Influences of up-milling and down-milling on surface integrity and fatigue strength of X160CrMoV12 steel

• Published in: International journal of advanced manufacturing technology Vol. 105; no. 1-4; pp. 1209 - 1228
• Main Authors: Laamouri, Adnen, Ghanem, Farhat, Braham, Chedly, Sidhom, Habib
• Format: Journal Article
• Language: English
• Published: London Springer London 01.11.2019; Springer Nature B.V; Springer Verlag
• Subjects: Bending fatigue; CAE) and Design; Chromium molybdenum vanadium steels; Compressive properties; Computer-Aided Engineering (CAD; Crack propagation; Damage; Engineering; Engineering Sciences; Fatigue cracks; Fatigue limit; Fatigue strength; Fatigue tests; Fracture mechanics; Hardening; Heat treating; High alloy steels; Industrial and Production Engineering; Integrity; Materials; Mechanical Engineering; Media Management; Metal fatigue; Microcracks; Original Article; Peripheral milling; Residual stress; Roughness; Stress concentration; Tool steels; Surface integrity; Dang Van’s criterion; Down-milling; Fatigue; Up-milling
• ISSN: 0268-3768; 1433-3015
• DOI: 10.1007/s00170-019-04280-2

This paper aims to compare the influences of the two peripheral milling modes, up-milling and down-milling, on surface integrity and fatigue strength of X160CrMoV12 high-alloy steel. The experimental investigations showed an important difference between integrity of both milled surfaces. The down-milled surface is lowly work-hardened and well finished (lower roughness), but subjected to tensile residual stresses and severely damaged by folds of metal and short micro-cracks. The up-milled surface is highly work-hardened and subjected to compressive residual stresses, but poorly finished (higher roughness) and damaged by a density of micro-cavities due to carbide extraction. The results of 3-point bending fatigue tests revealed that the fatigue limit at 2 × 10 6  cycles of the up-milled state is largely higher of about 26% in comparison with the down-milled state. The effects of surface integrity induced by each milling mode on fatigue strength were evaluated using a HCF behaviour predictive approach based on Dang Van’s multiaxial criterion. The predictive results estimated that the pre-existing micro-cracks play a dominant role in the fatigue strength degradation of the down-milled surface while the other surface effects seem to be lower. On the contrary, the fatigue strength of the up-milled surface is less affected by the pre-existing micro-cavities. The detrimental roughness effect (stress concentration effect) is significantly reduced by the beneficial effects of superficial hardening and compressive residual stresses. So, this study revealed that up-milling is the more appropriate mode for a better surface integrity towards fatigue strength of X160CrMoV12 steel than the down-milling mode.