Study of a Welded Joint of 12Kh18N10T Steel Using Acoustic and Magnetic Methods

Abstract

The paper presents results from studies on the influence of plastic deformation on magnetic and acoustic characteristics of a welded joint material of 12Kh18N10T (analogue AISI 321) austenitic steel. We have shown that an inhomogeneous structure in the heat-affected zone causes a nonuniform distribution of acoustic parameters and magnetic properties of the welded joint material. The formation of the martensitic phase occurs upon plastic deformation, which influences the properties of the whole material and has elastic moduli differing from that of the original austenitic phase. The increase in the volume fraction of martensite leads to the decrease in the elastic moduli of the material and, as a consequence, to the decrease of ultrasonic waves velocity. The variation of ultrasonic waves velocities leads to significant errors upon measurements of the material parameters under study, for instance, of a sheet thickness using ultrasonic thickness measurement. The formation of martensite changes also the magnetic properties of the material. We have found the dependence of the shear ultrasonic wave velocity on a parameter governed by the change in the phase composition of the austenitic steel upon plastic deformation. We have developed an algorithm for the determination of the thickness of the welded joint metal undergoing pressure forming and plastic deformation upon operation of constructions. We have shown that the additional measurement using the magnetic method of the parameter governed by the change in the phase composition of the steel upon deformation substantially decreases the errors of the thickness measurement of the welded joint metal.