The softening behavior of Inconel 718 alloy at different temperatures was studied using two- stage interrupted compression method on Gleeblel500D thermal stimulator, and the 2% offset method was applied to analyze the...The softening behavior of Inconel 718 alloy at different temperatures was studied using two- stage interrupted compression method on Gleeblel500D thermal stimulator, and the 2% offset method was applied to analyze the experimental dates. Finally, the static reerystallizafion fraction was obtained, At the same times, optical microscope （OM） and transmission electron microscopy （TEM） were employed to investigate the microstructure characteristic. The experimental results showed that the recrystallization was more sensitive to temperature than holding time. The reerystaUization process finished quickly above 1 050℃, and significantly prolonged below 1 025℃. Additionally, the dynamical model of static recrystallization follows the Avrami equation. The nucleating mechanism was characterized by bulging at grain boundary and merging of sub-grain.展开更多
Effects of alloying elements,Si,Nb,Ti,W,Mo,V,Al and rare earth metals on the microstructure and properties of high speed steels(HSSs) have been reviewed.More attention is paid to effects of Si on the secondary hardeni...Effects of alloying elements,Si,Nb,Ti,W,Mo,V,Al and rare earth metals on the microstructure and properties of high speed steels(HSSs) have been reviewed.More attention is paid to effects of Si on the secondary hardening and V on the morphology of eutectic carbides in HSSs.A lot of work has been carried out on the behavior of alloying elements in HSSs in the past decade,and some new types of HSSs containing silicon,aluminum or rare earth metals have been successfully developed in the world.展开更多
It is well known that the strengthening mechanisms of Nb microalloying on low carbon flat product have been widely studied and recognized since microalloying 75, but the application research and strengthening effects...It is well known that the strengthening mechanisms of Nb microalloying on low carbon flat product have been widely studied and recognized since microalloying 75, but the application research and strengthening effects of niobium on middle carbon steel like rebars have been incomplete and under argument due to some factors like limited solubility of Nb（CN） in reheating stage, dominant application of vanadium in rebars, as well as uncertain strengthening effect resulted from high rolling temperature and fast rolling speed in finishing rolling stage. Combining with new version of GB1499.2-2018： Steel for the reinforcement of concrete-Part 2： Hot rolled ribbed bars, it is very necessary to clarify the strengthening effects of niobium on high strength rebars for cost saving. In this paper, some new phenomena have been presented and discussed based on industrial trial results of Nb-bearing HRB400E, HRB500E and HRB600（E）, and then strengthening effects of niobium on high strength rebars were discussed.展开更多
High-strength,anti-seismic requirements represent the development tendency to hot-rolled ribbed bar used for the reinforcement of concrete.In this paper,metallurgical design,development and strengthening mechanisms fo...High-strength,anti-seismic requirements represent the development tendency to hot-rolled ribbed bar used for the reinforcement of concrete.In this paper,metallurgical design,development and strengthening mechanisms for 600 MPa reinforcing bar with anti-seismic requirements have been studied and presented based on the production practice of 335 MPa,400 MPa and 500 MPa grades.Through trial and error,it was found that alloy design with niobium plus vanadium is the best way to achieve the optimum combination of yield strength and anti-seismic properties,especially,small amount niobium addition can improve upon tensile-to-yield ratio.In order to clarify the underlying theoretical principles for the strengthening effects,qualitative and quantitative analysis for microstructure had been conducted with the aid of optical microscopy,scanning electron microscopy,transmission electron microscopy and chemical extraction technique,together with the solution and precipitation behavior of niobium and vanadium during the hot-rolling and cooling processes.Based on analysis results,it was found strengthening effects of both niobium and vanadium demonstrate some additional strengthening effects apart from predominated precipitation strengthening and grain refinement strengthening respectively.Although adding high vanadium contents is indispensable to achieve needed yield strength through precipitation strengthening effects,but fine VN particles precipitated in relatively high temperature also bring grain refinement effects for austenite and ferrite.Equally,grain refinement is not overall to describe the effects of niobium in long products,small amount of niobium contents is marked to improve upon tensile-to-yield ratio due to transformation strengthening resulted from the niobium contents in solution.Through the development of HRB600E,strengthening mechanisms of vanadium and niobium in medium carbon long products had been enriched.展开更多
Controlling of the solution and precipitation for microalloying additions of Nb,V,Ti and their combination is the basic building block of microalloyed steels.Among three microalloying elements,Nb has been regarded the...Controlling of the solution and precipitation for microalloying additions of Nb,V,Ti and their combination is the basic building block of microalloyed steels.Among three microalloying elements,Nb has been regarded the most effective microalloying ingredient used for low carbon flat products due to marked strengthening effect of grain refinement and relatively weak precipitation strengthening effect by matching proper thermomechanical processing(TMP).However,Nb was not viewed as attractive as V for medium carbon long products in the past because of limited solubility during reheating process.What is more,hot working is usually carried out at high temperatures in the recrystallization regime,so it is difficult to exert conventional controlled rolling to obtain pancaked austenite,which has further affected the research and application of Nb in medium carbon long products.Because of these factors,studies of Nb in medium carbon long products were incomplete,and even some recognitions and conclusions are subjected to debate.In order to clarify the strengthening effects of Nb in medium carbon long products,the reinforcing bars have been chosen as experimental steels to clarify the role of Nb on microstructural changes along the whole hot working,cooling processes.In addition,qualitative and quantitative analyses of Nb’s state and distribution in reheating,rolling and cooling had been carried out to illustrate some singularities.展开更多
