Magnetic properties of cementite and the coercive force of a Fe-5 at % C alloy after hardening and tempering

The role of cementite in the mechanisms of formation of H _c for specimens of a model high-carbon Fe-5 at % C alloy after hardening and tempering is determined from the analysis of the temperature dependences of the coercive force measured in the range from the temperature of liquid nitrogen to the Curie point for cementite. This analysis is based on the different characters of the temperature dependences of the contributions to H _c due to cementite as weakly magnetic inclusions at which the matrix’s domain walls are decelerated and cementite as a hard magnetic phase. It is shown that the magnetic hardness of cementite makes the main contribution to the formation of the coercive force in the region of medium and high tempering temperatures.     

On the causes of the formation of a maximum in the dependences of the coercive force of simple carbon steels on the tempering temperature

The dependences of the coercive force H _c of quenched specimens made of simple carbon steels on the tempering temperature T _t were measured at room and liquid-nitrogen temperatures. These studies showed that the formation of the character of H _c(T _t) dependences for the mentioned steels within the region of medium and high tempering temperatures is caused by the content of cementite and its magnetic hysteresis properties.     

The effect of the plastic tension of steels on the dependences of the coercive force on elastic compressive stresses

The effect of compressive stresses σ^? on the coercive force H _c of annealed isotropic low-carbon steels, which were preliminarily subjected to plastic tension ? _pl ⁺ of different values, has been studied. It was shown that the shape of hysteresis loops H _c (σ^?) and their changes with increasing ? _pl ⁺ are related to induced residual compressive and tensile stresses, which result from plastic tension, and also to the occurrence of plastic compressive deformations ? _pl ^? because of the Bauschinger effect. The causes of the openness of the first cycle of the H _c (σ^?) dependence and also for the occurrence of maximum of the H _c (σ^?) function in the ascending branch of this cycle are considered. A procedure for determining the residual tensile stresses, which result from the preliminary plastic tension, has been suggested and achieved experimentally. It was shown that the magnetoelastic change of magnetization, which is observed in the plastic compression, can serve as an indicator of these deformations σ _pl ^? .     

The role of cementite in the formation of magnetic hysteresis properties of plastically deformed high-carbon steels: I. Magnetic properties and structural state of cementite

Magnetic properties of cementite after strong plastic deformations and subsequent annealing in a broad range of temperatures are studied. The plastically deformed cementite is shown to exist in a soft (H _c ≈ 80 A/cm) state; the annealed cementite, in a hard (H _c ≈ 240 A/cm) state. The nature of the cementite’s soft and hard states is discussed. The field dependence of the cementite’s magnetostriction is measured. The longitudinal magnetostriction of the polycrystalline cementite’s saturated state is shown to be negative and approximately four times smaller than iron’s magnetostriction in the saturated state.     

The influence of biaxial elastic deformation on the coercive force and local remanent magnetization of construction steels

The influence of biaxial elastic tension-compression and tension-tension deformation on the coercive force and remanent magnetization of Cτ3 steel and 09Γ2C pipe steel cross-shaped specimens is studied. It is shown that coercive force grows monotonically with increasing load in the direction of compression under elastic tension-compression deformation and almost does not change under elastic tension-tension deformation. The local remanent magnetization decreases for all the considered types of biaxial elastic deformation. The possibility of using these methods for the evaluation of the stressed state of complexly deformed carbon steel products is discussed.     

The effect of cementite on the formation of the magnetic hysteresis properties of thermally treated carbon steels

The role of cementite in the mechanisms of formation of the coercive force of high-purity 60 and 13 model steels and 9A and 12A industrial steels after quenching and subsequent medium- and high-temperature tempering is determined from the analysis of the temperature dependences of the coercive force. It is shown that cementite as a hard-magnetic phase plays an important part in the formation of the dependence H _c (T _temp) measured at room temperature. The maximum contribution caused by the coercivity of cementite to H _c of the model steels is proportional to the volume content of cementite. In the industrial steels, an effect on the coercivity of cementite is produced by carbideforming unavoidable impurities.     

