Patent ID: 6290789
Filing Date: 2001-09-18
Classification: C21D

Abstract:
A method for producing a steel pipe which comprises heating or soaking a base steel pipe having an outer diameter of ODi (mm) and having ferrite grains with an average crystal diameter of di (.mu.m) in the cross section perpendicular to the longitudinal direction of the steel pipe, followed by reducing by drawing at an average rolling temperature of .theta.m (.degree.C.) and a total reduction ratio Tred (%) to obtain a product pipe having an outer diameter of ODf (mm),said reducing comprises performing it in the temperature range of 400.degree. C. or more but not more than the heating or soaking temperature, and in such a manner that said average crystal diameter of di (.mu.m), said average rolling temperature of .theta.m (.degree.C.), and said total reduction ratio T red (%) are in a relation satisfying equation (1) as follows:di.ltoreq.(2.65-0.003.times..theta.m).times.10.sup.{(0.008+.theta.m/ 50000).times.Tred} (1)where, di represents the average crystal diameter of the base steel pipe (.mu.m); .theta.m represents the average rolling temperature (.degree.C.) (=(.theta. i+.theta. f)/2, where .theta. i is the temperature of starting rolling (.degree.C.), and .theta. f is the temperature of finishing rolling (.degree.C.)); and T red represents the total reduction ratio (%) (=ODi-ODf).times.100/ODi, where ODi is the outer diameter of the base steel pipe (mm), and ODf is the outer diameter of the product pipe (mm)).