反复焊接对超低碳奥氏体不锈钢耐腐蚀性能的影响

通过对反复焊接1～5次的超低碳奥氏体不锈钢的晶间腐蚀试验及应力腐蚀试验，研究了反复焊接对超低碳奥氏体不锈钢的耐腐蚀性能的影响。试验结果显示，在同一部位反复焊接5次后，超低碳奥氏体不锈钢的晶间腐蚀倾向和应力腐蚀敏感性没有发生明显变化，表明超低碳奥氏体不锈钢在选择合适的焊接材料、焊接工艺和焊接方法的前提下，同一部位可反复焊接5次，而其耐腐蚀性能不会受到影响。     

奥氏体不锈钢压力管道的应力腐蚀开裂及预防

在化工领域,输送腐蚀性介质的压力管道常用的材料为奥氏体不锈钢,而应力腐蚀开裂是奥氏体不锈钢压力管道最主要的失效方式。该文主要对奥氏体不锈钢压力管道应力腐蚀开裂的机理、主要影响因素及预防措施进行了分析讨论。分析发现:奥氏体不锈钢压力管道应力腐蚀开裂机理根据输送介质的不同可分为氢致应力腐蚀开裂和"滑移-溶解-断裂"模型;其腐蚀速率主要受拉应力、输送介质腐蚀性、运行温度、氢元素、输送介质对管壁的冲蚀等因素的影响;可通过采取合理选用材料及焊条、优化焊接工艺、避免产生应力集中点、防止腐蚀溶液富集、改变输送介质成分及运用阴极保护法等措施减缓应力腐蚀开裂的发生。     

含锰奥氏体钢的发展（续）

应力腐蚀裂纹奥氏体不锈钢,其抗应力腐蚀裂纹的能力一般不如铁素体不锈钢。Cihal曾提出镍是造成奥氏体不锈钢应力腐蚀裂纹的主要原因。他发现无镍不锈钢(例如03X 13АГ19)有着良好的抗应力腐蚀性.至少与Cr-Mo铁素体钢相等,但如果     

奥氏体不锈钢在高浓度氯化物溶液中的应力腐蚀断裂

本文主要是讨论奥氏体不锈钢在高浓度氯化物溶液中的应力腐蚀断裂速度和形态与环境因素、材料因素和应力因素的关系。对不锈钢的实际应用和开发耐氯化物应力腐蚀的新型奥氏体不锈钢有一定的参考意义。     

304不锈钢焊接接头的耐应力腐蚀性能

碳钢/304不锈钢复合管如果不锈钢钢管的焊接工艺参数不当,焊接接头便容易发生应力腐蚀。采用钨极氩弧焊方法焊接了304不锈钢钢管,通过慢应变速率拉伸和双环动电位再活化试验研究了不同焊接工艺参数焊接接头的耐应力腐蚀性能。结果表明,可有效提高耐应力腐蚀性能的最优焊接工艺:氩气流量为12~15 L/min,焊丝为ER308,焊接电压为50 V,电流为50 A,焊接速度为8~10 cm/min;选择合适的焊丝和降低焊接电流可有效增加304不锈钢焊接接头处的耐应力腐蚀性能。     

国外某些特种钢和特种合金的发展动向

不锈钢的发展趋势在不锈钢方面,铬仍保持较高的比例。由于铁素体不锈钢所需的合金元素含量低,成本低,所以发展的趋势是用铁素体不锈钢代替奥氏体不锈钢。铁素体不锈钢具有它独特的使用性能。如抗氯化物应力腐蚀裂纹、在氧化性水介质中的耐蚀性、高温抗氧化性和在氯化物介质中抗锈斑和腐蚀裂纹等。而且这种钢的塑性好,便于成形和焊接。     

聚合装置金属腐蚀与防护

本文简述聚合装置常见的金属腐蚀,并对腐蚀类型提出防护措施。近年来,在化工装置中铬镍不锈钢(奥氏体)的用量越来越多,据统计,其用量约占不锈钢用量的80%但奥氏体不锈钢在含有对应力腐蚀敏感离子(如Cl-、OH-一等)的溶液中,受应力的部分(如焊缝附近)则可能产生危险的应力腐蚀破裂。尤其是含Cl-的溶液,在造成奥氏体不锈钢应力腐蚀破裂的事故中约占70%以上。Cl-浓度越大,越容易开裂,但并没有明确的不发生开裂的限界浓度。     

