Nano-carbide precipitates in Ti microalloyed steel under ultra fast cooling condition and their strengthening effect

Ti microalloyed steel is a high strength steel and has been widely used in national economy and defense industry. The nano-carbide precipitates in the Ti microalloyed steel produced by the ultra fast cooling process with a rolling cooling rate up to 64 ℃/s were obtained by nondestructive electrolysis extraction technology, and investigated through chemical phase analysis, X-ray small angle scattering and transmission electron microscopy. In addition, its effect on steel strengthening was also discussed. The results show that a large number of nano-sized Fe_xC and TiC precipitates exist in the Ti microalloyed steel and their average particle size are 76.06 nm and 133.95 nm, respectively. The Fe_xC precipitation behavior is strengthened by the ultra fast cooling process. Thus, the yield strength induced by FexC precipitate reaches 243.8 MPa, while that of TiC precipitate is only 63.1 MPa. However, the increasing mass fraction of TiC precipitate (＜40 nm) by 0.01 % can obviously improve the yield strength by 77.1 MPa, which is far higher than that of Fe_zC precipitate (＜40 nm). Therefore, strengthening the precipitation behavior of TiC plays an important role in improving steel yield strength.