A method of metallurgical processing includes, providing a workpiece that has been formed by additive manufacturing of a nickel-chromium based superalloy. The workpiece has an internal porosity and a microstructure with a columnar grain structure and delta phase. The workpiece is then hot isostatically pressed to reduce the internal porosity and to at least partially retain the columnar grain structure and the delta phase. The workpiece is then heat treated to at least partially retain the columnar grain structure and the delta phase.