Role of inclusions in formation of high strength steel weld metal microstructures

Abstract

A series of high strength weld metals with varying Al content are studied. The inclusions are characterised using energy dispersive X-ray analysis and electron diffraction. The tendency for alignment of the microstructure is characterised quantitatively using electron backscatter diffraction and a recently developed post-processing technique. Correlation is found between the inclusion phases present and the amount of aligned neighbouring grains in the microstructure. It is shown that amorphous Si–Al oxides form at low Al weld metal contents and an Mg–Al spinel at higher contents. The former is associated with less alignment of the microstructure and therefore higher impact toughness. The effect of these inclusions on the formation of the microstructure is discussed.

Keywords:

• EBSD
• Bainite
• Acicular ferrite
• Weld metal
• Inclusions
• Nucleation

Professor L.-E. Svensson at University West and Prof. H.-O. Andrén and Dr J. Weidow at Chalmers University of Technology are gratefully acknowledged for helpful suggestions, discussion and in the latter case, preparation of lift-out specimens.