Effect of a Pulsed Plasma Beam on the Structure and the Phase Composition of the Surface Layers in Ferritic–Martensitic Steels

Abstract

The structure–phase changes that are caused in the surface layers of ferritic–martensitic Eurofer 97 and 10Cr9WV steel samples by the action of pulsed powerful fluxes of deuterium plasma and deuterium ions, which are generated in a plasma focus (PF) setup, are studied. Before tests, the steels were subjected to standard heat treatment (normalizing, tempering), and the 10Cr9WV steel samples were additionally annealed at 600°C for 600 h to determine the stability of the structure and properties at the temperatures that are close to the operating temperatures. During irradiation, the power densities of plasma (qpl = 107–1010 W/cm2) and ion (qi = 109–1012 W/cm2) fluxes and the number of plasma beam pulses (5–12 at a pulse duration of ~100 ns) are varied. The irradiation of the Eurofer 97 steel at qpl = 108–1010 W/cm2 in the PF setup is shown to cause melting and ultrafast solidification of the surface layer with the subsequent formation of a fine cellular structure with a cell size of 100–150 nm in it. The surface film formed on the 10Cr9WV steel samples during preliminary long-term annealing is found to begin to fail at qpl = 108 W/cm2; this film is fully removed at qpl = 1010 W/cm2. This process is accompanied by the segregation of particles 1–3 μm in size, which are enriched in manganese, chromium, and oxygen. After the surface film is removed, irradiation promotes the removal of manganese from the surface layers, and manganese is also removed from the Eurofer 97 steel, which has no surface film in the initial state. The plasma beam treatment of the Eurofer 97 steel in the PF working chamber at qpl = 108 W/cm2 is found to cause the formation of retained austenite in its structure, and the content of retained austenite in the 10Cr9WV steel subjected to similar treatment is lower than in the Eurofer 97 steel by a factor of 20 because of the presence of a film on its surface. The irradiation of the 10Cr9WV steel at a higher power density (qpl = 1010 W/cm2), when the surface film is removed, equalizes the contents of retained austenite in the steels under study.