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1.
2.
The postweld heat-treatment response of simulated coarse-grained heat-affected zones in a new ferritic steel 总被引:1,自引:0,他引:1
J. G. Nawrocki J. N. DuPont A. R. Marder C. V. Robino 《Metallurgical and Materials Transactions A》2001,32(10):2585-2594
The tempering behavior of simulated coarse-grained (CG) heat-affected zones (HAZs) in two ferritic alloy steels, 2.25Cr-1Mo
and HCM2S, was investigated. The hardness of HCM2S was found to be stable at longer times and higher temperatures than the
2.25Cr-1Mo steel, even though the “as-welded” hardnesses were approximately equal. Both materials reached a peak secondary
hardness after tempering for 5 hours at 575 °C. The increase in hardness of the 2.25Cr-1Mo steel was due to precipitation
of Fe-rich M3C carbides within the prior-austenite grains, whereas the secondary hardening in HCM2S was due to a fine dispersion of intragranular,
W-rich carbides. The HCM2S steel retained its hardness at longer times and higher temperatures than 2.25Cr-1Mo steel, because
of the precipitation of intragranular, W-rich carbides and V-rich MC carbides that stabilized the lath structure. This study
shows that HCM2S should not be heat treated in the same way as 2.25Cr-1Mo steel and also provides a basis for defining the
postweld heat treatment (PWHT) of HCM2S. 相似文献
3.
A study was conducted on dilution of single pass arc welds of type 308 stainless steel filler metal deposited onto A36 carbon steel by the plasma arc welding (PAW), gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), and submerged are welding (SAW) processes. Knowledge of the arc and melting efficiency was used in a simple energy balance to develop an expression for dilution as a function of welding variables and thermophysical properties of the filler metal and substrate. Comparison of calculated and experimentally determined dilution values shows the approach provides reasonable predictions of dilution when the melting efficiency can be accurately predicted. The conditions under which such accuracy is obtained are discussed. A diagram is developed from the dilution equation which readily reveals the effect of processing parameters on dilution to aid in parameter optimization. 相似文献
4.
JJ Mathewson ZD Jiang A Zumla C Chintu N Luo SR Calamari RM Genta A Steephen P Schwartz HL DuPont 《Canadian Metallurgical Quarterly》1995,171(6):1636-1639
Diarrhea occurs commonly in African human immunodeficiency virus (HIV) infections. A case-control (HIV-positive vs. -negative) study of adults with diarrhea was done in Lusaka, Zambia, to determine the prevalence of intestinal infection by HEp-2 cell-adherent Escherichia coli. Adherent E. coli were more common in HIV-positive patients with acute diarrhea than among HIV-negative controls (60% vs. 33%) and were found significantly more often in HIV-positive patients with chronic diarrhea than among HIV-negative controls with chronic diarrhea (79% vs. 17%, P < .002). Adherent strains were found significantly more often among HIV-positive patients (69%) than in 22 asymptomatic subjects (36%, P < .02). The HEp-2 cell adherence of the E. coli strains did not show a common pattern. Adherent bacteria were also observed in colonic biopsies from 32% of Zambians with chronic diarrhea who underwent endoscopy. Adherent E. coli may be an important cause of HIV-associated diarrhea in Zambia. 相似文献
5.
J. N. DuPont 《Metallurgical and Materials Transactions A》1998,29(5):1449-1456
Solubility data are combined with the new PHACOMP calculation procedure and solute redistribution equations to propose a simple
method for estimating temperatures of the secondary solidification reactions that occur in superalloy weld metals. The variation
in the primary solid composition with temperature is calculated with the Scheil equation for substitutional elements, while
the lever law is used for C. The calculated compositions are used to determine the temperature-dependent variation in the
solubility parameter and the metal d-level parameter, which is used in the new PHACOMP routine. The solubility parameter and metal d-level profiles are compared to temperature-dependent critical values to predict temperatures of secondary solidification
transformations involving carbides and topologically close-packed phases such as Laves. The general approach is applied to
experimental Ni-base and Fe-base alloys containing systematic variations in Nb, Si, and C. The procedure correctly predicts
formation of the NbC phase prior to the Laves phase and reveals the effect of nominal alloy content on reaction temperature.
Calculated reaction temperatures are in reasonable agreement with experimentally measured values, particularly when considering
the relatively large range of material constants that are needed to make the calculations. 相似文献
6.
