Improvement of the mechanical properties of austenitic stainless steel after plasma nitriding

In this paper, we report on a series of experiments designed to study the i nfluence of plasma nitriding on the mechanical properties of austenitic sta inless steel. Plasma nitriding experiments were conducted on AISI 304L stee l in a temperature range of 375-475 degreesC using pulsed-DC plasma with di fferent N-2-H-2 gas mixtures and treatment times. Firstly the formation and the microstructure of the modified layer will be highlighted followed by t he results of hardness measurement, adhesion testing, wear resistance and f atigue life tests. The modified surface was analyzed directly after plasma nitriding as well as using a depth profiling method. The microhardness afte r plasma nitriding is increased up to 19 GPa, that is a factor of five high er compared to the untreated material (3.3 GPa). The adhesion is examined b y Rockwell indentation and scratch test. No delamination of the treated lay er could be observed. The wear rate after plasma nitriding is significantly reduced compared to the untreated material. Plasma nitriding produces comp ressive stress inside the modified layer, which can be easily derived from the bending of thin metal foil, which was treated only on one side. The tre atment influences the fatigue life, which can be raised by a factor of 10 a t a low stress level (230 MPa). (C) 2000 Elsevier Science B.V. All rights r eserved.