CN109825688B

CN109825688B - Hot working process for P20 and 718 plastic die steel

Info

Publication number: CN109825688B
Application number: CN201910168371.3A
Authority: CN
Inventors: 丛文龙; 季建新; 陈孝荣; 苏佳; 陈科; 阮树荣; 鲁成飞; 孙志华
Original assignee: Jiangsu Pinmou Information Technology Co ltd
Current assignee: Jiangsu Pinmou Information Technology Co ltd
Priority date: 2019-03-06
Filing date: 2019-03-06
Publication date: 2020-12-25
Anticipated expiration: 2039-03-06
Also published as: CN109825688A

Abstract

The invention relates to the field of processing of plastic die steel, and discloses a hot working process for P20 and 718 plastic die steel, which comprises the steps of forging, forging and forming a steel billet, controlling the finish forging temperature to be 800-850 ℃, the rolling reduction to be 15-120 mm and the anvil feeding amount to be 100-200 mm in the last firing time of forging, and ensuring the grain size and UT flaw detection; after forging and forming a steel billet, air-cooling the steel billet to 300-400 ℃, then sending the steel billet into a furnace at 300-400 ℃ for heat preservation for 3-5 h, then heating the furnace to 600-700 ℃ at the speed of 30-60 ℃/h, and then preserving the heat, wherein the heat preservation time is T, T is (5D/100) +/-2, and the unit is h, and D is the effective thickness of the steel billet and the unit is mm; and after the heat preservation is finished, raising the temperature of the furnace to the quenching temperature for quenching and tempering. The invention solves the technical problems that the production period of the die steel is long and the production cost is high in the prior art, and shortens the production period, reduces the energy consumption and reduces the cost on the premise of ensuring the product quality.

Description

Hot working process for P20 and 718 plastic die steel

Technical Field

The invention relates to the field of processing of plastic die steel, in particular to a hot processing technology for P20 and 718 plastic die steel.

Background

P20 and 718 are two important pre-hardened plastic die steels, P20 is American standard number, the corresponding national standard number is 3Cr2Mo, 718 is Sweden Wingbai ASSAB standard steel number, the corresponding national GB standard steel number is 3Cr2NiMnMo, German DIN standard material steel number 1.2738, American AISI/SAE standard steel number P20+ Ni.

Because the steel grades containing Cr and Ni have the highest sensitivity to white spots, the post-forging dehydrothermal treatment of the steel grades by the traditional process is usually carried out for a longer time.

In order to ensure that free hydrogen in the die steel is fully eliminated and the grain size in the die steel is ensured, the traditional heat treatment of the die steel after forging is normalizing and dehydrogenation annealing, and the purpose of normalizing is

(1) Subjecting the die steel to phase change recrystallization to refine grains;

(2) the die steel is made to obtain a pearlite structure and fully carry out hydrogen diffusion. According to the data, the solubility and diffusion speed of hydrogen in steel are not only related to temperature, but also related to the steel structure, the solubility of hydrogen in face-centered cubic lattice r-Fe is the largest, the solubility in body-centered cubic lattice a-Fe is the smallest, and the diffusion speed of hydrogen in a-Fe is much larger than that of hydrogen in r-Fe, so that the hydrogen diffusion annealing is performed under the structure taking ferrite as a matrix in principle.

(3) Normalizing is carried out at high temperature (850-900 ℃), so that high requirements on equipment are put forward, and the production cost and the production period are greatly improved.

Therefore, in the traditional process, the heat treatment time of the die steel containing Cr and Ni after forging is long, and the heat treatment cost is high.

Disclosure of Invention

In view of the defects of the background art, the invention provides a hot working process for P20 and 718 plastic die steel, and aims to solve the technical problems of long production period and high production cost of the die steel in the prior art.

In order to solve the technical problems, the invention provides the following technical scheme:

forging, namely heating a steel ingot (namely a steel billet) to a temperature higher than the phase transition temperature (1200-1280 ℃) for forging forming, wherein the finish forging temperature is generally higher than 800 ℃, so that the internal structure of the steel billet is completely converted into an austenite structure, normalizing treatment is not carried out after forging, the primary phase transition recrystallization process is reduced, in order to ensure the grain size and UT flaw detection of the steel billet, the finish forging temperature is controlled to be 800-850 ℃ at the last firing time of forging, the rolling reduction is controlled to be 15-120 mm, and the anvil feeding amount is controlled to be 100-200 mm, so that the grain size and UT flaw detection are ensured;

after the last heating time of forging, performing supercooling heat preservation on the steel billet, namely air cooling the steel billet to 300-400 ℃, and sending the steel billet into a furnace at 300-400 ℃ for heat preservation for 3-5 h, wherein the internal structure of the steel billet is completely converted into a pearlite structure;

then, the furnace temperature is increased to 600-700 ℃ at the speed of 30-60 ℃/h, then heat preservation is carried out, the heat preservation time length is T, dehydrogenation treatment is carried out, T is set according to the calculation formula T (5D/100) +/-2, the unit is h, and D is the effective thickness of the steel billet, and the unit is mm;

and after the steps are finished, the furnace temperature is increased to the quenching temperature to carry out quenching and tempering treatment on the steel billet.

