TWIP钢的拉伸应变硬化行为

采用静态拉伸、金相组织观察方法研究了5种不同锰含量的TWIP钢的拉伸应变硬化行为.结果表明:5种钢的真应力与真应变不遵循Hollomond的线性关系,其中1号钢的应变硬化指数n值随真应变的增大先升后降,其它4种成分钢的n值随真应变的增大而提高.对于同一成分的钢,其n值均随应变速率的增大而减小.其微观变形机制是:随着锰含量的增加,孪晶形成逐渐起主导作用;拉伸前组织中有退火孪晶;随着变形的进行,产生大量的形变孪晶,孪晶与位错之间的交互作用与硬化率相协调,从而延迟了颈缩的产生,导致TWIP钢具有很高的均匀变形能力.     

Fe Mn C系TWIP钢的拉伸应变硬化行为研究

 通过试验研究了Fe Mn C系TWIP钢的拉伸应变硬化行为。结果表明：试验钢在拉伸过程中的应变硬化表现为阶段性多n值行为。其应变硬化机制有两种：在0.4%～3%的应变区间为位错强化阶段,10％～50%的应变区间为孪晶强化阶段。在这两个区间内n值皆为定值,而在4％～10％的应变区间n值呈不断上升趋势。     

Tensile Properties of TWIP Steel at High Strain Rate

 Tensile tests of TWIP steels of two compositions are performed in the strain rate range of 10-5-103 s-1. Results indicate that steel 1# does not exhibit TWIP effect but deformation induced martensitic transformation appears only. There exists TWIP effect in steel 3#. Tensile properties at room temperature are sensitive to strain rate in the studied strain rate ranges. Analysis on the relationship between strain hardening exponent and strain rates shows that strain induced martensitic transformation and formation of twins during deformation have significant influence on their strain hardening behavior.     

Influence of Carbon Content on Strain Hardening Behaviour of Sintered Plain Carbon Steel Preforms

 Complete experimental investigation on the instantaneous strain hardening behaviour of powder metallurgy (P/M) preforms of pure iron, Fe-0.35%C, Fe-0.75%C and Fe-1.1%C was carried out. The strain hardening behaviour of the above-mentioned P/M sintered steel preforms with aspect ratio of 0.4 under triaxial stress state condition was determined by cold upsetting under nil/no and graphite lubricant conditions. The instantaneous strain hardening value (ni), strength coefficient (Ki), and the stress as a function of strain and densification were obtained and analyzed. Furthermore, a relation was obtained from a semi-log plot of stress against relative density and analyzed to study the hardening behaviour owing to densification as stress was a function of induced strain as well as densification in the P/M materials.     

碳含量对Fe-Ni-Mn-Si-C系TWIP钢应变硬化行为的影响

采用单向拉伸、金相组织观察、TEM等方法,研究了3种不同碳含量Fe-Ni-Mn-Si-C系TWIP钢的拉伸应变硬化行为。研究结果表明,随着碳含量的增加,合金的强度和伸长率均提高,当碳质量分数为1.0%时,该TWIP钢具有较好的综合力学性能,强塑积达到83 160 MPa.%。3种TWIP钢的真应力-真应变曲线均不完全遵...     

