Features: For those with high core strength requirements, quenching at 820 ~ 850oC, low-carbon martensite in the core structure; high hardness on the surface, using 780 ~ 810oC heating quenching can refine the grains
Scope: carbon steel after solid carburization and low alloy steel workpiece. Coarse grain steel after gas and liquid carburizing, parts that are not suitable for direct quenching after carburizing, and parts that need to be machined after carburizing
2, carburizing, high temperature tempering, one heating quenching, low temperature tempering, carburizing temperature 840 ~ 860oC
Characteristics: high temperature tempering decomposes martensite and retained austenite. Carbon and alloying elements in the layer are precipitated as carbides, which facilitates the reduction of retained austenite in the layer after work-shaping and quenching.
Scope of application: mainly used for carburizing workpieces of CR-NI alloy steel
3, secondary quenching low temperature tempering
Features: The first quenching (or normalizing) can eliminate the reticulated carbide and refine the heart tissue. The second quenching mainly improves the microstructure of the layer, but it should be quenched above the core AC3 when the performance of the core is high.
Scope of application: It is mainly used for important carburized parts with high mechanical properties, especially for coarse grain steel. However, after carburizing, two high-temperature heating is required to increase the deformation and oxidative decarburization of the workpiece, and the heat treatment process is complicated.
4, secondary quenching cold treatment low temperature tempering
Features: Temperature quenching above AC1 or AC3 (heart), high austenitic steel has more retained austenite on the surface layer, and cold treatment (-70 ~ 80oC) promotes austenite transformation, thereby improving surface hardness and wear resistance
Scope of application: mainly used for high alloy steel workpieces that do not require machining after carburizing
5, direct quenching low temperature tempering
Features: Can not refine the grain of steel. The quenching distortion of the workpiece is large, and the amount of retained austenite on the surface of the alloy steel carburized part is large, and the surface hardness is low.
Scope of application: simple operation and low cost. The pit furnace is used to treat parts that are not deformed and subjected to impact loads, and is suitable for gas carburizing and liquid carburizing processes.
6, pre-cooling direct quenching low temperature tempering, quenching temperature 800 ~ 850oC
Features: It can reduce the quenching distortion of the workpiece. The amount of retained austenite in the carburized layer can also be slightly reduced, the surface hardness is slightly improved, but the austenite grains are not changed.
Scope of application: Simple operation, small oxidation, decarburization and quenching deformation of the workpiece. Widely used in a variety of workpieces made of fine grain steel.
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