Technical Deep Dive · Mould Engineering · Korean ISBM 2026

ISBM Mould Steel Guide:
P20, 718H & 2316 for Korean Buyers

The steel grade selection for an ISBM mould determines cavity life, polishability for optical clarity, resistance to corrosive resins, and the total cost of ownership over a 5–15 year production cycle. A wrong steel choice cannot be corrected after the mould is machined — this guide gives Korean ISBM buyers the material science basis to specify correctly the first time.

P20 · 718H · 2316
HRC 28–56 Range
Cavity Life 500K–5M+

Korean Ever-Power Engineering Desk · Ansan-si · May 2026

 

1. Why Steel Grade Defines ISBM Mould Total Cost of Ownership

Korean ISBM mould procurement decisions are routinely made on tooling cost alone — the KRW 30–80M quoted for a mould set is evaluated primarily as a capital expenditure line item, with steel grade appearing as a minor specification detail rather than the primary determinant of whether the investment performs over its intended production life. This approach consistently produces the most expensive outcomes in the Korean ISBM industry: moulds that wear prematurely, require early refurbishment, or fail to achieve the surface quality required for premium applications — all because the steel grade was specified for cost rather than for the application’s requirements.

The total cost calculation that Korean ISBM buyers should apply is: (mould capital cost + maintenance cost over life + refurbishment cost) ÷ total cavity shots over life = cost per cavity shot. At this level, the steel grade premium that separates P20 from 718H — approximately KRW 3–8M per mould set — commonly reverses the cost equation: the premium steel lasts 2.5–3× as long, reducing the annualised mould cost by 40–60% compared to the cheaper option. For a Korean ISBM producer running 8 million units/year on a 4-cavity mould, the difference between P20 (requiring rework or replacement at 500K shots) and 718H (lasting to 2M shots) is KRW 12–18M in avoidable mould cost over four years, on a mould that cost KRW 5M more at purchase.

The mould selection framework that positions steel grade within the broader 9-factor evaluation — including cavity count, cooling channel design, hot runner specification, and delivery lead time — is documented in the 9-factor Korean ISBM mould selection guide.

2. P20 (DIN 1.2311): Entry Grade and Its Specific Limits

P20 (DIN 1.2311, also supplied under the Korean designation SCM415M and similar equivalents) is a chromium-molybdenum pre-hardened tool steel delivered at HRC 28–34. Its position in Korean ISBM mould production is as a prototype or low-volume commodity grade — it costs the least of the serious tool steels, machines readily without further heat treatment, and weld-repairs easily when cavities require correction after initial trial. For these reasons, P20 is appropriate for Korean ISBM mould applications where production volume projections do not exceed 500,000–700,000 cavity shots, or where the mould is a development tool intended to validate bottle design before committing to a production-grade steel.

P20’s primary limitation for Korean ISBM production is its relatively low hardness (HRC 28–34 compared to 718H at HRC 36–42). At this hardness level, abrasive wear from PET and PETG resin particles — particularly in production runs that include masterbatch pigments with inorganic particle content (TiO₂, iron oxide) — progresses faster than on harder grades. Cavity surface roughness increases over the production run, manifesting as progressive haze increase in K-Beauty PETG bottles, or as visible weld-line widening in the neck finish zone as the cavity surface loses its initial mirror polish. The surface quality degradation typically becomes commercially significant at 400,000–600,000 shots for P20 in Korean K-Beauty PETG production — significantly earlier than the 1.5–2.0 million shots a 718H cavity would achieve at equivalent quality.

P20 is correctly specified for Korean ISBM applications where the production volume is genuinely low (pharmaceutical niche applications at <200K units/year, custom supplement formats, export pilot runs), where the budget for tooling development does not accommodate the premium for 718H, or where cavity design revisions are anticipated during the product qualification phase. Specifying P20 for a Korean standard beverage or personal care production mould expected to run 2M+ shots is the specification error that most predictably generates avoidable mould replacement cost in the Korean ISBM industry.

