Hydrogen-Scavenging Additive
Hydrogen-binding additive forms stable hydrides or fluorides that make hydrogen diffusible and prevent cracking.
Physical-Chemical Mechanism of Action
A hydrogen-binding additive reacts with the water vapor in the weld pool and forms hydrides or fluorides. These compounds hold the hydrogen at the crystal grains, prevent its diffusion into the weld, and thus protect against cracks.
Metallurgical Relevance & Risks in Welding
Without a hydrogen-binding additive, hydrogen can accumulate in the weld pool and diffuse into the weld. This leads to hot cracks, especially at high temperatures and long cooling times. Such an additive prevents this diffusion and improves the crack resistance of the weld.
Workshop Practice & Instructions
Use a hydrogen-binding additive like silicon or titanium in the filler metal when you expect high crack resistance. For steels with high carbon content (e.g., HSS), such an additive is especially important. The amount varies depending on the material and welding process, but typically it is between 0.1% and 0.5%. Make sure the additive dissolves well in the melt and doesn't cause unwanted reactions.