The effect of austempering and induction surface hardening processing on the microstructure and mechanical properties of ductile cast iron GGG40

In this study, effects of induction surface hardening heat treatment on microstructure, hardness, wear behavior, and tensile strength of austempered ductile cast irons GGG40 (DCI) were investigated. For this purpose, it was determined that austenitizing temperature was 900 °C and austenitizing time was 90 minutes for GGG40 (DCI) samples. By applying austempering temperature as 320 °C and 380 °C in two individual parameters, it was kept in salt bath for 120 minutes in order to see the effect of upper and lower bainite/ausferrite morphology. Induction surface hardening heat treatment was performed to austempered ductile cast iron. In order to determine structural changes occurring in ductile cast irons GGG40 (DCI) after heat treatment, Optical Microscopy, SEM, EDS, and X-ray analyses were carried out after they were cleaned and polished by using traditional polishing method. Microhardness measurements were also taken from the surface of materials by using Vickers hardness scale (HV). Tensile tests were carried out at 1mm/min of tensile speed under 50000 N of load in accordance with TS 287 EN 895 standard in order to determine tensile strengths of heat treated and non-heat treated ductile cast iron GGG40 (DCI) samples. Fracture surface morphology of the samples was examined by SEM-EDS and X-ray analyses. Wear tests were carried out in wear test device displaying vertical pivoted motion with 320 and 800 mesh abrasive by applying 10, 20, 30 N load and using 8 m and 15 m road distance. Values of abrasion loss in materials were measured while examining wear surfaces of the samples with SEM microscope. The reason behind why abrasion resistance of experimental samples increased was thought that nodular graphites found in microstructure had lubrication effect and induction surface hardening heat treatment increased surface hardness. Hardness values increased as austempering temperature increased. In the first section of this study, the subject was introduced. In the second section, place and importance of the present study in the literature were mentioned. In the third section, general information about ductile cast iron were given. In the fourth section, general information about heat treatments were given. The fifth section presented general information on mechanical tests. The sixth section mentioned the experimental study. In the seventh section, the information about experimental study and evaluation were given. The eighth section included results, discussion, and suggestions.