Oxygen surface tension gradient
The oxygen surface tension gradient affects Marangoni convection in the weld pool, which changes the penetration geometry and can lead to porosity.
Physical-Chemical Mechanism of Action
The oxygen surface tension gradient is created by the different concentrations of dissolved oxygen at the surface of the molten material. This tension drives a Marangoni convection flow that moves the liquid around the surface.
Metallurgical Relevance & Risks in Welding
Changes in penetration profile due to the oxygen surface tension gradient can cause uneven melting and lead to porosity. This can impair the strength and mechanical properties of the weld.
Workshop Practice & Instructions
To minimize the oxygen surface tension gradient, the weld pool should be well shielded from atmospheric oxygen. Use suitable deoxidizers and ensure a uniform distribution of oxygen in the weld pool. With high heat input, the concentration of dissolved oxygen can increase, leading to a stronger gradient.