Round billet for seamless metal tube and method for producing seamless metal tube

Abstract

Provided is a round billet capable of reducing damage on a piercing plug in a method of producing a seamless metal tube with a Mannesmann process. The round billet ( 5 ), for use in a seamless metal tube, to be produced into a seamless metal tube with a Mannesmann process includes a body having a hole ( 6 ) formed in an axial direction of the body. The hole ( 6 ) includes an aperture ( 6 a ) opening at least at one end face of the round billet ( 5 ), and a tapered portion ( 61 ) continued to the aperture ( 6 a ) and having a diameter gradually increasing toward the aperture ( 6 a ).

1 . A round billet, for use in a seamless metal tube, to be produced into a seamless metal tube with a Mannesmann process,
 the round billet comprising:   a body having a hole formed in an axial direction of the body,   wherein   the hole including:   an aperture opening at least at one end face of the round billet; and   a tapered portion continued to the aperture and having a diameter gradually increasing toward the aperture.   
     
     
         2 . The round billet according to  claim 1 , wherein
 the tapered portion has a length in the axial direction less than a length of a rolling portion of a piercing plug for use in the Mannesmann process.   
     
     
         3 . The round billet according to  claim 1 , wherein
 the tapered portion has a taper angle greater than a taper angle of a piercing plug for use in the Mannesmann process.   
     
     
         4 . The round billet according to  claim 1 , wherein
 a region adjacent to the aperture among the tapered portion is chamfered.   
     
     
         5 . A method for producing a seamless metal tube comprising:
 a step of preparing the round billet according to  claim 1 ; and   a step of piercing-rolling the round billet with the tapered portion of the round billet opposite to the piercing plug.   
     
     
         6 . The round billet according to  claim 2 , wherein
 the tapered portion has a taper angle greater than a taper angle of a piercing plug for use in the Mannesmann process.   
     
     
         7 . A method for producing a seamless metal tube comprising:
 a step of preparing the round billet according to  claim 2 ; and   a step of piercing-rolling the round billet with the tapered portion of the round billet opposite to the piercing plug.   
     
     
         8 . A method for producing a seamless metal tube comprising:
 a step of preparing the round billet according to  claim 3 ; and   a step of piercing-rolling the round billet with the tapered portion of the round billet opposite to the piercing plug.   
     
     
         9 . A method for producing a seamless metal tube comprising:
 a step of preparing the round billet according to  claim 4 ; and   a step of piercing-rolling the round billet with the tapered portion of the round billet opposite to the piercing plug.   
     
     
         10 . A method for producing a seamless metal tube comprising:
 a step of preparing the round billet according to  claim 6 ; and   a step of piercing-rolling the round billet with the tapered portion of the round billet opposite to the piercing plug.