Hardfacing is a way of protecting metal tools or parts from failing due to wear, stress, or abrasion. A wear-resistant layer is added to the metal by welding thin layers of stronger metals to the surface of weaker metals. Arc welding, oxyfuel welding, or other forms of welding are used to attach the wear-resistant layer. The alloys to be used for a particular facing job are chosen based on the underlying material and the type of wear the material is expected to encounter.
Hardfacing is sometimes applied immediately after production to prevent a tool or part from wearing down over time. It may also be applied to repair a tool or part to working order after wear has occurred. Copper is often used to repair worn parts, while cobalt-based tool steel is used to prevent wear from the beginning. The kind of metal used for hardfacing also depends on the kind of wear to which the metal will be exposed.
Wear can be caused by impact, abrasion, metal-to-metal contact, or a combination of the three. Impact wear occurs when metal is used to crush some hard material, such as stone. Each time the metal impacts with the stone, the metal deforms a little more, eventually resulting in failure of the tool. For example, a sledgehammer could suffer impact wear if used to break up stone. Manganese alloy is often used as hardfacing in this case.
Abrasive wear rarely occurs on its own, but is common in conjunction with impact wear. Abrasive wear happens when metal is continuously rubbed by dirt or sand. Hardfacing with cobalt of nickel-based alloys can prevent this issue. Metal-to-metal wear occurs when metal surfaces rub against each other. The metal is gradually worn down or transferred from one surface to the other over time. Hardfacing with tool steel can prevent metal-to-metal wear.
Almost any metal can be hardfaced, but different materials require different types of hardfacing. For example, cast iron must be carefully temperature controlled to prevent breakage. It also contains carbon, which can interfere with the facing process if the wrong metals are used.
Hardfacing can help reduce both maintenance and manufacturing costs. Maintenance costs are reduced because hardfaced parts are less likely to fail and therefore need to be replaced less often. Also, parts that would otherwise need to be replaced can be repaired using hardfacing. Production cost is also reduced because parts do not have to be made out of expensive metal alloys. They can be made out of less expensive metals and then hardfaced for strength.