Hydrogen Effect on Strength and Plasticity of Steels After Ion Nitriding in Hydrogen and Hydrogen-Free Environments

Abstract

The authors present the results of experimental investigations of strength and plasticity characteristics, as well as fracture nature, of the specimens of different steels under tension after ion nitriding in hydrogen (nitrogen with hydrogen) and hydrogen-free (nitrogen with argon) environments. The obtained characteristics are compared with those before nitriding. It is established that during ion nitriding in the hydrogen-free environment, tensile strength of the specimens has increased by 4–11%, whereas relative elongation and contraction have decreased by 1.1–3 times based on the nitriding mode and steel type. The authors have built the tensile stress-strain diagram for the specimens made of steel St3, 40Kh, and 12Kh18N10T without chemical and thermal treatment, ion nitriding in the hydrogen and hydrogen-free environments. The influence of hydrogen concentration in the saturation environment on the strength and plasticity characteristics has been defined. Under concentrations higher than 10 vol.% there is embrittlement with the decrease of strength characteristics (to 15%) and a significant decrease of plasticity (to 40%) for low-alloyed steels. For high-alloyed steels, the negative influence of hydrogen on the strength characteristics does not increase by 3%, while the influence on the plasticity characteristics – by 8%. The authors have investigated the initiation and propagation of microcracks under external loading on the steel with nitride layers.