David J. Wright M. Rachel Bumstead David T. Coxon Hugh S. Ellis M. Susan DuPont Henry W.-S. Chan 《Journal of the science of food and agriculture》1984,35(5):531-542
The pea-milling and subsequent air classification of whole peas was investigated on laboratory scale equipment. Two approximately linear but divergent calibration graphs were constructed for the air classifier based on two different definitions of particle size cut-point. At high classifying speed (11 000 rev min?1) a fine fraction or protein concentrate was produced containing 55.1% protein (cf. 22% in original flour) although this represented only 29% of the total protein. The yield of protein in the fine fraction could be increased by using a three-stage milling and classifying procedure, although the actual protein content of the concentrate remained more or less the same. This procedure also had the effect of reducing protein contamination of the starch (coarse) fraction. Other effects of air classifying observed included the concentration of the lipid component into the fine fraction and the rough fractionation of the fibre constituent between the coarse (testa) and fine (cell wall material) fractions. Various aspects and problems associated with the use of air classification for the preparation of pea protein concentrates are discussed. 相似文献
7.
RH Dean RW Kieffer BM Smith JA Oates JH Nadeau JW Hollifield WD DuPont 《Canadian Metallurgical Quarterly》1981,116(11):1408-1415
Serial renal function studies were performed on 41 patients wtih renovascular hypertension (RVH) secondary to atherosclerotic renal artery disease who had been randomly selected for nonoperative management. In 19 patients, serum creatinine levels increased between 25% and 120%. The glomerular filtration rates dropped between 25% and 50% in 12 patients. Fourteen patients (37%) lost more than 10% of renal length. In four patients (12%), a significant stenosis progressed to total occlusion. Seventeen patients (41%) had deterioration of renal function or loss of renal size that led to operation. One patient required removal of a previously reconstructible kidney. Of the 17 patients with deterioration, 15 had acceptable blood pressure (BP) control during the period of nonoperative observation. Progressive deterioration of renal function in nonoperatively treated patients with atherosclerotic renal artery stenosis and RVH is common, and occurs even in the presence of BP control with drugs. 相似文献
8.
Kathleen Rooney Michael A. Levy Sadegheh Haghshenas Jennifer Kerkhof Daniela Rogaia Maria Giovanna Tedesco Valentina Imperatore Amedea Mencarelli Gabriella Maria Squeo Eleonora Di Venere Giuseppe Di Cara Alberto Verrotti Giuseppe Merla Matthew L. Tedder Barbara R. DuPont Bekim Sadikovic Paolo Prontera 《International journal of molecular sciences》2021,22(16)
9.
Erin J. Barrick Divya Jain John N. DuPont David N. Seidman 《Metallurgical and Materials Transactions A》2017,48(12):5890-5910
10 wt pct Ni steel is a high-strength steel that possesses good ballistic resistance from the deformation induced transformation of austenite to martensite, known as the transformation-induced-plasticity effect. The effects of rapid heating and cooling rates associated with welding thermal cycles on the phase transformations and microstructures, specifically in the heat-affected zone, were determined using dilatometry, microhardness, and microstructural characterization. Heating rate experiments demonstrate that the Ac3 temperature is dependent on heating rate, varying from 1094 K (821 °C) at a heating rate of 1 °C/s to 1324 K (1051 °C) at a heating rate of 1830 °C/s. A continuous cooling transformation diagram produced for 10 wt pct Ni steel reveals that martensite will form over a wide range of cooling rates, which reflects a very high hardenability of this alloy. These results were applied to a single pass, autogenous, gas tungsten arc weld. The diffusion of nickel from regions of austenite to martensite during the welding thermal cycle manifests itself in a muddled, rod-like lath martensitic microstructure. The results of these studies show that the nickel enrichment of the austenite in 10 wt pct Ni steel plays a critical role in phase transformations during welding. 相似文献
10.
R. M. Deacon J. N. DuPont C. J. Kiely A. R. Marder P. F. Tortorelli 《Oxidation of Metals》2009,72(1-2):67-86
Due to their excellent corrosion resistance, iron aluminum alloys are currently being considered for use as weld claddings in fossil fuel fired power plants. The susceptibility to hydrogen cracking of these alloys at higher aluminum concentrations has led researchers to examine the effect of chromium additions on the corrosion resistance of lower aluminum alloys. In this work, three iron aluminum alloys were exposed to simulated coal combustion environments at 500 and 700 °C for short (100 h) and long (5000 h) isothermal durations. Scanning electron microscopy was used to analyze the corrosion products. All alloys exhibited excellent corrosion resistance during short term exposures. For longer test times, increasing the aluminum concentration improved alloy corrosion resistance. The addition of chromium to the binary iron aluminum alloy prevented the formation iron sulfide and resulted in slower corrosion kinetics. A general classification of the scales developed on these alloys is presented. 相似文献