Scientific basis for cold brittleness of structural BCC steels and their structural degradation at below zero temperatures

The paper considers the physics of cold brittleness of structural bcc steels and methods of reducing the ductile-brittle fracture temperature. A complex study was performed to examine the degradation of structural phase state of pipe steel 09Mn2Si from the main gas pipeline of Yakutia after long-term (over 3 0 years) operation. Important regularities of degradation of pearlite colonies with carbide precipitation on ferrite grain boundaries were revealed. This phenomenon is associated with brittle fracture of gas pipelines. It is shown that the low-temperature kinetic processes in main pipelines which define the degradation of their structure and properties are related to interstitial athermal structural states in the zones of local crystal structure curvature. This is a fundamentally new, as yet unknown, mechanism. Pipe steels in warm rolling acquire a longitudinal textured band structure with alternating bands of initial ferrite grains and bands of fine grains with carbide precipitates formed during lamellar pearlite degradation. This type of structure allows for a shift of ductile-brittle transition temperature down to -80°C and ductility δ = 22% at this temperature. The production of high-curvature vortex structure in pipe steel surface layers results in a 3.5-fold increase in their service life.     

Carbon-content dependent effect of magnetic field on austenitic decomposition of steels

The transformed microstructures of the high-purity Fe-0.12C alloy and Fe-0.36C alloy heat treated without and with a 12 T magnetic field have been investigated to explore the carbon-content dependent field effect on austenitic decomposition in steels. Results show that, the field-induced transformed morphology characteristics in different alloys differ from each other. In the Fe-0.12C alloy, the pearlite colonies are elongated along the field direction, and shaped by the chained and elongated proeutectoid ferrite grains in the field direction. However, in the Fe-0.36C alloy, the field mainly reduces the amount of Widmänstatten ferrite and elongates the formed proeutectoid ferrite grains in the field direction. No clear field direction alignment is obtained. The magnetic field also demonstrates carbon-content dependent effect on the texture of the formed ferrite. It clearly enhances the 〈001〉 fiber of the ferrite in the transverse field direction in the Fe-0.36C alloy. This field effect is related to the crystal lattice distortion induced by carbon solution and this impact becomes stronger with the increase of the carbon content. For the Fe-0.12C alloy, this field effect is greatly reduced due to the reduced carbon oversaturation in ferrite and elevated formation temperature. The orientation relationships (ORs) between the pearlitic ferrite and the pearlitic cementite in both alloys are less affected by the magnetic field. No obvious changes in the either type of the appearing ORs and their number of occurrences are detected.     

Microscopic examination of the 2,300-year-old excavated steel plowshare from northern India

In the present investigation, X-ray diffractometer, optical microscope, and scanning electron microscope were used to analyze the plowshare excavated from Ganwaria, UP, India. The main objective of the investigation was to determine the type of alloy, analysis of slag inclusion, and corrosion behavior. X-ray diffraction analysis showed the presence of α-iron. Microstructure consists of ferrite and pearlite grains; ferrite phase was soft in comparison to the pearlite. Optical micrograph at lower magnification revealed slag inclusions aligned in a specific direction, which indicates that the forge welding technique was used in the manufacturing of the object. The microstructural examination revealed that the object was manufactured from carbon steel. Entrapped slag inclusions were observed by scanning electron microscope and X-ray mapping, and slags were identified as SiO₂ and MgO. Goethite and lepidocrocite corrosion compound were found on the surface of the object.     

Dependences of magnetic Barkhausen emission and magnetoacoustic emission on the microstructure of pearlitic steel

