Title: Influence of tempering on contact fatigue

Authors: Johan Fahlkrans; Arne Melander; Krister Johansson; Sven Haglund; Seyed B. Hosseini

Addresses: Department of Mechanical Properties, Swerea KIMAB, P.O. Box 55970, SE-102-16 Stockholm, Sweden; Scania, SE 151 87 Södertälje, Sweden. ' Production Engineering, KTH Royal Institute of Technology, SE-100-44 Stockholm, Sweden. ' Scania, SE 151 87 Södertälje, Sweden. ' Swerea KIMAB, P.O. Box 55970, SE-102 16 Stockholm, Sweden. ' SKF Group, Manufacturing Development Centre, SE-415 50, Göteborg, Sweden

Abstract: Most components are tempered after heat treatment operations such as case hardening or induction hardening. The common opinion is that the martensitic structure after heat treatment is too brittle and tempering is necessary to increase toughness. Tempering is an additional operation which leads to increased costs by energy, handling, and investments. Eliminating tempering from the heat treatment process leads to increased productivity, energy savings, and lowered environmental impact. Two carburised steels, Ovako 253A (?EN 22NiCrMo12-5F mod. A) and EN 20NiCrMo2 (SAE 8620, SS2506), were tested for contact fatigue resistance in a roller to roller rig. The tested samples were characterised with respect to amount of fatigue damage, residual stress, amount of retained austenite and hardness. The objective was to determine if tempering is always necessary after a heat treatment operation. The contact fatigue tests show that tempering results in lower contact fatigue resistance. Further, fatigue cracks were found to have initiated in different ways between tempered and untempered steel.

Keywords: tempering; carburising; case hardening; rolling contact fatigue; EN 20NiCrMo2; Ovako 253; heat treatment; productivity; energy savings; environmental impact; carburised steels; contact fatigue resistance; retained austenite; hardness.

DOI: 10.1504/IJMMP.2011.044365

International Journal of Microstructure and Materials Properties, 2011 Vol.6 No.6, pp.465 - 478

Available online: 14 Dec 2011 *

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