Microstructural evaluation and high-temperature erosion characteristics of high chromium cast irons

This present study investigated effect of chromium content on high temperature erosive wear characteristics of high chromium cast irons (Cr contain: 12%, 17%, 22% and 27% mass) for as cast specimens (AC) and heat treated specimens (QT), respectively. High temperature erosion test machine was used to investigate the erosive wear property of specimens at 1173 K. Alumina ball were used as particles at impact angles 30 degrees, 60 degrees and 90 degrees and velocity is 100 m/s. As result, the addition of Cr is effective to increase the hardness of AC specimen, therefore, the erosion rate is also gradually reduced. On the other hand, for QT specimens, the erosion rate of 17Cr is almost same with 22-27Cr due to tempering process occurs that made M7C3 as dominant carbides in the matrix. The maximum difference hardness between AC with QT specimens is only 40 HV that difficult to consider its influence on the erosion rate. Therefore, the carbides of AC and QT were focused. From Cr/C ratio, it can be seen that there precipitated M3C and M7C3 into 12Cr and 17Cr, M7C3 into 22Cr and 27Cr. From the phase diagram, the microstructure is gamma + M7C3 for each sample at 1173 K. Type and hardness of carbides are not changed at 1173 K for 22-27Cr AC and 22-27CrQT that resulted there is no significant difference in erosion rate after quenching compare to as cast. Therefore, the type of carbides is one of the main factors that can enhance the erosion resistance at 1173 K.