Deoxidation loss of silicon
Silicon reacts with oxygen in the weld pool to form silicate. This prevents porosity, increases strength and scale resistance, but too much silicon can lead to embrittlement.
Physical-Chemical Mechanism of Action
Silicon reacts in the liquid weld pool with oxygen (O₂) to form silicate (SiO₂). This process prevents oxygen from entering the weld and causing porosity. At the same time, silicon increases the strength and scale resistance of the joined steel.
Metallurgical Relevance & Risks in Welding
Too high silicon content (over approx. 0.40% combined with carbon) can lead to embrittlement of the weld. This increases susceptibility to hot cracking and reduces mechanical strength. Moreover, improper silicon content can lead to a wet, glass-hard structure, endangering weld integrity.
Workshop Practice & Instructions
To make the most of silicon deoxidation, the silicon content in filler material should be between 0.15% and 0.30%. This ensures a porosity-free weld without embrittlement or glass-hard structures. At high travel speeds or when using filler with high silicon, control the melting time and cooling to ensure even cooling.