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Low hydrogen annealing, commonly known as "baking" is a heat treatment in metallurgy for the reduction or elimination of hydrogen in a material to prevent hydrogen embrittlement. Hydrogen embrittlement is the hydrogen-induced cracking of metals, particularly steel which results in degraded mechanical properties such as plasticity, ductility and fracture toughness at low temperature. Low hydrogen annealing is called a de-embrittlement process. Low hydrogen annealing is an effective method compared to alternatives such as electroplating the material with zinc to provide a barrier for hydrogen ingress which results in coating defects.
The underlying mechanism for hydrogen embrittlement is different for the surface compared to hydrogen penetrated into the bulk of the solid. Studies have shown that annealing at 200° C weakens hydrogen embrittlement caused by internal hydrogen but has little effect on surface-absorbed hydrogen. At 200° C, hydrogen atoms can diffuse out of iron and partial stainless steel and is the minimum temperature needed for the process. The exact mechanism or its effects are not fully understood because it is also hypothesized that 200° C allows for vacancy elimination in the solid which can affect its mechanical properties too.