拉伸应变硬化指数（n值）的测量结果不确定度评定

介绍了拉伸应变硬化指数（n值）的测量结果不确定度的评定方法。按照力和相应的应变等不同因素,对用最小二乘法得到的n值进行不确定度评定。     

超高强热成形钢的应变速率敏感性

利用CMT5105电子万能试验机和HTM 16020电液伺服高速试验机对超高强热成形钢进行拉伸试验,应变速率范围为10^-3~10³ s^-1,模拟热成形零件在不同应变速率下的碰撞情况.结果表明:在低应变速率阶段(10^-3~10^-1 s^-1)实验钢的应变速率敏感性不高,随应变速率的升高,实验钢的强度和延伸率变化不大;在高应变速率阶段(10⁰~10³ s^-1)实验钢具有高的应变速率敏感性,随应变速率的升高,实验钢的强度和延伸率都呈增大的趋势,并且抗拉强度的应变速率敏感性要大于屈服强度.这主要是由于在高应变速率阶段拉伸时产生的绝热温升现象和应变硬化现象共同作用造成的.实验钢颈缩后的延伸率随应变速率的增大而减小,主要是由于高应变速率下马氏体局部变形不均匀造成的.实验钢吸收冲击功的能力随应变速率的升高而增大,实验钢达到均匀延伸率时吸收冲击功的大小对应变速率更敏感.与低应变速率阶段相比,实验钢在高应变速率阶段的断口韧窝的平均直径更小,韧窝的深度更深,这与高应变速率阶段部分马氏体晶粒的碎化有关.通过扫描电镜和透射电镜观察发现,在高应变速率拉伸时晶粒有明显的拉长趋势,并且在应力集中的地方有一些微空洞的存在,应变速率为10³ s^-1时部分区域有碎化的现象.     

Effects of Twin-Dislocation and Twin-Twin Interactions on the Strain Hardening Behavior of TWIP Steels

 In the present paper, tensile tests of Fe-30Mn-5Si -2Al steel were carried out for different strains of 0.05, 0.14, 0.26, and up to the strain-to-failure in order to observe the evolution of microstructure during deformation and investigate the strain hardening behavior. Three-stage strain hardening behavior was observed in this steel during tensile test. In stage I, planar dislocation structure was observed by TEM to be the main deformation mechanism, and low strain hardening rate exponent was exhibited. Primary deformation twinning occurred in stage II, and the strain hardening rate exponent increased due to the blockage of dislocations’ motion by twin boundaries. In stage III, the strain hardening rate exponent had increased to be higher than 0.5. The obstacle effect of twin boundaries and twin-twin interaction had been observed by TEM, and the interactions between primary and secondary twins were found to cause the additional hardening in addition to the obstacle effect on dislocations’ motion, which led to the twinning induced plasticity effect in the later stage of deformation.     

奥氏体中锰钢加工硬化的微观机制

应用固体与分子经验电子理论对中锰钢奥氏体的价电子结构进行的计算表明，有Ｃ－Ｍｎ原子的偏聚；用ＴＥＭ组织观察和能谱分析发现奥氏体中有锰元素的偏聚；在ＴＥＭ薄膜原位动态拉伸变形试验中观察到应变诱发马氏体中有锰元素的偏聚；在ＴＥＭ薄膜原位动态拉伸变形试验中观察到应变诱发马氏体的形核与长大及高密度位错产生的过程；能谱分析发现马氏体相变区锰含量较低，从而提出应变诱发马氏体相变强化与高位错强化的双重作用是中锰     

Microstructural Refinement and Strain Hardening Behavior in Low-Density Ultrafine Pearlite Steel

Advanced low-density steels that meet energy shortages and high safety requirements have become a hot research topic in materials science. The addition of light elements with medium-Al content (5 wt%) to ultrahigh-strength pearlite cable steel alloy reduces the material density and causes a microstructural change from traditional θ-pearlite (ferrite + cementite) to θ-pearlite and κ-pearlite (ferrite + cementite + κ-carbide). The results show that the moderate addition of Al and Mn (5 wt%) promotes the formation of κ-carbide, which inhibits the diffusion of C and significantly delays the eutectoid transformation process of pearlite. Meanwhile, the transformation free energy of pearlite increases and obviously refines the lamellar spacing of the ultrafine pearlite by κ-carbide. Simultaneously, the interaction between κ-carbides and dislocations is initiated, which increases the strain hardening rate of ultrafine pearlitic steel.     

Strain Hardening Behavior of High Performance FBDP,TRIP and TWIP Steels

Based on n‐value differential equation and microstructural observation, strain hardening behaviors of FBDP, TRIP, and TWIP steels during uniaxial tension were investigated. TRIP steel exhibits both superior strength and ductility than FBDP steel, and TWIP steel displays much higher total and uniform elongations in comparison to FBDP and TRIP steels. The instantaneous n values of FBDP and TRIP steels increase at small strains, reach a maximum value, smoothly decrease at higher strains, and then rapidly drop up to the specimen rupture. The strain hardening of TRIP steel persists at higher strains where that of FBDP steel begins to diminish. TWIP steel exhibits gradually increased instantaneous n values over the whole uniform plastic deformation, implying that TWIP steel shows a much larger strain hardening capability than FBDP and TRIP steels.     

