Role of Matrix Structure on Impact-Wear Resistance of As-Quenched 27%Cr Cast Iron

The role of retained austenite and martensite on impact-wear resistance of 27%Cr cast iron quenched at temperatures of 1223 K and 1423 K was investigated at various impact angles by impact wear tests using an air blasting machine. Measurement of the hardness and volume fraction of martensite in the matrix of both samples as well as SEM observation were performed. Quenching treatment at 1223 K resulted in a higher volume of initial martensite in the matrix, and wear rate reached maximum at 60 degrees. On the contrary, the matrix with a high volume of retained austenite obtained by quenching at 1423 K showed a maximum impact-wear rate at 45 degrees. The difference in the wear resistance between the two types of as-quenched samples can be explained by the transformation from metastable austenite to strain induced martensite and self-tempering of the initial martensite occurring under impact wear environment. As the volume of retained austenite increases, hardening due to strain induced martensite was found to overlap with softening due to tempering of the initial martensite, which contributed to the suppression of the wear rate.