高速冲击拉伸条件下TWIP钢的力学性能

采用气动式间接杆杆型冲击拉伸试验装置对5种不同成分的TWIP钢在102～103s-1应变速率范围内的动态拉伸变形行为进行了研究,并和静态拉伸性能作了比较.结果表明:随应变速率的提高,材料动态条件下的抗拉强度、断裂延伸率和能量吸收值均显著增加,均匀延伸率略有提高.TWIP钢在形变过程中产生形变孪晶显著改善了材料的塑性,因此在高应变速率下的延伸率仍较好.     

高速冲击拉伸条件下TWIP钢的力学性能

采用气动式间接杆杆型冲击拉伸试验装置对5种不同成分的TWIP钢在10^2～10^3 s^-1应变速率范围内的动态拉伸变形行为进行了研究,并和静态拉伸性能作了比较。结果表明：随应变速率的提高,材料动态条件下的抗拉强度、断裂延伸率和能量吸收值均显著增加,均匀延伸率略有提高。TWIP钢在形变过程中产生形变孪晶显著改善了材料的塑性,因此在高应变速率下的延伸率仍较好。     

TWIP钢的组织与力学性能研究

采用金相、静态拉伸试验方法研究了5种不同锰含量的TWIP钢的组织和力学性能。结果表明,5种钢的屈服强度随应变率的增大而提高,最大屈服强度可达280MPa;抗拉强度随应变率的增大而略有降低,最高抗拉强度超过1000MPa;1#钢的断裂延伸率和强塑积随应变率的增大而提高,其它4种成分钢的断裂延伸率和强塑积随应变率的增大而减小。1#钢只具形变诱发马氏体相变,不出现孪晶;而2#-5#钢具TWIP效应,其中3#钢的最大延伸率可达75%,强塑积最高可达45000MPa（%）。TWIP钢拉伸前组织中有退火孪晶,变形过程中产生大量的形变孪晶,孪晶诱导塑性,从而推迟了颈缩的产生,导致很高的均匀变形能力。     

不同应变率下 TRlP钢的拉伸性能

在自制气动式间接杆杆型冲击拉伸试验机上对含1.6Si-1.58Mn-0.195C的TRIP（Transformation-induced Plasticity)钢在不同应变率下的高速冲击拉伸性能进行了研究，并和静态拉伸性能进行了比较。结果显示，随应变速率的提高，材料的抗拉强度显著增加，延伸率降低。由于TRIP钢组织中残余奥氏体在应力应变作用下向马氏体的相变诱发转变显著改善了材料的塑性，因此在高应变率下的延伸率仍较好。     

不同应变速率下DP钢变形行为的微观机理研究

利用3 000 kN电子万能试验机和ZWICK HTM5020高速拉伸试验装置研究了双相钢(DP钢)在不同应变速率(10-4~600 s-1)下的拉伸变形行为,并结合XRD分析对双相钢组织中的位错密度进行了计算。结果表明,在准静态拉伸过程中,双相钢组织中的位错密度基本不变,其抗拉强度、断裂延伸率随应变速率变化也不明显;而在动态拉伸条件下,随着应变速率的增加,双相钢组织中的位错密度不断增加,抗拉强度也相应增加,塑性降低,最终导致能量吸收下降。     

应变速率对奥氏体不锈钢应变诱发α'-马氏体转变和力学行为的影响

以5×10-4s-1(慢速拉伸)和2×10-2 s-1(快速拉伸) 2种应变速率对EN1.4318(AISI301L)和EN1.4301(AISI304)冷轧和退火态奥氏体不锈钢板试样(厚度为2 mm)进行了拉伸实验,用TEM,SEM以及XRD分析应变诱发α'-马氏体转变机制和转变量.结果表明,相同应变速率拉伸时,EN1.4318钢的α'-马氏体转变量远远高于EN1.4301钢;快速拉伸可明显抑制冷轧EN1.4318钢中α'-马氏体的转变速率,降低硬化率.在均匀变形阶段,2种钢中α'-马氏体的转变速率和转变量比慢速拉伸时有不同程度地下降,而且冷轧比退火态更显著.奥氏体稳定性较高的EN1.4301钢,常温拉伸α'-马氏体转变饱和值低于0.3(体积分数),增强效果小,快速拉伸导致较快发生塑性失稳和均匀延伸率大幅降低;而对于层错能低、α'-马氏体饱和值很高的EN1.4318钢,快速托伸则使抗拉强度大幅降低,而且下降的幅度随α'-马氏体饱和值增加而增大;EN1.4318钢的应变速率敏感性远大于EN1.4301钢.     

