Thu, 21 Jun 2018 02:17:04 +0000
The heat treatment of vacuum furnace after carburizing
Carburization can only change the chemical composition on the surface of the parts, to make the parts for hard toughening performance, also after carburizing heat treatment must be quenching and low temperature tempering, to improve the size of the steel strong toughness and stability of the parts. According to the composition, shape and mechanical properties of the workpiece, the following heat treatment methods are often adopted after carburizing.
1) direct quenching + low temperature tempering
Take the parts out of the heat treatment furnace and quench them directly. There are two conditions for direct quenching: the austenite grain size after carburizing treatment is above grade 5-6; There is no obvious network and block carbide in the cementized layer. Most of 20CrMnTi steel adopt direct quenching after carburizing.
2) precooled direct quenching + low temperature tempering
The purpose of precooling is to reduce the deformation of two parts. The residual austenite on the surface is reduced by the precipitation of carbides. Cooling, direct quenching surface hardness increased slightly, but the grain size no change, precooling temperature should be higher than Ar3, precipitation of prevent the core ferrite, high temperature affects the precooling process of carbide precipitation, the residual austenite volume increased, at the same time make quenching deformation increases.
3) one-time heating and quenching + low temperature tempering
The carburized parts are cooled to room temperature and then reheated for quenching and tempering at low temperature. It is suitable for parts with high strength and good toughness in the core after quenching.
4) high temperature tempering + quenching + low temperature tempering
After high temperature tempering, the residual austenite was decomposed, and the carbon and alloy elements in the infiltration layer were precipitated out in the form of carbides. Mainly used for Cr-Ni alloy steel parts.
5) secondary quenching + low temperature tempering
After the workpiece is cooled to room temperature, it is quenched twice and then tempered at low temperature. This is a heat treatment method that ensures high performance at both the core and the surface. Twice quenching is beneficial to reduce the amount of residual austenite on the surface.
6) secondary quenching + cold treatment + low temperature tempering
Also known as high alloy steel to reduce the surface residual austenite heat treatment.
7) induction heating and quenching after carburizing + low temperature tempering