用微型杯突试验法评价和估算钢的强度和塑性

采用一种新型在线无损检测的试验方法--微型杯突试验法研究电站锅炉管道用9Cr-1Mo-V-Nb-N钢的强度和塑性.结果表明:该试验方法与常规的单轴拉伸试验之间有很好的可比性,并且通过微型杯突试验的结果估算9Cr-1Mo-V-Nb-N钢的屈服强度与抗拉强度及伸长率,给出相应的经验公式.同时在采用微型杯突试验法估算9Cr-1Mo-V-Nb-N钢的塑性时,首次提出断裂挠度率的概念.     

Wedge tension test of a high-strength bolt of fully pearlitic high-carbon steel

Using a wedge tension test for service and safety reasons, this study determines the fracture location of a previously developed high-strength M8 bolt with a tensile strength of 1600 MPa. The strength distributions of the manufactured bolt are examined in compression and microhardness tests to ensure a better understanding of the experimental results of the wedge tension test. The strength variations of the manufactured bolt were confirmed through scanning electron microscope measurements of the interlamellar spacing of the pearlite. Because of the strength condition in the neck of the bolt and the geometry-induced stress concentration, the head of the manufactured bolt can be separated from the neck during the wedge tension test. In this study, stress analyses were therefore conduced to prevent the head separation. That is, the stress concentration on the neck of the bolt was checked by varying the fillet radius for a given pitch size of the bolt. The numerical findings were subsequently validated by the wedge tension test. The findings are the basis of practical industrial design guidelines on the fillet radius to prevent the head of the manufactured bolt from being separated.     

Stress Relaxation in Tensile Deformation of 304 Stainless Steel

Improved ductility by stress relaxation has been reported in different kinds of steels. The influence of stress relaxation and its parameters on the ductility of 304 stainless steel has not been established so far. Stress relaxation behavior during tensile tests at different strain rates is studied in 304 stainless steel. It is observed that stress relaxation can obviously increase the elongation of 304 stainless steel in all cases. The elongation improvement of interrupted tension reaches to 14.9% compared with monotonic tension at 0.05 s^?1. Contradicting with the published results, stress drop during stress relaxation increases with strain at all strain rates. It is related with dislocation motion velocity variation and martensitic transformation.     

简易拉伸装置的设计及其在含氮奥氏体钢中子散射中的应用

结合原位中子小角度散射的实际要求,设计了一种整体结构简单、试样安装方便的U型悬臂式拉伸变形装置.该装置通过导向滑孔与移动滑杆间的耦合来确保实现单向拉伸变形;分别贴于试样平直部位与夹头圆柱部位的应变片组用于获取试样的应力-应变响应.分步拉伸试验表明,塑性变形过程中试样的应力松弛在停止加载后的前200 s最为显著,过后松弛较为缓慢.中子小角散射初步结果表明该装置能满足原位拉伸变形的要求,并在含氮奥氏体钢中纳米偏聚团对材料形变强化过程的影响机制研究中发挥着重要作用.     

The chloride stress-corrosion cracking behavior of stainless steels under different test methods

Chloride-induced stress-corrosion cracking (SCC) is one of the failure modes of stainless steels. Highly alloyed austenitic stainless steels S32654, S31254, and N08028, and duplex grades S32750 and S31803 possess much improved resistance to SCC compared with S30400 and S31600 steels. With the development of a database, SSData, experimental data collected from calcium chloride tests, autoclave tests, and drop evaporation tests were evaluated. Stress-corrosion cracking data generated by autoclave tests agreed well with the practical service conditions and can be used to discriminate alloys for SCC resistance in sodium chloride solution. Drop evaporation test data can be used in situations where evaporation may occur and cyclic loading may be involved. The SCC resistance of alloys under each method increased with increasing molybdenum equivalent Mo + 0.25Cr + 0.1Ni. For a given alloy, the testing result depends on the stress state and environment; different test methods can give different ranking orders concerning SCC resistance. The performance of duplex stainless steels in a chloride-containing environment at higher temperatures was not as good as expected when dynamic loading was involved.     

