High-temperature oxidation resistance of ultrafine-grained 14 %Cr ODS ferritic steel (original) (raw)
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Role of Cr and Ti Contents on the Microstructure and Mechanical Properties of ODS Ferritic Steels
Advanced Materials Research, 2009
Six oxide dispersion strengthened (ODS) ferritic steels, with the composition of Fe-(12-14)Cr-2W-(0.1-0.3-0.5)Ti-0.3Y2O3 (wt.%), have been prepared by mechanically alloying elemental powders of Fe, Cr, W, and Ti with Y2O3 nano-particles followed by hot isostatic pressing. The influence of the chemical composition on the microstructure and mechanical properties of various materials was studied. It was found that the chromium content has a significant influence on the microstructure and mechanical properties of the compacted ingots. The 14Cr ODS steel exhibits slightly higher ultimate tensile strength and yield strength values than the 12Cr ODS steel. The total elongation and uniform elongation of both materials, in general, decrease with raising the test temperature, although in the case of the 12Cr ODS steel the elongation is about 30% higher than that of the 14Cr ODS material. In what concerns the effect of titanium content it can be concluded that variations between 0.1 and 0.3% h...
High-temperature oxidation of pure Fe and the ferritic steel 2.25Cr1Mo
Materials Research-ibero-american Journal of Materials, 2005
The global pressure for recycling and ecological energy production increases steadily in combination with the demand of cost-effective application of materials. However, some severe corrosion problems, associated with the high internal/intergranular corrosion rates in boiler components need to be avoid. Some commercial boiler materials contain a Cr content of 0.55 (wt. (%)) - 2.25 (wt. (%)). This Cr concentration in the alloys is not sufficient for the formation of a complete dense Cr2O3 scale. Hence, high oxidation kinetics may result. In this study, pure Fe and the steel 2.25Cr1Mo were oxidized in laboratory air at 550 °C using a thermobalance system. The surface as well as the cross section of oxidized specimens were analysed using scanning electron microscopy in order to quantify several factors (e.g. surface finishing, cold working and grain size) on the overall oxidation kinetics. For alloys with low Cr content, a decreasing in the grain size leads to an acceleration of the oxidation rate by facilitating the oxygen diffusion along alloy grain boundaries leading to an inward oxide layer formation. The study of effects of surface finish and cold working yielded results revealing that the oxidation process is complex and comparison of results from different laboratories is difficult and should be done.
Oxidation Behavior of ODS Fe?Cr Alloys
Oxidation of Metals, 2005
Four experimental oxide dispersion strengthened (ODS)Fe-(13-14 at.%)Cr ferritic alloys were exposed for up to 10,000 hr at 700-1100 • C in air and in air with 10 vol.% water vapor. Their performance has been compared to other commercial ODS and stainless steel alloys. At 700-800 • C, the reaction rates in air were very low for all of the ODS Fe-Cr alloys compared to stainless steels. At 900 • C, a Y 2 O 3 dispersion showed a distinct benefit in improving oxidation resistance compared to an Al 2 O 3 dispersion or no addition in the stainless steels. However, for the Fe-13%Cr alloy, breakaway oxidation occurred after 7,000 hr at 900 • C in air. Exposures in 10% water vapor at 800 and 900 • C and in air at 1000 and 1100 • C showed increased attack for this class of alloys. Because of the relatively low Cr reservoirs in these alloys, their maximum operating temperature in air will be below 900 • C.
Key Engineering Materials, 2011
The oxidation behaviour of developed Fe 80 Cr 20 alloy and commercial ferritic steel at 1173 -1373 K in air is studied. Effects of crystallite size and titanium implantation on the oxidation behaviour of specimens were analyzed based on oxide morphologies and microstructures. Oxide scales characterisations of specimen after oxidized were identified by X-ray diffraction (XRD). The surface morphology of oxide scales were examined with scanning electronic microscope (SEM) and energy dispersive X-ray analysis (EDX). The rate constant of oxidation were determined using Wagner method. The results show that crystallite size and titanium implantation has remarkably enhanced the oxidation resistance. The oxidation kinetics indicate that the developed Fe 80 Cr 20 as the finer crystallite size both unimplanted and implanted specimens show better performance.
