on opposite sides thereof extending along the length of the blade root 38 the root section 38 of such a multi lobed type is often referred to as a firtree because of this characteristic shape the turbine rotor disc 32 includes a web section 33 extending radially outwardly from a hub not shown which is mounted to the rotating shaft of the high pressure spool assembly 20 of fig1 and a rim section 50 extending radially outwardly from the web section 33 rim section 50 has an axial thickness defined by respective front and rear sides thereof not indicated and also defines an outer periphery 55 the turbine rotor disc 32 further includes a plurality of dovetail slots 48 only one shown in fig3 circumferentially spaced apart one from another and axially extending through the periphery 55 of the turbine rotor disc 32 which in this embodiment is the entire axial thickness of the rim section 50 each of the axial dovetail slots 48 includes a pair of opposed side walls each being defined in an undulating profile having substantially smoothly curved to thereby provide a profiled space defined between the opposed side walls substantially in accordance with the firtree profile of the root section 38 of the respective turbine rotor blades 34 that are received within these dovetail slots 48 prior to assembling the rotor assembly 30 the disc 32 is formed by forging metal such as forged or powder metallurgy nickel alloys for example into an annulus with a peripheral surface 55 and a rim section 55 the thermal treatment as well as the spinning step may create stresses within the metal that can.