Carbon (C)
Carbon increases the hardness and strength of iron-based materials by enlarging the structure to martensite. This also makes the weld more prone to hot cracking and heat-affected zone cracking.
Physical-Chemical Mechanism of Action
Carbon reacts with iron in the molten pool to form martensite. This metallic structure is very hard and tough but prone to hot cracking under heat.
Metallurgical Relevance & Welding Risks
High carbon content (above 0.7%) leads to a strong martensitic structure, which increases hardness but simultaneously reduces the toughness and ductility of the weld. This can cause hot cracking and heat-affected zone cracking.
Workshop Practice & Action Guidelines
To minimize risks, the carbon content in the molten pool should be controlled. With high carbon content, slow cooling (t8/5 > 25 s) is recommended to make the structure softer and tougher.