Characteristics of lath martensite: Part II. The martensite-austenite interface

This investigation, using an Fe-20 pct Ni-5 pct Mn (wt pct) alloy, deals with the nature of the lath martensite-austenite interface. For the first time the misfit dislocation structure associated with a martensite interface has been observed experimentally. The interface consists of a single set of parallel dislocations having Burgers vector α/2[l?1l]_martensite = α/2[011]_austenite. Relative to the austenite, the observed dislocation line direction is [0?57], and the dislocation line deviates about 10 and 15 deg from the pure screw orientation in the austenite and martensite, respectively. However, the dislocations are in screw orientation on an atomic scale, although the interface step structure causes them to deviate from the exact screw orientation macroscopically. The spacing of the interface dislocations varies from 26 to 63Å. The observed interface dislocation array satisfies the requirements for a glissile interface, which suggests that the dislocations are misfit dislocations which accomplish the lattice invariant shear of the crystallographic theories.     

Characteristics of lath martensite: Part III. Some theoretical considerations

Using newly available experimental information, the phenomenological crystallographic theory of martensite transformations has been applied to lath martensite. Experimental observations on the habit plane, orientation relationship, and the interface dislocations are in agreement with the theory using the Bain strain and two lattice invariant shears, one on (lll)[?101]_f and the other on (100)[0?11]_f. The theoretical approach is based on the maintenance of a glissile interface when experimentally observed misfit dislocations are incorporated in the experimental habit plane. The predicted shape deformation magnitude is 0.96, which is comparatively quite large, but because of extensive accommodation deformation in the martensite, the experimentally observed shape strain magnitude may be considerably smaller than the true value. The large martensite shape deformation appears to be responsible for the intrinsic lath morphology and the restricted growth of the martensite in a direction parallel to the shape deformation. The high density of dislocations in the laths probably arises because of accommodation distortion. Theory predicts a highly coherent martensite/austenite interface consisting of one set of steps on (lll)_f with associated dislocations and one set of screw dislocations in the direction [0?11]_f.     

The tempering of Fe-C lath martensite

The changes in matrix structure that occur during tempering of an Fe-0.2C martensite at 400° to 700°C have been investigated. Light and electron metallographic observations show that when tempered, the fine martensitic lath structure coarsens while retaining the elongated packet-lath morphology. The as-quenched hardness 504 Khn and total grain boundary area per unit volume 50,800 cm⁻¹ decrease abruptly at the higher tempering temperatures and in seconds reach relatively stable values that decrease slowly with time. The decrease in low angle boundaries accounts for most of the initial grain boundary area change, while the large angle boundary component of total boundary area decreases gradually with tempering time. Recovery processes are responsible for the initial changes in matrix structure, and carbide boundary pinning suppresses recrystallization until grain growth dominates in the later stages of tempering.     

形变对板条马氏体回火组织的影响

对Q235级低碳钢板条马氏体在550℃多道次单向压缩变形后退火和室温大塑性变形轧制后在此温度退火的显微组织演变规律进行了对比研究,结合未变形板条马氏体在此温度的回火组织演变,讨论了变形对马氏体分解过程、铁素体再结晶晶粒尺寸和析出碳化物形貌的影响.实验结果表明,变形显著影响马氏体分解过程,促进渗碳体的析出和铁素体回复及再结晶.热变形组织铁素体再结晶晶粒尺寸在0.5μm左右;渗碳体形貌从细棒状向球状转变,随变形量增大渗碳体尺寸增大,继续保温60min导致铁素体晶粒长大到1μm左右,晶粒内部的渗碳体消失,原先在铁素体晶界析出的渗碳体球化、粗化.冷轧试样在550℃退火保温时间在30min内得到0.3~0.4μm超细晶粒和尺度小于150nm的弥散渗碳体颗粒组织;随退火保温时间延长到60min,铁素体再结晶晶粒长大到1.9μm,渗碳体颗粒尺寸约160nm.     

On the elastic interaction of hydrogen with precipitates in lath martensite

The interaction of hydrogen with dislocations is well established, but its interaction with other structural features in a material has not been investigated or discussed to any appreciable degree. It is the intent of this discussion to examine the preference of precipitates for hydrogen atoms in a plain carbon steel, which is quenched to a martensitic structure and tempered. This structure represents one of the most susceptible to hydrogen embrittlement in the as-quenched condition and the most resistant in the highly tempered condition. One of the prominent features of this microstructure is the carbide precipitate and its transformational and morphological changes that result on tempering. The ability for trapping hydrogen, from an elastic energy standpoint, is seen to decrease with increasing loss in coherency of the precipitate. An energy for interaction between coherent precipitates and hydrogen atoms is calculated.     

