Hi,

I have another problem with carburizing, I know that carburizing diffuses carbon atoms to the surface of the steel to increase it's hardness. However, I have no idea how carburizing can improve the fatigue resistance of the steel. Are there any correlation with hardness and fatigue resistance?

Thanks!

Hi Melrose

Generally, processes that cause expansion of the surface layers of a material producing a compressive stress within the surface tend to have improve fatigue resistance. Many surface hardening processes like carburising. nitriding, induction hardening produce this effect. With carburising you are adding carbon to the surface of steel, which will have a limited expansion/stressing effect, but on hardening this carbon rich surface you get a martensitic reaction and expansion. The core material on the other hand does not, so the surface expansion is restrained by the core causing compressive stress in the surface.