Huakai Metal The short version: S50C is a Japanese-standard medium-carbon steel with about 0.5% carbon. It is cheap, machines well and is strong enough for mould bases, mechanical parts and general structural work. In China it is the default material for plastic mould frames.
What is S50C?
S50C is defined in JIS G4051 as a medium-carbon, non-alloy steel. The “S” means steel, “50” means roughly 0.50% carbon. Because it has no expensive alloying elements, it is one of the lowest-cost steels that is still hardenable and strong enough for real load-bearing parts.
It is not a mould cavity steel. Its main job in a mould is the base and frame — the block that holds the cavity inserts, ejector plates and guide pins. For the cavity itself you would use P20, 1.2738, H13 or similar.
Typical chemical composition
| Element | Typical range (%) | What it does |
|---|---|---|
| C | 0.47 – 0.53 | Strength and hardness after heat treatment |
| Si | 0.15 – 0.35 | Deoxidation |
| Mn | 0.60 – 0.90 | Hardenability and strength |
| P | ≤ 0.030 | Impurity — kept low |
| S | ≤ 0.035 | Impurity — kept low |
Equivalent grades
The table below maps S50C to the other common systems. As always, “equivalent” means similar composition and properties — not a drop-in guarantee for a critical part. Check the MTC.
| Standard | Grade | Note |
|---|---|---|
| JIS | S50C | Reference grade |
| DIN / EN | 1.1213 · C50 / C50E | Close match; C50E has tighter S/P control |
| AISI / SAE | 1050 | 0.50% carbon, same family |
| GB | 50# (50 steel) | Chinese national standard equivalent |
Hardness and heat treatment
- Annealed supply: typically around 187–220 HBW — easy to mill, drill and tap.
- Hardening: austenitise around 820–860 °C, then water or oil quench.
- Tempering: 400–600 °C depending on the strength/toughness you need.
- Usable hardness: about 45–52 HRC after hardening and tempering; higher as-quenched but too brittle for most tooling.
Where S50C is used
- Plastic mould base and frame plates — the most common use in tooling
- Mechanical parts: shafts, gears, connecting rods, keys
- General structural and machine-building components
- Jigs, fixtures and support blocks
Why it is the default mould base material
Three reasons: it machines cleanly, it is cheap relative to alloy steels, and it has enough strength that a well-designed frame will not deflect under injection pressure. For a mould that will run for years, saving money on the base is usually not worth the risk — and S50C is the pragmatic middle ground.
How to specify S50C plate correctly
- State the condition — annealed (machining) or pre-hardened at a target HRC.
- Give thickness and size — specify thickness, width, length and tolerance; mould bases often need accurate thickness.
- Ask for flatness — long plates can bow; if you are machining a base, flatness matters.
- Request the MTC — chemistry and hardness, so you can confirm the carbon and condition on arrival.
Need S50C plate for a mould base?
Tell us thickness, size and condition — we will confirm stock at our supplier warehouses and quote with MTC.
Request a Quote See Steel Range