Compared with the prior art, the invention has the beneficial effects that: on the premise of ensuring the product quality, the production period is shortened, and the energy consumption cost is reduced.

Drawings

The invention has the following drawings:

FIG. 1 is a schematic diagram of the temperature change of a steel billet in the conventional process and the process of the present invention.

Detailed Description

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

The first embodiment is as follows:

forging, heating a steel ingot (namely a steel billet) to a temperature above the phase transition temperature (1200-1280 ℃) for forging forming, wherein the finish forging temperature is generally above 800 ℃, so that the internal structure of the steel billet is completely converted into an austenite structure, normalizing treatment is not carried out after forging, the one-time phase transition recrystallization process is reduced, in order to ensure the grain size and UT flaw detection of the steel billet, the finish forging temperature is controlled to be 800-850 ℃ at the last firing time of forging, the rolling reduction and the anvil feeding amount are controlled to ensure the grain size and UT flaw detection, and the control of the rolling reduction and the anvil feeding amount refers to the following table 1;

TABLE 1 comparison table of final hot reduction, stock feeding and billet thickness in forging

Comparing the process provided by the invention with the traditional process from various aspects, the results are as follows:

1. quality of the product

(1) Grain size: the grain size of the process method is not reduced by reducing the primary phase change recrystallization process, and the grain size is ensured to be 7-8 grade;

(2) UT flaw detection: 3 million tons of die steel are produced in total under the process method, the materials are P20 (the national standard mark of China is 3Cr2Mo) and 718 (the GB standard steel number of China is 3Cr2NiMnMo, the German DIN standard material steel number 1.2738), the UT flaw detection qualification rate is 98.3 percent, and the UT flaw detection qualification rate of the traditional process method is 94.4 percent. The UT flaw detection qualification rate of the traditional process method is recorded as the following table 2 (intercepting partial records), and the total record is 54 times, wherein the qualification times are 51; the UT flaw detection qualification rate of the method of the invention is recorded as the following table 3 (intercepting part of record), 657 times of total record and 646 times of qualification.

TABLE 2 UT flaw detection record of die steel under traditional process

TABLE 3 UT flaw detection record of lower die steel by the method of the present invention

(4) Energy consumption and cost

The traditional process method comprises normalizing and high-temperature tempering, and the heat treatment cost is as follows: 700-800 yuan/ton;

the process method comprises supercooling heat preservation and dehydrogenation annealing, and the heat treatment cost is as follows: 200-300 yuan/ton, compared with the two phases, the invention obviously reduces the energy consumption cost.

(5) Comparison of procedures

The traditional process mainly comprises the steps of normalizing, cooling to room temperature and then carrying out dehydrogenation annealing after forging a steel billet, cooling to room temperature and then heating to quenching temperature for quenching and tempering after the dehydrogenation annealing; the process method comprises the steps of cooling the steel billet to 300-400 ℃ after the steel billet is forged, supercooling and preserving heat, then heating to 600-700 ℃ for dehydrogenation, and then heating to quenching temperature for quenching and tempering, wherein the temperature of the steel billet is controlled according to two methods shown in figure 1, wherein a dotted line represents the traditional process, a solid line represents the process of the invention, and the two methods are compared.

In light of the foregoing, it is to be understood that various changes and modifications may be made by those skilled in the art without departing from the spirit and scope of the invention. The technical scope of the present invention is not limited to the content of the specification, and must be determined according to the scope of the claims.

Claims

1. The hot working process for the P20 and 718 plastic die steel comprises forging and forming a steel billet by forging, and is characterized in that: after forging, normalizing treatment is not carried out, the final forging temperature is controlled to be 800-850 ℃ in the last firing time of forging, the rolling reduction is controlled to be 15-120 mm, the anvil feeding amount is controlled to be 100-200 mm, and the grain size and UT flaw detection are guaranteed; after forging and forming a steel billet, air-cooling the steel billet to 300-400 ℃, sending the steel billet into a furnace at 300-400 ℃ for heat preservation for 3-5 h, then heating the furnace to 600-700 ℃ at the speed of 30-60 ℃/h, and then preserving the heat, wherein the heat preservation time is T, the T is (5D/100) +/-2, the unit is h, and the D is the effective thickness of the steel billet and the unit is mm; and after the heat preservation is finished, raising the temperature of the furnace to the quenching temperature for quenching and tempering.