A detailed analysis of the effect of variable stresses on the intensity of retained austenite transformation into martensite was carried out in the work. Tests were done for three bending stress (σmax) levels, lower than the value of the yield stress (R0.2) the material tested. Preliminary tests conducted for one bending stress value have shown that a certain amount of untransformed retained austenite remains in the material in spite of applying as many as 40 000 fatigue cycles. It is therefore necessary to determine whether and, if so, in what extent the magnitude of applied bending stress will increase or decrease that amount of retained austenite. It should be established whether, for different bending stress levels, the curves describing the variation in the volumetric fraction of retained austenite of the tested wire structure, will approximate asymptotically the same value, or the values will, after all, be different.The results of these studies have a practical dimension, since, e.g. a screw made of the TRIP steel, subjected to variable stresses in service, may undergo additional hardening to a varying extent, which will influence its mechanical properties, life and operation safety.The knowledge acquired from the studies will constitute a novelty in this scope of applications, and will be useful from the point of view of both the manufacturer and the user.
X-Ray Residual Stress and Strain-Induced Transformation of Retained Austenite in TRIP-Aided Dual-Phase Steels.
