Study on Phases Development and Mechanical Properties in a Fe-Ni-Al Carbide Free Bainitic Steel Based on Lateritic Steel After Warm Rolling

Abstract

The abundant reserve of lateritic ores in Indonesia is currently processed and studied to fulfil the national steel demand in several sectors, one of which is for railway application. The development of lateritic steel (Fe-Ni) as carbide free bainitic steel is carried out by adding Al to the Fe-Ni alloy. In this research, the effect of warm rolling and Al addition to the formation of carbide, phases development and mechanical properties was studied. The warm-rolled thermomechanical process (TMCP) was carried out by heating the material at 945°C for 20 minutes followed by second heating to 400°C, 450°C and 500°C with holding time for 30 minutes. The materials then warm rolled with 50% and 70% reductions using 20 tons capacity roller machine and then air cooled outside the furnace chamber. The microstructure of the as-rolled materials was characterized using optical microscope (OM) and scanning electron microscope (SEM), while the phases, the chemical distribution and the possibility of carbide formation were examine using X-Ray Diffraction (XRD) pattern and energy dispersive X-Ray spectroscopy (EDS). The mechanical properties of the material were observed using macro Rockwell hardness test. It was revealed that the addition of Al altered the phases of Fe-Ni lateritic steel significantly. Furthermore, Al addition gives positive effects to the Fe-Ni lateritic steel by increasing hardness. The reductions applied during warm rolling were observed to have effect on the growth of the grains in the Fe-Ni-Al lateritic steel.