Research On The Inner Surface Quality Of Cold-rolled 316L Stainless Steel Pipe Based On The Theory Of Crystal Plasticity

As a high-precision and high-finish pipe,316 L stainless steel EP pipe is widely used in industries such as medical biology,microelectronics,and precision instrumentation.When using the LG30 rolling mill to initially process EP pipes,it was found that microscopic folds appeared on the inner surface of the rolled steel pipe.The microscopic folds belonged to the grain-scale defects.Therefore,this paper introduces the theory of crystal plasticity,establishes a steel pipe micro-element crystal plastic rolling model,and combines Theoretical calculations and macro-rolling finite element analysis are used to explore the generation and evolution of folds.According to the roll pass and mandrel data of the LG30 rolling mill,54 deformation history sections reflecting the rolling deformation process and their corresponding rolling deformations are obtained through theoretical calculations;It is pointed out that the prone area of microscopic folds on the inner surface is in the roll gap area.A finite element model of the 316 L stainless steel pipe macro-rolling is established,and the macro-rolling simulation and comparative analysis with theoretical calculations are used to give a preliminary inference of the occurrence of microscopic folds on the inner surface of the pipe.According to the principle of Voronoi diagram,the secondary development of ABAQUS Python is used to establish the micro-element polycrystalline model of the steel pipe and determine the relevant geometric parameters;by calling the UMAT user material subroutine in ABAQUS to realize the embedding of the crystal plastic constitutive,the crystal plastic material parameters of the micro-element polycrystalline model of the steel pipe are determined by the combination of references and the fitting compression experiment curve.Select representative history sections from the theoretical calculation results,simplify them through appropriate models,establish crystal plastic rolling models of the steel pipe micro-element on the inner surface of the roll gap area on these sections,and analyze the evolution of the inner surface microscopic folds;Through the comparison and analysis of the inner surface folds under ideal rolling conditions,the final conclusion is that folds have been generated at the beginning of the wall thickness reduction section of the working section and aggravated after the middle section,but weakened at the end section.In the end,it was not eliminated,resulting in microscopic folds defects in the finished pipe.