1.2311 vs 1.2738: Choosing the Right Prehardened Mold Steel

Both are prehardened P20-family mold steels. The nickel in 1.2738 decides the question — here is when it matters and when 1.2311 is enough.

The short answer

Choose 1.2311 for small and medium molds. Choose 1.2738 when the block is thick (roughly over 400 mm) or the cavity needs a high, uniform polish.

What actually differs

	1.2311	1.2738
Nickel	—	0.90–1.20%
Hardness uniformity in thick sections	Drops toward core	Uniform surface to core
Polishability	Good	Better
Price	Lower	Higher

Why nickel matters

Prehardened mold steels are quenched before delivery. In thick blocks the core cools slowly and ends up softer with plain P20 chemistry. Nickel raises hardenability, so 1.2738 holds 290–330 HB through the whole section — critical for large automotive molds where the cavity sits deep in the block.

Cost logic

The price gap is real but small next to the machining cost of a large mold. For blocks under ~300 mm, 1.2311 (or P20) delivers the same result for less money; above that, 1.2738 is cheap insurance.