Die Verschiebung des Nonvarianzpunktes zwischen Eisen, Wüstit, Magnetit und Sauerstoff im System Eisen—Sauerstoff durch Legierungselemente oder fremde Oxyde, Auswirkungen auf das Verhalten von Eisenlegierungen beim Verzundern

Brauns, E.; Rahmel, A.; Christmann, Helmut

doi:10.1002/srin.195903079

Cited by 8 publications

(3 citation statements)

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“…It appears that the magnetite nucleates preferentially. Brauns et al (19) showed that the temperature below which wustite formed in the scale increased as the Ni concentration increased: 21% Ni raised the temperature from 570 ~ to 680~ and this may indicate a tendency to form magnetite under conditions of rapid Ni enrichment. However, it appears likely that magnetite forms because it can dissolve up to 25% Ni whereas wustite can only dissolve a maximum of 0.84% (15).…”

Section: Eleetrochem Soe: S O L I D -S T a T E Sciencementioning

confidence: 99%

Oxidation of an Fe‐9 w/o Ni Alloy in CO 2 at 700°–1000°C

Tomlinson

Menzies

1978

J. Electrochem. Soc.

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The oxidation of an Fe-9.21% Ni alloy in dry CO2 has been studied at 700~176 using thermogravimetry, metallography, and electron-probe microanalysis. At all temperatures the kinetics for oxygen consumption (weight gain) followed a linear-parabolic-linear sequence. During the initial linear stage the scale consisted mainly of magnetite with pockets of wustite at the scale/alloy interface, and the observed activation energy of 193 _+ 74 kJ mole -1 is considered to be due to the dissociation of CO2 into CO and adsorbed oxygen on the outer magnetite surface. During the parabolic oxidation stage a continuous alloy layer containing ~60% Ni at the scale/alloy interface forms a barrier to Fe diffusion, and the associated activation energy of 207 • 33 kJ mole -1 is for the diffusion of Fe through the layer. The final linear kinetic stage corresponds to the breakdown of the barrier layer and a return to linear oxidation kinetics with an activation energy of 155 • 13 kJ mole -1 for the dissociation of COs on the outer surface. During the final linear stage extensive subscale formation with pronounced intergranular penetration occurs and alloy particles containing ~55-60% Ni are isolated in the wustite matrix. The wustite of the scale and subscale are continuous and contain ~1.0 w/o Ni. Detailed information is presented of the Ni redistribution during oxidation and its correlation with the morphological structures and the oxidation kinetics. The associated oxidation processes are discussed.Reviews on the oxidation of Fe-Ni alloys (1,2) showed a considerable amount of information on their high temperature behavior in oxygen and air, but relatively little was known about their oxidation behavior in other gases. Morris and Smeltzer (3) have determined the kinetics and general morphological structures on Fe-Ni alloys containing up to 40% Ni oxidized in COs at 1000~C. However, except for alloys containing 2, 36, and 48% Ni (4, 5, 6) there have been no investigations involving detailed and systematic information on the changing Fe and Ni distribution during oxidation of Fe-Ni alloys in COs over a range of temperatures. The objects of the present investigation were to study the kinetics of oxidation of an Fe-9.21% Ni alloy at 700~176 in CO2, to examine the scale and subscale morphology as a function of temperature and time, and to determine qualitatively and quantitatively the Fe and Ni composition changes during the oxidation process. ExperimentalThe chemical analysis (w/o) of the alloy was: Ni,

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Section: Eleetrochem Soe: S O L I D -S T a T E Sciencementioning

confidence: 99%

Oxidation of an Fe‐9 w/o Ni Alloy in CO 2 at 700°–1000°C

Tomlinson

Menzies

1978

J. Electrochem. Soc.

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“…A further decrease in temperature below 570 • C leads to an unstable wuestite layer. Thus the oxide scale layer consists of two iron oxides, a thick layer of magnetite with about 80 wt %, and a thin haematite cover layer [10]. In the temperature range between 700 • C and 1250 • C, the oxide scale composition is nearly constant with a ratio of 1:4:95 for the layers of haematite, magnetite, and wuestite, respectively [11].…”

Section: Introductionmentioning

confidence: 99%

Sensitivity Analysis of Oxide Scale Influence on General Carbon Steels during Hot Forging

Behrens

Chugreev

Awiszus

et al. 2018

Metals

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Abstract:Increasing product requirements have made numerical simulation into a vital tool for the time-and cost-efficient process design. In order to accurately model hot forging processes with finite, element-based numerical methods, reliable models are required, which take the material behaviour, surface phenomena of die and workpiece, and machine kinematics into account. In hot forging processes, the surface properties are strongly affected by the growth of oxide scale, which influences the material flow, friction, and product quality of the finished component. The influence of different carbon contents on material behaviour is investigated by considering three different steel grades (C15, C45, and C60). For a general description of the material behaviour, an empirical approach is used to implement mathematical functions for expressing the relationship between flow stress and dominant influence variables like alloying elements, initial microstructure, and reheating mode. The deformation behaviour of oxide scale is separately modelled for each component with parameterized flow curves. The main focus of this work lies in the consideration of different materials as well as the calculation and assignment of their material properties in dependence on current process parameters by application of subroutines. The validated model is used to carry out the influence of various oxide scale parameters, like the scale thickness and the composition, on the hot forging process. Therefore, selected parameters have been varied within a numerical sensitivity analysis. The results show a strong influence of oxide scale on the friction behaviour as well as on the material flow during hot forging.

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“…Because of the brittle nature of the scale, the sample preparation process for metallographic examination of the scale is difficult and time-consuming. 3,4) It was not uncommon in the open literature that some scale structures were presented with preparation damages, [5][6][7][8][9][10][11] which in some cases were treated as genuine porosities in the scales, and explained in great depths of their fundamental mechanisms of formation. 6,10) In many of these cases, it was either stated that the 'conventional method' was used for metallographic sample preparation, 5,11) or the metallographic preparation was conducted in 'the usual way'.…”

Section: Introductionmentioning

confidence: 99%

Examination of Oxide Scales of Hot Rolled Steel Products

Chen¹,

Yuen²

2005

ISIJ Int.

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Porosities in the scale layer and wavy scale-steel interfaces are two common artefacts generated during metallographic preparation of oxide scale samples. This paper presents the techniques used by the authors to effectively remove porosities in the scale and reduce the waviness of the scale-steel interface so that the true scale structures can be examined. The techniques have been successfully applied to the examination of oxide scales on hot-rolled steel with various thicknesses and structures.

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Die Verschiebung des Nonvarianzpunktes zwischen Eisen, Wüstit, Magnetit und Sauerstoff im System Eisen—Sauerstoff durch Legierungselemente oder fremde Oxyde, Auswirkungen auf das Verhalten von Eisenlegierungen beim Verzundern

Cited by 8 publications

References 0 publications

Oxidation of an Fe‐9 w/o Ni Alloy in CO 2 at 700°–1000°C

Oxidation of an Fe‐9 w/o Ni Alloy in CO 2 at 700°–1000°C

Sensitivity Analysis of Oxide Scale Influence on General Carbon Steels during Hot Forging

Examination of Oxide Scales of Hot Rolled Steel Products

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