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What this guide covers
This article is the definitive technical comparison of 1.2738 steel (DIN designation for 40CrMnNiMo8-6-4, also sold as P20+Ni or 718) and P20 steel (AISI designation, DIN 1.2311, GB 3Cr2Mo) for plastic injection mold tooling. It is written by the engineering team at Jiangsu Liangyi Co., Ltd., an ISO 9001:2015 certified forging manufacturer based in Jiangyin, Jiangsu Province, China, with 25+ years of experience supplying mold steel forgings to 50+ countries.
The guide covers: chemical composition differences, hardness and through-hardening by cross-section size, polishability ratings, machinability and EDM performance, weldability, industry application guidance, a head-to-head performance scorecard, a procurement decision framework, documentation requirements when sourcing from China, and 8 frequently asked questions.
Key conclusion: 1.2738 and P20 are not interchangeable in large-section molds. The 1% nickel addition in 1.2738 is an engineering solution to hardenability limits that P20 cannot overcome in blocks exceeding 300 mm cross-section.
Section 01
What Are 1.2738 and P20? Origins and Technical Definitions
Both 1.2738 and P20 belong to the pre-hardened chromium-molybdenum mold steel family. They are delivered in a ready-to-machine condition requiring no further heat treatment after rough machining, which makes them the globally dominant material for large plastic injection mold blocks, cavity plates, and core inserts.
P20 (AISI designation) is the original grade, developed in the United States and later adopted internationally as DIN 1.2311 (40CrMnMo7) and GB 3Cr2Mo in China. P20 contains chromium (~2%) and molybdenum (~0.4%) with essentially no nickel (<0.25%). Pre-hardened to 280–320 HB, it became the industry standard through the 1970s–1990s for molds where cross-sections were manageable.
1.2738 (DIN designation, full name 40CrMnNiMo8-6-4) was developed specifically to address P20's hardenability limitation in large-section blocks. Commercially sold as P20+Ni or 718 (ASSAB trade name), its sole critical difference from P20 is the addition of approximately 1.0% nickel (Ni: 0.85–1.15%). This single change extends effective through-hardening from P20's practical limit of 300 mm to over 600 mm in cross-section.
⚡
Core Principle
1.2738 is not a universally "better" P20 — it solves a specific physics problem: hardenability in large cross-sections. Within P20's effective range (under 300 mm cross-section), both grades perform comparably. The mistake is specifying P20 where 1.2738 is required — not choosing 1.2738 everywhere.
Grade Equivalents Across International Standards
Table 1: 1.2738 and P20 international grade equivalents by standards system
| Standard |
1.2738 Designation |
P20 Designation |
| DIN (Germany) | 1.2738 / 40CrMnNiMo8-6-4 | 1.2311 / 40CrMnMo7 |
| AISI (USA) | P20+Ni / 718H | P20 |
| GB (China) | 3Cr2NiMnMo | 3Cr2Mo |
| JIS (Japan) | PX5 / NAK80 (variant) | PX4 |
| ASSAB / Uddeholm | 718 / 718H | UHB 31 (approximate) |
| Böhler | M238 / M261 | M200 |
Section 02
Chemical Composition: Where the Difference Begins
Chemical composition drives every downstream property — hardenability, toughness, polishability, and weldability. The table below shows the full typical analysis range for both grades per DIN specification.
Table 2: Chemical composition comparison — 1.2738 vs P20 (% by weight, DIN specification)
| Element |
1.2738 (40CrMnNiMo8-6-4) |
P20 / 1.2311 (3Cr2Mo) |
Metallurgical Role |
| C — Carbon | 0.35 – 0.45% | 0.35 – 0.45% | Identical — determines base hardness potential and wear resistance |
| Si — Silicon | 0.20 – 0.40% | 0.20 – 0.80% | Deoxidation; P20 has a wider permissible range |
| Mn — Manganese | 1.30 – 1.60% | 1.30 – 1.60% | Both elevated; significant hardenability contribution |
| Cr — Chromium | 1.80 – 2.10% | 1.80 – 2.10% | Identical — corrosion resistance, wear, hardenability |
| Mo — Molybdenum | 0.15 – 0.55% | 0.30 – 0.55% | Temper resistance, secondary hardening, hardenability |
| Ni — Nickel | 0.85 – 1.15% | ≤ 0.25% (residual) | THE CRITICAL DIFFERENCE — deep hardenability, toughness in large sections |
| P — Phosphorus | ≤ 0.030% | ≤ 0.030% | Controlled impurity — limits embrittlement risk |
| S — Sulfur | ≤ 0.010% | ≤ 0.010% | Low sulfur = better polishability and isotropy |
The ~1% nickel addition in 1.2738 increases the ideal critical diameter (DI) by approximately 40–65 mm compared to equivalent P20, meaning 1.2738 achieves full hardening transformation significantly deeper into the cross-section during the quench step of pre-hardening heat treatment.
