P20 (1.2333) and 1.2738 are the two most widely used pre-hardened mold steels in the plastic molding industry.
Their combined annual domestic procurement exceeds 80,000 tonnes.
The two materials differ in hardness, thermal conductivity, hardenability, alloy composition, and machining performance.
These differences directly affect mold cooling efficiency, service life, dimensional accuracy, and first-pass yield rates of molded parts.
This article compares the two steels across three dimensions: Material Properties, Machining Performance, and Application Suitability.
It provides mold design engineers and procurement teams with a data-driven basis for material selection through 9 sets of core technical data.
Choosing the correct mold steel grade can reduce overall mold cost by 20%-40% while improving first-pass yield rates.
Choosing the correct mold steel grade can reduce overall mold cost by 20%-40% while improving first-pass yield rates.
Material Properties
Hardness Comparison
P20 mold steel is typically delivered at a hardness of 28-32 HRC in the pre-hardened condition.
Some select grades can reach about 34 HRC.
After final heat treatment, P20's maximum hardness generally does not exceed 36 HRC.
Its dimensional change rate during heat treatment is about 0.02%-0.05%.
This is relatively stable behavior, which is well-suited for molds where rework after heat treatment must be minimized[1].
1.2738 mold steel contains about 1.05% nickel — more than twice the 0.45% nickel found in P20.
Nickel strengthens the steel matrix and improves both hardenability and core strength.
After quenching and tempering, 1.2738 achieves a hardness range of 30-38 HRC.
High-strength batches can approach 40 HRC.
Under identical heat treatment, the surface-to-core hardness differential in 1.2738 typically does not exceed 2 HRC.
In contrast, P20 in large-section plates may show a 3-5 HRC gradient between the outer layer and the inner core.
· P20 max applicable cross-section: about 400 mm × 300 mm. Beyond this size, core hardness drops noticeably and a soft-core structure develops.
· 1.2738 max applicable cross-section: up to 600 mm × 500 mm, while maintaining core hardness above 30 HRC.
For deep molds or those with non-uniform wall thickness, core strength directly influences the mold's resistance to deformation under high-pressure injection.
1.2738's superior hardenability ensures more uniform hardness distribution from surface to core throughout the entire mold block.
This reduces the risk of local buckling and elastic deflection of mold inserts during injection.
P20 in large mold applications requires either thicker walls or additional ribbing to compensate for core strength deficiencies.
This directly increases overall mold weight and material cost.
For mold blocks exceeding 400 kg, switching from P20 to 1.2738 typically reduces required wall thickness by 10%-15% while maintaining equivalent rigidity.
Thermal Conductivity
P20 mold steel has a thermal conductivity of about 29-32 W/(m·K).
This places it among the better-performing pre-hardened mold steels in terms of heat dissipation.
Higher thermal conductivity means heat absorbed at the mold surface transfers more rapidly to the cooling water channels.
This directly improves cooling efficiency.
For high-volume multi-cavity molds, using P20 can reduce cooling time by 15%-25%.
That translates directly into higher production output per shift and lower per-part energy consumption costs.
According to the fundamental heat transfer equation Q = k × A × ΔT / d, under identical heat exchange area and temperature differential, P20's heat flow Q is about 30% higher than that of 1.2738.
This means cooling cycles for identically sized molds can be shortened by 20%-30% when using P20 instead of 1.2738.
1.2738 mold steel has a thermal conductivity of about 20-24 W/(m·K).
That is about 25%-30% lower than P20.
This lower thermal conductivity produces a more uniform mold surface temperature distribution, with a smaller temperature gradient across the cavity.
This characteristic is particularly useful when molding temperature-sensitive high-precision optical plastic components — such as lenses or light guide plates that need the mold temperature differential to stay within 3 °C across all cavity surfaces.
1.2738's uniform temperature field effectively reduces part warpage and internal molecular orientation stress.
This improves the dimensional stability and optical performance consistency of the final product.
P20's rapid cooling advantage translates directly into measurable economic benefits for high-volume standard parts — potentially increasing output per shift by 15%-20%.
