Bainite, the main microstructure of ultrahigh-strength complex-phase(CP) sheet steel, usually exhibits various micro-morphologies when subjected to different austempering treatments.In the current study, conventional ...Bainite, the main microstructure of ultrahigh-strength complex-phase(CP) sheet steel, usually exhibits various micro-morphologies when subjected to different austempering treatments.In the current study, conventional austempering treatment at the bainite nose temperature resulted in two bainite types with distinct micro-morphologies: polygonal blocky bainite and acicular bainite, which resulted in large fluctuations in the mechanical properties of CP steel, particularly yield strength and hole expansion ratio.Therefore, the precise control of bainite micro-morphology was studied and applied to separate the two bainite types through austempering optimization.The two bainite types of different micro-morphologies had different effects on the mechanical properties of CP steel: the acicular bainite favored hole expansion and flangeability but deteriorated ductility, while the polygonal blocky bainite favored ductility but deteriorated hole expansion and flangeability.Accordingly, two types of ultrahigh-strength CP steels of different mechanical properties can be stably manufactured through the precise control of bainitic micro-morphology to satisfy the specific demands of vehicle components in terms of the mechanical properties of CP steels.展开更多
For the purpose of developing a 1 500 MPa grade steel sheet with excellent strength and ductility, a 0.15C-10Mn-1.5Al steel was employed to study austenite stability and microstructural evolution based on a novel doub...For the purpose of developing a 1 500 MPa grade steel sheet with excellent strength and ductility, a 0.15C-10Mn-1.5Al steel was employed to study austenite stability and microstructural evolution based on a novel double annealing processing.After a conventional intercritical annealing process, the sample was heated again to a temperature higher than A_(c3) for a very short time to generate austenite grains with different manganese content;thus, the microstructure of martensite plus austenite can be obtained at room temperature.The experimental results show that with increasing annealing temperature, the tensile strength and yield strength increase.When the annealing temperature was higher than 820 ℃,the microstructure consisted of martensite plus austenite, and the tensile strength almost remained invariant with the annealing temperature.A tensile strength of 1 537 MPa and an elong-ation of 25.1% were achieved for the 820 ℃ condition.The volume fractions of austenite and martensite were identified by X-ray diffraction.It was found that with increasing annealing temperature, the volume fraction of the retained austenite decreased, and the ductility also had a gradual downward trend.The related austenite stability was discussed here as well.展开更多
As cold-formed steel has the highest strength-to-weight ratio of any material,ultra-high strength martensitic steel is attracting great interest from global car manufacturers. This paper explores the effects of the qu...As cold-formed steel has the highest strength-to-weight ratio of any material,ultra-high strength martensitic steel is attracting great interest from global car manufacturers. This paper explores the effects of the quenching and over-aging temperatures on the strength and cold bendability of C-Mn-Si martensitic steel. Due to its high carbon content,water-quenched C-Mn-Si martensitic steel has high hardenability and can obtain ultra-high tensile strength and uniform martensitic morphology when the water-quenching temperature is higher than 710 ℃.Increasing the over-aging temperature of this experimental steel decreases its tensile strength,increases the total elongation,and first increases then decreases the yield point until reaching a peak at 180 ℃. Besides,when increasing the over-aging temperature,the bendability of this experimental steel initially improves and then decreases,and reaches its optimal bendability at an over-aging temperature of 180 ℃. Based on SEM characterization and a microhardness distribution analysis,the over-aging temperatures were found to affect the size of the carbides and differences in the microhardness of the experimental steel. Therefore,they have significant influence on bendability.展开更多
Cold rolled martensitic sheet steels are achieving more and more applications in car-making because of their ultra-high strength and potential for weight reduction. The relatively low plasticity of ultra-high strength...Cold rolled martensitic sheet steels are achieving more and more applications in car-making because of their ultra-high strength and potential for weight reduction. The relatively low plasticity of ultra-high strength martensitic steels might be a drawback for the applications in the aspects of forming and safety protection function and should be significantly noted. A 1 500 MPa grade cold rolled martensitic sheet steel has been studied to investigate the bendability at 90 degree bending and impact toughness as well as fracture surface morphology at various temperatures. Some discussions have been made basing upon the experiment data to get some understanding on the performance of the materials under various conditions and on how to make use of this kind of ultra high strength steel properly.展开更多
