EVALUATING METHOD OF AREA OF OCCURRENCE OF MICRO- CRACKING DUE TO HYDROGEN ATTACK IN STEEL MATERIAL

摘要

PURPOSE:To evaluate a micro crack area due to hydrogen attack, which exists in a steel material, with a high precision by propagating ultrasonic waves in the thickness direction of the steel material and detecting propagation times of their longitudinal waves and transverse waves and obtaining a ratio of them. CONSTITUTION:Times when bottom echoes of the longitudinal wave and the transverse wave of an ultrasonic wave are received by a transmitter and receiver 3 after a transmission pulse is given from the transmitter and receiver 3 to a probe, namely, going and returning propagation times tL and tS are measured to obtain a ratio VL/VS of propagation speed. In this case, a speed ratio operating circuit 5 operates the speed ratio VL/VS on a basis of propagation times tL and tS, and the operation result is inputted as an address signal to a memory 6 where relations indicated on a characteristic graph are preliminarily stored. Then, value 0.5 indicating a proportion TA/T of hydrogen attack is read out from the memory 6 when the speed ratio VL/VS is, for example, 0.567. Thus, dimensions in the depth direction of a hydrogen attack area 2 in a steel material 1, namely, its layer thickness TA is evaluated accurately.