Structuroscopy of Heat-Treated Steel Bars by the Speed of Propagation of Rayleigh Waves

Abstract

The paper discusses the possibility of assessing the structural state after different types and modes of heat treatment of bars of steel 45 according to the results of measuring the speed of a Rayleigh wave using the multiple shadow method. To ensure the developed methodology, a DEMA flaw detector and a special overhead electromagnetic-acoustic (EMA) transducer with a magnetization system were used. The converter provides the excitation and reception of Rayleigh waves propagating around the circumference of the bar. Samples of bars in the conditions of supply, annealing, normalization, hardening, and tempering were investigated. For the qualitative measurement of the speeds of Rayleigh waves, the diameters of the rods were measured with an accuracy of 0.01 mm. The results of a change in the velocity of a Rayleigh wave in bars at all heat treatment modes are presented. In the delivery state, the speed of the Rayleigh wave in the bar was 3017 m/s. The speed of the Rayleigh wave in the bar after quenching dropped to 2995 m/s. After normalization, the velocity of the Rayleigh wave increased to 3049 m/s. A gradual increase in tempering temperature leads to an increase in wave velocity. The obtained experimental data show that tempering at a temperature of 600°С and normalization at 850°С increase the propagation velocity of a Rayleigh wave in a bar by 55 m/s relative to quenching without tempering, which indicates similar structural states in the surface layers of the samples.