Nobuya Sasaguri

Solidification and abrasion wear of white cast irons alloyed with 20% carbide forming elements

Three different white cast irons with compositions of Fe-3%C-10%Cr-5%Mo-5%W (alloy no. 1), Fe-3%C-10%V-5%Mo-5%W (alloy no. 2) and Fe-3.5%C-17%Cr-3%V (alloy no. 3) were prepared in order to study their solidification and abrasion wear behaviors. Melts were super-heated to 1873 K in a high frequency induction furnace, and poured at 1823 K into Y-block pepset molds. The solidification sequence of these alloys was investigated. The solidification structures of the specimens were found to consist of austenite dendrite (γ); (γ + M 7 C 3 ) eutectic and (γ + M 6 C) eutectic in the alloy no. 1; proeutectic MC; austenite dendrite (γ); (γ + MC) eutectic and (γ + M 2 C) eutectic in the alloy no. 2, and proeutectic M 7 C 3 and (γ + M 7 C 3 ) eutectic in the alloy no. 3, respectively. A scratching type abrasion test was carried out in the states of as-cast (AS), homogenized (AH), air-hardened (AHF) and tempered (AHFT) using the abrasive paper with 120 mesh SiC and 10 N application load. In all the specimens, the abrasion wear loss was found to decrease in the order of AH, AS, AHFT and AHF states. Abrasion wear loss was lowest in the specimen no. 2 and highest in the specimen no. 1 except for the as-cast and homogenized states in which the specimen no. 3 showed the highest abrasion wear loss. The lowest abrasion wear loss of the specimen no. 2 could be attributed to the fact that it contained proeutectic MC carbide, eutectic MC and M 2 C carbides having extremely high hardness. The matrix of each specimen was fully pearlitic in the as-cast state but it was transformed by heat-treatments to martensite, tempered martensite and austenite. From these results, it becomes clear that MC carbide is a significant phase to improve the abrasion wear resistance of white cast iron.

Effect of Chromium and Vanadium Contents on Continuous Cooling Transformation Behavior of Multi-Component White Cast Iron

In this study, the multi-component white cast irons with 5wt% of Mo, W, 2 wt% of C, Co each and varying Cr content from 1 to 9 wt% and V content from 3 to 9 wt% independently were employed and effect of Cr and V contents on the behavior of continuous cooling transformation (CCT) was investigated. When the Cr content increases to 5wt%, the critical cooling rate of pearlite transformation (VC-P) does not change much, but the VC-P decreases gradually as the Cr content is increased over 5 wt%. The critical cooling rate of bainite transformation (VC-B) increases with an increase in the Cr content. In the case of V effect, on the other hand, the VC-P decreases as the V content increases. However, the VC-B decreases with an increase in the V content up to 4mass%, but over 4wt%V, it increases, and at 9wt%V, the precipitation of ferrite phase occurred. Ms temperature decreases continuously as the Cr content increases to 5wt%, and then increases. As the V content increases, Ms temperature rises gradually. In the case that Mf point appears, the Mf temperature goes up with an increase in the Cr and V contents.