Effect of nitrocarburizing and post-oxidation on fatigue behavior of 35CrMo alloy steel in very high cycle fatigue regime

The 35CrMo alloy steel was nitrocarburized and post-oxidized in salt bath and the 109 cycles fatigue tests were carried out. The results show that for the untreated specimens all the cracks initiate from the surface while for the treated specimens the cracks originate from the subsurface in short fatigue life regime and from internal inclusion in longer fatigue life regime. The treated specimens do not fracture in very high cycle fatigue regime and the fatigue limit increases by 51% after the treatment. No granular-bright-facet is observed in the vicinity of a non-metallic inclusion on the fracture surface.

Research highlights
► The nitrocarburized 35CrMo steel has fatigue limit in very high cycle regime.
► The specimens show different fracture behaviors in short and long life regime.
► The granular-bright-facet cannot form in very high cycle regime.