Damage phenomena in lubricated rolling-sliding wear of a gas carburised 0.85%Mo low-alloyed sintered steel: theoretical analysis and experimental verification

Abstract

The resistance to surface and subsurface damage during lubricated rolling-sliding wear of a carburised low-alloy sintered steel and the effect of shot peening were investigated. The formation of both contact fatigue cracks and of brittle tensile cracks may be predicted by a theoretical model that was experimentally validated. Carburising is effective in increasing the resistance to contact fatigue, but pores in a hard and brittle matrix may act as pre-existing cracks. Shot peening increases the contact fatigue resistance since compressive residual stresses oppose the nucleation of surface cracks.

Influence of the microstructure on the subsurface and surface damage during lubricated rolling–sliding wear of sintered and sinterhardened 1.5%Mo–2%Cu–0.6%C steel: theoretical analysis and experimental investigation

“…The nucleation of the fatigue crack in the subsurface layers is anticipated by local plastic deformation that occurs when the maximum stress σ exceeds the yield strength of the matrix σ y 0 , as by Eq. (7) The maximum stress is determined from the Hertzian equivalent stress σ εθ [4], by Eq. (8), introducing two parameters to account for the stress raising effect of porosity is the notch factor of fatigue stress concentration factor and Φ is the fraction of load bearing section.…”

“…The maximum stress is determined from the Hertzian equivalent stress σ εθ [4], by Eq. ( 8), introducing two parameters to account for the stress raising effect of porosity…”

“…This phenomenon has been investigated in a previous work [3] with a theoretical approach validated by wear tests, aimed at predicting the nucleation of the crack on different diffusion bonded steels and highlighting the influence of the microstructure heterogeneity in the Ni steels. The same model was then refined to investigate the surface damage mechanisms in carburised pre-alloyed steels and the effect of shot peening [4,5]. A discussion on the possible surface embrittlement caused by carburising is presented in [6], where the formation of surface brittle cracks is theoretically investigated and verified by wear tests.…”

Surface Hardening Vs. Surface Embrittlement in Carburizing of Porous Steels

“…By combining equations (3) and (5) an expression for the critical pore size may be obtained, as by eq. (6).…”

“…(1) [4], while the maximum local stress  can be calculated from the equivalent stress  eq by eq. (2) [5].…”