On-line thermo mechanical controlled processing(TMCP) was conducted to develop the third generation high strength low alloy(HSLA) steel with high toughness economically.The ultra-low carbon content ensured a high leve...On-line thermo mechanical controlled processing(TMCP) was conducted to develop the third generation high strength low alloy(HSLA) steel with high toughness economically.The ultra-low carbon content ensured a high level of upper shelf energy while ultrafine lath martensitic structure transformed from super-thin pancaked austenite during controlled rolling and cooling.The reduction of martensite block size decreased ductile-to-brittle transition temperature(DBTT) and compensated the strength loss due to carbon reduction.Consequently,the excellent balance of strength and toughness values was obtained as 950-1060 MPa for yield strength,180 J for Charpy V-notch impact absorbed energy at 30℃,which is much superior to that of traditional martensitic steel.Two mechanisms for the refinement of lath martensite block were proposed:One is the austenite grain refinement in the direction of thickness,and the other is the reduction in the fraction of sub-block boundaries with small misorientation and the increase in the fraction of block boundaries with large misorientation,possibly due to austenite hardening.展开更多
In order to clarify effects of prior pancaked austenitic structure on microstructure and mechanical properties of transformed martensite in ausformed steel,a super-thin pancaked austenite was processed by multi-pass r...In order to clarify effects of prior pancaked austenitic structure on microstructure and mechanical properties of transformed martensite in ausformed steel,a super-thin pancaked austenite was processed by multi-pass rolling in a 0.03-2.6Mn0.06Nb-0.01Ti(wt%) low alloy steel.The evolution of prior pancaked austenite grain during multi-pass rolling was studied using Ni-30Fe model alloy.Related with the structure and texture in the prior super-thin pancaked austenite in Ni-30Fe alloy,the texture and anisotropy of mechanical properties of transformed martensite in the studied ausformed steel were focused on.There were mainly three kinds of rolling texture components in the super-thin pancaked austenite:Goss {110} 001,copper {112} 111 and brass {110} 112.They were further transformed into the weak {001} 110 and strong {112} 110,{111} 112 texture components in the martensitic structure.The orientation relationship(OR) of lath martensite transformation from pancaked austenite in the ausformed steel deviated larger from the exact Kurdjumov-Sachs(K-S) OR than in the case of equiaxed austenite without deformation.The tensile and yield strengths of the ausformed martensitic steel first decreased and then increased as the angle between tension direction and rolling direction increased.The main reason for the anisotropy of strength was considered as the texture component {112} 110 in martensite.However,the anisotropy of impact toughness was more complex and the main reasons for it are unknown.展开更多
文摘The softening behavior of Inconel 718 alloy at different temperatures was studied using two- stage interrupted compression method on Gleeblel500D thermal stimulator, and the 2% offset method was applied to analyze the experimental dates. Finally, the static reerystallizafion fraction was obtained, At the same times, optical microscope （OM） and transmission electron microscopy （TEM） were employed to investigate the microstructure characteristic. The experimental results showed that the recrystallization was more sensitive to temperature than holding time. The reerystaUization process finished quickly above 1 050℃, and significantly prolonged below 1 025℃. Additionally, the dynamical model of static recrystallization follows the Avrami equation. The nucleating mechanism was characterized by bulging at grain boundary and merging of sub-grain.
文摘Effects of alloying elements,Si,Nb,Ti,W,Mo,V,Al and rare earth metals on the microstructure and properties of high speed steels(HSSs) have been reviewed.More attention is paid to effects of Si on the secondary hardening and V on the morphology of eutectic carbides in HSSs.A lot of work has been carried out on the behavior of alloying elements in HSSs in the past decade,and some new types of HSSs containing silicon,aluminum or rare earth metals have been successfully developed in the world.
文摘It is well known that the strengthening mechanisms of Nb microalloying on low carbon flat product have been widely studied and recognized since microalloying 75, but the application research and strengthening effects of niobium on middle carbon steel like rebars have been incomplete and under argument due to some factors like limited solubility of Nb（CN） in reheating stage, dominant application of vanadium in rebars, as well as uncertain strengthening effect resulted from high rolling temperature and fast rolling speed in finishing rolling stage. Combining with new version of GB1499.2-2018： Steel for the reinforcement of concrete-Part 2： Hot rolled ribbed bars, it is very necessary to clarify the strengthening effects of niobium on high strength rebars for cost saving. In this paper, some new phenomena have been presented and discussed based on industrial trial results of Nb-bearing HRB400E, HRB500E and HRB600（E）, and then strengthening effects of niobium on high strength rebars were discussed.
