Quick Answer
P20 is usually the more economical choice for general automotive plastic parts, lower production volumes and molds without demanding cosmetic surfaces.
718H is normally preferred for larger automotive molds, visible exterior or interior parts, deeper mold blocks and projects requiring more uniform hardness, better polishing and longer service life.
For large automotive exterior parts such as bumper covers, grilles and visible trim components, 718H is often the safer choice. For smaller functional parts or cost-sensitive projects, P20 may provide better overall value.
However, mold steel selection should never be based only on the expected number of shots. The plastic resin, part size, surface finish, mold structure, maintenance plan and production conditions must also be evaluated.
What Are P20 and 718H Mold Steels?
P20 and 718H are commonly used prehardened plastic mold steels.
Because they are supplied in a hardened and tempered condition, they can normally be machined without performing a complete heat-treatment process after rough machining. This reduces the risk of heat-treatment distortion and can shorten mold manufacturing time.
P20 is a broad mold steel designation rather than one completely identical material worldwide. Chemical composition, sulfur content, hardness and cleanliness can vary among different steel mills and commercial grades.
718H is generally considered an upgraded P20-type mold steel. It is often associated with 1.2738 or P20 plus nickel-type steel. The additional nickel helps improve through-hardness and hardness uniformity in larger steel blocks.
This difference becomes more important when manufacturing large automotive molds with deep cavities or thick mold plates.
718H vs P20: Main Differences
| Comparison Item | P20 Mold Steel | 718H Mold Steel |
|---|---|---|
| Steel type | Prehardened plastic mold steel | Higher-hardness, nickel-alloyed prehardened mold steel |
| Typical delivered hardness | Approximately 28–32 HRC | Commonly approximately 33–37 HRC, depending on supplier and grade |
| Machinability | Generally good | Good, but normally slightly slower to machine because of higher hardness |
| Hardness uniformity in large blocks | Acceptable for many general molds | Usually better for large and thick mold blocks |
| Polishing performance | Suitable for normal surface requirements | Generally better for higher cosmetic surface requirements |
| Photo-etching and texturing | Suitable when steel quality is controlled | Often preferred for demanding texture and appearance surfaces |
| Wear resistance | Moderate | Better than standard P20 in comparable conditions |
| Welding and repair | Generally convenient | Possible, but correct welding procedures and preheating should be followed |
| Material cost | Lower | Higher |
| Typical application | General plastic molds and cost-sensitive projects | Large automotive molds and molds with higher surface or life requirements |
| Indicative production planning range | Often considered for approximately 200,000–300,000 cycles in suitable conditions | Often considered for approximately 300,000–500,000 cycles in suitable conditions |
| Best value | Lower initial mold cost | Better balance of surface quality, consistency and service life |
The cycle ranges in this table are not guaranteed material limits. They are only preliminary planning references.
Actual mold life can be higher or lower depending on the molded material, mold design, lubrication, cooling, maintenance, molding pressure, cycle time and production environment.
Is 718H Always Better Than P20?
No.
718H provides advantages in hardness uniformity, polishing and wear resistance, but these advantages also increase material and machining costs.
Using 718H for every mold may increase the project budget without creating a meaningful production benefit.
For example, a small automotive bracket molded in unfilled PP with moderate annual volume may not require 718H. A properly specified P20 mold could deliver acceptable service life and stable production at a lower investment cost.
On the other hand, selecting standard P20 only to reduce the initial price may create risks in a large bumper, instrument panel or visible grille mold.
The correct question is not:
“Which steel is better?”
The better question is:
“Which steel provides the best balance of mold cost, part quality, production volume and maintenance risk for this specific project?”
When Should You Choose P20 Mold Steel?
P20 can be a practical and cost-effective choice when the project has the following conditions:
- Moderate production volume
- Normal surface finish requirements
- Small or medium-sized plastic parts
- Non-abrasive plastic resin
- Limited cavity depth
- Cost-sensitive mold budget
- Easy access to mold maintenance
- Replaceable inserts used in high-wear areas
Typical automotive applications may include:
- Small brackets
- Protective covers
- Internal support components
- Air duct connectors
- Small housings
- Non-visible functional components
- Low- to medium-volume replacement parts
P20 is also useful when the customer expects future product changes.
Because it is generally easier and less expensive to machine, weld and modify, P20 may reduce the cost of later engineering changes.
When Should You Choose 718H Mold Steel?
