Behaviour of coatings with AWS ERNiCrMo-3 electrode on ASTM A516 Gr.60 steel in ageing tests

Abstract

This work is intended to evaluate the microstructure of nickel-based overlay welds after ageing heat treatments. GMA welds using an AWS ERNiCrMo-3 electrode were deposited with a robot on ASTM A516 Gr.60 steel. Two weld heat inputs were used, 1.0 and 1.4 kJ/mm, with a current of 290 A, arc voltage of 33 V, and welding speeds of 9.7 and 6.8 mm/s, respectively. The ageing processes were conducted at 600°C using times of 100 and 300 h. Micro-hardness profiles and scanning electron microscopy together with energy dispersive spectrometry analysis were carried out to characterize the overlay. The hardness profile indicated that, in the ‘as welded’ condition, the overlay and heat-affected zone (HAZ) hardness were about 240 and 190 VH, respectively. The ageing process decreased the HAZ hardness to 120 VH and increased the overlay hardness to 290 VH after 100 h and to 310 VH after 300 h. These changes occurred due to HAZ decarburization and transformation of micro phases. After ageing, hard zones with values of around 800 VH were observed in the partially diluted zone, caused by the higher concentration of carbides and microstructural changes.