掺杂钨丝脆断劈裂的研究

<正> 一、前言掺杂钨丝脆断和劈裂是灯丝质量方面最突出的问题。多数文献在论述脆断、劈裂的原因时,笼统地认为是由于掺杂元素和间隙杂质在晶界上富集所致。个别文献也提到组织不均匀是导致钨丝脆断、劈裂的原因之一。本文用扫描电镜和显微镜等手段对掺杂钨丝生产中主要环节和绕丝时所出现的脆断、劈裂的典型样品进行观测;探索恶化钨丝韧性,影响     

大规格高碳硬线82B拉拔脆断原因分析

采用金相组织检验分析等方法,分析了大规格82B拉拔劈裂脆断问题.结果表明:劈裂断口试样的中心处,由于锰、铬偏析而出现异常的马氏体组织,导致其变形与基体不一致,在拉拔过程中中心马氏体断裂成为裂纹源.断口附近表面存在结疤和擦伤等表面缺陷,中心马氏体和表面缺陷共同导致大规格82B拉拔劈裂脆断.通过优化合金元素锰、铬的成分含量...     

高碳硬线82B 劈裂状断裂原因分析

为探究引起高碳82B盘条劈裂状断裂原因,分析了82B的金相组织、夹杂物、断裂形貌及线材表面特征。结果表明:盘条表面质量缺陷导致拉拔过程中钢丝表面润滑不良、受力不均,引起钢丝表面组织异常,造成钢丝最终产生劈裂状脆断。     

对钨丝生产引进线的工艺改进

针对本公司所引进日本东芝公司钨丝生产线在生产中钨材经常出现脆断，劈裂等质量问题在进行大量分析、试验的基础上，采取对钨坯按晶型分类，对焊后钨杆进行不完全退火，对半成品和成品用加工率控制其力学性能等一系列改进措施，使产品质量得明显提高。     

氢与回火脆化对2．25Cr－1Mo钢局部脆断应力的影响

采用恒温有限元法，研究了一定温度下氢原子与回火脆化对三种不同成分２．２５Ｃｒ－１Ｍｏ钢局部脆断应力的影响。结果发现，可用局部脆断应力σｆ＊的变化衡量材料的回火脆化倾向，但由于晶界上杂质元素与氢原子分布的随机性，可能导致沿晶脆断应力的分散。在降低局部脆断应力的作用上，氢脆与回火脆化具有叠加关系。     

氢与回火脆化对2.25Cr—1Mo钢局部脆断应力的影响

采用恒温有限元法，研究了一定温度与氢原子回火脆化对三种不同成分２．２５Ｃｒ－１Ｍｏ钢局部脆断应力的影响，结果发现，可用局部脆断应力σ１的变化衡量材料的回火脆化倾向，但由于晶界上杂质元素与氢原子分布的随机性，可能导致沿晶脆断应力的分析，在降低局部脆断应力的作用下，氢脆与回火脆化具有叠加关系。     

炉卷轧机轧制温度对2507超级双相不锈钢脆性区长度的影响

应用EBSD技术研究了2507脆断处的组织,结果表明,脆断区域存在σ相,σ相比例偏高是其脆断的主要原因。分析了炉卷轧机轧制温度对其脆断区域长度的影响,轧制温度提高30℃头部区域脆性区长度缩短为35m,提高50℃缩短为28m,提高100℃则为16m。     

HRB400电弧焊接头弯折脆断分析

HRB400热轧带肋钢筋电弧焊接接头发生弯折脆断现象．昆钢技术中心对钢筋化学成分和物理性能进行检验,进行焊接模拟试验,分析钢筋脆断原因,并提出改进措施。试验研究表明,焊接缺陷、焊接工艺及冷弯弯心直径的选择太小,是造成焊接接头弯折脆断的主要原因。选用电孤焊T型焊接接头,可以避免施工中校正时钢筋发生脆断。     

HRB400E热轧带肋钢筋直螺弯曲脆断原因分析

某钢厂生产的HRB400EΦ22 mm直螺在反弯试验时发生脆断现象。通过成分分析、金相检验、扫描电镜以及力学性能等检验,分析脆断原因。结果表明:加热温度过高引起异常组织,使得钢筋产生脆断现象。     