The year 2014 marks the 33rdyear of CAFIU.During its 33 years of exploration,innovation,glory and dreams,CAFIU never stopped narrating the China Story to the world.As an important force of people-to-people diplomacy,C...The year 2014 marks the 33rdyear of CAFIU.During its 33 years of exploration,innovation,glory and dreams,CAFIU never stopped narrating the China Story to the world.As an important force of people-to-people diplomacy,CAFIU plays an active role in promoting understanding and exchanges between China and the world,and demonstrates an open,inclusive and confident image of the nation.展开更多
文摘Bainite, the main microstructure of ultrahigh-strength complex-phase(CP) sheet steel, usually exhibits various micro-morphologies when subjected to different austempering treatments.In the current study, conventional austempering treatment at the bainite nose temperature resulted in two bainite types with distinct micro-morphologies: polygonal blocky bainite and acicular bainite, which resulted in large fluctuations in the mechanical properties of CP steel, particularly yield strength and hole expansion ratio.Therefore, the precise control of bainite micro-morphology was studied and applied to separate the two bainite types through austempering optimization.The two bainite types of different micro-morphologies had different effects on the mechanical properties of CP steel: the acicular bainite favored hole expansion and flangeability but deteriorated ductility, while the polygonal blocky bainite favored ductility but deteriorated hole expansion and flangeability.Accordingly, two types of ultrahigh-strength CP steels of different mechanical properties can be stably manufactured through the precise control of bainitic micro-morphology to satisfy the specific demands of vehicle components in terms of the mechanical properties of CP steels.
文摘For the purpose of developing a 1 500 MPa grade steel sheet with excellent strength and ductility, a 0.15C-10Mn-1.5Al steel was employed to study austenite stability and microstructural evolution based on a novel double annealing processing.After a conventional intercritical annealing process, the sample was heated again to a temperature higher than A_(c3) for a very short time to generate austenite grains with different manganese content;thus, the microstructure of martensite plus austenite can be obtained at room temperature.The experimental results show that with increasing annealing temperature, the tensile strength and yield strength increase.When the annealing temperature was higher than 820 ℃,the microstructure consisted of martensite plus austenite, and the tensile strength almost remained invariant with the annealing temperature.A tensile strength of 1 537 MPa and an elong-ation of 25.1% were achieved for the 820 ℃ condition.The volume fractions of austenite and martensite were identified by X-ray diffraction.It was found that with increasing annealing temperature, the volume fraction of the retained austenite decreased, and the ductility also had a gradual downward trend.The related austenite stability was discussed here as well.
文摘As cold-formed steel has the highest strength-to-weight ratio of any material,ultra-high strength martensitic steel is attracting great interest from global car manufacturers. This paper explores the effects of the quenching and over-aging temperatures on the strength and cold bendability of C-Mn-Si martensitic steel. Due to its high carbon content,water-quenched C-Mn-Si martensitic steel has high hardenability and can obtain ultra-high tensile strength and uniform martensitic morphology when the water-quenching temperature is higher than 710 ℃.Increasing the over-aging temperature of this experimental steel decreases its tensile strength,increases the total elongation,and first increases then decreases the yield point until reaching a peak at 180 ℃. Besides,when increasing the over-aging temperature,the bendability of this experimental steel initially improves and then decreases,and reaches its optimal bendability at an over-aging temperature of 180 ℃. Based on SEM characterization and a microhardness distribution analysis,the over-aging temperatures were found to affect the size of the carbides and differences in the microhardness of the experimental steel. Therefore,they have significant influence on bendability.
文摘Cold rolled martensitic sheet steels are achieving more and more applications in car-making because of their ultra-high strength and potential for weight reduction. The relatively low plasticity of ultra-high strength martensitic steels might be a drawback for the applications in the aspects of forming and safety protection function and should be significantly noted. A 1 500 MPa grade cold rolled martensitic sheet steel has been studied to investigate the bendability at 90 degree bending and impact toughness as well as fracture surface morphology at various temperatures. Some discussions have been made basing upon the experiment data to get some understanding on the performance of the materials under various conditions and on how to make use of this kind of ultra high strength steel properly.
文摘The year 2014 marks the 33rdyear of CAFIU.During its 33 years of exploration,innovation,glory and dreams,CAFIU never stopped narrating the China Story to the world.As an important force of people-to-people diplomacy,CAFIU plays an active role in promoting understanding and exchanges between China and the world,and demonstrates an open,inclusive and confident image of the nation.
