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Carbon Steel Hydrogen Embrittlement
The analysis of hydrogen embrittlement of carbon steel
Carbon steel is widely used in various industries. However, the problem of hydrogen embrittlement cannot be ignored.
Hydrogen embrittlement occurs because hydrogen atoms enter the lattice of carbon steel, causing its performance to deteriorate. In the environment of carbon steel, if there is hydrogen-rich state, such as pickling, electroplating, or service in hydrogen-containing media, hydrogen atoms are easy to enter. At the beginning, there is no appearance, but after a long time of accumulation, the internal microstructure of carbon steel gradually changes.
After hydrogen atoms enter the lattice, they interact with dislocations. Dislocations are also defects in crystals. Hydrogen atoms tend to gather at the dislocation, forming an air mass. This air mass hinders the movement of the dislocation, just like a boulder blockage, causing the plasticity of the material to gradually decrease. When stress is added, the dislocation should slip and climb to slow down the stress, but due to the fetters of the hydrogen atom air mass, the dislocation is difficult to travel smoothly, and the stress then accumulates locally.
If the accumulated stress is within the limit that the ultra-carbon steel can bear, micro-cracks will occur. The crack starts at the beginning, and it is subtle and difficult to detect. However, with the passage of time, or the repeated action of stress, the crack is like a silverfish eating wood, and gradually expands. The extension path, or along the grain boundary, or passes through the crystal. Expanding along the grain boundary, due to the irregular arrangement of atoms at the grain boundary, hydrogen atoms are easily enriched, weakening the bonding force of the grain boundary; transcrystalline expansion is due to the concentration of stress inside the grain.
Once the crack extends to the critical size, the carbon steel component suddenly breaks, and its state is very dangerous. This fracture state is different from ordinary ductile fracture, and it often shows a brittle appearance without obvious plastic deformation. Therefore, in the design, manufacture and use of carbon steel products, the anti-hydrogen embrittlement policy is crucial.
To prevent hydrogen embrittlement, choose carbon steel with excellent hydrogen embrittlement resistance, consider its chemical composition and microstructure. Control the content of impurities, such as sulfur and phosphorus, because it affects the diffusion and accumulation of hydrogen. At the time of processing, optimize the process. After pickling, it is advisable to remove hydrogen quickly, and use thermal diffusion method to raise the temperature to make the hydrogen escape. Electroplating process also needs to be improved to reduce the amount of hydrogen.
During use, monitor the environment. Control the hydrogen content of the medium. If it is unavoidable, add a corrosion inhibitor to prevent the reaction of hydrogen atoms with the surface of the carbon steel. Periodic inspection, micro-cracking, and disposal at the time of germination to avoid major disasters. In this way, the danger of hydrogen embrittlement of carbon steel can be reduced, and its safe service can be guaranteed.
Carbon steel is widely used in various industries. However, the problem of hydrogen embrittlement cannot be ignored.
Hydrogen embrittlement occurs because hydrogen atoms enter the lattice of carbon steel, causing its performance to deteriorate. In the environment of carbon steel, if there is hydrogen-rich state, such as pickling, electroplating, or service in hydrogen-containing media, hydrogen atoms are easy to enter. At the beginning, there is no appearance, but after a long time of accumulation, the internal microstructure of carbon steel gradually changes.
After hydrogen atoms enter the lattice, they interact with dislocations. Dislocations are also defects in crystals. Hydrogen atoms tend to gather at the dislocation, forming an air mass. This air mass hinders the movement of the dislocation, just like a boulder blockage, causing the plasticity of the material to gradually decrease. When stress is added, the dislocation should slip and climb to slow down the stress, but due to the fetters of the hydrogen atom air mass, the dislocation is difficult to travel smoothly, and the stress then accumulates locally.
If the accumulated stress is within the limit that the ultra-carbon steel can bear, micro-cracks will occur. The crack starts at the beginning, and it is subtle and difficult to detect. However, with the passage of time, or the repeated action of stress, the crack is like a silverfish eating wood, and gradually expands. The extension path, or along the grain boundary, or passes through the crystal. Expanding along the grain boundary, due to the irregular arrangement of atoms at the grain boundary, hydrogen atoms are easily enriched, weakening the bonding force of the grain boundary; transcrystalline expansion is due to the concentration of stress inside the grain.
Once the crack extends to the critical size, the carbon steel component suddenly breaks, and its state is very dangerous. This fracture state is different from ordinary ductile fracture, and it often shows a brittle appearance without obvious plastic deformation. Therefore, in the design, manufacture and use of carbon steel products, the anti-hydrogen embrittlement policy is crucial.
To prevent hydrogen embrittlement, choose carbon steel with excellent hydrogen embrittlement resistance, consider its chemical composition and microstructure. Control the content of impurities, such as sulfur and phosphorus, because it affects the diffusion and accumulation of hydrogen. At the time of processing, optimize the process. After pickling, it is advisable to remove hydrogen quickly, and use thermal diffusion method to raise the temperature to make the hydrogen escape. Electroplating process also needs to be improved to reduce the amount of hydrogen.
During use, monitor the environment. Control the hydrogen content of the medium. If it is unavoidable, add a corrosion inhibitor to prevent the reaction of hydrogen atoms with the surface of the carbon steel. Periodic inspection, micro-cracking, and disposal at the time of germination to avoid major disasters. In this way, the danger of hydrogen embrittlement of carbon steel can be reduced, and its safe service can be guaranteed.
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