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The secret of hydrogen embrittlement: why does metal become brittle after welding?
In metal processing, a welding defect is any defect that prevents the effectiveness of the weld. The causes of these defects can be traced to a variety of factors, among which hydrogen embrittlement has received particular attention. Hydrogen embrittlement is a common phenomenon after welding that can cause metal to become brittle or even break during long-term use. This article aims to explore the causes of hydrogen embrittlement and how to effectively prevent this problem.
Causes of hydrogen embrittlement
Hydrogen embrittlement is mainly due to the dissolution of hydrogen during the welding process. As the metal cools, the hydrogen is trapped inside the grains of the material, resulting in the embrittlement of the metal. This embrittlement usually occurs within a few hours of welding being completed and can continue even after complete cooling.
"Hydrogen embrittlement is a material failure phenomenon closely related to the welding process, especially in structures that are periodically stressed."
Influencing factors of hydrogen embrittlement
A variety of factors may contribute to the occurrence of hydrogen embrittlement, including the materials used in the welding process, welding techniques, and post-processing procedures. Here are some of the main influencing factors:
1. Welding materials
Filler materials used during welding can increase the risk of hydrogen embrittlement if they contain a high hydrogen content. Certain filling materials tend to absorb moisture in natural environments, thereby increasing hydrogen production. Therefore, choosing hydrogen-free or low-hydrogen materials is one of the effective ways to reduce hydrogen embrittlement.
2. Residual stress
Residual stress after welding can make the metal more susceptible to cracking. By preheating the base material or performing post-weld heat treatment, residual stresses in the material can be reduced, which is important to avoid hydrogen embrittlement.
3. Coating and alloy composition
The material composition of the metal and its hardness affect the degree of hydrogen embrittlement. High-hardness alloys have low solubility for hydrogen, causing hydrogen to be trapped. Therefore, when the hardness of the welding material is reduced, the risk of hydrogen embrittlement decreases.
Measures to prevent and control hydrogen embrittlement
To effectively prevent hydrogen embrittlement, corresponding measures need to be taken during and after welding:
1. Adopt proper welding techniques
Hydrogen production can be reduced by selecting appropriate welding techniques based on material properties. Using slower cooling rates and appropriate welding heat input will help avoid martensite formation and improve the toughness of the metal.
2. Preheating before welding
Preheating before welding operations can significantly reduce the risk of hydrogen embrittlement. This process helps expel hydrogen gas from within the metal and reduces thermal stress.
3. Post-weld heat treatment
Post-weld heat treatment can not only release residual stress, but also promote the escape of hydrogen, effectively reducing the occurrence of hydrogen embrittlement.
Conclusion
The impact of hydrogen embrittlement cannot be ignored, especially in structures that are subject to cyclic stress, and the damage it can cause is unbearable. In the future, as welding technology continues to advance, hydrogen embrittlement prevention and control measures will also need to evolve to ensure the long-term reliability of the structure. Have you considered the impact of welding materials and techniques on your project?
