Microstructural Evolution of Cr-Rich ODS Steels as a Function of Heat Treatment at 475 °C (original) (raw)
Related papers
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...
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.
Powder Metallurgy, 2016
The conventional PM ODS Ferritic Steel (FS) processing route includes gas atomisation of steel powder and its mechanical alloying (MA) with Y 2 O 3 powder particles to dissolve yttrium and form, during consolidation, a dispersion of oxide nanoparticles (Y-Ti-O) in a nanostructured matrix. This work presents an alternative route to produce ODS steels avoiding MA: STARS (Surface Treatment of gas Atomized powder followed by Reactive Synthesis). STARS FS powders with composition Fe-14Cr-2W-0.3Ti-0.23Y, already containing the nanoparticles precursors, were gas-atomized. Oxygen, Y and Ti contents were tailored to the required values to form Y-Ti-O nanoparticles during processing. Powders were HIPped at 900, 1220 and 1300°C. Specimens HIPped at 900 and 1220°C were heat treated (HT) at temperatures ranging from 1200 to 1320°C. The microstructural evolution with HIP and HT temperatures, including characterisation of nanoparticles and feasibility of achieving complete dissolution of prior particle boundaries (PPBs) were assessed.
Advanced Engineering Materials, 2019
In this study, two kinds of Fe-9Cr-8Al ODS steels (pre-alloyed and post-alloyed) were fabricated via mechanical alloying (MA), hot isostatic pressing (HIP) and subsequent hot forging. Microstructures of the milled powder and forged bulk materials were carefully characterized. The results show that the adding sequence of the Al has a significant impact on the microstructure. For the post-alloyed sample (adding Al during ball-milling), a dual-phase structure composed of reticular Al-rich regions
Microstructural characterization of oxide dispersion strengthened ferritic steel powder
Journal of Nuclear Materials, 2013
Oxide dispersion strengthened ferritic steel powder was prepared by mechanical alloying of pre-alloyed ferritic steel powder together with nano Y 2 O 3 in a dual drive planetary ball mill. A detailed investigation was carried out using X-ray diffraction, field emission electron microscopy and transmission electron microscopy. Microstructural parameters such as, crystallite size, lattice strain, deformation stress and dislocation character were evaluated using different Williamson-Hall models; uniform deformation model, uniform stress deformation model and modified Williamson-Hall model and the results obtained were compared and discussed. Uniform stress deformation model and modified Williamson-Hall model were observed to give better estimation of crystallite size as they consider strain anisotropy. With mil ling, dislocation character was observed to be changing, from near edge to mixed type. Lattice parameters of the milled powders were also estimated. Uniform milling with convoluted particle shape and homogeneous distribution of Y 2 O 3 throughout the matrix was observed by using electron microscopy.
The structural changes of Y< sub> 2 O< sub> 3 in ferritic ODS alloys during milling
Oxide dispersion strengthened (ODS) ferritic steels are usually fabricated via mechanical alloying and subsequent consolidation via hot extrusion or hot isostatic pressing. During the individual process steps, a complex evolution of the nanoparticle structure is taking place. Powders with different Y 2 O 3 contents were milled and examined by means of X-ray diffraction (XRD) and atom probe tomography (APT). It has been observed that the Y 2 O 3 is fragmented and becomes partially amorphous upon milling due to the grain refinement of Y 2 O 3 during the milling process. There was no compelling evidence for Y 2 O 3 dissociation and dissolution into the steel matrix.
Metals
Two different zirconium contents (0.45 and 0.60 wt.%) have been incorporated into a Fe-14Cr-5Al-3W-0.4Ti-0.25Y2O3 oxide dispersion-strengthened (ODS) steel in order to evaluate their effect on the final microstructure and mechanical properties. The powders with the targeted compositions were obtained by mechanical alloying (MA), and subsequently processed by spark plasma sintering (SPS) at two different heating rates: 100 and 400 °C·min−1. Non-textured bimodal microstructures composed of micrometric and ultrafine grains were obtained. The increase in Zr content led to a higher percentage of Zr nano-oxides and larger regions of ultrafine grains. These ultrafine grains also seem to be promoted by higher heating rates. The effective pinning of the dislocations by the Zr dispersoids, and the refining of the microstructure, have significantly increased the strength exhibited by the ODS steels during the small punch tests, even at high temperatures (500 °C).
Characterization of untransformed ferrite in 10Cr and 12Cr ODS steels
Materialia, 2021
Two new ferrito-martensitic oxide dispersion strengthened (ODS) steels reinforced with (Y, Ti, O) nanoparticles were elaborated using a high-energy attritor. The milled powder was consolidated by hot extrusion at 1050°C. The two types of ODS steels differ by chromium content, with 10 wt% Cr and 12 wt% Cr respectively. According to thermodynamic calculations, those grades are supposed to exhibit an austenitic transformation at high temperatures. X-ray diffraction (XRD) above austenitic temperature transformation reveals the presence of both ferrite and austenite phase. This unexpected ferrite phase is assumed to be untransformed low temperature ferrite. The α→γ phase transformation specific enthalpy is monitored by differential scanning calorimetry (DSC).The untransformed ferrite fraction is calculated using dilatometric data and confirmed by electron backscatter diffraction (EBSD) microstructural analysis. The quenched samples from the austenitic domain give an image of the high-temperature partitioning. EBSD maps reveal two distinct elementary microstructures, one martensitic inherited from austenite and the other corresponds to the untransformed ferrite. This untransformed ferrite keeps the crystallographic α-fiber conferred by hot-extrusion. The 10Cr ODS has equiaxed untransformed ferrite areas. In contrast, the untransformed ferrite into 12Cr ODS is distributed as elongated areas, parallel to the hot-extrusion direction. Moreover, electron probe micro analyzer (EPMA) mapping exhibits chromium content gradients, consistent with phase partitioning at high temperatures. Creep properties are evaluated at 650°C for both grades. Small-angle X-rays scattering (SAXS) shows a similar size and distribution of the oxide particles in both grades.
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...