In order to improve the strength, hardness and wear resistance, most iron-based powder metallurgy parts need integral quenching, that is, quenching and tempering treatment. The iron-based powder metallurgy parts that need to be quenched as a whole should have a bonded carbon content of ≥0.3% (mass fraction) and be in an austenitic state above A3 temperature.

The integral quenching of iron-based powder metallurgy parts consists of the following three processes:

Austenitization. In the protective atmosphere where the carbon potential is equivalent to the combined carbon content, the parts are heated to a temperature higher than A3, usually 850℃, and kept for a certain time, which depends on the shape and size of the parts. Say 30 minutes.

Quenching. From the austenitizing temperature or slightly lower temperature, but still higher than A3, the parts are quenched in oil or water to transform austenite into hard and brittle martensite or bainite. For iron-based powder metallurgy parts, it is best to quench in warm oil (50℃), because powder metallurgy parts have pores, and when the quenching cooling rate is too fast, the parts may crack. In addition, when quenching with salt water, the residual salt water in the pores will lead to serious corrosion of the quenched parts.

Tempering. According to GB/T 19076-2003 "Sintered Metal Materials-Specification", iron-based powder metallurgy parts are usually tempered at 180℃ (sintered nickel steel is 260℃), and the tempering time is usually 1h according to the section thickness of the parts. Its purpose is to eliminate the internal stress produced when austenite transforms into martensite and bainite. Tempering can reduce the brittleness of martensite and bainite and improve the toughness of parts materials.