On Α- MARTENSITE NUCLEATION IN STEELS AND IRON ALLOYS

Abstract

Purpose. To investigate the possibility of martensite nucleation on magnetic (concentration) inhomogeneities of chrome-nickel steels austenite.
 Research methods. Generalization of experimental and theoretical studies of the strong magnetic field effect on the martensitic transformation in steels and iron alloys, taking into account the magnetic state of austenite
 Results. The analysis of the magnetic state of austenite and the abnormally large strong magnetic field effect on the martensite point displacement in 40X2H20 steel indicates that the transformation of austenite into martensite in it is a “magnetic first order phase transition”.
 Scientific novelty. Some features of the martensitic transformation in steels and iron alloys are explained. It is assumed that martensite during the “magnetic γ→α- transition” originates on magnetic inhomogeneities with a disoriented magnetic structure of the spin glass type. Forced magnetostriction during paraprocess and spontaneous magnetostriction below the Curie point lead to the emergence of collinear ferromagnetism with a change in the coordination number from 12 to 8. High all-round pressure leads to the occurrence of collinear antiferromagnetism and the γ-phase stabilization. In paramagnetic austenite the nucleation of α-martensite occurs on dislocation nuclei, the sizes of which have the same order of magnitude (by volume) as the magnetic inhomogeneities in the Fe-Ni system.
 Practical value. The results obtained in the work expand the concept of martensitic transformation in steels and provide grounds for explaining some kinetic features in them.