Formation criterion of fissure defects in the inner wall of the radial forged steel tube

The fissure defects were observed in the radial forged thick-walled steel tube which affects the safety of the forged tube subjected to withstanding internal pressure. The present work is to find the formation criterion of fissure defects, so as to control the formation of fissure defects and improve the quality of the radial forged tubes. There are two kinds of steel used in the present study, 30SiMn2MoVA steel and Ni–Cr-Mo steel. The radial forging experiments, finite element simulation, and the observation experiments of inner wall morphology were carried out. The results show that there is a linear relationship between the radial strain εr and the circumferential strain εθ of nodes in the inner wall in the sinking zone. The changes of process parameters can be simplified as the changes of slope of the linear relationship. With the increase of the absolute value of the slope, it is easier for fissures to form. The fissure formation is inversely proportional to the material property, which is the height reduction of the cylindrical specimen with crack initiation under the unidirectional compressive load. According to the abovementioned influence law, the formation criterion of fissure defects is obtained. The radial forging experiment verified the feasibility of this forming criterion.