The relationships between microstructure, mechanical behaviour and magnetic properties of completely pearlitic steels have been investigated, with the objective of determining the applicability of magnetic measurements to non-destructive evaluation of the properties of high-strength pearlitic steels. High-carbon steels were heat treated to produce completely pearlitic structures with various interlamellar spacings, and their magnetic properties, including hysteresis loops, Barkhausen emission (BE) and magnetoacoustic emission (MAE) profiles, were measured. MAE profiles were found to have two peaks at the knee of hysteresis loop, while BE profiles show only a single peak at about the coercive field for all samples. The peak height ratio of the MAE profiles and the amplitude of the BE profiles increase monotonically with increasing pearlite spacing, whereas coercivity is inversely proportional to pearlite spacing. These results can be interpreted in the context of magnetic domain structures and magnetization reversal processes observed by Lorentz transmission electron microscopy, which revealed that, in specimens with smaller pearlite spacing, reverse domains nucleated and grew at higher reverse magnetic field, and domain wall jumps across cementite lamellae were smaller than in samples with coarser pearlites. The good correlation observed between the magnetic properties, mechanical strength and microstructures of these steels provides the basis for rapid and effective non-destructive assessment of their properties for industrial applications.     

SINS初始对准中光纤陀螺EMD滤波

为了实现低成本SINS初始对准,降低对准过程复杂程度,提高系统对准精度,缩短对准时间,本文引入了EMD滤波技术。首先,采集IMU输出信号,根据EMD算法将信号分解为IMF簇,按照CMSE标准对信号进行重构,完成信号滤波处理;接着,按照AR模型对经EMD滤波前后的数据噪声进行建模;然后,分别利用原始信号和EMD降噪后信号进行SINS姿态粗对准;最后,根据IMU模型和SINS误差模型,采用零速对准方式,完成SINS精对准。实验结果表明:经EMD降噪后的信号粗对准精度为1.3°,精对准精度为0.87 mrad,精对准收敛时间为200 s。     

Stress corrosion cracking behavior of Nd:YAG laser-treated aluminum alloy 7075

Nd-YAG laser surface treatment was conducted on 7075-T651 aluminum alloy with the aim of improving the stress corrosion cracking resistance of the alloy. Laser surface treatment was performed under two different gas environments, air and nitrogen. After the laser treatment, coarse constituent particles were removed and fine cellular/dendritic structures had formed. In addition, for the N₂-treated specimen, an AlN phase was detected. The results of the stress corrosion test showed that after 30 days of immersion, the untreated specimen had been severely attacked by corrosion, with intergranular cracks having formed along the planar grain boundaries of the specimen. For the air-treated specimen, some relatively long stress corrosion cracks and a small number of relatively large corrosion pits were found. The cracks mainly followed the interdendritic boundaries; the fusion boundary was found to be acting as an arrestor to corrosion attacks. In contrast, only few short stress corrosion cracks appeared in the N₂-treated specimen, indicating an improvement in corrosion initiation resistance. The superior corrosion resistance was attributed to the formation of the AlN phase in the surface of the laser-melted layer, which is an electrical insulator. The electrochemical impedance measurements taken during the stress corrosion test showed that the film resistance of the laser-treated specimens was always higher than that of the untreated specimen, with the N₂-treated specimen showing the highest resistance.     

A modified alignment method based on four-quadrant-grating moiré for proximity lithography

In this paper, we demonstrate a modified coarse-fine alignment scheme designed for proximity lithography. Both wafer alignment mark and mask alignment mark consists of linear grating arrays and “+” bar. Coarse alignment and fine alignment could work together to achieve the perfect alignment. Thereinto, coarse alignment, measured from two superposed “+” bars, guarantees the misalignment across wafer and mask within the measurement range of fine alignment, which is based on moiré fringes formed by the superposition of linear grating arrays. Then we conduct the experiments using a nanometer actuator to drive the wafer alignment mark meanwhile keeping the mask alignment mark motionless, which validates the feasibility and rationality of our designed scheme.     

Near-eutectic Zn-Mg alloys: Interrelations of solidification thermal parameters,microstructure length scale and tensile/corrosion properties

