Carbide-Strengthened Reduced Activation Heat-Resistant Steels

Abstract

Higher strength and lower ductile-brittle transition temperature are obtained by vacuum induction melting (VIM), electroslag remelting (ESR) and vacuum consumable electrode melting (VAR) compared to VIM alone, because of the good solution of the tantalum in martensite. Processes of VIM+ESR+VAR decrease the size of laths and improve the distribution of non-metallic inclusions in the China Low Activation Martensitic (CLAM) steel. The effect of the rare earth element yttrium on the mechanical properties of 9Cr22WVTa low activation martensitic steel for fusion reactor is discussed. It is easy for yttrium to aggregate and form blocky yttrium-rich inclusions in the steel, which disrupts the continuity of the matrix and produces microcracks for fracture. The yttrium-rich inclusions are distributed along the rolling direction, which makes the fracture surface delaminated under tension and impact. The final part of the chapter analyses the effect of normalising and tempering heat treatment processes on the microstructure and mechanical properties of ton-scale CLAM steel. The normalising temperature decides the prior austenite grain size, while the tempering temperature influences the substructures. Compared with the normalising temperature, tempering temperature has larger effect on the mechanical properties of CLAM.