Cornelius Temmel

Bending fatigue of gear teeth of conventional and isotropic steels

Abstract The bending fatigue strength of case hardened pulsator test gear wheels has been investigated for wheels in V2158 (20MnCrS5) and fatigue isotropic 158Q (≈ 20NiMo10) steels. The gear wheels in V2158 were forged either vertically or horizontally, the wheels in 158Q just vertically. Structural anisotropy levels were investigated in the horizontally forged V2158 gears. There was no noteworthy level of bending fatigue anisotropy to detect in the V2158 gears. However, the horizontally forged gears performed some 4% better than the vertically forged ones which may be explained by a somewhat more beneficial orientation and dispersion of sulfide inclusions in the horizontal gears. The fatigue isotropic 158Q steel is, in case-hardened components, obviously not required for isotropy reasons but highly appreciated for its outstanding fatigue performance. With identical heat treatment and surface condition, gears in 158Q outperform V2158 gears by some 23% in bending fatigue strength. This is explained by the materials resistance against internal surface oxidation and, to some extend, by its low inclusion content.

The bending fatigue strength of gears in isotropic 20NiMo10 steel in as-machined, single-peened and double-peened condition

Abstract The bending fatigue strength of case-hardened pulsator test gear wheels has been investigated for wheels in fatigue isotropic 20NiMo10 (Ovako 158Q) steel. The pulsator gears where either in un-peened (but shot-cleaned), single shotpeened or double shot-peened condition. Single shot peening increased the bending fatigue strength of the gears by some 11 per cent as compared with the un-peened. Double shotpeening was not successful and did not result in any further increase of bending fatigue strength. That was explained with wrongly chosen parameters of the second shot peening moment and therewith over-peening of the component. That second moment was a trial and had never been tested before. 20NiMo10 can be used on current production lines and can be case-hardened in current production furnaces. If availability of the steel is guaranteed, 20NiMo10 has the potential to replace current production material.

Quenching Cracks in Medium Carbon Steel Initiated at Manganese Sulfide Inclusions

Abstract Quench crack propensity has been investigated for two identical medium carbon steels (50CrMo4) which only differed in sulfur content. The standard variant of the material was affected by manganese sulfide inclusions whereas the low sulfur material was essentially free of sulfides. 80 mm, cylindrical test specimens were used. The test specimens had been cut out of cross rolled steel plates in which the manganese sulfide were flattened to discoid shape. The specimen orientation was in direction of principal deformation where the flattened sulfides were aligned with the test specimen axis. The largest sulfides reached lengths of 150 mm. Both materials were austenitized at 850°C for 60 minutes, quenched in a salt-bath at 180°C and immediately annealed at 425°C for one hour. It turned out that the standard material developed quench cracks which initiated at manganese sulfide. No cracks could be found in the low sulfur material. Thermal and transformational stresses, which develop during quenching, aggravate the stress situation around the manganese sulfide and cause the cracking. The results are interpreted in fracture mechanical terms.

Investigation on Manganese Sulfide Inclusion Sizes in 50CrMo4 Steels by means of Fractography, Micrograph Analysis and Immersion Ultrasound

Abstract Increasing loads in powertrain components have put manganese sulfide inclusions in the spotlight of engineers. The indigenous sulfides are accounted responsible for the poor fatigue performance of highly loaded steel parts. In order to relate fatigue performance to manganese sulfide inclusion size, an accurate geometrical description of the sulfides is necessary. Fatigue testing generally reveals maximum inclusion sizes, since the largest inclusions will initiate fatigue failure. Micrograph analysis and immersion ultrasonic testing have been carried out in order to compare those methods with the referenced values of fatigue testing. It showed that immersion ultrasound is not capable of detecting manganese sulfide inclusions of the present sizes. Micrograph analysis, however, is applicable, if analysis data is modified subjectively.