CHANGES OF MAGNETIC MINOR HYSTERESIS LOOPS DURING CREEP IN CR-MO-V FERRITIC STEEL

Satoru Kobayashi – Masashi Tanaka – Takashi Kimura – Yasuhiro Kamada – Hiroaki Kikuchi – Seiki Takahashi – Toshihiro Ohtani

   We analyzed magnetic minor hysteresis loops of 1Cr-0,5Mo-0.25V ferritic steel subjected to creep at 923 K under tensile stress of 25 MPa. The minor-loop coefficients, which are obtained from the power-law scaling rules and indicators of internal stress, sharply decrease at the primary creep, become almost constant at the secondary creep, and then slowly decrease at the ternary creep. This behavior is similar to that of Vickers hardness and both the properties show a linear relation. The good relationship between the coefficients, creep strain and hardness as well as a low measurement field required for the coefficients indicate that magnetic method using minor hysteresis loops can be a possible technique for nondestructive evaluation of ferritic steels during creep.

Keywords: Cr-Mo-V ferritic steel, magnetic minor hysteresis loops, creep damage, nondestructive testing

[full-paper]