Plastic Mold Steel ComparisonP20 · XPM · NAK80 · SKD61 (H13)
Updated: Aug 20
Summary Executive Summary
There is no single "best" plastic mold steel. Sound selection means finding the material and supply condition that best controls the project's primary failure risk.
That risk may come from machining time, mold size, surface quality, wear resistance, high-temperature load, corrosive environment, dimensional stability, weld repair, and the mold's entire service life. For automotive lighting and multi-shot molds, a single tool may also face large sections, deep cavities, transparent or high-gloss surfaces, texturing, multi-material interfaces, shut-off wear and long cooling channels at the same time.
So the question should not be "which of P20, XPM, NAK80 or SKD61 is better?"
The better question is: how is this mold most likely to fail, and which steel and heat treatment best controls that risk?
Key Key Conclusions
P20 is a common pre-hardened steel for general plastic molds. Uddeholm's data lists it as generally supplied pre-hardened at about 28–32 HRC, with good machinability, polishability and hardness uniformity, suitable for general plastic molds.
SWG XPM is a proprietary plastic mold steel from Schmiedewerke Gröditz, positioned by the maker for medium-to-large molds and high-surface-finish cavities, and explicitly listing bumpers, automotive interiors and automotive lighting as applications. Official hardness ranges span roughly 33–37.6 HRC and 38–42 HRC, so the name "XPM" alone does not imply a single hardness.
NAK80 is Daido Steel's 40 HRC-class precipitation-hardened plastic mold steel, about 37–43 HRC after solution and aging treatment, with high mirror-polishability, good EDM surfaces, and transparent and high-mirror applications as its main strengths.
SKD61 / AISI H13 / 1.2344 belong to the commonly cross-referenced 5% Cr hot-work tool steel family. Böhler W302's data directly lists the three as corresponding grades; its main strengths are high-temperature strength, thermal-fatigue resistance and wear resistance, and it can also be used for injection molds, hot-runner systems and glass-fibre reinforced plastics.
Therefore: general, non-high-wear molds where cost and machining efficiency come first can start from P20-class steels; large, high-surface-finish automotive molds can consider XPM; transparent and high-mirror parts can evaluate NAK80 or a verified high-cleanliness / remelted material; and when high temperature, thermal cycling or high wear becomes the primary risk, evaluate SKD61 / H13-class or other dedicated tool steels.
01 Quick Comparison Matrix
Steel | Officially supportable typical supply / use condition | Main characteristics | Corrosion positioning | Applications to evaluate |
P20 | Generally pre-hardened ~28–32 HRC; specs vary by mill | Balance of machinability, toughness and general polish | Not corrosion-dedicated | General plastic molds; cost and lead-time priority |
SWG XPM | ~33–37.6 HRC or 38–42 HRC, confirm by supply spec | Large sections, high surface finish, texturing reliability | Not corrosion-dedicated | Medium-large molds, bumpers, interiors, lighting |
NAK80 | ~40 HRC class; Daido lists 37–43 HRC | High mirror finish, good EDM surface, uniform hardness | Not corrosion-dedicated | Transparent, mirror, high-appearance precision molds |
SKD61 / H13 / 1.2344 | Usually machined annealed, then hardened/tempered; working hardness set per project | High-temp strength, thermal-fatigue resistance, wear resistance | Not corrosion-dedicated | High heat load, hot runners, local high load, glass-fibre reinforced plastics |
On cost
This paper does not use a fixed cost ranking such as "P20 economical, XPM medium, NAK80 high." Actual steel cost depends on mill, size, weight, stock, machining allowance, supply hardness, remelting process, heat treatment, purchase quantity and exchange rate. A real project should compare on specified requirements plus a current quotation, not by equating a material name with a fixed price tier.
02 Why Mold Steel Selection Is a Systemic Decision
Mold steel affects far more than purchase price. It also drives machining time, tool consumption, EDM, polishing hours, weld repair, heat-treatment distortion, dimensional retention, surface treatment and later maintenance. A higher-hardness mold is not automatically "better" — higher hardness usually helps reduce indentation and wear, but can also make cutting, EDM, grinding, fitting and weld repair harder. Likewise, a steel with excellent polishability may not be the most sensible choice if it does not meet the mold's primary wear, heat-load or dimensional requirements.
