بررسي تاثير عنصر نايوبيم بر روي خواص مكانيكي و زيرساختار جوش ترميت

In this work, the effects of niobium on mechanical properties and microstructure of thermite welded medium carbon - steel rails are investigated, so that various quantities of niobium have been added to the thermite powder before welding. The results show that the microstructure of weld zone includes peroeutectoid ferrite at grain boundary and as polygonal shape in pearlitic matrix. Niobium increases the amount of ferrite and decreases the amount of pearlite in weld zone. The study of the mechanical properties also shows that, the addition of niobium in thermite welding leads to higher hardness and wear resistance. Increasing niobium content up to 0.2% leads to increase the reduction in area and toughness in tensile tests of welded parts, but the higher amounts of niobium reduce the tensile properties.