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Composite heat treatment

A composite heat treatment and composite treatment technology, applied in the field of heat treatment

Inactive Publication Date: 2003-06-18
SHANGHAI JIAO TONG UNIV
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

This method is low-temperature nitrocarburizing + 800°C water quenching, and there is a loose layer with low hardness on the surface. These treatments can only be applied to thin stamping parts such as instrument parts.

Method used

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Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0013] Example 1: Needle cylinder of textile machine, outer circle φ150mm, inner circle φ120mm, height 250mm, knitting needle grooves with width 1.5mm, depth 10mm, length 110mm are evenly distributed along the 360° circumferential direction on the upper part of the outer circumference, material 20 steel, surface The hardness is >750HV, and the depth of the infiltration layer is required to be 0.2 ~ 0.3mm.

[0014] The parts are processed in a sealed pit furnace. The first stage is carbonitriding. Methanol, acetone and ammonia can be used as infiltration agents. The temperature is 840 ° C. After 1 hour, the temperature is lowered to 620 ° C. Austenite nitriding 3 hour, the ammonia decomposition rate was controlled to 75% to obtain an austenite layer with high nitrogen content, and then it was quenched into the isothermal quenching tank at 250°C for 3 hours. The surface hardness of the workpiece is 950HV, the depth of the seepage layer is 0.3mm, the deformation of the workpiece ...

Embodiment 2

[0015] Example 2: Nail clippers, made of 45 steel, the surface hardness is required to be more than 850HV, and the depth of the infiltration layer is required to be 0.1 to 0.2 mm. Carburizing and quenching, post-carbonitriding quenching and surface quenching have been used, but all of them cannot meet the surface hardness requirements. Moreover, due to the asymmetric shapes on both sides of some parts, the deformation is out of tolerance during quenching and cooling, and correction is difficult. .

[0016] Parts are processed in a mesh belt furnace capable of segmented atmosphere control: carbonitriding is carried out at 800-820 °C in the front section of the furnace, methanol and ammonia can be selected as infiltration agents, and the temperature is lowered to 640 °C in the rear section of the furnace for 30 minutes. Austenite nitriding was carried out in ammonia gas for 30 minutes, then quenched into a quenching tank (oil or water), and then the workpiece was taken out and a...

Embodiment 3

[0017] Example 3: The crankshaft of the sewing machine, the material is 20Cr, the depth of the infiltrating layer is required to be 0.4-0.5mm, the surface hardness is higher than 850HV, and the deformation of the workpiece after carburizing treatment is out of tolerance. With ferritic nitrocarburizing, the depth of the infiltrated layer cannot meet the requirements.

[0018] The treatment is carried out in a sealed box furnace. Carburizing is carried out at 900 °C in the early stage, and the carbon potential is controlled to 0.85-0.90% for 2 hours. The infiltration agent is methanol + acetone. The decomposition rate is controlled to 85-90%, and the time is 3 hours, so that the workpiece is treated to obtain a 0.5mm high nitrogen austenite layer, followed by quenching (oil or water), and aging at 250 ° C for 3 hours. The surface hardness of the workpiece after treatment reaches 900HVHV.

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Abstract

A duplex heat treating process for workpiece includes such steps as heating to austenite state, penetrating C or C and N to obtain a prepenetrated layer, lowering temp to 620-720 deg.c, penetrating N or N and C, direct quenching, and having time effect at 200-300 deg.c or isothermal quenching at 200-300 deg.c. Its advantages are high hardness (greater than 900 HV) and lower deformation.

Description

technical field [0001] The invention relates to a heat treatment method, in particular to a composite heat treatment method for increasing the depth of austenite nitriding / nitrocarburizing layer and reducing deformation, and belongs to the technical field of heat treatment. Background technique [0002] Carburizing or carbonitriding is a surface modification technology that changes the chemical composition and microstructure of the part surface through the infiltration of carbon or carbon and nitrogen in the austenitic state of steel, with high hardness and wear resistance, and the highest hardness Up to 56 ~ 62HRC, equivalent to 600 ~ 750HV. The core part obtains low martensite (or bainite, sorbite) and other structures, and has a certain toughness, so it has been widely used. However, the improvement of surface hardness and wear resistance of parts is limited. In addition, due to these treatments (carbonitriding is 840-880°C, carburizing is 860-930°C, and quenching temper...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C21D1/20C23C8/34C23C8/80
Inventor 胡明娟沈甫法苏智辉朱祖昌卑多慧
Owner SHANGHAI JIAO TONG UNIV
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