阅读说明：本技术 一种合金弹簧钢的热处理工艺 (Heat treatment process of alloy spring steel ) 是由 赵小军 谷杰 黄飞 于 2020-06-04 设计创作，主要内容包括：本发明提供了一种合金弹簧钢的热处理工艺,包括对钢坯进行预热、加热、等温球化退火、淬火、冷却、中温回火、两次喷丸处理和加工检验,通过控制等温球化退火的温度在650～700℃,退火时间在2～3h,避免出现部分碳化物未能充分球化的现象,降低弹簧钢的硬度至32～48HRC,改善后续热处理中容易产生变形或开裂的问题,降低相应的抗拉强度至1810～1930MPa,使用应力幅度比传统工艺制成的弹簧钢提高10～15％,使其具有更高的延展性和韧性；通过控制淬火的温度来降低淬火应力,减小形变,以获得较高屈强比和良好的综合力学性能,通过控制冷却方式以及采用两次喷丸处理,强化弹簧钢的表面,改善了弹簧钢的表面质量并在表面产生残留压应力,提高了弹簧钢的疲劳强度和使用寿命。(The invention provides a heat treatment process of alloy spring steel, which comprises the steps of preheating a steel billet, heating, isothermal spheroidizing annealing, quenching, cooling, medium-temperature tempering, shot blasting for two times and processing inspection, wherein the isothermal spheroidizing annealing temperature is controlled to be 650-700 ℃, the annealing time is 2-3 hours, the phenomenon that partial carbides cannot be fully spheroidized is avoided, the hardness of the spring steel is reduced to 32-48 HRC, the problem that deformation or cracking is easy to generate in subsequent heat treatment is solved, the corresponding tensile strength is reduced to 1810-1930 MPa, the stress amplitude is increased by 10-15% compared with that of the spring steel manufactured by the traditional process, and the spring steel has higher ductility and toughness; the quenching stress is reduced by controlling the quenching temperature, the deformation is reduced, so that higher yield ratio and good comprehensive mechanical property are obtained, the surface of the spring steel is strengthened by controlling the cooling mode and adopting two times of shot blasting treatment, the surface quality of the spring steel is improved, the residual pressure stress is generated on the surface, the fatigue strength of the spring steel is improved, and the service life of the spring steel is prolonged.)

1. The heat treatment process of the alloy spring steel is characterized by comprising the following steps of:

(1) preheating: preheating an alloy spring billet in a heating furnace to 670-750 ℃ and preserving heat;

(2) heating: heating the steel billet to 800-840 ℃ and preserving heat;

(3) isothermal spheroidizing annealing: cooling to 650-700 ℃ along with the furnace, and carrying out isothermal spheroidizing annealing;

(4) quenching: after isothermal spheroidizing annealing, heating to 830-870 ℃ for quenching and heat preservation;

(5) and (3) cooling: after heat preservation, oil-cooling the steel billet to 150 ℃, taking out the steel billet and cleaning the steel billet;

(6) medium temperature tempering: putting the cleaned steel billet into a tempering furnace, heating the steel billet to 400-500 ℃, tempering, preserving heat, and taking out of the furnace and air cooling at room temperature;

(7) shot blasting for two times;

(8) and finally obtaining the alloy spring steel after processing and inspection.

2. The heat treatment process of the alloy spring steel according to claim 1, wherein the alloy spring steel billet in the step (1) is 50 CrVA.

3. The heat treatment process of the alloy spring steel according to claim 1, wherein the preheating time of the steel billet in the step (1) is 20-40 min.

4. The heat treatment process of the alloy spring steel according to claim 1, wherein the heat preservation time of the steel blank heated in the step (2) is 30-60 min; the heating furnace in the step (2) is a tubular furnace or a resistance furnace, and protective gas is introduced in the heating process; the protective gas is nitrogen or argon, and the flow of the protective gas is 4-4.5L/h.

5. The heat treatment process of the alloy spring steel according to claim 1, wherein the cooling rate in the step (3) is 100-120 ℃/h, and the isothermal spheroidizing annealing is performed for 2-3 h after the steel billet is cooled to 650-700 ℃ along with the furnace.

6. The heat treatment process of the alloy spring steel according to claim 1, wherein the quenching and heat preservation time in the step (4) is 40-60 min.

7. The heat treatment process of the alloy spring steel according to claim 1, wherein in the step (6), the steel blank is tempered and kept warm for 1-2 hours; the tempering furnace in the step (6) is a roller hearth type heat treatment furnace.

8. The heat treatment process of alloy spring steel according to claim 1, wherein the step (7) of shot peening twice is divided into a rough peening and a fine peening process; the time of the coarse spraying process is controlled to be 10-20 min.

Technical Field

The invention relates to the technical field of heat treatment, in particular to a heat treatment process of alloy spring steel.

Background

The spring steel is widely applied to industries such as modern industrial equipment, mechanical parts, automobiles, engines, railways and the like. The spring mainly works under dynamic load, namely under the conditions of impact and vibration or under the action of alternating stress, and absorbs impact energy by elastic deformation to play a role in buffering. Since springs are often subjected to vibrations and operate under phase change stresses for long periods, mainly fatigue failure, spring steels must have high elastic and fatigue limits. In addition, it should have sufficient toughness and plasticity to prevent sudden brittle failure under impact forces. With the enhancement of industrial capacity in China, industrial equipment develops towards the direction of large load capacity and high running speed, mechanical parts bear larger and larger loads, and the action frequency is more frequent. The practical use requirements require that the spring steel parts have excellent comprehensive performance, mechanical property, anti-elastic degradation performance, anti-fatigue performance, hardenability and physical and chemical properties. Meanwhile, from the viewpoint of energy conservation and economy, the equipment is required to be light in weight. At present, the research on spring steel at home and abroad mainly aims to improve the strength level and the service life of the spring steel.

