STEEL MATERIAL HAVING 50KG/MM2 TENSILE STRENGTH AND SUPERIOR RESISTANCE TO CRACKING OF GALVANIZED SURFACE

摘要

PURPOSE:To prevent the cracking of a structural steel material due to hot- dipping at its weld heat-affected zone when the steel material is galvanized after welding so as to prevent corrosion, by adding a specified element to the steel material. CONSTITUTION:A structural steel material having =50kg/mm.2 tensile strength and a composition consisting of 0.05% C, 0.3% Si, 1.0-2.0% Mn, 0.03% Ti and the balance Fe is welded and galvanized so as to improve the corrosion resistance. At this time, the weld heat-affected zone causes cracking at grain boundary due to embrittlement of molten Zn, that is, a liq. metal. To prevent the cracking the Pcm value of the steel material is regulated to =0.15% by adding at least one among 0.02-0.10% Nb and/or V, =1% at least one among Cu, Ni and Mo, and 0.0005-0.0020% B to the steel material or by further adding 0.04- 0.08% sol. Al and 0.0040% N. The resistance to cracking due to hot-dipping at its weld heat-affected zone is improved.