| 摘要 |
PURPOSE:To produce a tough steel pipe which has high strength and toughness and excellent corrosion resistance and is considerably decreased in the anisotropy of the toughness by subjecting a specifically composed billet successively to heating, hot rolling, quick cooling, reheating and diametral reducing under specific conditions. CONSTITUTION:The billet which contains (hereafter wt%) 0.2-0.55% C, 0.01-0.6% Si, 0.3-1.8% Mn, 0.005-0.06% solAl, and consists of the balance Fe and inevitable impurities is heated in a 1,050-1,250 deg.C range. AFter the heated billet is hot rolled at >=800 deg.C finishing temp. with a Pilger mill and mandrel mill, the billet is quickly cooled down to <=350 deg.C under the conditions under which the billet is cooled at >=200 deg.C/min cooling rate in a 800-500 deg.C range to form the structure consisting of substantially >=50vol% martensite and the balance mainly bainite. The rolled steel is further reheated to the temp. range of the Ac1 transformation point - (AC1 transformation point -200 deg.C) at which the austenite is substantially not formed; thereafter the steel is subjected to diametral reducing at >=5% reduction in area by using a reducer and is air-cooled to obtain the rolled steel pipe essentially consisting of martensite.
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