The Effect of Sub-Zero Cooling on Microstructure and Mechanical Properties of a Low Alloyed Austempered Ductile Iron

摘要

The effect of sub-zero cooling on microstructure and mechanical properties of a low alloyed austempered ductile iron has been investigated. Austempering of samples was performed at 325 and 400°C after austenitising at 875 and 950°C. The sub-zero treatments were carried out by cooling down the samples to -30, -70 and -196°C. The changes in volume fraction of austenite and mechanical properties were determined after cooling to each temperature. The austenite volume fraction of samples which were austenitised at 875°C and austempered at 325°C remained unchanged, whilst it reduced in samples austenitised at 950 and 875°C for austempering temperature of 400°C. In these specimens, some austenite transformed to martensite after sub-zero cooling. Mechanical property measurements showed a slight increase in strength and hardness and decrease in elongation and toughness due to this transformation behavior.