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Hydrogen embrittlement refers to the phenomenon in which metallic materials experience a severe degradation of their mechanical properties and become brittle and prone to fracture, as a result of hydrogen absorption or diffusion into the material, during processes such as smelting, processing, heat treatment, pickling, and electroplating, or when they are used for extended periods in hydrogen-containing environments. Hydrogen embrittlement is observed not only in ordinary steel, but also in stainless steel, aluminum alloys, titanium alloys, nickel-based alloys, and zirconium alloys. In terms of mechanical properties, hydrogen embrittlement is characterized by the following effects: hydrogen has little impact on the yield strength and ultimate strength of metal materials, but it causes a significant decrease in elongation and reduction in area, a marked reduction in fatigue life, and a substantial drop in impact toughness. Under the continuous action of tensile stress below the fracture strength, the material will suddenly fracture after a period of time. II. Mechanisms of hydrogen embrittlement. Images. The mechanisms of hydrogen embrittlement remain a subject of debate in academic circles; however, most scholars believe that the following effects are the main causes of hydrogen embrittlement: 1. During the solidification of metal, hydrogen dissolved in it fails to be released in time. Instead, it diffuses toward areas with defects in the metal. At room temperature, atomic hydrogen combines to form molecular hydrogen at these defect sites, which then accumulates continuously. This results in tremendous internal pressure, leading to cracking in the metal. 2. In the hydrocrackers of the petroleum industry, the operating temperature ranges from 300 to 500 degrees, while the hydrogen pressure reaches dozens to hundreds of atmospheres. Under these conditions, hydrogen can penetrate into steel and react chemically with carbon to form methane. Methane bubbles can nucleate at sites such as inclusions or grain boundaries within steel, grow, and generate high pressure that causes damage to the steel. 3. Under stress, hydrogen dissolved in metals can also cause hydrogen embrittlement. In metals, atoms are arranged periodically in a certain pattern, known as a lattice. Hydrogen atoms are generally found in the gaps between metal atoms. Local areas in the lattice where atoms are displaced are called dislocations, and hydrogen atoms tend to accumulate near these dislocations. When a metal material is subjected to external forces, the stress distribution within the material is uneven; stress concentration occurs in areas where the shape of the material changes rapidly, as well as at internal defects and microcracks. Under the action of a stress gradient, hydrogen atoms diffuse within the lattice or move along dislocations toward stress concentration areas. The interaction between hydrogen and metal atoms weakens the bonding forces between metal atoms; as a result, cracks form and propagate in regions with high hydrogen content, leading to brittle fracture. Furthermore, the accumulation of hydrogen in stress concentration areas promotes plastic deformation in those areas, thereby causing cracks to form and propagate. Additionally, there are many microcracks in the crystal. When hydrogen accumulates in these cracks, it adsorbs onto their surfaces, reducing the surface energy; as a result, the cracks tend to propagate. 4. Certain metals have a strong affinity for hydrogen; supersaturated hydrogen readily combines with these metal atoms to form hydrides, or high concentrations of hydrogen that accumulate in stress concentration areas can also combine with such metal atoms to form hydrides. Hydrides are a brittle phase structure that often serve as sources of fracture under external forces, thereby leading to brittle failure. 3. Prevention of hydrogen embrittlement. Images: Hydrogen embrittlement poses a risk to the use of metals by humans; therefore, the purpose of research on this phenomenon is primarily to prevent it. Since there are many causes of hydrogen embrittlement, and human understanding of them is not yet complete, it is still not possible to completely prevent it at present. Currently, the following measures are taken to prevent hydrogen embrittlement: 1. Avoid excessive introduction of hydrogen – reduce the relative humidity during the metal smelting process, and bake various additives and steel ingot molds to keep them dry. Dehydrogenation – slowing down the cooling rate of the steel ingot to give hydrogen enough time to escape, or annealing the steel in a vacuum furnace to remove hydrogen. 2. Appropriate alloying elements are added to the steel to form a dispersed second phase, which acts as irreversible traps for hydrogen; this reduces the amount of mobile hydrogen in the material, thereby decreasing its tendency to suffer from hydrogen embrittlement. 3. Develop new hydrogen-resistant steel grades. Hydrogen diffuses much more rapidly in a body-centered cubic crystal structure than in a hexagonal close-packed or face-centered cubic structure; therefore, hydrogen-resistant steels are usually based on phases with a face-centered cubic structure, with additional strengthening measures applied to meet the required strength specifications. 4. Adopt appropriate protective measures–add corrosion inhibitors to the acid or electrolyte during pickling or electroplating, so that the large number of hydrogen atoms generated in the solution combine with each other on the metal surface to form hydrogen molecules that escape directly from the solution, preventing these hydrogen atoms from penetrating into the metal. 5. Furthermore, applying an anti-corrosion coating to the component or imposing a protective potential in the working medium can prevent hydrogen from being generated as a result of the reaction between the component and the medium.