Dislocation engineering concept has been successfully employed to tackle the strength-ductility trade-off in steels, resulting in the development of high-strength high-ductility deformed and partitioned(D&P)steel....Dislocation engineering concept has been successfully employed to tackle the strength-ductility trade-off in steels, resulting in the development of high-strength high-ductility deformed and partitioned(D&P)steel. The present perspective proposes to employ such dislocation engineering concept to develop strong and ductile magnesium(Mg) alloys. High density of < c + a > dislocations could be generated at appropriate temperature and retained in the Mg alloy after quenching to room temperature. Those < c + a > dislocations inherited from the warm deformation could provide < c + a > dislocation sources when the Mg alloy is deformed at room temperature, resulting in good ductility. The high dislocation density generated at warm deformation provides dislocation forest hardening, leading to improved yield strength of Mg alloy.展开更多
Press-hardened steel(PHS)with an ultimate tensile strength(UTS)of 1500 MPa has been widely used in automotive body-in-white in the last two decades,due to its ultra-high strength and excellent formability that is achi...Press-hardened steel(PHS)with an ultimate tensile strength(UTS)of 1500 MPa has been widely used in automotive body-in-white in the last two decades,due to its ultra-high strength and excellent formability that is achieved by hot stamping process.However,the application of PHS with UTS exceeding 1500 MPa in automotive industry could be deferred due to the increased risk of hydrogen embrittlement.To reduce this kind of risk,recent research efforts have been focused on various ways to optimize the microstructure of PHS.The present review intends to summarize these efforts,to highlight present solutions to address hydrogen embrittlement,and to shed light on directions for future improvement.The influence of microstructure on the hydrogen embrittlement of PHS has been discussed in terms of both the steel substrate and the surface condition.The substrate part covers the influence of martensite,carbides,inclusions,and retained austenite,while the surface part covers decarburization and oxidation,pre-coating,and trimming.展开更多
Two distinct regimes of strain rate sensitivity on yield strength are found in a high-strength nantwinned steel.The yield strength increases from 1410 to 1776 MPa when the strain rate increases from 10–3 to 1400 s-1....Two distinct regimes of strain rate sensitivity on yield strength are found in a high-strength nantwinned steel.The yield strength increases from 1410 to 1776 MPa when the strain rate increases from 10–3 to 1400 s-1.It is proposed from the measured small activation volume that the yielding of the nanotwinned steel at higher strain rates is governed by the dislocation bowing out from the carbon atmosphere.At lower strain rates,however,the yielding is controlled by the continuous re-pinning of dislocations due to the fast diffused carbon atoms,which leads to the relative insensitivity of yield strength to the strain rate.展开更多
1.Introduction The pursuit of advanced high-strength steels(AHSS)has been rising for the automobile industry to build lightweight and fuelefficient vehicles without compromising crashworthiness[1,2].The group of press...1.Introduction The pursuit of advanced high-strength steels(AHSS)has been rising for the automobile industry to build lightweight and fuelefficient vehicles without compromising crashworthiness[1,2].The group of press hardening steels(PHS)is an excellent candidate that comprises high strength,high toughness,and good formability,which are optimal to build intrusion resistant components such as(ⅰ)A/B-pillar reinforcements,(ⅱ)bumper and door beams.展开更多
Ultra-high strength alloys with good ductility are ideal materials for lightweight structural application in various industries. However, improving the strength of alloys frequently results in a reduction in ductility...Ultra-high strength alloys with good ductility are ideal materials for lightweight structural application in various industries. However, improving the strength of alloys frequently results in a reduction in ductility, which is known as the strength-ductility trade-off in metallic materials. Current alloy design strategies for improving the ductility of ultra-high strength alloys mainly focus on the selection of alloy composition （atomic length scale） or manipulating ultra-fine and nano-grained microstructure （grain length scale）. The intermediate length scale between atomic and grain scales is the dislocation length scale. A new alloy design concept based on such dislocation length scale, namely dislocation engineering, is illustrated in the present work. This dislocation engineering concept has been successfully substantiated by the design and fabrication of a deformed and partitioned （D＆P） steel with a yield strength of 2,2 GPa and an uniform elongation of 16%. In this D＆P steel, high dislocation density can not only increase strength but also improve ductility. High dislocation density is mainly responsible for the improved yield strength through dislocation forest hardening, whilst the improved ductility is achieved by the glide of intensive mobile dislocations and well-controlled transformation-induced plasticity （TRIP） effect, both of which are governed by the high dislocation density resulting from warm rolling and martensitic transformation during cold rolling. In addition, the present work proposes for the first time to apply such dislocation engineering concept to the quenching and partitioning （Q＆P） steel by incorporating a warm rolling process prior to the quenching step, with an aim to improve simultaneously the strength and ductility of the Q＆P steel. It is believed that dislocation engineering provides a new promising alloy design strategy for producing novel strong and ductile alloys.展开更多