文摘High-strength,anti-seismic requirements represent the development tendency to hot-rolled ribbed bar used for the reinforcement of concrete.In this paper,metallurgical design,development and strengthening mechanisms for 600 MPa reinforcing bar with anti-seismic requirements have been studied and presented based on the production practice of 335 MPa,400 MPa and 500 MPa grades.Through trial and error,it was found that alloy design with niobium plus vanadium is the best way to achieve the optimum combination of yield strength and anti-seismic properties,especially,small amount niobium addition can improve upon tensile-to-yield ratio.In order to clarify the underlying theoretical principles for the strengthening effects,qualitative and quantitative analysis for microstructure had been conducted with the aid of optical microscopy,scanning electron microscopy,transmission electron microscopy and chemical extraction technique,together with the solution and precipitation behavior of niobium and vanadium during the hot-rolling and cooling processes.Based on analysis results,it was found strengthening effects of both niobium and vanadium demonstrate some additional strengthening effects apart from predominated precipitation strengthening and grain refinement strengthening respectively.Although adding high vanadium contents is indispensable to achieve needed yield strength through precipitation strengthening effects,but fine VN particles precipitated in relatively high temperature also bring grain refinement effects for austenite and ferrite.Equally,grain refinement is not overall to describe the effects of niobium in long products,small amount of niobium contents is marked to improve upon tensile-to-yield ratio due to transformation strengthening resulted from the niobium contents in solution.Through the development of HRB600E,strengthening mechanisms of vanadium and niobium in medium carbon long products had been enriched.
文摘Controlling of the solution and precipitation for microalloying additions of Nb,V,Ti and their combination is the basic building block of microalloyed steels.Among three microalloying elements,Nb has been regarded the most effective microalloying ingredient used for low carbon flat products due to marked strengthening effect of grain refinement and relatively weak precipitation strengthening effect by matching proper thermomechanical processing(TMP).However,Nb was not viewed as attractive as V for medium carbon long products in the past because of limited solubility during reheating process.What is more,hot working is usually carried out at high temperatures in the recrystallization regime,so it is difficult to exert conventional controlled rolling to obtain pancaked austenite,which has further affected the research and application of Nb in medium carbon long products.Because of these factors,studies of Nb in medium carbon long products were incomplete,and even some recognitions and conclusions are subjected to debate.In order to clarify the strengthening effects of Nb in medium carbon long products,the reinforcing bars have been chosen as experimental steels to clarify the role of Nb on microstructural changes along the whole hot working,cooling processes.In addition,qualitative and quantitative analyses of Nb’s state and distribution in reheating,rolling and cooling had been carried out to illustrate some singularities.
基金supported by the National Basic Research Program of China ("973" Program) (Grant No. 2010CB630805)the National Natural Science Foundation of China (Grant No. 51071089)
文摘On-line thermo mechanical controlled processing(TMCP) was conducted to develop the third generation high strength low alloy(HSLA) steel with high toughness economically.The ultra-low carbon content ensured a high level of upper shelf energy while ultrafine lath martensitic structure transformed from super-thin pancaked austenite during controlled rolling and cooling.The reduction of martensite block size decreased ductile-to-brittle transition temperature(DBTT) and compensated the strength loss due to carbon reduction.Consequently,the excellent balance of strength and toughness values was obtained as 950-1060 MPa for yield strength,180 J for Charpy V-notch impact absorbed energy at 30℃,which is much superior to that of traditional martensitic steel.Two mechanisms for the refinement of lath martensite block were proposed:One is the austenite grain refinement in the direction of thickness,and the other is the reduction in the fraction of sub-block boundaries with small misorientation and the increase in the fraction of block boundaries with large misorientation,possibly due to austenite hardening.
基金supported by the National Basic Research Program of China("973" Program) (Grant No. 2010CB630805)the National Natural Science Foundation of China (Grant No. 51071089 and 51171087)
文摘In order to clarify effects of prior pancaked austenitic structure on microstructure and mechanical properties of transformed martensite in ausformed steel,a super-thin pancaked austenite was processed by multi-pass rolling in a 0.03-2.6Mn0.06Nb-0.01Ti(wt%) low alloy steel.The evolution of prior pancaked austenite grain during multi-pass rolling was studied using Ni-30Fe model alloy.Related with the structure and texture in the prior super-thin pancaked austenite in Ni-30Fe alloy,the texture and anisotropy of mechanical properties of transformed martensite in the studied ausformed steel were focused on.There were mainly three kinds of rolling texture components in the super-thin pancaked austenite:Goss {110} 001,copper {112} 111 and brass {110} 112.They were further transformed into the weak {001} 110 and strong {112} 110,{111} 112 texture components in the martensitic structure.The orientation relationship(OR) of lath martensite transformation from pancaked austenite in the ausformed steel deviated larger from the exact Kurdjumov-Sachs(K-S) OR than in the case of equiaxed austenite without deformation.The tensile and yield strengths of the ausformed martensitic steel first decreased and then increased as the angle between tension direction and rolling direction increased.The main reason for the anisotropy of strength was considered as the texture component {112} 110 in martensite.However,the anisotropy of impact toughness was more complex and the main reasons for it are unknown.
