Equalization Time for Hydrogen Diffusion
The time a weld needs for a post-weld heat treatment to remove hydrogen and prevent delayed cracking.
Physical-Chemical Mechanism of Action
Hydrogen can diffuse into the metal structure and be stored as hydrides. During post-weld heat treatment, this hydrogen is released and removed from the metal. The holding time determines how long these diffusion processes must occur.
Metallurgical Relevance & Risks in Welding
Too short a post-weld heat treatment can leave hydrogen in the weld, causing delayed cracking (such as cracks or hot cracks). However, excessively long times are inefficient and unnecessarily expensive.
Workshop Practice & Instructions
The holding time depends on the metal used and the welding technique. For steel with a hydrogen content of 100 ppm, the post-weld heat treatment should last at least 24 hours. For higher hydrogen content, this can be increased up to 7 days.