Turbine housing and method of producing turbine housing

A method of producing a turbine housing for housing a turbine wheel configured to rotate by exhaust gas,

• the turbine housing comprising:
• a scroll part forming a scroll flow path of an annular shape through which the exhaust gas to be supplied to the turbine wheel flows, around the turbine wheel;
• an exhaust duct part forming an exhaust flow path through which the exhaust gas having passed through the turbine wheel flows along an axial direction of the turbine wheel;
• and
• a shroud part protruding toward a hub at a connection section between the scroll part and the exhaust duct part, the shroud part having an outer peripheral surface facing the scroll flow path and an inner peripheral surface formed at a predetermined gap from rotor blades of the turbine wheel,
• wherein, an opening part is formed on a hub side of the scroll part, the opening part having a radius R2 which satisfies a relationship R1<R2, provided that R1 is a radial directional distance from an axis of the turbine wheel to a tip of the shroud part and R2 is a radial directional distance from the axis of the turbine wheel to an inner peripheral edge of a hub-side wall surface of the scroll part in a cross section taken along the axial direction of the turbine wheel,
• the method comprising:
• processing a flow-path surface in a region A after casting the turbine housing so that a roughness of the flow-path surface in the region A becomes smaller than a roughness of a flow-path surface in a region B, provided that the region A is a region extending over a predetermined range from the tip of the shroud part toward a radial outer direction and the region B is a region extending over predetermined range from boundary position with the region A toward the radial outer direction, among flow-path surfaces of the shroud part and the scroll part facing the scroll flow path on an outer side, in a radial direction, of the tip of the shroud part in a cross section taken along the axial direction of the turbine wheel.