| 摘要 |
PURPOSE:To manufacture the titled steel tube having superior sulfide cracking resistance by heating the joining edges of a steel strip having a specified compsn. under specified conditions, carrying out resistance welding to form a steel tube, hardening the tube by heating to a specified temp. and tempering it. CONSTITUTION:The joining edges of a steel strip consisting of, by weight, 0.15-0.35% C, 0.1-0.8% Si, 0.2-0.5% Mn, 0.2-0.6% Cr, 0.05-0.25% Mo [0.2<=Mo(%)/Cr(%)<=0.4], 0.01-0.06% sol.Al, 0.01-0.15% Zr and/or 0.001-0.150% Hf, 0.01-0.15% each of one or more among Nb, V and Ti and the balance Fe with inevitable impurities including <=0.02% P and <=0.005% S are heated in a nonoxidizing atmosphere and resistance welding is carried out so that the amt. of upset is regulated to 25-125% of the thickness. The resulting steel tube is hardened by heating to 920-1,020 deg.C and tempered at about 670-710 deg.C for about 1min-1hr.
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