Screw rotor and screw-type fluid machine main body

A fluid machine main body comprising:

• a screw rotor having:
• a screw portion of which an outer periphery has teeth and grooves having a helical shape and extending by a predetermined length in an axial direction,
• wherein a radial cross section of at least a part of the screw portion includes a cross section of an outer surface portion forming the teeth and the grooves, a cross section of an axial center portion, a cross section of a support portion that connects an axial center side of the outer surface portion and an outer diameter side of the axial center portion, and a cross section of a hollow portion formed by the support portions adjacent to each other in a rotational direction and an axial center side inner surface of a tooth bottom or a tooth tip,
• in at least the radial cross section of the screw portion, different members are continuously joined as an integral structure in a cross section of at least one of the axial center portion and the support portion and the outer surface portion,
• the hardness of the member forming the outer surface portion is higher than the hardness of the member forming the at least one of the axial center portion and the support portion;
• and
• a casing of the screw rotor.