Failure Analysis For Roll Surfacing

Roller is one of the most important components in steel rolling process, and surfacing is an effective and economical method to repair compound roller. Surfacing prolongs work duration and reduces abrasion of a roller; it improves efficiency of rolling mill and quality of productions as well. Therefore, research and progress on roller repairing technology are praiseworthy.Up to now, most of the researches on roller repairing are merely about repairing technique or about simulation on thermal field and stress field, few of them take chemical component, stress and technology into account altogether. In contrast, this study investigates the effect of the three factors, including microstructures and components, various forces, and welding procedure, on the roller end spalling. Numerical simulation method is used to forecast the transformation process of welding residual stress, and to find out the cause of failing to repair a roller using surfacing method, which helps to improve this surfacing technology.XRD is utilized to analyze the phases of spalling layer, SEM and EDS methods are taken to analyze the microstructures and components of surfacing layer metal, respectively. According to the results, the location of spalling could be found out.Contact stress calculation bases on the classical Hertz theory, and tangential load (friction) was taken into account, as well as the effects of microstructures and property distinction between harden layer in the surface area and inner part of a roller on contact stress distribution were analyzed.Welding process of a roller surfacing is very complicate, accurate forecasting on thermal and stress field helps a lot to achieve welding structures with high quality. This thesis grounds on the ANSYS software, dynamically analyzes the thermal and stress field distribution during surfacing process, including thermal field at different times, variation of residual stress in the stress field and its radial distribution within roller. It is found that simulating results and experimental results was basically identical. This thesis provides valid basis for determination of surfacing tehcnics parameters, and therefore saves time and reduces costs.This study aims at surfacing girth joint, builds a Gauss distribution of heat source and used JMatPro software to calculate thermophysical constants of parent metal and deposited metal. Heat source movement was achieved through using APDL sentences, and then simulation of stress field during roller surfacing process was accomplished.Several considerations are involved in making the surfacing technique. When choosing welding material, match between surfacing layer and transitional layer, and thermal interval of temper brittleness are taken into account; in the aspect of technique, changing pre-heat and heat treatment temperature to avoid thermal interval of temper brittleness, and adjusting surfacing sequences are utilized to improve resistance to fracture of roller shoulder and homogeneity of stress concentration location, in order to decrease the negative effects of heterogeneity on tangential stress within roller. Isothermal treating is applied to the roller neck to avoid thermal stress and hardening caused by cooling fast at shoulder.The repair process of spalling roller has been revised in this paper. This revised process has been proved to be feasible.