Graphitization Tendency

Thermodynamic tendency of carbon-rich iron to precipitate elemental carbon in the form of graphite during long-term exposure in the high-temperature range. This leads to a drastic weakening of mechanical strength.

Graphitization means: the carbon in the steel gives up its bond as carbide and deposits as soft graphite. This happens mainly during long, hot exposures. For welding this means: if you hold carbon-rich steel at high temperature for too long, the structure can "flip" and the material becomes soft and brittle at that spot. So you have to keep the heat input short and crisp and let the part cool down quickly after welding, so that the carbon remains bound as carbide. Otherwise you'll have a spot that gives way or cracks under load.

MetallurgieSchweißtechnik