CN109593929B

CN109593929B - Spheroidizing annealing method of cold forging steel

Info

Publication number: CN109593929B
Application number: CN201811519712.9A
Authority: CN
Inventors: 张贺佳; 汪青山; 李亚彦; 孙显东; 孔超; 白瑞国
Original assignee: HBIS Co Ltd Chengde Branch
Current assignee: HBIS Co Ltd Chengde Branch
Priority date: 2018-12-12
Filing date: 2018-12-12
Publication date: 2020-10-30
Anticipated expiration: 2038-12-12
Also published as: CN109593929A

Abstract

The invention discloses a spheroidizing annealing method of cold forging steel, wherein the cold forging steel is heated to be more than or equal to 693 ℃, and the heat preservation time is calculated according to the effective section thickness of 3.3-4.3 mm/min; quickly cooling to be less than or equal to 200 ℃; then heating to 650-690 ℃, and preserving heat for 6-20 h; and finally, slowly cooling along with the furnace. The method changes the distribution condition of carbide particles in the spheroidized steel by controlling the cooling and temperature speed, so that the carbide particles are more uniformly distributed in a matrix and inside crystal grains, and the segregation of the carbide at the grain boundary is reduced, thereby enhancing the plasticity, and the reduction of area of the product is more than or equal to 65 percent; the other remarkable characteristic is that the spheroidizing annealing can be well realized under the condition of no plastic deformation.

Description

Spheroidizing annealing method of cold forging steel

Technical Field

The invention belongs to the technical field of metallurgy, and particularly relates to a spheroidizing annealing method of cold forging steel.

Background

The SWRCH22A cold forging steel is low carbon steel, is widely used for producing standard parts such as screws, pins, nuts and the like, has larger deformation in the production and processing process, and needs to be interpenetrated with heat treatment softening processes such as spheroidizing annealing and the like, thereby enhancing the shaping of the steel. However, the SWRCH22A cold heading steel still has the cold heading cracking phenomenon after being softened by the conventional spheroidizing annealing. This is mainly because most of carbide particles in the spheroidizing annealed steel are precipitated along grain boundaries, reducing the plasticity of the steel. In addition, in the case of mild steel, it is impossible to spheroidize it using undissolved carbides as spheroidized nuclei, as in the case of hypereutectoid steel, without plastic deformation. Therefore, no effective method for spheroidizing annealing of low-carbon steel or hypoeutectoid steel without plastic deformation exists in the industry.

Disclosure of Invention

The invention aims to provide a spheroidizing annealing method of cold forging steel with good product plasticity.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows: heating the cold forging steel to be more than or equal to 693 ℃, and calculating the heat preservation time according to the effective section thickness of 3.3-4.3 mm/min; quickly cooling to be less than or equal to 200 ℃; then heating to 650-690 ℃, and preserving heat for 6-20 h; and finally, slowly cooling along with the furnace.

The cooling rate of the rapid cooling is 20-50 ℃/s.

The cold heading steel comprises the following chemical components in percentage by weight: 0.18 to 0.22 percent of C, less than or equal to 0.07 percent of Si, 0.75 to 0.95 percent of Mn, 0.025 to 0.055 percent of Al and the balance of Fe and impurity elements.

Adopt the produced beneficial effect of above-mentioned technical scheme to lie in: the invention changes the distribution condition of carbide particles in the steel after spheroidization by controlling the cooling and temperature speed, so that the carbide particles are more uniformly distributed in the matrix and inside crystal grains, and the segregation of the carbide at the crystal boundary is reduced, thereby enhancing the plasticity; the other remarkable characteristic is that the spheroidizing annealing can be well realized under the condition of no plastic deformation. After the treatment of the invention, carbide particles in the steel can be more uniformly distributed in the crystal grains, and the grain boundary segregation of the carbide is reduced, so that the plasticity of the steel can be better improved, and the reduction of area of the product is more than or equal to 65%.

Drawings

The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

FIG. 1 is a photograph of a metallographic structure after spheroidizing annealing according to the present invention;

fig. 2 is a metallographic structure photograph after conventional spheroidizing annealing.

Detailed Description

Examples 1 to 8: the spheroidizing annealing method of the cold forging steel adopts the following process.

(1) The product comprises the following components: the hot-rolled disc round SWRCH22A cold forging steel with the diameter of 5.5-6.5 mm is selected for production, and the chemical components and the weight percentage of the steel of each embodiment are shown in the table 1.

Table 1: chemical composition (wt) of the steels of the examples

(2) The method comprises the following steps: the technical process of heating, heat preservation, quick cooling, reheating, heat preservation again and furnace slow cooling is adopted. Heating in an air furnace, wherein the first heating temperature is higher than the austenitizing temperature, namely not less than 693 ℃; in order to bring the surface and the interior of the steel to austenitizing temperature, heat preservation is required; the shorter the heat preservation residence time of the steel temperature at the austenitizing temperature is, the better the heat preservation residence time is, the purpose is to ensure that C is distributed unevenly in the steel, and the heat preservation time is calculated according to the effective section thickness of 3.3-4.3 mm/min. Cooling to 200 ℃ or below at a cooling rate of 20-50 ℃/s during rapid cooling. The reheating temperature is 650-690 ℃, and the heat preservation time is 6-20 h. And finally, slowly cooling to 400 ℃ or below along with the furnace. The specific process of each example is shown in table 2.

Table 2: process parameters of the examples

(3) FIG. 1 is a photograph of a metallographic structure of a spheroidizing annealed product according to example 1, and FIG. 2 is a photograph of a metallographic structure of the same product after a conventional spheroidizing annealing; as can be seen from FIGS. 1 and 2, the method effectively reduces the segregation of carbides at the grain boundary, and the distribution of carbide particles after spheroidization is more uniform. The properties of the product obtained after spheroidizing annealing of each example are shown in Table 3.

Table 3: properties of the products obtained in the examples

Claims

1. A spheroidizing annealing method of cold forging steel is characterized by comprising the following steps: heating the cold forging steel to be more than or equal to 693 ℃, and calculating the heat preservation time according to the effective section thickness of 3.3-4.3 mm/min; rapidly cooling to be less than or equal to 200 ℃, wherein the cooling rate of the rapid cooling is 20-50 ℃/s; then heating to 650-690 ℃, and preserving heat for 6-20 h; finally, slowly cooling to 400 ℃ or below along with the furnace;

the cold forging steel comprises the following chemical components in percentage by weight: 0.18 to 0.22 percent of C, less than or equal to 0.07 percent of Si, 0.75 to 0.95 percent of Mn, 0.025 to 0.055 percent of Al and the balance of Fe and impurity elements;

the cold forging steel is hypoeutectoid steel without plastic deformation.