Microchemical Analysis of Non-Metallic Inclusions in C-Mn Steel Shielded Metal Arc Welds by Analytical Transmission Electron Microscopy

摘要

Microchemical analyses of the inclusions present in several shielded metal-arc steel weld metals were made by analytical transmission electron microscopy (TEM). Low alloy C-Mn steel weld metal samples were studied in which only the titanium and aluminum contents varied significantly. Carbon extraction replicas were made from each of the weldments and the inclusions were analyzed in the TEM by energy dispersive x-ray (EDX) and parallel electron energy loss spectroscopy (PEELS). The results indicated that, for weld metals containing small amounts of M (13 ppm), the inclusions were comprised of MnO-SiO2, TiO (maybe as a compound) and Cu(Mn)S. As the M content was increased to 160 ppm, Mn and Si no longer took part in the deoxidization process and the inclusion compositions were dominated by TiO and A12O3 along with some sulfides. For weld metal containing a much higher amount of Al (580 ppm) the inclusions became essentially mixtures of TiO, Al2O3 and TiN sometimes complexed with sulfides. These inclusion chemistries were predicted by the use of equilibrium thermodynamics and their effect on the microstructure and mechanical properties of the steel weld metals investigated.