Austempering is one of the trendiest heat treatment processes to promote the strength and toughness of ductile iron. However, such practice is complex because it involves using aqueous solutions as quenchant (salt bath solution). This study was conducted to analyse the heat treatment of the combination processes of annealing-austenitising and evaluate the correlation between microstructure constituent and hardness of the ductile iron. Ductile iron samples in form of double cylinder was produced by conventional CO2 sand casting method. The new heat treatment process was started by annealed at 873 K for 1.8 ks before being oil quenched. Subsequently, the samples were austenitised at austenitising temperatures 1123 K, 1173 K and 1223 K for 3.6 ks respectively before being immediately oil quenched to room temperature. A series of microstructure analysis tests, including optical microscopy and X-ray diffraction (XRD) was applied. Vickers microhardness tester was used to measure the hardness for each microstructure constituent. The results showed that ductile iron matrix transforms to martensitic during heat treatment of annealing-austenitising combination processes, which in turn contributes to increasing microhardness of martensite and the bulk hardness of ductile iron.
The aim of this study is to examine the effect of surface treatments involving shot blasting and paste boronizing on the microstructure, microhardness and density of 316L stainless steel. Shot blasting using glass beads was carried out prior to paste boronizing at fix boronizing temperature and soaking time of 850°C and 8 hours respectively. The results show paste boronizing produces boride layers that consist of FeB and Fe2B on the surface of 316L stainless steel with high hardness. Shot blasting on the other hand creates grain refinement on the metal’s surface which increases boron diffusion into the surface and improves the case depth of boride layers formed and also its hardness. Higher shot diameter used in shot blasting also influence in improving the case depth of boride layers produced and hardness of 316L stainless steel. The effect of shot blasting using a higher shot diameter and paste boronizing reduces the density of 316L stainless steel very slightly.