Flame Hardening

Flame Hardening 4140 & Other Steel Grades of Machined Parts & Stampings


Flame hardening sometimes begins with a preheat operation depending on the alloy and degree of machining.

Next, the component is fixtured to the spin table and torch heads are adjusted to ensure proper positioning.

The torches are then ignited and the part surface is heated to the desired temperature and automatically quenched in agitated polymer solution for pre-set time.

The part is then immediately transferred to tempering where it is drawn back to the desired hardness range.

The Spin Flame Hardening process produces a hardened case layer on the material in the heat affected zone. The core of the gear remains relatively unheated and ductile.

This process will provide a strong wear surface on the flame hardened area and may allow for machined parts to be made from less expensive alloys in cases where through hardening is not required.

Flame hardening can also reduce overall component distortion as only the critical wear surface needs to be heated as opposed to the entire part when using other quench and temper processes.


Thermtech performs Spin Flame hardening on a fully automated flame table equipped with infrared temperature control, ensuring that the material is fully and uniformly heated prior to quenching.

This also allows for more precise control of the hardened case depth from part to part and prevents over or under heating of the material which can cause detrimental properties in-use.

ThermTech also has the ability to custom-design tooling for any flame-hardening job, especially in cases with unique part geometry. Please be aware that if this is necessary it will add 2-4 weeks depending on the exact design needed.

ThermTech can spin flame harden almost any alloy grade as the concentration of the polymer quench system can be changed to suit the needs of the particular alloy grade and part configuration that is in process.


ThermTech offers spin flame hardening for components up to a max weight of 2,500 pounds with a 45” max OD. ThermTech’s spin flame hardening processes span a wide range of materials, but the following are most common:

  • Flame Hardening 4140 Steel
  • Flame Hardening 4150 Steel
  • Flame Hardening 1045 Steel
  • Flame Hardening 1060 Steel
  • Flame Hardening Ductile Cast Iron (DCI)

Flame hardening is a good processing option for:

  • Very large gears or machined components that may be impractical to perform a whole-part quench & temper or carburizing process on.
  • Cases of very tight dimensional tolerances, as the smaller heated area will result in less distortion.
  • Cases when hardness is only required on a small segment or particular surface of the gear.

It is strongly suggested that all spin flame hardening jobs go through the formal quoting process to ensure all aspects of the job can be performed to customer satisfaction.

Contact ThermTech today to learn more about how our flame hardening process can benefit your machined parts!