常温拉伸应力松弛试验初始试验力保持时间的研究

本文探讨了预应力钢材常温拉伸应力松弛试验中,初始试验力保持时间的意义与作用。分析和论述了试验设备、试验方法及试样结构等因素对应力松弛试验结果的影响。验证了初始试验力保持时间,可以一定程度地消除和抑制干扰因素对松弛试验结果的影响。     

D6A+20钢自动焊焊缝射线检测及裂纹成因分析

针对D6A 20钢异种金属机器人自动焊焊缝质量的射线检测问题,从焊接结构入手,合理安排射线检测工艺,在缺陷评定中排除焊缝成形干扰,实现了该椭圆多层焊缝的高质量检测和缺陷的准确定性.并分析了焊缝中裂纹产生在焊接性能良好的20钢根部的机理,其原因是D6A与20钢的厚度和抗拉强度差异太大,导致在焊接应力和拉伸应力的作用下,在20钢焊缝根部区域沿熔合线方向产生焊接裂纹.根据分析结果,改进焊接工艺后,裂纹得到了有效的控制.     

Calibration of anisotropic yield function by introducing plane strain test instead of equi-biaxial tensile test

The equi-biaxial tensile test is often required for parameter identification of anisotropic yield function and it demands the special testing technique or device. Instead of the equi-biaxial tensile test, the plane strain test carried out with the traditional uniaxial testing machine is suggested to provide the experimental data for calibration of anisotropic yield function. This simplified method by using plane strain test was adopted to identify the parameters of Yld2000-2d yield function for 5xxx aluminum alloy and AlMgSi alloy sheets. The predicted results of yield stresses, anisotropic coefficients and yield loci by the proposed method were very similar with the experimental data and those by the equi-biaxial tensile test. It is validated that the plane strain test is effective to provide experimental data instead of equi-biaxial tensile test for calibration of Yld2000-2d yield function.     

A Simplified Micromechanical Modeling Approach to Predict the Tensile Flow Curve Behavior of Dual-Phase Steels

Micromechanical modeling is used to predict material’s tensile flow curve behavior based on microstructural characteristics. This research develops a simplified micromechanical modeling approach for predicting flow curve behavior of dual-phase steels. The existing literature reports on two broad approaches for determining tensile flow curve of these steels. The modeling approach developed in this work attempts to overcome specific limitations of the existing two approaches. This approach combines dislocation-based strain-hardening method with rule of mixtures. In the first step of modeling, ‘dislocation-based strain-hardening method’ was employed to predict tensile behavior of individual phases of ferrite and martensite. In the second step, the individual flow curves were combined using ‘rule of mixtures,’ to obtain the composite dual-phase flow behavior. To check accuracy of proposed model, four distinct dual-phase microstructures comprising of different ferrite grain size, martensite fraction, and carbon content in martensite were processed by annealing experiments. The true stress–strain curves for various microstructures were predicted with the newly developed micromechanical model. The results of micromechanical model matched closely with those of actual tensile tests. Thus, this micromechanical modeling approach can be used to predict and optimize the tensile flow behavior of dual-phase steels.     

300M钢疲劳热耗散的试验研究

研究了300M钢疲劳损伤过程中的热耗散和温度演化规律,测试了300M钢在热处理和未经热处理状态下力学性能和疲劳性能。试验结果显示:经过热处理的300M钢其拉伸性能和疲劳性能都有显著提高,且在拉伸以及疲劳损伤过程中,温度升高更为明显。两种处理方式的试件显现出不同的热耗散规律。根据疲劳损伤过程中温度演化规律估算了疲劳极限σ-1,与试验值吻合很好,为快速确定300M钢的疲劳极限提供了一个方法。     

