Aulnoye-Aymeries, France
Aulnoye-Aymeries, France

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Barbier D.,Vallourec Research Center France | Guerin J.-D.,University of Valenciennes and Hainaut‑Cambresis | Guerin J.-D.,University of Lille Nord de France | Dubar M.,University of Valenciennes and Hainaut‑Cambresis | And 4 more authors.
Materials Science and Engineering A | Year: 2017

The present communication reports the main findings of an investigation that has been conducted in order to examine the ductility of both the AISI 4130 and 52100 steel grades, in a wide range of temperatures, spanning from room temperature up to 1250 °C, deformed in tension at strain rates of approximately 0.005 s−1. The ductility of the investigated alloys has been determined employing two different methodologies. The first one is based on the classical definition of this property, as determined from the reduction in the cross sectional area of the tensile specimen after fracture. The second method, which is proposed in this work, is based on the measurement of the energy under the engineering stress-strain curve and the decomposition of the total deformation energy into the uniform plastic and non-uniform or fracture energy components. Complementary axisymmetric compression tests have also been carried out in the temperature range of 600 °Cto 900 °C, in order to determine the strain related to the onset of dynamic recrystallization (DRX) at temperatures above 800 °C, as well as the strain corresponding to the occurrence of necking at these temperatures. The ductility values determined from both methods are observed to increase from approximately 10–80% when the testing temperature increases from room temperature to 1200 °C. Both measurements are also observed to agree up to temperatures of about 600 °C. Also, it has been determined that above this temperature, the ductility values derived from the energy criterion are somewhat higher than those computed from the reduction in the cross section area of the specimens. It has been shown that the onset of DRX gives rise to an improvement in the ductility of both steels, which is also related to a significant increase in the strain for the beginning of necking. The advantage of the energy criterion, in comparison with that based on the area reduction after fracture, is discussed. © 2017 Elsevier B.V.

Guedes D.,University of La Rochelle | Guedes D.,Vallourec Research Center France | Oudriss A.,University of La Rochelle | Frappart S.,University of La Rochelle | And 10 more authors.
Scripta Materialia | Year: 2014

A specific dependency of elastic tensile stress on the hydrogen solubility is identified for martensitic steels. The lattice hydrogen concentration under applied stress may be underestimated when predicted by a classical law which associates hydrostatic stress with the partial molar volume of hydrogen. We have explored the impact of elastic distortions on hydrogen solubility from two different sources: internal stresses arising from heterogeneous microstructures and elastic fields around vacancy clusters. Only the latter seems to be in reasonable agreement with our results. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Thebault F.,Vallourec Research Center France | Bureau-Bayart A.-S.,Vallourec Research Center France | Pineau F.,Vallourec Research Center France | Koschel D.,Vallourec Research Center France | And 3 more authors.
NACE - International Corrosion Conference Series | Year: 2014

NACE TM0177 Method D (DCB) test allows the determination of the critical stress intensity factor KISSC, below which the propagation of a sulfide stress crack in the material is stopped. For a given severity of the sour medium (pH, PH2S, T, [Cl-]...), KISSC is not a material constant since it depends for instance on the testing arm displacement. Recently, the Klimit concept was proposed to circumvent this issue. Klimit is a conservative KISSC value and would be more representative of the material corrosion resistance.A previous communication highlighted that the value of KIapplied is sensitive to the calculation procedure. Consequently, Klimit can be over or underestimated. The present work focused on the influence of experimental parameters on Klimit: the DCB specimen size and the initial crack length. While the influence of those both parameters on KISSC is now well documented, this has not been yet the case for Klimit.Klimit values have been obtained on a C110 casing in NACE TM0177 Solution A for three distinct situations:• with 9.53 mm thick specimens• with 9.53 mm thick specimens that were precracked by fatigue.• with 4.76 mm thick specimens. ©2014 by NACE International.

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