🔬
Engineering Note
Strip the nickel from 1.2738 and the chemistry is nearly identical to P20. Ni is the entire technical story separating these two grades. If you see a material sold as "P20+Ni" or "718" with Ni content below 0.85%, it does not conform to 1.2738 specification. Always verify Ni content on the EN 10204 3.1 mill test certificate.
Section 03
Hardness and Through-Hardening: The Critical Performance Metric
Both grades are nominally pre-hardened to 280–320 HB. On paper this looks identical. The engineering reality is that hardness means nothing without specifying where in the block cross-section that hardness is measured.
A P20 block measured at the surface may read 300 HB. That same block measured at the geometric center at 400 mm depth may read only 240–260 HB — well below specification and insufficient for cavity performance. This is not a quality failure on the supplier's part; it is a physics limitation of P20's hardenability. Nickel in 1.2738 directly addresses this limitation.
Table 3: Typical core hardness by block cross-section — 1.2738 vs P20
| Block Cross-Section (smallest dim.) |
1.2738 Core Hardness (HB) |
P20 Core Hardness (HB) |
Verdict |
| Up to 200 mm | 280–320 (fully uniform) | 280–315 (fully uniform) | TIE |
| 200 – 300 mm | 275–315 (minimal drop) | 255–295 (slight surface bias) | 1.2738 WINS |
| 300 – 400 mm | 265–305 (acceptable) | 235–270 (significant drop) | 1.2738 WINS |
| 400 – 500 mm | 255–290 (still usable) | Not recommended | 1.2738 ONLY |
| 500 mm and above | 245–280 (specialist review) | Not viable | 1.2738 ONLY |
⚠️
Procurement Risk Warning
Some suppliers deliver material labeled "P20" that is actually a lower-grade cast 3Cr2Mo block with surface heat treatment only. The surface hardness passes inspection; the core does not meet specification and fails in service. Always require an EN 10204 3.1 mill test certificate with core hardness measurements taken from multiple cross-section locations, not just the block surface.
Section 04
Large-Section Performance: The Defining Engineering Requirement
Large-cross-section performance is the primary reason 1.2738 exists as a separate grade from P20. Automotive bumper molds, large appliance housing molds, and industrial packaging molds regularly require cavity blocks with smallest cross-sections of 400–600 mm — dimensions where P20's hardenability reaches its physics boundary.
The Metallurgy: Why Nickel Solves the Problem
During quench hardening, the hardening transformation (austenite → martensite) must propagate inward from the block surface faster than the steel cools. In thick sections, the center cools more slowly, and if the hardenability runs out before the transformation completes, the center remains as pearlite or bainite — softer phases that do not meet mold specifications. Nickel depresses the martensite-start temperature (Ms) and stabilizes austenite during quenching, allowing the hardening transformation significantly more time to propagate into the center of thick sections. The specific 1% Ni addition in 1.2738 is calculated to extend practical through-hardening to blocks up to approximately 600 mm.
ℹ️
P20 Is Not "Bad" Steel
P20's hardenability limit is a design boundary, not a quality defect. Within that boundary — mold blocks under 300 mm cross-section — P20 performs excellently and at lower cost than 1.2738. The specification error occurs when buyers apply P20 outside its effective hardenability range, typically driven by material cost savings during procurement.
