The creation of new structural materials for cladding tubes of fast neutron reactors is an urgent task of modern nuclear power engineering. A three-layer radiation-resistant and corrosion-resistant material based on vanadium alloy and stainless steel, intended for work under extreme conditions (high temperatures, radiation and aggressive environment) of operation of fast neutron reactor cladding tubes has been developed in recent years. The most important aspect determining the operability of this material during operation is the quality of the joining of different materials layers among themselves, determined by the modes of thermomechanical treatment. The effect of the annealing on the chemical composition, structure, and fracture resistance of the “steel/vanadium alloy” interface in the steel/vanadium alloy/steel three-layer tube, obtained by hot co-extrusion of three-layer tube billet at 1100 °C was studied. The 20Kh13 (AISI 420 type) steel for the outer layers and V – 4Ti – 4Cr vanadium alloy for the core were used as the components of the tube. The structure and chemical composition in the layer joining zone were studied using the optical microscopy and electron microscopy with X-ray microspectral analysis. The fracture resistance of the “steel/vanadium alloy” interface was evaluated by a compression test of a three-layer ring sample with notch using an acoustic emission (AE) measurement. It is shown that after co-extrusion a “transition” area of diffusion interaction having a variable chemical composition with a width of 10–15 μm is formed between vanadium alloy and steel, which represents the continuous series of solid solutions, without precipitation of brittle phases, providing a strong bonding between vanadium alloy and steel in the three-layer material. No voids, delaminations or defects were detected at the “steel/vanadium alloy” interface. However, a crack is formed in the steel layer during the compression tests of the notched semi-ring three-layer samples after hot co-extrusion. Annealing favorably influences the formation of the “transition” area due to the increase in the width of the diffusion interaction area. No cracks or delaminations at the boundary between steel and vanadium layers were observed in the three-layer tube samples after annealing, and the three-layer material behaves like a monolith material during testing.
Effects of thermomechanical treatment on the occurrence of coincident site lattice boundaries in high strength low alloy steel