The relative stability of a mercury stain at room temperature and liquid helium temperature

Observations of the localization of the mercurial stain TAMM [tetrakis (acetoxymercuri) methane] have been made at room temperature and liquid helium temperature. Mercurial stains do not maintain a fixed position at room temperature in the electron microscope. In order to record room temperature micrographs with the minimum possible dose, a special single-electron-counting electron microscope system was used. Micrographs were taken at liquid helium temperature using a prototype microscope with a superconducting electron objective lens. Tropomyosin paracrystals were chosen as a convenient test object. At room temperature the fine banding pattern of the paracrystals was barely resolvable or not resolvable at all. At liquid helium temperature the fine banding pattern of the paracrystals was easily observed and more than one micrograph could be taken before the banding pattern faded. These observations indicate that this mercurial stain is more stable in position at liquid helium temperature than at room temperature.     

The role of cementite in the formation of magnetic hysteresis properties of plastically deformed high-carbon steels: II. Magnetic properties of patented wire made of steel 70

It is shown that, during discussion of the mechanism reliable for formation of the coercive force in high-carbon steel, in addition to the interaction between the domain walls and weakly magnetic cementite inclusions, the contribution from the cementite’s magnetic hardness should be considered. With the use of the temperature dependence of the coercive force in deformed and annealed specimens, the contribution of each of the considered mechanisms to the specimens’ coercive force is estimated.     

The role of cementite in the formation of magnetic hysteresis properties of plastically deformed high-carbon steels: III. Magnetic properties of patented wire made of steel 25

Temperature dependences of the coercive force of mechanically alloyed cementite and wires made of patented steel 25 that were subjected to plastic deformation and subsequent annealing are presented. As is shown, cementite can be in both low-and high-coercivity states, for which the coercive force measured at room temperature is 80 and 240 A/cm, respectively; the coercive force measured at liquid-nitrogen temperature (?196°C) is 190 and 530 A/cm, respectively. Based on an analysis of the temperature dependences of the coercive force of deformed wires made of patented steel 25, the role of cementite in the formation of the coercive force of low-carbon steels was determined. It is shown that, in spite of a relatively small amount of pearlite, the contribution due to the magnetic hardness of cementite to the coercive force should be taken into account. In this case, the contribution due to the interaction of ferrite domain walls with weakly magnetic cementite inclusions is substantially lower.     

Using a corrected least-squares procedure and accounting for structural parameters when analyzing the correlation between the impact strength of low-alloyed steels and their coercive force

The use of a corrected least-squares procedure that takes the error of impact-strength estimation into account, as well as several structure parameters, such as the equiaxial grain size number, Widmanstätten ferrite grain size number, and bainite percentage, allowed us to substantially improve the constraint equations between the impact strength and coercive force for a group of specimens. These specimens were sampled from no. 60 flange beams made of 09Г2 steel and exhibited no preliminary correlation between these parameters.     

Fretting on the cubic face of a single-crystal Ni-base superalloy at room temperature

Fretting experiments were conducted on the (1 0 0) crystal (cubic) face of a single crystal Ni-base superalloy in two directions, 〈1 0 0〉 and 〈1 1 0〉, to study the effect of crystallographic orientation on the fretting response in both partial slip and gross slip regimes. The study involved point contacts using a tungsten carbide (WC) ball with radius 10 mm tested at room temperature. Ball indentation was used to determine secondary crystallographic orientations. Under sufficiently high normal force, the friction on the cubic face in the 〈1 1 0〉 direction was larger than in the 〈1 0 0〉 direction. This difference can be explained by the extent of plastic deformation in the surface layer and associated microstructure changes, both of which depend on the coupling between the crystallographic orientation and the cyclic deformation field.     

