Breaking Conditions And Numerical Simulation Of Al₂O₃ Inclusions In Steel During Hot Deformation

As the foundation and pillar of the heavy industry,the steel industry is one of the important criteria for measuring the level of economic development of a country.However,in the process of smelting steel,it is necessary to add some deoxidizer or inevitably dope to mix some refractory materials.It will lead to the presence of inclusions in the cooled steel ingot,especially the brittle inclusions such as Al₂O₃.Al₂O₃ is often one of the main reasons for the scrapping of steel products.In order to reduce the economic losses caused by inclusions and promote the development of the steel industry,it is urgent to carry out relevant research on the fracture and evolution conditions of inclusions in steel.In this paper,the steel ingot of 2.25Cr-1Mo large pressure vessel containing Al₂O₃ inclusions was studied.The morphology of Al₂O₃ inclusions in steel was analyzed by scanning electron microscopy?SEM?and metallographic microscope?OM?.It is clear that the morphology of Al₂O₃ inclusions in steel ingots is mainly cluster form.The clustered Al₂O₃ inclusions are porous and not dense.In response to these characteristics,a 1-2?m irregular Al₂O₃powder was sintered using a discharge plasma sintering apparatus?SPS?.The sintering temperatures were 1100??1200?and 1300?,respectively,the sintering pressure was30 MPa and the holding time was 10 min.In the sintering test,Al₂O₃ cylindrical samples with porosity of 33.08%,26.82%and 14.52%were prepared.Because the Al₂O₃ samples were non-conductive and not solderable,in particular,a device which can be used to analyze the hot deformation characteristics of Al₂O₃ samples was designed on the Gleeble-3800 thermal simulation test machine.Three sets of different porosity Al₂O₃thermal compression tests were carried out.The strain rates were 0.1s^-1?0.01s^-1 and0.001s^-1,respectively,and the deformation temperature was 1150°C.The fracture peak stress was used to establish a model of the relationship between fracture stress and strain rate at different porosities.A numerical simulation with a condition of 1150°C?initial deformation temperature?,5 mm/s?deformation speed?,30%?total deformation?was analyzed by introducing a sub-model on Abaqus finite element software.A relationship between the breaking stress of Al₂O₃ inclusions with different porosity and the total deformation was obtained.It was found that the total deformation for breaking of Al₂O₃inclusions with any porosity in steel is greater than or equal to 20%.