相同成分DP钢和TRIP钢部分力学性能的比较

对同一种钢板进行不同热处理分别制成具有相同铁素体含量的双相钢(DP钢)和相变诱发塑性变形钢(TRIP钢),并对其部分力学性能进行对比。比较发现,铁素体基体上不同的第二相使得材料力学性能产生巨大差异:马氏体使DP钢具有很高的抗拉强度,残余奥氏体则赋予TRIP钢优良的伸长率;DP钢拥有更加优良的加工硬化能力,TRIP钢则具有较为理想的烘烤硬化能力。试验还表明,考察DP钢和TRIP钢的烘烤硬化能力时,除柯氏气团外,内应力的消除也应该考虑其中。     

2D-C/SiC陶瓷基复合材料拉伸试验的声发射特性

对2D-C/SiC陶瓷基复合材料试样在室温条件下单调拉伸试验和循环拉伸试验的损伤声发射信号进行研究,利用无监督层次聚类分析方法对单调和循环拉伸试验的声发射信号进行损伤模式识别,得出了两种拉伸试验下试样都有相同的损伤分类。对每次单调加/卸载试验分别进行应力和声发射信号分析,得到了在循环加载区间和卸载区间试样的损伤情况。对比分析两种拉伸试验的声发射信号,得到两次试验中首次加载相同应力时,两个试样有同一种类的声发射损伤信号,从而说明循环加载对试样的主要损伤影响较小。     

Rapid Flow Stress Characterization of Steel

This rapid flow stress characterization concept involves rapid heating to an initial test temperature, T ₁, followed by loading and short-time stress relaxation measurement, followed by heating to a higher temperature, T ₂, followed by loading and short-time stress relaxation measurement, followed by heating to T ₃, and so on. This test sequence can generate stress-strain rate-temperature data over a wide spectrum, with a single specimen. The principal advantage of this method of flow stress characterization is its short-time format. The cost of specimen preparation is modest, as well. Beyond this, the test methodology provides very accurate temperature control. It also tests a given metallurgical structure, with minimal complications from structural evolution due to plastic deformation. This study has demonstrated the feasibility of this method on plain carbon and austenitic stainless steels, using a Gleeble testing machine. This includes demonstrated consistency between single-test-per-specimen data and data derived from sequential testing on a single specimen, as well as consistency with conventionally developed flow stress data.     

氢在钢的硫化物应力腐蚀破裂中的作用

本文研究了12MnMoVNbTi低合金钢在饱和H_3S溶液中的极化和应力腐蚀行为,并与电解充氢条件下的应力破裂行为进行了对比。证明钢中Mo、Nb含量的变化与热处理条件的不同对其一般腐蚀行为影响很小,但能显著改变其抗应力腐蚀性能,12MnMoVNbTi钢在H_2S介质中的应力腐蚀破裂行为与它们在充氢条件下的应力破裂行为非常类似,显示其应力腐蚀破裂的实质是氢脆。充氢条件下应力弛豫和恒载荷拉伸试验结果表明,氢有引起钢的软化和硬化的双重作用。由于氢的进入所产生的软化作用使钢在屈服强度以下发生塑性变形,但随后的硬化过程又使变形速度逐步减慢。这种由氢的作用引起的在较低应力下发生的塑性变形过程并不直接导致断裂,但塑性变形行为和氢应力破裂行为之间的关系表明,这种变形过程中的位错运动能够帮助氢的移动和向塑变区及裂纹尖端集中,促进氢脆断裂。     

残余应力对钢轨焊接接头落锤试验性能的影响

对钢轨窄间隙电弧焊接头热处理前后的残余应力分布进行了测量和比较,结合落锤试验结果和断口形貌,分析了焊接残余应力对钢轨接头落锤试验性能的影响.结果表明,热处理前,钢轨接头的轨腰和轨颚部位存在较大残余拉应力,在落锤冲击载荷作用下容易形成裂纹源,并沿轨腰向母材延伸、扩展、断裂;热处理后,钢轨接头的残余应力最大值下降1/2~2/3,抗冲击载荷能力显著提高,落锤试验时的钢轨接头沿焊缝中心或热影响区垂直断裂.钢轨接头存在较大残余应力时,在落锤冲击载荷作用下,容易在残余应力较大的部位产生裂纹,并加速扩展和断裂.     

