Low_hydrogen_annealing
Low hydrogen annealing
Heat treatment in metallurgy
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.[1]
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.[2] 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.