大厚度奥氏体不锈钢筒体填丝激光焊接变形和应力分析

目的 研究大厚度奥氏体不锈钢筒体填丝激光焊接,优化结构设计和工艺设计。方法 建立大厚度奥氏体不锈钢筒体填丝激光焊接数值分析模型,通过数值模拟的方法,定量分析大厚度奥氏体不锈钢筒体焊接变形和应力。结果 零件下部38 mm厚焊缝位置处的最大径向收缩量为1.2 mm;零件下部60 mm厚焊缝位置处的最大径向收缩量为2.0 mm;零件中部60 mm厚焊缝位置处的最大径向收缩量为1.9 mm;零件上部60 mm厚焊缝位置处的最大径向收缩量为1.8 mm。填丝激光焊接轴向收缩量为0.55 mm。焊接残余应力最大值在450 MPa左右,应力主要分布在焊缝附近。热处理后,焊接残余应力都有明显降低,最大残余应力从450 MPa左右降低到200 MPa左右,焊接残余应力范围存在一定程度减小;焊接残余变形变化较小,热处理后某些位置的变形略微有所增大。结论 模拟结果表明,大厚度奥氏体不锈钢筒体填丝激光焊接变形和应力在可接受范围内,焊后热处理对释放残余应力有重要作用。     

二元结构不锈钢可抵御氯化物应力腐蚀

芬兰奥托昆普炼钢厂报道，LDX2101是一种二元结构不锈钢。它拥有高强度和出色的抗氯化物应力腐蚀断裂性能。双炼钢由50％铁素体和50％奥氏体组成。这种钢材拥有400系列铁素体不锈钢的高强度和抗应力腐蚀断裂性能，同时具有300系列奥氏体不锈钢的一般抗腐蚀能力与易于制造的综合性能。     

不锈钢卡箍条带的沿晶应力腐蚀开裂

本文通过对某型飞机不锈钢(2Cr13Ni4Mn9)凸缘卡箍条带断裂件的化学成分、金相组织、晶间腐蚀性能、宏观及微观断口形貌、零件应力状态及工作环境的分析,以及模拟试验,评定其断裂为沿晶形态的应力腐蚀断裂;还讨论了奥氏体不锈钢应力腐蚀裂纹的扩展途径,认为具有部分形变马氏体的奥氏体不锈钢在含有Cl~-的弱腐蚀介质中,在50～150℃温度下长期服役,受拉伸应力与腐蚀介质的共同作用,     

book reviews

Book reviewed in this article:
Electrical Transducers for Industrial Measurement by P. H. Mansfield
Statics, Structures and Stress by W. Fisher Cassie     

Stress distribution in damaged composite laminates under transverse impact

Studies on damage in composite laminates subjected to central and normal impact are conducted by a 3-D finite element analysis. The stress analysis is carried out by developing a constitutive equation of composite laminates coupled with the damage. Effects of the damage on the stress distribution in the laminates are investigated in details. The obtained contact force history correlates well with the results reported in literatures. Stress distributions across the thickness of the elastic non-damaged laminate show a probable distribution of delamination. The simulated result for delamination is coincided with the observation of experiments. Stress distributions for the damaged laminates show that the damage releases strain energy and lessens stress concentration.     

The strength of structures and the applications of the fracture mechanics

After a short review of the papers by Odorico and Bathias presented to the AGARD Structures and Materials Panel Specialists' Meeting on Fracture Mechanics Design Methodology, 28–29 September 1976, London, the place of Fracture Mechanics in the Strength of Structures domain is considered as well as the still limited help afforded to the designer by the mass of published Fracture Mechanics data and the means of increasing the practical usefulness of these data by carrying out detailed investigations of actual cases of local failures occurring in static strength tests, full-scale fatigue tests and of damages in operations are discussed. It is proposed to discard the academic domain of cracks assumed to exist at the centres of thin sheet panels, far from the most probable damage origins, and to attempt to define classes of actual problems related to known or unknown stress concentrations in assemblies. These classes are so general that they justify detailed investigations which will supply tables of numerical data rapidly usable by the designer.     

