Cryo / sub-zeroOptional — optional — not tested in the KSN study
Temper2× 2 h · cool to room temp between cycles; 1–2 h per cycle
Reliable hardness58–62 HRC
Nickel low-alloy — among the toughest knife steels tested by KSN (chart-topping at 59–61 HRC). KSN furnace recipe: 1500°F/10 min, fast oil, temper 2× at 350–400°F for the optimal hardness/toughness balance. Targeting 63+ HRC is NOT optimal for this steel.
⚠︎ Temper↔HRC points are read from KSN toughness-study charts (±0.5 HRC) — verify with supplier datasheet.
Temper → hardness chart
Approximate HRC after a double-temper at each temperature (from the sources below). Set your target and pick the matching temper.
Temper °F
Temper °C
Hardness
300°F
149°C
61.5 HRC
350°F
177°C
60.5 HRC
400°F
204°C
59.5 HRC
Composition (typical, wt%)
Element
%
C
0.72%
Cr
0.45%
Ni
0.85%
Mn
0.8%
Si
0.25%
AKS/Pops 8670 typical (via KSN)
HeatTreatBench — the recipes in your shop, offline
Get the full 8670 recipe plus 25 more steels offline — set your target HRC and the app gives you the exact temper, with a forge timer and a per-blade log. Works in the shop with no signal.