STRAIN-INDUCED-TRANSFORMATION COMPOSITE-STRUCTURE STEEL PLATE AND METHOD OF MANUFACTURING SAME.

摘要

A strain-induced-transformation composite-structure steel plate according to the present invention has a predetermined chemical composition; a structure thereof at 1/4 of the plate thickness contains, in terms of area proportions, 50 to 85 % polygonal ferrite, 3 to 10 % residual austenite, 5 to 47 % bainite, and 1% or less fresh martensite and tempered martensite in total; and 0.01 Ex.C/fsd = 0.015 is satisfied, wherein the aforementioned structure contains TiC-containing precipitates in an amount equal to or greater than 1x1016 /cm3, the average particle size of the residual austenite is 1.0 to 5.0 µm in the circle-equivalent diameter, the average closest distance of the residual austenite is 3.0 to 10.0 µm, and the average size of the precipitates is equal to or less than 3 nm.