疲劳失效机理及热轧H型钢疲劳断口分析

介绍了疲劳断口类型、形貌及形成机理,并对热轧H型钢疲劳断口进行了分析,为今后型钢产品疲劳研究奠定基础。     

16Mn拉伸断口白斑形成原因分析

本文通过金相和断口分析，对１６Ｍｎ拉伸断口白斑形成的原因及形成机理进行了分析。     

桥梁钢断口与工艺参数的关系

本文根据生产实验数据,用逐步判别分析的方法建立了断口判别函数及预控方程,对影响16Mn桥板断口的主要因素进行了定量分析。且根据分析结果修订了16Mn桥板的内控化学成分。通过对断口的预控,明显地提高了断口合格率,使1985年至1986年上半年热轧状态断口合格率达94.03％,比1984年提高了9.84％。     

室温大气环境下欠时效态3J21合金的拉伸性能

在万能拉伸试验机上对室温大气环境下欠时效态3J21合金的拉伸性能进行研究,并采用金相显微镜、X射线衍射仪对欠时效态金相组织及物相进行分析,采用TEM对固溶态、欠时效态试样及拉伸断口附近形变的显微组织进行分析,采用扫描电镜（SEM）对拉伸断口进行观察。结果表明,室温大气环境下欠时效态3J21合金的拉伸断口为韧窝断口,断口附近显微组织中滑移线之间的距离较小。欠时效态3J21合金具有较好的强度和塑性配合。同时讨论了室温大气环境下欠时效状态对3J21合金拉伸性能的影响。     

SWRH82B钢盘条拉伸试样断口形貌分析

采用宏观检验及扫描电镜等方法,对SWRH82B钢盘条热轧后及不同时间时效后的拉伸试样断口形貌进行观察,并结合断面收缩率变化规律对两者之间的关系进行分析研究。结果表明:SWRH82B钢盘条热轧后拉伸试样断口的纤维区较小、断面收缩率低,随着时效时间的延长,纤维区逐渐增大,断面收缩率提高。另对异常断口的产生原因进行了分析。     

高强度船板拉伸断口分层原因分析

针对高强度船板拉伸试样断口出现分层的问题,对典型断口分层试样和断口合格试样取样进行金相检验及扫描电镜能谱分析,结果表明,异常断口试样夹杂物级别高,试样心部组织晶粒粗大,带状组织明显且有裂纹,分析认为,2.0级以上的硅酸盐夹杂和MnS夹杂、28μm宽的珠光体带及Ti、Nb元素的富集是导致拉伸裂纹进而出现断口分层的主要原因。     

X100管线钢断口分层机理分析

根据X100管线钢断口分层现象,对该钢圆棒形及板形拉伸试样断口及不同温度下冲击试样断口进行宏观观察、显微分析、金相观察和EBSD织构分析。结果表明,随拉伸试样形状及尺寸的变化,裂纹分层现象趋势不同,随冲击试验温度降低,裂纹趋势加剧,裂纹的萌生以及扩展受晶界的限制。EBSD织构分析表明,沿{113}〈110〉方向,在一定微区存在较强的织构,促进了断口分层的产生。     

82B盘条断口典型形貌及产生原因分析

利用扫描电镜和光学显微镜对82B盘条典型断口样的形貌及夹杂物进行观测和对用4%(质量分数)硝酸酒精侵蚀的金相样的表面质量和心部组织进行分析。结果表明,造成黑心白点断口异常断裂的原因是熔渣卷入形成的大颗粒夹杂;脆性平齐断口断裂主要是由心部马氏体、网状渗碳体及边部增碳组织等不良组织和夹杂物造成的;斜茬状横裂纹断口断裂主要是由于组织存在马氏体和铸坯中存在有缩孔;劈裂断口主要是由于碳偏析造成的;而笔尖断口主要是由于组织中的人字微裂纹和网状渗碳体组织造成的。     

