Portal de Periódicos da CAPES

Plasma nitriding improvements of fatigue properties of nodular cast iron crankshafts

1991; Elsevier BV; Volume: 140; Linguagem: Inglês

10.1016/0921-5093(91)90464-x

1873-4936

M.M. Tošić, R. Gligorijević,

Mechanical Failure Analysis and Simulation

Crankshafts of the pearlitic-sorbitic nodular cast iron type JUS NL.80 (similar to DIN GGG-80) heat treated to get a tensile strength of 820–900 GPa (i.e. a Vickers hardness of 268–295 HV) were plasma and ammonia gas nitrided. The glow discharge plasma nitriding was performed for 20 h at about 500 °C in a gas mixture of 55% N2 and 45% H2. The gas nitriding was performed for 28 h at 510 °C in the ammonia gas. Evaluation of the nitrided surfaces was conducted by optical microscopy, X-ray diffractometry and microhardness measurements. Journal and crank pin dimensions and surface roughness were measured both before and after nitriding. Bending fatigue testing of crankshafts was performedv using a fatigue testing rig. The fatigue limit was evaluated at 5.0 × 106 cycles. The fractures happened at the transition radius of the journal with cracks starting beneath the nitrided layer. It was found that the nitrided crankshafts had 18% higher dynamical strength in relation to the unnitrided crankshafts. In this respect, no differences were found between plasma- and gas-nitrided crankshafts. The changes in the surface roughness and journal and crank pin diameters after plasma nitriding can be well controlled. In this respect, plasma nitriding gave better results than ammonia gas nitriding.