ULTRASONIC FLAW DETECTION METHOD, ULTRASONIC FLAW DETECTION DEVICE, FACILITY FOR MANUFACTURING STEEL MATERIAL, METHOD FOR MANUFACTURING STEEL MATERIAL, AND STEEL MATERIAL QUALITY CONTROL METHOD

An ultrasonic flaw inspection method is a method for inspecting an inner part of an inspection material by transmitting an ultrasonic signal from an ultrasonic probe to the inspection material, and receiving the ultrasonic signal reflected from the inner part of the inspection material as a reflection signal by the ultrasonic probe, and includes: a reception step of receiving the reflection signal by the ultrasonic probe while changing positions of the inspection material and the ultrasonic probe; an extraction step of extracting, from the reflection signal received at the reception step, a flaw signal as reflection from a flaw in the inspection material; and a flaw shape estimation step of estimating a shape of the flaw based on an expected sound pressure and a received sound pressure obtained from a strength of the flaw signal extracted at the extraction step, wherein the expected sound pressure is a strength of a flaw signal from a virtual flaw expected from ultrasonic directivity of the ultrasonic probe.