Investigation of Elastic Anisotropy and Texture of Austenitic Stainless Steel Weld Metal Using Diffraction and Self-Consistent Modelling

Abstract

Welding of austenitic stainless steels is a prominent process in several industrial sectors including nuclear, aerospace, chemical and process. During finite element modelling of weld properties, it is assumed that the weld metal is homogeneous. During the modelling process weld metal is assigned the same elastic constants as that of parent metal. This can introduce erroneous results during the calculation of strains. Weld metal is usually highly anisotropic due to directional solidification. Weld metal also possesses typical fibre texture as the grains grow along the maximum thermal gradient when cooling and the result is long, columnar grains. These grains usually have a particular crystallographic direction along the solidification direction. Weld metals usually have [011] crystallographic planes along the solidification direction, and it has been termed as [011] fibre texture. The resulting fibre texture due to solidification has an important consequence on weld metal properties. Depending on the grain orientations, different mechanical properties are observed as compared with an ideal homogeneous and isotropic material. Different types of austenitic weld metals have been investigated in this work. The mechanical response of different types of weld metal, in different directions has been analysed using in-situ tension/compression and neutron diffraction. It has been observed that the Young's modulus for the weld metal is direction dependent. These variations have been explained on the basis of texture investigation using the electron backscatter diffraction (EBSD) technique. The texture results have been correlated with the material response and it has been observed that the more pronounced the crystallographic texture, the more anisotropic is the material response under applied loading. Finally, the directional Young's modulus has also been calculated from elasto-plastic self-consistent modelling using Hutchinson's formalism (using the FORTRAN sub-routine written by Carlos Tome)