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 influence of plasma nitriding on the mechanical properties of austenitic stainless steel. Plasma nitriding experiments were conducted on AISI 304L steel in a temperature range of 375-475°C using pulsed-DC plasma with different N2-H2 gas mixtures and treatment times. Firstly the formation and the microstructure of the modified layer will be highlighted followed by the results of hardness measurement, adhesion testing, wear resistance and fatigue life tests. The modified surface was analyzed directly after plasma nitriding as well as using a depth profiling method. The microhardness after plasma nitriding is increased up to 19 GPa, that is a factor of five higher compared to the untreated material (3.3 GPa). The adhesion is examined by Rockwell indentation and scratch test. No delamination of the treated layer could be observed. The wear rate after plasma nitriding is significantly reduced compared to the untreated material. Plasma nitriding produces compressive 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 treatment influences the fatigue life, which can be raised by a factor of 10 at a low stress level (230 MPa).