The relationship between hydrogen corrosion and hydrogen embrittlement
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Hydrogen corrosion, or hydrogen attack, occurs when steel is exposed to a high-temperature, high-pressure hydrogen environment; hydrogen atoms react with unstable carbides on the surface of the equipment or within the steel itself to form methane, resulting in carbon loss from the steel and permanent damage to its mechanical strength. The methane generated inside the steel cannot escape and accumulates there, creating high local pressures that lead to severe bulging and cracking. Hydrogen embrittlement occurs when hydrogen dissolved in steel combines to form hydrogen molecules, resulting in stress concentration that exceeds the steel’s strength limit and leads to the formation of tiny cracks within the steel, also known as white spots. Hydrogen embrittlement can only be prevented, not cured. Once hydrogen embrittlement occurs, it cannot be eliminated. Trace amounts of hydrogen (on the order of 10 to the negative 6 power) that enter the steel during its smelting process and during the manufacturing and assembly of parts (such as electroplating and welding) can cause the material to become brittle or even crack under the effect of internal residual stresses or external stresses. The heat treatment method involves heating the workpiece to a certain temperature, holding it at that temperature for a period of time, and then cooling it slowly, so that the solubility of hydrogen decreases gradually and it precipitates out over time. However, heating will damage the coating, so heat treatment is not suitable for electroplated workpieces.
Hydrogen corrosion and hydrogen embrittlement are two distinct concepts, but there is a certain relationship between them. Hydrogen corrosion refers to the reaction between hydrogen and the surface or interior of steel in a high-temperature, high-pressure hydrogen environment, resulting in decarburization of the steel and a loss of its mechanical strength. This phenomenon is mainly caused by hydrogen atoms reacting with the carbides in the steel to produce methane, resulting in decarburization of the steel. The methane generated inside the steel cannot escape; it accumulates, creating tremendous local pressure that ultimately leads to bulging and cracking. Hydrogen embrittlement refers to the phenomenon where, when hydrogen is present in steel, hydrogen atoms combine to form hydrogen molecules, resulting in stress concentration that exceeds the strength limit of the steel; this leads to the formation of tiny cracks within the steel, also known as white spots. Hydrogen embrittlement cannot be cured; once it occurs, it cannot be eliminated. Trace amounts of hydrogen can enter steel during its smelting process, as well as during the manufacturing and assembly of components (such as electroplating and welding), leading to brittleness and cracking in the steel when stress is present. A common method for preventing hydrogen corrosion and hydrogen embrittlement is heat treatment. Heat treatment involves heating the workpiece to a certain temperature, holding it there for a period of time, and then cooling it slowly, which allows the hydrogen dissolved in the steel to gradually decrease and precipitate out. It should be noted, however, that heat treatment may damage the surface coating; therefore, for workpieces that have already been electroplated, heat treatment may not be suitable. .