Optimisation of post-weld heat treatment — A simple, practical method

The authors have evolved an empirical method for characterizing resistance to ductile fracture using two parameters Γ _f andηf that can be determined from tensile test data of smooth cylindrical specimens. This method stipulates that the post-necking regime during tensile deformation is dominated by microvoid growth and coalescence processes, and therefore the energy absorbed in this regime can be used to estimate the resistance of the necked region to ductile fracture. The test procedure employed is simple and does not require gauge-length extensometry, a distinct advantage at non-ambient temperatures. The tests are carried out in a screw-driven machine at a constant crosshead speed, with online computerized acquisition of load-time data; it is also necessary to have a prior precise calibration for the (nonlinear) elastic deformation of the load train. The method of computing Γ _f and η_f, from tensile data is described, and its engineering application demonstrated by characterizing the effect of ageing of two dissimilar metal welds, namely Alloy 800/2.25Cr-lMo steel and Alloy 800/9Cr-1Mo steel. From these results, it has been established that this procedure of estimating the ductile fracture toughness from tensile tests can be used as a simple, practical method for optimisation of post-weld heat treatment of weld joints.     

The coolant penetration in grinding with a segmented wheel—Part 2: Quantitative analysis

This paper develops a quantitative model to predict the power of coolant penetration into the grinding zone of a segmented wheel. The model accounts for the coolant properties and system design characteristics governing the penetration mechanism revealed by the theory established in Part 1 of this series study. By coupling with the author's previous mist formation analysis, the model offers a quantitative control guideline for the optimal use of grinding coolants.     

副叶轮密封在气体压缩机上的应用

简单介绍了对气体压缩机上的轴封改造后的副叶轮密封装置的结构及设计计算。     

Wheel access duration in rats: I. Effects on feeding and running.

The effects of 0-, 2-, and 24-hr wheel access on the pattern of running, feeding, and weight were explored over 24 days in 3 groups of 8 male rats. Both 2 and 24 hr of wheel access suppressed feeding by about 15% for about 8 days before feeding gradually returned to normal. Weight in these 2 groups was similar and was suppressed for the 24 days. Like the pattern seen with drug self-administration (S. H. Ahmed & G. F. Koob, 1998, 1999), running levels stayed low with short, 2-hr daytime wheel access, but with long, 24-hr access, rats' running escalated over days to chronically high levels. These results may have relevance for the understanding of addiction and anorexia nervosa. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Correlation between cyclic deformation behaviour and microstructure in a duplex steel between 300 and 773 K

Cyclic tests performed in the temperature range 300–773 K on duplex stainless steel DIN 1.4460 show that the cyclic stress–strain behaviour of this steel is strongly temperature dependent. At 300 and 473 K an almost constant peak tensile stress stage, is followed by a slight softening that continues up to failure in the case of 300 K, but by a secondary hardening at 473 K. Pronounced initial cyclic hardening followed by secondary hardening was the main feature of the temperature range between 573 and 723 K. At 773 K, after a weak hardening stage, a strong softening continues up to failure. The mechanical behaviour and the evolution of the microstructure were analysed, and the internal and the effective stresses were studied. It was found that the internal stress is responsible for the strong hardening that occurs in the intermediate temperature range and for the softening at 773 K.     

A Novel Parsimonious Neurofuzzy Model Applied to Railway Carriage System Identification and Fault Diagnosis

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Metal dusting

This introductory review paper summarizes shortly the research on metal dusting, conducted in the MPI for Iron Research during the last dozen years. Metal dusting is a disintegration of metals and alloys to a dust of graphite and metal particles, occurring in carburizing atmospheres at a_C > 1 and caused by the tendency to graphite formation. The cause of destruction is inward growth of graphite planes into the metal phase, or in the case of iron and low alloy steels into cementite formed as an intermediate. The kinetics of metal dusting on iron and steels was elucidated concerning dependencies on time, temperature and partial pressures. High alloy steels and Ni‐base alloys are attacked through defects in the oxide scale which leads to pitting and outgrowth of coke protrusions, after initial internal formation of stable carbides M₂₃C₆, M₇C₃ and MC. A dense oxide layer prevents metal dusting, but formation of a protective Cr‐rich scale must be favored by a fine‐grain microstructure and/or surface deformation, providing fast diffusion paths for Cr. Additional protection is possible by sulfur from the atmosphere, since sulfur adsorbs on metal surfaces and suppresses carburization. Sulfur also interrupts the metal dusting mechanism on iron and steels, causing slow cementite growth. Under conditions where no sulfur addition is possible, the use of high Cr Nickelbase‐alloys is recommended, they are largely protected by an oxide scale and if metal dusting takes place, its rate is much slower than on steels.     

On the pitting corrosion resistance of nitrogen alloyed cold worked austenitic stainless steels

Pitting corrosion studies were carried out on cold worked (5%, 10%, 15%, 20%, 30% and 40%) nitrogen-bearing (0.05%, 0.1% and 0.22% N) type 316L austenitic stainless steels in neutral chloride medium. Potentiodynamic anodic polarisation study revealed that cold working up to 20% enhanced the pitting resistance, and thereafter a sudden decrease in pitting resistance was noticed at 30% and 40% cold working. Increase in nitrogen content was beneficial up to 20% cold work in improving the pitting corrosion resistance, beyond which it had a detrimental effect at 30% and 40% cold working. The role of nitrogen in influencing the deformation band width and dislocation configuration is explained based on the results of transmission electron microscopy investigations. Scanning electron microscopy observation of the pitted specimens indicated decreasing size and increasing density of pits, along the deformation bands with increasing nitrogen for 40% cold worked specimens. The macrohardness values increased as the cold working increased from 0% to 40%. X-ray diffraction studies revealed the increased peak broadening of austenite peak {0 2 2} with increase in cold working. The relationship between pitting corrosion and deformation structures with respect to nitrogen addition and cold working is discussed.     

高压传输线附近磁场环境的理论分析

应用复镜象理论计算了高压传输线和电气化铁路附近磁感应强度的量值，指出了低于千分之二高斯的安全区域，并对高压传输线和电气化铁路的磁污染进行了讨论。     

An upper-shelf fracture toughness master curve for ferritic steels

When assessing the resistance of a steel structure to failure under load, fracture toughness is a key input variable. Since it is usually not possible to establish a priori if the anticipated service temperature (or temperatures) is in the fracture mode transition or on the upper shelf, it is useful to know the temperature dependence of fracture toughness in both the transition and on the upper shelf. In the transition, the master curve proposed by Wallin defines both the variation of the median value of fracture toughness with temperature and the scatter of fracture toughness about this median value. However, Wallin's master curve does not quantify fracture toughness on the upper shelf. In this paper we assemble a database of upper shelf fracture toughness data (J_Ic) for ferritic steels. These data demonstrate that the temperature dependence of upper J_Ic is consistent for all ferritic steels contained in the database and has the same form as the temperature dependence of the flow strength anticipated from dislocation mechanics considerations. This similarity between the temperature dependence of flow strength and the temperature dependence of J_Ic is physically expected because both directly depend upon the energy required for dislocation mobility in the ferrite matrix. Both the empirically derived model and the physical basis for the model are described.