Method for preparing ultrafine-grained superalloy bar

A method using a rolling machine for reducing a cross-section of a superalloy blank and thereby producing a superalloy bar, the method comprising:

• 1) preparing the rolling machine comprising two rollers and two guide plates, wherein each of the two rollers comprises a first section and a second section, and comprises a rotational axis that the roller rotates about;
• the first section and the second section each are in a shape of a circular truncated cone, the circular truncated cone comprising a bottom base, a top base that has a smaller diameter than the bottom base, and a lateral surface that is formed by rotating a generatrix around the rotational axis;
• the generatrix is curved and therefore the lateral surface is concave or convex;
• the generatrix comprises a virtual chord connecting two endpoints of the generatrix;
• the top base of the first section is connected to the bottom base of the second section;
• a diameter of the top base of the first section is identical to a diameter of a bottom base of the second section;
• the bottom base of the first section forms a wide end of the roller;
• the top base of the second section forms a narrow end of the roller;
• and the two guide plates each comprise a curved surface;
• 2) disposing the two guide plates opposite to each other wherein the curved surfaces of the two guide plates face each other;
• disposing the two rollers between the two guide plates, thereby forming a deformation zone of the rolling machine between the two rollers and the two guide plates and defining a pass line longitudinally along the deformation zone;
• wherein:
• the two rollers are axially symmetrical with each other 180° around the pass line;
• the rotational axis of one of the two rollers tilts with respect to the pass line such that a center of the narrow end of the roller is closer to the pass line than a center of the wide end;
• an ovality of a cross-section of the deformation zone is constant along the pass line;
• wherein the ovality of the cross-section of the deformation zone represents a ratio of a minimum distance between the two plates to a minimum distance between the two rollers in the cross-section of the deformation zone;
• and
• a cone angle α is in the range of 7° to 8°;
• a cross angle γ is in the range of 22° to 24°;
• a feed angle β is fixed and is in the range of 19° to 21°;
• a rotational speed of the rollers is in the range of 31 to 58 rpm;
• a slant angle of the first section is 4° to 7° larger than a slant angle of the second section;
• wherein:
• the cone angle represents an angle formed by the virtual chord of the generatrix for the first section and the pass line of the superalloy blank;
• the cross angle represents an angle formed by the pass line and the projection of the rotational axis of one of the two rollers on a first plane passing through the pass line;
• the feed angle represents an angle formed by the pass line and the projection of the rotational axis of one of the two rollers on a second plane passing through the pass line and perpendicular to the first plane;
• and
• the slant angle of the circular truncated cone represents an angle formed by the virtual chord of the generatrix and the bottom base of the circular truncated cone;
• 3) selecting a superalloy blank having a diameter of 60-500 mm and a length of 300-15000 mm;
• and
• 4) heating the superalloy blank and feeding the heated superalloy blank into the deformation zone of the rolling machine via a gap between the wide ends of the two rollers;
• rotating the two rollers such that the superalloy blank rotates around the pass line and moves along the pass line to a gap between the narrow ends of the two rollers;
• and after the superalloy blank moves out from the deformation zone, cooling the superalloy blank.