However, cooling time is not the only factor that determines production efficiency.
For high-volume standard parts with extremely demanding cycle time requirements — such as bottle caps, single-use food packaging containers, or disposable medical device housings — P20's rapid cooling advantage translates directly into measurable economic benefits.
For precision parts with inherently longer cycle times or more stringent requirements for temperature field uniformity, 1.2738's stable temperature distribution delivers quality benefits that outweigh its cooling speed disadvantage.
The material selection decision between P20 and 1.2738 must balance production volume, part precision requirements, and expected mold service life across all three dimensions.
Wear Resistance
P20 mold steel after carburizing or nitriding can achieve surface hardness values of 55-65 HRC.
This significantly enhances wear resistance against abrasion.
However, P20's relatively lower core hardness means that once the surface-hardened layer is worn through under high-friction conditions, the substrate wear resistance drops rapidly and surface degradation accelerates.
· P20 is well-suited for: glass fiber-filled plastics with GF content below 20%, general polypropylene, and polyethylene formulations without abrasive mineral fillers.
· When P20 encounters plastics with calcium carbonate fillers, talc extenders, or short glass fiber reinforcements: these hard particles create micro-cutting action against the mold cavity surface, accelerating surface deterioration and increasing surface roughness at a rate about 30%-40% faster than with unfilled materials.
1.2738 contains 0.8%-1.2% chromium.
Chromium carbides dispersed at grain boundaries and within the matrix form a dispersion-strengthening structure.
This structure maintains good baseline wear resistance even without surface treatment.
In applications where surface treatment is difficult to apply uniformly — such as deep cavity molds with complex geometry — 1.2738 provides more consistent wear resistance across all cavity surfaces.
Experimental wear test data shows that under dry friction conditions, 1.2738's wear rate is about 15%-20% lower than P20[2].
This performance gap widens further when molding with hard filler materials.
For example, when molding PA66 with 30% glass fiber reinforcement, 1.2738 demonstrates a wear failure life about 60%-80% longer than P20 in accelerated aging tests.
Additionally, 1.2738's as-delivered polishability reaches Ra 0.2 μm or better.
A smoother cavity surface reduces melt adhesion to the mold wall, lowering adhesive wear risk and extending maintenance intervals between polishing cycles.
· For engineering plastics with hard fillers — such as PA66+30%GF, PBT+30%GF, or PC+20%Talc: 1.2738's wear resistance advantage becomes even more pronounced.
· It effectively reduces problems of die swelling, flash thickening, and dimensional drift caused by progressive cavity wall wear.
Machining Performance
Machinability
P20 in its pre-hardened state offers good machinability.
At about 30-34 HRC, it can be milled, turned, and drilled using standard uncoated or coated carbide tooling.
No pre-heating or special equipment is required[3].
P20's cutting force requirement is about 20% lower than S7 tool steel and is similar to H13 in hot-work condition.
Chips from P20 form in banded shapes and break cleanly.
This makes P20 well-suited for automated machining operations where chip evacuation must be reliable and consistent across long milling runs.
1.2738 in its pre-hardened state has a hardness range of about 30-38 HRC.
This higher hardness demands greater cutting force and cutting power than P20 under identical cutting parameters.
Tool life in end milling operations may be shortened by 20%-30% compared to P20.
This means more frequent tool changes and higher per-part tooling costs.
However, 1.2738's machined surface finish is notably superior, with significantly less burr formation at machined edges.
This benefits finishing operations that require direct polishing after semi-finishing without intermediate deburring steps.
· Recommended tooling for 1.2738: TiAlN-coated carbide, to improve tool life under high-temperature, high-hardness cutting conditions.
· P20 typical cutting speed: 120-180 m/min (at 30-34 HRC).
· 1.2738 typical cutting speed: 80-140 m/min (due to higher hardness and nickel content).
· Result: identical cavity machining operations may take 20%-35% longer with 1.2738 compared to P20.
P20's rough-cut surface typically carries higher residual tensile stress at the subsurface, often requiring an additional stress-relief treatment before precision finishing.
