EFFECT OF CARBON CONTENT ON HEAT TREATMENT BEHAVIOR AND ABRASIVE WEAR RESISTANCE OF MULTI-ALLOYED WHITE CAST IRON

Abstract

Effect of carbon content on heat treatment behavior of multi-alloyed white cast irons with basic alloy composition was investigated. The multi-alloyed white cast irons with varying C content from 1.73 to 2.34% were prepared. After annealing, the specimens were hardened from 1323 and 1373 K, and then tempered at 673 to 873 K. In as-hardened state, the hardness increased first as C content rose except that the hardness of 2.34% C specimen hardened from 1373 K decreased remarkably. The volume fraction of retained austenite (Vγ) increased continuously with increasing C content. In the tempered state, hardness curve of each specimen clearly showed secondary hardening due to the precipitation of carbides as well as the transformation of retained austenite to martensite. The maximum tempered hardness (HTmax) was obtained by tempering between 798 to 823 K where the Vγ ranged from 4 to 14%. Abrasive wear resistance was evaluated by a rubber wheel wear test of each specimen tempered at three levels of temperatures. The relationship between weight loss (Wl) and wear distance (Wd) was expressed by linear function and wear rate (RW) was obtained from the slope of the straight line. In each heat treatment condition, the RW value decreased or the wear resistance increased as C content increased. In the tempered state, the lowest RW or the highest wear resistance was obtained mostly in HTmax specimens. When the Vγ values less than 5%, the RW covered in wide range but it was found that the RW lowered roughly in proportion to the increase in hardness. In the region of Vγ over 5%, the RW decreased with increasing Vγ value.