CN108866298B

CN108866298B - Forging heat treatment process of Cr12MoV steel

Info

Publication number: CN108866298B
Application number: CN201810688758.7A
Authority: CN
Inventors: 任帅; 常金宝; 张雲飞; 张坤; 信瑞山; 樊明强; 稽爽; 白丽娟; 吕达
Original assignee: HBIS Co Ltd
Current assignee: HBIS Co Ltd
Priority date: 2018-06-28
Filing date: 2018-06-28
Publication date: 2020-07-28
Anticipated expiration: 2038-06-28
Also published as: CN108866298A

Abstract

The invention discloses a forging heat treatment process of Cr12MoV steel, which comprises the working procedures of heating, forging and heat treatment, wherein the heating working procedure comprises the following steps: three-stage heating is adopted; the first stage heating is heating to 600-650 ℃ and preserving heat for 2-4 hours; the second stage heating is to heat up to 800-900 ℃ and preserve heat for 3-5 hours; the third heating stage is heating to 1150-1170 ℃, and keeping the temperature for 2-3 hours; the forging step: adopting two-weight and one-weight and repeated upsetting-drawing processes, and controlling the forging temperature to be 900-1100 ℃; the heat treatment step: preserving the heat of the forge piece at 950-970 ℃ for 1-2 hours, and taking the forge piece out of the furnace and air-cooling to 20-30 ℃; then heating to 850-870 ℃, and preserving heat for 3-4 hours; then cooling to 700-720 ℃ along with the furnace, and carrying out three-stage isothermal spheroidizing annealing at 700-720 ℃ → 730-750 → 700-720 ℃ for 2-3 hours in each stage; and finally, cooling the mixture along with the furnace to 450-550 ℃ and discharging the mixture. The process can crush the net carbide fully, raise the impact toughness of steel and prolong the service life greatly.

Description

Forging heat treatment process of Cr12MoV steel

Technical Field

The invention relates to a forging and post-forging treatment process of a forging, in particular to a forging heat treatment process of Cr12MoV steel.

Background

In modern industry, a mould is firstly used, the shape of the mould determines the appearance of a product, and the production level of the mould is an important mark for measuring the national industrial level and largely determines the quality and performance of the product. The mold industry is superior, the material application is key, the performance of the mold material is good, the service life is long, and the quality of a processed product and the production benefit are directly influenced. Cr12MoV is cold-work die steel widely used in China, belongs to ledeburite steel, and eutectic carbide dendrite in the structure is very developed. These coarse eutectic carbides are difficult to dissolve in austenite during heating, and segregation is large, which seriously affects the mechanical properties of steel and the service life of the die. Therefore, it is necessary to sufficiently forge the eutectic carbide to break it up and to uniformly distribute it. However, it has poor plasticity and poor thermal conductivity, and is liable to cause structural defects such as overheating and overburning due to improper temperature control during the forging heating process. Meanwhile, due to a large amount of segregation and reticular carbides existing in the core of the steel ingot, cracks are easily generated in the core during forging, and the forging difficulty is high. In production, the die steel is cracked when the die steel does not reach the expected service life in the stamping process, so that the die steel cannot be used due to failure because the traditional forging process and the post-forging treatment system cannot eliminate massive carbides or serious reticular carbides.

Disclosure of Invention

The invention aims to provide a forging heat treatment process of Cr12MoV steel, which can effectively eliminate large blocky carbides and broken net-shaped carbides.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows: it comprises the working procedures of heating, forging and heat treatment; the heating step: three-stage heating is adopted; the first stage heating is heating to 600-650 ℃ and preserving heat for 2-4 hours; the second stage heating is to heat up to 800-900 ℃ and preserve heat for 3-5 hours; the third heating stage is heating to 1150-1170 ℃, and keeping the temperature for 2-3 hours;

the forging step: adopting two-weight and one-weight and repeated upsetting-drawing processes, and controlling the forging temperature to be 900-1100 ℃;

the heat treatment step: preserving the heat of the forge piece at 950-970 ℃ for 1-2 hours, and taking the forge piece out of the furnace and air-cooling to 20-30 ℃; then heating to 850-870 ℃, and preserving heat for 3-4 hours; then cooling to 700-720 ℃ along with the furnace, and carrying out three-stage isothermal spheroidizing annealing at 700-720 ℃ → 730-750 → 700-720 ℃ for 2-3 hours in each stage; and finally, cooling the mixture along with the furnace to 450-550 ℃ and discharging the mixture.

