Step 4 of 6
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Steel selection by application — hot-work, warm-work, and the special cases
Pick H13, H11, premium hot-work grades (DIEVAR, QRO 90 Supreme, W360 ISOBLOC), PM hot-form grades (CPM 1V), or Nitralloy 135M for the right job. Read a Uddeholm or Bohler datasheet without getting sold.
Step 4 of 6Warm-work specialty steels: 6F3, L6, Inconel 718
Warm-forging dies running below about 350-400°C die surface temperature open a different solution space. 6F3 (medium-carbon Ni-Cr-Mo alloy steel) and L6 (Ni-Cr-Mo tool steel) trade hot hardness for toughness and machinability, and are competitive on heavy warm-work or impact-dominated tooling that does not need H13's secondary-hardening retention. Their temper resistance curves crash above 450°C, so they fail fast in real hot-forge service.
Inconel 718 is the special case at the other extreme. It is a precipitation-hardened nickel-based superalloy, not a tool steel, and it appears on hot-extrusion dies for stainless and superalloy billet stock where the die face routinely sees 800-1000°C. The machinability is poor and the heat-treat schedule is unforgiving. The application that justifies it is hot enough that any 5% Cr steel softens through within a few hundred cycles. On a steel-billet forge die where H13 at proper hardness still has temperature margin, Inconel 718 is the wrong call.
Quick check
A warm-forging die for low-carbon steel runs with a die-surface temperature peaking near 380°C and is impact-dominated, not wear-dominated. The shop's current grade is standard H13 at 48 HRC. The dies are cracking at 25,000 cycles. Which grade family opens up at this service temperature, and what does the substitution buy?