Zn-Mg alloys are considered to have potential application in bone implants, since both metals are biocompatible and have biodegradable characteristics. Adding Mg to Zn can boost mechanical and corrosion resistances. However, the literature is very limited on quantifying the interrelation of solidification parameters, microstructural features and mechanical/corrosion properties of Zn-Mg alloys. The present study examines the interrelations of alloy Mg content, macrosegregation effects, morphology and scale of the matrix and eutectic phases, nature of intermetallics and tensile and corrosion properties of near-eutectic Zn-Mg alloys. The alloys samples are obtained by unsteady-state directional solidification resulting in a wide range of solidification thermal parameters and microstructures. We examine microstructural features of both dendritic and complex regular eutectic phases. It is shown that the eutectic exhibits a bimodal pattern with neighboring areas of coarse and fine lamellae. Experimental growth laws relating the primary, secondary and eutectic spacings to the solidification cooling rate and growth rate are proposed. Hall-Petch type equations are derived expressing tensile strength and elongation to dendritic and eutectic spacings. Electrochemical parameters determined by polarization curves during corrosion tests and SEM analyses of corroded areas have shown that the alloy having an essentially eutectic microstructure is associated with better corrosion resistance.     

A novel electrodeposited Cu-Zn-Bi film with increased corrosion resistance in a 0.05 M K2SO4 solution

A single phase Cu-Zn-Bi film is fabricated on the steel wire by electrodeposition. Bi addition (∼1 wt.%) greatly increases the corrosion resistance of brass (Cu−36 wt.% Zn) film in a 0.05 M K₂SO₄ solution as shown by potentiodynamic polarization and electrochemical impendence spectroscopy (EIS) experiments. It is proposed that the main reason for the improvement in the corrosion resistance by the Bi addition is that it greatly increased the crack resistance, which thus prevents crack-induced galvanic corrosion occurring between the brass film and the steel substrate.     

基于偏振衍射色散共焦的光学元件轴向间距测量

光学元件轴向间距测量对精密光学系统的定位和装调具有重要意义.针对现有色散共焦测量系统中色散物镜结构复杂、色散范围小的问题,提出基于偏振衍射色散共焦的光学元件轴向间距测量方法,将传统折射共焦镜头几百毫米的轴向尺寸和复杂的装调需求简化为数毫米的单片镜,简化了系统结构.透镜间距和厚度测量实验表明,间距测量误差为10μm.     

Experimental and theoretical study of the formation and growth of pearlite colonies in eutectoid steels

Optical and electron-microscopy observations of pearlite structures in eutectoid steels are described. These observations suggest that in such steels the processes of sidewise growth of pearlite colonies along grain boundaries may occur even though they were not observed in noneutectoid steels. A simple theoretical model is proposed to study the thermodynamics and kinetics of pearlite transformations. Simulations of the growth of pearlite colonies carried out on this model reveal that, for the usually assumed mechanism of volume diffusion of carbon, such growth is always unstable, and the steady-state growth can only be realized via interfacial carbon diffusion. A model is proposed for the formation of pearlite colonies near the grain boundaries of austenite. This model is based on the assumption that the diffusion of carbon is strongly enhanced near these boundaries, and it can be applied to plastically deformed steels. The results of simulations with this model qualitatively agree with some microstructural features of the formation of pearlite colonies observed in such steels.     

Stabilization of growth of a pearlite colony because of interaction between carbon and lattice dilatations

The previously proposed model of pearlite transformation develops taking into account the possible interaction between carbon and lattice dilatations arising in austenite near the pearlite colony. The normal stresses caused by the colony stimulate autocatalysis of plates, and tangential stresses promote the stabilization of the transformation front. The mechanism of ferrite branching, which can play an important role in the kinetics of pearlite and bainite transformations, is discussed.     

Digital moiré fringe measurement method for alignment in imprint lithography

Accurate layer-to-layer alignment, which is of prime importance for the fabrication of multilayer nanostructures in integrated circuits, is one of the main obstacles for imprint lithography. Current alignment measurement techniques commonly involve an image detection process for coarse alignment followed by a grating interference process for fine alignment. Though this kind of two-level alignment system is reasonable for measurement, when it is used in real imprint lithography, it is inconvenient because of the existence of a complex loading system that needs space for alignment. In this study, we propose a fine alignment method using only image detection using grating images and digital moiré fringe technology. In this method, though the gratings are also selected as alignment marks for accurate measurement, they do not interfere with the physics. The grating images captured from the template and wafer are used to measure angular displacement and to form parallel digital moiré fringes. The relative linear displacement between the template and wafer is determined by detecting the spatial phase of parallel digital moiré fringes. Owing to the magnification effect of digital moiré fringes, this method is capable of generating accurate measurements. According to the experimental results, this digital moiré fringe technique is accurate to less than 10 nm. In addition, without a complex grating interference system, this method has the advantage of being easy to operate.     