718H is often the preferred option when the mold has one or more of the following requirements:
- Large mold dimensions
- Deep cavity geometry
- Visible automotive surfaces
- High polishing requirements
- Fine texture or photo-etching
- Higher production volume
- More demanding dimensional consistency
- Long production programs
- Reduced risk of hardness variation in thick steel blocks
Typical automotive applications may include:
- Front and rear bumper molds
- Instrument panel molds
- Large door trim molds
- Automotive grille molds
- Center console molds
- Large interior trim molds
- Visible exterior cover molds
- Air conditioning housing molds
- Large functional housings
For these molds, the cost difference between P20 and 718H may represent only a limited percentage of the complete mold price.
If the improved steel reduces polishing problems, surface defects, repair frequency or premature wear, the higher initial investment may be justified.
Why 718H Is Often Recommended for Automotive Bumper Molds
Automotive bumper molds are usually large and can contain deep or wide cavity surfaces.
The final plastic part may also require:
- Controlled surface appearance
- Stable dimensions
- Consistent part fitting
- Large-area polishing or texturing
- Reliable production over many cycles
- Reduced risk of local steel hardness variation
In a large steel block, uniform hardness is important.
If different areas of the cavity behave differently during machining, polishing or texturing, the final surface may become inconsistent.
For this reason, a higher-quality 718H or equivalent 1.2738-type steel is often selected for the cavity and core of large bumper molds.
This does not mean that every bumper mold must use the same steel grade.
The final decision should consider:
- Bumper resin
- Paint or no-paint surface
- Texture requirements
- Annual production quantity
- Mold life target
- Customer mold standard
- Mold dimensions
- Steel supplier and certification
- Local repair and maintenance capability
Does 718H Guarantee a 500,000-Shot Mold Life?
No mold steel can guarantee a specific mold life by itself.
A mold made from 718H may fail before 500,000 cycles if it has:
- Insufficient cooling
- Weak slides or lifters
- Incorrect steel treatment
- Poor lubrication
- Excessive injection pressure
- Abrasive glass-filled resin
- Poor water quality
- Corrosion
- Inadequate maintenance
- Unprotected shut-off areas
A well-designed and properly maintained P20 mold may also exceed an initial 300,000-cycle expectation in a low-wear application.
Therefore, shot life should be treated as a complete mold-system requirement, not only as a steel specification.
When a quotation states a target mold life, the supplier should also confirm:
- Steel brand and grade
- Cavity and core material
- Hardness range
- Steel certificate
- Mold base material
- Slide and lifter material
- Wear plate material
- Surface treatment
- Cooling design
- Spare parts
- Maintenance recommendations
How Plastic Material Affects the Steel Choice
The molded resin can be more important than the annual production quantity.
PP and TPO
PP and TPO are commonly used for automotive bumpers, trims and interior parts.
These materials are generally less abrasive than glass-filled engineering plastics. P20 or 718H may both be suitable depending on mold size, appearance and production volume.
For a large visible bumper mold, 718H is normally more attractive because of the mold size and surface requirements.
ABS and PC/ABS
ABS and PC/ABS are often used for automotive interior components.
When the part has a visible polished or textured surface, steel cleanliness and polishability become important. 718H may provide a better and more consistent surface result.
PA with Glass Fiber
Glass-fiber-reinforced PA is abrasive.
For high-volume glass-filled applications, neither standard P20 nor 718H should automatically be assumed to be sufficient for every high-wear area.
Hardened inserts, nitrided surfaces or higher-wear-resistance steels may be required around gates, shut-offs, slides and cavity areas exposed to material flow.
Flame-Retardant or Corrosive Materials
Some flame-retardant plastics can produce corrosive gases during molding.
In these applications, corrosion-resistant steel may be more suitable than either standard P20 or 718H.
The steel decision must therefore consider both wear and corrosion.
Cost Comparison: P20 vs 718H
P20 normally has a lower raw material cost.
It is also generally easier to machine because of its lower delivered hardness. This can reduce CNC cutting time, tool wear and polishing labor.
718H usually costs more because of:
- Higher alloy content
- Higher delivered hardness
- Better steel cleanliness
- Better through-hardness
- More controlled production quality
- Potentially longer machining time
However, raw steel price should not be evaluated separately from the complete mold cost.
For a large automotive mold, the complete project cost may include:
- Mold design
- Steel
- CNC machining
- Deep-hole drilling
- EDM
- Wire cutting
- Hot runner system
- Standard components
- Slides and lifters
- Polishing
- Texture
- Mold assembly
- Trial production
- Modification
- Export packing
If upgrading from P20 to 718H improves stability and reduces later polishing or maintenance problems, the total lifecycle cost may be lower even if the initial mold quotation is higher.
