20th International Forgemasters Meeting - IFM 2017

The use of hollow ingot technology presents may advantages in safety critical applications such as nuclear island components. Although not new technology to Sheffield Forgemasters International Ltd. (SFIL), in order to implement large-scale hollow ingots in the conservative nuclear power market, the material behaviour must be proven to be equivalent to or better than material from conventional solid ingots. Recent collaborative work at SFIL has cast a 151t ingot of next generation nuclear alloy (NGNA) that may be forged into a variety of commercial pressure vessel geometries. In order to expand the component size and capability, whilst advancing in-house fabrication capacity, electron beam welding has been investigated as a method to join hollow ingot components. The quality heat treatment of the hollow ingot components has been scheduled after electron beam welding to re-austenitise the weld, with the aim of largely removing its influence on mechanical properties. Microstructural evolution and the resultant mechanical behaviour of heat treated electron beam welded NGNA has been evaluated and is presented. Data reveals it is possible to erase weld microstructure and dramatically improve the mechanical properties of the weld material. Full material characterisation and mechanical testing has been carried out to demonstrate the improvement in microstructural and chemical homogeneity of hollow ingot material. Segregation mapping has been carried out through a combination of surface measurements and multiple through-wall trepanned samples. Mechanical properties have been shown to match and exceed conventionally produced ingot material.