Study on precipitation behavior of Ce and Nb during solidification

In order to solve the problem of forming liquid precipitated NbC when Nb is added excessively in high carbon steel. This study proposed to introduce Ce to form Ce-containing inclusions to inhibit the growth of large liquid precipitated NbC. The results show that in the high strength valve spring steel with 0.63 % carbon mass fraction, the large liquid precipitated NbC will be formed only if the mass fraction of Nb exceeds 0.0192 %. When the mass fraction of Ce in steel is higher than 0.0364 %. In addition to the formation of high melting point Ce 2 O 3, Ce 2 C 3 carbide will be precipitated at the end of solidification. And the amount of Ce 2 C 3 precipitation will increase with the increase of Ce mass fraction in steel. Ce 2 O 3 and Ce 2 C 3 have low two-dimensional lattice mismatch degree with NbC. both of them can be nucleation sites of NbC, which lead to multi-point precipitation and avoid aggregation and growth of NbC. However, the content of Ce should not be too high, which will be dominated by the precipitation of Ce, and the best mass fraction of Ce and Nb is between 0.02 % and 0.05 %.