The effect of first step holding time of low high austempering heat treatment to the mechanical properties of Austempered Ductile Iron (ADI)

Abstract

A low-high austempering process can be referred to as the application of undercooling condition in the austempering process of Austempered Ductile Iron (ADI). Undercooling condition promote more grain nucleation and producing finer grains with good mechanical properties. This study aims to investigate the influence of the first stage of lower temperature austempering holding time on its mechanical properties and find the best holding time which can produce the highest toughness of ADI materials. The experiment began with the heating of the nodular cast iron sample up to 927 °C and held for 120 minutes. Then it quenches to a liquid salt bath with a temperature of 260 °C as a lower temperature of the first austempering stage with a variation of holding time at 30, 60 and 90 minutes. Then it was transferred to a second salt bath medium of 400 °C as the second austempering stage with a holding time of 120 minutes then it was given the air cooling. The sample was tested by hardness, tensile, impact, and metallographic examination. The results show that the best toughness value in this research is obtained at 30 minutes holding time on first austempering stage with mechanical properties is tensile strength 1273 MPa, yield strength 1162 MPa, elongation 4,87% and impact value at 54.15 J. Value modulus of toughness is 5.93x107 J/m3.