Abnormal manifestation of the high-temperature degradation of the weld metal of a low-alloy steel welded joint

We have shown that hardness, impact toughness, mechanical properties in tension, and the local parameters of fracture mechanics (static and cyclic crack resistance) are sensitive to the operating degradation of weld metal of steam pipelines of thermal power plants made of 15Kh1M1F steel. The simultaneous decrease in the resistance to brittle and plastic fracture (hardness, strength, and impact toughness) represents a phenomenon of the operating degradation of weld metal. We have established a specific correlation between the characteristics of plasticity and other mechanical parameters of operated metal: the increase in °₅ of operated weld metal is in good agreement with the decrease in its strength, whereas the reduction of Ψ correlates with the lowering of resistance to brittle fracture. Electrolytic hydrogenation decreases the characteristics of strength and plasticity of operated weld metal much stronger than in the initial state. The absence of ferritic edgings on the boundaries of primary austenitic grains makes for a low resistance to brittle fracture, and the change in acicular ferrite deteriorates the mechanical properties. The ductile fracture of nonoperated metal is replaced by brittle intercrystalline failure in operated metal. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 1, pp. 73–79, January–February, 2007.     

PbS与PbO及硅酸铅反应的动力学和PbO的活度

为了阐明QSL法直接炼Pb的化学反应动力学,研究PbS与PbO及xPbO·SiO_2的交互作用是具有实际意义的。为了避免高温造成PbS和PbO的挥发损失,在较低温度下研究该体系的交互反应动力学,对探索火法炼Pb新工艺具有一定价值。试料是分析纯PbO,PbS和合成的纯xPbO·SiO_2,试料粒度均为100—120 mesh,在配比试样中以PbO:PbS=2:1作基础并混匀,以便保证按化学计量反应产生SO_2。装有试料的刚玉坩埚在密封竖直刚玉管底部低温区用Ar气保护升温加热,待达到预期温度后,坩埚由密封系统中的活动撑杆推到高温区并同时用Ar气载流使产生的SO_2连续为碘量法所测     

Some aspects of twist drill design

A mathematical approach to the flute disposal capacity based on the diameter of the circle which could be inscribed in the flute space is presented. It is important to know what order of drill rigidity is required for good performance when drilling various work materials. The main features of the cross-section profile which could affect the stiffness of a twist drill are the cross-sectional area and the second moment of area. The relationship between the various drill parameters and these features is one aspect to be investigated in this paper. Empirical equations based on the results obtained from this investigation are presented.     

On the determination of the stacking fault energy from extended nodes in Cu2NiZn

Stacking fault energies can be determined from the dimensions of extended dislocation nodes. Different theoretical treatments of the node problem have been published. The aim of the present paper is to compare the results obtained using the theories of Brown and Thöléen, Siems and Jøssanget al and to provide quantitative information about the dependence of the stacking fault energy for Cu₂NiZn on the model used. Extended nodes in networks with mesh size larger than the outer radius of the node (R) can be used for the determination of the stacking fault energy. Isolated nodes as well as network nodes are used to obtain the stacking fault energy in Cu₂NiZn, which appeared to be 33 ± 9 mJ/m².     

意大利移动市场考察报告

截至2002年4月底,意大利的移动通信用户数已超过5200万,普及率高达88%,用户规模仅次于德国,是欧洲第二大移动通信市场。目前,意大利共有4家GSM移动运营商:TIM,OmnitelVodafone,Wind和Blu,分别占有市场份额的46.7%、34.4%、15.3%和3.6%。意大利的运营商早在1998年就开始了移动互联网业务的市场培育工作,现在,移动互联网业务收入在意大利各运营商的总业务收入中已经占到10%～15%的比例。意大利的3G牌照是通过拍卖的方式颁发,OmnitelVodafone,TIM,Wind,IPSE2000,Wind,和H3G五家运营商获得了3G执照。ReportofStudyTouro     

