A scanning electron microscopy study of carbides in high-speed steels

Investigations were made using scanning electron microscopy to examine deeply etched specimens and electrolytically extracted carbides of as-cast high-speed steels. It is shown that eutectic carbides appear in three types of eutectic morphologies. A carbide “wall” exists around type I skeleton eutectic, and growth steps are evident on the top of carbide platelets of the lamellar type II eutectic. Type III generally develops a thick plate or bar form. The delta-eutectoid carbide attains a “bunched fiber” shape. Increasing molybdenum and decreasing tungsten leads to a change of eutectic carbide from skeleton to platelike and fiberlike morphologies. Vanadium not only promotes the formation of MC carbide, but also the formation of M 2C carbide. It was noted to be unfavorable to the formation of M 6C carbide, and increasing the vanadium content results in an increase in the size of eutectic and eutectoid carbides.