Irreversible change in steel articles shape during thermal cycling

To identify the rules of shape variations of steel specimens at thermal cycling the theoretical and experimental investigations of high-alloyed refractory steels not undergoing phase transformations in the temperature range of interest have been conducted. The results show that the irreversable shape variations observed are due to relaxation of stresses brought about by nonuniform volume changes along a specimen cross-section at temperature cycling. Thermal stresses cause the largest shape variations. The shape variation criterion (N phi) is drawn which relates temperature, stress, thermal and strength parameters of the materials and allows to determine not only the possibility of plastic deformation, but the features of shape variations as well. At N phi > 1 the material is plastically deformation under total thermal stresses, and at N phi < 1 it is deformed elastically