Refinement of tempered martensite structure and its effect on wear mechanism in SAE 8620

Abstract

All mechanical components that undergo sliding or rolling contact are subjected to some degree of wear. Carburising treatment is important in improving wear characteristics of AISI 8620 gear steel. An experimental investigation was conducted on carburised AISI 8620 steel. Gas carburising of the specimens was carried out in sealed quenched furnace at 1198 K for 6 h followed by hardening at 1133 K, oil quenching at 393 K and followed by tempering at 453 K. Carburised cryotreated samples were cooled in a controlled manner soaked at 88 K for 16 h in a cryoprocessor subsequently followed by soft tempering at 373 K. Specimens were characterised by microhardness test, wear test and retained austenite content by XRD. 3D wear surface response and 2D contour map showed that wear rate decreased by 32% in the case of carburised cryotreated specimens as compared to only carburised specimens. It was concluded that there was an improvement in hardness and wear resistance of carburised cryotreated steel as compared to only carburised steel. Refinement and densification in martensitic structure resulted in shift in wear transition from severe wear regime to mild wear regime.