H section steel and its production method null for tunnel support

摘要

PROBLEM TO BE SOLVED: To produce a wide flange shape for tunnel timbering good in weld cracking resistance, extremely small in hydrogen defects, furthermore good in toughness and having tensile strength of a 590N/mm2 class and to provide a method for producing the same. SOLUTION: This steel has a compsn. contg., by weight, 0.04 to 0.13% C, 0.05 to 0.40% Si, 0.3 to 1.5% Mn and 0.005 to 0.10% Al, furthermore contg., as impurities, =0.010% S, =0.020% P and =2.5ppm H, and the balance Fe with inevitable impurities. The steel is rolled under the rolling conditions of =1200 deg.C heating temp. and =900 deg.C rolling finishing temp. and is thereafter cooled to =650 deg.C at a cooling rate of 2 to 30 deg.C/s, by which the wide flange shape for tunnel timbering in which both of the flange thickness and web thickness are regulated to 6 to 25mm, having 590 to 780N/mm2 tensile strength and having a structure in which the fraction of (ferrite + pearlite) is regulated to =60% can be produced.