Study On Thermal Fatigue Failure Behavior And Life Prediction Method Of Converter Oxygen Gun Coating

As the key equipment for converter steelmaking,the oxygen gun nozzle is the main tool for supplying oxygen to the furnace.In the smelting process,the sticky steel slag on the end face of the nozzle and the thermal fatigue erosion and dissolution are important factors affecting the continuity and production efficiency of the converter steelmaking process.Therefore,in this paper,the thermal spray surface strengthening technology is used to spray the double-layer structure ZrO₂-MgO protective coating on the surface of the lance head.The thermal fatigue damage test is designed and the coating is studied by SEM,EDS and XRD.Thermal fatigue crack initiation,expansion and phase structure change of oxygen-free copper matrix.At the same time,the service life of the coating was predicted by ANSYS Workbench finite element analysis software and Ncode DesignLife fatigue life simulation analysis software.The main research contents and conclusions of this paper are as follows:Firstly,the thermal fatigue damage behavior of oxygen-free copper in the base material of oxygen lance nozzle under thermal cycling conditions was studied.The results show that during the thermal cycle,the structure of the oxygen-free copper matrix is deformed,and the maximum deformation rate reaches 1.566%.The microstructure and phase structure of the surface of the substrate show that the surface cracks are in the inclusions or the pressed area,and the thermal stress is Under the action of oxidative corrosion,the crack propagates along the grain boundary direction,and no new phase is formed before and after the thermal cycle.Observing the metallographic structure,the thermal cycle promotes the grain refinement inside the matrix,and the flat equiaxed crystal evolves into a band or Strip grains,and are accompanied by twinning.Secondly,Based on understanding the thermal fatigue damage of the substrate,the thermal fatigue damage behavior of the protective coating is studied in depth.The results show that the thermal cycle promotes the axial and radial deformation of the protective coating structure,wherein the axial deformation rate reaches 11.10%,the radial direction reaches 4.23%,and the macroscopic appearance of the coating appears to be warped and bulge deformation failure.The surface,cross-section microstructure,phase composition and chemical composition analysis showed that the Al₂O₃ thermal growth oxide layer grew at the interface between the bonding layer and the substrate,and its thickness reached 48.01?m,which reduced the mechanical bond between the bonding layer and the substrate,accelerated cracking failure of coatings;In addition,the pores existing on the surface of the coating during thermal spraying can release the thermal stress inside the coating on the one hand,and oxidize and external thermal stress concentration at the pores on the other hand,accelerating the pores and microcracks to expand along the crystal expansion mode,and Along with the oxidative corrosion,the crack propagates toward the inside of the coating in the direction perpendicular to the coating,and the crack end expands into a dendritic crack due to stress concentration.Finally,the thermal coupling analysis of the thermal cycle coating specimens was carried out by ANSYS Workbench to obtain the temperature field and thermal stress field results of the coated specimens.The finite element results were input into Ncode DesignLife fatigue life prediction software,and the thermal fatigue life was calculated as 197.1.The basic and experimental fatigue damage times are consistent,and the fatigue life prediction results are verified to be reasonable and effective.The life prediction of the coated oxygen gun nozzle model is carried out by this method,and its service life is 643.3 times.Compared with the conventional oxygen gun nozzle,the service life is significantly improved,and the application of this protective coating to practical production has guiding significance.