Before formal selection, Howmin recommends confirming at least: molding resin, filler, estimated output, mold temperature, product appearance, dimensional precision, mold size, number of cavities, hot runners, cooling layout, texturing or mirror requirements, weld-repair strategy and the customer's material specification.
CORE PRINCIPLE
The core of steel selection is not chasing the highest grade, but reducing the failure most likely to occur in the project.
03 "Comparable" and "Equivalent" Are Not Automatically Interchangeable
Mold steel names mix national standards, mill brands, proprietary improved grades and market trade names. "Looks similar on a cross-reference table" does not equal "can be substituted unconditionally."
P20
AISI P20 is a common plastic mold steel grade. For Gröditz's SWG 2311, the maker lists AISI P20 as a comparable grade. But even within the P20 family, different suppliers' composition, cleanliness, supply hardness, size capability and process may differ.
XPM
XPM is Schmiedewerke Gröditz's proprietary grade. Most importantly: the comparable-grade field in the XPM datasheet is "–," so XPM should not be written as "P20HH" or as a formal equivalent of any standard grade.
NAK80
NAK80 is Daido's proprietary precipitation-hardened plastic mold steel, listed as a 40 HRC-class NAK-series steel emphasizing mirror finish, EDM surface and transparent-product use. It should not be substituted with another 40 HRC pre-hardened steel merely because "the hardness is close."
SKD61 / H13 / 1.2344
These three names have a mature cross-standard correspondence: Böhler W302 lists 1.2344 / AISI H13 / JIS SKD61 together, and Daido DHA1 also cross-references SKD61 / H13 eq. / 1.2344 eq. But even with matching grade numbers, different mills' cleanliness, ESR or not, forging quality, heat-treatment capability and large-section performance may still differ.
PURCHASING RULE
A formal specification should not just say XPM / NAK80 / P20 / SKD61, but at least define: mill and full grade name, supply hardness, material dimensions, whether substitution is allowed, the substitution approval process, remelting requirements, ultrasonic inspection, heat-treatment requirements, mill test certificate, and any special surface requirements.
04 P20: The Baseline for Cost, Machinability and General Use
Uddeholm positions AISI P20 as a pre-hardened plastic mold steel, generally supplied at about 28–32 HRC, with good machinability, polishability and hardness uniformity. P20's greatest engineering value is not a single peak property, but the balance of machinability, toughness, availability, general polishability and a pre-hardened machining route. Because it is already pre-hardened, many applications can complete machining at the existing hardness, avoiding an overall re-hardening step to reach working hardness and reducing post-heat-treatment dimensional change and rework risk.
When to evaluate P20
General thermoplastic molds with moderate surface and wear requirements, where output and cost control matter and no special corrosion resistance, high heat load or ultra-high mirror finish is needed, can list P20-class steels as a first-round candidate.
P20's limits
P20 is not a corrosion-resistant steel, nor is it positioned for extreme wear or extreme mirror finish. When glass fibre, mineral fill or other high-wear conditions become the primary risk, re-evaluate hardness, surface treatment or other tool steels. For long-term humid, condensing or corrosive environments, evaluate a stainless-type mold steel rather than continuing with P20 on price alone.
05 XPM: A High-Hardness Pre-Hardened Option for Large, High-Finish Molds
SWG XPM's own data applies it directly to medium-to-large plastic molds, high-surface-finish cavities, TV housings, bumpers, automotive interiors and automotive lighting, and specifically emphasizes good texturing reliability. Official hardness ranges can include 315–355 HB (~33–37.6 HRC) and 359–400 HB (~38–42 HRC). So a formal project cannot just say "use XPM," but should specify which supply hardness range.
One of XPM's values is providing higher pre-hardened strength than a typical ~30 HRC-class P20, without fully switching to the traditional high-hardness quench-and-temper tool-steel machining route, while retaining the machining, texturing, weld-repair and surface-treatment capability that large plastic molds need.
Surface quality
At 38–42 HRC, Gröditz lists ISO/SPI N2 / A-2 for general SWG XPM. For higher transparent / high-gloss surfaces, Gröditz offers SWG XPM VICTORY ESU (an ESR remelted version), listed at ISO/SPI N1 / A-1, with transparent plastics, high-gloss plastics and headlamp systems as applications. General XPM and the high-cleanliness ESR version should not be treated as the same surface-capability tier.
