| 摘要 |
PROBLEM TO BE SOLVED: To provide a high tensile steel material having little attenuation of reflected echoes when an ultrasonic flaw detection test is performed. SOLUTION: A high tensile steel material which has a prior-austenite grain having a size of over 100μm in the plate thickness direction by≤1 grain per 1 mm<SP>2</SP>in any cross section including the plate thickness direction and which shows≤0.1 (dB/mm) ultrasonic attenuation coefficientαis manufactured by heating a billet produced by continuous casting of a steel composition having≥680 MPa tensile strength at≥1,180°C for≥3 hours, cooling the billet down to≤800°C at a≥1°C/s cooling rate, then again heating and rolling. COPYRIGHT: (C)2005,JPO&NCIPI
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