Investigation on the mechanisms and mitigation strategies for adhesive wear in reformer HP40Nb steel

HP40Nb Reformer tubes have excellent corrosion resistance, resistance to oxidation and carburization, good weldability, and structural stability at elevated temperatures due to the high percentage of nickel and chromium as well as niobium. The material maintains its high hardness and does not undergo microstructure degradation when exposed to temperatures at 650 °C for 11 ½ years. Therefore, reformer tubes could be utilized in applications demanding exceptional wear resistance even after completing their high-temperature service life. This work aims to investigate the adhesive wear behaviour of HP40Nb. Wear tests were carried out by applying the design of experiments technique with 2 parameters like disc rotational speed and normal loads, 4 levels each. The effect of operating variables on coefficient of friction (COF), wear, sliding distance and surface roughness was investigated. The wear track was investigated using different microscopes and measurements of the wear profile were conducted using an optical profilometer. At the lowest rotational speed, the COF has only a marginal effect for all loads. However, at higher rotational speeds, it reduces as the load increases from 5 to 10 N. The wear rate increases as the load increases. Microscopic observation of the wear track reveals ploughing, micro-cutting, plastic deformation, adhesion, and delamination indicating adhesive wear. At lower rotational speeds, the disc track wear is by plastic deformation along with delamination whereas at higher rotational speeds, the mechanism is by plastic deformation along with metal transfer.