温度和应变速率对FeCrNi合金位错组态的影响

 利用透射电镜观察了不同温度及不同应变速率下FeCrNi合金的位错组态,分析了位错组态与温度及应变速率的关系。结果表明：温度使交滑移频率提高,位错组态从位错墙向位错胞方向发展,而应变速率升高使交滑移频率降低,位错组态从位错胞向位错墙、高密度层错方向发展。     

Effects of Pre-strain and Temperature on Bake Hardening of TWIP900CR Steel

The effects of pre-strain and baking temperature on bake hardening behaviour of TWIP900 CR steel were investigated.The results reveal that the bake hardening process contributes to an increase in yield strength up to 65 MPa at the baking temperature of 200℃.The difference in yield strength between baking temperatures of 170 and 200℃is almost insignificant.It is clearly observed that baking at a high temperature does not result in a significant increase in yield strength.For a reasonable bake hardening,agood combination of pre-strain and baking temperature is necessary.Besides,the toughness of the material is found to decrease with increasing pre-strain.     

5052铝合金板材的应变硬化行为模型探讨

研究了5052铝合金板材的应变硬化特征,并根据几种经验关系模型对该合金板材应变硬化行为进行非线性拟合,通过拟合结果残差平方和、相关系数的平方值R2检测法和应变指数n值的变化趋势检测法来共同评判应变硬化行为数学模型的准确性。结果表明,应变硬化指数n随着应变的增加呈抛物线式曲线变化,=B数学模型是最为适合描述5052铝合金应变硬化行为的经验关系模型。     

Comparative Study on Constitutive Modeling of Tantalum and Tantalum Tungsten Alloy

As a model bee metal, tantalum and its alloys have wide applications in defense-related fields. The KHL （Khan, Huang, Liang, 1999） model and the constitutive model proposed by Nemat-Nasser et al （Nemat-Nasser and Kapoor, 2001） for tantalum and its alloys were analyzed and compared with each other. A set of published data recorded during elastic-plastic deformations of tantalum, tantalum alloy containing tungsten of 2.5% （Ta-2.5W）, over a wide range of strains, strain rates, and temperatures were used to correlate the two models. Overall, it can be concluded that KHL model correlates much better with the data than the model used by Nemat-Nasser et al.     

亚稳态奥氏体钢的形变硬化

研究了亚稳态奥氏体不锈钢的形变硬化,结果表明：低温下由于产生应变诱发马氏体相变,其拉伸曲线硬化阶段呈现Ｓ形,硬化指数ｎ为非恒定值,硬化率与硬化指数ｎ随应变量的增加表现为抛物物型。     

Influence of Pre‐Straining and Bake Hardening on the Strain Rate Sensitivity of Automotive Sheet Steels

The present investigation deals with the influence of pre‐straining with or without bake hardening on the strain rate sensitivity of automotive sheet steels in typical crash conditions. The strain rate sensitivity m has been determined by means of dynamic tensile tests in the strain rate range 0.005‐1000 s^?1 and in the temperature range 233‐373K. A bake hardening heat treatment at 170 °C for 20 min without pre‐straining does not influence the m‐value in comparison to the base material condition. A small pre‐straining near plane strain condition, as commonly found in outer door panels, or a 10% uniaxial, plane strain and biaxial pre‐straining, as typically used in formed automotive crash components, without bake hardening does not affect the m‐value of sheet steels in comparison to the base material condition. Uniaxial 2% to 10% pre‐straining, longitudinal or transverse to rolling direction with subsequent bake hardening, does not clearly change the m‐value in comparison to the base material condition either. Small differences in the strain rate sensitivity behaviour are rather attributed to experimental scattering without real physical background.