A highly efficient copper-catalyzed approach to form amide bonds from formamides and carboxylic acids was developed. This protocol shows broad substrate scopes and high yields in the presence of 1 mol% catalyst and 4....A highly efficient copper-catalyzed approach to form amide bonds from formamides and carboxylic acids was developed. This protocol shows broad substrate scopes and high yields in the presence of 1 mol% catalyst and 4.0 equiv, formamides.展开更多
Reduction pretreatment(RP)process,which is implemented after the billet is completely solidified,is an alternative process to further improve billet quality.Finite element method and experiment were used to investigat...Reduction pretreatment(RP)process,which is implemented after the billet is completely solidified,is an alternative process to further improve billet quality.Finite element method and experiment were used to investigate the effect of the RP process on the internal quality of 42CrMo billet.An ultrasonic testing technology was used to study the influence of the RP process on the micro-porosities.Through a three-dimensional finite element model,the mechanism of the RP process on the porosity closure was studied.The experimental results show that the RP process eliminates the macro-porosities of the billet center.The number of micro-porosities in the billets is effectively reduced,and the increase in deformation contributes to the reduction in micro-porosities.Compared with isothermal rolling,the RP process leads to a larger equivalent strain and hydrostatic integration in the billet center because of the temperature gradient,and the effect of the temperature gradient is greater with the increase in deformation.The closure effect of micro-porosity is related not only to the stress state,but also to the distribution of micro-porosity.The increase in three-dimensional compressive stress is beneficial to the porosity closure.If the micro-porosities distributed densely,excessive stress could induce micro-porosity coalescence,which has the risk of inducing cracks.展开更多
Comparative analysis was conducted to illustrate the effect of high-temperature reduction pretreatment on the internal quality of 42CrMo casting billet.Analysis of macrostructure clarifies that reduction pretreatment ...Comparative analysis was conducted to illustrate the effect of high-temperature reduction pretreatment on the internal quality of 42CrMo casting billet.Analysis of macrostructure clarifies that reduction pretreatment could reduce the size of central cavities and equiaxed crystals and improve the segregation degree and porosity on statistics.Lath bainite matrix and granular structure on segregation bands mainly dominate the microstructure of original billet,while pro-eutectoid ferrite and its accompanying troostite are added due to the application of reduction pretreatment.Additionally,C,Mn,and Mo are suggested to be enriched in segregation bands where pores and inclusions tend to be generated.By clarifying the microstructure evolution during cooling process,physical compression and multiplication of prior austenite grain boundaries caused by recrystallization are regarded as the main reasons in improving the internal quality of 42CrMo billet.展开更多
基金supported by the National Natural Science Foundation of China(No.21372176)Tongji University 985 Phase Ⅲ funds+1 种基金Pujiang Project of Shanghai Science and Technology Commission(No.11 J1409800)the Program for Professor of Special Appointment(Eastern Scholar) at Shanghai Institutions of Higher Learning
文摘A highly efficient copper-catalyzed approach to form amide bonds from formamides and carboxylic acids was developed. This protocol shows broad substrate scopes and high yields in the presence of 1 mol% catalyst and 4.0 equiv, formamides.
文摘Reduction pretreatment(RP)process,which is implemented after the billet is completely solidified,is an alternative process to further improve billet quality.Finite element method and experiment were used to investigate the effect of the RP process on the internal quality of 42CrMo billet.An ultrasonic testing technology was used to study the influence of the RP process on the micro-porosities.Through a three-dimensional finite element model,the mechanism of the RP process on the porosity closure was studied.The experimental results show that the RP process eliminates the macro-porosities of the billet center.The number of micro-porosities in the billets is effectively reduced,and the increase in deformation contributes to the reduction in micro-porosities.Compared with isothermal rolling,the RP process leads to a larger equivalent strain and hydrostatic integration in the billet center because of the temperature gradient,and the effect of the temperature gradient is greater with the increase in deformation.The closure effect of micro-porosity is related not only to the stress state,but also to the distribution of micro-porosity.The increase in three-dimensional compressive stress is beneficial to the porosity closure.If the micro-porosities distributed densely,excessive stress could induce micro-porosity coalescence,which has the risk of inducing cracks.
文摘Comparative analysis was conducted to illustrate the effect of high-temperature reduction pretreatment on the internal quality of 42CrMo casting billet.Analysis of macrostructure clarifies that reduction pretreatment could reduce the size of central cavities and equiaxed crystals and improve the segregation degree and porosity on statistics.Lath bainite matrix and granular structure on segregation bands mainly dominate the microstructure of original billet,while pro-eutectoid ferrite and its accompanying troostite are added due to the application of reduction pretreatment.Additionally,C,Mn,and Mo are suggested to be enriched in segregation bands where pores and inclusions tend to be generated.By clarifying the microstructure evolution during cooling process,physical compression and multiplication of prior austenite grain boundaries caused by recrystallization are regarded as the main reasons in improving the internal quality of 42CrMo billet.
