Role of non-metallic inclusions in formation of acicular ferrite in low alloy weld metals

Abstract

A critical investigation into the role of non-metallic inclusions in the nucleation of acicular ferrite in low alloy C-Mn-Niweld metals was carried out using rapid in situ quenching, transmission electron microscopy, energy dispersive X -ray spectroscopy analysis, and dilatometric techniques. The relationship between the transformed acicular ferrite, the inclusions, and the chemical nature of the inclusions which had actually nucleated ferrite laths was examined in detail. By employing weld metals with either intermediate (200-350 ppm) or low (15-30 ppm) oxygen levels, the inclusion chemistry and nucleation behaviour of acicular ferrite in welds with different oxygen contents were compared. In addition, the influence of the [Al]/[O] ratio in lower oxygen content weld metals was also examined. It was found that the first acicular ferrite laths nucleated from the inclusions at both oxygen levels, and the chemical composition of the active inclusions varied considerably. The inclusions nucleated acicular ferrite by acting simply as inert substrates with the ability to reduce the free energy barrier to nucleation. The number and size distribution of the inclusions appeared to be the dominant factors; the thermal stress-strain fields and lattice disregistry were less important. The mostfavourable type of inclusions were within the size range 0'3-0'9 flmfor the higher oxygen content weld metals and 0·35-0·75 flmfor the lower oxygen level weld metals. A high [Al]/fO] ratio depresses the formation of acicular ferrite by increasing the soluble matrix aluminium content, which encourages extensive ferrite sideplate formation; the concurrent variation in inclusion chemical composition did not appear to influence the nucleation of acicular ferrite.MST/3209

Modeling of manganese sulfide formation during the solidification of steel

“…12b, which is detrimental to steel properties. Additionally, there is a favorable diameter, ranging from approximately 0.3 to 0.9 lm when utilizing inclusions such as heterogeneous nucleation sites for acicular ferrite [51,52]. In industrial solidification processes, the local cooling rate varies between several hundred degrees per second for welding and strip casting, whereas for continuous casting or ingot casting the local cooling rate might decrease to less than 0.1 degree per second close to the center of the cast part.…”

Inclusion Evolution Behavior of Ti-Mg Oxide Metallurgy Steel and Its Effect on a High Heat Input Welding HAZ

“…The most accepted explanation is that an Mn-depleted zone (MDZ) can be formed around Ti-containing oxides. An MDZ is formed because of the difference between the There are several mechanisms that explain the nucleation of AF: (1) the solute depletion in the vicinity of non-metallic inclusions [25][26][27][28]; (2) thermal strain energy due to a different thermal contraction [29]; (3) reduced interfacial energy between austenite and ferrite [30]; and (4) provision of an inert surface [31]. The most accepted explanation is that an Mn-depleted zone (MDZ) can be formed around Ti-containing oxides.…”

Study on the Control of Rare Earth Metals and Their Behaviors in the Industrial Practical Production of Q420q Structural Bridge Steel Plate

“…People studied the optimum mass ratio of La and Ce in La + Ce combined treatment, and the best incubation time of Le + Ce (3:1) treatment [10]. There were some works on the efficiency of Ti-bearing inclusions in refining the grain size, and dealing with Al and Mn contents in weld metal inclusions [11,12]. Moreover, some research has focused on the effect of RE in high-heat-input welding, and the induction of acicular ferrite behavior [13][14][15].…”