Low-Carbon Steel Plate Having Excellent Toughness of Heat Affected zone and A Method for Welding It

摘要

PURPOSE: A low carbon steel sheet for structures having superior toughness of heat affected zone and a method for welding the steel sheet are provided which have not local brittle zone by controlling transformation of Austenite non-transformed in the structure of the heat affected zone, thereby reducing generation of M-A (Martensite-Austenite) constituent. CONSTITUTION: The low carbon steel sheet having superior toughness of heat affected zone comprises 0.08 to 0.15 wt.% of C, 0.2 wt.% or less of Si, 1.0 to 2.0 wt.% of Mn, 0.10 to 0.3 wt.% of Al, 0.005 to 0.03 wt.% of Ti, 0.0005 to 0.003 wt.% of B, 0.002 to 0.02 wt.% of N and a balance of Fe and inevitable impurities, wherein the structure of heat affected zone which is second heated (welded) to the area that is above the middle zone of an Ac1 and Ac3 transformation temperature, a γ+α zone after first heating (welding) the steel sheet to a temperature of 1300 deg.C or more has 1 wt.% or less of M-A (Martensite-Austenite) constituent. The method for welding the low carbon steel sheet comprises the processes of first heating (welding) a thick steel sheet comprising 0.08 to 0.15 wt.% of C, 0.2 wt.% or less of Si, 1.0 to 2.0 wt.% of Mn, 0.10 to 0.3 wt.% of Al, 0.005 to 0.03 wt.% of Ti, 0.0005 to 0.003 wt.% of B, 0.002 to 0.02 wt.% of N and a balance of Fe and inevitable impurities to a temperature of 1300 deg.C or more; and cooling the second heated (welded) steel sheet from 800 to 500 deg.C for 10 to 150 seconds after second heating (welding) the first heated steel sheet to the area that is above γ+α zone in which a heat affected zone is the middle zone of an Ac1 and Ac3 transformation temperature.