Effects of alloying elements on microstructure and fracture properties of cast high speed steel rolls: Part I: Microstructural analysis

A study was made of the effects of alloying elements on microstructural factors of six high speed steel (HSS) rolls manufactured by centrifugal casting method. Particular emphasis was placed on the role of hard carbides located along solidification cell boundary and the type of the martensite matrix. Microstructural observation, X-ray diffraction analysis, and hardness measurement were conducted on the rolls to identify carbides. Various types of carbides were formed depending on the contents of strong carbide forming elements. In the rolls containing the high Cr content, MC carbides inside cells and M7C3 carbides along cell boundaries were primarily formed, while in the rolls containing the high W and Mo contents, MC carbides inside the cells and fibrous M2C carbides in the intercellular regions were dominantly formed. The most important microstructural factor affecting overall roll hardness was the intercellular carbides and their distribution. The effects of alloying elements were analyzed on the basis of the liquidus surface diagram, suggesting that the proper contents of carbon, tungsten, molybdenum, chromium, and vanadium were 1.9–2.0, 3–4, 3–4, 5–7, and 5–6%, respectively.