Retained austenite in the matrix of high-cr white cast irons tends to increase the spalling rate resulting from repeated impacts. The as-cast condition results in the most retained austenite and the highest spalling rate. As the retained austenite is reduced to about 10 vol pct, the spalling rate decreases. Below 10 vol pct austenite the spalling rate depends upon other factors, probably residual stress, martensite strength, and ferrite formation. Heat treatments can be used to greatly reduce the spalling rate, although many heat treatments resulted in an increase in pin wear over that of the as-cast condition. Retained austenite content of about 20 pct or more is desired for low pin wear. As the carbide volume fraction increases from 20 to 40 vol pct by adjusting the carbon and chromium contents, the possibility of achieving low pin wear and low spalling rate by heat treatment improves, but the tendency for catastrophic failure greatly increases. A desirable heat treatment is austenitizing at about 1,000 deg c for 4 h followed by air cooling, with or without a subcritical treatment at 495 deg to 525 deg c for 12 h, dependig upon the desired combination of wear and spalling resistance. Heat treatments should be adjusted for section thicknesses other than the 75 mm used here. When selecting a high- cr white cast iron, one must choose an appropriate composition and heat treatment to provide a combination of abrasion resistance and spalling life that will best satisfy a particular impact-abrasion wear condition.
Wear of Metals, V.1, 1989, PP. 175-183