Cyclic annealing versus continuous annealing of 20 wt.% chromium white cast iron

Abstract

To destabilize as-cast microstructure of 20 wt.% chromium white iron, cyclic annealing involving repeated austenitization for short duration of 0.6 h at 900, 950, 1000, 1050 and 1100 °C followed by forced air cooling is conducted as an alternative to continuous annealing requiring austenitization for longer period of 4–6 h at the said temperatures followed by furnace cooling. Continuous austenitization destabilizes the austenite matrix through precipitation of secondary carbides and transforms the alloy depleted austenite to pearlite on furnace cooling, thereby reducing the as-cast hardness from HV 669 to HV466. In contrast, repeated austenitization not only destabilizes the austenite matrix through precipitation of secondary carbides followed by its transformation to martensite on forced air cooling, but also causes disintegration of longer eutectic carbides to shorter segments with subsequent increase in hardness to as high as HV 890. Notched impact toughness after both continuous and cyclic annealing remains uniformly at 12.0 J as compared to as-cast value of 6.0 J. Besides, an unexpected rise in abrasive wear resistance after cyclic annealing treatment makes the alloy superior than that obtained by continuous annealing treatment as practiced in industries.