真ひずみによる実機空隙閉鎖評価の有効性検証

―大型鋼塊の空隙閉鎖に関する研究 第4報―

抄録

Previous studies have shown that true strain is effective for evaluating void closure in multipass forging. However, the above-mentioned result was obtained by numerical simulation and an experiment using hot steel with a reduced-scale model having a spherical void, and it has not been confirmed whether it is effective with a real machine. Therefore, in this study, the effectiveness of using true strain was verified in real machine tests. The following conclusions were obtained. 1) In the ultrasonic test (UT) after the third forging, despite the equivalent strain applied to two steel ingots being the same, a large difference occurred in the defect distribution. From this result, it was clarified that the closing behavior of the void in actual machines under multipass forging cannot be evaluated using equivalent strain. 2) In the UT after the fourth forging, as a result of applying the same true strain to two steel ingots, the defects of both steel ingots almost disappeared and the results were the same. Therefore, it was clarified that the closing behavior of the void in actual machines under multipass forging can be evaluated using true strain.