阅读说明：本技术 一种提高c级钢断后伸长率的热处理方法 (Heat treatment method for improving elongation after fracture of C-grade steel ) 是由 苗昕旺 刘希德 臧玉郡 李金红 马宇 李明 于 2020-06-30 设计创作，主要内容包括：一种提高C级钢断后伸长率的热处理方法,将C级钢铸件放入热处理炉中,加热到1100℃保温4小时,随炉冷却到500℃出炉,空冷至室温；重新装入热处理炉,加热到910℃保温3小时,出炉空冷；然后先升温至900℃保温3小时淬火,出炉后水冷,再升温至680℃回火3小时,随炉冷却到500℃出炉,空冷,获得高断后伸长率C级钢。优点是：该热处理工艺与传统的调质工艺相比,成分组织均匀,消除了铸造偏析,提高C级钢的综合力学性能,特别是断后伸长率指标得到大幅提高,满足TB/T 2942-2015标准要求,保证产品合格率。(A heat treatment method for improving the elongation of C-grade steel after fracture comprises the steps of putting a C-grade steel casting into a heat treatment furnace, heating to 1100 ℃, preserving heat for 4 hours, cooling to 500 ℃ along with the furnace, discharging, and cooling to room temperature in air; loading into a heat treatment furnace again, heating to 910 ℃, preserving heat for 3 hours, discharging and air cooling; and then heating to 900 ℃, keeping the temperature for 3 hours, quenching, discharging, cooling by water, heating to 680 ℃, tempering for 3 hours, cooling to 500 ℃ along with the furnace, discharging, and cooling by air to obtain the C-grade steel with high elongation after fracture. The advantages are that: compared with the traditional quenching and tempering process, the heat treatment process has the advantages of uniform component structure, elimination of casting segregation, improvement of the comprehensive mechanical property of C-grade steel, great improvement of the elongation index after fracture, satisfaction of the standard requirement of TB/T2942-doped 2015 and guarantee of the product percent of pass.)

1. A heat treatment method for improving elongation after fracture of C-grade steel is characterized by comprising the following steps:

the method comprises the following steps:

(1) high temperature diffusion annealing

Putting the C-grade steel casting into a heat treatment furnace, heating to 1100 ℃, preserving heat for 4 hours, cooling to 500 ℃ along with the furnace, discharging, and cooling to room temperature;

(2) normalizing treatment

Reloading the C-grade steel workpiece subjected to air cooling in the step (1) into a heat treatment furnace, heating to 910 ℃, preserving heat for 3 hours, discharging and air cooling;

(3) thermal treatment for hardening and tempering

And (3) carrying out quenching and tempering heat treatment on the C-grade steel workpiece subjected to air cooling in the step (2) to obtain the C-grade steel with high elongation after fracture.

2. The heat treatment method for increasing elongation after fracture of C-grade steel according to claim 1, wherein: when in quenching and tempering heat treatment, quenching is carried out firstly, water cooling is carried out after discharging, tempering is carried out, and the furnace is cooled to 500 ℃ along with the furnace and discharged for air cooling.

3. The heat treatment method for increasing elongation after fracture of C-grade steel according to claim 2, wherein: when quenching, the quenching temperature is 900 ℃, and the quenching time is 3 hours.

4. The heat treatment method for increasing elongation after fracture of C-grade steel according to claim 2, wherein: when tempering, the tempering temperature is 680 ℃, and the tempering time is 3 hours.

5. The heat treatment method for increasing elongation after fracture of C-grade steel according to claim 2, wherein: when water cooling is carried out, the temperature of the C-grade steel workpiece is less than or equal to 80 ℃.

6. The heat treatment method for increasing elongation after fracture of C-grade steel according to claim 2, wherein: during tempering treatment, the C-grade steel workpiece is placed into a heat treatment furnace, and the temperature of the heat treatment furnace is less than or equal to 500 ℃.

7. The heat treatment method for increasing elongation after fracture of C-grade steel according to claim 1, wherein: in the heat treatment processes of the step (1), the step (2) and the step (3), the temperature rising speed is less than or equal to 200 ℃/h.

Technical Field

The invention relates to a heat treatment method for improving the elongation of C-grade steel after fracture.

Background

The C-grade steel (ZG25MnCrNiMo) is widely applied to manufacturing railway mechanical parts, along with the continuous development of the high-speed rail, motor train and urban rail industries in China, the coverage of the high-speed rail and motor train products in China is wider and wider, and the requirements on railway part product suppliers are higher and higher.

