Investigation of Mechanical Properties and wear behavior of Ni-alloyed Specially Heat Treated Permanent Moulded Austempered Ductile Iron (PMADI) for Power Plant Applications

Austempered ductile iron (ADI) is relatively newer material, which has attracted researchers and manufacturers alike mainly because of its immense properties and also at the same time cheaper to process and produce. Utilization of permanent moulds to ADI has many advantages such as very good dimensional stability, good nodule size count, better surface finish and environmental cleanness. Extensive literature survey reported that ADI out-performs proprietary abrasion resistant steels at similar bulk hardness levels.

Experiments were systematically planned to study the mechanical and wear properties of Ni-alloyed PMADI and are processed by a novel two step austempering process. All specimens were initially austenitized at 950 °C for 2 h. These samples were initially quenched for 5 min in a salt bath maintained at 250° C and then austempered for 2 h at several austempering temperatures. These temperatures were 280° C, 310° C, 340° C, 370° C, 400° C, and 430° C. The results show that this novel process has resulted in higher tensile strength, yield strength, hardness and wear resistance than the conventional single step austempering process. The tensile strength value improved by about 11% for 2% Ni PMADI samples over 1.5% i PMADI samples while maintaining reasonable levels of ductility. The results are analyzed based on the micro structural features.