Effect of Ni content on the microstructure and mechanical properties of weld metal with both-side submerged arc welding technique

The effects of nickel (Ni) content on the mechanical properties and microstructure evolution in the weld metals of commercial K65 oil and gas pipeline steel were studied. Increase Ni content could significantly improve the strength and low temperature impact toughness (−40 °C and −60 °C) of the weld...

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Bibliographic Details
Published in:Materials characterization 2018-04, Vol.138, p.67-77
Main Authors: Wang, Z.Q., Wang, X.L., Nan, Y.R., Shang, C.J., Wang, X.M., Liu, K., Chen, B.
Format: Article
Language:English
Subjects:
AUSTENITE
BACKSCATTERING
CRYSTALLOGRAPHY
ELECTRON DIFFRACTION
FERRITE
GRAIN BOUNDARIES
Grain boundary ferrite
High angle boundary
M/A constituent
MARTENSITE
MATERIALS SCIENCE
MECHANICAL PROPERTIES
NICKEL ADDITIONS
PHASE TRANSFORMATIONS
STEELS
SUBMERGED ARC WELDING
Weld metal
WELDED JOINTS
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Summary:The effects of nickel (Ni) content on the mechanical properties and microstructure evolution in the weld metals of commercial K65 oil and gas pipeline steel were studied. Increase Ni content could significantly improve the strength and low temperature impact toughness (−40 °C and −60 °C) of the weld metal. The above influences of Ni were attributed to the formation of predominant acicular ferrite (AF), at the expense of grain boundary ferrite (GBF), ferrite side plates (FSP) and martensite/austenite (M/A) constituent in weld metal. EBSD results indicated that GBF keeps K-S or N-W relations only with the prior austensite grain that belongs to one side of the grain boundary and the variants belong to the same bain group which always forms low angle boundary. Moreover, the retained austenite as one part of M/A constituent was mainly found in the weld metal with lower Ni content. It indicated that the transformation process could be promoted more completely by the increase of Ni content. The mechanism of the toughness improvement brought by Ni increasing was ascribed to the relatively uniform transformation to final microstructure, which reduces the appearance of GBF and M/A constituents. •This manuscript primarily studied the effects of Ni content on the K65 weld metals;•Increase Ni content could significantly improve the strength and low temperature impact toughness of the weld metal.•The beneficial effect of Ni is attributed to its positive effect on phase transformation.•GBF keeps K-S or N-W relations only with one austenite and the variants belong to the same bain group are two reasons.•The M/A islands are considered to be another reason for the reduced toughness.
ISSN:1044-5803
1873-4189
DOI:10.1016/j.matchar.2018.01.039