Ni-Based Alloy Coating on Plain-Carbon Steel by Hot Dipping Process

Abstract

A layer of Ni-Cr-Si-B-Fe alloy was successfully coated on plain steel substrate by hot dipping process. The Ni-Cr-Si-B-Fe alloy coating has a homogeneous thickness of 3mm. The chemical composition and microstructure were studied with SEM and XRD in this paper. The result shows that the Ni-Cr-Si-B-Fe alloy coating is defect-free and chemical bonded with plain steel substrate. A light band zone of 8-10 m width is between Ni-Cr-Si-B-Fe alloy coating and plain steel substrate, and may be considered as a quickly solidified layer. The coating microstructure is a heterogeneous microstructure and changes from the light band zone to the surface of the coating, which is composed mainly of coarse columnar dendrite, needle-like precipitates and scattered eutectic structures. Four regions across the thickness of Ni brazing alloy coating, due to solidification conditions upon hot-dipping, have been identified with distinguished microstructure. In γ-(Fe, Ni) solid solution matrix, the hard phases of CrB, Fe2B and Cr23C6 is identified in the coating.