Bainite transformation has yet to be utilized and even thoroughly studied in medium Mn steels.Here,we investigate the isothermal bainite transformation in a 10Mn steel at 450°C experimentally and theoretically,fo...Bainite transformation has yet to be utilized and even thoroughly studied in medium Mn steels.Here,we investigate the isothermal bainite transformation in a 10Mn steel at 450°C experimentally and theoretically,focusing on the effect of dislocations introduced by warm deformation.We show that the bainite transformation in the studied medium Mn steel exhibits extremely sluggish kinetics(on a time scale of days),concurrent with the pearlite formation.The introduced dislocations can significantly accelerate bainite transformation kinetics while also facilitating the pearlite reaction.This is likely the first report on the simultaneous occurrence of these two solid-state reactions in medium Mn steels.With respect to the roles of dislocations in the acceleration of bainite transformation observed in this work,we propose a new‘carbon depletion mechanism’,in which dislocations-stimulated pearlite formation makes a twofold contribution:facilitating the formation of bainitic ferrite sub-units to further enhance the autocatalytic effect and preventing the carbon enrichment in the remaining austenite.On this basis,a physical model is developed to quantitatively understand the bainite transformation kinetics considering the effect of concurrent pearlite formation,revealing good agreements between model descriptions and experiment results.Our findings,herein,offer fundamental insights into the bainite transformation in medium Mn steels and uncover a previously unidentified role played by introduced dislocations in influencing the kinetics of bainite formation,which may guide its future application in manipulating microstructure for the development of advanced high-strength steels.展开更多
Hydrogen embrittlement(HE)in 2 GPa-grade press-hardened steel(PHS)has posed a great risk to its lightweighting application in automotive crash-resistant components.While conventional slow strain rate tensile tests sho...Hydrogen embrittlement(HE)in 2 GPa-grade press-hardened steel(PHS)has posed a great risk to its lightweighting application in automotive crash-resistant components.While conventional slow strain rate tensile tests show that the precharged hydrogen concentration of 3.5 wppm induces a severe loss in strength and ductility,the high strain rate tests conducted at 1–103 s−1 that simulate the crash condition demonstrate no loss in strength and a minimal loss in ductility.Such strain rate dependency cannot be exclusively explained via hydrogen diffusion and redistribution to susceptible prior austenite grain boundaries,as the tensile testing of precharged samples with jumping strain rates offers a sufficient redistribution period at slow-strain-rate loading,but does not necessarily lead to a high level of HE afterwards.Detailed fractography analysis acknowledges that hydrogen-induced microcracks nucleated within early deformation stages are directly responsible for the high HE susceptibility of all test conditions.A phase-field simulation comprising 2 GPa-grade PHS's microstructure features and the hydrogen diffusion under tested loading conditions is applied.The calculation reveals that the hydrogen redistribution behavior is spatially confined to the crack tip areas but to a much greater extent.It thus facilitates continuous crack growth following the main crack with minimal plastic deformation and avoids branching to form secondary cracks.The combined experiments and modeling highlight the vital role of microcracks in the HE performance of 2 GPa-grade PHS,upon which the safety factor of HE in high-strength martensitic steels shall be established.展开更多
文摘Dislocation engineering concept has been successfully employed to tackle the strength-ductility trade-off in steels, resulting in the development of high-strength high-ductility deformed and partitioned(D&P)steel. The present perspective proposes to employ such dislocation engineering concept to develop strong and ductile magnesium(Mg) alloys. High density of < c + a > dislocations could be generated at appropriate temperature and retained in the Mg alloy after quenching to room temperature. Those < c + a > dislocations inherited from the warm deformation could provide < c + a > dislocation sources when the Mg alloy is deformed at room temperature, resulting in good ductility. The high dislocation density generated at warm deformation provides dislocation forest hardening, leading to improved yield strength of Mg alloy.
