The paper describes the investigation of mechanisms of cast structure formation in Hadfield steel depending on the changes in the cooling rate of a casting in the following two temperature ranges： crystallization tem...The paper describes the investigation of mechanisms of cast structure formation in Hadfield steel depending on the changes in the cooling rate of a casting in the following two temperature ranges： crystallization temperature（1,200-1,390 ℃） and the temperature of excessive phase separation（560-790 ℃）. Changes in the cooling rate of the crystallization temperature range from 1.1 to 25.0 ℃s^-1 result in the reduction of the average size of austenite grains from 266 to 131 μm. At the same time, the magnitude of developing shrinkage stresses changes from ＋195 to 0 MPa. When the cooling rate is higher than 16 ℃^-1, no shrinkage stresses are formed in the casting. Changes in the cooling rate of the casting in the temperature range of the excessive phase separation influence the number of phases, their morphology and chemical composition, the values of phase stresses, and the possibility of martensitic transformation. Changing in the cooling rate from 0.24 to 5.46 ℃^-1 results in the decrease of the amount of the excessive phase from 14.8% to 2.1%, which is composed of eutectic and carbides depending on the cooling rate, their quantitative ratio and morphology change. Such changes in the microstructure are reflected on the changes of value of developing phase stresses. When the cooling rate is 0.24 ℃^-1, it is ＋100 MPa, while the increase of the cooling rate to 1.4 ℃^-1 results in the decrease of tensile stresses to 0 MPa and their qualitative stresses change to compressive ones. Further increase of the cooling rate results in the increase of the value of compressive stresses. When the cooling rate is 5.5 ℃^-1, their value reaches-92 MPa. Martensite forming in the structure of Hadfield steel is possible if the cooling rate of the casting in the range of excessive phase separation is less than 0.25 ℃^-1.展开更多
Systematic thermodynamic analysis reveals that an essential condition for the thermodynamically valid chemographic projec-tions proposed by Greenwood is completely excessive.In other words,the phases or components fro...Systematic thermodynamic analysis reveals that an essential condition for the thermodynamically valid chemographic projec-tions proposed by Greenwood is completely excessive.In other words,the phases or components from which the projection is made need not be pure,nor have their chemical potentials fixed over the whole chemographic diagram.To facilitate the analy-sis of phase assemblages in multicomponent systems,all phases and components in the system are divided into internal and external ones in terms of their thermodynamic features and roles,where the external phases are those common to all assem-blages in the system,and the external components include excess components and the components whose chemical potentials(or relevant intensive properties of components) are used to define the thermodynamic conditions of the system.This general classification overcomes the difficulties and defects in the previous classifications,and is easier to use than the previous ones.According to the above classification,the phase rule is transformed into a new form.This leads to two findings:(1) the degree of freedom of the system under the given conditions is only determined by the internal components and phases;(2) different external phases can be identified conveniently according to the conditions of the system before knowing the real phase rela-tions.Based on the above results,a simple but general approach is proposed for the treatment of phases and components:all external phases and components can be eliminated from the system without affecting the phase relations,where the external components can be eliminated by appropriate chemographic projections.The projections have no restriction on the states of the phases or the chemical potentials of components from which the projections are made.The present work can give a unified ex-planation of the previous treatments of phases and components in the analysis of phase assemblages under various specific conditions.It helps to avoid potential misunderstandings or errors in the topological analysis of phase relations.展开更多
基金financially supported by the grant of the Russian Science Foundation(project no.15-19-10020)
文摘The paper describes the investigation of mechanisms of cast structure formation in Hadfield steel depending on the changes in the cooling rate of a casting in the following two temperature ranges： crystallization temperature（1,200-1,390 ℃） and the temperature of excessive phase separation（560-790 ℃）. Changes in the cooling rate of the crystallization temperature range from 1.1 to 25.0 ℃s^-1 result in the reduction of the average size of austenite grains from 266 to 131 μm. At the same time, the magnitude of developing shrinkage stresses changes from ＋195 to 0 MPa. When the cooling rate is higher than 16 ℃^-1, no shrinkage stresses are formed in the casting. Changes in the cooling rate of the casting in the temperature range of the excessive phase separation influence the number of phases, their morphology and chemical composition, the values of phase stresses, and the possibility of martensitic transformation. Changing in the cooling rate from 0.24 to 5.46 ℃^-1 results in the decrease of the amount of the excessive phase from 14.8% to 2.1%, which is composed of eutectic and carbides depending on the cooling rate, their quantitative ratio and morphology change. Such changes in the microstructure are reflected on the changes of value of developing phase stresses. When the cooling rate is 0.24 ℃^-1, it is ＋100 MPa, while the increase of the cooling rate to 1.4 ℃^-1 results in the decrease of tensile stresses to 0 MPa and their qualitative stresses change to compressive ones. Further increase of the cooling rate results in the increase of the value of compressive stresses. When the cooling rate is 5.5 ℃^-1, their value reaches-92 MPa. Martensite forming in the structure of Hadfield steel is possible if the cooling rate of the casting in the range of excessive phase separation is less than 0.25 ℃^-1.
基金supported by National Natural Science Founda-tion of China (Grant No.40873018)Open Foundation of the State Key La-boratory of Ore Deposit Geochemistry,Guiyang Institute of Geochemistry,Chinese Academy of Sciences (Grant No.200807)+1 种基金the Open Fund (Grant No.PLC201001) of the State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation (Chengdu University of Technology)the Natural Science Foundation of Hebei Province (Grant No.D2008000535)
文摘Systematic thermodynamic analysis reveals that an essential condition for the thermodynamically valid chemographic projec-tions proposed by Greenwood is completely excessive.In other words,the phases or components from which the projection is made need not be pure,nor have their chemical potentials fixed over the whole chemographic diagram.To facilitate the analy-sis of phase assemblages in multicomponent systems,all phases and components in the system are divided into internal and external ones in terms of their thermodynamic features and roles,where the external phases are those common to all assem-blages in the system,and the external components include excess components and the components whose chemical potentials(or relevant intensive properties of components) are used to define the thermodynamic conditions of the system.This general classification overcomes the difficulties and defects in the previous classifications,and is easier to use than the previous ones.According to the above classification,the phase rule is transformed into a new form.This leads to two findings:(1) the degree of freedom of the system under the given conditions is only determined by the internal components and phases;(2) different external phases can be identified conveniently according to the conditions of the system before knowing the real phase rela-tions.Based on the above results,a simple but general approach is proposed for the treatment of phases and components:all external phases and components can be eliminated from the system without affecting the phase relations,where the external components can be eliminated by appropriate chemographic projections.The projections have no restriction on the states of the phases or the chemical potentials of components from which the projections are made.The present work can give a unified ex-planation of the previous treatments of phases and components in the analysis of phase assemblages under various specific conditions.It helps to avoid potential misunderstandings or errors in the topological analysis of phase relations.
