The paper presents the results of investigations of the 5% cobalt and 2% molybdenum additions in the W-Mo-V and W-V high-speed steels of the 9-2-2, 11-2-2 and 11-0-2 types with economically designed chemical composition on the wear mechanism during cutting and erosion tests. The 5% cobalt addition results in increasing the secondary hardness effect by 1.6 to 1.9 HRC, depending on a steel grade. Secondary hardness effect is caused by the dispersive carbides of the M4C3 type and martensite transformation of the retained austenite. The maximum secondary hardness effect about 66.3-67.6 HRC, depending on a grade of steel, occurs in each steel after tempering at 540oC and austenitizing at 1240oC. The 5% cobalt addition results in enhancing the working properties of tools, longer tool life and makes it possible to increase cutting speed by about 50%, compared with the steels of identical concentration of other alloying elements but without cobalt addition. Cobalt does not have any significant influence on erosion resistance, which is independent of the steel hardness but depends on molybdenum addition in steel.
High-speed steels; cobalt; molybdenum; secondary hardness effect; precipitation strengthening effect; cutting ability; erosion resistance
