离子渗碳层中的晶间脆性SCIEI

本文对20Cr2Ni4A钢离子渗碳层出现的沿晶断裂的原因进行了分析,结果表明,渗碳层中的残余奥氏体与在该区域产生的沿晶脆断无关。TEM分析和Auger电子能谱分析表明,形成沿晶断裂的主要原因是S,P等杂质元素在原奥氏体晶界的偏聚。采用二次加热淬火可以消除这种现象。     

EFFECTS OF CARBON AND YTTRIUM ON 500℃ AGING EMBRITTLEMENT OF ALLOY Fe-15Cr-4Al

测定了Ｆｅ－１５Ｃｒ－４Ａｌ合金在５００℃的时效脆化动力学，利用内耗，ＴＥＭ，ＥＰＭＡ和ＳＥＭ等手段研究了合金在时效后的组织变化和断裂行为。结果表明，时效脆化第一阶段（０－１００ｈ）主要是碳化物在α相晶界析出的作用，它损害界面结合，降低断裂应力，使塑性在时效０．２５ｈ后消失；第二阶段（１００－１０００ｈ）主要是富Ｃｒ－α＇相均匀析出的作用，它通过强化基体引起二次脆化。含０．２和０．４％的Ｆｅ－１５     

The influence of aging treatments on sulfide stress corrosion cracking of PH 13-8 Mo steel welds

Slow displacement rate tensile tests were carried out to study sulfide stress corrosion cracking (SSCC) of PH 13-8 Mo stainless steel welds in a saturated H₂S solution. The welds aged in the temperature range of 482-593 °C were susceptible to SSCC; the fracture surfaces revealed mainly quasi-cleavage fractures after notched tensile tests. However, the SSCC susceptibility in terms of the percentage loss of the notched tensile strength (NTS) of the welds was dependent on the aging treatment. The SSCC resistance and the austenite content of the welds increased with the aging temperatures. The presence of greater amounts of austenite, mainly reverted austenite, in the W1100 specimen (the weld aged at 1100 °F or 593 °C) than that in other aged specimens could account for its lower hardness and better SSCC resistance. On the other hand, the AW (as-welded) specimen containing a small amount of retained austenite films in a soft matrix exhibited a slightly improved SSCC resistance than that in the W1100 specimen. The lower hardness of the AW specimen was owing to the absence of fine coherent precipitates, leading to a reduced local stress and an enlarged plastic zone located in front of the notch in the test. With lower hardness, the local stress would also be lower and less likely to exceed some critical stress for failure in the saturated H₂S solution. For the aged specimens, the hardness/strength level and the amount of reverted austenite were the important factors that affect SSCC susceptibility.     

Hydrogen embrittlement susceptibility and permeability of two ultra-high strength steels

Slow displacement rate tensile tests were carried out in a saturated H₂S solution to investigate the effect of hydrogen embrittlement on notched tensile strength (NTS) and fracture characteristics of two ultra-high strength steels (PH 13-8 Mo stainless steel and T-200 maraging steel). Hydrogen permeation properties were determined by an electrochemical permeation method. The results of permeation tests indicated that over-aged specimens showed a lower diffusivity/hydrogen flux and higher solubility than those solution-annealed. The great increase in reverted austenite (irreversible hydrogen traps) together with numerous precipitates at the expense of dislocations (reversible) in the over-aged specimen led to such a change in permeability. Ordinary tensile tests indicated that four tested specimens had roughly the same yield strength level. Hence, the hydrogen embrittlement susceptibility of the material could be related to their permeation properties. The uniform distribution of strong hydrogen traps in over-aged specimens instead of weak traps in the solution-annealed impeded the hydrogen transport toward the strained region, thus, the resistance to sulfide stress corrosion cracking was improved in over-aged specimens.     

