Effects of microalloying Ti and B on themicrostructures and low temperature toughness ofmanual metal arc (MMA) deposits were investi-gated.Weld metals containing 200-300 ppm Ti and29-60 ppm B deposited by manual coated elec-trodes provided an optimum low temperaturetoughness.The addition of B in weld metals low-ered the γ→α transformation temperature whichpromoted the acicular ferrite (AF) transformation.Solid solutioned B suppressed grain boundaryferrite as well as side plate ferrite formation andbenefited the acicular ferrite formation.Titaniumprotected B from oxidizing as well as nitriding andformed Ti-Mn silicate inclusions.Ultra-high volt-age electron microscope analyses showed that TiOstructure in the Ti-Mn silicate inclusions was thefavorable nucleation site for acicular ferrite forma-tion.
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