For plastic mold manufacturers, picking qualified pre-hardened mold steel directly decides mold surface finish, production cycle and long-term manufacturing costs. 718 mold steel and P20 mold steel are two mainstream alloy pre-hardened steels widely adopted in consumer electronics, automotive and daily plastic product molds. Many mold makers struggle to distinguish their applicable scenarios and performance gaps. This article sorts out core properties, application boundaries and selection standards of the two materials to solve your material selection confusion.
What is P20 Mold Steel?
P20 mold steel is entry-level pre-hardened alloy mold steel without nickel element, with standard delivery hardness at 28–32 HRC. It features outstanding machinability, low cutting tool loss and affordable raw material price. No complex secondary heat treatment is needed after rough machining, which greatly shortens mold processing cycle. Its weldability is stable, convenient for later mold modification and repair.
P20 fits small & medium simple plastic molds for low-to-medium batch production, including PP/PE daily necessities, small electronic shell prototypes, with service life around 300,000 shots. Its weaknesses are obvious: poor hardness uniformity on large cross-section blanks, mediocre polishing capacity, prone to surface scratches when molding glass-filled plastics, and weak toughness under long-term high-load production.
What is 718 Mold Steel?
718 mold steel is an upgraded modified version based on P20 formula, with extra nickel alloy element added. Its factory pre-hardened hardness reaches 33–38 HRC. The nickel component optimizes internal material structure, realizing uniform hardness distribution even on thick large steel blocks. It features premium mirror polishing performance, excellent impact toughness and moderate wear resistance.
718 targets medium-to-high volume precision plastic molds: automotive interior parts, large home appliance shells, cosmetic high-gloss plastic casings, with stable mold life up to 800,000–1,000,000 shots. It can bear long-term continuous production and effectively reduce mold deformation and surface abrasion caused by reinforced plastic raw materials. The only drawback is higher material cost than P20.
| Comparison Items | P20 Mold Steel | 718 Mold Steel |
| Alloy Composition | Basic Cr-Mo alloy, no nickel | Cr-Mo base +~1% nickel added |
| Pre-hardened Hardness | 28–32 HRC | 33–38 HRC |
| Machining Performance | Excellent, low tool consumption | Good, slightly higher cutting resistance |
| Mirror Polishing | Only matte surface, unable to reach high gloss | High-gloss mirror polishing available |
| Hardness Uniformity | Uneven for thick blanks | Uniform for large cross-section steel blocks |
| Typical Mold Life | ≤300,000 shots | 800,000–1,000,000 shots |
| Material Cost | Low, budget-friendly | 15%–20% higher than P20 |
| Best Application | Small simple prototype molds, low-volume production | Large precision molds, high-gloss appearance parts, mass continuous production |
Both steels are pre-hardened alloy mold steels, so secondary quenching after machining is unnecessary. Neither material has natural corrosion resistance; when molding corrosive plastics such as PVC and POM, surface nitriding or hard chrome plating treatment is required.
Material Selection Guide Based on Production Demand
Choose P20 mold steel if you develop new product prototypes, produce small-batch simple plastic parts, or control mold manufacturing budget strictly. It cuts processing time and lowers initial material investment, fully meeting low-demand molding tasks.
Choose 718 mold steel if you mass-produce high-gloss appearance plastic products, process large-size mold bases, or adopt glass-reinforced plastic raw materials. Though the upfront cost rises, fewer mold maintenance and replacement costs will save total lifecycle expenses in mass production.
Summary
Do not judge materials only by unit price when selecting between 718 and P20 mold steels. Combine production volume, product surface requirements, mold size and plastic raw material type to calculate overall lifecycle cost.
FAQ
Q1: Can 718 fully replace P20 in all mold projects?
A1: No. 718 has better performance yet higher cost. For small-batch prototype molds with no high polishing requirements, P20 is more cost-effective and sufficient for production needs.
Q2: Why does 718 have better polishing performance than P20?
A2: Nickel alloy inside 718 refines the internal metal grain structure and minimizes internal impurities, enabling the steel to achieve a flawless mirror finish after fine polishing. Without nickel addition, P20 has uneven grain distribution and can only deliver a matte surface.
Q3: Are surface anti-rust treatments necessary for P20 and 718?
A3: Yes. Both are non-stainless pre-hardened alloy mold steels. When molding corrosive plastics, nitriding or hard chrome plating must be done to avoid mold cavity rust and product surface defects.
Q4: What will happen if using P20 for mass production of glass-filled plastic?
A4: P20 has inadequate wear resistance. Obvious scratches will form on the mold cavity after short-term production, resulting in defective plastic parts and frequent production halts for mold maintenance.