Nanoindentation of hard multilayer coatings: Finite element modelling

Stress concentrations undermine the load-bearing ability of superhard TiSiN coatings. Experimental studies have shown that multilayer coatings that contain TiSiN layers alternating with ceramic layers with dissimilar mechanical properties suppress contact damage during nanoindentation. In this work, nanoindentation-induced deformation in TiSiN-based multilayer coatings was simulated by means of finite element modelling (FEM). Stress distributions under moderate indentation loading in the structure were quantified with particular emphasis on the relationship between stress concentrations and crack initiation. The results showed that the structural layering can be used to modify the stress distribution, and lower the overall stress level within the coating. In the case of radial tensile stresses at the coating/substrate interface, a reduction ∼50% has been achieved through layering. The resistance to shear damage can also be improved by optimising the multilayer structure.     

Weight Function Method for Stress Intensity Factor of Internal Surface Semi-elliptical Crack in Elliptical Holes

The hatches for inspecting are usually designed with elliptical holes in airplane structures, so computation of the stress intensity factor of three dimensional crack at elliptical holes is pivotal for damage tolerance analysis of these structures. In this paper, weight function is derived for a two dimensional through cracks at elliptical holes by applying a compounding method. Stress intensity factor formulas for an internal surface semi-elliptical crack in elliptical holes are obtained wing the three dimensional weight function method. Stress intensity factors for an internal surface semi-elliptical crack in elliptical holes under remote tension are computed. At the same time, research on how radius of curvature for elliptical holes affect stress intensity factors was conducted. Stress intensity factors decrease when radius of curvature increases. Some results and conclusions which are of practical value are given.     

Evaluation of different advanced finite element concepts for detailed stress analysis of laminated composite structures

Despite their high specific stiffness and strength, laminated composite materials, e.g. fibre-reinforced plastic plies stacked at different fibre orientations, are susceptible to damage. Damage can be divided into interalaminar damage and interlaminar damage. Delamination is a typical kind of interlaminar damage which occurs in laminated composite materials, often accompanied with intralaminar damage, and may lead to a catastrophic structural collapse. The first and most crucial step in the prediction of failure of Laminated Composite Structures (LCS) is to accurately determine the stresses, particularly the three transverse stress components, also called the interlaminar stresses. It is proposed in the present paper that the integration of a displacement based solid-shell formulation and partial-hybrid stress formulation will lead to an accurate and robust solid-shell element, suitable for the efficient and detailed interlaminar stress calculation.     

Line spread function formulation proposed by W. H. Steel: a revision

A revised formulation of the image light distribution of an incoherent line source proposed by Steel [Rev. Opt. 31, 334-340 (1952)] is presented. Analytical and numerical results based on this new representation are given. We explicitly show that a major error in Steel's final expression generates singularities, thereby preventing convenient numerical computation.     

Thermoelastic Stress Analysis of damage mechanisms in composite materials

A methodology for the application of Thermoelastic Stress Analysis (TSA) in damage studies of glass reinforced polymers is established. Test specimens have been designed to promote certain damage types and the methodology applied to each. It is shown that a TSA approach can evaluate fibre breakage, matrix cracking and delamination damage. Metrics are established based on calibrated strain data obtained from the TSA. It is shown that these can be used to assess the condition of a component throughout its fatigue life.     

Analytical modeling for life extension of aging equipment

Rising replacement costs for all types of structures continue to pressure the technical community to find methods for reliably extending the useful lifetime of existing structures. Structures having significantly long remaining lives from reliably detectable levels of damage are the best candidates for lifetime extension. Methods for identifying the best candidates, methods for developing and validating analytical life prediction models, and areas which need improvement are discussed.     

含银纹的高聚物裂纹扩展

根据已有的实验结果,考虑银纹损伤演变规律,假设裂尖银纹模型,导出Ⅰ型裂纹准静态下裂纹尖端银纹增长的微分方向和稳态扩展的方程,研究了裂纹长度及其扩展速度随时间的演变规律,初步分析了银纹损伤区平均,应力的变化,对含Ⅰ型裂纹ＰＭＭＡ的寿命进行了探讨。