锗单晶脆断强度的研究

不同生长条件和冷却方式下拉制的锗单晶按规定晶向切、磨成一定尺寸的试样片状,用CP-4A腐蚀液抛光,使表面光亮、平整,无划痕,无位错蚀坑,用三点弯曲方法测出脆断强度;研究了脆断强度与拉晶条件的关系;应用位错模型说明了锗单晶的脆断过程,探讨了锗单晶的脆断机理。     

Theoretical prediction of tensile strength of fibers as a function of thickness of brittle zones on fiber surfaces

A theoretical model of longitudinal strength of fibers as a function of the thickness of brittle zones on fiber surfaces was presented. Unifying parameters, corresponding to a formation of a notch due to a premature failure of the brittle zone, to an extension of the notch and to an interfacial debonding between the fiber and the brittle zone, were derived by modifying Weibull theory, fracture mechanics and shear lag analysis of Dow, respectively. A framework for interpreting the interrelation between the magnitudes of these unifying parameters and the failure mode of the fiber/brittle zone composites was carried out. It was shown that, if the thickness of the brittle zone is thicker than a critical value and if the interfacial bonding is stronger than a critical value, the fiber strength is reduced. Some examples of combinations of these unifying parameters given as a function of the thickness of the brittle zone were presented and the failure mode of the fiber/brittle zone composite was described schematically also as a function of the thickness of the zone.     

岩石材料脆性剪切破坏模式下的强度分析

使用声发射法与三轴试验相结合的方法对岩石试样微裂隙产生和发展进行监测,以获取岩石脆性剪切混合破坏模式的特点.采用断裂力学与岩石力学理论相结合的方式进行理论分析和试验数据处理,得到了试样三阶段特征强度随应力状态变化的规律,并提出了一种适用于岩石脆性、剪切混合型破坏强度分析方法,据此建立了Mohr-Coulomb、Griffith和Hoek-Brown等强度准则与脆、剪混合强度模型的关系.采用此模型对水厂边坡混合花岗岩的全应力-应变试验数据进行脆剪混合强度分析,理论值与试验值具有良好的一致性.     

Effects of the Loading History on the Local Buckling Behavior and Failure Mode of Welded Beam-to-Column Joints in Moment-Resisting Steel Frames

The cyclic behavior of welded beam-to-column joints for moment-resisting steel frames was assessed by constant amplitude cyclic quasi-static tests. Reanalysis of the results showed that the failure mode of the joints strongly depends on cycle amplitudes. A premature brittle failure of the welds may occur if the cycle amplitude is not large enough to cause local buckling of beam flanges. Influence of both flange and web slenderness ratios on local buckling behavior, investigated through an experimental parametric study, is discussed. Four tests, carried out adopting different variable amplitude displacement histories, confirmed that isolated large amplitude cycles have beneficial effects on the joint response, extending its life; on the contrary, many large cycles clustered together endanger the seismic performance of beam-to-column joints. Numerical analyses allowed interpretation of the experimental data in terms of local stresses and strains. For “large amplitude” cycles numerical results indicate a local state of strain causing a progressive collapse for low-cycle fatigue while, in case of “small amplitude” cycles, brittle failure mode is due to the ratcheting of material.     

FCB法焊缝CTOD测试及安全性评定

 用FCB法对船板钢进行焊接试验,发现在焊缝中存在内埋裂纹。通过CTOD试验对焊接试样进行测试,利用试验数据对船板的侧板和底板进行脆断分析和疲劳分析,考察在船板钢中存在的6 mm×2 mm的内埋裂纹的安全性。脆断评定结果表明等效裂纹尺寸a值小于侧板和底板的容许裂纹尺寸am值,这种缺陷可以接受。疲劳评定是假设在侧板和底板承受最大应力幅度条件下进行的,计算结果表明,经过40年,裂纹扩展甚微。     

粗轧区变形量对16MnR钢板探伤合格率的影响分析

针对某中板厂生产的16MnR钢板超声波探伤不合格现象,依照探伤结果取缺陷严重部位进行微观组织分析,结果表明：造成探伤不合格的主要原因是连铸坯中心偏析、非金属夹杂物造成的分层,从而导致脆性相与钢基体的剥离而出现内部裂纹。在其他轧制条件不变的情况下,通过优化粗轧阶段延伸轧制的压下规程,显著提高了探伤合格率。     

