Method of evaluating workability in cold pilgering

A new method of evaluating the workability of a tube in cold pilgering has been studied on the basis of material deformability and the effects of process conditions. A circumferential compression test of a tube is confirmed to be an effective evaluation method for deformability. The critical reduction in height upon crack initiation in the compression test is also found to be a good measure of material deformability. Systematic cold pilgering tests and the numerical analysis of cold pilgering are conducted. As a result, the ratio of radial strain to circumferential strain during pilgering is a good indicator of process conditions, and a common mechanism of inner fissure formation during pilgering in stainless steel, titanium alloy, and zirconium alloy is proposed. Finally, a suitable expression for workability is obtained by considering material deformability and the effects of pilgering conditions. These findings will assist the selection of appropriate pilgering conditions to prevent the formation of fissures on the inner surface of a tube.