Many mold makers struggle with rust marks and poor surface finish when producing transparent or corrosive–material plastic parts. S136 steel is one of the most widely used stainless mold steels to solve these common pain points.
What is S136 Mold Steel?
S136 is martensitic stainless mold steel delivered in annealed condition. Its biggest advantage lies in excellent corrosion resistance, which handles acid–releasing plastics like PVC and PET well. Besides anti–rust performance, it delivers superior mirror polishing capability, ideal for cosmetic, transparent plastic products. However, it comes with higher material cost and slightly lower hardness compared with hot–work steel such as H13. To help you make quick decisions, below is a concise comparison between S136 and NAK80, a popular pre–hardened mold steel.
Note: Unlike pre–hardened mold steels such as NAK80, S136 requires quenching and tempering heat–treatment to obtain high hardness and corrosion–resistant properties. Without proper heat–treatment, it cannot deliver ideal mirror finish or anti–rust effect. Below table compares key properties between S136 and NAK80.
| Comparison Items | S136 Mold Steel | NAK80 Mold Steel |
| Hardness | 48–52 HRC | 37–43 HRC |
| Corrosion Resistance | Excellent | Poor |
| Polishing Performance | 12000–15000 grit mirror | 15000 grit mirror |
| Mold Life | 500k–1000k shots | 500k–1000k shots |
| Crack Risk | Medium | Medium–High |
| Cost | Slightly higher | Lower |
| Main Use | Corrosive & transparent plastic molds | High–gloss non–corrosive molds |
As shown in the table above, S136 stands out for anti–corrosion and transparent part applications, while NAK80 is a ready–to–use pre–hardened option for high–gloss non–corrosive plastics. Select material according to your plastic type, surface requirement and budget.
Summary
When should you pick S136? Prioritize S136 if you process corrosive plastics, require mirror surface appearance, or molds face humid working environment. If your project only needs ordinary glossy surface without corrosion risk, NAK80 can be a cost–effective alternative. Proper heat treatment is critical to unlock S136’s full performance.
Many operators overlook daily maintenance. Even S136 stainless mold steel still needs regular cleaning after molding corrosive materials to extend service life.
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FAQ
Q1: Does S136 steel completely avoid mold rust?
A1: No. Though it features great corrosion resistance, long–term residual corrosive plastic residue will still cause surface stains. Daily cleaning is still necessary.
Q2: S136 vs NAK80, which one gives better mirror finish?
A2: Both can reach high–level mirror polish. NAK80 has slightly better polishing potential, while S136 wins on anti–corrosion.
Q3: Can S136 be used for large–size mold bases?
A3: Yes. Select ESR refined S136 grade for large molds to guarantee uniform material structure.