特种钢用结晶器铜管裂纹原因分析

通过对某特钢厂破裂的结晶器铜管进行金相实验，扫描电镜和能谱分析，并结合结晶器的生产，使用及失效过程情况，综合受力分析，认为铜管破裂原因主要是环境介质硫渗入形成硫化物，在拉应力作用下，裂纹沿脆性质眯扩展导致的破坏。     

影响结晶器寿命的原因及提高措施

通过对莱钢炼钢厂3#连铸机结晶器使用寿命低的问题进行调研分析,提出了降低结晶器铜管镀铬层磨损、一冷水质改善、改造结晶器铜管固定方式等措施,使得结晶器使用寿命明显提高。     

新型管式结晶器铜管的开发与应用

通过对管式结晶器铜管上口变形问题的分析、研究 ,开发出一种新结构的铜管 ,解决了影响结晶器铜管寿命的的一些难题 ,延长了其使用寿命 ,降低了生产成本     

结晶器铜管导热过程的研究

针对结晶器铜管导热过程进行研究，分析了影响顺铜管温度场的因素，对结晶器铜管变形造成的危害进行了论述。     

圆坯结晶器铜管温度场模拟

为了延长结晶器的使用寿命 ,必须了解铜管的温度场分布 ,故建立了圆坯结晶器铜管温度场的二维稳态柱坐标数学模型 ,并用该模型模拟了包头钢铁公司35 0 m m大圆坯连铸机结晶器铜管的温度场。得出的计算结果与实测结果相符 ,证明该结晶器铜管的设计合理     

淮钢方坯结晶器铜管温度的测定

通过分别在结晶器铜管内弧面、外弧面和侧面的不同位置埋设16支热电偶,并采用相应的测温软件,测定了不同拉速下铜管温度随浇注时间的变化关系,计算了不同高度上结晶器热流分布,分析了拉速对结晶器传热的影响。结果表明,开发的测温系统能够测量出铜管的温度场．结晶器热流与拉速之间没有明显的规律性变化。     

提高结晶器铜管使用寿命的措施

根据生产实际情况,对影响结晶器铜管使用寿命的原因进行了分析,采取改进设备和工艺参数,规范操作等措施后,结晶器铜管寿命显著提高。     

结晶器铜管电镀质量的改进

通过对结晶器铜管电镀质量差的问题的分析，结合生产实际，对影响结晶器铜管电镀质量的有关参数进行了改进，提高了铜管电镀质量，满足了生产需要。     

冷却水对结晶器铜管使用寿命影响的研究

本文分析了连铸结晶器铜管用的冷却水的流量，温度，流速，水质对铜管寿命的影响。找出了相关因素，提出了相应的对策，使结晶器铜管寿命大幅提高。     

圆坯结晶器铜管温度场模拟

为了延长结晶器的使用寿命,必须了解铜管的温度场分布,故建立了圆坯结晶器铜管温度场的二维稳态柱坐标数学模型,并用该模型模拟了包头钢铁公司Х３５０ｍｍ大圆坯连铸机结晶器铜管的温度场。得出的计算结果与实测结果相符,证明该结晶器铜管的设计合理。     

The relation between microstructure and toughness in 7075 aluminum alloy

Electron microscopy, fractography, and notched tear tests have been used to investigate the effects of heat treatment upon the fracture behavior of aged 7075 aluminum alloy sheet. Toughness, as measured by crack propagation energy, decreases as the yield stress increases; the toughness of an overaged structure is inferior to that of an underaged structure at the same yield stress. The decrease of toughness with increased aging time is accompanied by a change in fracture mode from predominantly transgranular to intergranular. Transgranular fracture proceeds by dimple rupture and is facilitated by chromium-rich particles which are dispersed throughout the microstructure. Intergranular fracture proceeds by the fracture of grain boundary precipitate particles. The variation of fracture mode with aging time is attributed to a steady decrease of the intergranular fracture stress relative to the transgranular fracture stress, due to increasing grain boundary particle size. A possible explanation of this effect is discussed using the stress concentration due to colinear crack arrays as an analogy. The effects of quenching variations and two-step aging are discussed. It is shown that, in aged 7075, microstructural variables such as the width of precipitate-free zones and the nature of the matrix precipitate do not have a controlling effect on toughness.     

