Abstract
In this work the effect of protective gas on annealing of cold-rolled 42CrMo4 steel pipes was analysed. The production of protective gas (CO₂-CO-H₂-N₂ mixture) and the annealing of pipes at the different temperatures are discussed. By annealing of pipes in industrial conditions at 920 °C a bright steel surface was obtained. Decarburization of pipes at depth of 0.09-0.12 mm was observed. However, annealing the pipes at 700 °C the decarburization did not occur. The process of decarburization is explained by means of diffusion of carbon and surface reactions of solid solution of carbon in austenite and some components of protective gas.

Key words
protective gas, annealing, cold-rolling, steel, decarburization, microstructure

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