Structural transformation in 12Kh1MF steel induced by heat treatment

Abstract

1. In the case of uninterpreted cooling of 12Kh1MF steel the austenite is transformed into ferrite-pearlite, intermediate phase, or martensite, depending on the cooling rate. Therefore, machine parts of various sizes must be cooled at approximately the same rate, changing only the cooling conditions. 2. Tempering of quenched or normalized 12Kh1MF steel at 600\2-650\dgC induces precipitation of highly dispersed particles of vanadium carbide; this, in turn, increases the ultimate strength, yield strength, and hardness, but decreases the impact strength. Increasing tempering temperatures lead to coagulation of vanadium carbide, which decreases the strength of the alloys but increases the ductility and the impact strength. Tempering of annealed steel does not induce precipitation of vanadium carbides, and the mechanical properties remain unchanged, since the vanadium carbide is completely precipitated during annealing. 3. The low and variable values of the impact strength of heat treated thick-walled pipes result from insufficiently high rates of cooling and the fluctuation of the temperature during tempering in industrial furnaces. 4. High heat resistance and good mechanical properties during short exposures to high temperatures are obtained as the result of heating to 960\2-980\dgC, cooling from this temperature at a rate not less than 250\2-300 deg/min, and tempering at 730\2-750\dgC.