Precipitation of Carbides during Tempering of Cr-Mo Steels

Carbide phase changes in various Cr-Mo steels during tempering were investigated by means of X-ray analyses, electron microscopic observations and chemical analyses. Two sequences of carbide precipitation were recognized, viz., (1)M3C→M2C→M23C6 or M3C, and (2)M3C→M7C3→M23C6. The carbide reaction (1)occurred in such the Cr-Mo steels of relatively lower chromium. content, while the carbide reaction (2)occurred in those of higher chromium content. In such the Cr-Mo steels of medium chromium content, the carbide reaction (1) and (2) occurred simultaneously. The carbide phase diagrams were proposed to describe the type of carbide reaction and the period of individual carbide precipitation for 12 types of Cr-Mo steels