Improving impact toughness of a high chromium cast iron regarding joint additive of nitrogen and titanium

In this work, the effect of nitrogen on the as-cast microstructure and impact toughness of high chromium cast irons(HCCIs) mainly containing 2.2%C, 25.0%Cr and 0.8%Ti was studied (all compositions are in wt.% in this work). The experimental results showed that with the addition of N(0.028%, 0.075%, 0.2%, respectively), Ti(C,N) precipitates were formed in the high chromium cast irons, and dispersedly distributed in M₇C₃ carbides and austenite matrix. With the increase of nitrogen content, the microstructure was significantly refined, especially the M₇C₃ carbides, which was related to the heterogeneous nucleation of M₇C₃ carbide where Ti(C,N) precipitates act as the heterogeneous nuclei substrates. The Rockwell hardness of the specimen with 0.2% nitrogen increased to 49HRC in comparison to the specimen with 0.028% nitrogen (47HRC). The impact toughness of the specimen reached its peak value of 20.79J/cm² with 0.075% nitrogen, improving almost 80% compared with the specimen with 0.028% nitrogen (11.80J/cm²).