Influence of cooling speed on the microstructure and wear behaviour of hypereutectic Fe-Cr-C hardfacings

The main focus of this work is to show influences of the cooling rate on the microstructure and wear performance of Fe-Cr-C hardfacings. The coatings were produced by welding. The weld overlays were cooled from the molten stage in selected variations: (i) standard cooling - cooling on air at the steel welding table; (ii) passive cooling - cooling of the base material during the hardfacing process with a water cooled cooper plate with 12 degrees C; (iii) active cooling-cooling of the welding seam behind the main arc with CO2 gas at temperature of -80 degrees C. For each cooling situation the temperature of the weld seam was measured in the melt pool with help of thermocouple. It was shown, that different cooling conditions can lead to the significant changes in the cooling-off time t(8/5), dilution of the hardfacing with substrate and microstructural features of the hardfacings under investigation. Three different wear tests (three-body abrasion according to ASTM G65 standard, impact/abrasion and solid particle erosion) were performed to study the wear performances of Fe-Cr-C hardfacing. Testing results have shown that if the cooling-off time t(8/5) is too short it influences the brittleness and increases the residual stresses of the Fe-Cr-C hardfacing, which lowers its impact resistance. The effect of the cooling rate is in good correlation with wear test results and gives promise for further microstructure and process optimisation for the improved tribological performance. (C) 2013 Elsevier B.V. All rights reserved.