Forge stainless steel at 1,100-1,250 °C and stop working it before it falls below 900 °C, because working it colder cracks it. It is tougher than carbon steel, so expect more blows and more reheats, and judge temperature by a measured colour chart, not by habit from carbon steel. Cool the part slowly in air or in the furnace, and follow with solution annealing for austenitic grades.
Part of Stainless Steel Production
Shaping stainless steel by hammering at forging heat: the temperature window, the colour cues and the cooling rules.
The Window Is Narrower And Hotter Than For Carbon Steel
The carrier gives the forging range as 1,100-1,250 °C, calls it bright yellow to light yellow, and sets a hard floor: never forge below 900 °C, since working the cooled metal causes cracking. For comparison, the corpus’s Metalworking colour chart for carbon steel calls cherry red about 750 °C, orange about 950 °C (ideal), yellow about 1,100 °C (maximum) and white 1,200 °C and above (welding only). So the top of the carrier’s stainless range lies where that chart is already calling the colour white. Colour naming is unreliable across fires and light; check against a test piece you have measured, or against Pyrometric Cones as a reference.
What You Need
- A forge that reaches at least 1,250 °C. Metalworking gives 1,200-1,400 °C for a charcoal forge; Forge Setup and Bellows Building cover building and blowing it.
- Clean charcoal (Forge Fuel).
- Tongs, hammer, anvil kept clean of rust and scale.
- A slow-cooling bed of dry ash or sand.
Method: A Forging Session
Step 1: Heat slowly and evenly. I recall that stainless conducts heat poorly, so rushing the heat risks cracking; the carrier does not say this and I cannot source it. Bring the work up in stages.
Step 2: Soak at forging temperature until the colour is even through the section.
Step 3: Forge quickly. The carrier notes more blows are needed. Work the part while it is in the window and return it to the fire before it drops toward 900 °C.
Step 4: Reheat as often as the colour demands. Stopping early to avoid a reheat is how cracks start.
Step 5: Cool slowly. The carrier says to air cool or furnace cool. For martensitic grades I recall that rapid cooling can crack the part because they harden on cooling; bury the part in dry ash. For austenitic grades the carrier says not to quench after forging; see the discussion in Austenitic (300 Series) for the conflict with its own annealing quench.
Step 6: Finish. Descale and passivate (Passivation Treatment).
Common Mistakes
- Forging at orange heat as for carbon steel. The metal is too cold and cracks.
- Overheating in charcoal. I recall charcoal contact can add carbon to a hot surface, which would work against Carbon Control; unsourced. Keep the work off the burning charcoal where possible.
- Hammering with a rusty anvil or tongs. Iron transfers to the surface and later rusts through the film.
Safety
Forge heat and flying scale
Work at 1,100-1,250 °C throws hot scale and can burn through gloves in seconds. Wear eye protection, a leather apron and closed boots. Never forge on a wet anvil, because water flashes to steam and throws scale. Chromium-bearing fume is released at these temperatures; stay upwind of the forge.
What’s Next
- Learn next: Solution Annealing - restoring corrosion resistance after forging
- Combine with: Welding Stainless - joining forged pieces