Effect of Borides Addition on the Sintering Process of Austenitic Stainless Steel Powder Compacts

Abstract

Effect of boride powder (FeB, CrB and NiB) addition on the densification of SUS304L (Fe-18 wt%Cr-11wt%Ni) powder compacts are investigated in relation to liquid phase sintering. The mechanism of liquid phase formation and sintering process are mainly discussed for the case of CrB addition. The results are summarized as follows:
CrB powders added to SUS304L compacts change to Cr₂B during heating for sintering and a eutectic reaction occurs between the Cr₂B and the matrix to form liquid phase. Liquid phase formed through the eutectic reaction permeates among SUS304L powders and this results in disappearance of small pores finely dispersed in the matrix and formation of large pores at spots where CrB powders have originally situated. Densification of the compacts is greatly promoted because of the liquid phase which remains during sintering. The liquid phase finally solidifys to the mixed structure of austenite and Cr₂B on cooling. Almost the same results are also obtained for FeB or NiB addition.