基金M.X.Huang acknowledges the support from Guangzhou Municipal Science and Technology Project(No.202007020007)Guangdong Basic and Applied Basic Research Foundation of China(No.2020B1515130007).
文摘Press-hardened steel(PHS)with an ultimate tensile strength(UTS)of 1500 MPa has been widely used in automotive body-in-white in the last two decades,due to its ultra-high strength and excellent formability that is achieved by hot stamping process.However,the application of PHS with UTS exceeding 1500 MPa in automotive industry could be deferred due to the increased risk of hydrogen embrittlement.To reduce this kind of risk,recent research efforts have been focused on various ways to optimize the microstructure of PHS.The present review intends to summarize these efforts,to highlight present solutions to address hydrogen embrittlement,and to shed light on directions for future improvement.The influence of microstructure on the hydrogen embrittlement of PHS has been discussed in terms of both the steel substrate and the surface condition.The substrate part covers the influence of martensite,carbides,inclusions,and retained austenite,while the surface part covers decarburization and oxidation,pre-coating,and trimming.
文摘Two distinct regimes of strain rate sensitivity on yield strength are found in a high-strength nantwinned steel.The yield strength increases from 1410 to 1776 MPa when the strain rate increases from 10–3 to 1400 s-1.It is proposed from the measured small activation volume that the yielding of the nanotwinned steel at higher strain rates is governed by the dislocation bowing out from the carbon atmosphere.At lower strain rates,however,the yielding is controlled by the continuous re-pinning of dislocations due to the fast diffused carbon atoms,which leads to the relative insensitivity of yield strength to the strain rate.
基金the support from the National Natural Science Foundation of China(No.U1764252)the Guangzhou Municipal Science and Technology Project(No.202007020007)+2 种基金the National Key Research and Development Program of China(No.2019YFA0209900)the Guangdong Basic and Applied Basic Research Foundation of China(No.2020B1515130007)the Research Grants Council of Hong Kong(Nos.R7066–18,17255016,17210418)。
文摘1.Introduction The pursuit of advanced high-strength steels(AHSS)has been rising for the automobile industry to build lightweight and fuelefficient vehicles without compromising crashworthiness[1,2].The group of press hardening steels(PHS)is an excellent candidate that comprises high strength,high toughness,and good formability,which are optimal to build intrusion resistant components such as(ⅰ)A/B-pillar reinforcements,(ⅱ)bumper and door beams.
基金the support from Research Grants Council of Hong Kong (Grants No. 17203014, HKU712713E and 17255016)the National Natural Science Foundation of China (Grant No. U1560204)
文摘Ultra-high strength alloys with good ductility are ideal materials for lightweight structural application in various industries. However, improving the strength of alloys frequently results in a reduction in ductility, which is known as the strength-ductility trade-off in metallic materials. Current alloy design strategies for improving the ductility of ultra-high strength alloys mainly focus on the selection of alloy composition （atomic length scale） or manipulating ultra-fine and nano-grained microstructure （grain length scale）. The intermediate length scale between atomic and grain scales is the dislocation length scale. A new alloy design concept based on such dislocation length scale, namely dislocation engineering, is illustrated in the present work. This dislocation engineering concept has been successfully substantiated by the design and fabrication of a deformed and partitioned （D＆P） steel with a yield strength of 2,2 GPa and an uniform elongation of 16%. In this D＆P steel, high dislocation density can not only increase strength but also improve ductility. High dislocation density is mainly responsible for the improved yield strength through dislocation forest hardening, whilst the improved ductility is achieved by the glide of intensive mobile dislocations and well-controlled transformation-induced plasticity （TRIP） effect, both of which are governed by the high dislocation density resulting from warm rolling and martensitic transformation during cold rolling. In addition, the present work proposes for the first time to apply such dislocation engineering concept to the quenching and partitioning （Q＆P） steel by incorporating a warm rolling process prior to the quenching step, with an aim to improve simultaneously the strength and ductility of the Q＆P steel. It is believed that dislocation engineering provides a new promising alloy design strategy for producing novel strong and ductile alloys.
