ENHANCED MECHANICAL PROPERTIES OF AUSTEMPERED SG-CAST IRON BY TWO-STEP AUSTEMPERING HEAT TREATMENT

Study of a single step austempering and two-step high-low temperature regimes has been carried out. The results have shown that with increasing austempering temperature from 320 to 400°C, the morphology of ausferritic ferrite changes from acicular or lath to feathery. This microstructural evolution leads to an increase in ductility and a decrease in strength and hardness. Two-step high-low, (400- 320°C) temperature austempering produced a mixture of upper and lower ausferrite matrix microstructure. An improvement in the elongation to fracture and impact properties was observed after 400-320°C two-step processing.