连续退火工艺对超高强双相钢力学性能的影响

为研究连续退火工艺参数对超高强冷轧双相钢组织及力学性能的影响,在Gleeble-3500热力模拟实验机上,使用正交实验法设计连续退火工艺获得超高强冷轧双相钢.研究发现:连续退火工艺参数对抗拉强度和总延伸率的影响程度依次是:临界区退火温度>保温时间>过时效温度;两阶段应变硬化特性随马氏体体积分数的增加而更加明显:当马氏体体积分数在35%左右时,冷轧双相钢的应变硬化关系明显呈线性;当马氏体体积分数接近50%时,冷轧双相钢的应变硬化关系呈非线性,但两阶段的应变硬化指数n值变化不大,两阶段并由曲线过渡;当马氏体体积分数在65%左右时,冷轧双相钢的应变硬化关系呈非线性,两阶段的应变硬化指数n值变化较大,并出现明显拐点.     

18-8型不锈钢的应变硬化特性研究

利用小载荷维氏硬度,借鉴用拉伸方法确定应变硬化指数的原理,测定了奥氏体不锈钢的强度系数K和应变硬化指数n.测得18-8型不锈钢应变硬化指数为0.418.所得数据与工程应用的奥氏体不锈钢硬化规律吻合的非常好.用硬度法测定和分析应变硬化规律简便易行、人为影响和数据分散度小、结论准确、更接近工程实际.     

18-型不锈钢的应变硬化特性研究

利用小载荷维氏硬度，借鉴用拉伸方法确定应变硬化指数的原理，测定了奥氏体不锈钢的强度系数K和应变硬化指数n。测得18-8型不锈钢应变硬化指数为0．418。所得数据与工程应用的奥氏体不锈钢硬化规律吻合的非常好。用硬度法测定和分析应变硬化规律简便易行、人为影响和数据分散度小、结论准确、更接近工程实际。     

多边形铁素体/针状铁素体双相管线钢的应变硬化行为

对X70管线钢进行临界区热处理,制备出四种铁素体/针状铁素体(PF/AF)体积分数不同的双相管线钢。用电子背散射衍射(EBSD)分析了PF含量对这种双相管线钢的晶粒尺寸、大角度与小角度晶界的比例以及几何必要位错密度(GND)的影响;通过Hollomon和修正C-J方程分析了这种钢的应力比与应变硬化指数(n值)的关系,以及不同PF体积分数双相管线钢的塑性变形和应变硬化的机理。结果表明,PF/AF双相管线钢的应变硬化能力几乎与应力比无关,而应变硬化指数与均匀延伸率表现出特定的线性关系。随着PF体积分数的提高,这种钢的颈缩点后移且应变硬化行为由两阶段向三阶段转变。PF体积分数的改变,对其第I和第II阶段的应变硬化能力有显著的影响。     

生产检验中测试材料n值的方法

针对目前测试材料在高温条件下应变硬化指数n值无相应试验标准,但针对超超临界汽轮机组中所用材料在高温条件下测试n值需求较大的状况,采用CMT 5105万能试验机在常温和高温条件下对汽轮机密封圈材料06Cr25Ni20测试真应力—应变曲线和n值,并采用数理统计的方法对n值进行统计。讨论不同拉伸速率和取点数量对n值统计结果的影响,试验结果表明:当取点数量达到或超过10点时,材料06Cr25Ni20在620℃的n值的离散程度明显降低,其95%的置信区间更加精确。     

n.m.r值与金属板的成形性

确定金属板成形性可以应用如下材料参数:应变硬化指数n,应变速度敏感性指数m和塑性应变比r。因为它们影响应变的分布及缩颈扩展的阻力,对金属板成形至关重要。基于成形性和应变硬化行为(n、m、r)以及材料冶金学性能之间的关系,金属板的成形性可以通过工艺参数的控制得到改善。文中阐述了n、m值对单轴塑性流动的影响,以及平面应变状态塑性失稳判据。并提出了通过常规拉力试验获得失稳应力的作图方法.应用n,m、r值将铝、黄铜、软钢的成形性作了比较;指出体心立方晶型(如钢)更多地受到择优取向的影响。在面心立方晶型中(如铝、黄铜)晶粒尺寸的影响则不可忽视。     

