Evolution Of Microstructure And Properties Of Crystallizer Remanufactured By Electroforming Technology During Service

As one of the important equipments for continuous casting production,crystallizers will inevitably suffer losses due to many factors in the actual industrial production process.Replacing the failed crystallizer will bring huge economic losses to the company,so it is hoped to find a way to repair the crystallizer to reduce the economic loss of the enterprise.In present thesis,the research object is a billet crystallizer,which has been repaired by electroforming.By considering the actual use temperature and usage time of crystallizer in continuous casting production,the heat preservation temperature of 100-400 °C and the holding time of 50-200 hours were designed to simulate the service conditions of crystallizer.The hardness and microstructure of substrate chromium-zirconium copper and electroformed copper were tested by microhardness tester,scanning electron microscopy(SEM),transmission electron microscopy(TEM)and electron backscatter diffraction(EBSD).Based on this,the wear resistance and creep resistance of electroformed copper were analyzed,discussion on the industrial feasibility of crystallizer remanufactured by electroforming technology.The mainly results could be concluded as follows.After research,we found the hardness of substrate chromium-zirconium copper and electroformed copper will decrease with the increase of service temperature,but the hardness value of electroformed copper is always higher than substrate chromium-zirconium copper.This indicates that electroformed copper has a higher hardness than substrate chromium zirconium copper under the high temperature service conditions.And electroformed copper exhibits better high temperature creep resistance than the substrate.Electroformed copper is deposited on the substrate,and the grain is a nano-scale equiaxed crystal at the beginning.Internal stress exists in the joint between the cast layer and the substrate,As the thickness of the deposit increases,the grain size gradually increases to the micron-sized columnar crystal.The substructure of the equiaxed crystal in original sample is dislocation,and the substructure of columnar crystals is twin.There are a large number of ∑3 coherent twin boundaries with {111} as twin planes in the electroformed copper layer of the samples which have been treated for different service hours atthe same service temperature and the same service time for different service temperatures,followed is the ∑9 non-coherent crystal boundary of the twin plane.The grain size of the base and electroformed copper layer in the original sample and in the samples,which subjected to300 °C and 200 °C for 200 h increased with the service temperature.At 300 °C to 400 °C,the crystal Significant increase in grain size.The cast layer has a <111> texture along the deposition direction,and the texture strength also decreases with the increase of the service temperature,corresponding to the change of the hardness value.The hardness values of the casts at 300°C for50 h,100 h and 150 h are reduced at the beginningand then increased,the grain size increases within 50 h to 100 h,and the <111> texture strength decreases,the grain size of the cast layer is basically unchanged within 100 h to 150 h,but the texture strength in the <111> direction corresponds to the change in hardness value and enhanced within 100 h to 150 h.According to this,there are two main factors that affect the hardness of electroformed copper in the cast layer:grain size and <111> direction texture strength.