Several heat treatment methods after carburizing
Carburizing can only change the chemical composition of the surface of the parts, to make the parts to obtain the outer hardness and toughness of the performance of the carburizing heat treatment must also be quenched after low-temperature tempering to improve the toughness of steel and stabilize the size of the parts. According to the composition, shape and mechanical properties of the workpiece, the following heat treatment methods are often used after carburizing.
(1) direct quenching + low temperature tempering
The parts will be removed from the heat treatment furnace direct quenching, and then tempered to obtain the required hardness of the surface. Direct quenching conditions are two: carburizing heat treatment austenite grain size in 5-6 or more; carburizing layer without obvious network and massive carbides. 20CrMnTi and other steels in the carburizing most of the direct quenching.
(2) pre-cooling direct quenching + low temperature tempering
The purpose of pre-cooling is to reduce the deformation of the parts, so that the surface of the residual austenite due to the precipitation of carbides and reduce. Pre-cooling direct quenching surface hardness slightly increased, but the grain does not change, pre-cooling temperature should be higher than Ar3, to prevent the heart precipitation of ferrite, the temperature is too high to affect the pre-cooling process of precipitation of carbides, the amount of residual austenite increased, but also make the quenching deformation increased.
(3) A heating quenching + low temperature tempering
Carburized parts fast cooling to room temperature and then reheat for quenching and low-temperature tempering, suitable for quenching the heart of the higher strength and better toughness requirements of the parts.
(4) High temperature tempering + quenching + low temperature tempering
After high-temperature tempering residual austenite decomposition, penetration layer of carbon and alloying elements in the form of carbide precipitation, easy to machine while the residual austenite reduction, mainly for Cr-Ni alloy steel parts.
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5）Second quenching + low temperature tempering
The workpiece will be cold to room temperature, and then two quenching, and then low temperature tempering. This is a heat treatment method to ensure that both the heart and the surface of the high performance, two quenching is conducive to reducing the amount of residual austenite on the surface.
6) Secondary quenching + cold treatment + low temperature tempering
Also known as heat treatment of high alloy steel to reduce the amount of residual austenite on the surface, mostly used for gears and shaft parts.