A Practical Steel Selection Guide
Choose P20 when:
- The part is small or medium-sized
- The surface requirement is normal
- Production volume is moderate
- The resin is not abrasive
- Budget is a major priority
- The mold can be maintained locally
- High-wear areas use replaceable inserts
Choose 718H when:
- The mold is large
- The cavity is deep
- The part has a visible cosmetic surface
- Polishing or texturing quality is important
- The production program is longer
- Hardness uniformity is important
- The customer wants a lower risk of early surface wear
Consider higher-grade steel or hardened inserts when:
- The resin contains glass fiber
- The material is corrosive
- The production volume is very high
- Gate areas experience severe wear
- Shut-offs and slides operate under high load
- Mirror polishing is required
- The target life is substantially above 500,000 cycles
Expert Recommendation for Automotive Mold Buyers
For large automotive exterior parts such as bumper covers and visible grilles, 718H is usually the better starting recommendation.
The reasons are:
- Better hardness uniformity in large steel blocks
- Better polishing and texturing performance
- Better resistance to indentation and surface wear
- Lower risk of inconsistent cavity surface quality
- Better suitability for longer production programs
For ordinary automotive functional parts, small housings and budget-sensitive projects, P20 often provides better cost performance.
The best solution may also be a combined steel strategy.
For example:
- P20 for the mold base or lower-risk structural areas
- 718H for the main cavity and core
- Hardened inserts for gates and high-wear zones
- Specialized steel for slides, lifters and shut-offs
This approach controls the mold budget while protecting the areas that have the greatest effect on mold life and part quality.
What Buyers Should Confirm in a Mold Quotation
Do not accept a quotation that only says:
“Mold steel: P20”
or:
“Mold steel: 718H”
Ask the mold supplier to confirm:
- Steel manufacturer or approved equivalent
- Exact commercial grade
- International equivalent
- Cavity steel
- Core steel
- Mold base steel
- Delivered hardness
- Steel certificate availability
- Heat treatment or nitriding
- Insert materials
- Slide and lifter materials
- Target mold life
- Plastic resin and filler content
- Surface finish requirement
- Maintenance and spare-part plan
Two quotations may both mention P20 but use steels with different cleanliness, hardness control and polishing performance.
Steel name alone is not enough to evaluate mold quality.
Frequently Asked Questions
Is 718H the same as P20?
718H belongs to the same general family of prehardened plastic mold steels, but it is normally treated as an upgraded P20-type material. It commonly contains nickel to improve through-hardness and uniformity in larger steel sections.
Which steel is harder, P20 or 718H?
Standard P20 is commonly supplied at approximately 28–32 HRC. Commercial 718H grades are often supplied at approximately 33–37 HRC, although the exact range depends on the steel manufacturer and grade.
Is 718H suitable for automotive bumper molds?
Yes. 718H is commonly considered for large automotive molds such as bumper, grille, instrument panel and door trim molds because of its hardness uniformity and polishing performance.
Can P20 be used for automotive injection molds?
Yes. P20 can be used for many small and medium-sized automotive plastic parts, especially when production volume and surface requirements are moderate.
How many shots can a P20 mold produce?
There is no universal guaranteed number. A preliminary planning range may be approximately 200,000–300,000 cycles for suitable applications, but actual life depends on the resin, mold structure, maintenance and production conditions.
How many shots can a 718H mold produce?
For suitable non-abrasive plastic applications, a planning range of approximately 300,000–500,000 cycles may be used during early project discussion. This is not a steel guarantee, and the complete mold design must support the target life.
Is 718H suitable for glass-filled plastic?
718H may be used in some glass-filled applications, but high-wear areas may require hardened inserts, nitriding or more wear-resistant steel. The fiber percentage, production volume and gate design must be evaluated.
Which steel gives a better polished surface?
718H normally offers better hardness uniformity and polishing performance than basic commercial P20, especially in larger mold blocks. The actual result also depends on steel cleanliness, machining, heat treatment and polishing technique.
Conclusion
P20 and 718H are both useful prehardened steels for automotive injection molds.
P20 offers lower cost, good machinability and practical performance for general plastic parts and moderate production volumes.
718H offers better hardness uniformity, polishing performance and wear resistance, making it more suitable for large automotive molds, visible surfaces and longer production programs.
For large exterior parts such as automotive bumpers, 718H is usually the safer recommendation.
For small functional parts or projects with a controlled budget, P20 may provide better cost performance.
The final decision should be based on the complete mold application rather than steel price or shot count alone.