3. 718H and 738H: The Korean ISBM Production Standard

718H (DIN 1.2738, also called P20+Ni in some Korean supplier catalogues) is the baseline production standard for Korean ISBM moulds in standard PET, PETG, K-Beauty, and beverage applications. It is a nickel-chromium-molybdenum pre-hardened steel delivered at HRC 36–42 — harder than P20, more polishable, and approximately 2.5–3× the cavity life at equivalent maintenance schedules. The nickel addition in 718H compared to P20 provides two production benefits: higher core toughness (reduced cracking risk in moulds with complex water channel geometries) and better polishability response, achieving consistent A2 high-gloss surfaces that K-Beauty brand quality auditors require.

738H (DIN 1.2738M) is a modified 718H with improved cleanliness (lower sulphur and phosphorus impurity levels) and refined grain structure, delivering superior polishability to A1 optical-clarity finish — the grade required for premium K-Beauty PETG bottles where gloss ≥92 GU is specified. The difference between 718H and 738H is most visible in the bottle’s optical performance at the cavity parting line zone: 718H cavities may show a very faint parting line impression in high-gloss K-Beauty bottles at high magnification under direct LED lighting; 738H cavities polished to A1 standard are essentially invisible in the parting line zone. At the premium pricing Korean K-Beauty brands pay for glass-clarity PETG bottles, this optical quality difference justifies the 738H premium of approximately KRW 2–5M per mould set.

For standard Korean beverage, food, and personal care production where gloss specifications are ≤90 GU (high-gloss but not optical clarity), 718H is the correct specification. Upgrading to 738H for these applications adds cost without delivering a commercially significant quality benefit. The hot runner system specification that accompanies 718H cavity blocks — and the compatibility between hot runner steel grades and cavity steel grades at the manifold interface — is covered in the hot runner systems engineering guide.

4. 2316 Stainless: Pharma, Corrosive Resins, and rPET Production

2316 (DIN 1.2316, a martensitic stainless tool steel with 16–17% chromium content) is the Korean ISBM mould steel for applications where corrosion resistance is the overriding requirement. Its stainless composition provides inherent corrosion protection against the three main corrosive attack vectors in Korean ISBM production: condensation moisture in high-humidity production environments (Korean production facilities during summer, 85–95% RH), acidic degradation products from PVC or certain masterbatch pigments, and the higher organic acid content of some rPET resin feedstocks.

For Korean pharmaceutical ISBM production — eye drop bottles, oral liquid containers — 2316 is increasingly the specified cavity steel because pharmaceutical GMP auditors evaluate cavity cleanliness standards that standard tool steels cannot consistently meet without surface passivation treatments. A 2316 stainless cavity can be cleaned with pharmaceutical-grade oxidising agents (hydrogen peroxide solutions, peracetic acid) between production lots without cavity surface damage, while 718H would require re-polishing after the same cleaning protocol. This cleanability advantage, alongside the mirror-finish polishability of 2316, makes it the steel grade specified in the Korean Ever-Power pharmaceutical ISBM mould range — consistent with the pharmaceutical GMP ISBM production guide‘s specification requirements.

2316’s primary trade-off against 718H is thermal conductivity: 2316 conducts heat at approximately 15 W/m·K versus 718H’s 34 W/m·K. This 55% lower thermal conductivity means 2316 cavity blocks require significantly more aggressive cooling channel design to achieve equivalent mould cycle cooling times — typically 40–55% more cooling channel surface area, with smaller-diameter channels positioned closer to the cavity surface. Korean ISBM mould designers specifying 2316 who use the same cooling channel layout as a 718H mould design will consistently produce cycle times 25–40% longer than their 718H equivalent, making the per-unit production economics significantly worse unless the cooling channel design is appropriately optimised for 2316’s lower conductivity.

The maintenance implications of 2316 versus 718H also differ: 2316’s hardness (HRC 30–36, slightly lower than 718H) means the cavity surface is more susceptible to mechanical damage from handling during mould changeover. Korean ISBM maintenance programmes for 2316 moulds should include protective cavity insert storage practices (cavity-specific polyethylene foam inserts) and strict prohibition on metallic tools contacting cavity surfaces during changeover — requirements documented in the Korean ISBM 5-tier maintenance framework at the Korean ISBM preventive maintenance checklist.

