We investigated the bending and rolling limit of 9Cr-1Mo-V steel plate used in pressure vessels for the purpose of improving its manufacturing efficiency. Hereafter in this report, the bending limit refers to bending by press or by roller. It includes acceptable crack size, temperature, introduced plastic strain and other factors.
When fracture toughness tests of 9Cr-1Mo-V steel plate were performed at bending temperature in production, unstable fracture rarely occurred. Since fracture probability during the bending process seems to be low, it was not possible to evaluate aspects of the degree of safety factor for brittle fracture. To estimate the bending limit at high temperature where unstable fracture rarely occurs, a method was proposed for estimating fracture probability using master curve and failure assessment diagram (FAD).
In order to verify the proposed method, loading tests simulating the bending process were performed. The bending limits obtained from the loading tests were in good agreement with the values predicted by the proposed method.
In this study, guidelines such as required toughness value and bending temperature for preventing brittle fracture during the bending process of 9Cr-1Mo-V steel plate were investigated.