Hydrogen trapping mechanism of different duplex stainless steels alloys

Abstract

Characteristics properties of duplex stainless steels (DSS) include excellent resistance to stress corrosion cracking, high strength and good weldability. The success of the duplex stainless steels in the industry has led to the development of an entire family of duplex alloys, such as the lean duplex stainless steel (LDS) and the super duplex stainless steel (SDSS), which vary in corrosion resistance depending on their alloy content. In this research we examine the austenite (γ) phase’s stability (S) of each steel in the presence of hydrogen and its effect on hydrogen trapping mechanisms. It was found that the dominant phase transformation, as a result of hydrogen permeation in LDS, is γ→εH→α′. After long aging times the εH-martensite lattice parameters continuously approached those of free ε-martensite or α′-martensite, which were formed by plastic deformation. It was shown using different methods that hydrogenated lean duplex stainless steel demonstrated higher amount of ε and α′ martensite compared with those of super duplex stainless steel, due to the dominant phase transformation of γ→ε→α′ in the former.A linear model of Lee and Lee was applied to calculate the trap activation energies of lean duplex and super duplex stainless steels. It was found that the lean duplex stainless steel presents ∼30% higher activation energy’s values than the super duplex stainless steel, due to a less steady γ phase, which will eventually cause an increase in hydrogen diffusion. The relation between the microstructure and the hydrogen trapping of lean duplex stainless steel and super duplex stainless steel in the presence of hydrogen is discussed in detail.