The forging process comprises two processes of lightening and doubling: when the forging temperature is more than 1050 ℃, the reduction is controlled to be less than or equal to 50 mm; when the forging temperature is 950-1050 ℃, the rolling reduction is controlled to be 70-120 mm; when the forging temperature is less than 950 ℃, the rolling reduction is controlled to be less than or equal to 50 mm.

In the heating procedure, the heating speed of the first stage of heating is 40-50 ℃/h; the temperature rise speed of the second-stage heating is 60-70 ℃/h; the temperature rise speed of the third stage heating is 80-100 ℃/h.

In the heat treatment process, the temperature is increased to 850-870 ℃ at the speed of 80-100 ℃/h.

Adopt the produced beneficial effect of above-mentioned technical scheme to lie in: according to the invention, through sufficient preheating before forging, the risk of cracking of the forged piece caused by thermal stress is reduced; repeated upsetting and drawing and two forging and pressing modes of lighter and heavier during forging can fully crush the reticular eutectic carbide on one hand, and can avoid overheating and overburning of the structure caused by the fact that the temperature of the center of the forging rises to be higher than the eutectic melting temperature due to over violent hammering and forging temperature rise on the other hand; after the forging is finished, the hot forging is conveyed into a furnace at 950-970 ℃ for heat preservation, so that internal stress caused by the forging can be fully released, the risk of cracking of a forging stock is further reduced, austenite grains with long forging time can be refined, passivation of large block-shaped sharp-angled carbides and dissolution of small block-shaped carbides are facilitated, the forging stress concentration caused by carbide aggregation and sharp angles is relieved and relieved, the brittleness is reduced, and the toughness is improved; and then, the large blocky sharp-angled carbides are further passivated, the reticular carbide chains are broken, the heredity of a coarse structure is eliminated, and the carbides are uniformly distributed and rounded. The invention refines the carbide of Cr12MoV steel, passivates the edges and corners, eliminates the massive sharp-angled carbide, has fine austenite structure and fully crushes the reticular carbide, thereby obviously improving the impact toughness of the steel and greatly prolonging the service life.

Drawings

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

FIG. 1 shows the metallographic structure of Cr12MoV steel obtained in example 1 of the present invention;

FIG. 2 shows the metallographic structure of Cr12MoV steel obtained by a conventional process.

Detailed Description

Examples 1 to 5: the forging heat treatment process of the Cr12MoV steel comprises the working procedures of heating, forging and heat treatment, and the working procedures are as follows:

(1) a heating procedure: putting the forge piece into a heating furnace for three-section heating; firstly, heating to 600-650 ℃ at a heating rate of 40-50 ℃/h, and preserving heat for 2-4 hours; then heating to 800-900 ℃ at a heating rate of 60-70 ℃/h, and preserving heat for 3-5 hours; finally, heating to 1150-1170 ℃ at a heating rate of 80-100 ℃/h, and preserving heat for 2-3 hours. The specific process parameters of the heating procedure of each example are shown in table 1.

Table 1: process parameters of heating process

(2) Forging: and after the heat preservation of the forge piece is finished, taking out the forge piece for forging processing, wherein the two parts are light and one heavy, and repeatedly upsetting and drawing.

During upsetting-drawing forging, the temperature of a forged piece is always controlled within a forging temperature range, the initial forging temperature is 1050-1100 ℃, and the final forging temperature is 900-920 ℃; the forging temperature is controlled to be 900-1100 ℃, when the temperature of the forge piece is lower than 900 ℃, the forging is immediately stopped, the forge piece is returned to the furnace for heating, the risk of forge piece cracking can be reduced to the greatest extent by strictly controlling the forging temperature, and the quality of the forge piece is improved.

The two weights are the weight and weight of the forging, and the upsetting amount is controlled according to the forging temperature when the forging is upset. When the forging temperature is more than 1050 ℃, the rolling reduction is controlled not to exceed 50 mm; when the forging temperature is 950-1050 ℃, the rolling reduction is controlled to be 70-120 mm; when the forging temperature is less than 950 ℃, the rolling reduction is controlled not to exceed 50 mm; the reasonable rolling reduction can avoid the generation of cracks during forging. The specific process parameters of the forging process for each example are shown in Table 2.

