Precipitation behavior of novel 1 GPa ferritic advanced high strength steels

Abstract The precipitation of nanosized carbides in the hot-deformed low-alloy Ti-Mo-V-Nb and Ti-Mo-V- steels during the isothermal dwell at three different temperatures (590 °C, 630 °C, and 680 °C) was investigated. Scanning transmission electron microscopy (STEM) revealed that the formation of regularly and irregularly distributed interphase precipitates (IP) and their orientation relationship with the polygonal ferrite matrix depended strongly on steel chemistry, dwelling time, and temperature. Results also showed that precipitation occurred not only at the austenite/ferrite phase boundary during the phase transformation, but nanosized precipitates also formed within the supersaturated polygonal ferrite grains after the phase transformation. Interpretation of the results suggested that finely dispersed interphase precipitated V(Mo)C carbides, formed rows in which the spacing and the size of the precipitates grew slightly during the isothermal dwell time in the Ti-Mo-V-Nb steel at the temperatures of 680 °C and 630 °C, whereas spherical V(Mo)C carbides formed within the supersaturated ferrite matrix at all temperatures. In the case of the Ti-Mo-V steel, the formation of the interphase precipitated Ti(Mo,V)C carbides occurred only at the highest dwell temperature of 680 °C. No IPs was detected at the other dwell temperatures in this steel, but an irregular carbide distribution consisting mostly of spherical Ti(Mo,V)C carbides was formed within the supersaturated polygonal ferrite matrix

Evaluation of strengthening mechanisms in novel fully ferritic advanced high-strength steels

Abstract New steel alloying concepts are designed in order to produce a fully ferritic, low-alloy steel with high (1 GPa) ultimate tensile strength (TS). A simulated hot-deformation process of the Ti–Mo–V–Nb and Ti–Mo–V steels is designed for that purpose, and the strengthening mechanisms of the steels are evaluated after the isothermal dwell at three different temperatures (590, 630, and 680 °C). The TS and the yield strength (YS) of the test alloys are estimated via hardness measurements. Results show that the estimated TS of over 1000 MPa and YS of over 900 MPa can be achieved in both steels, although the contribution of different strengthening mechanisms to the YS varies between the steels. The effect of the dislocation strengthening can especially compensate the reduced effect of the precipitation strengthening at all tested coiling temperatures (CTs). Based on the results, a CT range of 590–630 °C with the 1800 s dwell time seems to be a potential process window for the studied steels after the present thermomechanically controlled processing (TMCP) route

Catalytic oxidation of dimethyl disulfide over bimetallic Cu–Au and Pt–Au catalysts supported on γ-Al₂O₃, CeO₂, and CeO₂–Al₂O₃

Abstract Dimethyl disulfide (DMDS, CH3SSCH3) is an odorous and harmful air pollutant (volatile organic compound (VOC)) causing nuisance in urban areas. The abatement of DMDS emissions from industrial sources can be realized through catalytic oxidation. However, the development of active and selective catalysts having good resistance toward sulfur poisoning is required. This paper describes an investigation related to improving the performance of Pt and Cu catalysts through the addition of Au to monometallic “parent” catalysts via surface redox reactions. The catalysts were characterized using ICP-OES, N2 physisorption, XRD, XPS, HR-TEM, H2-TPR, NH3-TPD, CO2-TPD, and temperature-programmed 18O2 isotopic exchange. The performance of the catalysts was evaluated in DMDS total oxidation. In addition, the stability of a Pt–Au/Ce–Al catalyst was investigated through 40 h time onstream. Cu–Au catalysts were observed to be more active than corresponding Pt–Au catalysts based on DMDS light-off experiments. However, the reaction led to a higher amount of oxygen-containing byproduct formation, and thus the Pt–Au catalysts were more selective. H2-TPR showed that the higher redox capacity of the Cu-containing catalysts may have been the reason for better DMDS conversion and lower selectivity. The lower amount of reactive oxygen on the surface of Pt-containing catalysts was beneficial for total oxidation. The improved selectivity of ceria-containing catalysts after the Au addition may have resulted from the lowered amount of reactive oxygen as well. The Au addition improved the activity of Al2O3-supported Cu and Pt. The Au addition also had a positive effect on SO2 production in a higher temperature region. A stability test of 40 h showed that the Pt–Au/Ce–Al catalyst, while otherwise promising, was not stable enough, and further development is still needed

Dual contrast CT method enables diagnostics of cartilage injuries and degeneration using a single CT image

Cartilage injuries may be detected using contrast-enhanced computed tomography (CECT) by observing variations in distribution of anionic contrast agent within cartilage. Currently, clinical CECT enables detection of injuries and related post-traumatic degeneration based on two subsequent CT scans. The first scan allows segmentation of articular surfaces and lesions while the latter scan allows evaluation of tissue properties. Segmentation of articular surfaces from the latter scan is difficult since the contrast agent diffusion diminishes the image contrast at surfaces. We hypothesize that this can be overcome by mixing anionic contrast agent (ioxaglate) with bismuth oxide nanoparticles (BINPs) too large to diffuse into cartilage, inducing a high contrast at the surfaces. Here, a dual contrast method employing this mixture is evaluated by determining the depth-wise X-ray attenuation profiles in intact, enzymatically degraded, and mechanically injured osteochondral samples (n\ua0=\ua03\ua0×\ua010) using a microCT immediately and at 45\ua0min after immersion in contrast agent. BiNPs were unable to diffuse into cartilage, producing high contrast at articular surfaces. Ioxaglate enabled the detection of enzymatic and mechanical degeneration. In conclusion, the dual contrast method allowed detection of injuries and degeneration simultaneously with accurate cartilage segmentation using a single scan conducted at 45\ua0min after contrast agent administration

Reobservations on ordering, precipitation and polymorphic phase transformation phenomena during annealing of a severely cold rolled magnetic Fe-Co-10V alloy

Abstract Despite extensive investigations conducted on magnetic Fe-Co-V alloys, some aspects of microstructural evolution during annealing of cold rolled sheets have not yet been clarified yet. Various techniques such as dilatometry, X-ray diffraction (XRD), transmission and scanning electron microscopy (TEM, SEM) as well as ThermoCalc predictions were employed to study ordering, precipitation and austenite transformation in an 86% cold-rolled 40Fe-50Co-10 V alloy. Dilatometric results revealed atomic ordering initiated from disordered martensite at 350 °C, while XRD patterns ascertained the completion of the process at 600 °C and its disappearance close to 750 °C. X-ray and electron diffraction patterns exhibited the B2 type ordered structure in this temperature range. Rod-shaped precipitates with HCP crystalline structure and the constant composition of (Co,Fe)₃ V were detected by SEM within the deformed ferrite grains after annealing in the temperature range of 500–700 °C. The percentage of the precipitates decreased by raising the annealing temperature and they vanished above 700 °C, in accordance with ThermoCalc prediction. Austenite grains formed below 750 °C had an ordered L1₂-type structure as revealed by TEM and XRD patterns. A combination of different techniques demonstrated that the two-phase ferrite-austenite region exists in the temperature range of 495–840 °C. Vanadium partitioning into austenite during isothermal holding in addition to austenite grain size were evaluated as the main parameters affecting austenite stability during quenching from temperatures between 500 and 800 °C. As a final result, most of the existing disagreements and ambiguities in previous works could be explained