Impact fracture toughness of porous iron and high-strength steels

The impact fracture toughness of sintered iron and high-strength sintered steels, with densities between 7.0 and 7.25 g/cm³, have been investigated by means of instrumented impact testing on fatigueprecracked as well as 0.17-mm-notched specimens. Experimental results show that the fracture behavior is controlled by the properties of the resisting necks at the crack/notch tip. The materials with impact yield strengths of up to 700 MPa display an increase in fracture toughness as the yield strength is increased. These materials undergo continuous yielding during loading, and ductile fracture takes place once the critical plastic strain is attained within a large process zone. A process-zone model, physically consistent with the fractographic observations, correctly rationalizes their impact fracture toughness. The materials with higher impact yield strengths display an impact curve which is linear up to fracture and are characterized by a fracture toughness which is independent of the yield strength. For these materials, the process zone reduces to the first necks at the crack/notch tip, and fracture takes place once the local applied stress-intensity factor reaches the fracture toughness of the matrix.     

The effect of hydrogen on fracture toughness of the Fe-Ni-Co superalloy IN903

Fracture toughness values and tensile properties were determined in the Fe-Ni-Co superalloy IN903* as a function of hydrogen concentration, loading rate, and grain size to define the effects of hydrogen on fracture toughness and failure modes. Tests using precracked, precharged three point bend samples showed that fracture toughness decreased from 90 to 50 MPa-m^1/2 as hydrogen increased from zero to 5000 appm. The decrease in fracture toughness was accompanied by a fracture mode change from microvoid coalescence in the uncharged samples to principally slip band fracture with some twin band and ductile intergranular fracture in the hydrogen charged samples. Fractographic observations and application of ductile fracture toughness models showed that fracture initiated at matrix carbides in all samples. These carbides established the critical fracture distance for all fracture processes observed in the fracture toughness samples. Hydrogen promoted the secondary fracture processes of slip band, twin band, and ductile intergranular fractures which lowered both the critical fracture strain and the fracture toughness of IN903.     

Fracture Toughness to Understand Stretch-Flangeability and Edge Cracking Resistance in AHSS

The edge fracture is considered as a high risk for automotive parts, especially for parts made of advanced high strength steels (AHSS). The limited ductility of AHSS makes them more sensitive to the edge damage. The traditional approaches, such as those based on ductility measurements or forming limit diagrams, are unable to predict this type of fractures. Thus, stretch-flangeability has become an important formability parameter in addition to tensile and formability properties. The damage induced in sheared edges in AHSS parts affects stretch-flangeability, because the generated microcracks propagate from the edge. Accordingly, a fracture mechanics approach may be followed to characterize the crack propagation resistance. With this aim, this work addresses the applicability of fracture toughness as a tool to understand crack-related problems, as stretch-flangeability and edge cracking, in different AHSS grades. Fracture toughness was determined by following the essential work of fracture methodology and stretch-flangeability was characterized by means of hole expansions tests. Results show a good correlation between stretch-flangeability and fracture toughness. It allows postulating fracture toughness, measured by the essential work of fracture methodology, as a key material property to rationalize crack propagation phenomena in AHSS.     

Fatigue and fracture behavior of an aluminum-lithium alloy 8090-T6 at ambient and cryogenic temperature

An investigation has been made of the fatigue and fracture behavior of an Al-Li-Cu-Mg-Zr 8090-T6 alloy at room (300 K) and liquid nitrogen (77 K) temperatures. The fatigue and fracture strengths, as well as ductility of the alloy, have been found to increase with decreasing temperature. The observations by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) reveal that the changes in fatigue and fracture behavior with temperature are considered to be associated with the change in the deformation and fracture modes. It has been found that the occurrence of the localized shear deformation bands in which the hard precipitates are sheared by moving dislocations is responsible for the reduction of fatigue and fracture strengths as well as ductility of the alloy at room temperature. However, the improvement of both strength and ductility of the alloy at liquid nitrogen temperature might be attributed to the deeper and larger delamination that occurred on the fracture surface.     