The effect of an alumina counterface on friction reduction of CuO/3Y-TZP composite at room temperature

The friction behavior of CuO/yttria-stabilized tetragonal zirconia (3Y-TZP) composite in dry sliding against alumina at room temperature has been investigated. The results show that an alumina counterface has a crucial role on the frictional behavior when sliding against CuO/3Y-TZP composite in comparison with other counter materials. Pure 3Y-TZP shows high friction and wear under the same conditions. It is found that the friction reduction behavior is dependent on the sliding test conditions such as load and humidity. A thin aluminum-rich layer less than 200 nm thick on the contact surface during the low friction situation has been found by various analyzing techniques including interference microscopy, micro-Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microcopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The induced change of contact conditions and interfacial chemical reaction between CuO and alumina to form the phase CuAlO₂ increase the wear of alumina and accelerates the formation of an aluminum-rich surface layer. The presence of such a layer in the contact is beneficial for reducing friction. After a certain sliding distance, the coefficient of friction shifts from a low value to a high value due to a change in the dominating wear mechanism. This transition is shown to be caused by a different composition and thickness of the interfacial layer.     

The friction and wear behaviour of nickel-base alloys in air at room temperature

Measurements are presented of the friction and wear during sliding of specimens of Nimonic 75, C263, Nimonic 108 and Incoloy 901 on like specimens in air nominally at room temperature. The worn specimens have been examined using microhardness measurements, optical and scanning electron microscopy, X-ray diffraction and electron diffraction. These techniques suggest mechanisms for the room-temperature wear of these alloys associated with their strength properties. In particular, changes in the coefficient of friction and the wear rate during sliding can be correlated with work hardening, and possibly some degree of age hardening, of the load-bearing areas, due to the severe mechanical and thermal stresses developed. There is no evidence that oxide films formed on the contact areas during sliding have a significant effect on the tribological behaviour of these alloys. Such films are merely removed from the surface as wear debris.     

煤油蒸干温度与压力的关系

分别在100KPa、200KPa、300KPa、400KPa、500KPa和800KPa六个不同压力下通过实验研究了煤油(航空煤油RP-3)在微小圆管内传热的情况.实验管长为360mm,外径为2mm,内径为1mm,实验结果表明:在一定的压力下,传热系数先随煤油温度升高而增大,当温度达到沸点后,传热系数显著增大,然后突然减小,最后再慢慢增大.并且传热系数显著升高时的温度值随压力的增加而升高.传热系数突然降低时的温度值(蒸干温度)随压力增加而升高.     

Use of Peldri II (a fluorocarbon solid at room temperature) as an alternative to critical point drying for biological tissues

A new chemical, Peldri II, is evaluated as a compound for drying soft biological tissues for scanning electron microscopy. Peldri II, a fluorocarbon, is a solid at room temperature and is a liquid above 25°C. Cells or tissues are embedded in Peldri II by immersing them in the liquid form and allowing it to solidify. Once solidified, Peldri II will sublime with or without vacuum to dry tissues, probably without introducing surface tension. Several types of cells and tissues have been examined to compare preservation with Peldri II and critical point drying techniques. No differences were detected between the two techniques when normal surface structures were examined. Peldri II appears to be a significant improvement over hexamethyldisilazane as a drying agent for scanning electron microscopy. It is also very convenient for drying large numbers of samples.     

The difference in the uplift force at each support point of a container crane between FSI analysis and a wind tunnel test

We analyzed the difference between FSI (fluid-structure interaction) analysis and a wind tunnel test regarding the uplift force at each support point of a container crane and also design stowing devices — a tie-down rod and a stowage pin — and an alarm system to prevent overturning of a container crane under wind loads. We know that FSI analysis agrees more with wind tunnel tests than with structural analysis, but the results of FSI analysis are different from those of the tests. To evaluate the effect of the wind load on the stability of the crane, two container cranes that are widely used in container terminals-50 ton-class and 61 ton-class container cranes-are adopted for the analytic model and 19 values are considered for the wind direction as the design parameter. First, a wind tunnel test for the reduced-scale container crane model is performed according to the wind direction using an Eiffel-type atmospheric boundary-layer wind tunnel. Next, FSI analysis for a full-scale container crane is conducted using ANSYS and CFX. Then, the uplift force obtained from FSI analysis is compared with that yielded by the wind tunnel test. Finally, a formula is suggested to compensate the difference between FSI analysis and the wind tunnel test.     

