The effects of Ti, B and N on the notch toughness of submerged arc weld metals were investigated and systematic studies on characterization of these elements were undertaken with various analytical techniques, including EPMA, EDAX and conventional ayalyses, boron autoradiography, hydrogen hot extraction analysis of N, infrared absorption analysis of BN and X-ray diffraction analysis of non-metallic inclusions.
Based on the experimental results and some model calculation, it has been concluded that the coexistence of Ti and B has dual advantage in improving notch toughness of the weld metals because
i) during terminal transient solidification, B has a unique ability to reduce "free N" while Ti protecting B from oxygen, and
ii) during r to a transformation, active B being present at a weld metal's grain boundaries retards nucleation of proeutectoid ferrite, and titanium monoxide promotes nucleation of acicular ferrite intragranularly since it has quite small crystallographic disregistry with a iron, thus producing very fine and homogeneous microstructures.