Research On Surface Color Controling And Structure Property Of The Steel After Composite Heat Treatment

The surface of steel Q235 is red sometimes after gas multicomponent thermochemical treatment. The thermodynamic calculation of Fe-O system and Fe2O3-H system was researched, and the surface color could be controlled by reduction reaction treatment. The chemical heat treatment on the surface of steel Q235 was researched, a composite heat treatment process,which including diffusion aluminizing+gas multicomponent thermochemical treatment+reduction reaction treatment,was explored,in order to improve the surface corrosion resistance to salt spray, improve the uneven,unsightly color and change the other shortcomings of the surface after gas multicomponent thermochemical treatment only.Samples in each group treated by different process, was analyzed by salt spray corrosion test,metallographic examination phase analysis,tensile strength analysis,impact properties test,wear-resistance test and hardness analysis.The results show that, the surface of the samples, processed by composite heat treatment, is more uniform and beautiful than the samples, which are processed by gas multicomponent thermochemical treatment and by diffusion aluminizing+gas multicomponent thermochemical treatment respectively. The major components is Fe2O3 on the surface of samples processed by gas multicomponent thermochemical treatment and by diffusion aluminizing+gas multicomponent thermochemical treatment, but Fe3O4 on the surface of samples processed by composite heat treatment, The corrosion resistance of which has a substantial increase than samples processed by gas multicomponent thermochemical treatment. The tensile strength of the composite heat treatment samples is slightly higher than samples without composite heat treatment, whose yield strength is 10% lower but impact properties is better than composite heat treatment samples, whose wear resistance and hardness values is not decreased. Consider all of the factors, in a word, samples with composite heat treatment, have a good performance in surface color,corrosion resistance,tensile strength,wear-resistance and hardness.