Sintering Mechanisms of Boron Alloyed AISI 316L Stainless Steel

Abstract

The effect of boron on sintering of austenitic stainless steel was studied with reference to atmosphere (nitrogen-hydrogen mixtures) and temperature conditions. Specimens were characterised by the usual microstructural techniques and the boron distribution in the microstructure was also studied by means of Auger electron spectroscopy and secondary ion mass spectroscopy. In addition, tensile tests were carried out to verify the influence of the process parameters on the mechanical properties of the materials. Boron strongly enhances sintering by liquid phase formation only when the process is carried out in pure hydrogen at a temperature higher than 1200°C. In those conditions a eutectic reaction between austenite and a complex boride of the type (Fe, Cr, Mo )₂B occurs favouring densification through the well known mechanisms of liquid phase sintering. A very low fraction of residual porosity is obtained. Conversely, the presence of nitrogen in the sintering atmosphere impedes boron–steel interaction and sintering is inhibited. The liquid phase sintered specimens exhibit a dense microstructure which should provide good corrosion resistance. PM/0631