ULTRASOUND VELOCITY VARIATION AT PLASTIC DEFORMATION OF HIGH-CHROMIUM STEEL

Abstract

The paper is devoted to the research of velocity variation of ultrasound propagation at plastic deformation of corrosion-resistant highchromium steel 40KH13 with ferrite-carbide (as-received condition), martensitic (after hardening) and sorbite (after high-temperature tempering) structures. It has been revealed that each condition demonstrates its own load curve. In as-received condition the load diagram is practically a parabolic one on the whole extent, while in a martensitic condition there is only the stage of a linear deformation hardening, and in a sorbite condition the plastic fl ow curve is three-stage. Using the methods of optic and atomic-force microscopy, the authors have researched the structure of steel at diff erent kinds of thermal treatment. Simultaneously with the regist ration of load curves the researches have conducted the velocity measurement of ultrasound surface waves (Rayleigh waves) in the researched steel at the extension. The realization of the method of velocity variation of Rayleigh waves is in a periodic generation of rectangular impulses with the duration of 100 ns at the input of a radiant piezoelectric transducer and the registration of the passed-by one according to the sample of the wave by means of the receiving piezoelectric transducer, connected up to the digital oscilloscope. The registered signal in a digital form has been used to measure time, passed from the moment of impulse generation at the input of the radiant transducer up to the moment of signal initiation at the output of the receiving transducer. The distance between the transducers during the experiment is constant. It has been shown that the dependence of ultrasound velocity at active loading is defined by the plastic fl ow rule, i.e. the staging of the appropriate loading diagram. The structural condition of the researched steel changes not only the type of the deformation curve at uniaxial tension, but it also changes the dependence character of ultrasound velocity on the deformation.