Inclusion Characteristics and Acicular Ferrite Nucleation in Ti‐Containing Weld Metals of X70 Pipeline Steel

Abstract

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.

Acicular Ferrite Identification in Heat‐Affected Zone of a Ti‐Killed High Strength Low Alloy Steel

“…[20] Ti-deoxidation has been found as an effective way of promoting AF-nucleation effective particles, and it has been successfully implemented in steel industrial production. [4] Various inclusions after Ti-deoxidation have been found effective in stimulating AF nucleation, including MnTi 2 O 4, [21][22][23] TiO, [24,25] and Mn-Si-Al-Ti-O amorphous phases. [26] Despite the wide range of effective inclusions found…”

“…[ 20 ] Ti‐deoxidation has been found as an effective way of promoting AF‐nucleation effective particles, and it has been successfully implemented in steel industrial production. [ 4 ] Various inclusions after Ti‐deoxidation have been found effective in stimulating AF nucleation, including MnTi 2 O 4, [ 21–23 ] TiO, [ 24,25 ] and Mn–Si–Al–Ti–O amorphous phases. [ 26 ] Despite the wide range of effective inclusions found in the literature, only those compositions and structures confirmed by scanning transmission electron microscopy combined with energy dispersive spectrometry (EDS) and selected area diffraction pattern were listed here.…”

The Effect of Electrochemical Composite Coatings with LaF3-LaB6 Particles in Nickel–Copper Matrix on the Metallurgical Processes in Arc Welding of Low Alloy Ferrite-Pearlite Steels

“…Thus, all these compounds formed in the weld pool increase the amount of crystallization nuclei, which contributes to the grain refinement of the microstructure and acicular ferrite nucleation [ 16 , 17 ]. Non-metallic spherical inclusions TiO, TiO 2 , Ti 2 O 3 can also be the effective nuclei of acicular ferrite formation [ 18 , 19 , 20 , 21 , 22 ]. However, REMs have an advantage because they are more active in desulfurization and deoxidation reactions [ 23 , 24 ].…”