Influence of microstructural heterogeneities and gaseous impurity on physicochemical properties of stainless steels

Chnages in mechanical and physicochemical properties of stainless steel as a result of hydrogen and microstructural heterogeneity (MH) interaction have been investigated. Hydrogen effect on steel samples preheated at different temperatures from room one to 800 deg C has been estimated by the embrittlement degree, by changes in the fracture mode, and in residual electric resistance (RER), by the electron microscopic investigation, by degassing kinetics at linear heating and by the hydrogen role during intercrystalline corrosion (ICC). It is shown that the stainless (sensibilized) steel aged at T0=650 deg C is subjected to increased hydrogen embrittlement, when fracture mode changes from the ductile for intercrystalline one. Hydrogen interaction with grain boundary precipitations without using external stress leads to formation of stable defects (interphase microcracks) causing anomalous growth of RER. Hydrogen yield accelerates in steel samples aged at T0=400 deg C in comparison with the initial samples, and decelerates in steels aged at T0=650 deg C. The supposition on the relation between hydrogen yield acceleration and the increase of hydrogen grain boundary diffusion, and deceleration - with its delay in microcracks, has been made. This supposition is confirmed by gas release calculations based on the kinetic balance equations