Deformation analysis of ferrite/pearlite banded structure under uniaxial tension using digital image correlation

The ferrite/pearlite banded structure causes the anisotropic behavior of steel. In this paper, digital image correlation (DIC) was used to analyze the micro deformation of this microstructure under uniaxial tension. The reliability of DIC for this application was verified by a zero-deformation experiment. The results show that the performance of DIC can satisfy the requirements of the tensile deformation measurement. Then, two uniaxial tensile tests in different directions (longitudinal direction and transverse direction) were carried out and DIC was used to measure the micro deformation of the ferrite/pearlite banded structure. The measured results show that the ferrite bands undergo the main deformation in the transverse tension, which results in the relatively weaker tensile properties in the transverse direction than in the longitudinal direction. This work is useful to guide the modification of the bands morphology and extend the application scope of DIC.     

On the causes of formation of non-optimal structures in a pressure-treated low-carbon steel

An electron microscopy investigation of structural-phase and stress-strained state of a hot-forged material workpiece is performed. It is found out that the scalar dislocation density in ferrite grains and ferrite interlayers of pearlite of steel from the forged piece fractured after technological processing is one and half times higher than that in the commercial material. The metal in this state has a higher content of sulfides of lamellar morphology. The volume fraction of pearlite in it is 1.5–2 times larger, with the lamellar pearlite prevailing, and the local long-range stresses being comparable with the yield stress. It is found out that the reason for formation of an unfavorable structural-phase state is the elevated carbon content, which resulted in overheating of the metal both during pressure treatment and final thermal treatment. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 8–12, October, 2007.     

Atomic structure of the Fe/Fe3C interface with the Isaichev orientation in pearlite

Abstract

The pronounced mechanical property of pearlitic steels highly correlates with the ferrite (bcc-Fe)/cementite (Fe₃C) boundaries inside. Unraveling the interface structure at an atomic level is essential for interpreting the material’s property. In the present study, using aberration-corrected scanning/transmission electron microscopy combined with density functional theory calculations, we reveal the atomic configuration as well as the electronic structure of the Fe/Fe₃C interfaces with the Isaichev orientation in pearlite. The interface with terminating layer Fe–C–Fe in cementite has the lowest energy due to the formation of interfacial Fe–C bonds. Terrace steps which are frequently observed at the interfaces would not break the lattice match between the two phases.     

The twice ferromagnetic resonance in hexagonal ferrite single rod and paired rods

The microwave electromagnetic properties of Co₂-Y hexagonal ferrite single rod and paired rods are demonstrated using a standard waveguide method. With the sweeping of the bias magnetic field, the ferromagnetic resonance occurs twice in the transmission spectra of single ferrite rod, which are induced by the self-bias magnetization and the external field magnetization, respectively. The zero/low-field resonance is determined by the shape anisotropy mainly, and disappears as the rod?s aspect ratio is relatively low. For the paired rods, when the interval between two parallel rods is small, the zero/low-field resonance vanishes due to the dipolar interaction between two rods.     

采用脉冲悬丝法测量强流加速腔聚焦场磁轴

 介绍了利用脉冲悬丝法校正、测量加速腔磁轴，以及对10MeV LIA束输运系统中40cm长聚焦线圈磁轴偏差的测量，详细描述了实验装置和实验方法。从测得的电压波形可区分出磁轴的倾斜与偏移，并可辨别出倾斜与偏移的方向，在聚焦线圈轴向磁场最强为0.072T的条件下，通过多次实验改变悬丝电流从0 .3A到3.8A，并改变电流脉冲宽度从0.3ms到1.5ms，测出了40cm聚焦线圈磁轴的偏差，并给出了磁轴偏差分布的对应波形。测试灵敏度估计为磁轴倾斜1mrad, 偏移0.2mm。