5. H13 (1.2344): Hot-Fill PP and Elevated Temperature Applications

H13 (DIN 1.2344) is a hot-work tool steel hardened to HRC 48–56 through a vacuum heat treatment cycle after rough machining. Its principal advantage for Korean ISBM is thermal fatigue resistance: the cyclic heating and cooling of ISBM blow moulding — from the hot preform contact temperature (~110–140°C at cavity surface during blow) to the mould cooling water temperature (~10–25°C) — represents a thermal fatigue cycle that accumulates micro-crack damage in softer tool steels over time. For standard PP and PET applications, 718H handles this thermal cycling well. For hot-fill PP ISBM production at mould temperatures of 130–160°C (heat-set moulds for hot-fill bottles), H13’s superior thermal fatigue resistance extends mould life significantly compared to 718H at equivalent mould temperature cycles.

H13 is specifically the correct grade for Korean heat-set ISBM blow moulds (not the injection mould component — the injection mould still uses 718H or 738H) where the mould body must sustain 130–160°C operating temperature during production. The specification error Korean buyers most frequently make with H13 is applying it to the entire mould assembly rather than only the blow mould body — the hot runner manifold, neck inserts, and injection cavity components do not require H13’s elevated temperature fatigue resistance, and using H13 for these components adds unnecessary cost and machining complexity without performance benefit. H13 mould components should be clearly documented separately from 718H components in the Korean ISBM mould specification, and only the blow mould body should carry the H13 designation.

6. Korean Sourcing: Domestic vs Import Steel for ISBM Moulds

Korean ISBM mould steel is sourced from two channels: POSCO’s domestic tool steel product line and imported European grades from Böhler (Austria), Uddeholm (Sweden), and Assab. The quality decision between Korean domestic and European import steel for 718H is less clear-cut than it was five years ago — POSCO’s NAK80 and S-STAR pre-hardened steels now meet the cleanliness and consistency standards required for K-Beauty A2 polishing at competitive prices. The practical difference in the Korean 2026 mould market:

The practical sourcing recommendation for Korean ISBM mould buyers: use domestic POSCO-grade steel for standard PET beverage and food production moulds at 718H-equivalent specification; specify European Böhler or Uddeholm import steel for K-Beauty PETG moulds requiring A1 polishability and for pharmaceutical 2316 cavity inserts. The performance premium at standard beverage production volumes does not justify import steel cost; at K-Beauty and pharmaceutical premium pricing, the polishability advantage is commercially recoverable within the first production run.

7. Heat Treatment and Cavity Dimensional Stability

Pre-hardened steels (P20, 718H, 738H) are supplied in a through-hardened condition by the steel manufacturer — no further heat treatment is required after machining, which eliminates the risk of dimensional distortion from heat treatment cycles that would affect the tight dimensional tolerances of ISBM cavity geometry. This is the primary reason Korean ISBM mould makers favour pre-hardened grades over through-hardening grades: the ISBM cavity dimensions (±0.05mm tolerance on critical neck insert geometry) cannot be reliably maintained through post-machining heat treatment, because the steel distorts non-uniformly during quenching and tempering in proportion to section thickness variations.

H13 moulds require post-machining vacuum hardening and tempering — typically at 1,020–1,050°C austenitise, gas quench, double temper at 530–580°C — and dimensional distortion of 0.05–0.15mm must be expected and accounted for in the machining allowance. Korean ISBM mould shops with experience in H13 vacuum hardening reliably hold final cavity dimensions within ±0.08mm after heat treatment, but this requires deliberate allowance management and a verified heat treatment specification. Korean buyers ordering H13 ISBM moulds from shops without documented vacuum hardening capability risk dimensional non-conformance that cannot be corrected post-hardening without complete cavity remachining. The connection between mould dimensional accuracy and its downstream effect on scrap rate is documented in the Korean ISBM scrap rate reduction guide.

8. Steel Grade Selection by Korean ISBM Application

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