Oxidation of Metals, 2010
Selective oxidation behavior of ferritic martensitic Fe-Cr base alloys, exposed in various atmospheres containing combinations of O 2 , CO 2 , and H 2 O, were studied at various temperatures relevant to oxy-fuel combustion. This paper begins with a discussion of the required Cr content to form a continuous external chromia scale on a simple binary Fe-Cr alloy exposed in oxygen or air based on experiments and calculations using the classic Wagner model. Then, the effects of the exposure environment and Cr content on the selective oxidation of Fe-Cr alloys are evaluated. Finally, the effects produced by alloying additions of Si, commonly present in various groups of commercially available ferritic steels, are described. The discussion compares the oxide scale formation on simple binary and ternary Fe-Cr base model alloys with that on several commercially available ferritic steels.
Journal of Nuclear Materials, 2011
The Fe-14Cr-2W-0.3Ti-0.3Y 2 O 3 oxide dispersion strengthened (ODS) reduced activation ferritic (RAF) steel was fabricated by mechanical alloying of a pre-alloyed, gas atomised powder with yttria nano-particles, followed by hot isostatic pressing and thermo-mechanical treatments (TMTs). Two kinds of TMT were applied: (i) hot pressing, or (ii) hot rolling, both followed by annealing in vacuum at 850°C. The use of a thermo-mechanical treatment was found to yield strong improvement in the microstructure and mechanical properties of the ODS RAF steel. In particular, hot pressing leads to microstructure refinement, equiaxed grains without texture, and an improvement in Charpy impact properties, especially in terms of the upper shelf energy (about 4.5 J). Hot rolling leads to elongated grains in the rolling direction, with a grain size ratio of 6:1, higher tensile strength and reasonable ductility up to 750°C, and better Charpy impact properties, especially in terms of the ductile-to-brittle transition temperature (about 55°C).
Metals
In this work, new oxide dispersion strengthened (ODS) ferritic steels have been produced by powder metallurgy using an alternative processing route and characterized afterwards by comparing them with a base ODS steel with Y2O3 and Ti additions. Different alloying elements like boron (B), which is known as an inhibitor of grain growth obtained by pinning grain boundaries, and complex oxide compounds (Y-Ti-Zr-O) have been introduced to the 14Cr prealloyed powder by using mechanical alloying (MA) and were further consolidated by spark employing plasma sintering (SPS). Techniques such as x-ray diffraction (XRD), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM) were used to study the obtained microstructures. Micro-tensile tests and microhardness measurements were carried out at room temperature to analyze the mechanical properties of the differently developed microstructures, which was considered to result in a better strength in the ODS steels contain...
Microstructural Evolution of Cr-Rich ODS Steels as a Function of Heat Treatment at 475 °C
2012
In the current research, the effect of heat treatment on the morphology of the dispersoids and their phase composition were investigated in three Cr-rich ferritic oxide dispersion strengthened (ODS) steels: PM2000, MA956, and ODM751. The steels were aged at 475°C for times ranging from 100 to 1,000 h. The microstructure was characterized using transmission electron microscopy. Study of the as-recrystallized samples revealed nano-scale Y-Al-O complex-oxide particles dispersed in the ferritic matrix. These dispersoids, which differ in size (10-160 nm) and geometry (polygonal and spherical), were identified as Y 4 Al 2 O 9 , YAlO 3 , and Y 3 Al 5 O 12 . After heat treatment, a significant change in the morphology, size, and distribution of the dispersoids was observed. Changes in the phase composition of the oxide dispersoids were also observed: YAlO 3 (with perovskite structure) was identified as the most dominant phase, indicating that it is probably the most stable phase in the Cr-rich ferritic ODS steels.
Nuclear Materials and Energy, 2016
The age-hardening in oxide dispersion strengthened (ODS) ferritic steels with various additions of Cr (12, 15 and 18 wt.%) and Al (0, 5, 7 and 9 wt.%) were investigated. After 50 0 0 h aging at 475 º C, the hardness increases in all these ODS steels, while the increased level depends on the Cr/Al contents. In 12Cr-ODS steels, the more the Al, the higher the increased hardness is. However, in 18Cr-ODS steels, higher Al addition suppresses the age-hardening. TEM observations of 18Cr-ODS steels reveal that 9Al suppresses the formation of Cr-enriched α' phase, while the 18Cr-5Al-ODS steel comprises a plenty of α phases. Adding Zr in ODS steels appears to increase the age-hardening. The susceptibility to age-hardening is remarkably lower in the ODS ferritic steels than in the non-ODS ferritic steel with the similar concentration of Cr.