两种方法测定冷轧薄板应变硬化指数、塑性应变比值和伸长率的结果比较

借助两种不同的方法，测定了冷轧薄板的应变硬化指数（n）、塑性应变比（r）值和伸长率。在GALDABINI SUN1000试验机上，用光学非接触引伸计在GRAPHWORK 1软件上实现冷轧薄板的n和r值及伸长率的自动测量；在INSTRON1186试验机上，用YYU5050引伸计在LZC软件上自动测量冷轧薄板的n值，手工测量r值和伸长率。将两种方法得到的试验结果进行比较，发现两种方法的结果非常接受。用光学非接触引伸计在GRAPHWORK1软件上自动测量的n和r值及伸长率具有较高的可靠性和重现性。     

影响冷轧薄板力学性能测试结果的试验研究

应用INSTRON5569型电子拉力试验机，在不同测试条件下，对冷轧薄板力学性能进行了测试分析。结果表明，设置试验机的控制参数、拉伸速度和试样尺寸等均对力学性能测试结果有影响。提高拉伸速度使规定非比例伸长应力σ0.2增加，应变硬化指数n值减小，塑性应变比r值无明显变化；试样尺寸对r值有影响；建立了不同试样尺寸之间δ值的换算关系。     

应变硬化指数(n值)公式的探讨

按GB／T 5028-1999标准规定的应变硬化指数（n值）方法进行测试和计算，则其中数据的分析和计算非常繁琐且容易出错。通过大量的试验证明，采用两点法分析既方便又准确，与用五点法分析相比两者相对误差在0．5％以内，极大地提高了工作效率。     

18.8%MnTRIP/TWIP钢拉伸应变硬化行为

对锰含量为18.8%的TRIP/TwIP钢进行单轴拉伸实验,研究了这种钢的应变硬化行为.结果表明:这种高锰TRIP/TWIP钢的真应力应变曲线不完全遵循Holliomon的线性关系,在不同变形阶段强化机制不同.在塑性变形的开始阶段TRIP效应比较明显,且应变硬化指数n是恒定的;而真应变在O.14-0.35之间时二阶导数d2σ/dε2>0,应变硬化指数n随着应变量的增加而增加,其微观机制是形成大量的形变孪晶,并有孪晶和位错的交互作用,TWIP效应在该阶段占主导作用.真应变大于0.35后有少量TRIP效应,此时两相均发生变形.     

SiC颗粒增强6061Al基复合材料的动态拉伸性能Ⅰ应变硬化

利用拉伸split Hopkinson bar实验装置研究了SiCp/6061Al复合材料及其基体合金的动态拉伸性能及应变硬化行为。结果表明，与静态加载类似，在动态加载条件下，SiCp/6061Al复合材料的强度高于基体合金的强度，其断裂延伸率低于基体合金的断裂延伸率，在低应变动态拉伸时，复合材料的应变硬化指数高于Al合金材料的应变硬化指数，随着应变的增加，复合材料的应变硬化指数迅速下降，以至低于基体合金的应变硬化指数。     

Effect of heat treatment on strain hardening of ZK60 Mg alloy

Strain hardening behaviors of extruded ZK60 Mg alloy under different heat treatments (T4, T5 and T6) were studied using uniaxial tensile tests at room temperature. Hardening capacity, strain hardening exponent as well as strain hardening rate curve were obtained according to true plastic stress–strain curves. T5 and T6 treatments decrease strain hardening of extruded ZK60 alloy, and subsequently give rise to an obvious reduction in tensile uniform strain. While, as-T4 treated specimen shows the strongest strain hardening ability among these specimens, and its hardening capacity and strain hardening exponent are nearly twice those of as-T5 and T6 treated specimens. These effects were analyzed in terms of the microstructural variation and dislocation storage in ZK60 alloy.     

形变铝合金的形变硬化特性

采用单轴拉伸方法测试了LD10,LF6,LC4和LY12几种形变铝合金的形变硬化指数,分析了合金的硬化率和硬化指数与应变的关系。结果表明,这几种形变铝合金的硬化指数在不同的应变区域具有不同的变化趋势。在低应变区域,形变硬化指数呈上升趋势,在高应变区域,形变硬化指数趋于平稳。四种形变铝合金中,LF6的硬化指数最高,LY12,LD10次之,LC4最低。形变铝合金的硬化率随着应变的增加不断降低。     

Parametric Analysis of Tensile Properties of Bimodal Al Alloys by Finite Element Method

