Study On The Cracks Of Large-diameter Stainless Steel Pipe In Cross Piercing

Seamless steel pipe is a kind of economic material, one of the important rawmaterials of national economic construction and modern national defence. Large-diameterstainless steel pipe is mainly used in nuclear power, oil cracking and other energyengineering departments. In these areas, because of the particularity of the requirements,the quality of the pipe should also be quite high. In the process of production, we find thatcracks often appear on the surface of pillet. This will not only reduces the quality of theproducts, but also influences the production efficiency. So, to analyze the causes of crackshas lots of meanings.Cross piercing includes linear motion and rotation motion, which is very complicateto analysis its space geometry, mechanics and kinematics. Three-dimensional finiteelement technology can solve the problems in metal plastic deformation properly. Articleuses ABAQUS software to establish three-dimensional coupled thermo-mechanical finiteelement models of barrel roller and tapered roller cross piercing, analysis thethermodynamic parameters such as equivalent stress, equivalent strain, temperature,additional strain, etc. By comparing the results of the two models, the reason of cracks inthe angle of process is found.Material TP321is analyzed through hot tensile tests under different temperatures andstrain rates, stress-strain curves are obtained. By calculating the reduction of cross sectionof the samples the plastic rule is found, and a reference for practical production isprovided.Hot tensile experiment is carried out for samples of different gap radius, combinedwith experimental results and finite element simulation results, the adaptability of thecriterion of critical void growth ratio under high temperature is verified. The rule of thecriterion of critical void growth ratio changes with temperatures and strain rates isobtained, the relationship between the criterion and its plasticity is also found. Four factorsas temperature, strain rate, strain and stress state are considered, a new theory and methodto predict the cracks in metal plastic deformation under high temperature is provided. Through the forecast of crack defects in cross piercing, the rationality of the theory isverified.