Phase transformations in different batches of 40Kh steel

Conclusions

• 1. The differences in the properties of different batches of 40Kh steel are due to the presence of surface-ac-tive SiO. The concentration of SiO in the metal can be predicted from the physicochemical conditions of the smelting process.

• 2. The presence of surface-active impurities considerably slows down the rate of isothermal transformation of supercooled austenite, which leads to an increase of the depth of the effect of heat treatment.

• 3. In the presence of a surface-active impurity in the steel the martensite and other products of isothermal decomposition of supercooled austenite become oriented. Furthermore, the intensity of the process of coagulation of the carbide phase decreases when the metal is kept for long periods of time near the critical temperature.

• 4. The effect of surface-active impurities is particuarly great in the α-phase and during the γ»α transformation at certain temperatures. The intensity of the effect is determined by the ratio between the amount of the impurity and the rate of its displacement, which is characterized by a curve with a peak between 450 and 650°C.