Silicon graphitization tendency
Silicon promotes the breakdown of cementite into carbon and iron, which leads to graphite formation during solidification or heat treatment.
Physical-Chemical Mechanism of Action
Silicon reacts in the molten weld pool with cementite (a carbon-iron mixed crystal) and strips away carbon. This freed carbon then forms graphite as the temperature drops.
Metallurgical Relevance & Risks in Welding
Silicon's graphitization tendency can lead to increased graphite formation, which reduces the hardness and strength of the steel. It can also cause porosity and altered mechanical properties in the weld.
Shop Practice & Action Points
To control silicon's graphitization tendency, the Si content in cast iron must be precisely controlled. Too high a Si content can lead to increased graphite formation and reduced mechanical properties. If needed, additives like nickel or molybdenum can be used to reduce graphite formation.