Decarburering

Decarburering, also known as decarburization, is a metallurgical phenomenon in which the carbon content at the surface of a steel component decreases during high-temperature exposure. The surface layer becomes softer than the surrounding material due to its lower carbon content, which can affect mechanical performance.

The process occurs as carbon diffuses from the surface into the environment or toward the interior of the material, depending on the chemical potential gradient. In oxidizing or decarburizing atmospheres, carbon can leave the steel surface as gases such as carbon monoxide or carbon dioxide. The rate of decarburization depends on temperature, exposure time, steel composition, and the presence of alloying elements that form carbides.

Decarburization commonly happens during heat treatments and forming operations conducted at elevated temperatures in air, steam, or other decarburizing environments. Processes such as annealing, normalizing, hot rolling, and welding can promote decarburization, particularly for steels with higher carbon content or inadequate protective atmospheres.

The main effects are a softer, less hard surface with reduced wear resistance and potentially lower fatigue strength. The decarburized zone is typically a thin layer, ranging from micrometers to a few hundred micrometers, depending on the conditions and steel grade. In many applications, decarburization is undesirable and can compromise component life.

Prevention strategies include processing in protective atmospheres (inert gases, nitrogen, hydrogen-rich mixes), vacuum processing, or applying surface coatings. Limiting high-temperature exposure time and using carburizing or carbide-forming inhibitors can also help maintain surface carbon levels.

Detection and assessment are usually done by hardness profiling across the surface, microstructural examination, or chemical analysis to determine the carbon concentration as a function of depth.