Variation of chemical composition of carbides with heat treatment in 12Cr-1MoVW steel

Dissolution and precipitation reactions of the carbides occurred during heat treatment of 12Cr-1MoVW steel were studied. Transmission electron microscopy and energy dispersive X-ray spectroscopy were used to determine types and chemical compositions of precipitates. The dissolution of the M23C6 carbide took place during normalizing treatment through the diffusion of chromium atoms. Upon tempering, types of M3C and M23C6 precipitates were formed depending on the tempering conditions. The chemical composition of M3C formed at low tempering temperature is similar to the base material, but the enrichment of chromium and depletion of iron in M3C occur with increasing the tempering time and temperature. On the other hand chromium content decreases and iron content increases in M23C6 carbide with increasing the tempering temperature. M23C6 forms at the δ-ferrite/tempered martensite interface regardless of tempering temperatures. The chromium content of M23C6 formed at low temperature is low, but chromium content increases and iron content decrease in M23C6 with increasing the tempering time and temperature. (author)