Residual carbon enrichment
Residual carbon enrichment increases the carbon content in austenite, which increases its stability and prevents transformations.
Physico-Chemical Mechanism of Action
Residual carbon enrichment occurs during the diffusion phases. Carbon atoms diffuse from the martensitic regions into the remaining austenite pockets and accumulate there. This leads to a local increase in the carbon content in these areas.
Metallurgical Relevance & Welding Risks
Carbon enrichment in austenite can increase the stability of this structure, which promotes an avoidable transformation into martensite during cooling. This reduces the risk of hot cracking and improves the mechanical properties of the weld.
Shop Practice & Action Guidelines
To ensure effective residual carbon enrichment, it is important to design the melting process so that carbon atoms can diffuse from the weld pool into the austenite pockets. This requires careful control of temperature and time during cooling. Too rapid cooling can prevent enough carbon from diffusing, which in turn increases the risk of hot cracking.