Acicular ferrite nucleation and growth in API5L-X65 steel submerged arc welded joints

Abstract

In the present study, acicular ferrite nucleation and growth were investigated from a crystallographic point of view in API5L-X65 steel weld metals. It was observed that acicular ferrite was nucleated on inclusions in weld metal. The titanium-enriched layer around inclusions was characterised as the TiO phase by selected area diffraction patterns. A scanning electron microscope equipped with an electron backscatter diffraction technique was applied to investigate the crystallographic orientation relationship. The results showed that acicular ferrite lathes had a Baker–Nutting orientation relationship with the TiO layer on the inclusion surface in the nucleation of acicular ferrite. However, it is confirmed that the growth of acicular ferrite lathes depends on the deviation from the Kurdjumov–Sachs relationship between lathes and primary austenite.

Influence of Shielding Gas on Microstructure and Properties of GMAW DSS2205 Welded Joints

“…On the other hand, it is also related to the incomplete formation of austenite and the faults in WS and HAZ. Controlling the appropriate ferrite-austenite ratio (1:1) is an excellent method to improve the strength and toughness of dual-phase stainless steel [31]. The crystal defects can reduce the strength of welded joints because it promotes dislocation movement and crack initiation in tensile process [32,33].…”

Review of Research on Titanium Oxides in Low‐Carbon Steel

“…There are two additional mechanisms that explain the nucleation of IGF on the surface of titanium oxides: 1) Because the mismatch between the structure of titanium oxide lattice (especially TiO) and that of ferrite lattice is smaller than the mismatch between titanium oxide lattice and the surrounding austenite lattice, austenite transforms easily into ferrite on the surface of titanium oxide. [32][33][34][35][36][37][38][39][40][41] 2) Because the expansion coefficient of titanium oxide may be roughly half that of austenite, a large stress-strain field can form around titanium oxide during the cooling process. [42] Such distortion can provide activation energy for ferritic nucleation and can promote an austenite-ferrite transition.…”

“…IGF grows on relatively large-sized titanium oxides (diameter in the range of 2-5 μm), as shown in Figure 5a,b. [36,54,56] Many literature showed that MnS attaches to the surface of titanium oxide at this size range. [54][55][56][57][58][59][60][61][62][63][64][65][66][67][68][69][70] This kind of complex titanium oxides has a stronger nucleation promotion ability than the unattached titanium oxides.…”

Effect of Mg, La and Ca addition order on inclusions and microstructure of Ti-bearing C–Mn steel

“…MDZ formed in the vicinity of inclusions has been widely believed to induce the nucleation of AF effectively [42]. Results of researches indicated that the precipitation of MnS on the surface of oxide led to the formation of MDZ [43,44]. Meanwhile, Mabuchi et al [45] verified that the existence of MDZ in the vicinity of MnS by FE-TEM.…”