SYNTHESIS OF HIGH-SPEED TOOL STEEL SURFACES ON MILD-STEEL

Wear-resistant, hard surfaces of high-speed tool steel were synthesize d on mild steel specimens. Discs of mild steel were subjected to carbu rization to a depth of 2.5 mm. Thin strips of tungsten were spot welde d and the specimen was subjected to electron beam surface melting. The beam power was varied from 60 kV, 10 mA to 60 kV, 20 mA. Oscillation frequency and the specimen translation velocity were kept at 1000 Hz a nd 2 cm s(-1), respectively. The width of the modified layer was 10 mm while the depth varied from 0.7-2.3 mm. A concentration of up to 30 w t% tungsten could be achieved in the surface layer by varying the thic kness of the foil spot welded prior to electron-beam melting. Tungsten concentration was uniform along the depth. The hardness achieved in t he as-solidified layer was uniform along the depth and reached 800 H-v . The reprocessing of the alloyed layer with the beam promoted fine ca rbide precipitation which then resulted in refinement of martensite pl ates.