| When N₂was used as a shielding gas during the TiN surface-alloying treatment by irradiation of CO₂laser beam on TiN-coated steel, TiN did not decompose completely into Ti and nitrogen regardless of C-content in steel. When scanning speed of laser beam was fast, energy density was not enough to melt down TiN and this was dispersed in surface-alloyed region. Even though Ti content was more than 1.2% in surface-alloyed layer, it was believed that part of Ti content was inactive to shrink austenite region due to the formation of TiC and also C was austenite former in steel, thus martensitic structure was formed by rapid cooling of that layer, Therefore the increase in hardness of the surface-alloyed layer was attributed to refinement of grain size and dispersion of TiN in low carbon steel, while it was due to the formation of martensitic structure in addition to dispersion of TiN in high carbon steel. |
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