How to further enhance the oxidation resistance of high-temperature bolts?
Publish Time: 2025-12-25
Under high-temperature conditions, bolts face challenges far beyond simple mechanical loads. As ambient temperatures rise, metal surfaces begin to react with oxygen in the air, forming an oxide layer. Initially, this oxide film may offer some protection, but as temperatures increase or time prolongs, oxidation deepens, leading to brittleness, reduced strength, and even pitting, spalling, or stress corrosion cracking. For high-temperature bolts performing critical connections, oxidation failure can result in anything from loosened preload to equipment leaks, downtime, and even safety accidents. Therefore, relying solely on the basic alloy composition is insufficient; a systematic approach involving material optimization, surface engineering, and integrated processes is necessary to enhance their oxidation resistance.Firstly, a special alloy matrix is the first line of defense against oxidation. High-quality high-temperature bolts typically utilize high-performance alloys containing elements such as chromium, nickel, molybdenum, and titanium. Chromium is particularly crucial—it spontaneously forms a dense, strongly adherent chromium oxide (Cr₂O₃) film on the bolt surface. This chemically stable film effectively blocks oxygen diffusion inward and metal ion migration outward, significantly delaying further oxidation. The addition of nickel enhances the alloy's microstructure stability at high temperatures, molybdenum strengthens creep resistance, and titanium helps refine grains and form stable carbides, collectively creating a self-protective internal mechanism.Secondly, advanced surface treatment technologies provide bolts with an "armor." Even with excellent base alloy performance, additional protection is needed under extreme or long-term service conditions. Therefore, high-end high-temperature resistant bolts often employ processes such as surface aluminizing, aluminum-silicon coating, micro-arc oxidation, or special high-temperature anti-oxidation coatings. These treatments form a thicker, more stable ceramic or intermetallic compound protective layer on the bolt surface, with an oxidation resistance temperature far exceeding that of the base material itself. For example, the alumina film formed by the aluminizing layer at high temperatures has an extremely low oxygen diffusion coefficient, maintaining its integrity even under repeated thermal cycling, greatly extending the service life of bolts in oxidizing atmospheres.Furthermore, the upsetting forging process itself indirectly improves oxidation resistance. Unlike machining, upsetting forging uses plastic deformation to continuously distribute metal flow lines along the bolt's contour, resulting in a dense internal structure with virtually no porosity or shrinkage defects. This high-integrity structure not only improves mechanical properties but also reduces the microscopic channels for oxidizing media intrusion. Simultaneously, the dynamic recrystallization during forging refines the grains, and fine-grained structures typically have higher grain boundary density, facilitating the faster formation of a uniform protective oxide film.In addition, precise control of the heat treatment regime is equally crucial. Appropriate solution treatment and aging treatment not only optimize the strength and toughness matching of bolts but also promote the enrichment of beneficial elements on the surface, enhancing the formation kinetics of the oxide film. Some processes can even introduce a protective atmosphere during heat treatment to prevent early oxidation of bolts during the manufacturing stage, ensuring a clean surface and high activity upon delivery, laying the foundation for self-passivation during subsequent service.At a deeper level, improved oxidation resistance is essentially a respect for the "time dimension." High-temperature equipment is often designed for lifespans of several years or even decades. As fasteners that cannot be easily replaced, bolts must maintain functional integrity throughout their entire lifespan. Therefore, oxidation resistance is not about pursuing temporary tolerance, but about ensuring slow and controllable evolution over a long period, rather than sudden failure.Ultimately, the advancement of oxidation resistance in high-temperature bolts does not rely on a single method, but rather on the synergy of the entire chain, from material properties and surface modification to manufacturing processes. It allows a seemingly ordinary bolt to firmly "grip" critical components even under intense flames and high pressure, protecting the system's seal and stability. As aircraft engines roar into the sky and refining plants operate day and night, those silent bolts, with their invisible oxidation barrier, support visible safety and reliability—this is the deepest power of high-end fasteners.