M1600钢的动态力学性能

利用分离式Hopkinson杆对一种新型高强度马氏体M1600钢进行了动态拉伸力学性能测试,对M1600钢的应变速率敏感性、动态断裂方式及吸能特点进行了研究,研究结果表明:M1600钢具有一定的应变速率敏感性,且应变速率敏感性随应变速率的增加而逐渐增强。M1600钢的断裂机理会随应变速率的增加发生变化,并影响M1600钢的塑性。当应变速率为3000 s~(-1)时,M1600钢的伸长率最高,为20.5%。在准静态3000~4500 s~(-1)范围内,M1600钢形变吸收的能量随应变速率的提高先增加后减少,应变速率为3000 s~(-1)时,M1600钢吸收能量最多,为321.3 J/cm~3。     

预应变对TRIP钢力学性能及硬化行为的影响北大核心CSCD

为了研究TRIP钢不同变形量后的使用性能,对TRIP690冷轧镀锌板进行了分别为5%、10%、15%、20%的预应变准静态拉伸,研究不同预应变对TRIP钢的力学性能及加工硬化行为的影响,并通过XRD技术测量残留奥氏体的变化规律。结果表明:预应变对TRIP钢的屈服强度、屈强比、平均加工硬化值影响显著,其中屈服强度和屈强比均随预应变量增大而显著增大,抗拉强度和强塑积均小幅增大;同时由于随拉伸预应变量增大,残留奥氏体持续地向马氏体发生渐进式转变,残留奥氏体含量降低,且剩余的残留奥氏体较为稳定难以诱发相变,使得材料的加工硬化能力明显减弱。     

EFFECT OF STRAIN RATE ON STRAIN INDUCED α'--MARTENSITE TRANSFORMATION AND MECHANICAL RESPONSE OF AUSTENITIC STAINLESS STEELS

以5×10^-4 s^-1(慢速拉伸)和2×10^-2 s^-1(快速拉伸) 2种应变速率对EN1.4318 (AISI301L)和EN1.4301(AISI304)冷轧和退火态奥氏体不锈钢板试样(厚度为2 mm)进行了拉伸实验, 用TEM, SEM以及XRD分析应变诱发 α'--马氏体转变机制和转变量. 结果表明, 相同应变速率拉伸时, EN1.4318钢的α'--马氏体转变量远远高于EN1.4301钢; 快速拉伸可明显抑制冷轧EN1.4318钢中α'--马氏体的转变速率, 降低硬化率. 在均匀变形阶段, 2种钢中α'--马氏体的转变速率和转变量比慢速拉伸时有不同程度地下降, 而且冷轧比退火态更显著. 奥氏体稳定性较高的EN1.4301钢, 常温拉伸 α'--马氏体转变饱和值低于0.3(体积分数), 增强效果小, 快速拉伸导致较快发生塑性失稳和均匀延伸率大幅降低; 而对于层错能低、α'--马氏体饱和值很高的EN1.4318钢, 快速拉伸则使抗拉强度大幅降低, 而且下降的幅度随α'--马氏体饱和值增加而增大; EN1.4318钢的应变速率敏感性远大于EN1.4301钢.     

预应变对TRIP钢力学性能及硬化行为的影响

为了研究TRIP钢不同变形量后的使用性能,对TRIP690冷轧镀锌板进行了分别为5%、10%、15%、20%的预应变准静态拉伸,研究不同预应变对TRIP钢的力学性能及加工硬化行为的影响,并通过XRD技术测量残留奥氏体的变化规律。结果表明:预应变对TRIP钢的屈服强度、屈强比、平均加工硬化值影响显著,其中屈服强度和屈强比均随预应变量增大而显著增大,抗拉强度和强塑积均小幅增大;同时由于随拉伸预应变量增大,残留奥氏体持续地向马氏体发生渐进式转变,残留奥氏体含量降低,且剩余的残留奥氏体较为稳定难以诱发相变,使得材料的加工硬化能力明显减弱。     

