Applying electron backscattering diffraction to macroscopic residual stress characterisation in a dissimilar weld

A.D. Warren,H.E. Coules,K. Abburi Venkata,C.E. Truman

doi:10.1016/j.jmatprotec.2016.11.003

A.D. Warren, H.E. Coules + Show 2 more

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https://doi.org/10.1016/j.jmatprotec.2016.11.003

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Abstract

Dissimilar metal welds are complicated in nature because of the complex microstructure characteristics in the weld fusion zone. It is often necessary to know the phase distribution in a dissimilar metal weld especially at the interface such as fusion zone and heat affected zone to be able to predict the behaviour of the joint and its fitness for service. In this paper, a dissimilar metal weld made between ferritic/martensitic modified 9Cr-1Mo steel (P91) and austenitic AISI 316LN stainless steel using autogenous electron beam (EB) welding was analysed. The weld fusion zone has a local segregation of bcc and fcc phases. The EBSD technique was applied to determine the volume fractions of each of these phases in the weld fusion zone. This information was incorporated into the analysis of neutron diffraction data from the weld zone, and the macro-scale residual stresses were calculated from phase-specific stresses arising from the welding process. The results indicate that the overall macroscopic residual stress distribution in the weld centre is predominantly compressive in nature driven by the solid-state phase transformation of the weld pool during rapid cooling, with tensile peaks pushed adjacent to the heat affected zone (HAZ)/Parent boundaries on both sides of the fusion zone.

Highlights

Dissimilar metal welds are often used in industrial applications and usually create a complex fusion zone that is essentially different from the parent materials
According to a case study conducted by Hajri et al (2015) on dissimilar metal weld joint in a superheater tube, indicated that failure occurred on alloy steel side rather than stainless steel side because of decrease in creep strength and increase in hardness at the weld interface on alloy steel side as a result of the microstructure
EBSD technique has been applied to a dissimilar weld joint between P91 ferritic steel and 316LN stainless steel using electron beam (EB) welding, to analyse the microstructure in terms of grain size and phase distribution in the fusion zone and heat affected zone (HAZ)

Summary

Introduction

Dissimilar metal welds are often used in industrial applications and usually create a complex fusion zone that is essentially different from the parent materials. Dawson (2012) in his research has studied the interfaces in transition joints made between ferritic steels of different Cr percentages. EBSD technique has been applied to a dissimilar weld joint between P91 ferritic steel and 316LN stainless steel using EB welding, to analyse the microstructure in terms of grain size and phase distribution in the fusion zone and HAZ. This information was used to determine the macroscopic residual stress state in the fusion zone, from the phase dependent macrostresses measured by neutron diffraction on the welded plate, based on the identified phases and phase fractions. The details of the experiment and the final results are presented and discussed

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Experimental setup

Results