INFLUENCE OF DIAMOND BURNISHING PROCESS PARAMETERS ON STRAIN-INDUCED α’-MARTENSITE IN 304 CHROMIUM-NICKEL AUSTENITIC STAINLESS STEEL

When chromium-nickel austenitic stainless steels must satisfy a requirement for a high degree of strain-hardening, the nickel content is limited to 8 - 9 wt. %. The surface cold working of these steels causes the martensitic transformation γ → α′. Thus, the surface microhardness and residual compressive stresses increase due to the presence of the harder strain-induced a’-martensite phase. This article investigates the influence of the governing factors of diamond burnishing (DB) on the percentage content of the a’-martensite in the surface layer of AISI 304 steel using planned experiment, analysis of variance and regression analysis. A mathematical model of the percentage content of a’- martensite depending on the burnishing force, feed rate and burnishing velocity was created. Of the three governing factors, the most significant is feed rate, and the least important is burnishing force. Thermal effects have a greater impact on martensitic transformation γ → α′ compared to the mechanical effect. The percentage of martensite in the surface and subsurface layers is necessary information for determining the residual stresses by the X-ray method when studying the effect of DB on the surface integrity of austenitic stainless steels.