Influence of particle impact conditions and temperature on erosion-oxidation of steels at elevated temperatures

The behaviour of four steels that are used in fluidized-bed boilers (16Mo3, T91, 304L and 253MA) has been studied in air (oxidation) and under impacts by sand particles in air (erosion-oxidation) at 350-650 °C in an extensive test programme and their performance compared in terms of the resulting weight changes and surface appearances.The results show that the oxidation rates for the steels increase with temperature but decrease with increases in chromium contents of the steels, as expected. Through oxidation rate, temperature has a significant influence on overall weight changes during combined erosion-oxidation, with material losses often increasing with temperature. The lowest particle velocities often cause deposition of particle debris and some weight gains, whereas the highest velocities cause essentially loss of material. Ductile erosion behaviour is observed under most conditions, with higher material losses at a shallow than at a steep impact angle, but the overall angle-dependency slightly changes with increase in temperature. The explanations for these observations are discussed in this paper. Furthermore, materials selection maps are constructed from the results generated, demonstrating that choosing the most highly alloyed material available is not necessarily the best rationale for materials selection.     

Influence of environment on the unlubricated wear of 316 stainless steel at room temperature

The wear of a type 316 austenitic stainless steel has been studied in a variety of gaseous atmospheres at constant load and slidind speed under reciprocating conditions. The environments reported include air, CO₂, argon and partial vacuum. The wear debris in all cases was essentially metallic and its rate of production per unit length was constant with sliding distance. On this evidence the wear process was classified as being of the severe type. There was, however, a wide range of specific wear rates which varied by a factor 30 extending from 1 × 10⁻¹³ m³/N m in air to 3 × 10⁻¹⁵ m³/N m in argon, decreasing with decreasing oxygen partial pressure.It is thought that the wear process in all the atmospheres examined was basically the same, being one of prow formation with the subsequent breakdown of these features to wear particles. The initial stage in prow growth is the formation of transfer elements or platelets by asperity interactions and their accumulation to form plateaux. There was a correlation between wear rate and platelet size, the wear rate decreasing with decreasing platelet size. The prow formation stage is considered to be the rate limiting step in the severe wear of ductile materials, but the influence of oxygen partial pressure on transfer element size needs further investigation.     

Generation of radiation-induced defects at room temperature in silicon in a HVEM and their annihilation

During the observation of silicon samples in a high-voltage electron microscope at room temperature, radiation defects are generated in near surface regions which are characterized by spherical amorphous regions of a diameter of about 10 nm. It could be shown that these defects are not caused by electrons, but by a pure ion damage. From the measurements of their size and depth it must be assumed that the incident particles are heavy ions or molecules. According to high resolution many-beam images and to the theory of ion damage a model of the structure of these defects is discussed. In addition, the recrystallization process of the amorphous regions, induced by electron irradiation as well as by tempering of the samples, was analyzed by means of high resolution micrographs.     

The friction and sliding wear of unlubricated 316 stainless steel at room temperature in air

The friction and reciprocating wear of unlubricated type 316 austenitic stainless steel on itself was investigated in air at room temperature in the load range 8–50 N. The wear kinetics were followed by intermittently collecting and weighing the wear debris. A model of the wear process was developed in terms of the interaction of asperities to form adhesive transfer platelets which agglomerate to layered prows. It is postulated that wear debris is subsequently produced by prow breakdown. This occurs by two main modes: at low loads to fine particles and at high loads prows are flattened to thin flakes which fracture at the prow-matrix interface, possibly by a fatigue mechanism. There is evidence to suggest that the rate-limiting step is located at a stage prior to prow formation.