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

Abstract

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,

Effect of Compressive Stress on the High-Temperature Oxidation Behavior of a Fe-20Ni Alloy in Air

“…Those microstructures of scales were in accordance with Guo [12], who studied the high temperature oxidation of Fe-36% Ni alloy. As for the formation of FeO, Tomlinson [4] suggested that the formation of FeO was the result of decomposition of Fe 3 O 4 . In addition, compared with Figs.…”

“…Figure 5 shows the cross-sectional microstructures of the specimens oxidized at 800 ℃ with a compressive stress of 2.5 MPa for 20 h and without stress for 44 h. It also can be observed that crack developed within subscale for the specimen with a stress of 2.5 MPa, while no crack generated within subscale in the case of unstressed specimen even the oxidation time up to 44 h. The appearance of cracks within subscale was related to the stress relaxation of oxide scales. According to the XRD analysis, FeO generated in the subscale which was the result of decomposition of Fe 3 O 4 [4]. As we known that the transformation from Fe 3 O 4 to FeO accompanied the volume changes owing to the difference of PBR (PBR(FeO/α-Fe)=1.78, PBR(Fe 3 O 4 /FeO)=1.20 [15]).…”

“…Foley [1] summarized the high temperature oxidation behavior of Fe-Ni alloys and emphasized on the kinetics and the growth of scales. And many other studies were carried out to analysis the effect of oxidizing atmospheres on the oxidation behavior, such as CO 2 [3,4], Ar-H 2 O [5]. In recent years, the effect of mechanical load on the oxidation behavior of alloys has been studied, and the subjects contained the kinetics [6][7][8], the oxide-scale failure [6,9], the scale-crack healing [10], and so on.…”

Influence of Ni and Cu on Oxide-Scale Structure of Steel

“…In hot rolling processes, heterogeneous structure of oxide scales, such as an uneven scale/steel interface, causes surface defects. For steels containing Ni, the structure of oxide scales at the scale/steel interface has been reported to be characteristic and complicated (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15).…”

High-Temperature Oxidation Behavior and Formation Mechanism of Rolling Cracks of Fe-36Ni Invar Alloy

“…It is therefore important to understand the oxidation behavior of Fe-36Ni invar alloy. To date, much work has been done on the oxidation of Fe-Ni systems in various atmospheres, such as pure oxygen, Ar-H 2 O mixed gas, CO 2 atmosphere and air [4][5][6][7][8][9]. Furthermore, according to the type of scales formed, Fe-Ni systems have been divided into four major compositional ranges: 0-2%Ni, 2-35%Ni, 35-80%Ni and 80-100%Ni [10].…”