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Influence of the heat treatment on corrosion characteristics of the superston alloy

100%

Serbiński W. , Olive J.-M. , Kibitlewski A.

Advances in Materials Science

2007

tom Vol. 7, nr 2(12)

147-158

Microstructure and mechanical properties of the manganese-aluminium bronze (SUPERSTON alloy) used in ship propeller's production can be changed by the heat treatment, including hardening and tempering. In the paper is performed an influence of hardening and tempering temperature on the microstructure, microhardness and corrosion characteristics of the SUPERSTON alloy. The microstructure of the SUPERSTON alloy as a casting and after heat treatment is characterized by measure-ment of the HV0.05 and LM, SEM as well as AFM observations. On the base of potentiostatic corrosion test results is con-cluded that the best corrosion characteristics of the SUPERSTON alloy are obtained after hardening from 900°C and tempering 550°C, in comparison to heat untreated {as casting) copper alloy.

Modification of plastic strain localization induced by hydrogen absorption

100%

Aubert I. , Plessier F. , Saintier N. , Olive J.-M.

Advances in Materials Science

2008

tom Vol. 8, nr 1(15)

5-13

In order to highlight hydrogen effects on the plasticity, the slip morphology after straining (under tension up to 4% of plastic strain in ambient air) of hydrogenated (at 135 wt.ppm) and non-hydrogenated 3161 stainless steel polycrystals was compared. A statistical analysis of both slip band spacings (SBS) and slip band heights (SBH) was performed using atomic force microscopy. Tensile tests were performed at low strain rate, specimens being previously charged at controlled hydrogen concentration. The plastic strain field heterogeneity in polycrystals was taken into account thanks to numerical simulation of crystalline plasticity. On each grain, the calculated plastic shear was correlated with the distribution of SBS and the average number of emerging dislocations per slip band. In comparison with uncharged specimen and for an equivalent cumulated plastic strain, the hydrogenated specimen shows an increase of the slip band spacing (SBS) and of emerging dislocations. This result confirms a plastic localization induced by absorbed hydrogen.

Stress corrosion cracking on cold-worked austenic stainless steels in PWR environment

100%

Tribouilloy L. , Vaillant F. , Olive J.-M. , Puiggali M.

Advances in Materials Science

2007

tom Vol. 7, nr 1(11)

61-69

Types 304L and 316L austenitic Stainless Steels (SS) are widely used in PWR environment. These past few years, a limited number of cases of intergranular stress corrosion cracking (IGSCC) have been detected in cold worked areas of non sensitized austenitic stainless steel components. A first study has been initiated at EDF to assess the conditions of the cracking. The main results include cold work thresholds of 240 HV 0,1 for initiation cracking, and of 310 HV 0,1 for crack propagation, and propose that a dynamic loading is necessary for SCC. The aim of the present paper is to provide a basis of a crack propaga-tion model by investigating the effcet of loading, material and cold-work. In order to try to approach a static loading, a trape-zoidal cyclic loading is applied on high cold-worked (by rolling or by tensile loading) materials. It is shown that, for the most severe loading, the rolling cold-worked (RCW) materials undergo TGSCC whereas IGSCC is observed after tensile cold-working (TCW). The ratio of loading R bas such a strong impact on the crack growth rate (CGR) that it modifies the mechanism of cracking. Moreover, we notice that CGR increases with the applied K max but this evolution depends on the R value. Therefore, [delta K] is chosen to represent the mechanical loading effects on CGRs. Finally, the CGR after a hold time of 1 hour is quite the same than for 3 hours. Additionally, to address the critical issue of the effecet of the crack tip strain rate on crack growth rate, Slow Strain Rate Tests (SSTR) are carried out on RCW specimens and provide a first relation which is not consistent to a pure anodic process. This study is going on TCW specimens.