Nitrogen absorption
Nitrogen pickup is the process where nitrogen from the air or shielding gas is absorbed into the weld pool. Too much nitrogen causes porosity and reduces strength, while controlled amounts increase toughness.
Physical-Chemical Mechanism of Action
Nitrogen is a chemical element designated as N. It does not react directly with most metals, but it can be absorbed into the melt and move as gas or as molecules within the metal structure.
Metallurgical Relevance & Welding Risks
Too much nitrogen leads to porosity in the weld, which reduces mechanical strength and makes the material softer. This can cause hot cracks and other stability problems. However, controlled amounts of nitrogen can increase toughness and stabilize the structure.
Workshop Practice & Instructions
When welding, it is important to control the nitrogen content in the shielding gas. For low-carbon steel (e.g., 0.1 %), the nitrogen content in the shielding gas should be between 2 and 4 vol.%. For high-carbon steels (e.g., > 0.5 %), a higher nitrogen content of up to 8 vol.% may be appropriate. Monitor nitrogen pickup through measurements and adjust the shielding gas flow accordingly.