BEHAVIOR AND MODELING OF A 17-12-SPH STAINLESS-STEEL UNDER CYCLIC, UNI AND BIDIRECTIONAL, ANISOTHERMAL LOADINGS .1. BEHAVIOR

It is shown in this article that a knowledge of the mechanical behavio r of the 17-12 SPH stainless steel for different isotherms (20 less th an or equal to 7 less than or equal to 650 degrees C) is insufficient to correctly describe its behavior under anisothermal thermomechanical loadings. Indeed, this alloy possesses a temperature history memoriza tion effect at intermediate temperatures. This phenomena is studied in detail with experiments performed under uniaxial and biaxial mechanic al loadings (in-phase or out-of-phase tensile-torsion tests) for diffe rent isotherms belonging to judiciously chosen temperature history seq uences. The results of cyclic torsion tests under anisothermal thermom echanical conditions are presented where strain and temperature loadin g evolve simultaneously in-phase, in-phase-opposition, in 1/4 and 3/4 phase. The analysis of the totality of results shows that the material memorizes the maximal value of the cyclic stress peak reached in the zone where the derivative of the maximal cyclic stress with respect to the temperature is positive. This observation can also be applied to both uniaxial or biaxial cyclic tests. From a physical point of view, this behavior is closely related to the interaction phenomena between dislocations and point defects in insertion solid solutions. A bibliog raphical study of different materials tested under anisothermal condit ions confirms this observation.