Mechanical Behavior Characterization of a Stainless Steel Dissimilar Metal Weld Interface : In-situ Micro-Tensile Testin

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RESEARCH PAPER

Mechanical Behavior Characterization of a Stainless Steel Dissimilar Metal Weld Interface : In-situ Micro-Tensile Testing on Carburized Martensite and Austenite ´ G. Ben Salem1,2,3 · E. Heripr e´ 2 · P. Bompard2 · S. Chapuliot1 · A. Blouin1 · C. Jacquemoud3 Received: 18 March 2019 / Accepted: 6 July 2020 © Society for Experimental Mechanics 2020

Abstract Background Stainless Steel Dissimilar Metal Welds (SS DMW) between low-alloy steel 18MND5 and austenitic 316L stainless steel are critical junctions in the currently operating reactors because of their heterogeneous microstructure and mechanical properties. The presence of a narrow hard layer of carburized martensite and austenite in the ferritic-austenitic interface creates an important hardness gradient which affects the crack behavior of the SS DMW. Objective In order to evaluate the plastic properties of this hard layer, a micro tensile testing method was developed. Methods Tensile specimens of 15 x 80 x 6 μm were extracted from the martensitic and carburized austenitic layers by focused ion beam (FIB) micro-processing and tested using an in-situ tensile testing device. A platinum FIB deposition was used to measure local strain in the specimen during the test through digital image correlation (DIC). Isotropic elasto-plastic constitutive laws for the martensite and carburized austenite were obtained from the true strain-stress curves calculated from the micro-tensile tests. Results It was found that the corresponding plastic properties were in a good agreement with nanoindentation measurements and with values obtained from macroscopic tensile tests on crossweld specimens machined perpendicularly to the ferritic-austenitic interface and characterized using laser beam local diameter measurements. Conclusions In-situ tensile testing is a promising technique for plastic behavior characterization of small scale materials and local hard layers in dissimilar metal welds. Keywords Dissimilar metal welds · Martensite · Carburized austenite · Plastic properties · Micro-tensile testing

Introduction Stainless Steel Dissimilar Metal Welds (SS DMW) between low-alloy steel 18MND5(∼A533) and austenitic 316L stainless steel are widely used within the French nuclear power plants, where they connect the main components to the primary circuit pipes (Fig. 1(a)). Because of their highly  G. Ben Salem

[email protected] 1

FRAMATOME, 1 Pl. Jean Millier, 92400, Courbevoie, France

2

Laboratoire MSSMat, UMR CNRS 8579, CentraleSupelec, 3 Rue Joliot Curie, 91190, Gif-sur-Yvette, France

3

DEN-Service d´ e´ tudes m´ecaniques et thermiques (SEMT), CEA, Universit´e Paris-Saclay, F-91191, Gif-sur-Yvette, France

heterogeneous microstructure, mechanical properties [1–3] and the existence of residual stresses [4], these components are critical for the integrity of the currently operating reactors [5–7]. The DMW under consideration is a 18MND5/316L weld with a 309L/308L buttering. The buttering is made on the ferritic component surface and then welded to a 316L stainl

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