Nucleation Effect of Ca-Oxysulfide Inclusions of Low Carbon Steel in Heat Affected Zone by Welding

Abstract

In order to achieve excellent toughness of heat affected zone (HAZ) of low carbon steel plates by welding, several microstructure control techniques using fine particles have been developed. In particular, Ca-oxysulfide inclusions have been used in a lot of steel plate products, because they are thermally stable even in near the fusion line of weld joint and they have grain refining effect in HAZ. In cases where heat input is large (>100kJ/cm) and microstructure of HAZ mainly consists of polygonal ferrite, it has been clarified that Ca-oxysulfide inclusions act as nucleation sites of polygonal ferrite in HAZ during the cooling process after welding. However, in cases where heat input is medium (≈50kJ/cm) and microstructure of HAZ mainly consists of bainite, nucleation effect of Ca-oxysulfide inclusions and that of mechanism have not been clarified. This study investigated the nucleation effect of Ca-oxysulfide inclusions in medium heat input welding by in-situ laser microscope observation and the lattice misfit between Fe-matrix and Ca-oxysulfide inclusions.

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

“…A similar mechanism of dendritic crystallization with additional crystallization nuclei, oxides, and sulfides is shown in other publications [ 31 , 32 , 33 , 34 , 35 ]. The austenitic grain size in the dendritic crystallization is reduced from 770 to 344 µm in columnar and equiaxed zones of primary crystallites, as shown in the study by Salas-Reyes et al [ 36 ].…”

Effect of Welding Heat Input on the Microstructure and Impact Toughness of HAZ in 420 MPa-Grade Offshore Engineering Steel

“…It is well known that the Ca treatment can change the elongated MnS inclusions to the spherical CaS inclusions to improve the transverse toughness of the steel plate and change the Al 2 O 3 inclusions into the CaO-Al 2 O 3 complex inclusions with low melting point to inhibit the clogging of the submerging entry nozzle during continuous casting. In recent years, the oxide metallurgy with Ca deoxidation was utilized to improve the CGHAZ toughness in the steel plate (Terazawa et al, 2018). Kato et al (2011) found that Ca addition can increase the number density of fine TiN particles, inhibit the coarsening of TiN particles, and finally, achieve a fine-grained HAZ to improve its toughness.…”