Forged vs Cast 1.2738 Blocks in Large Sections
For blocks above 200 mm, open die forged 1.2738 is significantly superior to cast 1.2738 for three engineering reasons. First, forging closes internal shrinkage porosity inherent in cast ingots. Second, forging refines grain structure via thermomechanical processing, which is critical for uniform hardness response. Third, cast blocks at large cross-sections are susceptible to centerline segregation — a solidification phenomenon where alloying elements (including the critical nickel) concentrate unevenly, producing variable hardness within a single block that no heat treatment can fully correct.
At Jiangsu Liangyi, our 1.2738 forged mold blocks undergo complete EAF melting, vacuum degassing, ingot casting, open die forging on 2,000T–6,300T hydraulic presses, controlled normalizing and quench-temper heat treatment, and full non-destructive testing under one roof — no subcontracting at any stage.
Section 05
Polishability and Surface Finish Performance
Polishability directly affects cavity surface quality and is non-negotiable for molds producing high-gloss consumer products, optical components, and clear packaging. Both grades can achieve VDI 12 surface finishes, but their behavior during fine polishing operations differs in ways that matter at scale.
Table 4: Polishability performance comparison — 1.2738 vs P20
| Polishability Factor |
1.2738 |
P20 |
| Max achievable VDI (forged block) | VDI 3–6 (mirror-near) | VDI 6–9 |
| Pitting resistance during fine polish | Excellent — Ni reduces carbide banding | Moderate — higher pitting risk |
| Hardness uniformity during polishing | Uniform across full section | Surface-dependent on large blocks |
| Suitable for optical-clarity molds | Marginal — specify 1.2083 for optical | Not suitable |
| Texturing / VDI graining response | Excellent — uniform etch response | Good for small blocks |
| Orange-peel risk at VDI 6 and finer | Low | Moderate to High |
The nickel in 1.2738 reduces carbide banding — the alignment of carbide stringers parallel to the original rolling or forging direction — which is the primary cause of pitting and orange-peel effect during fine stone and diamond polishing. For cavity surfaces requiring better than VDI 9, 1.2738 is the lower-risk specification. For optical-clarity molds (VDI 0–3), neither grade is optimal — specify 1.2083 (AISI 420) or 1.2316 stainless mold steel.
Section 06
Machinability and EDM Performance
At 280–320 HB, both grades fall into the same machinability window. Neither requires soft-annealed roughing before cavity machining — the defining commercial advantage of pre-hardened mold steel over hot work tool steels like 1.2344 (H13) that must be hardened after machining.
Table 5: Machining and EDM performance comparison
| Performance Factor |
1.2738 |
P20 / 1.2311 |
| Relative machinability index | ~85–90% (vs. free-cutting) | ~90–95% P20 EDGE |
| Surface finish in finish milling | Excellent | Excellent |
| EDM sinker erosion rate | Slightly slower (~5–8%) | Slightly faster |
| Wire EDM performance | Good | Good |
| Chip formation | Short, manageable chips | Short, manageable chips |
| Coolant requirement | Standard flood coolant | Standard flood coolant |
| Carbide tooling wear | Comparable | Comparable |
In practice, the machinability difference is small enough that most mold shops run identical CNC programs on 1.2738 and P20 without modification. The EDM erosion rate difference (~5–8% slower for 1.2738 due to nickel) is rarely a scheduling factor unless the shop is severely EDM-bottlenecked.
Section 07
Weldability and Mold Repair
Mold repair welding is routine in production environments, and the weldability of the base material directly affects repair quality, HAZ hardness recovery, and the risk of crack initiation at the weld interface. Both grades can be welded successfully with proper procedure.
Table 6: Weldability comparison — 1.2738 vs P20
| Welding Parameter |
1.2738 |
P20 / 1.2311 |
| Preheat temperature | 250–300°C recommended | 200–250°C (lower requirement) |
| Interpass temperature | Max 350°C | Max 350°C |
| Post-weld stress relief | 550–600°C, min. 1 hr per 25 mm | 550–600°C, min. 1 hr per 25 mm |
| HAZ hardness peak risk | Moderate — Ni increases hardenability of HAZ | Lower — more forgiving |
| Recommended filler wire | Ni-bearing match composition (e.g. UTP 73G4) | Standard CrMo filler |
| Laser weld repairability | Good with preheat | Very good — less preheat sensitive |
| Overall weld repairability | Good | Very Good P20 ADVANTAGE |
P20 has a genuine edge in weld repairability. The higher nickel in 1.2738 increases the hardenability of the heat-affected zone (HAZ), making it more susceptible to hydrogen cracking if preheat and post-weld procedures are not followed correctly. For mold shops performing frequent in-situ laser welding repairs without formal preheat stations, P20 is more forgiving and lowers repair risk. For shops with established TIG or MIG welding procedures including preheat, 1.2738 is fully weldable without issue.