管线钢落锤撕裂性能评定影响因素

从冲击能量、锤击速度、对中装置及异常断口四个方面对管线钢落锤撕裂性能的影响因素进行了分析和讨论。结果表明,锤击能量过大不能真实反映材料断裂撕裂性能,锤击速度过大会使材料脆性增加且易发生异常断口,对中装置必须经常检查和调整,异常断口评定遵循原则才能得出准确的评定结果。     

Q345B钢Z向拉伸断口形貌的分析

通过对不同炉、批次Q345B钢Z向拉伸断口形貌进行分析,研究了断口形貌与塑性夹杂物级别和Z向断面收缩率（Z）之间的关系,指出在一定的硫含量条件下,塑性夹杂物级别是决定断口形貌及Z向断面收缩率的关键.     

Quantitative fractography: A modern perspective

The important aspects of quantitative fractography as a new analytical tool for understanding material fracture are discussed. The special considerations that rise in the quantification problems are examined from the purview of stereology. Two major experimental techniques for obtaining geometrical information about the fracture surface topography are critically evaluated. These methods are based on stereophotogrammetry or vertical sectioning procedures-both of which yield estimates of the true fracture surface area. The profile and surface roughness parameters which are required to transform measurements made on flat SEM fractographs to the true quantities in the fracture surface are introduced. The two roughness parameters are related by a simple parametric equation, permitting the fracture surface area to be calculated from the experimental measurement of the profile roughness parameter. Alternatively, it is shown how the fracture surface area can be obtained from the angular distribution of the profile elements by employing a transform procedure. The concept of “fractals” as it applies to quantitative fractography is introduced. Recently developed relationships which describe the true variation of the profile and surface roughness parameters with the size of the measuring unit are presented. Calculations are made of the mean area and perimeter length of dimples in the fracture surface of a 4340 steel. Three fracture surface configurations are examined: (1) an assumed flat- , (2) an assumed randomly-oriented- , and (3) the actual partially-oriented fracture surface. Significant differences are demonstrated between the true and the assumed situations, illustrating the importance of quantitative methods in fractography. By means of examples, it is shown how the quantitative methods permit detection of subtle changes in the fracture surface topography as influenced by the materials’ microstructure. This paper is based on a presentation made at the symposium “Stochastic Aspects of Fracture” held at the 1986 annual AIME meeting in New Orleans, LA, on March 2-6, 1986, under the auspices of the ASM/MSD Flow and Fracture Committee.     

Cu-5%Cr合金拉拔断丝原因检测分析

针对Cu-5%Cr复合材料在拉拔过程中常出现的断丝现象,用扫描电镜对拉拔断丝样品进行宏观和微观断口形貌观察及分析.结果表明,断口形貌为杯锥断口,属典型的微孔聚集型断裂.在拉拔过程中,丝材中存在的大量细小弥散的第二相Cr颗粒与Cu基体变形不协调,是微孔产生和裂纹扩展的主要原因.试验发现去除退火后丝材表面氧化皮、保证良好的润滑效果、采用合适的拉拔变形量可以有效的避免断丝现象的发生.     

Φ35mm40CrNiMoA钢剪切断面异常分析与改进

对比分析了不同批次Φ35mm40CrNiMoA钢剪切正常断面与异常断面的宏观形貌、化学成分、金相组织、硬度,综合分析确定钢材交货状态不同、金相组织差异较大、导致硬度差别大,是造成剪切断面异常撕裂的主要原因。热轧态钢材硬度高,剪切断面质量较好;退火态钢材硬度值低,剪切断面易出现撕裂。     

Use of the spiral pin for fracture of the humeral neck

Our new method of intramedullary fixation of humeral neck fracture is described. Spiral pin is made of stainless steel. The top is coiled, and the end is threaded. It is inserted from a small incision over the posterior surface of the supracondyle. It is passed across the fracture site into the head of the humerus, where it locks the head. The fracture surface is pressed together by tigtening nuts. The fracture fixation allows early movement of the shoulder joint. The method was used in eight patients. The average age was one-year-old.     