1.2738's machined surface has a deeper compressive stress layer with smaller residual tensile stress.
This yields better long-term dimensional stability after final machining.
It also reduces the risk that finished mold components will shift out of tolerance during the assembly and debugging phase.
Surface Treatment
P20 exhibits broad surface treatment compatibility.
Common surface treatment methods applicable to P20 include gas carburizing, carbonitriding, gas nitriding, and ion nitriding.
Gas carburizing can raise P20 surface hardness to 58-62 HRC with a typical case depth controlled at 0.5-1.5 mm.
However, grinding is required after carburizing to restore dimensional accuracy to precision mold tolerances, adding a secondary machining step that increases lead time and cost[4][5].
1.2738, with its approximately 1% nickel content, produces superior adhesion between electroplated nickel coatings and the substrate.
Unlike P20, which requires an intermediate copper strike layer before nickel plating to prevent coating peeling, 1.2738 can be nickel-plated directly.
This simplifies the plating process flow and reduces the risk of coating delamination during injection molding under high cavity pressure.
1.2738's typical nickel plating thickness of 10-25 μm achieves a surface hardness of about 45-55 HRC.
· This effectively enhances the mold cavity's corrosion resistance against acidic plastic melts.
· It also reduces chemical attack risk from flame-retardant plastic formulations.
PVD and CVD coating technologies are increasingly applied in high-performance plastic molds.
P20 and 1.2738 respond differently to these coatings.
P20's lower core hardness creates a larger hardness gradient between the substrate and the coating, making PVD or CVD coatings more prone to chipping or delamination under high-cavity-pressure flushing conditions.
1.2738's higher core hardness produces a gentler hardness transition from substrate to coating, generally yielding superior coating adhesion strength and longer retained coating performance under cyclic loading.
For precision molds where post-heat-treatment correction is difficult or costly, 1.2738's lower heat treatment distortion propensity — about 30%-40% lower than P20 — reduces the correction workload after heat treatment, shortening manufacturing lead times and reducing scrap rates.
Deformation Tendency
P20 after quenching and tempering exhibits a dimensional change rate of about 0.02%-0.05%.
This is among the smaller distortion ranges for pre-hardened mold steels.
However, in molds with significant section thickness variations, uneven cooling rates in P20 during quenching can lead to cumulative residual stress concentrations.
These may cause dimensional out-of-tolerance conditions or flatness defects after precision machining.
For mold plates and large framework components exceeding 500 mm in width, a sub-zero stress-relief tempering treatment held at 20-30 °C below the original tempering temperature is recommended.
1.2738's nickel content — more than twice that of P20 — significantly improves steel hardenability while simultaneously reducing the quenching cooling rate required to achieve full martensitic transformation.
1.2738's heat treatment distortion is about 30%-40% lower than P20 under identical section size and heat treatment conditions.
Its dimensional changes are more uniform across all critical dimensions.
This characteristic makes 1.2738 particularly suitable for precision mold components such as optical lens molds and micro-connector molds that have extremely tight dimensional tolerances.
· P20: requires faster quenching media (water or oil) to achieve full martensitic structure. This can generate structural stress concentrations at thick-thin section transitions, leading to warpage or twisting distortion that is difficult to predict and compensate for in advance.
· 1.2738: lower critical cooling rate allows the use of relatively mild quenching media such as air-atomized oil or high-pressure gas quenching, which produce gentler cooling curves that effectively reduce both thermal stress and transformation stress.
For complex mold structures with wall thickness ratios exceeding 3:1, P20's heat treatment distortion control becomes substantially more challenging, often necessitating larger machining allowances of 0.3-0.5 mm per side to accommodate anticipated distortion[6].
1.2738's recommended heat treatment regime is: austenitizing at 860-900 °C followed by oil quench or accelerated gas quench, then tempering at 520-580 °C.
For precision mold key components, this treatment often permits elimination of the correction step after heat treatment, allowing direct progression to precision grinding.
This shortens manufacturing cycles and reduces scrap rates associated with correction-induced re-stressing of the mold block.
Application Suitability
Mold Service Life
Mold service life is a core economic indicator that must drive mold steel selection decisions.
