Method of manufacturing a seamless steel tube

Abstract

A seamless steel tube is manufactured from a high alloy steel containing at least 5% of Cr while effectively preventing mandrel bar withdrawal troubles after elongation rolling of a material being rolled. A seamless steel tube of a high alloy steel containing at least 5% of Cr is manufactured by subjecting a material being rolled 3 to elongation rolling using a retained mandrel mill 1 in which the speed of a mandrel bar 2 in the axial direction is maintained constant while the speed of movement Vb of the mandrel bar 2, the speed Vi of the material being rolled 3 on the inlet side of the retained mandrel mill 1, and the speed Ve of the material being rolled 3 on the exit side of the retained mandrel mill 1 satisfy the relationship: 0.15 ≦Vb/{Vi+Ve)/ 2}≦0.70 by controlling the speed of movement Vb of the mandrel bar 2.

1 . A method of manufacturing a seamless steel tube characterized in that a seamless steel tube of a high alloy steel containing at least 5% of Cr is manufactured by a process comprising subjecting a material being rolled to elongation rolling using a retained mandrel mill having a constant speed of movement of a mandrel bar in the axial direction in such a manner that the speed (Vb) of the mandrel bar, the speed (Vi) of the material being rolled at the inlet side of the retained mandrel mill, and the speed (Ve) of the material being rolled on the exit side of the retained mandrel mill satisfy the following Equation 1.  
       0.15 ≦Vb/{ ( Vi+Ve )/2}≦0.70  (1)  
   
   
       2 . A method of manufacturing a seamless steel tube as set forth in  claim 1  wherein the above-described Equation 1 is satisfied by controlling the value of at least one of the speed (Vb) of the mandrel bar, the speed (Vi) of the material being rolled on the inlet side of the retained mandrel mill, and the speed (Ve) of the material being rolled on the exit side of the retained mandrel mill.