Study on Microstructure and Mechanical Properties of Welding Coarse Grain Heat-Affected Zone of High-Nb X80 Steels

摘要

The influences of welding thermal cycle on the microstructure and impact toughness of welding coarse grain heat-affected zone (CGHAZ) of three commercial X80 pipeline steels were investigated by means of welding thermal simulation carried out on Gleeble-3500 thermal machine mechanical simulator. The result shows that the impact toughness of CGHAZ of all kinds of pipeline steels decrease with the increase of welding input energy. While, under the same welding input energy, the values of impact toughness of CGHAZ of high-Nb steels are higher than that of conventional Mn-Mo-Nb steels. By increasing the amount of alloyed elements, the embrittlement inclining of CGHAZ is weakened, and the highest value of impact toughness of CGHAZ can be obtained at higher welding input energy. The austenite grain growth was restrained by some undissolved NbC particles remained in high-Nb steels, which ensures small and uniform austenite grain, furthermore, the higher impact toughness was obtained. Those results will provide an experiment conference for applications of high-Nb X80 pipeline steels.