Inflammatory bowel disease: Part I. Clinical features and diagnosis

Familial and epidemiologic studies of inflammatory bowel disease indicate a strong genetic predisposition that is modified by certain environmental factors. Abnormal submucosal immune activation may be important in the etiology of the disease. Yersinia enterocolitica infection, various "gay bowel syndromes" and other recently described enteric infections often mimic Crohn's disease. An initial barium study is useful in documenting the extent of disease and complications. Endoscopic biopsy confirms the surface appearance and histologic features of inflammatory bowel disease. Newer photodocumentation techniques are expected to improve the comparability of endoscopic observations. Complications of inflammatory bowel disease occur frequently, may involve any organ system and may precede the onset of bowel symptoms.     

Fiber texture and substructural features in the caliber-rolled low-carbon steels

Caliber rolling at the recrystallization temperatures of ferrite is a new process that was developed to fabricate an ultrafine-grained microstructure for low-carbon steels. In the present investigation, the electron backscattered diffraction (EBSD) measurement was carried out to characterize thoroughly the texture and substructural features in two caliber-rolled low-carbon steels, with special attention on the effects of a phosphorus addition to the steel and the annealing treatment after rolling. Finer ferrite grains appeared in the phosphorus-added steel under the same rolling condition. The phosphorus addition caused also the stronger <110>//rolling direction (RD) fiber texture in the caliber-rolled steel bars and, hence, showed a larger average Taylor factor than the steel without phosphorus. Microband features within the ultrafine ferrite grains were characterized with both transmission electron microscopy (TEM) observation and orientation-imaging micrograph (OIM) analysis. Nearly half of the low-angle boundaries, whose kernel average misorientation was larger than 0.8 deg, were found to have the planar character and were specifically parallel to the {110} or {112} planes. In the as-rolled condition, the total volume fraction of the low-angle boundaries was 0.3 and 0.23 in the steels with and without a phosphorus addition, respectively. More {112}-type planar boundaries were observed than the {110} type boundaries in both steels. Annealing treatment increased the volume fraction and changed the type of the low-angle boundaries in both steels. Using the model proposed by Peeters et al., the critical resolved shear stress (CRSS) of the 110 and 112 slip systems was calculated by considering the contributions of both the randomly distributed dislocations and the oriented planar boundaries. We concluded that the contribution of the planar low-angle boundaries to the total CRSS was less than 2 pct. The texture features and dislocation structure in the ultrafine-grained steels influenced the mechanical behavior to some extent, in addition to the refined ferrite grains. Phosphorus added to the steels showed a larger influence on the formation of texture and the retained dislocation structure, than that on the grain refinement in the caliber-rolling process.     

Some crystallographic characteristics of the (252)f martensite transformation in Fe-alloys

The crystallography and habit plane of the (252)_f martensite transformation in an Fe-8Cr-l.lC alloy have been investigated. A theoretical solution, based on experimental data, has been developed. The model implies that the (252)_f martensite crystallography can basically be explained using the phenomenological crystallographic theory, but plastic accommodation of the shape strain may lead to a significant difference between the true and observable shape strains. The calculated direction of the accommodation deformation is in good agreement with experimental observation on the substructure of (252)_f martensite.     

Human C-peptide. Part I: Radioimmunoassay

Synthetic human C-peptide bearing a Tyrosine group at its amino end is labelled with 125iodine using chloramin T or hydrogen peroxide and lactoperoxidase. The results are compared applying both methods. Antiserum to synthetic human C-peptide (without Tyrosine) which was partially compared to rabbit albumin, is raised in guinea pigs and goats. Goats show to be superior to guinea pigs concerning antibody production. The so-called "hook effect" phenomenon is observed in setting up the standard curves for the radioimmunoassay. Monotonically decreasing standard curves are obtained on dilution of antiserum with a high antibody titer which was produced by repeated immunization in goats. Free C-peptide and C-peptide bound to antiserum are separated with the anxion exchange resin Amberlite. Using this separation technique we excluded unspecific binding of labelled C-peptide to protein fractions in serum of diabetics. The sensitivity of our radioimmunoassay is approx. 0.3 ng C-peptide/ml serum. Intra- and interassay variability are below 10%. Human proinsulin is the only substance found to crossreact with the antiserum.     

