Study On Damage Model And Fracture Condition Of Alumina Based On Hoek Brown Criterion

The production level of iron and steel products plays an important role in the development of national economy.Since the tenth five year plan,the production level of heavy forgings in China has improved rapidly,but the problem of non-metallic inclusion control in steel has not been well solved,and the defects caused by inclusions are still one of the main reasons for the disqualification of forgings.When deoxidizing the liquid steel,non-metallic inclusions will inevitably mix into the liquid steel,among which the hard brittle inclusions represented by Al₂O₃ have the most serious adverse effect on the properties of steel.Therefore,it has a certain engineering application value to understand the deformation mechanism of Al₂O₃ inclusions and the conditions of fracture damage,and to formulate a reasonable forging process to control the adverse effects of inclusions on steel properties.According to the formation process of primary Al₂O₃ inclusions in steel during smelting process,sintered Al₂O₃ samples with properties similar to those of Al₂O₃inclusions in steel were prepared by spark plasma sintering(SPS).High temperature quasi-static uniaxial compression tests of sintered samples were carried out at different deformation temperatures and strain rates on Gleeble-3800 thermo mechanical simulator.Based on Hoek Brown criterion,the prediction model of crushing stress of alumina under different deformation conditions was established.The experimental results show that the crushing stress is negatively correlated with the deformation temperature and positively correlated with the strain rate.The upsetting process of ingot model with inclusions was simulated by finite element numerical simulation technology under different deformation conditions.The deformation temperature was 1050^oC,1100^oC,1150^oC,1200^oC and 1250^oC respectively,and the strain rate was 0.1s^-1.By comparing the real-time equivalent stress of Al₂O₃ inclusions in the process of simulation with the experimental results,the corresponding matrix reduction was obtained when the equivalent stress of inclusions in the ingot reached the crushing stress,and then the critical deformation of the matrix needed to crush the inclusions in the ingot at different deformation temperatures was obtained.The relationship between holding time and forming quality of 304 stainless steel powder in sintering process was explored by echelon experiment,and the complete sintering process scheme of 304 stainless steel powder was determined.The metal samples containing Al₂O₃ inclusions were prepared by spark plasma sintering(SPS)technology through the mixed sintering of Al₂O₃ powder and 304 stainless steel powder.Based on the simulated inclusion crushing conditions,upsetting experiments were carried out on the samples with inclusions.The morphology and quantity of the internal Al₂O₃ inclusions before and after deformation were observed and analyzed by means of metallographic microscope and scanning electron microscope.It was found that the inclusions in the samples were obviously crushed after deformation,which verified the feasibility of the research method and the feasibility of finite element simulation Accuracy.