High strength tempered 42CrMo4 for shafts in drive technology

Abstract Quenched and tempered steels are used in many areas of mechanical engineering. Globally valid standards for the technical delivery conditions of such materials ensure their quality and properties. The standards specify, for instance, heat treatment parameters to be used and resulting strength values. Consequently, many design guidelines in engineering are based directly on these strength value ranges. The lower limits are usually used to ensure a conservative design. As a result, many users in practice no longer question the actual potential of materials for the envisaged application and thus waste capacity. This study aims to address this problem by investigating 42CrMo4 in various heat treatment conditions. Tensile tests, hardness measurements, cyclic stress-strain tests, Charpy tests as well as light and electron microscopic structural analyses were carried out. A main variant was examined by numerous endurance tests with differently notched specimens under alternating tension-compression, bending and torsion. A lower tempering temperature leads to a significantly increased fatigue strength albeit a lower toughness under impact loads must be accepted. The ideal tempering temperature for maximum fatigue strength with still reliably stable crack propagation behavior during fatigue failure appears to be around 400 °C. This allows the fatigue limit to be increased by up to 51 % compared to the conservative assumption based on conventional standards. While toughness is almost never considered quantitatively in drive technology design, it might play an important role. The present study sheds some light onto the potential of quenched and tempered steels under rather unusual heat treatment conditions.