Contribution to the investigation of microsegregation processes in 13% Cr 4% Ni steel during long-term annealing at 400°C

The present paper deals with the study of the development of microsegregation processes in the 13% Cr 4% Ni martensiteaustenite stainless steel during long-term annealing. The long-term annealing of 13% Cr 4% Ni steel at 400°C is accompanied by the decrease in notch impact toughness values, which is associated with an increasing tendency to the occurrence of the brittle failures. The conditions for the transition from the transcrystalline brittle failure to the intercrystalline brittle failure depend on the initial heat treatment affecting the achieved microstructure of investigated steel. The higher frequency occurrence of intercrystalline failure on the fracture surfaces of notch impact toughness specimens is accompanied by an enrichment of the prior austenite grain boundaries by phosphorus and nitrogen. At the same time the enrichment of intercrystalline fracture surfaces by nickel, or chromium was also observed. The application of an additional intercritical annealing after quenching accelerates the formation of intercrystalline failure towards shorter times during the isothermal annealing at 400°C.     

Operational failure of large steel axles

Analysis of the failure of a shaft in the roof of the covered skating center at Krylatskoe (Moscow) indicates slow brittle failure by the hydrogen mechanism. Proposals are outlined for preventing defects that lead to brittle failure in such axles.     

The ductility of continuously-cast steel near the melting point—hot tearing

At temperatures near the melting point steels fail in a brittle manner. This brittle failure can lead to the formation of surface and internal cracks in continuously cast steel, during casting, if the steel is subject to a tensile strain. In this investigation the nature of the brittle failure has been considered for a wide range of continuously-cast steels, by examining the strength and ductility of the steels as a function of temperature, composition, and cast structure. The results show that for steels containing 0.05 to 0.12 pct C, brittle failure is due to incipient melting at grain boundaries at temperatures between approximately 40°C below the solidus and the solidus. The incipient melting is ascribed to solute or residual segregation, at the grain boundaries following extensive boundary migration. For steel containing approximately 0.16 pct C, with increasing test temperature brittle failure starts 70°C below the solidus. For steels containing 0.25 to 1.0 pct C brittle failure starts 40°C below the solidus over the entire carbon range. Failure due to melting alone occurs interdendritically at temperatures above the solidus. In general the melting or ductile-brittle transition temperatures are independent of the initial cast structure, or large increases in the solute or residual levels, other than carbon.     

The fatigue of pseudoelastic single crystals of α-CuAINi

The fatigue life of single crystal α-CuAINi has been studied on pseudoelastic cyclic loading. In general the fatigue life was quite poor with most specimens having less than 3000 cycles to failure. The fatigue life decreased significantly with increasing stress level. However, the fatigue failure was due primarily to stress-induced martensite formation, since if the stress level on cycling was not sufficient to form martensite, the specimen did not fail. The fatigue life appeared to be largely independent of percent strain, crystal orientation and environment of testing. Surface preparation, however, was very important with an electropolished specimen having a much longer life than an abraded one. Fatigue cracks grew only in the final few hundred cycles of the life of the specimen. Cracks initially grew in the direction of growth of the stress-induced martensite, approximately at 45 deg to the tensile axis. Final failure was due to brittle fracture caused by stress concentration at the tip of the fatigue crack, the α-CuAlNi being very brittle. Scanning electron micrographs of the fracture showed no fatigue striations but rather river markings spreading out from the point of nucleation of the fatigue crack, characteristic of a brittle material.     

External FRP Poststrengthening of Scaled Concrete Slabs

This research investigates the effect of externally bonded fiber-reinforced polymer composite strips and fabric to the soffit of scaled slabs. Thirteen slabs of size 2,290 × 480 × 102 mm were tested to failure with varying configurations of externally bonded composites, while monitoring deflections, strains, and damage development. The measured response is compared with analytical results to demonstrate an approximate analysis method. It is shown that, although the ultimate load level can be increased significantly, failure is associated with a drastically reduced deformation capability and a change from the conventional ductile mode of failure to a more brittle one. Failure is dependent on the form of the reinforcement used and is shown to be different based on type and configuration of the external strengthening system used. Failure mechanisms range from delamination within the concrete cover and separation between tows in the prefabricated strips, to tensile rupture in the case of fabric-reinforced composite layers. Mechanisms of failure and efficiency of strengthening schemes based on fiber configuration are discussed.