Heat treating is a process in which metal is heated to a certain temperature and then cooled in a particular manner to alter its internal structure for obtaining a desired degree of physical and mechanical properties. The purpose is to increase the metal’s hardness, as well as to obtain maximum strength and durability in the material.
Numerous industries utilize heat treated parts, including those in the automotive, aerospace, information technology and heavy equipment sectors. Specifically, manufacturers of items such as saws, axes, cutting tools, bearings, gears, axles, fasteners, camshafts and crankshafts all rely on heat treating to make their products more durable and to last longer.1
The heat treating processes require three basic steps:
1. Heating to a specified temperature.
2. Holding at that temperature for the appropriate amount of time.
3. Cooling according to prescribed methods.
Understanding the Part Material
According to the ASM International’s Heat Treating Society, about 80 percent of heat treated parts are made of steel, such as bars and tubes, as well as parts that have been cast, forged, welded, machined, rolled, stamped, drawn or extruded.1
Successful heat treating begins by understanding the make-up of the steel that is to be treated. The American Iron and Steel Institute (A.I.S.I.) and the Society of Automotive Engineers (S.A.E.) utilize a four-digit system to code various types of steel used in manufacturing. The alloying element in the AISI specification is indicated by the first two digits, and the amount of carbon in the material is indicated by the last two digits. The first digit represents a general category of the steel groupings, meaning that 1xxx groups within the SAE-AISI system represent carbon steel. The second digit represents the presence of major elements which may affect the properties of steel; for example, in 1018 steel the zero in the 10xx series depicts no major secondary element. The last two digits indicates the percentage of carbon concentration. SAE 1018 indicates non-modified carbon steel containing 0.18% of carbon, while SAE 5130 indicates a chromium alloy steel containing 1% chromium and 0.30% carbon.