A Method for Microstructure After Vacuum Carburizing

A technology of vacuum carburizing and vacuum low-pressure carburizing, which is applied in furnaces, heat treatment equipment, manufacturing tools, etc., can solve problems affecting material mechanics and performance, ineffective effects, and difficult to refine the surface structure.

Active Publication Date: 2020-12-29
BEIJING RES INST OF MECHANICAL&ELECTRICAL TECH
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AI Technical Summary

Problems solved by technology

The process cycle is shortened and the efficiency is improved, but what follows is that the material is in a high temperature state for a long time, which is easy to cause grain growth and martensitic needles, which will affect the material mechanics and performance
One of the previous microstructure refinement techniques is to study new high-temperature materials, adding alloy element Nb to hinder the growth of grains at high temperatures, and the effect is not obvious after practice tests
The second technique of refining structure is that after carburizing in the atmosphere furnace, it is directly cooled in the air, that is, the normalizing process can achieve the purpose of refining the surface structure, but it will cause oxidation on the surface of the part; vacuum low-pressure carburizing will not cause the surface of the workpiece Oxidation, but can not be directly normalized in the air, it is difficult to refine the surface structure

Method used

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  • A Method for Microstructure After Vacuum Carburizing
  • A Method for Microstructure After Vacuum Carburizing
  • A Method for Microstructure After Vacuum Carburizing

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specific Embodiment approach

[0020] The method for refining structure after vacuum carburizing of the present invention, its preferred embodiment is:

[0021] Including vacuum low-pressure carburizing stage, also includes slow cooling stage after carburizing, cycle slow cooling stage, secondary quenching stage;

[0022] The slow cooling stage after carburizing includes: after carburizing, the workpiece continues to be in the heating chamber, the heating is stopped, and nitrogen is filled in pulse mode, and slowly lowered to 600°C;

[0023] The cycle slow cooling stage refers to multiple rapid heating and multiple slow cooling;

[0024] The secondary quenching stage refers to a quenching method in which the first quenching solidifies and refines the crystal grains after the slow cooling cycle is completed, and the second quenching takes into account both the surface and the core.

[0025] In the slow cooling stage after carburizing, the heating chamber is charged with nitrogen gas in a pulsed manner with ...

Embodiment 1

[0045] see Figure 2~3 (and compare figure 1 ), in an embodiment of the present invention, a method for refining surface and core tissue during cooling after vacuum carburizing, including the following stages:

[0046] (1) Vacuum low-pressure carburizing stage: Set the carburizing time and diffusion time according to the technical requirements of the workpiece, and after preparing the corresponding process curve, put the workpiece in a vacuum furnace to evacuate, start heating, and preheat at 700°C for a period of time. After heating up to the carburizing temperature of 900-1050°C, the low-pressure carburizing process is started, and acetylene or propane is charged in pulses, with a pressure of generally 1.3-6.6kpa. After carburizing and diffusion stages, vacuum low-pressure carburizing is completed.

[0047] (2) Slow cooling stage after carburizing: After carburizing, stop heating and start pulse-type air-inflation cooling. The pulse cycle is generally 4-5min, and the air-in...

Embodiment 2

[0053] Example 2 – Gears

[0054] Dimensions (mm): addendum circle diameter φ630, inner hole φ270, tooth width 80, module 5mm

[0055] Material: 18CrNiMo7-6.

[0056] Heat treatment technical requirements: standard JB / T6141.3-1992 vacuum carburizing carbide ≤ 2 grades, surface martensite and retained austenite ≤ 2 grades, core structure ≤ 2 grades, carburized layer 0.9 ~ 1.2mm , Surface hardness HRC60~62.

[0057] Carburizing process: compare the traditional process of vacuum low-pressure carburizing with the microstructure process.

[0058] like Figure 4~5 It is the surface martensite structure obtained by the traditional process of vacuum low-pressure carburizing. According to JB / T6141.3-1992 rating: Martensite structure is 4 grades, and the needles are relatively thick; heart structure: 2 grades.

[0059] like Figure 6~7 It is the surface martensite structure obtained by vacuum low-pressure carburizing refinement process. According to JB / T6141.3-1992 rating: martensi...

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Abstract

The invention discloses a method for refining tissue after vacuum carburization. The method comprises a vacuum low-pressure carburization stage, and further comprises a post-carburizing slow cooling stage, a circulating slow cooling stage and a secondary quenching stage; after carburization, the slow cooling stage comprises the steps that after carburization is completed, the workpiece continues to be heated in the heating chamber and stops heating, the pulse mode is filled with nitrogen, and the nitrogen is slowly cooled to 600 DEG C; the circulating slow cooling stage refers to repeated rapid heating and slow cooling; and the secondary quenching stage refers to crystal grains which are subjected to primary quenching and solidification refining after circulating slow cooling is completed,and the quenching method of the surface and the core part is considered for the second time. The problem that crystal grains and tissues are refined can be solved, the method can achieve martensite refinement, in a hidden crystal form or a fine needle shape on the surface of the seepage layer, the heart tissue is refined, the real "external hard internal toughness" of the vacuum carburization isrealized, the comprehensive performance of the materials can be achieved to the best degree.

Description

technical field [0001] The invention relates to a vacuum heat treatment technology, in particular to a method for refining the structure after vacuum carburizing. Background technique [0002] Heat treatment is a key core technology in the machinery manufacturing industry. With the continuous emphasis on heat treatment technology, it is no longer the traditional technology of empirical control and quenching based on the two parameters of temperature and time, but has developed from extensive to refined, emphasizing new Craftsmanship, new technology, improving the intrinsic quality of products, saving energy and materials, reducing consumption and prolonging life, paying attention to economic benefits, etc. Vacuum low-pressure carburizing technology gradually replaces controllable atmosphere carburizing equipment with the advantages of less oxidation, energy saving and emission reduction, and clean heat treatment. It is more and more widely used in key parts such as gears and...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): C23C8/22C21D1/18C21D1/773C21D9/32C21D9/28
CPCC21D1/18C21D1/773C21D9/28C21D9/32C21D2211/008C23C8/22
Inventor 丛培武徐跃明周有臣刘俊祥杜春辉尹承锟何龙祥周新宇王京辉王同
Owner BEIJING RES INST OF MECHANICAL&ELECTRICAL TECH
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