Heat Treatment Process: Different Types

There are many stages in the process of manufacturing a metal part. Whether working in the automotive, power equipment or other manufacturing industry, there are several phases to complete before the final product is finished. One piece of the process is heat treating. While there are various heat treatment process types, the method used depends on the parts’ end application and property requirements.

Whole or a Piece

If the whole part needs to be heat treated or the hardness must penetrate to the core, it is usually advisable to use a furnace heat treating process. However, if only a portion of the part needs to be heated, a method of selective hardening can be used to heat treat. Additionally, the volume of parts that need heat treated determines which selective heating method works best.

If there are 10 parts to heat treat, flame hardening is best suited for the job as it typically does not require specialized tooling, which can be quite expensive. If there are 1,000-10,000+ parts, then induction heat treating may be the answer because it has quick cycle times and potentially lower production costs.

Here Is A Breakdown Of Some Different Classifications Of Heat Treatment Processes:

Induction Heat Treating

Induction heat treating uses an electrical current, transferred from a copper coil placed around the part. The directed current heats selected areas of the steel part to the required temperature and depth. The part is then quenched at a controlled rate to achieve the desired material hardness. A controlled amount of energy and quench allow for greater precision when hardening specific areas of a steel part, while leaving other areas unaffected.

If distortion was an issue for a part, induction heat treating is the preferred method. This can be important factor for circular parts such as gears. Induction heat treating allows for more control over distortion than some furnace heat treating methods. Since heat treating times are short with induction heat treating, it increases production and throughput and reduces labor costs.

Flame Hardening

Flame hardening is another heat treating method that only heats one area of the part. Instead of a coil system like induction heat treating, flame hardening uses a flame on the surface of the metal. This process works well for low volume jobs or very deep case depths, especially when there is a large part that needs only one section to be hardened. The part can be heated up with the flame then quenched, and this can often be done with very little specialized tooling.


Carburizing is a furnace method used to harden parts that are manufactured from low carbon steel. In most applications, the entire surface of a part is hardened during carburizing. Select areas of a part can be hardened using a carburizing furnace by covering non-hardened areas of the part with carbon stopping paint beforehand. Carburizing is a less labor-intensive method for hardening the outside of whole part, but can be costly if specific areas have to be masked with the paint process.

Carburizing can also be used to increase the carbon content of a part before induction hardening a select area, allowing the steel to achieve a higher Rockwell hardness.

Furnace Heating

Furnace heat treating is best used when the whole part can be heated at once. If an entire part needs to be hardened – and distortion is not an issue- furnace hardening is a cost-efficient option.

Choosing the Right Heat Treating Process

Choosing the best heat treating option ultimately depends on the design of the part and the engineering design requirements. If the whole part can be hardened, furnace hardening or carburizing could be the best method. If only certain areas of the part need to be hardened, that’s where selective hardening, such as flame or induction heat treating could be the best solution.

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