According to the GB/T13304 standard, spring steel in China is divided into non-alloy spring steel and alloy spring steel, wherein the basic composition series of the alloy spring steel comprises silicon-manganese spring steel, silicon-chromium spring steel, chromium-manganese spring steel, chromium-vanadium spring steel, tungsten-chromium-vanadium spring steel and the like. 50CrVA is used as a high-quality alloy spring steel, has good mechanical property and process property and higher hardenability, vanadium is added to refine the crystal grains of the steel, the overheating sensitivity is reduced, the strength and the toughness are improved, the steel has high fatigue strength and higher yield ratio, and the steel is used as a high-load important spring with larger cross section and a valve spring, a piston spring and a safety valve spring with the working temperature of less than 300 ℃. But the spring steel is subjected to dispersion strengthening during spheroidizing annealing, and supercooled austenite cannot be fully spheroidized, so that an upper bainite structure is generated, the hardness of the upper bainite structure is high, subsequent processing is not facilitated, and meanwhile, local stress concentration on the surface of the spring steel can cause microcracks to appear, early damage is caused, the service life of the spring steel is shortened, and the product performance is influenced.

Disclosure of Invention

The invention aims to provide a heat treatment process of alloy spring steel, which is used for reducing the surface hardness of a spring steel billet, improving the problems of local stress concentration and easy occurrence of microcracks on the surface, improving the fatigue strength of the spring steel and prolonging the service life of the spring steel.

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

a heat treatment process of alloy spring steel comprises the following steps:

(1) preheating: preheating the steel billet in a heating furnace to 670-750 ℃ and preserving heat;

(2) heating: heating the steel billet to 800-840 ℃ and preserving heat;

(3) isothermal spheroidizing annealing: cooling to 650-700 ℃ along with the furnace, and carrying out isothermal spheroidizing annealing;

(4) quenching: after isothermal spheroidizing annealing, heating to 830-870 ℃ for quenching and heat preservation;

(5) and (3) cooling: carrying out heat preservation, carrying out oil cooling on the steel billet to 100-150 ℃, taking out the steel billet and cleaning the steel billet;

(6) medium temperature tempering: putting the cleaned steel billet into a tempering furnace, heating the steel billet to 400-500 ℃, tempering, preserving heat, and taking out of the furnace and air cooling at room temperature;

(7) shot blasting for two times;

(8) and finally obtaining the alloy spring steel after processing and inspection.

Further, the alloy spring steel billet in the step (1) is 50 CrVA.

Further, the heat preservation time of the preheated billet in the step (1) is 20-40 min.

Further, the heat preservation time for heating the steel blank in the step (2) is 30-60 min; heating a furnace tube furnace or a resistance furnace in the step (2), and introducing protective gas in the heating process; the protective gas is nitrogen or argon, and the flow of the protective gas is 4-4.5L/h.

Further, the cooling rate in the step (3) is 100-120 ℃/h, and the isothermal spheroidizing annealing is carried out for 2-3 h after the billet is cooled to 650-700 ℃ along with the furnace.

Further, the quenching and heat preservation time in the step (4) is 40-60 min.

Further, tempering and heat preservation are carried out on the steel blank in the step (6) for 1-2 hours; the tempering furnace in the step (6) is a roller hearth type heat treatment furnace.

Further, the shot blasting treatment twice in the step (7) is divided into a coarse blasting process and a fine blasting process; the time of the coarse spraying process is controlled to be 10-20 min.

The invention has the beneficial effects that:

1. the invention adopts the isothermal spheroidizing annealing process, avoids the phenomenon that partial carbide is not fully spheroidized by controlling the temperature and time of spheroidizing annealing, ensures that granular pearlite is uniformly distributed and has high granulation degree, reduces the hardness of the spring steel to 32-48 HRC, ensures that the spring steel is easy to process and form in a cold and hot state, improves the problem that the spring steel is easy to deform or crack in subsequent heat treatment, simultaneously reduces the corresponding tensile strength to 1810-1930 MPa, improves the using stress amplitude by 10-15 percent compared with the spring steel prepared by the traditional process, stabilizes the structure and the size of the spring steel, and ensures that the spring steel has higher ductility and toughness.

2. The invention reduces the quenching stress and the deformation by controlling the quenching temperature so as to obtain higher yield ratio and good comprehensive mechanical property, strengthens the surface of the spring steel by controlling the cooling mode and adopting two shot blasting treatments, improves the surface quality of the spring steel, generates residual compressive stress on the surface, improves the fatigue strength of the spring steel and prolongs the service life of the spring steel.

Drawings

FIG. 1 is a flow chart of the heat treatment process of the alloy spring steel of the invention.

Detailed Description

The invention will be described in further detail below with reference to the drawings, but the scope of the invention is not limited thereto.

The invention provides a heat treatment process of alloy spring steel, which comprises an isothermal spheroidizing annealing process, a quenching process and a shot blasting process, wherein the isothermal spheroidizing annealing process is controlled to be at 650-700 ℃, the quenching temperature is controlled to be at 830-870 ℃, the shot blasting process is divided into a coarse blasting process and a fine blasting process, and the time of the coarse blasting process is controlled to be 10-20 min.