Extrema of micro-hardness in fully pearlitic compacted graphite cast iron

For improving the mechanical strength of cast irons, a fully pearlitic matrix is sought by alloying with tin, copper and manganese. This applies in particular to the compacted graphite irons considered here. While average macro- and micro-hardness values were similar for the four fully pearlitic alloys under study, it was found that high copper and low tin content showed some very high maximum micro-hardness values, significantly higher than the corresponding mean. Such values may be seen as hard points in the material that would certainly impair machinability. Discussion of the reasons for these extreme values opens directions for further studie

Effect of Cooling Rate on the Eutectoid Transformation in Compacted Graphite Cast Iron

Differential thermal analysis has been used to characterize the effect of cooling rate on the eutectoid transformation of a compacted graphite iron. The samples were machined out from an as-cast thermal cup, austenitized at 950°C and then cooled to room temperature at various rates within the range 1−55.5°C/min. It was found that even at the highest investigated cooling rate, significant amounts of ferrite could be observed. When comparing the microstructure before and after Nital etching on samples cooled at intermediate cooling rates, it appeared that ferrite formed preferentially along the worms. This is discussed in terms of graphite shape and microsegregation and this latter seems prevalent. Finally, analysis of the thermal records was performed to characterize the temperatures for the start of the stable and metastable eutectoid reactions which confirms the eutectoid transformation sets up in compacted graphite irons as in lamellar and spheroidal graphite irons

Microstructure and thermal analysis of Cu-Cu2O eutectic – Can we mimic archeological remains?

An attempt was performed to reproduce in laboratory the microstructure observed in ancient artefacts and metallurgical remains made of nearly pure copper cast under ambient atmosphere. Two samples of pure Cu were prepared for thermal analysis, then heated and held for various times in the liquid state under ambient air for oxidizing, and finally cooled down at given rate. It was observed that a thick Cu2O oxide layer developed around the samples which gives the metal the same outer appearance than reported for metallurgical remains, namely a highly oxidized surface with large voids. Further, the microstructure of the metal consisted of (Cu) or Cu2O dendrites and a (Cu)-Cu2O eutectic showing strong similarity with the observations made on remains and artefacts

Chinese Script vs Plate-Like Precipitation of Beta-Al9Fe2Si2 Phase in an Al-6.5Si-1Fe Alloy

The microstructure of a high-purity Al-6.5Si-1Fe(wt pct) alloy after solidification at various cooling rates was investigated. In most of the cases, the monoclinic beta-Al9Fe2Si2 phase was observed as long and thin lamellae. However, at a very slow cooling rate, Febearing precipitates with Chinese script morphology appeared together with lamellae. Further analysis showed all these Chinese script precipitates correspond also to the monoclinic beta phase. This finding stresses that differentiating second phases according to their shape may be misleading

EFFICACITE DE LA ROPIVACAINE EN INFILTRATION PARIETALE DANS LA CHIRURGIE COLO-RECTALE (ETUDE RANDOMISEE, EN DOUBLE AVEUGLE CONTRE PLACEBO)

RENNES1-BU Santé (352382103) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

Phase equilibria and phase transformations in the Ti-rich corner of the Fe-Ni-Ti system

International audienceWhile the main features of the Fe-Ni-Ti system are well known at low Ti content, literature review of the Ti-rich corner revealed inconsistencies between experimental reports. This investigation presents new experimental results, defined to remove the uncertainties concerning melting behavior and solid-state phase equilibria of the (Ni,Fe)Ti2 phase with the adjacent (Fe,Ni)Ti (B2, CsCl-type structure) and Beta-Ti (A2, W-type) phases. Six samples have been prepared and examined by differential thermal analysis performed in yttria and alumina crucibles, and by scanning electron microscopy in the as-cast state as well as equilibrated at 900°C

Learnings from EDF investigations on SG divider plates and vessel head nozzles: evidence of prior deformation effect on stress corrosion cracking

Nickel Based alloys Stress Corrosion Cracking (SCC) has been a major concern for all the Nuclear Power Plants (NPP) utilities since the beginning of the 1970’s. At EDF, the 1990’s were marked by the occurrence of cracks on vessel head nozzles. These cracks were responsible for a leak at Bugey 3 vessel head, which was the precursor leading to the replacement of all vessel heads. From 2002, new cases of Stress Corrosion Cracking were reported on Steam Generator (SG) Divider Plates (SGDP) welded junctions. These cracks are periodically inspected in-service and reparations could be performed in case of a significant evolution of the phenomenon even if the safety issue is less relevant than for the vessel head nozzles. Both issues have lead to an important non-destructive testing (NDT) program and to destructive investigations campaigns. NDT were performed on an exhaustive basis for all vessel head nozzles and for all the divider plates of 900 MWe plants. Destructive investigations were performed on more than 30 vessel head nozzles and on 6 divider plates. The last investigations were performed on samples from two decommissioned Steam Generators of Chinon B1 which present SCC cracks. In this article, the main conclusions driven from the analysis of both NDT and destructive investigation results are reported and a comparison of the behaviours of divider plates and vessel head nozzles is given. Results give evidence that prior plastic deformation of the components before operation is fundamental for the further environmental behaviour of the material. Analysis of field experience based on parameters characteristics of prior deformation and parameters characteristics of material microstructure can be used to account for the components which are the most sensitive to SCC cracking. Some perspectives on SCC predictive models are also presented

Microstructural Evolution of Neutron Irradiated Stainless Steels

Materials of the core internals of Pressurized Water Reactors (austenitic stainless steels) are submitted to neutron irradiation. Some baffle/former bolt cracking were detected by non-destructive examinations and removed for metallurgical examination. The most likely cause to cracking was deduced to be Irradiation Assisted Stress Corrosion Cracking. To understand the ageing mechanisms associated to irradiation and propose life predictions of the component, irradiation damage is investigated experimentally by Transmission Electron Microscopy for two representative austenitic stainless steels, SA 304L and CW 316. The microstructure of these austenitic stainless steels constitutive of internals structures of PWR is characterized by TEM and compared to the microstructure obtained after irradiation for high doses up to 40 dpa at 320°C in experimental OSIRIS (mixed flux spectrum) and BOR-60 (fast breeders) reactors and at 300°C in experimental SM-2 (mixed flux spectrum) reactor. Only minor differences were detected