Nitriding is a process that bonds nitrogen to a metal to harden it, creating a thin layer of a strong alloy on the outside. It can be used with various metals and for different components, with three main processes available. The process involves a nitrogen-rich medium, metal, and heat, and was discovered in the 1930s. Ammonia gas, cyanide salt baths, and plasma nitriding are three methods used.
Nitriding is the process of bonding nitrogen to a metal to harden it. This is a form of cementation, which involves creating a thin layer of a strong alloy on the outside of a metal object. Some of the most commonly nitrided materials are low carbon steels, although the process can also be used with other metals such as titanium or molybdenum. Nitriding can be used for a wide variety of different components, including gears, dies, and cam or crankshafts. There are three main nitriding processes, each of which uses a different nitrogen-rich substance to achieve the desired level of carburization.
The nitriding process can be achieved through the combination of a nitrogen-rich medium, metal, and heat. When subjected to intense heat, some of the nitrogen in the donor medium can bind to the metal. If done correctly, this can result in a very hard alloy of nitrogen and the metal used. Some of the first studies involving this type of cementation took place in the 1930s. The process was discovered around the same time in both the United States and Germany, although it did not come into widespread use until after World War II.
Ammonia gas was one of the first mediums used to bond nitrogen with steel in a process called ammonia nitriding. The procedure typically involves heating a piece of metal and then subjecting it to ammonia. Due to the heat, the gas can then decompose into hydrogen and nitrogen, at which point some of the nitrogen can sublimate into the metal. This method can allow great control over the depth of penetration of the nitrogen and the specific properties of the resulting alloy. Other advantages, compared to other methods, include the ease with which large batches can be processed and inexpensive equipment.
Another process that can bond nitrogen with metal typically involves a cyanide salt bath. This type of nitriding requires the heated metal to be placed in a nitrogen-rich salt. In addition to bonding with nitrogen, the metal can also take carbon from the salt in a process known as carbonitriding. This is a relatively quick and cheap process, although the salts involved are usually very toxic. The overall cost of the procedure can increase if a jurisdiction has strict rules governing the disposal of toxic substances.
Plasma nitriding is another process that can be used to harden metal. In this process, pure nitrogen is typically superheated in the plasma. Other gases can also be used, although the general concept is to create nitrogen ions which can then bond with the metal. This type of cementation is typically very thorough, fast, and can result in parts that are immediately ready to use.
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