Effect of Silicon Content on Sub-critical Heat Treatment Behavior of 16%Cr-2%Mo Cast Iron: doi: 10.14456/mijet.2015.4

Pisizchai KOSASU; Sudsakorn INTHIDECH; Kaoru YAMAMOTO; Nobuya SASAGURI; Yasuhiro MATSUBARA

Authors

Pisizchai KOSASU Department of Manufacturing Engineering, Faculty of Engineering, Mahasarakham University, Mahasarakham, 44150
Sudsakorn INTHIDECH Department of Manufacturing Engineering, Faculty of Engineering, Mahasarakham University, Mahasarakham, 44150
Kaoru YAMAMOTO Department of Materials Science and Engineering, Kurume National College of Technology, Fukuoka, 830-8555
Nobuya SASAGURI Department of Materials Science and Engineering, Kurume National College of Technology, Fukuoka, 830-8555
Yasuhiro MATSUBARA Department of Materials Science and Engineering, Kurume National College of Technology, Fukuoka, 830-8555

Keywords:

Sub-critical heat treatment, 16 wt% Cr-2 wt% Mocast iron, hardness, retained austenite, silicon effect

Abstract

The objective of this research is to clarify the effect of Si content on variation of hardness and retained austenite during sub-critical heat treatment of the 16 wt% Cr cast iron. The hypoeutectic 16 wt% Cr-2% Mo cast irons with 0.5-2.0 wt% Si were prepared. As-cast specimens were heated up to sub-critical temperatures at 50 K intervals from 673-923 K for 14.4, 28.8 and 43.2 ks and then, cooled to the room temperature in the air. The hardness and volume fraction of retained austenite (V) were measured. In the as-cast state, the hardness increased and then decreased as Si content increased. The Vdecreased gradually with increasing the Si content to 1.5 wt% and after that, it decreased abruptly. In the sub-critically heat-treated state, the hardness increased first and subsequently decreased as the holding temperature was increased. The reason could be due to the transformation of austenite into martensite and the precipitation of secondary carbides. The degree of an increase in hardness becomes small with increasing the Si content. The Vdecreased remarkably when the holding temperature increased over 823 K under the same holding time. The maximum hardness (H _STmax ) was obtained by the treatment condition of 873 K for 14.4-18.8 ks where the Vwas less than 15%. The highest value of H _STmax ,745 HV30, was obtained in the 1.5 wt% Si specimen.