Papers by Author: J.G. Xue

Abstract: The hot workability of modified 9Cr-1Mo, as a grade of heat resistant steels, is inferior to that of low-alloy steel, so the inner surface crack (ISC) easily occurs in seamless boiler tubes produced by the Mandrel Mill under improper rolling conditions. With the aid of FEM, the metal flow status during the rolling process was analyzed in 140mm 8-stand mandrel mill of Bao Steel. Both the metallographic shape and size of the ISC together with the result from the simulation show that the ISC of seamless tube forms at the elongation stage of shell. The mechanism of the ISC was discussed. With its initiation in stand No.1 and No.2 due to poor hot workability of modified 9Cr-1Mo steel, the ISC develops in subsequent passes. Based upon the mechanism devised was a special roll pass system which substantially upgraded the yield of qualified products.

Abstract: Using Oyane ductile fracture criterion, a 2-D coupled thermo-mechanical simulation of center crack occurrence in round billet during 2-roll rotary rolling process is presented with the aid of FE code MSC.Superform. Based on an existing flat-die-model, an improved FE model is advanced, in which not only the influence of roll feed angle and entry cone angle but also the diameter of the piercing roll on the process are taken into account. By adopting the parameters of the Diescher piercer in 140mm Mandrel Mill of Bao Steel in China, the distribution and development of strain/stress in tube rounds are analyzed, and the eigenvalue of ductile fracture as well. The critical percentage of diameter reduction is obtained from the simulation. The result shows a good agreement with the experimental value, and therefore is of widely guiding significance to practical process for rationally formulating deformation parameters of steel tube piercing.