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Inclusion Characteristics and Acicular Ferrite Nucleation in Ti‐Containing Weld Metals of X70 Pipeline Steel
Author(s) -
Wang Bingxin,
Liu Xianghua,
Wang Guodong
Publication year - 2018
Publication title -
steel research international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.603
H-Index - 49
eISSN - 1869-344X
pISSN - 1611-3683
DOI - 10.1002/srin.201700316
Subject(s) - acicular ferrite , spinel , materials science , metallurgy , nucleation , acicular , ferrite (magnet) , scanning electron microscope , bainite , microstructure , composite material , austenite , chemistry , organic chemistry
The X70 steel weld metals with Ti content of 0.003–0.13% are prepared by single pass submerged‐arc welding process. The effects of Ti content in weld metals on the constituent phases of inclusions and potential of acicular ferrite nucleation on the inclusions are in detail investigated by means of electron probe micro‐analysis, scanning transmission electron microscopy, and thermodynamic calculation. The obtained results show that with an increase of Ti content, primary constituent phases of inclusions are changed from (Mn–Al–Si–O) compound to a mixture of spinel and pseudobrookite solid solutions, eventually to pseudobrookite. The spinel solid solution is characterized by MnTi 2 O 4 constituent. The proportion of Ti 3 O 5 in pseudobrookite is increased remarkably with an increase in Ti content at the expense of MnTi 2 O 5 constituent. Compared with pseudobrookite, spinel has lower Ti concentration, but significantly higher Mn content regardless of Ti content in the weld metals. In the case of presence of a considerable amount of spinel primarily composed of MnTi 2 O 4 , Mn element is enriched strongly in the inclusions, resulting in the development of Mn‐depleted zone in matrix around the inclusions, which enhances the capability of inclusions nucleating intragranular acicular ferrite.