Cooling Curve, Microstructure and Hardness in Welding Heat-Affected zone of High Tensile Steel (Report 1)

Effects of Three Dimensions of Base Plate

Abstract

The shape of base plate used for welding test was changed in thickness, width and length independently. A single bead was deposited on the center-line of each plate over wholelength with the covered electrode under uniform conditions.
The thickness influences most severly on the cooling curve of heat-affected zone near the fusion line. The width has also certain effect on the curve, but the length scarcely concerns. The cooling curves are similar, when the plate-size is 11mm in thickness and is larger than 150mm in width. The maximum hardness in the heat-affected zone also inclines to become constant over this size.
In this investigation, the microstructure in the heat-affected zone was classified into three kinds; the structure which contains primary ferrite, the intermediate transformation structure (Zwischenstufengefuge) and the structure which contains martensite among the intermediate transformation structure.
The maximum hardness in the heat-affected zone depends on the cooling time from A3 point to any constant temperature between 400 and550°C as shown in Fig. 8, 9 and 10.