| 摘要 |
A thick iron sheet in which a heat affected zone has the excellent toughness is provided to increase the elongation ratio while securing the enough toughness of a base material. A thick iron sheet comprises C of 0.03~0.150 mass%, Si of 0.50 mass%, Mn of 1.0~2.0 mass%, P of 0.015 mass% or less, S of 0.005 mass% or less, Al of 0.005~0.06 mass%, Ti of 0.008~0.030 mass%, N of 0.0050~0.010 mass%, Ca of 0.0010~0.0035 mass%, and O of 0.003 mass% or less. The volume percentage of the residue gamma of the thick iron sheet is 2~10%. The average circle equivalent diameter of the island shape martensite(MA) is 3.0mum or less. The thick iron sheet is made of B of 0.0035 mass% or less, Cu of 2.0 mass% or less, Ni of 2.0 mass% or less, and one from groups including Cr of 1.50 mass. |