Thermosolutal convection during directional solidification

During solidification of a binary alloy at constant velocity vertically upward, thermosolutal convection can occur if the solute rejected at the crystal-melt interface decreases the density of the melt. We assume that the crystal-melt interface remains planar and that the flow field is periodic in the horizontal direction. The time-dependent nonlinear differential equations for fluid flow, concentration, and temperature are solved numerically in two spatial dimensions for small Prandtl numbers and moderately large Schmidt numbers. For slow solidification velocities, the thermal field has an important stabilizing influence: near the onset of instability the flow is confined to the vicinity of the crystal-melt interface. Further, for slow velocities, as the concentration increases, the horizontal wavelength of the flow decreases rapidly — a phenomenon also indicated by linear stability analysis. The lateral in-homogeneity in solute concentration due to convection is obtained from the calculations. For a narrow range of solutal Rayleigh numbers and wavelengths, the flow is periodic in time. Formerly with the Mathematical Analysis Division, Center for Applied Mathematics, National Bureau of Standards, Washington, DC 20234. This paper is based on a presentation made at the symposium “Fluid Flow at Solid-Liquid Interfaces” held at the fall meeting of the TMS-AIME in Philadelphia, PA on October 5, 1983 under the TMS-AIME Solidification Committee.     

Numerical simulation of macrosegregation: a comparison between finite volume method and finite element method predictions and a confrontation with experiments

Micro-macrosegregation calculations have been performed for a rectangular cavity containing either a Pb-48 wt pct Sn alloy or a Sn-5 wt pct Pb alloy. The numerical results calculated with a finite volume method (FVM) and a finite element method (FEM) are compared with experimental results previously obtained by Hebditch and Hunt. The two methods are based on the same average conservation equations governing heat and mass transfer and the same assumptions: lever rule, equal and constant density of the solid and liquid phases (except in the buoyancy term), permeability of the mushy zone given by the Carman-Kozeny relation, and no transport of the solid phase. Although the same parameters are used in both calculations, small differences are observed as a result of the different formulations. In particular, the instabilities appearing in the mushy zone (channels) of the Sn-5 wt pct Pb alloy are more pronounced with the FVM formulation as compared with FEM, whereas the opposite trend is observed for the Pb-48 wt pct Sn alloy. Nevertheless, the final segregation maps at the end of solidification compare fairly well with the experimental findings.     

The mechanisms of formation and prevention of channel segregation during alloy solidification

Conditions for the formation of macroscopic segregation channels have been examined in the ammonium chloride-water and lead-tin systems, using base chilled molds. Such channels develop when the rejected solute is less dense than the solvent and are therefore a result of density inversion, but slow (≺5 rpm) rates of mold rotation, about axes inclined to the vertical by 20 deg to 30 deg, throughout the time of solidification, effectively prevent the formation or propagation of these channels. Artificially created channels or those momentarily blocked fail to continue and are overgrown, but channels can be initiated by drawing liquid upward from close to the growth front in fine capillaries. Examination of these effects leads to the conclusion that channels originate at the growth front, rather than within the dendritic array, and that their formation is necessarily preceded by a liquid perturbation from the less dense boundary layer into the supernatant, quiescent bulk liquid. Intermittent ‘solute fingers’ are then fed by dendritic entrainment to produce stable convective plumes and concomitant channels. It is considered that the effects of mold precession are primarily caused by translation of bulk liquid across the dendritic growth front, shearing off convective perturbations from the boundary layer before they have time to develop. The nature of the liquid movements is discussed and shown to be a function of the mold dimensions. The inclination of the gravitational vector within the solid-liquid, dendritic array is considered to be of secondary importance to the formation or prevention of channels. This paper is based on a presentation made at the symposium “Fluid Flow at Solid-Liquid Interfaces” held at the fall meeting of the TMS-AIME in Philadelphia, PA on October 5, 1983 under the TMS-AIME Solidification Committee.     

冷作磨具钢Cr12MoV磨削温度场的仿真

针对冷作磨具钢Cr12MoV进行了磨削温度场的研究,并依据建立的有限元仿真模型,对扩径头外扇形块模型进行了磨削温度场的仿真,实现了扇形块磨削温度场的预测,为研究磨削参数对磨削温度的影响提供了理论依据。