微量碳对淬态Fe－Si－B非晶丝表面层结构及脆性的影响

用旋转水中熔融金属纺丝法制备了Ｆｅ－Ｓｉ－Ｂ非晶金属丝。拉伸和弯折性能表明，当合金中杂质碳原子分数含量≥０．２％时，制备态（淬态）非晶丝发生脆化。电子探针、Ａｕｇｅｒ能谱分析与透射电镜观察发现，非晶丝表面具有大约１５０－３００ｎｍ宽的富碳层且包含Ｆｅ＿（２３）（Ｃ，Ｂ）＿６相。该相是Ｆｅ－Ｓｉ－Ｂ非晶丝脆化的原因。     

Al—Li—Cu—Mg合金应力腐蚀性能及机理研究

利用恒应变速率方法研究了Al—Li—Cu—Mg合金的应力腐蚀开裂,包括时效条件及外加电位对应力腐蚀的影响,同时研究了试样表面相对氢浓度与外加电位及应力腐蚀时间的关系,实验结果表明,合金的应力腐蚀性能取决于时效条件,其中峰时效条件下最差,自然时效条件下最好,应力腐蚀敏感性及试样表面氢浓度与外加电位有关,阳极电位增加应力腐蚀敏感性,阴极电位低于临界电位时加速应力腐蚀,认为合金在应力腐蚀过程中阳极溶解与氢脆机制联合作用。     

一种基于H.264视频内容认证的水印算法

提出一种基于H.264视频内容认证的半脆弱水印,该水印方案对视频内容恶意篡改敏感,而对于视频重编码等内容保持操作鲁棒。水印方案建立在视频压缩域上利用图像块之间不变的能量关系构建基于内容的特征码。由于DCT系数块能量主要集中在低频部分,所以用低频部分来生成特征码,用高频部分来嵌入水印。实验结果证明算法是有效的,并且较好地实现了篡改定位。     

材料氢脆涡流评价的有限元仿真研究*

针对扩散氢在材料内部渗透和聚集引起的氢脆问题,提出了一种基于涡流信号的表征方法。以电化学充氢试样为研究对象,首先基于Fick定律计算了电化学充氢过程中试样的氢分布,然后基于电磁感应原理运用COMSOL Multiphysics建立了不同氢分布状态下材料氢脆的涡流检测有限元模型,通过数值计算分析时谐电磁场激励下试样的感生涡流场分布及检测线圈的电磁场量图,并通过原位拉伸实验定量表征氢脆程度,最后分析了氢脆指数-涡流响应信号之间的关联机制,进行实验验证。研究结果表明,金属材料的氢脆程度与所含氢含量密切相关,时谐电磁场作用下的涡流信号与氢脆程度呈现线性相关,验证了材料氢脆涡流评价的有限元模型的有效性。     

Effects of alloy 718 microstructure on hydrogen embrittlement susceptibility for oil and gas environments

The effects of alloy 718 microstructure on hydrogen embrittlement susceptibility and tensile fracture mode were assessed through slow strain rate tensile testing and fracture surface analysis. Alloy 718 was annealed and aged to produce microstructures with variations in grain size and amount of grain boundary precipitates. Furthermore, the different ageing conditions likely resulted in differences in volume fractions and sizes of γ′ and γ′′ precipitates. The extent of grain boundary precipitation had the strongest effect on hydrogen embrittlement susceptibility, while grain size did not have any significant effect. Hydrogen embrittlement susceptibility was also correlated with differences in strength level, which was primarily controlled by the γ′ and γ′′ precipitate populations.     

Effect of grain refinement on the hydrogen embrittlement of 304 austenitic stainless steel

The effect of grain size (in the range from 4 μm to 12 μm) on the hydrogen embrittlement (HE) of 304 austenitic stainless steel (ASS) was studied. HE susceptibility result shows that HE resistance increases with grain refinement. Electron backscattered diffraction kernel average misorientation (EBSD-KAM) mapping shows that the strain localization can be mitigated by grain refinement. Hence, strain localization sites which act as highways for hydrogen diffusion and preferred crack initiation sites can be reduced along with grain refinement, leading to a high HE resistance. Meanwhile, grain size shows no influence on the strain induced martensite (SIM) transformation during the hydrogen charging slow strain tensile test (SSRT). Hence, the SIM formed during hydrogen charging SSRT is not responsible for the different HE resistance of 304 ASSs with various grain sizes. Hydrogen diffusion is supposed to be controlled by a competition between short-circuit diffusion along random grain boundary (RGB) and hydrogen trapping at dislocations, leading to a maximum hydrogen diffusion coefficient in the 304 ASS with an average grain size of 8 μm.