Under standard operating conditions — clean materials, well-maintained injection molding machines, and properly trained operators — a P20 mold typically achieves a service life of about 100,000 to 200,000 molding cycles before showing significant wear that requires maintenance intervention.
Beyond this range, molds begin showing visible wear at the parting line and gate area, increased flash formation, and rising part burr rates.
This necessitates scheduled shutdown for maintenance or insert replacement.
· P20 mold failure modes (standard conditions): dominated by abrasive wear, typically manifesting as surface spalling and cavity wall pitting that progressively degrade product surface quality.
1.2738 mold under identical operating conditions has an expected service life of about 150,000 to 300,000 cycles — about 1.5 to 2 times the life of P20.
This life extension stems from 1.2738's higher core hardness, superior hardenability, and finer prior austenite grain size, which collectively enhance both fatigue resistance and wear resistance under high-cycle injection operation.
1.2738 mold failure modes are more gradual and predictable.
The mold progresses from initial polished surface dulling through minor flash formation to visible wear over a longer time interval.
This provides operators with a longer maintenance window and substantially lower risk of unexpected catastrophic failure that halts production and causes costly unplanned downtime.
When molding unfilled general-purpose plastics such as polypropylene, polyethylene, or ABS resin, P20 mold life can reach or exceed 200,000 cycles.
However, when molding engineering plastics with hard mineral or glass fillers — such as PA66 with 30% glass fiber, PBT with 30% glass fiber, or PC with talc reinforcement — filler-induced cavity wall abrasion and particle impact wear dramatically accelerate P20 failure.
Actual mold life may drop to only 50,000 to 80,000 cycles.
Additionally, plastics containing flame retardant additives — such as V0-rated polyamide formulations — release corrosive gases during the injection process that chemically attack P20 mold cavity surfaces, accelerating surface roughness deterioration beyond what pure mechanical wear would predict.
· Practical data from injection molding operations running glass-filled engineering plastics: 1.2738's wear failure life extends about 60%-80% longer than P20 under equivalent operating conditions.
· For medium-to-large injection parts with annual production volumes exceeding 500,000 units: choosing 1.2738 translates directly into fewer mold repairs, longer equipment availability, and more stable product quality consistency — making it more economical across the full lifecycle cost analysis even at a 25%-35% higher initial material cost.
Molding Effect
Molding effect encompasses three interconnected quality dimensions: product appearance surface quality, dimensional accuracy stability, and internal molecular quality.
P20 molds cool rapidly due to their higher thermal conductivity.
This produces good molding results for thin-walled plastic parts such as mobile phone housing components with 0.4-0.6 mm thin-wall sections, where faster cooling reduces the risk of warpage caused by prolonged contact between the molten polymer and the relatively warm cavity wall.
However, P20's as-delivered polishability is moderate, typically achieving a surface finish of Ra 0.4-0.6 μm.
This may fall short for highly polished parts with stringent Class-A appearance requirements such as automotive interior panels, instrument cluster covers, and consumer electronics outer shells that need a mirror-like surface finish directly from the mold cavity without post-machining polishing.
1.2738's as-delivered polishability reaches Ra 0.2-0.3 μm, meeting most Class-A surface requirements without the need for post-machining polishing operations[7].
Its lower thermal conductivity produces a more uniform mold cavity temperature distribution throughout the injection and dwelling phases.
This stabilizes melt flow behavior and reduces the temperature differential that drives uneven polymer molecular orientation.
This temperature field uniformity directly translates into better product dimensional accuracy and reduced internal residual stress that can cause warpage after ejection or during thermal cycling in the end application.
· For textured grain-finished surfaces or molds requiring fine micro-surface structures (micro-undercuts, embossed text, raised features below 0.1 mm depth): 1.2738's superior polishability and finer grain structure better replicate microscopic mold surface features onto the molded part, delivering noticeably superior molding texture quality compared to P20.
The two materials also differ in elastic rigidity under high-pressure injection.
P20 and 1.2738 have similar elastic moduli in the 200-210 GPa range.
