Properties of Metals
The important information in this chapter is summarized below.
The conditions required for hydrogen embrittlement in steel is the presence
of hydrogen dissolved in the water and the carbon in the steel. The
hydrogen dissolved in the water comes from:
Making of steel
Storage or containment of hydrogen gas
Related to hydrogen as a contaminant in the environment that is
often a by-product of general corrosion.
Hydrogen embrittlement is the result of hydrogen that diffuses along the
grain boundaries and combines with the carbon to form methane gas. The
methane gas collects in small voids along the grain boundaries where it
builds up enormous pressures that initiate cracks and decrease the ductility
of the steel. If the metal is under a high tensile stress, brittle fracture can
Zircaloy-4 is less susceptible to hydrogen embrittlement than zircaloy-2 because:
Zircaloy-4 contains less nickel
The introduction of niobium into zircaloy-4 reduces the amount of
hydrogen absorption in the metal.