Enhanced sintering of austenitic stainless steel powder aisi 316l through boron containig master alloy addition

Abstract

It is well known that boron is widely used in order to enhance sintering process for obtaining high density of sintered iron alloys. It was found that even a small amount of elemental boron added to iron based powder compacts, produces significant increase in densification rate upon formation of a liquid phase. Due to the attractive characteristic the use of boron has also been actively investigated for enhancing sintering stainless steels powders. In present research boron was added as a part of master alloy, which has been designed to provide the formation of wetting liquid phase, with accomplished characteristics for manufacturing controlled densification of sintered austenitic stainless steels powders AISI 316L. In this paper the influence of sintering atmosphere and the boron in 0,1; 0,2; 0,3 and 0,4 wt. % amount on the density, microstructure and selected properties of sintered austenitic stainless steels were reported. Green compacts obtained by cold compaction at 600 MPa reached densities around 6,2 g/cm 3. The sintering process was carried out both in pure dry hydrogen atmosphere and in vacuum at temperature 1240°C using dilatometer Netzsch DIL 402C. In order to interpret the influence of sintering atmosphere and boron content on the sintering behaviour of boron alloyed austenitic stainless steels powders during heating and isothermal holding, the evolution of the dilatometric curves have been discussed. The as-sintered microstructures were characterized under the SEM (EDS), while the pore morphology by the image analysis. In conclusion it could be affirmed that the addition of the master alloy containing boron to austenitic stainless steels powders, produces a permanent liquid phase that enhances densification compacts during sintering, in particular in hydrogen atmosphere. For this reason the results are promising from a technological point of view, because boron addition could extend applications of sintered stainless steel both with respect to lower sintering temperature and shorter time necessary to obtain well rounded pores which are desirable with respect to mechanical properties and corrosion resistance.