The welding thermal effect section is difficult to soften the high-strength electric resistance welded steel tube and its production manner

摘要

PURPOSE: To inexpensively produce a high strength resistance welded steel tube practically free from softening in a heat-affected zone by subjecting a slab of steel having a specific composition containing Ti, B, Cr, Mo, etc., to hot rolling and to coiling at respectively specified temps. and applying resistance welding to the resulting hot rolled coil. ;CONSTITUTION: A slab of a material steel which has a composition consisting of, by weight, 0.10-0.20% C, 0.15-0.50% Si, 1.3-2.5% Mn, 0.005-0.020% P, 0.0005-0.0060% S, 0.01-0.08% Al, 0.02-0.2% Ti, 0.0010-0.0030% B, 0.002-0.005% N, 0.3-0.7% Cr, 0.3-1.0% Mo, and the balance Fe with inevitable impurities and further containing, if necessary, 0.01-0.10% Nb is hot-rolled. The finishing temp. is regulated to a value between 950°C and the Ar transformation point, and coiling is 3 done at 450-700°C. The resulting hot rolled coil is formed into a tube by means of resistance welding and then subjected, if necessary, to normalizing, annealing, and cold drawing. By this method, the resistance welded steel tube having a dimensional accuracy of ≤±0.15mm outside diameter and ≤±0.05mm thickness and also having (100 to 130)kgf/mm₂ tensile strength can be obtained.;COPYRIGHT: (C)1994,JPO&Japio