| The concept of oxide metallurgy was applied to Ti-containing low carbon steels in order to investigate the effect of fine Ti-oxide inclusions on the microstructures and mechanical properties of the steels. When Ti-containing low carbon steels were cooled at a rate of 3 to 6 K/sec after austenitized at 1623 K, fine intragranular acicular ferrite was formed instead of relatively coarse Widmansta¨tten ferrite which forms without Ti addition under the same austenitizing and cooling conditions. The effective grain size and volume fraction of acicular ferrite were found to be dependent of austenite grain size, cooling rate, and chemical composition of steels. It has been observed that once the acicular ferrite nucleation is initiated at the surface of titanium oxide inclusion, the so-called sympathetic nucleation seems to be prevalent in the rest of the nucleation process. The ultimate tensile strength, yield ratio, and elongation were about 600 ㎫. 0.8, and 24%. respectively, when the composition of steel is 0.14%C, 1.8%Mn, 0.18%Si, 0.011%Ti, 0.003%O, and 0.001%N. |
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