And under the condition of ensuring that the chemical components of the casting are qualified and the casting defects reach the standard, the mechanical property of the casting is obtained by a proper heat treatment mode. At present, in the heat treatment production process of C-grade steel castings, quenching and tempering heat treatment is generally adopted, but the elongation after fracture of C-grade steel after quenching and tempering heat treatment often has 18% -20% unqualified condition, and the TB/T2942-2015 standard of C-grade steel requires that the elongation after fracture is more than or equal to 22% as a qualified product. Therefore, a new heat treatment process is needed to solve the problem, so that the heat-treated workpiece meets the requirements of TB/T2942-2015 standard, and the product yield is ensured.

Disclosure of Invention

In order to solve the problems, the invention provides a heat treatment method for improving the elongation of C-grade steel after fracture, which meets the standard requirement of TB/T2942-2015 and ensures the product percent of pass.

The technical solution of the invention is as follows:

a heat treatment method for improving elongation after fracture of C-grade steel comprises the following steps:

(1) high temperature diffusion annealing

Putting the C-grade steel casting into a heat treatment furnace, heating to 1100 ℃, preserving heat for 4 hours, cooling to 500 ℃ along with the furnace, discharging, and cooling to room temperature;

(2) normalizing treatment

Reloading the C-grade steel workpiece subjected to air cooling in the step (1) into a heat treatment furnace, heating to 910 ℃, preserving heat for 3 hours, discharging and air cooling;

(3) Thermal treatment for hardening and tempering

And (3) carrying out quenching and tempering heat treatment on the C-grade steel workpiece subjected to air cooling in the step (2) to obtain the C-grade steel with high elongation after fracture.

Further, during quenching and tempering heat treatment, quenching is carried out firstly, water cooling is carried out after discharging, tempering is carried out, and discharging and air cooling are carried out when the temperature is cooled to 500 ℃ along with the furnace.

Furthermore, the quenching temperature is 900 ℃ and the quenching time is 3 hours during quenching.

Furthermore, the tempering temperature is 680 ℃ and the tempering time is 3 hours.

Furthermore, during water cooling, the temperature of the C-grade steel workpiece is less than or equal to 80 ℃.

Further, during tempering treatment, the C-grade steel workpiece is placed into a heat treatment furnace, and the temperature of the heat treatment furnace is less than or equal to 500 ℃.

Further, in the heat treatment processes of the step (1), the step (2) and the step (3), the temperature rise speed is less than or equal to 200 ℃/h.

Before the quenching and tempering heat treatment, the invention carries out high-temperature diffusion annealing to fully homogenize the cast structure and completely eliminate the component segregation, and at the moment, although the components are uniform and eliminate the segregation, the crystal grains are coarse. Then, crystal grains are refined through normalizing, the structure preparation C-grade steel is prepared for the subsequent final quenching and tempering heat treatment, the sorbite structure and the good comprehensive mechanical property are obtained, and the elongation index after fracture is qualified. Compared with the traditional quenching and tempering process, the heat treatment process has the advantages that the composition structure is uniform, the casting segregation is eliminated, the comprehensive mechanical property of the C-grade steel is improved, particularly, the elongation index after fracture is greatly improved, the standard requirement of TB/T2942-2015 is met, and the product percent of pass is ensured.

Drawings

FIG. 1 is a graph showing a heat treatment process in example 1 of the present invention;

FIG. 2 is a metallographic microstructure of example 1 of the present invention;

FIG. 3 is a metallographic microstructure of comparative example 1 of the present invention;

FIG. 4 is a metallographic microstructure of comparative example 2 of the present invention;

FIG. 5 is a drawing graph of example 1 of the present invention.

Detailed Description

The present invention is described in further detail below with reference to examples.

In the following examples, the furnace used for the heat treatment was a heat treatment furnace heated by a resistance belt with a power of 250 KW. The thermocouple and the temperature control meter are calibrated once in half a year according to the calibration period, and the uniformity of the furnace temperature is calibrated once every year. The grade C steel castings used in the examples and comparative examples of the present invention were all of the same batch, and the chemical composition analysis thereof is shown in Table 1.

TABLE 1 analysis of chemical composition (% by mass) of C-grade steel in examples of the invention and comparative examples

	C	Si	Mn	P	S	Ni	Cr	Mo
									TB/T2942-2015	≤0.32	≤1.5	≤1.85	≤0.030	≤0.030	-	-	-
Internal control standard	0.22-0.28	0.20-0.40	1.20-1.50	≤0.030	≤0.030	0.35-0.55	0.4-0.6	0.2-0.3
									Actual measurement result	0.242	0.315	1.237	0.024	0.018	0.412	0.518	0.246