Influence of microstructure inhomogeneity and gas impurity of physical-chemical properties of stainless steels

Investigation into the change of mechanical and physico-chemical properies of stainless steel as a result of hydrogen and microstructural inhomogeneity (MI) interaction is conducted. Hydrogen effect on steel samples which have undergone preliminary thermal treatment under different temperatures-from the indoor temperature to 800 deg C one, was evaluated by embrittlement degree, changes in fracture mode and in residual electric resistance (RER), by electron microscope investigation, by outgassing kinetics under linear heating and hydrogen role in intercrystalline corrosion. It is shown that sensibilized stainless steel after thermal ageing at T0=650 deg C is subjected to increased hydrogen embrittlement under which fracture mode change from ductile to intercrystalline one occurs. Hydrogen interaction with the grain boundary precipitations without applying external stress leads to formation of stable defects (interfacial microcracks), causing RER anomalous growth. In steel samples aged at T0=400 deg C, hydrogen outgassing is moderated. An assumption is made concerning hydrogen outgassing acceleration connection with the increase of hydrogen grain-boundary diffusion part, and hydrogen outgassing slowing down-with its entrapment in microcracks. This assumption is proved by gas release calculations, based on kinetic balance equations