Induction Heating

eddy currents · frequency · forging · melting

Induction puts heat inside the metal itself, so a forge line heats a billet in seconds instead of soaking it in a gas furnace. For conductive parts below about 1,650 °C it is the mature electric replacement for combustion.

Chart of induction current reference depth in hot steel by coil frequency, on a log scale: 50 Hz about 78 mm for large melting furnaces, 1 kHz about 17 mm for billet heating, 10 kHz 5.5 mm for through-hardening, 100 kHz 1.7 mm for brazing and tube welding, 400 kHz 0.9 mm for case hardening. Below it, process temperature windows: annealing 300 to 700 degrees C, brazing 600 to 1,150, forging 1,150 to 1,250, melting 1,450 to 1,650. CURRENT DEPTH IN HOT STEEL FALLS WITH FREQUENCY 50 Hz - large melt furnaces78 mm 1 kHz - billet heating17 mm 10 kHz - through-hardening5.5 mm 100 kHz - brazing, tube1.7 mm 400 kHz - case hardening0.9 mm 1 mm 10 mm 100 mm Reference depth above the Curie point (about 770 °C), where steel is nonmagnetic. PROCESS TEMPERATURE WINDOWS Annealing 300-700 °C Brazing 600-1,150 °C Forging 1,150-1,250 °C Melting 1,450-1,650 °C
Frequency range
50 Hz - 500 kHz
Forging billet
~1,200 °C
Coil
Water-cooled copper
Companies tracked
12, 2 Chinese
Hub
Industry

Finding

Induction heating is already the default for forging, hardening and foundry melting, and the limits on wider use are power supply and lead time, not technology

An alternating field from a water-cooled copper coil induces eddy currents in the workpiece; magnetic steel also heats by hysteresis until it passes the Curie point. Frequency sets the heating depth, from line-frequency melt furnaces to 400 kHz surface hardening, and solid-state inverters let one power supply hold temperature to a few degrees.

Against a gas-fired forge or heat-treat furnace, induction cuts energy use by roughly 20-50% because it heats only the part, starts cold in seconds and has no flue losses. Coreless induction furnaces melt most of the world's foundry iron and a growing share of steel castings; China closed its unregulated induction-furnace rebar sector (ditiaogang) in 2017, and India still makes a large share of its steel in induction furnaces.

Semiconductors use induction where purity matters most: float-zone silicon is melted by an RF coil with no crucible, and silicon carbide boules grow by physical vapor transport in induction-heated graphite crucibles above 2,000 °C. Mainstream Czochralski silicon pullers mostly use resistive graphite heaters. The constraints are on the supply side: multi-megawatt melt and forging lines need new transformers and switchgear, and inverters and custom coils carry 6- to 12-month lead times.

Applications

Where induction is used

Each application uses a frequency band matched to part size and the depth that must be heated.

Induction heating applications
ApplicationTypical frequencyTemperatureTypical users
Foundry melting (coreless furnace)50 Hz - 10 kHz1,450-1,650 °CIron and steel foundries, precious metals
Billet and bar heating for forging0.5 - 10 kHz1,150-1,250 °CAutomotive and aerospace forging
Surface and through-hardening1 - 400 kHz850-950 °CGears, shafts, bearings, axles
Brazing and soldering10 - 400 kHz600-1,150 °CHVAC coils, carbide tools, EV busbars and motors
Annealing and stress relief1 - 50 kHz300-700 °CPipe seams, wire, tube
Tube and pipe welding100 - 450 kHzWeld seamERW pipe mills
Crystal growthRF1,400-2,400 °CFloat-zone silicon, SiC and sapphire boules

Suppliers

Equipment makers

A handful of Western groups dominate high-power systems; Chinese builders supply most of the domestic foundry market. Active companies first, then pilots, research groups and companies that exited.

Induction heating and melting equipment makers
CompanyProductsHQTechnologyStatus
ABP InductionFoundry melting furnacesGermanyCoreless induction meltingactive
Ajax Tocco MagnethermicForging heaters, melt furnaces, hardeningUSInduction heating and meltingactive: Park-Ohio subsidiary
AmbrellPrecision induction heating systemsUSRF induction to 400 kHzactive: inTEST subsidiary
EFD InductionHardening, welding and brazing systemsNorwayInduction heating and tube weldingactive
Fuji ElectricInduction melting furnacesJapanCoreless induction meltingactive
Inductotherm GroupCoreless melt furnaces, heating and hardening (includes Radyne)USMedium-frequency melting; heating systemsactive
Luoyang Hongteng ElectricalMedium-frequency melting furnacesChinaCoreless induction meltingactive
NeturenInduction hardening equipment and servicesJapanInduction hardeningactive
Otto JunkerFoundry melting and heat treatmentGermanyCoreless induction meltingactive
Pillar InductionHeating and melting power suppliesUSInduction power suppliesactive
Shandong RongtaiMedium-frequency melting furnacesChinaCoreless induction meltingactive
SMS ElothermHardening of automotive partsGermanyInduction hardeningactive

Sources

Sources and scope

Scope
Industrial Induction Heating
Sources
Supplier disclosures; ASM Handbook, Induction Heating; skin-depth values computed for hot steel
Updated
October 2026