Forge Temperature Calculator by Steel Type
Static heat-colour charts treat all steel the same. Pick your steel type to get the recommended forging colour range and a clear "do not exceed" warning, alongside the full standard reference chart. Nothing uploaded.
Recommendation
Heat Colour Reference Chart
| Colour | °C | °F | Meaning |
|---|
Steel heat colours and forge temperature control
How heat colour indicates temperature and workability
Steel glows different colours as it heats. Black (ambient) → dark red (500-650°C) → cherry red → orange → yellow → light yellow/white (1100°C+). Blacksmiths use these colours to judge temperature by eye without a thermometer. Orange heat (900-1000°C) is ideal forging temperature for most carbon steel - the metal is plastic and flows easily under the hammer without cracking. Below cherry red, the steel gets brittle and cracks when forged. Above yellow (1000-1100°C), steel begins to scale and burn, especially high-carbon grades. The darker your forge, the easier colours are to see - daylight makes judging very difficult.
Why each steel type has a different safe range
Mild steel (low carbon) tolerates high heat - you can work it all the way to light yellow without burning. Medium carbon steel is more sensitive: it prefers the orange range and gets weak above yellow. High carbon and tool steels are the most sensitive - work only between cherry red and orange, as yellow heat causes permanent grain growth and decarburization (carbon burns out of the surface, losing hardness). Stainless steel has completely different thermal properties: it conducts heat poorly, so it heats unevenly and work-hardens quickly. Always match your temperature range to your steel grade, not just the general chart.
FAQ
Why are temperature ranges different for each steel type?
Carbon content affects crystal structure and how the steel behaves when hot. Mild steel (low carbon) tolerates higher forging temperatures without burning. High carbon and tool steels burn easily - overheating above Orange changes the crystal structure permanently and ruins the hardness. Stainless steel has different thermal conductivity and scaling behavior, so it requires its own range.
What happens if I forge above the recommended temperature?
Steel begins to scale (oxidize heavily) and loses surface integrity. Above Yellow heat, carbon steel decarburizes - carbon burns out of the surface, leaving brittle, low-carbon metal that can't harden well. For tool steel especially, decarburization ruins the edge-holding ability. If you overheat, quench immediately and reheat at the correct temperature.
Can I see actual colour well in daylight?
Daylight makes heat colours much harder to see. Work in a darker forge or squint to block ambient light. The darker the workshop, the easier colours are to see. At night or indoors with shaded forge lighting, colours are very clear. Don't rely on this tool alone - experience and feel (listen for the sound of the strike, feel radiant heat) matter most.