Controlled surface treatment of mild steel with carbon nanotubes at austenitic temperature

This study reports a novel nanocarburization of mild steel using carbon nanotubes at specified austenitic temperature. Carbon nanotubes synthesized in a horizontal chemical vapour deposition reactor were used to enhance the surface hardness of mild steel at 750°C austenitic temperature for 40 minutes carburization period. Various samples of known composition of mild steel were carburized with as-synthesized carbon nanotubes, purified carbon nanotubes and amorphous carbon. The resultant carburized samples were subjected to surface hardness test, and the results of the analyses indicated improved surface hardness having the highest peak surface hardness value of 173.842 ± 4.89 GPa with the purified carbon nanotubes, followed by as-synthesized carbon nanotubes with 162.56 ± 1.55 GPa; and the least was the amorphous carbon with 155.74 ± 4.28 GPa. These values were still higher than that of the original metal substrate, which was 145.188 ± 2.66 GPa. The enhanced surface microhardness displayed by the carbon nanotubes can be attributed to their nano-sizes which assisted in increased diffusion of these materials at the austenitic temperature under study coupled with higher mechanical properties exhibited by these carbon materials.