Microstructure control and wear resistance of grain boundary allotriomorphic ferrite/granular bainite duplex steel

The abrasive wear resistance of a hot-rolled and air-cooled high strength low alloy (HSLA) steel with grain boundary allotriomorphic ferrite/granular bainite (FGBA/Bg) duplex microstructure was investigated by comparison with the granular bainitic steel with the same composition and other two commercial HSLA ferrite/pearlite steels. The results from the wet sand/rubber wheel abrasion test show that the FGBA/Bg duplex steel possesses remarkably higher wear resistance than the two ferrite/pearlite steels, even higher than the granular bainitic steel with a higher hardness. The cross-sectional morphology of the worn surfaces reveals that the higher resistance to abrasive wear is mainly ascribed to the dispersive hard martensite/austenite (M/A) islands. The qualitative analysis on the work hardening characteristics and the microcrack initiation mechanisms indicates that in the FGBA/Bg duplex steel, the existence of the grain boundary allotriomorphic ferrite and the retained austenite in the self-tempered M/A islands improves the accommodated deformation capacity of the subsurface microstructure, and prevents the brittle exfoliation occurring in the granular bainitic steel.