The effect of small differences in the content of carbon and nitrogen on the room temperature tensile deformation and fracture behaviour of an AISI 304 stainless steel was studied. In the steel containing the lower amount of carbon and nitrogen, a higher amount of strain induced ?’ martensite is formed, which increases strain hardening rate and both uniform and total elongation at fracture. The presence of large martensitic areas in the cross section causes strain localization at the austenite/martensite interface, which promotes the nucleation of cracks and their propagation along the interface. This results in a decrease of Ultimate Tensile Strength. Strain induced transformation slightly reduces strain rate sensitivity, as well.

The ultimate goal of the research in which the present work is framed, is to overcome, or at least to limit, the need of costly, time-consuming and complicated experimental tests towards different predictive methods of the fatigue life. Specific aim of this paper is to assess a novel formulation proposed in literature to predict the local fatigue life of components, in the high-cycle fatigue regime, with uneven stress distribution by means of Finite Element Analysis. The basic idea of this theory is that the relative stress gradient in the highly stressed region is the fundamental parameter governing the fatigue life phenomenon. The equations used to compute the slope of the S-N curves and the local fatigue limit are proved against data from literature. Whilst the fatigue limit’s formulation shows a good agreement with experimental data (mean percentage error of 7%), the slope is overestimated by the used formulation (mean percentage error of 123%). Thus, a novel equation is presented to compute the slope that attains a mean percentage error of 24% in the comparison with experimental data.

Fracture begins to be considered as a subject of investigation by Lonardo da Vinci and finds in Vannuccio Biringucci and Galileo Galilei the forerunners of a scientific appoach to the study of how and why rupture occur. In the sixteenh century the oldest written references of experiences and interpretation appear: the scarce technological properties and the lack of a materials science hinder a satisfactory interpretation of the rupture processes. Two more centuries are needed to introduce a linear relationship, firstly, between force and strain, and then between stress and strain.