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| D. Rodziňák, R.V. Zahradníček, P. Hvizdoš, D. Jakubeczyová |
| EFFECT OF NITRIDATION ON CONTACT FATIGUE AND WEAR DAMAGE OF ASTALOY CrL AND CrM STEELS |
Abstract
Contact fatigue of sintered Astaloy CrL and CrM type steels with 0.3-0.7%C additive after nitridation in gas was investigated using pin-on-disk technique and related to results obtained by wear testing. The results of contact fatigue resistance were evaluated in terms of Wöhler’s curves at 50.107 cycles. Fatigue limits determined by this way, which were between 1080 and 1575 MPa, follow the hardness HV10 of the nitrided surface. Such surface is covered by so-called ?-phase. Its hardness increases with increasing carbon content as well as with Cr/Mo content in the material. Influence on the contact fatigue lifetime is relatively small which can be attributed to other negative properties of this hard layer. This is supported by metallographic microscopic analysis and also by character of its brittle fracture damage. The main difference in damaging of materials produced in PM way, in comparison with classical wroughts, is the quantity of pittings. In the compact materials there is largely one. In PM materials little infringements occur practically all around materials track circumference.
Wear testing did not yield unambiguous results. They were not in direct accordance with contact fatigue results. The two damage mechanisms are based on different principles. Behaviour of PM materials is not sufficiently explored at present. It appears that the wear is more related to microhardness / type of resulting carbides and their exclusion, evenly in the grain or grain boundaries /. It is necessary to verify this supplementary observation by targeted laboratory procedures.
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| Keywords: Cr- sintered steels|Contact fatigue|Wear|Surface modification| |
| No 1 (2010), p. 12-19 |
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