Importance

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Abstract

Provided is a method for producing a seamless tube, in which after a starting material to be extruded has been heated to a heating temperature T [° C.] satisfying the relationship of Formula (1) or Formula (2) depending on the outside diameter d₀ [mm] thereof, the starting material is hot extruded by providing a solid lubricating glass between the starting material to be extruded and a die, whereby a transverse flaw on the outer surface in the top portion of tube can be prevented when hot extrusion is performed by using a starting material for extrusion having low deformability at high temperatures. When d₀<200, T≦1250+1.1487×A−7.838×ln(t₀/t)−10.135×ln(d₀/d) . . . (1); when d₀≧200, T≦1219+1.1487×A−7.838×ln(t₀/t)−10.135×ln(d₀/d) . . . (2), where A=L/V_av×1000 [msec.]. V_av=(V₀+V₀×ρ)/2 [mm/sec], ρ=(t₀×(d₀−t₀))/(t×(d−t)), t₀: wall thickness of starting material to be extruded [mm], d: outside diameter of extruded tube [mm], t: wall thickness thereof [mm], L: length of approach portion of die along extrusion direction [mm], and V₀: ram speed [mm/sec].

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First Claim