基金support from National Key Research and Development Program of China(No.2019YFA0209900)National Natural Science Foundation of China(No.52130102)+5 种基金Research Grants Council of Hong Kong(No.R7066–18)Guangzhou Municipal Science and Technology Project(No.202007020007)Guangdong Basic and Applied Basic Research Foundation of China(No.2020B1515130007)support from National Natural Science Foundation of China(No.52130110)support from National Natural Science Foundation of China(No.52271116)Hong Kong Scholars Program(No.XJ2019029).
文摘Bainite transformation has yet to be utilized and even thoroughly studied in medium Mn steels.Here,we investigate the isothermal bainite transformation in a 10Mn steel at 450°C experimentally and theoretically,focusing on the effect of dislocations introduced by warm deformation.We show that the bainite transformation in the studied medium Mn steel exhibits extremely sluggish kinetics(on a time scale of days),concurrent with the pearlite formation.The introduced dislocations can significantly accelerate bainite transformation kinetics while also facilitating the pearlite reaction.This is likely the first report on the simultaneous occurrence of these two solid-state reactions in medium Mn steels.With respect to the roles of dislocations in the acceleration of bainite transformation observed in this work,we propose a new‘carbon depletion mechanism’,in which dislocations-stimulated pearlite formation makes a twofold contribution:facilitating the formation of bainitic ferrite sub-units to further enhance the autocatalytic effect and preventing the carbon enrichment in the remaining austenite.On this basis,a physical model is developed to quantitatively understand the bainite transformation kinetics considering the effect of concurrent pearlite formation,revealing good agreements between model descriptions and experiment results.Our findings,herein,offer fundamental insights into the bainite transformation in medium Mn steels and uncover a previously unidentified role played by introduced dislocations in influencing the kinetics of bainite formation,which may guide its future application in manipulating microstructure for the development of advanced high-strength steels.
基金support from the National Natural Science Foundation of China(No.52130102)the National Key Research and Development Program of China(No.2019YFA0209900)+5 种基金the Research Grants Council of Hong Kong(No.R7066–18)the Guangzhou Municipal Science and Technology Project(No.202007020007)the Guangdong Basic and Applied Basic Research Foundation of China(No.2020B1515130007)Lunhua He and Mingxin Huang acknowledge the support from the International Partnership Program of the Chinese Academy of Sciences(No.113111KYSB20190029)the key program of the Chinese Academy of Sciences(CAS)China Spallation Neutron Source(CSNS)is acknowledged for supporting neutron diffraction experiments using the General Purpose Powder Diffractometer(GPPD).
文摘Hydrogen embrittlement(HE)in 2 GPa-grade press-hardened steel(PHS)has posed a great risk to its lightweighting application in automotive crash-resistant components.While conventional slow strain rate tensile tests show that the precharged hydrogen concentration of 3.5 wppm induces a severe loss in strength and ductility,the high strain rate tests conducted at 1–103 s−1 that simulate the crash condition demonstrate no loss in strength and a minimal loss in ductility.Such strain rate dependency cannot be exclusively explained via hydrogen diffusion and redistribution to susceptible prior austenite grain boundaries,as the tensile testing of precharged samples with jumping strain rates offers a sufficient redistribution period at slow-strain-rate loading,but does not necessarily lead to a high level of HE afterwards.Detailed fractography analysis acknowledges that hydrogen-induced microcracks nucleated within early deformation stages are directly responsible for the high HE susceptibility of all test conditions.A phase-field simulation comprising 2 GPa-grade PHS's microstructure features and the hydrogen diffusion under tested loading conditions is applied.The calculation reveals that the hydrogen redistribution behavior is spatially confined to the crack tip areas but to a much greater extent.It thus facilitates continuous crack growth following the main crack with minimal plastic deformation and avoids branching to form secondary cracks.The combined experiments and modeling highlight the vital role of microcracks in the HE performance of 2 GPa-grade PHS,upon which the safety factor of HE in high-strength martensitic steels shall be established.
