Martensitic stainless is the hardenable family, with 12-14% chromium and no nickel, used for knives, surgical tools and valves; it is hardened by heating to a high temperature and quenching, then tempered. It gives up corrosion resistance for hardness, since the carbon that makes it hard also ties up chromium, and it is the family that best tolerates the carbon a ferrochrome melt carries.
Part of Stainless Steel Production
The hardenable stainless family: composition, the hardening and tempering cycle, and its trade between edge and corrosion resistance.
Hardness Costs Corrosion Resistance
The carrier lists martensitic (410 type) at 12-14% chromium, no nickel, 0.15% carbon maximum, hardenable with moderate corrosion resistance, for knives, surgical tools and valves. The advanced-materials page gives 12-14% chromium with 0.1-1% carbon, a much wider carbon range; a higher-carbon version is harder and holds a better edge, and as Carbon Control explains, carbon ties chromium up in carbides and lowers corrosion resistance. I recall the same trade in commercial cutlery grades but cannot source specific values.
For an operator with carbon-rich ferrochrome this is the family where the extra carbon is least damaging, which is why Achievable Grades places it first on the ferrochrome route. For surgical use, remember that a rust-resistant edge still wants drying and care: Scalpel Forging and Instrument Making cover instruments from ordinary steel.
What You Need
- Forged blanks (Hot Forging).
- A furnace that holds a steady, high heat and a way to judge it.
- Quench medium: oil is the corpus norm for hardening (Heat Treatment, the steel article, not the rubber one).
- A tempering oven, or the oxide-colour method (Tempering, the steel article, not the clay-temper one).
Method: Harden And Temper
Step 1: Anneal the forged blank so it can be filed and ground (Heat Treatment covers annealing steel).
Step 2: Heat to the hardening temperature. For plain carbon steel the corpus gives bright cherry red, about 790-830 °C, with the work going non-magnetic near 770 °C. For martensitic stainless I recall a considerably higher hardening range, around 950-1,000 °C and above, and cannot source it. The magnet cue is therefore not enough: stainless is still not fully transformed when it stops sticking. Judge by a bright orange glow and trial pieces, not by the magnet alone.
Step 3: Quench. Move the work in oil as the corpus directs for steel. I recall these steels also harden in still air because of their chromium, which would make an oil quench more severe than needed; flagged as unsourced.
Step 4: Temper promptly before the part cools to room temperature and sits, since freshly hardened steel is brittle (Tempering). The steel-tempering colours in that article are for carbon steels; for stainless I recall that tempering in a mid-temperature band lowers corrosion resistance and toughness, so use the low end of the range for edges. Flagged as unsourced.
Step 5: Grind, polish and passivate (Surface Finishing, Passivation Treatment).
Common Mistakes
- Using the carbon-steel quench temperature. The part will not harden fully.
- Skipping the temper. Quenched stainless blades chip and shatter.
- Grinding hot. A blade that discolours at the edge has been tempered by the wheel.
- Expecting full stainless performance from a hard blade. Dry it after use.
Safety
Quenching hot steel
Oil quenching can ignite: keep the oil deep, covered nearby and away from the forge, as Heat Treatment warns. Heating steel above 900 °C and handling quenched blades risks burns and cuts; use tongs, eye protection and a leather apron.
What’s Next
- Learn next: Hot Forging - shaping the blank
- Combine with: Surface Finishing - finishing an edge