Effect of heat treatment on conditions of formation, shape, and stability of vanadium carbides in vanadium steels

Conclusions

• 1. It was found that the structure of steels 22F1B, 27F1B, and 35F2B resulting from isothermal transformation of supercooled austenite at 680–720°C consists of evenly distributed high-strength, oriented, dispersed vanadium carbide in a ferrite matrix. Such vanadium carbides impart high strength at normal and elevated temperatures, while ferrite provides fairly high ductility.

• 2. The structure of the steels after the double heat treatment (normalization at 1130°C for 5 min, tempering at 720°C for 3 h) consists of ferrite and unevenly distributed vanadium carbides. The strength characteristics at normal and elevated temperatures are lower than after the isothermal treatment at 680–720°C for 30 min.

• 3. The original structure of the steel after quenching or after isothermal treatment has different effects on the hardness during subsequent tempering. Tempering at 400–450°C after quenching or incomplete decomposition of supercooled austenite leads to reduction of the hardness due to coalescence of cementite, while complete decomposition of austenite, with formation of a ferrite-carbide structure, leads to an increase in hardness beginning at very low temperatures.