EVALUATION METHOD OF DELAY DESTRUCTION-RESISTANT CHARACTERISTICS OF STEEL MATERIAL FOR CAR STRUCTURAL MEMBER AND STEEL MATERIAL FOR CAR STRUCTURAL MEMBER EXCELLENT IN DELAY DESTRUCTION-RESISTANT CHARACTERISTICS

摘要

PROBLEM TO BE SOLVED: To provide a method for evaluating the delay destruction-resistant characteristics of a thin-walled steel material for a car structural member, and to provide the steel material for the car structural member excellent in delay destruction-resistant characteristics.;SOLUTION: After a plating film is formed on a test piece, which is collected from the steel material preferably adjusted in composition of C, Si, Mn and like and having a hardness HV of 250 or above, and a dummy piece having the same wall thickness and surface properties as the test piece while or after charging the same amount of diffusible hydrogen to both pieces by electrolytic treatment of the same condition, the plating film applied test piece and the dummy piece are subjected to a constant load test or a variable load test under a load stress condition and a diffusible hydrogen amount condition both of which simulate even an actual environment. After the test, a diffusible hydrogen amount is measured with respect to the dummy piece in a case that the test piece is destructed and with respect to the test piece or the dummy piece when the test piece is not destructed. By this method, the measurement of high precision of the hydrogen amount can be performed even with respect to the thin-walled steel material and the delay destruction-resistant characteristics of the steel material for the car structural member simulating actual use environment can be evaluated. The steel material markedly enhanced in the delay destruction-resistant characteristics is obtained by adjusting the relation of Ti and N, Ceq and the relation of C and P to a specific range.;COPYRIGHT: (C)2006,JPO&NCIPI