XPM's limits
XPM is not positioned primarily for corrosion resistance or high-temperature hot-work performance. Gröditz's data marks an application temperature below 250°C; its main positioning remains medium-to-large plastic molds, not a replacement for H13-class hot-work tool steels.
06 NAK80: Transparent Parts, High Mirror Finish and Precision Appearance Molds
Daido positions NAK80 as a 40 HRC-class high-performance precision plastic mold steel, about 37–43 HRC after solution and aging, with roughly 40 HRC-class uniform hardness from surface to core, and generally no need for overall re-hardening after machining. NAK80 is an improvement over NAK55 in mirror capability, EDM surface and toughness. Daido specifically recommends it for transparent products, products where mirror surfaces are especially important, and molds where EDM surface quality matters.
This makes NAK80 suitable to evaluate for transparent covers, transparent decorative parts, high-gloss products, precision appearance molds and products very sensitive to cavity surface.
IMPORTANT CLARIFICATION
NAK80 does not equal "automatically achieving SPI A-1." What the maker can support is that NAK80 has good mirror-polishability and suits transparent and mirror products — but using NAK80 itself cannot automatically guarantee any specific SPI grade. The final mirror finish still depends on steel batch quality, cavity geometry, pre-EDM machined surface, recast-layer removal, grinding and polishing procedure, polishing media, cleanliness management and technician skill. When a defined high-mirror finish is required, write the acceptance standard into the specification rather than only specifying NAK80.
07 SKD61 / H13 / 1.2344: High-Temperature, Thermal-Fatigue and High-Load Tool Steels
SKD61, AISI H13 and 1.2344 are very commonly cross-referenced. Böhler W302 lists 1.2344 / AISI H13 / JIS SKD61; Daido DHA1 also cross-references SKD61 / H13 eq. / 1.2344 eq. The main strengths of this 5% Cr hot-work tool steel family are high-temperature strength, high-temperature hardness, thermal-fatigue resistance and wear resistance; Böhler W302 ISOBLOC further uses an ESR process to improve cleanliness, uniformity and toughness.
Heat treatment and hardness
The usage logic differs from the pre-hardened P20, XPM and NAK80. Böhler W302 ISOBLOC's annealed hardness is up to 229 HB; working hardness after heat treatment is set by application, with the maker's hardened-and-tempered bar range reaching 40–55 HRC. So this paper does not write "SKD61 working hardness is fixed at 44–52 HRC" as a universal rule, but instead sets target hardness by supplier, size, heat-treatment spec and actual failure risk.
Plastic mold applications to evaluate
Böhler W302's official applications directly include injection molding, hot-runner systems and glass-fibre reinforced plastics. So when the primary issue is high mold temperature, thermal cycling, local high load, hot runners or glass-fibre wear, this hot-work steel family can be evaluated. But it cannot be simplified to "PEEK means SKD61" or "PPS means H13" — engineering-plastic steel selection must also consider fillers, corrosive additives, mold temperature, part geometry, wear location, surface requirements and repair method.
08 Engineering Performance Comparison of the Four Steels
Evaluation criterion | P20 | XPM | NAK80 | SKD61 / H13 class |
Machining in pre-hardened state | Strong | Strong | Strong | Generally machined annealed, then heat-treated |
Medium-large plastic molds | Good, by grade and size | A main maker positioning | Usable; assess size and cost | Feasible; manage heat-treat distortion |
High mirror / transparent parts | Fair to good, by steel quality | Evaluate VICTORY ESR for high needs | A main strength | High-quality / ESR feasible; not all H13 equal |
Texturing | By steel quality | Maker emphasizes good texturing reliability | Good | By steel quality and process |
High temperature / thermal cycling | Not a main strength | Not a main strength | Not a main strength | A main advantage |
High wear | Fair | Moderate, by load and surface treatment | Not a main advantage | Better with high hardness and correct heat treatment |
Corrosive environment | Not corrosion-dedicated | Not corrosion-dedicated | Not corrosion-dedicated | Not corrosion-dedicated |
Weld repair and maintenance | Mature methods | Maker provides weld-repair guidance | Daido provides dedicated weld procedure | Requires strict preheat, filler and post-treatment control |
09 Mold Life: Shot Count Alone Cannot Decide the Steel
This paper does not use fixed figures such as "P20 = 300k shots" or "SKD61 = 800k shots," because mold life is not determined by the grade alone. The same steel, used on small PP parts, glass-fibre reinforced resin, high-mold-temperature molding, sharp shut-offs, multi-material interfaces or high-load slides, may fail in completely different ways. What truly affects life includes resin, filler ratio, mold working hardness, heat-treatment quality, part geometry, gate and shut-off load, mold temperature, injection conditions, surface treatment and maintenance.
