POM Injection Mold Steel Selection Guide
2026-02-14 11:12:42
Injection Mold
POM (polyoxymethylene), also known as acetal resin, is a high‑crystallinity, high‑rigidity engineering plastic. With excellent wear resistance, fatigue resistance and dimensional stability, it is widely used in the injection molding of precision gears, automotive components, electronic housings and other high‑end products. However, during high‑temperature injection molding, POM decomposes and releases acidic gases such as formaldehyde and formic acid, which are highly corrosive to mold steels. Meanwhile, most POM products require high precision and high surface finish. Therefore, the selection of mold steel is particularly critical. The core principle is to prioritize steels with corrosion resistance, wear resistance, high toughness and good polishability, and make reasonable matches according to production volume and product requirements, so as to extend mold life and ensure product quality.
Core Pain Points in Material Selection
The selection of POM injection mold steel focuses on solving three key pain points: first, corrosion caused by acidic gases to avoid rust spots and pits on the mold cavity; second, dimensional stability for high‑precision products to reduce mold deformation; third, wear resistance for high‑frequency injection and friction to extend service life. According to cost performance and application scenarios, steels can be divided into four categories to cover all production needs.
Economic‑Grade Steels (Small & Medium Batches, Low Cost)Suitable for small and medium batches, ordinary appearance and low‑precision POM products, with the core advantages of low cost and easy processing, adapting to small‑scale production with limited budgets. The main grades include P20, 718H and NAK80. P20 and 718H are common pre‑hardened steels with hardness HRC 28–32, but they have no acid corrosion resistance and are easy to rust in humid environments, only suitable for products with less than 300,000 cycles, dry workshops and low appearance requirements. NAK80 is a pre‑hardened mirror steel with hardness HRC 38–41, and its polishing and rust resistance are better than P20, suitable for products with less than 500,000 cycles and medium appearance requirements.
General‑Purpose Steels (Medium Batches, Precision & High‑Gloss)The preferred choice for POM molds, balancing corrosion resistance, wear resistance, polishability and cost performance, covering most production scenarios. The main grades are S136H, 1.2316 pre‑hardened steel and TS400. S136H is a martensitic stainless steel with strong corrosion resistance, capable of resisting the erosion of POM decomposed gases, and its polishing can reach #8000, with stable dimensions, suitable for 500,000–1,000,000 cycles of precision high‑gloss products.
High‑End Long‑Life Steels (Large Batches, High Precision)Suitable for large batches, high‑precision, high‑wear‑resistance and high‑gloss mirror products, with the core advantages of high hardness, high toughness and strong corrosion resistance, supporting long‑term continuous production. The main grades include quenched S136, LG mold steel and TS520. Quenched S136 has hardness HRC 48–52 and ultra‑high polishability. LG steel has excellent toughness to avoid cracking. TS520 has outstanding corrosion resistance and thermal stability.
Steels for Special Scenarios (Glass‑Fiber Reinforced POM)
Glass‑fiber reinforced POM (≥20% fiber) has high hardness and will strongly abrade the mold during injection, so hot‑work die steels with high wear resistance and thermal fatigue resistance are required. The main grades are H13 and SKD61. After quenching, both steels reach hardness HRC 48–52, with excellent wear and thermal fatigue resistance, suitable for mass production of high‑strength products.
Key Selection PrinciplesMust choose corrosion‑resistant steels, especially stainless steels such as S136 series in humid environments. Determine hardness according to production volume: pre‑hardened for small batches, quenched for large batches. Prioritize mirror steels for precision parts to ensure surface gloss and dimensional accuracy. Choose high‑toughness steels for gears and sharp corners to prevent cracking.
Selection SummaryS136H is preferred for conventional POM parts; quenched S136 or LG steel for precision high‑gloss parts; H13/SKD61 for glass‑fiber reinforced POM; NAK80 for small‑batch low‑cost applications (dry environment).
