Deformation behavior of 1 Al containing Mg alloy has been investigated in the present study.After annealing,the Mg-1 Al alloy shows a typical basal texture.When compared to the pure Mg having a similar texture and gra...Deformation behavior of 1 Al containing Mg alloy has been investigated in the present study.After annealing,the Mg-1 Al alloy shows a typical basal texture.When compared to the pure Mg having a similar texture and grain size,the Mg-1 Al alloy shows much higher strength and larger elongation.Slip trace analyses of the tensile strained specimens show that non-basal slips such as pyramidal I and II slips can be easily activated at an early stage of deformation in the Mg-1 Al alloy and the grains in the Mg-1 Al alloy are seen to accommodate a larger degree of deformation than those in the pure Mg at a given strain.With increasing tensile strain,however,there is a strain localization along the initially formed slip lines of non-basal slips,forming surface steps without activating multiple slip lines.展开更多
There exists a great need for the development of high performance alloys due to increasing demands for energy conservation and environmental protection. Application of strip casting shows a strong potential for the im...There exists a great need for the development of high performance alloys due to increasing demands for energy conservation and environmental protection. Application of strip casting shows a strong potential for the improvement of properties of existing alloys and also for the development of novel alloy systems with superior properties. The present paper reviews our Center's activities in the development of high performance alloys by strip casting. Examples include (1) Al alloys, (2) wrought Mg alloys, and (3) bulk metallic glass (BMG) alloys.展开更多
The formability of austenitic high-Mn steels is a critical issue in automotive applications under nonuniformly-deformed environments caused by dynamic strain aging.Among austenite stabilizing alloying elements in thos...The formability of austenitic high-Mn steels is a critical issue in automotive applications under nonuniformly-deformed environments caused by dynamic strain aging.Among austenite stabilizing alloying elements in those steels,Cu has been known as an effective element to enhance tensile properties via controlling the stacking fault energy and stability of austenite.The effects of Cu addition on formability,however,have not been sufficiently reported yet.In this study,the Cu addition effects on formability and surface characteristics in the austenitic high-Mn TRIP steels were analyzed in consideration of inhomogeneous microstructures containing the segregation of Mn and Cu.To reveal determining factors,various mechanical parameters such as total elongation,post elongation,strain hardening rate,normal anisotropy,and planar anisotropy were correlated to the hole-expansion and cup-drawing test results.With respect to microstructural parameters,roles of(Mn,Cu)-segregation bands and resultant Cu-rich FCC precipitates on the formability and surface delamination were also discussed.展开更多
High-strength bainitic steels have created a lot of interest in recent times because of their excellent combination of strength,ductility,toughness,and high ballistic mass efficiency.Bainitic steels have great potenti...High-strength bainitic steels have created a lot of interest in recent times because of their excellent combination of strength,ductility,toughness,and high ballistic mass efficiency.Bainitic steels have great potential in the fabrication of steel armor plates.Although various approaches and methods have been conducted to utilize the retained austenite(RA)in the bainitic matrix to control mechanical properties,very few attempts have been conducted to improve ballistic performance utilizing transformationinduced plasticity(TRIP)mechanism.In this study,high-strength bainitic steels were designed by controlling the time of austempering process to have various volume fractions and stability of RA while maintaining high hardness.The dynamic compressive and ballistic impact tests were conducted,and the relation between the effects of TRIP on ballistic performance and the adiabatic shear band(ASB)formation was analyzed.Our results show for the first time that an active TRIP mechanism achieved from a large quantity of metastable RA can significantly enhance the ballistic performance of high-strength bainitic steels because of the improved resistance to ASB formation.Thus,the ballistic performance can be effectively improved by a very short austempering time,which suggests that the utilization of active TRIP behavior via tuning RA acts as a primary mechanism for significantly enhancing the ballistic performance of high-strength bainitic steels.展开更多
Effects of Cr addition(0,3,and 6 wt%) on Charpy impact properties of Fe-C-Mn-Cr-based steels were studied by conducting dynamic compression tests at room and cryogenic temperatures.At room temperature,deformation mech...Effects of Cr addition(0,3,and 6 wt%) on Charpy impact properties of Fe-C-Mn-Cr-based steels were studied by conducting dynamic compression tests at room and cryogenic temperatures.At room temperature,deformation mechanisms of Charpy impacted specimens were observed as twinning induced plasticity(TWIP) without any transfo rmation induced plasticity(TRIP) in all the steels.At cryogenic temperature,many twins were populated in the Cr-added steels,but,interestingly,fine ε-martensite was found in the OCr steel,satisfying the Shoji-Nishiyama(S-N) orientation relationship,{111}γ//{0002}ε and <101>γ//<1120>ε.Even though the cryogenic-temperature staking fault energies(SFEs) of the three steel were situated in the TWIP regime,the martensitic transformation was induced by Mn-and Cr-segregated bands.In the OCr steel,SFEs of low-(Mn,Cr) bands lay between the TWIP and TRIP regimes which were sensitively affected by a small change of SFE.The dynamic compressive test results well showed the relation between segregation bands and the SFEs.Effects of Cr were known as not only increasing the SFE but also promoting the carbide precipitation.In order to identify the possibility of carbide formation,a precipitation kinetics simulation was conducted,and the predicted fractions of precipitated M23C6 were negligible,0.4-1.1×10-5,even at the low cooling rate of 10℃/s.展开更多
文摘Deformation behavior of 1 Al containing Mg alloy has been investigated in the present study.After annealing,the Mg-1 Al alloy shows a typical basal texture.When compared to the pure Mg having a similar texture and grain size,the Mg-1 Al alloy shows much higher strength and larger elongation.Slip trace analyses of the tensile strained specimens show that non-basal slips such as pyramidal I and II slips can be easily activated at an early stage of deformation in the Mg-1 Al alloy and the grains in the Mg-1 Al alloy are seen to accommodate a larger degree of deformation than those in the pure Mg at a given strain.With increasing tensile strain,however,there is a strain localization along the initially formed slip lines of non-basal slips,forming surface steps without activating multiple slip lines.
