Influence of coating thickness and temperature on mechanical properties of steel deposited with Co-based alloy hardfacing coating

Hardfacing is widely used to improve the performance of components exposed to severe service conditions. In this paper, this surface modification was evaluated for heat-resistance steel DIN X45CrSi9-3 deposited with Co-based alloy Stellite 12 by the plasma-transferred arc welding (PTAW). The microscopic properties of the deposition coating, including the microstructure, the chemical phases, and the distribution of element, were first characterized by optical microscopy (OM), scanning electron microscope (SEM) equipped with energy dispersive spectroscopy (EDS), and X-ray diffractometer. To clarify the static mechanical degradation due to the decrease in coating thickness and the increase in temperature, the Vickers hardness and the bending strength were then investigated. The measurements of the Vickers hardness on surfaces of coatings with different thicknesses were conducted at room temperature (RT) and the three-point bending tests on specimens with different coating thicknesses were performed at both RT and 500 °C. The failure modes during the bending tests were finally proposed based on the observations of fracture surfaces. Experimental results showed that the decrease in coating thickness from 2.5 mm to 1 mm did not bring about much degradation of both the Vickers hardness and the bending strength, whereas the increase in temperature from RT to 500 °C led to a significant decrease in the bending strength.