Tensile behavior of TRIP-aided multi-phase steels studied by in situ neutron diffraction

TRIP-aided multi-phase steels were made by thermo-mechanically controlled process, where the ferrite grain size and the amount of the retained austenite were changed by controlling process conditions. The tensile behavior of four steels was studied by in situ neutron diffraction. It is found that the retained austenite bearing about 1.0 wt% C is plastically harder than the ferrite matrix. The steel with a ferrite grain size of ≈2.0 μm showed tensile strength of 1.1 GPa and a uniform elongation of 18.4%, in which stress-induced martensitic transformation occurs during plastic deformation but a considerable amount of austenite remains even after the onset of necking. It is concluded that the enhancement of uniform elongation is caused mainly by the work-hardening due to the hard austenite and martensite, where the contribution of the transformation strain is negligible.     

EFFECTS OF TEST TEMPERATURE AND STRAIN RATE ON THE MECHANICAL PROPERTIES IN AN INTERCRITICALLY HEAT-TREATED BAINITE-TRANSFORMED STEEL

1.IntroductionThe demand for high strength steels with excellent ductility has increased in the automotive indus-try in order to improve manufacturing and safety and to reduce weight. High strength transforma-tion-induced plasticity (TRIP) steel sheets have received increased attention, as they have both high strength and ductility due to the martensitic transformation of retained austenite during plastic defor-mation.Transformation-induced plasticity was the phenomenon first found in steel …     

ON THE TENSILE MECHANICAL PROPERTY OF Si-Mn TRIP STEELS AT HIGH STRAIN RATE

二．互ntYO*llCtloliAs kn OWOWn,the beh yyiors of the strength and ductility of material under dynamic con－dltlon are obviously differs尬from those under static condition．几ensure the reft劝ility ofstructure under dynamic or impact loading It Is necessar     

Effect of strain rate on deformation behavior of TRIP steels

Tensile deformation behavior of Si–Mn TRIP (TRansformation Induced Plasticity) steel with vanadium and without vanadium and the DP (Dual Phase) steel of the same composition were studied in a large range of strain rate (0.001–2000 s^?1) by routine material testing machine, rotation disk bar–bar tensile impact apparatus and high-speed material testing machine of servo-hydraulic type. In situ measurement of the transformation of retained austenite was performed by means of X-ray stress apparatus in order to have detailed knowledge about the transformation of retained austenite at quasi-static tensile. Microstructure of steels before and after tensile were observed by means of optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). It is shown that there is no yield plateau observed on the stress–strain curve at quasi-static condition for TRIP steel containing vanadium because the vanadium carbide suppress the formation of Cottrell atmosphere in matrix. Retained austenite of Si–Mn TRIP steel containing vanadium transforms to martensite at loading stress of 502 MPa (its yielding strength is 486 MPa), while the transformation of retained austenite in matrix of Si–Mn TRIP steel without vanadium happens when its yielding process is finished at quasi-static tensile. It is confirmed that phase transformation of retained austenite in TRIP steel is strain induced phase transformation. It is noted that tensile elongation of TRIP steel at dynamic tensile is always lower than that at quasi-static tensile. That is because gradually strain induced phase transformation of retained austenite in TRIP steel is suppressed by deformation localization at dynamic tensile.     

The high-speed deformation behavior of TRIP steels

The high-speed deformation behavior of TRIP steel was investigated at strain rates ranging from 10⁻² s⁻¹ to 10³ s⁻¹. The effects of metallurgical factors, such as the rolling direction, thickness, and gage length, on the tensile properties at various strain rates were evaluated. The ultimate tensile strength, uniform elongation, strain rate sensitivity, absorbed energy, and strain-hardening exponent are reported. In general, the strength increases and the ductility decreases as the strain rate increases. The samples with a high amount of retained austenite had two distinct regions of strain rate sensitivity, showing high strain rate sensitivity over a strain rate of 10² s⁻¹. The tensile properties were not affected by the gage length and thickness of the tensile samples; however, the rolling direction of the tensile samples affected the UTS values slightly. The absorbed energy of the TRIP steel greatly exceeded that of HSLA steel.     