Table 2: technological parameters of forging process

(3) A heat treatment process: A. after forging, hot conveying the forged piece into a furnace at 950-970 ℃, preserving heat for 1-2 hours, and discharging from the furnace and air cooling to 20-30 ℃; the method can eliminate internal stress caused by forging, prevent local cracking of the forged piece and refine austenite grains. And then heating the forging to 850-870 ℃ at a heating rate of 80-100 ℃/h, and preserving heat for 3-4 hours. The specific process parameters of the above process are shown in Table 3.

Table 3: heat treatment process the technological parameters of the above-mentioned technological process

B. And cooling the forge piece to 700-720 ℃ along with the furnace, and carrying out three-stage isothermal spheroidizing annealing at 700-720 ℃ → 730-750 → 700-720 ℃, wherein each stage lasts for 2-3 hours. And after isothermal spheroidizing is finished, cooling the forged piece to 450-550 ℃ along with the furnace, discharging the forged piece, and naturally cooling the forged piece in air. The specific process parameters of the heat treatment process of each example are shown in Table 3. The specific process parameters of the above process are shown in Table 4.

Table 4: heat treatment process the technological parameters of the above-mentioned technological process

(3) FIG. 1 shows the metallographic structure of Cr12MoV steel obtained in the present example, and FIG. 2 shows the metallographic structure of Cr12MoV steel obtained by a conventional forging and post-forging treatment process (slow cooling after forging, without heat-insulating treatment at 960 ℃ C.). Comparing fig. 1 and fig. 2, it can be found that the eutectic carbide can be effectively crushed by adopting the process, the corners of the large block carbide are passivated, and the small block carbide is round; and the Cr12MoV steel which is processed by adopting the conventional forging and post-forging treatment processes, namely after the forging is finished, the heat preservation treatment is not carried out at 960 ℃, then the air cooling is carried out, the slow cooling is directly carried out after the forging, and then the three-section type spheroidizing annealing treatment is carried out has obvious sharp corners of large-block carbides, is not completely passivated and has large cracking risk. Table 5 shows the values of the impact toughness in the V-notch Charpy impact test of the Cr12MoV steels obtained in the examples and the Cr12MoV steels treated by the conventional process in the comparative examples, and the test piece A, B, C is a parallel sample.

Table 5: impact work of examples and comparative examples

As can be seen from Table 5, the impact toughness of the Cr12MoV steel obtained by the heat treatment process is obviously improved.

Claims

1. A forging heat treatment process of Cr12MoV steel comprises the working procedures of heating, forging and heat treatment, and is characterized in that the heating working procedure comprises the following steps: three-stage heating is adopted; the first stage of heating is to heat up to 600-650 ℃ at the speed of 40-50 ℃/h and preserve the temperature for 2-4 hours; the second stage heating is to heat up to 800-900 ℃ at the speed of 60-70 ℃/h and preserve the temperature for 3-5 hours; the third heating step is heating to 1150-1170 ℃ at the rate of 80-100 ℃/h, and keeping the temperature for 2-3 hours;

the forging step: adopting two processes of light weight and heavy weight and repeated upsetting and drawing, and controlling the reduction to be less than or equal to 50mm when the forging temperature is higher than 1050 ℃; when the forging temperature is 950-1050 ℃, the rolling reduction is controlled to be 70-120 mm; when the forging temperature is less than 950 ℃, the rolling reduction is controlled to be less than or equal to 50mm, and the forging temperature is controlled to be 900-1100 ℃;

the heat treatment step: after forging, the forge piece is heated and sent to a furnace at 950-970 ℃, heat preservation is carried out for 1-2 hours, and the forge piece is taken out of the furnace and air-cooled to 20-30 ℃; heating to 850-870 ℃ at the speed of 80-100 ℃/h, and preserving heat for 3-4 hours; then cooling to 700-720 ℃ along with the furnace, and carrying out three-stage isothermal spheroidizing annealing at 700-720 ℃ → 730-750 → 700-720 ℃ for 2-3 hours in each stage; and finally, cooling the mixture along with the furnace to 450-550 ℃ and discharging the mixture.