Effect of interlayer temperature and extremely low terminal cooling temperature on the microstructure and wear resistance of Fe-based hardfacing alloy

Abstract

Hypereutectic high chromium cast iron (HHCCI) coatings were prepared by flux-cored arc welding (FCAW) under 230 °C, 80 °C and 30 °C interlayer temperatures, and an extra liquid nitrogen cooling was used to obtain −125 °C terminal cooling temperature. The microstructure evolution mainly primary carbide (P–C) and matrix, and abrasive wear behavior were evaluated. For natural air cooling, the amount of primary carbide increased, and the size and the mean free path between P–C decreased, with the decrease of the interlayer temperature. Due to the anisotropy in the P–C shape, the volume fraction of P–C, expressed by the area fraction, was significantly affected by the growth orientation. Liquid nitrogen cooling further optimized the morphology of P–C, in terms of the amount, size and distribution. Due to the −125 °C terminal cooling temperature, the martensitic transformation developed in the matrix, showing a body-centered tetragonal structure and exhibiting a Kurjumov-Sachs (K–S) orientation relationship with parent austenite. The linear relationship between wear resistance and P–C was investigated by Pearson's correlation coefficient, and the amount, size and mean free path expressed a strong correlation with wear resistance. Finally, the coating cooled by liquid nitrogen showed the best wear resistance, owing to the excellent morphology of P–C, and the strengthened matrix.