Analysis of liquid metal embrittlement from a bond energy viewpoint

Absorption induced embrittlement of solid metals by certain liquid metals is analyzed through an Engel-Brewer calculation of the solid-liquid interaction energy, and the effect of the latter in reducing fracture surface energy. The reduction in fracture surface energy is estimated by comparison of the electronic contribution to the solid-liquid interaction energy with solid-solid bond energy for some 40 liquid-solid couples. Regular solution theory is used to estimate mutual solubility as the relative difference in parameter values. Embrittlement can be predicted by using reduction in fracture surface energy and solubility parameter difference as critical variables. The effect of solute additions to the liquid on the degree of embrittlement is interpreted via the same two variables; the principal effect of solutes is to modify solubility relationships at the solid-liquid interface. Finally, since solute additions to the solid may affect the yield stress, Petch slope and fracture surface energy in air, the Cottrell-Petch fracture relation is shown to be a necessary framework for interpreting the effects of such additions on embrittlement phenomena.     

65Mn盘条拉拔过程中的断裂分析

对首钢65Mn弹簧盘条在拉拔过程中的断裂问题进行了探讨，通过观察分析不同形态的断口发现．杯锥状断裂、齐平状断裂和表面横裂是盘条在拉拔过程巾断裂的主要形式，盘条中的中心残余缩孔、大型夹杂及表面缺陷等是导致65Mn弹簧盘条断裂的主要因素。     

Relationship between fracture toughness, fracutre path, and microstructure of 7050 aluminum alloy: Part II. Multiple micromechanisms-based fracture toughness model

A multiple micromechanisms-based model is developed to quantitatively relate the fracture toughness of partially recrystallized 7XXX aluminum alloys to their fracture surface morphology. The model is verified using the experimental data on partially recrystallized 7050 alloy reported in the companion article. It is then used to obtain a quantitative relationship between the fracture toughness and microstructural attributes. The model relates fracture toughness to microstructural parameters such as degree of recrystallization, grain size of recrystallized grains, thickness of recrystallized regions, total surface area of the constituent particles per unit volume, and microstructural anisotropy. The model predicts the changes in the fracture toughness with the specimen orientation.     

高强船板拉伸试验断口分层的原因分析

高强船板拉伸试验后出现断口分层现象。利用低倍检测、扫描电镜能谱仪和金相显微镜,对断口以及平行于拉伸方向、垂直于钢板表面的剖面进行了观察、检测和分析,指出分层现象与板厚中心偏析处的硫化物夹杂、带状组织、未轧合孔洞有关。     

Fractal analysis on the fatigue fracture surface along the crack propagation direction

The fractal dimension along the crack propagation direction on the fatigue fracture surface of a dual-phase steel was investigated by both vertical section profile method and secondary electron line scanning method. Results from the vertical section profile method showed that during the crack propagation, the fractal dimension of the fracture surface increases with increasing stress intensity factor, however, the secondary electron line scanning method presented somewhat different results of fractal dimension and was proved not feasible in all kinds of fracture surfaces, so this method is not suggested in calculating the fractal dimension of the fracture surface.     

Environmental embrittlement caused by hydrogen for intermetallic compounds: Preliminary model of ductility reduction

The reduction of fracture elongation caused by environmental embrittlement has been dealt with for intermetallic alloys as follows. The fresh surface that is formed by plastic deformation increases with an increase in tensile deformation, and hydrogen permeating through the fresh surface into the specimen increases and embrittles its surface layer. Thus, a microcrack nucleates at the surface layer. The crack propagates unstably through the specimen because of the low fracture toughness of intermetallic alloys, resulting in the fracture of the specimen. Hydrogen permeating into the specimen increases with the increasing fresh surface area and increasing period of exposure to the environment. The dependence of fracture elongation on strain rate and hydrogen pressure has been described by a phenomenological and preliminary model, which has been proposed according to the consideration mentioned previously. The experimental data which were reported for intermetallic alloys have been compared to the phenomenological model.