Handbook-Hardsurfacing, Building

When cobalt-base or nickel-base alloys are properly applied with the oxy-acetylene flame, there will be very little

dilution of the deposit by the base metal, yet the bond between the alloy and the base metal will actually be stronger than the alloy deposit. Cooling. After completion of the welding operation, the part should be allowed to cool as slowly as possible. If possible, bury it in dry lime, shredded asbestos, dry sand, or wood ashes, or place it in a furnace capable of controlling the cooling rate. Finishing the Deposit. After the hard-faced part has cooled, finish grinding will usually be necessary to remove high spots, or to grind the surface to the exact size desired. For most alloys, a soft grade vitrified wheel (not coarser than 46 or finer than 60 in Grades I or J of the Norton system) should be used. Wheel speeds should be not less than 2800 nor more than 4200 surface feet per minute. Too high a speed may damage the alloy surface. Hard-Facing Cast Iron. Cast iron will not ”sweat” like steel, so a strongly excess acetylene flame is not necessary. A 1-1/2 X flame should be satisfactory. You will find that the cobalt-base and nickel-base alloys do not spread out so readily on cast iron, and that it may be necessary to tap the rod along the edges of the puddle to get it to spread evenly. Use a good cast iron fusion-welding flux if necessary. Often, it will make sense to deposit a layer of iron- base alloy, or plain carbon steel, before depositing the final hard-facing layer or layers of the more costly hard- facing alloys. Since the melting temperature of cast iron is lower than that of steel, and quite close to that of most hard-facing alloys, it will usually be quite difficult to avoid substantial dilution of the first layer deposited. On a thin section of cast iron, backing up the section with wet asbestos or carbon paste will help you to minimize the amount of melting on the working surface. Hard-Facing Other Materials. Many grades of steel – even some stainless steels – can be successfully hard- faced. However, the high- manganese steels, high-silicon steels, and the ”400” series of stainless steels will always present problems, and require special care in preheating and cooling. Because the nickel-chromium stainless steels (such as ”18-8” ) have relatively high coefficients of expansion, they must always be preheated very evenly, and allowed to cool very slowly after hard-facing has been completed. Hard-facing of steels containing more than 0.50% carbon is seldom successful. Hard-facing any metal which has a relatively low melting point (brass, bronze, aluminum) is impossible.