Microstructure formation in the powder HIPed hardfacing alloy Tristelle 5183 (Fe-21%Cr-10%Ni-7.5%Nb-5%Si-2%C in wt%)

Abstract

Tristelle 5183 (Fe-21%Cr-10%Ni-7%Nb-5%Si-2%C in wt%) is an alternative material to cobalt-based alloys for wear resistant hardfacing applications. In this work, gas atomised powder was consolidated by hot isostatic pressing (HIPing) at 1120 ± 10 o C which is ∼ 100 o C below the melting onset point. The microstructure formation in the alloy, following densification, was investigated using X-ray diffraction, scanning and transmission electron microscopy and electron backscatter diffraction. The hot isostatically pressed (HIPed) alloy contains principally fcc γ -Fe, NbC, and M 7 C 3 with a small fraction of bcc α/δ -Fe and a π -ferrosilicide phase. This contrasts with the metastable gas atomised powder microstructure in which M 7 C 3 formation is largely suppressed and NbC precipitation is reduced. Following HIPing, a wide distribution of γ -Fe grain sizes is found. The larger grains exhibit sub-grain structures with significant intra-grain misorientations as identified by kernel average misorientation (KAM) maps. The smaller grains (< 10 μm) contain annealing twins, indicating that recrystallization had occurred only in certain localised regions which underwent sufficient plastic deformation in the early stages of HIPing. The work demonstrates the potential for HIPing hardfacing alloys to achieve a fine scale homogeneous microstructure. • HIPing homogenises the rapidly solidified powder microstructure of the alloy. • Insufficient recrystallisation of the powder results in a bimodal matrix grain size. • A mainly austenitic iron matrix contains NbC and M 7 C 3 precipitates. • M 7 C 3 is largely suppressed in the powder but precipitates out during HIPing.