残余奥氏体增强低碳Q-P-T钢塑性的新效应

低碳Fe-0.25C-1.48Mn-1.20Si-1.51Ni-0.05Nb(质量分数,%)钢通过新型Q-P-T工艺处理后获得高的抗拉强度和良好延伸率的综合性能.对该低碳Q-P-T钢在拉伸过程中残余奥氏体含量的XRD测定和形变孪晶马氏体的TEM观测,证明了相变诱发塑性(TRIP)效应的存在.基于形变过程中马氏体和残余奥氏体中的平均位错密度测定和TEM的观察,验证了在中碳钢中最新发现的残余奥氏体吸收位错(DARA)新效应在低碳钢中同样存在,由此提出了DARA效应产生的条件,阐明了残余奥氏体增强高强度钢塑性的机制.     

Quasi-Situ Characterization of Deformation in Low-Carbon Steel with Equiaxed and Lamellar Microstructure Treated by the Quenching and Partitioning Process

The relationship between microstructure morphology and mechanical properties of the low-carbon steel (Fe-0.20C-2.59Mn-2.13Si) treated by different intercritical annealed quenching and partitioning (Q&P) processes was investigated through interrupted tensile tests plus quasi-situ electron backscatter diffraction measurements. Results show that size and distribution of retained austenite (RA) directly affect the sequence of deformation induced martensitic transformation. As strain increases, the equiaxed RA grains wrapped by ferrite transform first, followed by the equiaxed and film-like RA grains adjacent to martensite. Compared with traditional intercritical annealed Q&P steel with equiaxed structure, the steel with quenching pretreatment contains uniform lamellar structure and the relatively film-like type of RA, leading to the higher yield strength, tensile strength, and elongation, as well as the steady increase in dislocation density upon straining.     

EFFECT OF AUSTEMPERING ON TRANSFORMATION INDUCED PLASTICITY OF HOT ROLLED MULTIPHASE STEELS

Effect of austempering on the transformation induced plasticity (TRIP) of hot rolled multiphase steel was investigated. Polygonal ferrite, granular bainite, and a large amount of stabilized retained austenite could be obtained in the hot rolled multiphase steel. Strain induced martensite transformation (SIMT) of retained austenite and TRIP effectively occur under straining owing to austempering after hot rolling, and mechanical properties of the present steel remain at a relatively high constant value for austempering at 400℃. The mechanical properties of the steel exhibited a good combination of tensile strength (791MPa) and total elongation (36%) because the stability of retained austenite is optimal when the steel is held for 20min.     

Effects of Intercritical Annealing Temperature on the Tensile Behavior of Cold Rolled 7Mn Steel and the Constitutive ModelingEI北大核心CSCD

Medium Mn steel is composed of sub-micron grained ferrite and austenite, the unstable austenite may transform to martensite during plastic straining. Although the mechanical properties of medium Mn steel could be easily tested by tensile test, it is quite difficult to directly measure the influences of different constituent phases on the tensile and work hardening behavior. Thus, at the present work, EBSD, TEM, XRD and a constitutive model based on dislocation density have been used to study the effects of intercritical annealing (IA) temperature on the tensile properties and work hardening behavior of a newly designed medium Mn steel, Fe-7% Mn-0.3% C-2% Al (mass fraction). Experimental results showed that with the increase of IA temperature, the mechanic stability of reverted austenite decreased gradually and the kinetics of strain induced martensite rose rapidly. The stability of the reverted austenite was moderate when intercritically annealed at 700 degrees C this led to the best plasticity and the optimal mechanical properties. Simulated results exhibited that the mechanic stability of austenite has a decisive influence on the tensile behavior of the material. The austenite stability will be too high if the IA temperature is lower, and this will lead to the lower work hardening rate and uniform elongation; when the IA temperature is moderate, the stability of austenite will be optimum, consequently strain-induced martensite would be progressively produced during straining and result in the higher work hardening rate and prolonged uniform elongation; the stability of austenite will be too lower if the IA temperature is higher, thus larger volume fraction of strain- induced martensite would be formed in a short period, and this would result in the higher tensile strength but the inferior uniform elongation.