Microstructural Comparison of Spray-Formed and Conventionally Cast 2.5C–19Cr High-Chromium White Iron

A billet of hypoeutectic high-chromium white iron (2.5% C, 19% Cr) was spray formed using gas-to-metal ratios of ~0.9, ~1.0, and ~1.1. The as-sprayed material was close to full density and contained fine (Fe,Cr)₇C₃ carbides (27–30 vol%) uniformly distributed in a matrix consisting of pearlite and ferrite. Length of the carbides rarely exceeded 30 μm. This was in stark contrast to a conventionally cast starting material, which contained coarse (Fe,Cr)₇C₃ carbides (~22 vol%) non-uniformly distributed in a matrix consisting of austenite and martensite. Length of the carbides in the cast material occasionally exceeded 100 μm. Varying gas-to-metal ratio between 0.9 and 1.1 did not result in any significant changes in carbide morphology, although slightly coarser carbide morphology was produced with the gas-to-metal ratio of 0.9. Regardless of the gas-to-metal ratio, the finest carbide morphology was found in the surface region of the spray-formed billet.