1.5C, and the elements form enough fine dispersed and stable carbides, so that the fatigue strength of the spring steel at high temperature is improved while the normal temperature performance of the spring steel is better, and meanwhile, the obtained spring steel has certain stress relaxation resistance, and the spring steel meets the use requirements under various conditions.

According to the heat-resistant high-strength spring steel, the Co element is added into the steel, so that the precipitation of alloy carbide can be effectively promoted, the dispersity of the alloy carbide is increased, the secondary hardening effect is improved, the heat resistance and the heat stability are improved, and the corrosion resistance can be improved by a certain amount of Co. Co element is matched with W, M, and the three satisfy the relation: W/(Mo + Co) is not less than 1.5, and the hardenability, the heat resistance and the high-temperature tempering resistance of the spring steel are ensured while the red hardness of the spring steel is improved, so that the stress relaxation resistance of the spring steel at high temperature is further improved, and the high-temperature fatigue strength of the spring steel is further improved.

The production method of the heat-resistant high-strength spring steel provided by the invention has the advantages that when the steel is subjected to heat treatment, in order to prevent overhigh temperature during quenching from easily causing excessive austenite grains to grow and decarbonize, the fatigue life of the spring steel is influenced, and the quenching heating temperature is controlled to be 850-950 ℃. Meanwhile, in order to prevent the precipitation of insufficient carbon at too low tempering temperature or excessive growth of carbides at too high temperature, the tempering temperature is controlled to be 370-470 ℃. After the obtained spring steel is subjected to heat treatment, the normal-temperature mechanical property is as follows: the tensile strength is more than or equal to 1850MPa, the elongation after fracture is more than or equal to 10 percent, the reduction of area is more than or equal to 40 percent, and the fatigue strength is more than or equal to 860 MPa; the tensile strength is more than or equal to 900MPa at the high-temperature mechanical property of 400 ℃, the stress change rate of a high-temperature stress relaxation test is less than 35 percent, and the high-temperature-resistant and anti-relaxation material has good high-temperature performance and high-temperature relaxation resistance and can meet the use requirements under various conditions.

The spring steel comprises the following chemical components in percentage by weight: 0.55 to 0.65 percent of C, 1.30 to 2.00 percent of Si, 0.70 to 0.90 percent of Mn, 0.10 to 0.30 percent of Cr, 0.20 to 0.40 percent of V, 0.10 to 0.30 percent of Mo, 0.60 to 1.20 percent of W, 0.20 to 0.40 percent of Co, 0.015 percent of trace amount of P, 0.010 percent of trace amount of S, and the balance of Fe and other inevitable impurities. And the content of O is controlled to be less than or equal to 0.0012 percent and the content of N is controlled to be less than or equal to 0.006 percent.

Wherein, each element has the following functions:

c: c is the most effective reinforcing element in steel, and is an important element in spring steel for ensuring fire hardness and wear resistance, and is necessary for obtaining spring steel having high strength and hardness. The high carbon content is advantageous in strength, hardness, elasticity, and creep properties of the steel, but is disadvantageous in plasticity and toughness of the steel, and also lowers the yield ratio, increases decarburization sensitivity, and deteriorates fatigue resistance and workability of the steel.

Si: si is an important element for strengthening in steel, and the strong hardness of the steel is improved through the solid solution effect, and meanwhile, the sag resistance of the spring steel is improved. Silicon can improve the stability of the rust layer and the corrosion resistance. However, the increase of the Si element increases the diffusion of carbon in the steel, and thus the decarburization of the steel is promoted.

Mn: mn and Fe form a solid solution, so that the hardness and strength of ferrite and austenite in the steel are improved, and meanwhile, Mn is used for improving the stability of an austenite structure and remarkably improving the hardenability of the steel. However, excessive Mn lowers the plasticity of the steel. The addition of Mn is simultaneously beneficial to forming a rust layer on the surface of the steel and improving the corrosion resistance of the steel, but excessive Mn can cause the growth of corrosion product particles and improve the corrosion rate.

Cr: cr and C can form a stable compound, prevent segregation of C or impurities, improve the stability of a matrix, obviously improve the antioxidation of steel and increase the corrosion resistance of the steel. Chromium can significantly increase the hardenability of the steel, but excess Cr increases the temper brittleness tendency of the steel.

V: v is an excellent deoxidizer of steel, and vanadium is added into the steel to refine structure grains and improve the strength and the toughness. V forms carbide with C, and can improve the wear resistance and the impact resistance.

Mo: mo is a stronger carbide forming element, can improve the strength and hardness of steel, can also obviously improve the high-temperature strength, and is the most effective alloy element for improving the heat strength of the steel. In addition, Mo element can improve the hardenability and the tempering stability of the steel, effectively eliminate or reduce the residual stress therein and improve the plasticity thereof. The addition of Mo to spring steel improves the resistance to springing, since Mo can form finely dispersed carbides that prevent dislocation motion. The addition of Mo also reduces the incidence of pitting, but too much Mo content increases the deformation resistance and the inter-granular corrosion tendency.

W: high temperature resistance, which is a solid solution formed by partially dissolving iron in steel in addition to carbide, can improve the normal temperature strength and high temperature strength of steel, increase the tempering stability, red hardness, hot strength and wear resistance, but excessive W can reduce the toughness and high temperature oxidation resistance of steel.

Co: it is worth to say that proper amount of Co can effectively promote the precipitation of alloy carbide, increase its dispersivity, improve the secondary hardening effect, improve the heat resistance and thermal stability, and in addition, a certain amount of Co can also increase the corrosion resistance.

S and P: the sulfur is easy to form MnS inclusion with manganese in the steel, and is unfavorable for the fatigue property of the spring; p is an element with a strong segregation tendency and usually also causes co-segregation of sulphur and manganese, which is detrimental to the homogeneity of the product structure and properties. P is controlled to be less than or equal to 0.015 percent, and S is controlled to be less than or equal to 0.010 percent.

When the spring steel is smelted, O and N are impurities in the spring steel, and the content of the impurities needs to be controlled: o forms oxide inclusions in the steel, and the content of O is controlled to be less than or equal to 0.0012%; fe4N is precipitated from the steel by N, the diffusion speed is slow, the steel has timeliness, and meanwhile, the cold processing performance of the steel is reduced by N, and the N is controlled to be less than or equal to 0.006%.

For a further understanding of the contents of the present invention, reference will now be made in detail to the following examples.