浅谈铝型材室温断后伸长率的检测

从试样加工形状尺寸,取样方向,拉伸速率,以及人工测量与机器测量等方面,对公司生产的铝挤压型材断后伸长率进行测试分析.得出结论,圆形试样的断后伸长率比矩形试样的断后伸长率略大;平行长度越大,断后伸长率越大;横向取样的断后伸长率明显小于纵向取样的断后伸长率;人工测量比机器测量更可靠,更接近真实的断后伸长率.     

激光切割的钻具热影响区裂纹形成的研究

采用脉冲CO2激光切割的钻具出现了断裂的现象。研究了断口的表面形貌及成分,以及热影响区的尺寸和显微组织;通过断口显微分析,探讨了热影响区显微裂纹的形成,并提出了相应的改进措施。     

砂岩Ⅰ型断裂的尺寸效应试验研究

通过对尺寸成等比例的砂岩试样进行三点弯曲试验,研究了I型断裂问题中试样尺寸对砂岩断裂参数的影响.结果表明:随着试样尺寸的增大,名义张拉强度减小,名义断裂韧度和破裂过程区长度增大,三者均为试样尺寸的函数.基于试验结果,引入有效破裂过程区长度cf,建立等效线弹性断裂力学尺寸效应模型,通过理论分析,发现其尺寸效应曲线介于理想脆性和理想塑性材料之间,体现出准脆性材料的尺寸效应特点,并计算得到了不同尺寸试样的破裂过程区长度等断裂参数.为验证该尺寸效应模型在砂岩中的正确性,采用数字图像匹配技术(DIC)测定相应尺寸砂岩试样的破裂过程区长度,测定结果和理论模型计算值相符.      

河南龙门店银矿断裂构造分形特征分析

龙门店银矿断层发育,主要有NE、NW和NNE向3组断裂,其中NE和NNE向断裂与成矿关系密切,矿体的形成与分布严格受断裂控制。为研究断裂分维特征与矿体的关系,采用计盒维数法计算出龙门店银矿断裂的分维值为1.295,中部分维值为1.319,性质偏于剪性;与成矿有关的NE-NNE向断裂在全区和矿区中部的分维值分别为1.197和1.237,为剪性断裂。二者判定系数R²均＞0.98,说明矿区断裂具有良好的自相似性。与成矿相关的NE-NNE向断裂分维值D＞1.17所圈闭的太华群片麻岩是有利的成矿部位,全区断裂分维值D＞1.25作为辅助指标。采用分维值定量描述断裂的自相似性,对成矿预测有一定的指导作用。     

Variation of the fracture mode in temper embrittled 2.25 Cr-1 Mo steel

Temper embrittled 2.25 Cr-1 Mo steel was tested by slow bending of notched specimens at various temperatures, and the fracture mode was examined by SEM fractography. Comparison of the local fracture mode with the load-displacement curves showed that intergranular fracture occurred most prominently in the region where cracking initiated, but that the fracture mode tended to change to cleavage as the cracking propagated and accelerated. When the area fraction of intergranular fracture was plotted as a function of test temperature, a maximum appeared, and the temperature of this maximum tended to increase with specimen hardness. It is argued that the gap between the cleavage fracture stress (σ _F ^CL ) and that of intergranular fracture (σ _F ^IG ) was greatest at some particular temperature, allowing a maximum amount of grain boundary fracture. However, the gap (σ _F ^CL -σ _F ^IG ) diminished as cracking accelerated, and the fracture mode tended to switch to cleavage. The contrast in behavior between temper embrittled CrMo and NiCr steels is discussed.