The tempering process is a quenching and tempering step after the previous heat treatment. Although the martensite in the structure after quenching is very “hard”, it is all caused by dislocation distortion due to supersaturation of carbides. Such structure is unstable due to internal stress. In order to obtain stable structure and eliminate internal stress, the tempering step is also necessary.
Tempering process in Crl3 steel, in order to avoid tempering brittleness and obtain a combination of strength and toughness, it is usually tempered at 600-750 ° C at high temperature, and it is not advisable to temper at medium and low temperature. Martensite is obtained by quenching at 2Crl3. This structure with high hardness is hard, brittle and unstable because a large amount of C element is dissolved in supersaturated A-SOLID solution, Which increases the degree of lattice distortion. Low temperature tempering at 200-350 ° C is only applicable to high carbon Crl3 stainless steel, such as 4Crl3. It is only for the purpose of obtaining corrosion resistance and high hardness. In this state, carbides in martensite are precipitated but not much, and the internal stress is reduced to a certain extent. The structure changes into tempered martensite phase. Since the precipitation of Cr is not complete, Most of them are in the solid solution phase, which is very helpful for corrosion resistance. As for the high-temperature tempering temperature of 2Crl3, tempering at 600 ° C-750 ° C makes the microstructure of Crl3 martensitic stainless steel change into tempered sorbite. 2Crl3 at this tempering temperature can obtain a good match of strong initial property without losing corrosion resistance.
Why is there less carbide precipitation and good corrosion resistance and hardness in the medium and low temperature tempering state, but the mechanical properties of the medium and low temperature tempering will not be weakened in the whole line under the high temperature tempering state.
According to the research, it is found that the dispersion of alloy carbide is better and more sufficient under the temperature continuation under the high-temperature tempering state. The initial tempering restricts the dispersion of alloy carbide. At the beginning, the carbide is carburized. With the effect of temperature and time, the alloy carbide changes in Crl3 steel.
The change of mechanical properties of Cr13 type steel after heat treatment is basically similar to that of alloy steel under general conditions, which conforms to the objective law. With the increase of tempering temperature, the toughness and plasticity will be enhanced, and the strength and hardness will be weakened to a certain extent.