However, 1.2738's superior hardenability maintains higher overall rigidity in large molds where P20 would develop a softer core zone, reducing local elastic deflection at the cavity wall under injection pressure.
For molds with projected areas exceeding 400 cm², injection pressure can reach 50-80 MPa. Mold wall elastic deformation under this pressure directly causes product flash thickening and dimensional out-of-tolerance defects, making 1.2738's rigidity advantage particularly pronounced in such large-area mold applications.
Overall assessment:
· P20 is better suited for: applications prioritizing high cooling efficiency, standard appearance surfaces with Ra 0.5 μm or coarser, and high-volume general-purpose plastic products.
· 1.2738 is better suited for: high surface quality requirements including Class-A surfaces, highly polished cavities, optical-grade components, and complex precision industrial plastic parts.
Cost Analysis
P20 is one of the most widely used pre-hardened mold steels globally, with ample market supply and stable, transparent pricing that makes cost budgeting straightforward for mold procurement[8][9].
In the 2024 domestic Chinese market:
· P20 plate pricing: about 25-35 CNY per kilogram.
· P20 heat treatment cost: about 8-12 CNY per kilogram for standard pre-hardening treatment.
· Combined material and heat treatment cost: about 33-47 CNY per kilogram.
· For a medium-sized mold block weighing about 500 kg: combined cost is about 16,500-23,500 CNY.
1.2738 is a modified pre-hardened mold steel with higher nickel and chromium content.
This improves hardenability and core properties but increases raw material costs by about 25%-35% compared to P20.
In the same market period:
· 1.2738 plate pricing: about 32-42 CNY per kilogram.
· 1.2738 heat treatment cost: about 10-15 CNY per kilogram due to higher process temperature and atmosphere control requirements.
· Combined material and heat treatment cost: about 42-57 CNY per kilogram.
· For an equivalent 500 kg mold block: combined cost is about 21,000-28,500 CNY — about 4,000-5,000 CNY higher than the P20 equivalent.
Mold steel material cost should not be evaluated in isolation but rather through a total lifecycle cost framework that incorporates expected mold life, production efficiency gains, and product defect rate impacts.
Taking a 500 kg mold block as a representative example:
· P20-based solution: material + HT cost ~20,000 CNY, expected mold life 150,000 cycles → per-cycle material depreciation ~0.13 CNY/cycle.
· 1.2738-based solution: material + HT cost ~24,000 CNY, expected mold life 250,000 cycles → per-cycle material depreciation ~0.096 CNY/cycle.
· Result: from a per-cycle cost perspective, 1.2738 is about 26% lower than P20.
If the mold will produce parts at annual volumes exceeding 200,000 units, choosing 1.2738 typically recovers its material price premium over P20 within 2-3 years of production.
This is achieved through reduced mold repair frequency, longer equipment uptime, and fewer product defect-related losses.
For one-time mold development projects with annual production volumes below 50,000 units, where the mold may be retired or reworked before reaching its full service life potential, P20's lower initial cost makes it the more economical choice despite its shorter per-mold service life.
Summary across all data:
· P20 holds a significant advantage in: thermal conductivity (29-32 W/(m·K)) and material cost (20%-30% lower than 1.2738), making it suitable for high-volume general-purpose plastic mold production. In large-scale standardized product manufacturing, P20's comprehensive economic benefit significantly outweighs 1.2738.
· 1.2738 comprehensively leads in: hardness range (30-38 HRC), hardenability (max applicable cross-section 600 mm × 500 mm), polishability (Ra 0.2 μm), and wear resistance (15%-20% lower wear rate than P20), making it suitable for precision molds and engineering plastic parts with hard fillers, with mold service life extended 1.5-2× compared to P20.
Core selection principle: When annual production exceeds 200,000 units and product precision requirements are high, prioritize 1.2738. When annual production is below 100,000 units or product precision requirements are standard, prioritize P20.
Based on total lifecycle cost analysis (mold life × first-pass yield ÷ material unit price), 1.2738 saves 800-1,500 CNY per 10,000 units in scenarios exceeding 300,000 units annually.