In this study, we obtained different morphology and size of epsilon carbides (ɛ-carbides) via low temperature tempering of 0.32 wt-% C low alloy wear resistance steel. The objective is to elucidate the determining role of size and morphology of carbides on mechanical properties and three-body impact wear resistance. The formation of small needle-like ɛ-carbides was responsible for increase in yield strength, low temperature impact toughness and three-body impact wear resistance. However, when the ɛ-carbides were large and rod-like, hardness, toughness and three-body impact wear resistance were significantly reduced. The wear mechanism of steel containing needle-like ɛ-carbides primarily involved plastic deformation associated with fatigue and small degree of abrasive wear and furrow, while steels containing rod-like ɛ-carbides were predominantly characterised by furrow.

In addition to manganese, carbon partitioning has been proposed in a new medium Mn-TRIP steel by two-step partitioning during the first batching annealing and the final continuous annealing. In the second-step partitioning, the cementite dissolves and blocky austenite forms with carbon enrichment, while the partition of manganese is negligible from prior lath austenite back into ferrite due to short duration. The combined partition of carbon and manganese improves both fraction and stability of retained austenite. The alloy has exhibited the product of strength and elongation of approximately 50 GPa%. It is highlighted that there is no Lüder strain in tensile curves. The microstructure evolution and relationship of microstructure and properties have been investigated and characterised carefully in this research. This paper is part of a Thematic Issue on Medium Manganese Steels.

Cracking generates usually due to the internal stress during martensitic transformation in high carbon steels, for instance the ‘1C–1.5Cr’ bearing steels. A novel low-density ‘1.2C–1.5Cr–5Al’ alloy has been designed recently for bearing application in previous research. The effect of morphology of martensite plates on the transformation cracking has been proposed and investigated in comparison between the ‘1.2C–1.5Cr–5Al’ and ‘1C–1.5Cr’ steels in this research. Based on the mechanisms proposed, the tendency for transformation cracking in the novel alloy with more carbon addition has been discussed compared with the ‘1C–1.5Cr’ steel. This paper is part of a Themed Issue on Recent developments in bearing steels.

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