The effect of hydrogen on the properties of polymorphic metals during thermal cycling near the polymorphism temperature

Abstract

The effect of hydrogen on the numerous properties of metals is known. In general, it is associated with the structure of its atom, which consists of a proton and an electron. Getting into the metal, it turns into an elementary particle, which has its own special properties. The paper considers the case of the interaction of hydrogen with polymorphic metals during their thermal cycling around the temperature of polymorphism. The main metal of this study is iron. It was revealed that during thermocyclic treatment in a hydrogen medium in iron during cooling, the yield strength decreases catastrophically by 3–4 orders of magnitude (up to a certain time, it was considered one order). In the absence of hydrogen (thermal cycling in an inert atmosphere), such changes did not occur. It was determined that when the crystal lattice restructuring from the γ phase to the α phase, the solubility of hydrogen decreases and it accumulates at the transformation boundary. Depending on the process parameters (cooling rate, saturation pressure, overheating temperature, symmetry relatively to the transformation point, etc.), various types of involuntary metal flow can be obtained. Besides the iron, other polymorphic metals - manganese, cobalt, titanium, zirconium - have been investigated. The deformation effect was observed only for manganese. Cobalt, due to another mechanism of polymorphic transformation, can not be deformed. Hydride-forming metals under normal conditions of cycling are severely cracked (the formation of hydrides), their small deformation is possible under very low hydrogen pressure. The reason for the formation of such properties is the creation of a special zone on the boundary of two phases – the H-layer. The concentration of hydrogen in the H-layer can reach tens of atomic percentages. This is confirmed by numerous experiments on fixing a new phase (N-martensite) and change the physical and mechanical properties of iron. In the deformation process, protons actively interact with defects in the lattice, which causes the pores formation inside the metal. These studies were awarded a diploma for the opening No. 313 authors V.Yu. Karpov and V.I Shapovalov.