ADVANCE TREATMENT METHOD OF SAMPLE FOR HIGH-FREQUENCY ULTRASONIC FLAW DETECTION

PROBLEM TO BE SOLVED: To prevent a defect from being deformed and to rapidly and accurately evaluate the shape and size of the defect by increasing the temperature of a steel sample to a specific temperature range for performing the phase transformation of a sample structure to austenite, and then cooling it so that bainite of a noise generation source is not generated. SOLUTION: For pulverizing a cast piece structure by heat treatment, the structure is retained at a high temperature and then is rapidly cooled. In this case, when heating temperature exceeds three points Ac, ferrite is made minute to an average of 100 μm and a second-phase pearlite is also made minute to 20 μm or less but the particle diameter of ferrite becomes 200 μm or more when the three points Ac+60 deg.C is exceeded. Then, in a steel sample with a C concentration of 0.02