In Situ Observation of Grain Refinement in the Simulated Heat‐Affected Zone of Al–Ti‐0.05% Ce‐Deoxidized Steel

Abstract

The particles and microstructural characteristics in the simulated heat‐affected zone (HAZ) of the Al–Ti deoxidized steel with 0.05% Ce treatment are investigated using in situ, optical, and electron microscopes and an electron backscattered diffraction analysis, and compared with the Al–Ti deoxidized steel with Ca treatment. The results reveal that the fine CeAlO3 inclusions and nanoscale (Ti, Nb)N precipitates are formed in the Ce‐bearing steel instead of the Ca–Al oxides surrounded by TiN and nanoscale (Ti, Nb)N precipitates in the Ca‐bearing steel. The nanoscale precipitates with higher density in the Ce‐bearing steel can effectively pin austenite grain boundary, and the finer austenite grain is obtained during the welding thermal cycle. The inclusions in both steels are detrimental to the acicular ferrite nucleation. Thus, the transformation from austenite to bainite occurs actively, and bainite packets with different lengthening directions divide the prior austenite into several small regions at intermediate temperature. The fine‐grained microstructure is obtained in the simulated HAZ of the Ce‐bearing steel due to the pinning effect of finer precipitates with higher density and the formation of the bainite packets with high‐angle grain boundary.

Mechanism of Improving Heat-Affected Zone Toughness of Steel Plate with Mg Deoxidation after High-Heat-Input Welding

“…Nowadays, in situ observation with high-temperature laser scanning confocal microscopy (HT-LSCM) has been utilized extensively to investigate the behavior of austenite grain growth during the thermal cycle of HAZ [25,26]. Wan et al [27] found that the growth process of austenite grains in Ti-micro-alloyed steel was a continuous process during heating, isothermal holding, and cooling in the simulated HAZ thermal cycling.…”

Effect of Mg on the Evolution of Inclusions and Formation of Acicular Ferrite in La–Ti‐Treated Steels

“…The good combination of strength and toughness is usually associated with high density of the high‐angle grain boundary (HAGB) between the ferrite laths . The HAGB acts as obstacles to cleavage propagation and forces the cleavage crack to change the microscopic plane of propagation to accommodate the new local crystallography …”

Oxide Metallurgy Technology in High Strength Steel: A Review

“…The studies using RE to modify inclusions and improving steel microstructure and properties through the control of RE inclusions are also gradually increasing [7][8][9]. In addition, disperse high melting point RE inclusions are used to pin the austenite grain boundary and induce AF nucleation during the welding, which can also play the role in oxide metallurgy technology [10]. However, for high strength steel with high carbon equivalent, it is difficult to form AF, and easy to produce brittle structures such as upper bainite.…”