Effect of pre-heat treatments on wear behaviour of austempered ductile iron

In this study, the effects of heat treatments before austempering on the microstructure, mechanical properties and wear behavior of austempered ductile iron (ADI) were investigated. All of the EN-GJS-600-3 class low alloy pearlitic ductile cast iron (DI) samples were austenitized for 60 minutes at 900 °C as a pre-heat treatment. Then, the samples, which were cooled in air for normalization heat treatment, cooled in the furnace for full annealing heat treatment, and kept in a salt bath at 365 °C for 120 minutes for austempering heat treatment, were obtained separately. After the pre-heat treatments, all of the samples were only austempered. In this process, all samples were austenitized again at 900 °C for 60 minutes and then austempered in a salt bath at 365°C for 120 minutes. Microstructure changes of the samples were examined under optical microscope and scanning electron microscope (SEM). Residual austenite amounts were determined by X-ray diffraction (XRD) of the austempered samples. In order to determine the mechanical properties, hardness and tensile tests were carried out. Wear tests were carried out with pin on disc method in accordance with ASTM G99-17 standard. Worn surfaces were examined by SEM and their wear behavior was determined. The finest grained microstructure was obtained by double austempering heat treatment (DADI). The highest hardness, yield and tensile strength were obtained in DADI. These values were measured as 348 HV, 801.6 MPa and 1094.5 MPa, respectively. Normalized + austempered sample (NADI) and DADI presented very close mechanical property values. While the tensile strength for NADI is 1089.1 MPa, it is 1094.5 MPa for DADI, the total elongation is 8.7% for NADI, 8.4% for DADI, and the hardness value is 326 HV for NADI, while this value is 348 HV for DADI. measured. No improvement in yield and tensile strength was observed in the fully annealed + austempered specimen (FADI). The highest total elongation value was measured as 11.8% in FADI. The least weight loss was obtained in DADI with 0.6 mg. At the same time, this sample has the lowest average friction coefficient with μ = 0.356. On the other hand, the highest weight loss with μ = 0.697 was obtained in FADI, which has the highest average friction coefficient, as 2.9 mg.