Machinery's Handbook, 31st Edition
1606 Hard Facing metal increases. When cutting light material, the kerf might be 1 ∕ whereas for heavy stock, it might be 1 ∕ 4 or 3 ∕ 8 inch (6.35 or 9.5 mm) wide.
16 inch (1.59 mm) wide,
Hard Facing Hard facing is a method of adding a coating, edge, or point, of a metal or alloy capable of resisting abrasion, corrosion, heat, or impact, to a metal component. The process can be applied equally well to new parts or old worn parts. The most common welding methods used to apply hard-facing materials include the oxyacetylene gas, shielded-metal arc, sub merged arc, plasma arc, and inert-gas-shielded arc (consuming and nonconsuming elec trode). Such coatings can also be applied by a spraying process, using equipment designed to handle the coating material in the form of a wire or a powder. Hard-Facing Materials.— The first thing to be considered in the selection of a hard-facing material is the type of service the part in question is to undergo. Other considerations include machinability, cost of hard-facing material, porosity of the deposit, appearance in use, and ease of application. Only generalized information can be given here to guide the selection of a material as the choice is dependent upon experience with a particular type of service. Generally, the greater the hardness of the facing material, the greater is its resistance to abrasion and shock or impact wear. Many hardenable materials may be used for hard facing such as carbon steels, low-alloy steels, medium-alloy steels, and medium-high alloys but none of these is outstanding. Some of the materials that might be considered to be preferable are high-speed steel, austenitic manganese steel, austenitic high-chromium iron, cobalt- chromium alloy, copper-base alloy, and nickel-chromium-boron alloy. High-Speed Steels.— These steels are available in the form of welding rods (RFe5) and electrodes (EFe5) for hard facing where hardness is required at service temperatures up to 1100 ° F (593 ° C) and where wear resistance and toughness are also required. Typical sur facing operations are done on cutting tools, shear blades, reamers, forming dies, shearing dies, guides, ingot tongs, and broaches using these metals. Hardness: These steels have a hardness of 55 to 60 on the Rockwell C scale in the as-welded condition and a hardness of 30 Rockwell C in the annealed condition. At a temperature of 1100 ° F (593 ° C), the as-deposited hardness of 60 Rockwell C falls off very slowly to 47 Rockwell C. At about 1200 ° F (649 ° C), the maximum Rockwell C hardness is 30. Resistance Properties: As deposited, the alloys can withstand only medium impact, but when tempered, the impact resistance is increased appreciably. Deposits of these alloys will oxidize readily because of their high molybdenum content but can withstand atmo spheric corrosion. They do not withstand liquid corrosives. Other Properties or Characteristics: The metals are well suited for metal-to-metal wear especially at elevated temperatures. They retain their hardness at elevated temperatures and can take a high polish. For machining, these alloys must first be annealed. Full hard ness may be regained by a subsequent heat treatment of the metal. Austenitic Manganese Steels.— These metals are available in the form of electrodes (EFeMn) for hard facing when dealing with metal-to-metal wear and impact. Uses in- clude facing rock-crushing equipment and railway frogs and crossings. Hardness: Hardness of the as-deposited metals are 170 to 230 BHN, but they can be work- hardened to 450 to 550 BHN very readily. For all practical purposes, these metals have no hot hardness as they become brittle when reheated above 500–600 ° F (260–316 ° C). Resistance Properties: These metals have high impact resistance. Their corrosion and oxidation resistance are similar to those of ordinary carbon steels. Their resistance to abrasion is only mediocre compared with hard abrasives like quartz. Other Properties or Characteristics: The yield strength of the deposited metal in com pression is low, but any compressive deformation rapidly raises it until plastic flow ceases.
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