RECOMMENDED SPEC WORDING
"The mold shall achieve a mutually agreed production-life target under specified resin, filler ratio, molding conditions, maintenance plan and acceptance standards" — rather than "a given steel guarantees a fixed shot count." This wording also returns mold-life responsibility to conditions that can genuinely be controlled and verified.
10 Material Selection for Automotive Lighting and Multi-Shot Molds
Automotive lighting is not a single part. One lamp assembly may contain a lens, light guide, reflector, bezel/extension, housing and other transparent, translucent or structural plastic parts. So the molds for different parts should not all use one "automotive lighting mold steel."
Transparent lenses, light guides and high-mirror cavities
Selection should prioritize steel cleanliness, hardness uniformity, mirror capability, post-EDM handling and long-term surface stability. NAK80 is an important candidate; for larger parts also demanding very high surface quality, a verified ESR / high-cleanliness plastic mold steel can be evaluated (for example Gröditz's XPM VICTORY ESU, which the maker lists for transparent, high-gloss and headlamp systems, marked at N1/A-1 surface capability).
Large housings, bezels, extensions or high-appearance structural parts
When the main requirements are large sections, deep cavities, texturing, high surface finish and higher pre-hardened strength, XPM can be a candidate (Gröditz directly lists lighting, bumpers and automotive interiors as XPM uses). If wear and appearance requirements are more general and cost and machining efficiency come first, P20-class steels can still be a reasonable candidate.
High-wear and high-heat-load zones
If high temperature, thermal cycling or wear concentrates locally, the whole mold does not necessarily need high-hardness hot-work steel. A more sensible approach may be to use SKD61 / H13-class material at gates, slides, cores, shut-offs, rotating locators or high-wear inserts, while the large main body still uses a pre-hardened plastic mold steel suited to large-section machining. This mixed-steel architecture is often more sensible for cost and maintenance than using the highest grade throughout the whole mold.
2K / 3K / 4K multi-shot molds
Multi-shot molds add interface alignment, repeat positioning, shut-off wear, differing material shrinkage, thermal balance and in-mold mechanism load. Steel selection cannot look only at mirror finish or hardness — interface and shut-off zones should be separately evaluated for indentation resistance, wear, toughness, weld repair, dimensional retention and later fitting. For a large multi-shot lighting mold, the sensible solution may not be "all XPM" or "all NAK80," but a main-cavity material plus a local high-load insert material plus an optical-zone material, configured by each zone's failure risk.
11 A Five-Step Steel Selection Framework
Define the molding material: confirm the full resin grade (not just PC/PMMA/PP/PBT), plus glass/mineral ratio, flame retardant, additives, colorant, regrind, and actual mold temperature and injection conditions.
Define product quality: dimensional tolerance, optical requirements, mirror grade, texturing spec, appearance surfaces, allowed weld-line position, flash limits and post-processing.
Define mold load: annual and total output target, cavity count, cycle, mold temperature, hot runners, deep cavities, slides, shut-offs, inserts and maintenance plan.
Choose the steel architecture: do not assume the whole mold must use one grade; decide material by cavity, core, slide, insert, gate, shut-off, optical zone and high-wear zone.
Lock purchasing and verification: mill, grade, supply hardness, size, allowed substitution, ESR or remelting requirements, ultrasonic inspection, heat treatment, MTC, surface acceptance and material change control.