Cellular and dendritic growth: Part I. Experiment

An Al-4.1 mass pct Cu alloy was unidirectionally solidified under various growth rates. Features, such as tip radius of curvature, primary arm spacing, and tip concentration were measured as functions of growth rate. Dependence of tip radius on growth rate was different between cells and dendrites. Measured tip radius and primary arm spacing were maximum at the cellular-dendritic transition. Tip concentration, however, monotonously decreases with growth rate. Linear relationships between tip radius and characteristic dimensions of dendrites like core diameter, half length of tip arc, and the first secondary arm spacing are obtained to determine what affects growth rate, convection, and gravity segregation. Experimental results are compared with current theoretical models for dendrite growth under controlled solidification. It was determined that the measured tip radius is larger than that of theoretical predictions at fast growth rate, but the measured tip concentration is in good agreement with theoretical predictions.     

Culture and test session behavior: Part I.

The relationship between culture (circumscribed by race, ethnicity, country of origin, language, and/or social class) and test session behavior (TSB) on group and individual tests of intelligence and/or achievement is evaluated with respect to the quality of evidence offered in support of knowledge claims. Four relevant categories in the literature are identified: (1) speculative theories, (2) studies of standardized measures of test session behavior, (3) TSB experimental research, and (4) research in cross-cultural test development. In Part I of a two-part series, key literature from the first two categories is reviewed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Some features of the sintering of nickel fibers extruded from viscose-base suspensions. Part I

Conclusions The sintering of fibers extruded from a viscose-base nickel powder suspension is characterized by volume changes whose intensity varies with temperature: At 200–400°C the fibers undergo densification under the action of capillary forces set up by liquid fractions of the polymer binder being removed during the latter's thermal destruction, the mechanism of the process being analogous to that of high-intensity drying; at 400–800°C the magnitude of shrinkage is independent of temperature because the carbon-metal skeletons of the fibers are stable in hydrogen. Local agglomeration of particles in the temperature range 600–800°C too has no effect on the magnitude of the volume changes of the fibers because of the discreteness of this process; at 800–1200°C the metallic phase sinters by a diffusion-viscous flow mechanism. To the characteristic temperature ranges of densification of fibers extruded froma viscose-base nickel powder suspension there correspond characteristic temperature ranges of polymer binder removal, which points to the existence of a relationship between these two processes.Translated from Poroshkovaya Metallurgiya, No. 6(210), pp. 28–32, June, 1980.     

Interdendritic Spacing: Part I. Experimental Studies

Directional solidification experiments have been carried out in a succinonitrile-5.5 mol pct acetone system to characterize dendrite tip radius and interdendrite spacings as functions of growth rate and temperature gradient in the liquid. A maximum in primary dendrite spacing as a function of growth rate is observed, and this maximum is found to occur at the dendrite-cellular transition velocity. A scaling law is shown to exist between the secondary dendrite arm spacing, λ₂, near the tip and the dendrite tip radius, p, which is λ₂/ρ = 2.2 ± 0.3. Experimental results on ρ have been found to agree with the theoretical model based on the marginal stability criterion. This paper is based on a presentation made at the symposium “Establishment of Microstructural Spacing during Dendritic and Cooperative Growth” held at the annual meeting of the AIME in Atlanta, Georgia on March 7, 1983 under the joint sponsorship of the ASM-MSD Phase Transformations Committee and the TMS-AIME Solidification Committee.     

Oxidation of cobaltite: Part I. process mineralogy

The control of arsenic is important in oxidation roasting and leaching of cobaltite. Oxidation roasting below 823 K did not show any crystal structural change in cobaltite, but heating to 923 K yielded Co-As-oxide, whose composition is varied. Direct oxidation of cobaltite to cobalt oxides with traces of arsenic was observed by roasting at 1023 K or above. The distribution of arsenic within the particles gradually decreased from the outer region to the center of the particles. The arsenic concentration within the particles decreased with the increase of temperature, suggesting temperature dependence on arsenic removal from the lattice of cobaltite. In this article, the process mineralogy of the oxidation of cobaltite is presented at various temperatures. The results from X-ray diffraction (XRD) analysis, reflected light microscopic analysis, and scanning electron microscopic analysis of the roasted cobaltite concentrates together with a rationalized thermodynamic analysis are presented.