K417材料激光冲击强化残余应力松弛预测

针对某型发动机涡轮叶片材料K417激光冲击强化后残余应力在高温下松弛的现象,分析了残余应力松弛的机理,并运用灰色理论建立了温度作用下残余应力松弛的灰色预测模型.该模型的计算结果和实验结果吻合良好,精度较高,为激光冲击强化后残余应力松弛的预测提供一种可行的方法.     

混流式转轮焊接残余应力测试新装置与新方法

混流式转轮叶片出水边焊接接头区域存在的较高残余应力是导致转轮疲劳开裂的重要原因,混流式转轮焊后及热处理后的焊接残余应力测试已经成为转轮制造过程中的必要工艺,其测试精度及效率对转轮制造质量及效率有重要影响.根据转轮的结构特点研发了新型残余应力测试装置,并根据转轮疲劳开裂的特点确定了针对混流式转轮焊接残余应力测试的新方法,实际应用试验结果表明测试所得结果能够真实反映热处理前后转轮易开裂区域的残余应力分布情况.新型测试设备及方法完全适用于混流式转轮的残余应力测试,而且具有非常高的测试精度及效率.     

联轴器螺栓紧固件的有限元建模仿真和试验分析

研究了联轴器螺栓紧固件在复杂载荷作用下的应力状态,对分析联轴器螺纹螺栓的失效具有重要价值。采用精确几何形状螺纹建模方法对联轴器的螺纹进行了建模,并将其嵌入ANSYS软件对螺纹螺栓的预紧力、联轴器受载后的等效应力和联轴器螺纹螺栓的结构应力进行了仿真分析,并进行了试验对比研究。结果表明：所建立的模型能很好地仿真螺栓自松弛现象,可以认为螺栓松弛乃至结构的疲劳强度对扭转载荷的大小更敏感,能为深入研究联轴器螺纹螺栓的失效提供参考。     

TiAl合金涡轮压缩损伤与拉伸断裂行为

为研究TiAl合金涡轮经压力作用后的组织损伤机制及性能弱化规律,设计了对TiAl合金涡轮先压缩再拉伸的实验方法。利用扫描电镜(SEM)对压缩后的涡轮轴颈表面及内部的滑移和微裂纹进行了分析,并观察了拉伸断口形貌。实验结果表明：随着前期涡轮所受的压力的增大,压缩后的TiAl涡轮剩余抗拉强度逐渐降低,当压力为610 MPa时,剩余抗拉强度仅为86 MPa,强度损失率高达70%。TiAl合金压缩过程中形成了以沿层裂纹为主、穿层裂纹为辅的变形损伤特征。与压缩轴成45°的最大剪应力方向上的沿层裂纹是TiAl合金压缩损伤的主要形式。压缩损伤后的TiAl合金涡轮拉伸断裂均发生在靠近涡轮浇铸冒口侧的细轴颈部位。受压变形后的片层组织中的微小裂纹在随后拉应力作用下继续扩展直至韧带桥被贯穿,小裂纹合并成大裂纹,在断口上表现出沿层和穿层的混合断裂形貌。     

Stress Dependence of Transformation Plastic Behavior

Transformation plasticity is known to play an important role in the course of heat treatment processes, and so affect the results of heat treatment simulations, which means that the transformation plasticity coefficient is necessary to be identifies. The authors developed a new method by use of four-point bending system of a beam to identify transformation plasticity coefficient taking advantage of its easiness and high accuracy compared with other conventional methods like tension test, etc., and identified the coefficient for four kinds of steels; plane carbon steel, Cr-steel, Cr-Mo steel and bearing steel. In this paper, further experimental data are presented for the steels if the coefficient Kp during pearlite transformation depend on the applied stress. Obtained results reveals that the stress dependence of Kp is rather trivial except for uncertain tendency detected in plane carbon steel. The relation between the Kp and carbon content included is discussed in comparison with other data referred from references.