An axisymmetrical unit cell model was used to represent a bimodal Al alloy that was composed of both nano-grained (NG) and coarse-grained (CG) aluminum. Effects of microstructural and materials parameters on tensile properties of bimodal Al alloy were investigated by finite element method (FEM). The parameters analyzed included aspect ratios of CG Al and the unit cell, volume fraction of CG Al (VFCG), and yield strength and strain hardening exponent of CG Al. Aspect ratios of CG Al and the unit cell have no significant influence on tensile stress-strain response of the bimodal Al alloy. This phenomenon derives from the similarity in elastic modulus and coefficient of thermal expansion between CG Al and NG Al. Conversely, tensile properties of bimodal Al alloy are extremely sensitive to VFCG, yield strength and strain hardening exponent of CG Al.Specifically, as VFCG increases, both yield strength and ultimate tensile strength (UTS) of the bimodal Al alloy decreases, while uniform strain of bimodal Al alloy increases. In addition, an increase in yield strength of CG Al results in an increase in both yield stress and UTS of bimodal Al alloy and a decrease in uniform strain of bimodal Al alloy. The lower capability in lowering the increase of stress concentration in NG Al due to a higher yield strength of CG Al causes the lower uniform strain of the bimodal Al alloy. When strain hardening exponent of CG Al increases, 0.2% yield stress, UT5, and uniform strain of the bimodal Al alloy increases. This can be attributed to the increased work-hardening ability of CG Al with a higher strain hardening exponent.     

Die Kaltverfestigung von Nickelbasislegierungen

Strain Hardening of Nickel Base Alloys Tensile-, impact-, and hardness test were performed on solution treated and cold worked Nimonic 86 and Inconel 625. The characteristic values of strain hardening from the tensile-, impact-, and hardness tests were correlated, namely the strain hardening exponent m as determined from the stress-strain-curve of the tensile test. The impact test gave the lateral expansion and the hardness test the value (n?2), which corresponds approximately to the strain hardening coefficient of the tensile test.     

A neural network approach for predicting steel properties characterizing cyclic Ramberg–Osgood equation

This paper attempts to demonstrate the applicability of artificial neural networks to the estimation of steel properties, cyclic strain‐hardening exponent and cyclic strength coefficient, characterizing cyclic Ramberg–Osgood equation on the basis of monotonic tensile test properties. For this purpose, steel tensile data were extracted from the literature and two separate neural networks were constructed. One set of data was used for training the two networks and the remaining for testing purposes. Regression analysis and mean relative error calculation were used to check the accuracy of the system in the training and testing phases. Comparison of the results obtained from the neural networks and the values obtained from direct fitting of experimental data, indicated the reasonable prediction of cyclic strain‐hardening exponent and cyclic strength coefficient, which are often used to characterize the cyclic deformation curve by a Ramberg–Osgood type equation.     

Strain hardening of as-extruded Mg-xZn (x = 1, 2, 3 and 4 wt%) alloys

The influence of Zn on the strain hardening of as-extruded Mg-x Zn(x = 1, 2, 3 and 4 wt%) magnesium alloys was investigated using uniaxial tensile tests at 10~(-3)s~(-1) at room temperature. The strain hardening rate,the strain hardening exponent and the hardening capacity were obtained from true plastic stress-strain curves. There were almost no second phases in the as-extruded Mg-Zn magnesium alloys. Average grain sizes of the four as-extruded alloys were about 17.8 μm. With increasing Zn content from 1 to 4 wt%, the strain hardening rate increased from 2850 MPa to 6810 MPa at(б-б_(0.2)) = 60 MPa, the strain hardening exponent n increased from 0.160 to 0.203, and the hardening capacity, Hc increased from 1.17 to 2.34.The difference in strain hardening response of these Mg-Zn alloys might be mainly caused by weaker basal texture and more solute atoms in the α-Mg matrix with higher Zn content.     

Tensile properties of stainless steel-clad aluminium sandwich sheet metals

The various tensile properties, such as yield strength, tensile strength, strength coefficient, uniform elongation, strain hardening exponent and strain rate sensitivities, of stainless steel-clad aluminium sandwich sheet metals have been analysed on the basis of the fact that the flow stresses of the sandwich sheets follow the rule of mixtures, an average of component properties weighted by the volume fractions. The rule of mixtures can be applied to the tensile strengths and strength coefficients of the sandwich sheets, whereas the yield strengths do not follow the mixture rule. The force weighted average rule, an average of component properties weighted by volume fractions and forces, can be applied to uniform elongations, strain hardening exponents and strain rate sensitivities of the sandwich sheets.     

试样的形状公差对应变测定的影响

就形状公差对拉伸应变测定的影响做了理论分析。引入等效标距的概念，建立与等效标距、名义标距、应变硬化指数和形状公差相关的方程式。利用这些公式可以定量地描述形状公差的试样对拉伸应变测定的影响。以国家标准和国际标准中各自规定的形状公差为例，说明定量评定形状公差对应变测定误差的影响。根据应变误差的计算结果，可知国际标准允许的形状公差比国家标准宽得多。