CN104328259B - GCr15 high carbon chromium bearing steel on-line rapid spheroidizing annealing technology - Google Patents

Abstract

An online rapid spheroidizing annealing process for GCr15 high-carbon chromium bearing steel belongs to the field of material engineering. The GCr15 bearing steel is composed by mass ratio: C: 0.95-1.05%, Cr: 1.30-1.65%, Mn: 0.20-0.40%, Si: 0.15-0.35%, S≤0.015%, P≤0.02%, remainder The amount is Fe. The process steps are as follows: heating up to 1150-1250°C with the furnace for heat preservation; rapid cooling to 920-960°C and 40-60% compression deformation due to applied stress; then rapid cooling to 740-780°C, 30-50% compression deformation ; Then slowly cool to the range of 500-600°C at a cooling rate of 0.3-0.5°C/s; finally quickly cool to room temperature. The process of the invention is simple, and after thermal deformation, the microstructure is fine and uniform spherical carbides dispersed on the ferrite matrix, which is suitable for subsequent processing and prepares microstructure for final quenching+tempering.

Description

An online rapid spheroidizing annealing process for GCr15 high carbon chromium bearing steel

Technical field:

The invention belongs to the field of steel rolling and relates to an online rapid spheroidizing annealing process for hot-rolled rods and wires of GCr15 high-carbon chromium bearing steel.

Background technique:

The purpose of spheroidizing annealing is to obtain spheroidized structure, which has the best shape and the lowest hardness. After spheroidizing annealing, the distribution and shape of carbides can be modified to reduce the hardness of the material and improve the plasticity of the material. shape, reduce the deformation resistance of the material, improve the machinability, and prepare the tissue for subsequent heat treatment.

GCr15 steel is the most widely used high-carbon chromium bearing steel. It is mainly used to make various bearing rings and rolling elements, and sometimes used to make tools. It usually requires high strength, high elastic limit and high durability. Grinding etc. GCr15 bearing steel has moderate machinability, average cutting performance, and is easy to quench and crack and form temper brittleness. Therefore, after the rod and wire are hot-rolled, the subsequent plastic processing and quenching need to undergo spheroidizing annealing to soften the material and reduce deformation resistance. In addition, improving the shape and distribution of carbides in bearing steel can also prolong the service life of GCr15 steel bearings. The spheroidizing annealing process just plays the role of melting and spheroidizing the lamellar carbides in pearlite. People have done a lot of research on spheroidizing annealing, but the existing spheroidizing annealing treatment often takes a long period, consumes a lot of energy and resources, and pollutes the environment. For example, the traditional spheroidizing annealing process is slightly higher than After heat preservation, it is slowly cooled to below 650°C with the furnace and air-cooled. The processing time of this process is long (more than 20h), and the carbide particles are not uniform after annealing, which affects the structure and performance of the subsequent cold working and final heat treatment. Therefore, it is necessary to propose a new on-line rapid spheroidizing annealing process using waste heat.

Invention content:

The technical problem to be solved by the present invention is to provide an online rapid spheroidizing annealing process for GCr15 high-carbon chromium bearing steel. The process flow is simple, the efficiency is high, and energy and resources are saved. The annealed hardness and spheroidized structure ratio of rods and wires are significantly improved, and the spherical carbides are evenly distributed.

In order to solve the problems of the technologies described above, the technical solution of the present invention is as follows:

An online rapid spheroidizing annealing process for GCr15 high-carbon chromium bearing steel. The components of the GCr15 bearing steel are composed of: C: 0.95% to 1.05%, Cr: 1.30% to 1.65%, and Mn: 0.20% to 0.40%. , Si: 0.15% to 0.35%, S≤0.015%, P≤0.02%, and the balance is Fe.

The specific process steps are as follows:

Raise the temperature to 1150-1250°C at a heating rate of 10°C/s, and keep the temperature at this temperature for 60-120 minutes;

After rapid cooling to 920-960°C, 40-60% compression deformation occurs when the stress is applied, and the grains are refined;

Then rapidly cool down to 740-780°C, and 30-50% compression deformation occurs when the stress is applied, so that the pro-eutectoid carbides are broken and the retained austenite is deformed, which is conducive to the formation of spherical carbides;

Then slowly cool to 500-600°C at a cooling rate of 0.3-0.5°C/s to increase the amount of spheroidized carbides without affecting production efficiency.

Finally cool to room temperature quickly.

