高強度オーステナイト系ステンレス鋼の再熱割れ評価

抄録

In order to assess the susceptibility to reheat cracking of high-strength austenitic stainless steels of KA-SUS304J1HTB and KA-SUS310J1TB, we established a reheat cracking reproduction test method by using stress relaxation test. A HAZ-reproduction test piece of KA-SUS304J1HTB fractured during stress relaxation at 650°C when the strain exceeded 16.6%. On the other hand, an as-received test piece of KA-SUS310J1TB fractured during stress relaxation at 650°C when the strain was more than 10.3%. Subsequently, local reduction of area (RA) of the fractured HAZ-reproduction and as-received test pieces was measured. No appreciable local RA was observed in the vicinity of the fractured surface on both test pieces. Besides, test piece with larger grain size was found out to be fractured in shorter time, as compared to test piece with small grain size. These findings were in close accordance with the previously reported characteristics of the reheat cracking cases. We then calculated the stress relaxation processes on the basis of experimental results by using Norton's creep law. The calculation results showed that HAZ-reproduction material of KA-SUS304J1HTB would not generate reheat cracking for up to more than 100,000 hours when the initial stress was equal to or below 300 MPa. However, reheat cracking would occur on KA-SUS310J1TB after only about 40,000 hours when the initial stress was 300 MPa. Compared to KA-SUS304J1HTB, KA-SUS310J1TB was more susceptible to reheat cracking.