Effect of silicon on subcritical heat treatment behavior and wear resistance of 16 wt% Cr cast iron with 2 wt% Mo

บทคัดย่อ

Effects of Si content on the hardness, decomposition of austenite and abrasive wear resistance during subcritical heat treatment of hypoeutectic 16 wt% Cr -2 wt% Mo cast irons were investigated. The hypoeutectic 16 wt%Cr-2wt% Mo cast irons with 0.5-2.0 wt% Si were prepared. The as-cast specimens were heated up to subcritical temperatures at 50 K intervals from 673K for 14.4 ks ,28.8 ks and 43.2 ks and then, cooled to the room temperature by fan air cooling. In the as-cast state, the hardness increased gradually as Si content increased to 1.5 wt% and then decreased rapidly. The size and the amount of eutectic carbides increased with increasing Si content. In the subcritical heat treatment state, the hardness curves showed a secondary hardening due to the transformation of austenite into martensite and the precipitation of secondary carbides. The degree of secondary hardening decreased with increasing Si content. The decomposition fraction of austenite (f) increased abruptly when the holding temperature rose over 823 K. The maximum hardness (H_STmax) was obtained by the condition of 873 K for 14.4-28.8 ks where the f was about 70-80%. The highest value of (H_STmax) 740 HV30 was obtained in the 1.5 wt%Si specimen. The linear relation was obtained between the wear loss and wear distance. The wear loss decreased with an increase in Si content. The highest wear resistance was obtained in the specimen with HSTmax and the lowest wear resistance was obtained in over-tempered specimen.