Influences of sintering atmospheres on densification process of injection moulded gas atomised 316L stainless steel

Abstract

Densification of metal injection moulded 316L stainless steel is one of the hottest research fields in powder metallurgy in recent years. In the present work, various sintering atmospheres, i.e. N₂, N₂ + H₂, Ar and Ar + H₂, were adopted to investigate their influences on the sintered density, pore size, pore shape, grain size and mechanical properties. Relative densities of 98% of the theoretical density (7·84 g cm^-3 and 7·85 g cm^-3), pore sizes about 2~3 μm and mean grain sizes about 50 μm could be obtained after the specimens were sintered in Ar and Ar + H₂ atmospheres. Optimised mechanical properties could be acquired in Ar + H₂ atmosphere, i.e. σ _b = 630 MPa, σ _0·2 = 80 MPa, δ = 52%, HRB = 71. When sintered in N₂ and N₂ + H₂, the specimens have lower densities than those sintered in Ar and Ar + H₂. An ultimate tensile strength of 765 MPa and a hardness of 82 HRB could be obtained respectively in N₂ + H₂ and N₂, atmospheres. The dimensional tolerance of the sintered part is less than ±0·5% with the sintered dimension ranged from 2·64 to 43·07 mm.