BS in Materials Engineering
Materials Engineering Department
Steel-based hardfacing alloys are welded onto the outside diameter of tool joints in three beads with a slight overlap between welds for underground drilling to prolong the tool joints’ life. Current hardfacing alloys have a shortened life due to cracks occurring in neighboring weld beads. To decrease cracking, the effects of composition and heat treatment on the microstructure was investigated on five alloys. Five small arc-melt circular ingots roughly 1.4 x 0.3 inches were produced. Each sample had varying amounts of C, B, Cr, Mn, Mo, Nb, Si, Ti, V, and W. The carbon levels in the alloys were .91wt%, .98wt%, and 3 wt% resulting in a ferritic, martensitic, and austenitic matrix, respectively. The heat treated samples were solutionized at 1100°C for 2 hours, quenched followed by an aging treatment at 500°C for 5 hours and air cooled. Metallographic analysis was performed revealing the as cast microstructures to have a fine appearance compared to the coarser nature of the heat treated microstructures. Hardness values were measured and the effect of heat treatment on the ferritic and austenitic samples’ hardness was minimal. Increasing the weight percent of Nb in the ferritic alloy prohibited grain growth resulting in slight changes in hardness after heat treatment, while increasing the weight percent of Ti had little effect. The martensitic sample decreased in hardness from 61 to 49 HRC due to the reduction in strain from heat treatment. Micro-hardness data revealed similar trends. Nano-hardness is suggested to understand microstructural evolution and measure ferrite hardness.