The online rapid spheroidizing annealing process of GCr15 high-carbon chromium bearing steel implemented by the above technical scheme can realize the online spheroidizing of carbides through thermal deformation driving force and waste heat, and greatly shorten the spheroidizing annealing cycle. The spheroidized structure is that spherical carbide particles are dispersed on the ferrite matrix, and the hardness is 180-200HB. The technical process of the invention is simple, easy to implement, low in equipment requirements, low in cost, and greatly shortens the production cycle.

Description of drawings:

Fig. 1 is a schematic diagram of the process curve of the process of the present invention.

Fig. 2 is the metallographic structure diagram of the sample after being processed by the process of the present invention.

detailed description:

The content of the present invention will be further specifically described below through specific examples in conjunction with the accompanying drawings. As shown in Figure 1, a GCr15 high-carbon chromium bearing steel online rapid spheroidizing annealing process, the microstructure of the hot-rolled piece after treatment is fine and uniform spherical carbides dispersed on the ferrite matrix.

The GCr15 high-carbon chromium bearing steel is processed through an online rapid spheroidizing annealing process, which specifically includes the following steps of heating and heat preservation, two-step rapid cooling and deformation, slow cooling, and rapid cooling:

1. Heat up and keep warm. The GCr15 high-carbon chromium bearing steel was heated up to 1170°C at a heating rate of 10°C/s, and held at this temperature for 80 minutes. GCr15 high-carbon chromium bearing steel at 1170°C for high temperature insulation can ensure the melting of carbides and the redistribution of alloying elements.

2. Rapid cooling and deformation. GCr15 high-carbon chromium bearing steel is rapidly cooled to 920-960°C after heat preservation at 1170°C, and then 50% of the compression deformation occurs when the stress is applied. The deformation in this temperature range can refine the austenite grains through dynamic recrystallization, and can also inhibit the grain size. The excessive growth of the grains avoids the reduction of the grain boundary area, which can enhance the dispersion of the carbides; then rapidly cools to 740-780 ° C, and 30% compression deformation occurs, causing the pro-eutectoid carbides to be deformed and crushed and retained. The deformation of the tentenite is conducive to the formation of spherical carbides, and a small part of the carbide structure can be directly broken to form granular carbides.

3. Slow cooling and quick cooling. GCr15 high-carbon chromium bearing steel undergoes two rapid cooling deformations and then slowly cools to 550°C. During the slow cooling process in this temperature range, the furnace temperature of the workpiece can be reduced and the thermal stress can be reduced. In addition, in this temperature range, the carbide structure can be precipitated at the position where the line defect density is high, forming dispersed granular carbides in some areas, and finally forming a spheroidized structure, and the formed carbide particles are small in size and relatively round in shape Evenly, the distribution is dispersed; finally cool to room temperature quickly.

The present invention provides an online rapid spheroidizing annealing process for GCr15 high-carbon chromium bearing steel. The key to the process is to select a suitable heating temperature, deformation temperature, deformation amount and cooling rate. This process can greatly shorten the spheroidizing annealing cycle and obtain iron The structure of fine, small, uniform and round carbide particles dispersed on the body matrix, with a hardness of 180-200HB. The invention can ensure that the workpiece to be processed has good shaping processability and cutting performance, thereby improving the quality and service performance of the product.

The above description is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited thereto. Therefore, any equivalent replacement or change made according to the scope of the present invention is within the protection scope of the present invention.

Claims (1)

1. An online rapid spheroidizing annealing process for GCr15 high-carbon chromium bearing steel, characterized in that the GCr15 bearing steel is composed of: C: 0.95% to 1.05%, Cr: 1.30% to 1.65%, Mn: 0.20 %～0.40%, Si: 0.15%～0.35%, S≤0.015%, P≤0.02%, the balance is Fe; The specific process steps are as follows: 1) Raise the temperature to 1150-1250°C, and carry out high-temperature insulation at this temperature; 2) After rapid cooling to 920-960°C, compression deformation occurs when stress is applied, and fine recrystallized austenite grains are formed; 3) Rapid cooling to 740-780°C, compressive deformation occurs when stress is applied, which breaks proeutectoid carbides and deforms retained austenite, which is conducive to the formation of spherical carbides; 4) Cool slowly to 500-600°C, and increase the amount of spheroidized carbides without affecting production efficiency; 5) Quickly cool to room temperature; Wherein the heating rate of step (1) is 10 DEG C/s, and holding time is 60～120min; Step (2) compression deformation is 40～60%; Step (3) compression deformation is 30～50%; The slow cooling rate in step (4) is 0.3-0.5° C./s.