The effect of carbon: Carbon in austenitic stainless steel is an element that strongly forms and stabilizes austenite and expands the austenite region. The ability of carbon to form austenite is about 30 times that of nickel, carbon is a interstitial element, and the strength of austenitic stainless steel can be significantly improved by solution strengthening. Carbon can also improve the stress and corrosion resistance of austenitic stainless steel in highly concentrated chlorides (such as 42%MgCl2 boiling solution).
However, in austenitic stainless steel, carbon is often regarded as a harmful element, mainly because under some conditions in the corrosion resistance of stainless steel (such as welding or heating at 450~850 degree C), carbon can form high-chromium Cr23C6 carbon compounds with chromium in steel, resulting in local chromium depletion, so that the corrosion resistance of steel, especially the resistance to intergranular corrosion, is reduced. Therefore. Since the 1960s, the new development of chromium-nickel austenitic stainless steel is mostly carbon content less than 0.03% or 0.02% ultra-low carbon type, it can be known that with the reduction of carbon content, the intergranular corrosion sensitivity of steel is reduced, when the carbon content is less than 0.02% to have the most obvious effect, some experiments also pointed out that carbon will increase the point corrosion tendency of chromium-austenitic stainless steel. Due to the harmful effect of carbon, not only should the carbon content be controlled as low as possible in the process of austenitic stainless steel smelting as required, but also in the subsequent hot, cold processing and heat treatment process to prevent the surface of stainless steel carburization and avoid chromium carbide precipitation.