Influence of Acicular Ferrite Microstructure on Toughness of Ti-Rare Earth Metal (REM)-Zr Killed Steel

Novel oxide particles composed of Ti, rare-earth metal and Zr was found by the present authors to promote formation acicular ferrite (AF), but their effect on toughness has not yet been clarified. Therefore, influence AF low carbon steel investigated using Ti-Rare earth metal-Zr-killed (TRZ) Al-killed (AL) steels in this study. Dominant microstructure AL is bainite forming block/packet structure elongated from prior austenite grain boundaries. In contrast, a large amount which grows intragranular inclusions formed TRZ steel. Toughness better than addition, at higher austenitizing temperature, promoted steel, leading lowering ductile-brittle transition temperature. Cracks Charpy impact specimens propagate along {001}α plane deflect Bain unit boundary across planes are largely misoriented, means effective size for crack propagation size. smaller since subdivided pre-formed AFs belonging different groups bainite. Martensite-austenite constituent (MA) less-elongated comparison those thus MA less These results clarify that improves due refinement reduction MA.