Changes in ultrasound velocity in the plastic deformation of high-chromium steel

Resumo

The change in ultrasound velocity in the plastic deformation of high-chromium 40X13 stainless steel with ferrite–carbide structure (initially), martensite structure (after quenching), and sorbite structure (after high tempering) is investigated. The loading curve is different for each state. In the initial state, the loading curve is practically parabolic. In the martensitic state, linear strain hardening is the only stage. In the sorbitic state, a three-stage curve is observed. The structure of the steel after different types of heat treatment is studied by optical and scanning probe microscopy. In parallel with the recording of the loading curve, the change in properties of the ultrasonic surface waves (the Rayleigh waves) in the steel under tension is measured. To determine the speed of the Rayleigh waves, rectangular pulses (length 100 ns) are generated periodically at the input of the emitting piezoconverter and the wave is recorded after passage through the sample by the receiving piezoconverter, which is connected to a digital oscillograph. The resulting digital signal is used to measure the time from pulse generation to the appearance of a signal at the receiver output. The distance between the converters is constant. The changes in the ultrasound velocity during active loading are determined by the plastic flow—that is, by the stages in the corresponding loading diagram. The structure of the steel determines not only the type of deformation curve in uniaxial extension but also the dependence of the ultrasound velocity on the strain.