12 Quick Selection Guide
Primary project condition | First-round candidate | Engineering notes |
General plastic mold, low-to-moderate wear, cost and lead-time priority | P20 class | Confirm appearance, actual shot-count target and rust management |
Medium-large automotive mold, deep cavity, high finish and texturing | XPM | Specify full XPM version, supply hardness, size and MTC |
Transparent parts, mirror and high-end appearance | NAK80 / verified high-cleanliness material | Define surface acceptance directly; do not guarantee mirror by grade |
Large transparent / high-gloss needing higher cleanliness | XPM VICTORY ESR and similar remelted materials | Confirm the actual ESR version and surface spec |
High mold temp, thermal cycling, hot runners or local high wear | SKD61 / H13 / 1.2344 class | Plan heat treatment, allowance, distortion and later machining ahead |
Corrosive resin, humid or condensing environment | Evaluate a stainless-type mold steel | None of the four here is positioned primarily for corrosion resistance |
Large load differences across one mold | Mixed-steel architecture | Use high-grade material only where truly needed — optical, shut-off, gate, insert or wear zones |
A note on corrosive environments
If corrosion is the primary failure risk, none of the four steels compared here should be viewed as the best corrosion-resistant option. For example, Uddeholm Tyrax ESR is a 1.2083 / AISI 420-class high-hardness corrosion-resistant plastic mold steel, which the maker positions clearly for corrosion resistance, high mirror finish, glass-fibre reinforced plastics and lens applications. This illustrates an important principle: if the project's primary risk changes, the candidate steel should change too — a project should not be forced to choose from a fixed set just because those grades are familiar to the company.
Howmin's Selection Perspective
Mold steel is not an isolated purchased item. For large automotive lighting and multi-shot molds, material selection must be considered together with product design, mold structure, machining method, cooling, mold-flow analysis, heat treatment, trial and production conditions.
Howmin's working position is this — not every mold should use the most expensive steel; there is no "best," only "most suitable."
Before product development, we first assess the customer's product characteristics and expected annual volume, and then recommend the material and mold approach on that basis.
Annual volume and mold-life requirements directly change the sensible selection logic: a 50k-shot bridge tool and a several-hundred-thousand-shot production tool, even for the same product, may call for completely different material and hardness choices. This is why we do not start from "buy whatever steel the customer specifies" or "the harder the better," but instead first confirm the mold's primary failure risk, then decide which zone needs which material, hardness and surface treatment.
So transparent optical zones prioritize surface and cleanliness, high-wear shut-off zones may need different hardness and material, and the large mold body values large-section machining and dimensional stability — the best material solution for a high-end mold is often not a single steel, but a steel architecture.
We also put verifiability into the commitment: the steels we select can be supplied with a mill test certificate (MTC), so the quality of the customer's mold is traceable and confirmable from the material source onward.
End Conclusion
P20, XPM, NAK80 and SKD61 / H13 each represent a different engineering trade-off. P20's value is in maturity, pre-hardening, machinability and the balance for general use; XPM's is in medium-to-large molds, high surface finish, higher pre-hardened strength and texturing reliability, with the maker listing interiors, bumpers and lighting as applications; NAK80's is in roughly 40 HRC-class uniform hardness, high mirror finish, good EDM surface and transparent-appearance applications; and the SKD61 / H13 / 1.2344 class offers advantages different from pre-hardened plastic mold steels under high-temperature, high-heat-load, thermal-fatigue and wear conditions.
So what steel selection really has to answer is not "which steel is best?" but:
Where and under what conditions is this particular mold most likely to fail, and what material and engineering method will reduce that risk?
That is the real engineering value of mold steel selection.
Primary Technical Sources
Material data in this paper prioritizes each steelmaker's / brand's official technical documentation:
Schmiedewerke Gröditz — SWG XPM material data (hardness, dimensions, surface capability, texturing, medium-large molds and lighting / bumper / interior uses); SWG XPM VICTORY ESU (ESR version, N1/A-1, headlamp systems); SWG 2311 (40CrMnMo7 and AISI P20 comparable grade).
Daido Steel — NAK55 / NAK80 technical data (37–43 HRC, 40 HRC-class uniform hardness, mirror, EDM, transparent products, weld repair); tool steel product cross-reference (NAK80, DHA1, SKD61 / H13 / 1.2344).
Uddeholm — AISI P20 (28–32 HRC pre-hardened supply and performance positioning); Tyrax ESR (1.2083 / AISI 420-class corrosion-resistant, high-mirror, lens applications).
Böhler — W302 ISOBLOC / ISODISC (1.2344, AISI H13, JIS SKD61 cross-reference; high-temperature performance, ESR, injection and glass-fibre reinforced material uses).
