Does P20 need heat treatment?

Usually not. It is supplied prehardened to about 28–32 HRC, so the mould is machined and used as is; nitriding can be added for wear.

1.2738 adds nickel so that big blocks have even hardness through the thickness. For small and medium moulds P20 (1.2311) is enough.

Is P20 good for glass-filled plastics?

It works, but filled plastics wear it faster. Nitriding, or a harder mould steel for the cavity inserts, gives longer life.

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P20 mould steel

Also called: 1.2311, 40CrMnMo7, P20 tool steel, 1.2738, P20+Ni, prehardened mould steel

P20 is a chromium-molybdenum tool steel supplied already hardened, to about 28–32 HRC, so moulds can be machined straight from the block without heat treatment. It is the standard steel for plastic injection moulds and mould bases; P20+Ni (1.2738) is used for larger blocks.

Quick facts

Type: Prehardened plastic mould steel
Supplied hardness: About 28–32 HRC (about 280–325 HB)
Main alloys: About 2% chromium, 1.5% manganese, 0.2% molybdenum
Larger blocks: 1.2738 (P20 with about 1% nickel) hardens more evenly
Surface treatment: Can be nitrided for wear
Polishability: Good

Equivalent grades

Standard	Grade
AISI	P20
DIN / EN ISO 4957	1.2311 (40CrMnMo7)
With nickel	1.2738 (40CrMnNiMo8-6-4)
With sulphur, easier machining	1.2312

Typical chemical composition (1.2311)

Element	%
Carbon (C)	0.35–0.45
Manganese (Mn)	1.30–1.60
Chromium (Cr)	1.80–2.10
Molybdenum (Mo)	0.15–0.25

Working with it

Machine directly in the supplied prehardened condition
Polishes well for most plastic parts; for mirror finishes use a cleaner, harder mould steel
Nitriding adds surface hardness against wear from filled plastics
Can be welded for repairs with matching filler and preheat

Typical uses

Plastic injection mould cavities and cores
Mould bases and holder plates
Blow mould and die-casting die holders
Extrusion dies for plastics

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Questions

Does P20 need heat treatment?: Usually not. It is supplied prehardened to about 28–32 HRC, so the mould is machined and used as is; nitriding can be added for wear.
P20 or 1.2738?: 1.2738 adds nickel so that big blocks have even hardness through the thickness. For small and medium moulds P20 (1.2311) is enough.
Is P20 good for glass-filled plastics?: It works, but filled plastics wear it faster. Nitriding, or a harder mould steel for the cavity inserts, gives longer life.

The figures on this page are typical values for guidance, written by Diemeco from standard engineering practice. They are not a specification: confirm grades and properties with the relevant standard or the supplier's mill test certificate, and tolerances with your workshop. Last checked 8 October 2026.