Microstructural optimization of boron alloyed austenitic stainless steel

This work focuses on the role of boron as a sintering additive in powder metallurgy processing of the AISI 316L austenitic stainless steel. Boron effect was investigated regarding densification, microstructure, hardness and micro-scale abrasion resistance. Samples were prepared with 0.6 wt% and 0.8 wt% of boron and sintered at 1240 °C. The microstructure of the sintered bodies was characterized by field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), and Rietveld refinement of X-ray diffraction (XRD) patterns. Differential scanning calorimetry (DSC) was used to study the behavior of both the free and boron-containing 316L samples at solid and liquid states. The hardness of austenitic matrix and precipitated borides was determined by instrumented indentation tests. EDS and XRD results revealed the formation of M23(B,C)6 carboboride and hard M2B borides, which were concentrated mainly in intergranular sites. The formation of M2B borides favored material densification through the development of a liquid phase during sintering, promoting an increase in density, hardness and micro-scale abrasion resistance of the AISI 316L steel.