BANDING AND THE NATURE OF LARGE, IRREGULAR PEARLITE NODULES IN A HOT-ROLLED LOW-ALLOY PLATE STEEL .2.

The microstructure of a hot-rolled low-carbon plate steel has been exa mined using a combination of light microscopy and scanning electron mi croscopy. It has been found that in the hot-rolled condition, the micr ostructure consists of alternate bands of ferrite and pearlite, togeth er with relatively large, irregular pearlite nodules. These large nodu les were found to be comprised of pearlite, intragranularly nucleated ferrite (both Widmanstatten and idiomorphic), together with carbide-de ficient and/or carbide-free regions. It is argued that the carbide-def icient and carbide-free regions form as a result of the premature init iation of the pearlite reaction, i.e. pearlite forms prior to the body of the austenite grains attaining the eutectoid composition. In order to model the formation of the banded structure, specimens were reaust enitized at 1050-degrees-C for 10 min and furnace cooled. This heat-tr eatment cycle produced an austenite grain size which was less than the chemical banding wavelength. A model for the decomposition of austeni te, under these conditions, is presented.