"非氧化退火" can be translated as "non-oxidizing annealing" or "oxidation-free annealing" in English.
"Non-oxidizing annealing" emphasizes that the annealing process is conducted in an environment that prevents oxidation.
"Oxidation-free annealing" similarly conveys the idea that the annealing is done without causing oxidation.
Both terms are commonly used in materials science and metallurgy to describe such a heat treatment process.