文摘There exists a great need for the development of high performance alloys due to increasing demands for energy conservation and environmental protection. Application of strip casting shows a strong potential for the improvement of properties of existing alloys and also for the development of novel alloy systems with superior properties. The present paper reviews our Center's activities in the development of high performance alloys by strip casting. Examples include (1) Al alloys, (2) wrought Mg alloys, and (3) bulk metallic glass (BMG) alloys.
基金supported by the Korea Institute for Advancement of Technology(KIAT)grant funded by the Korea Government(MOTIE)(Grant No.P0002019)the Korea University Grant for the fifth authorthe Brain Korea 21 PLUS Project for Center for Creative Industrial Materials。
文摘The formability of austenitic high-Mn steels is a critical issue in automotive applications under nonuniformly-deformed environments caused by dynamic strain aging.Among austenite stabilizing alloying elements in those steels,Cu has been known as an effective element to enhance tensile properties via controlling the stacking fault energy and stability of austenite.The effects of Cu addition on formability,however,have not been sufficiently reported yet.In this study,the Cu addition effects on formability and surface characteristics in the austenitic high-Mn TRIP steels were analyzed in consideration of inhomogeneous microstructures containing the segregation of Mn and Cu.To reveal determining factors,various mechanical parameters such as total elongation,post elongation,strain hardening rate,normal anisotropy,and planar anisotropy were correlated to the hole-expansion and cup-drawing test results.With respect to microstructural parameters,roles of(Mn,Cu)-segregation bands and resultant Cu-rich FCC precipitates on the formability and surface delamination were also discussed.
基金supported by the Agency for Defense Development(grant No.UE161030GD)the Korea University Grant for Dr.S.S.Sohnthe BK21 Plus Project for Center for Creative Industrial Materials。
文摘High-strength bainitic steels have created a lot of interest in recent times because of their excellent combination of strength,ductility,toughness,and high ballistic mass efficiency.Bainitic steels have great potential in the fabrication of steel armor plates.Although various approaches and methods have been conducted to utilize the retained austenite(RA)in the bainitic matrix to control mechanical properties,very few attempts have been conducted to improve ballistic performance utilizing transformationinduced plasticity(TRIP)mechanism.In this study,high-strength bainitic steels were designed by controlling the time of austempering process to have various volume fractions and stability of RA while maintaining high hardness.The dynamic compressive and ballistic impact tests were conducted,and the relation between the effects of TRIP on ballistic performance and the adiabatic shear band(ASB)formation was analyzed.Our results show for the first time that an active TRIP mechanism achieved from a large quantity of metastable RA can significantly enhance the ballistic performance of high-strength bainitic steels because of the improved resistance to ASB formation.Thus,the ballistic performance can be effectively improved by a very short austempering time,which suggests that the utilization of active TRIP behavior via tuning RA acts as a primary mechanism for significantly enhancing the ballistic performance of high-strength bainitic steels.
基金supported financially by the Korea University Grant for the eighth author, the Ministry of Knowledge Economy (No. 10044574-2013-45)Brain Korea 21 Plus Project for Center for Creative Industrial materialsKorea Institute for Advancement of Technology (KIAT) grant funded by the Korea Government (MOTIE) (No. P0002020, The Competency Development Program for Industry Specialist)。
文摘Effects of Cr addition(0,3,and 6 wt%) on Charpy impact properties of Fe-C-Mn-Cr-based steels were studied by conducting dynamic compression tests at room and cryogenic temperatures.At room temperature,deformation mechanisms of Charpy impacted specimens were observed as twinning induced plasticity(TWIP) without any transfo rmation induced plasticity(TRIP) in all the steels.At cryogenic temperature,many twins were populated in the Cr-added steels,but,interestingly,fine ε-martensite was found in the OCr steel,satisfying the Shoji-Nishiyama(S-N) orientation relationship,{111}γ//{0002}ε and <101>γ//<1120>ε.Even though the cryogenic-temperature staking fault energies(SFEs) of the three steel were situated in the TWIP regime,the martensitic transformation was induced by Mn-and Cr-segregated bands.In the OCr steel,SFEs of low-(Mn,Cr) bands lay between the TWIP and TRIP regimes which were sensitively affected by a small change of SFE.The dynamic compressive test results well showed the relation between segregation bands and the SFEs.Effects of Cr were known as not only increasing the SFE but also promoting the carbide precipitation.In order to identify the possibility of carbide formation,a precipitation kinetics simulation was conducted,and the predicted fractions of precipitated M23C6 were negligible,0.4-1.1×10-5,even at the low cooling rate of 10℃/s.