Flame or Induction?
Flame hardening and induction hardening result in identical outcomes in many cases. The objective of both processes is to form a hard case on the surface of the material while retaining a soft core.
Depending on the geometry, material composition and hardness specification it is important to select the right process in order to minimize risk and achieve the best possible outcome.
With flame hardening the heat is applied to the surface of the part using a high temperature burner. The hardness and case depth are basically a function of material composition, surface temperature, soak time and quench media.
With induction hardening heat is generated or induced in the surface of the material by an electric field. Hardness and case depth are basically a function of material composition, frequency, soak time and quench media. Typical frequencies are 450 kHz (high frequency) for case-depths of 0.75mm (0.030″) to 2.0mm (0.080″). Heavier case-depths of 2.5mm (0.100″) to 4.0mm (0.150″) are typically obtained at 10 kHz.
Pins or shafts are the most common components that are flame or induction hardened. Because of their simple, symmetrical geometry they can be rotated between centres and are well suited to both processes.
With small diameter pins the high heat input involved in flame hardening may result in through hardening. For this reason we use high frequency induction for pins up to about 50mm diameter.
Flame hardening is a very flexible and cost effective process for small batch quantifies and complex shapes. Induction hardening is more suited to large batch quantities and simple geometries where the setup time and high tooling cost can be amortized over the larger quantities.