Hot Ductility of Low Carbon Nb-Microalloyed Weathering Steel

Abstract

High temperature tensile tests of novel developed Nb-microalloyed weathering steels were carried out with a constant true strain rate of 0.001/s at 650°C-1300°C using Gleeble3500 thermo-mechanical simulator. The tensile strength (TS) and reduction in area (RA) were calculated afterwards to obtain hot ductility curve and hot strength curve of the steel. The hot ductility behaviors were studied in detail under optical microscope (OM), scanning electron microscope (SEM) and transition electron microscope (TEM). The third brittle zone of the studied steels was between 650°C-800°C. SEM fractographs and microstructures of the tensile specimen showed that the occurrence of the third brittle zone was mainly related to the formation of pro-eutectoid ferrite film along the prior austenite grain boundaries, and secondly to the precipitation of second phases. Therefore, it was recommended that the straightening temperature of the studied steel after casting should be kept over 800°C to get crack free continuous casting (CC) slabs.