1.2316 (X38CrMo16) is a corrosion-resistant mould steel supplied pre-hardened at 280–325 HB, which is roughly 30–34 HRC. It carries about 16 % chromium — roughly twice the chromium of P20 — which is what lets it run in moulds for PVC, acetate and other resins that release corrosive gases.
Chemical composition
Typical ladle analysis for 1.2316, as supplied to DIN 17350:
| Element | Range (%) | What it does |
|---|---|---|
| Carbon, C | 0.33 – 0.45 | Sets the hardness ceiling after quenching |
| Chromium, Cr | 15.50 – 17.50 | Corrosion resistance; the defining addition |
| Molybdenum, Mo | 1.00 – 1.30 | Pitting resistance and tempering stability |
| Manganese, Mn | 1.00 – 1.30 | Hardenability |
| Silicon, Si | 0.30 – 0.50 | Deoxidation |
| Phosphorus / Sulphur, P / S | 0.030 max each | Impurity control — low sulphur keeps polishability |
Equivalent grades
| System | Designation |
|---|---|
| DIN / EN | 1.2316 — X38CrMo16 |
| AISI / SAE | 420 modified (high-chromium mould grade) |
| JIS | SUS420J2 modified |
The number is easy to confuse with 1.2311 (P20) and 1.2738. They are different steels: 1.2311 has about 2 % chromium, 1.2316 has about 16 %. If a quotation says “2316” without the chromium range, ask for the mill certificate before you accept it.
Hardness and heat treatment
As delivered, 1.2316 comes pre-hardened at 280–325 HB (about 30–34 HRC), which is hard enough to machine a mould and put it into production without a second heat treatment. If a harder cavity is needed, the steel can be quenched and tempered to roughly 50 HRC, but it loses toughness and gains distortion risk as it goes up.
Austenitising is normally carried out in the 1000–1040 °C range with oil or high-pressure gas quenching, followed by tempering at 200–300 °C for maximum hardness or 500–600 °C when toughness matters more than wear resistance. Stress relieving at about 650 °C after rough machining is standard practice on large blocks.
Corrosion resistance and where it matters
The 16 % chromium gives 1.2316 a passive layer that P20 and 1.2738 do not have. That changes which resins it can run:
- PVC and CPVC release hydrogen chloride as they process; on a P20 mould this attacks the cavity surface and the water channels.
- Acetate, POM and flame-retardant grades carry the same problem in a milder form.
- Medical and optical parts where the mould must be polished to a mirror and then cleaned with aggressive agents between runs.
What 1.2316 does not give you is stainless-steel corrosion resistance. It is a martensitic tool steel with 16 % chromium, not a 420 blade steel, and it will still rust in a damp tool room if the water channels are left wet.
Applications
- Injection moulds for PVC, acetate and other corrosive resins
- Large and complex cavities where a pre-hardened block saves a heat treatment cycle
- Moulds that need a high polish plus resistance to attack, such as optical and medical parts
- Wear parts that see moisture or chemical exposure alongside abrasion
Why specify it instead of P20 or 1.2738
P20 (1.2311) and 1.2738 are cheaper and easier to source, and for polyolefins and polystyrene they are the right answer. 1.2316 earns its premium only when the resin attacks the steel. Paying for 16 % chromium on a mould that runs PP is money spent on nothing.
For an even higher polish with similar corrosion resistance, 1.2083 / S136 is the next step up.
Related reading
- P20 / 1.2311 plastic mould steel — the general-purpose baseline this grade is compared against.
- 1.2083 / S136 stainless tool steel — higher chromium, better polish.
- 718H vs P20H — choosing between the two pre-hardened mould steels.
- Mirror-finish mould steel — what a polished cavity demands of the steel.
You get chemical composition, mechanical properties and a price — with inspection certificates to EN 10204 3.1 issued against the heat number.
