Role of Molybdenum in Increasing the Resistance of Steel to the Breaking Effect of Hydrogen at Elevated Temperatures and Pressures (Hydrogen Corrosion)

摘要

The physicochemical nature and the mechanism of the breaking effect of hydrogen on steel at elevated temperatures and pressures (hydrogen corrosion) are studied. This phenomenon is found to be based on the chemical reaction of hydrogen with carbon on the inner surface of closed micropores in the steel volume. Methane accumulates gradually in these micopores, and they transform into microcracks at a certain critical methane pressure. As a result, the metal embrittles catastrophically and undergoes cracking. When methane accumulates in micropores (incubation period of hydrogen corrosion), the mechanical properties of the steel remain almost unchanged. Alloying of steel up to 2.0 wt % (the upper limit of the concentration range under study) is shown not to affect the thermodynamics of carbon in steel in the pearlitic temperature range. However, this alloying element strongly affects the incubation period of hydrogen corrosion. Thus, prerequisites formed for a preliminary (before steel is put into operation) determination of the conditions of the absolute and relative (within the incubation period) hydrogen resistance of steel.