Section 08
Industry Applications: Where Each Grade Is Specified
1.2738 — Specify for These
- Automotive bumper and fascia injection molds
- Interior trim and instrument panel cavity blocks
- Large household appliance housing molds
- Industrial packaging and pallet molds
- High-gloss consumer electronics housing molds
- Structural foam molds with deep cavities
- Mold frames and bolster plates over 400 mm
- Glass-fiber reinforced polymer molds
- Export molds requiring EN/DIN material certification
- Automotive OEM-mandated P20+Ni or 718 specification
P20 — Specify for These
- Medium-volume injection molds under 300 mm section
- Prototype and short-run molds (<500,000 shots)
- Insert molds with controlled insert section sizes
- Compression molds for rubber and thermosets
- Non-critical blow mold tooling sections
- Mold bases and support plates (multi-cavity tools)
- Budget-sensitive projects with coarse surface finish
- Commodity parts with VDI 18 or coarser requirement
- In-situ weld repair without dedicated preheat fixtures
Need 1.2738 Forged Blocks for Your Mold Project?
Custom forged bars, flat blocks, and seamless rolled rings. EN 10204 3.1 MTCs supplied as standard. Pre-hardened 280–320 HB. Cross-sections up to 600 mm. MOQ 1 piece. 50+ countries served.
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Section 09
Head-to-Head Performance Scorecard
Relative performance scores out of 10 for standard mold applications. "Large block" context assumes cross-sections of 400 mm or above. Scores represent typical delivered performance, not theoretical maximum.
Section 10
Decision Framework: How to Choose Between 1.2738 and P20
🎯
Primary Screening Rule
If your mold block's smallest cross-section exceeds 300 mm: specify 1.2738. This is non-negotiable from a physics standpoint. Below 300 mm, evaluate based on surface finish, production volume, and budget. Below 250 mm with VDI 18 or coarser finish and short-run production: P20 is sufficient and costs less.
Choose 1.2738 when any of these apply
- Smallest block cross-section exceeds 300 mm
- Uniform core hardness required (validated by hardness survey)
- Surface finish requirement is VDI 9 or finer
- Production volume target exceeds 1 million shots
- Mold will process glass-filled or abrasive polymers
- Customer or OEM specification mandates P20+Ni / 718
- Toughness is critical — thin walls, sharp corners, impact loads
- Export mold requiring EN/DIN material grade compliance
Choose P20 when all of these apply
- All block cross-sections consistently under 250 mm
- Surface finish is VDI 18 or coarser (textured or matte)
- Production volume target is under 300,000 shots
- Project is prototype, pilot, or short-run production
- Budget constraint is the primary procurement driver
- In-house weld repair without formal preheat procedures
- Multi-cavity insert tool with individually small inserts
Section 11
Sourcing Forged 1.2738 Blocks from China: Verification Checklist
Procuring 1.2738 forgings internationally requires specific due diligence beyond price comparison. Delivered performance depends entirely on forging route quality, heat treatment, and proper documentation. The checklist below is the minimum verification standard for procurement engineers.
Table 7: Minimum documentation checklist for 1.2738 forged block procurement
| Document / Test | What to Verify | Why Critical |
|---|
| EN 10204 3.1 MTC | Full chemical analysis confirming Ni: 0.85–1.15%; hardness readings from 3+ cross-section locations including geometric center | Only document proving Ni content and through-hardening were both achieved |
| UT Test Report | Per EN 10228-3 Class 4 or buyer equivalent; 100% scan coverage of the block | Detects internal voids, inclusions, and segregation invisible in MTC |
| Core Hardness Survey | Hardness map from multiple cross-section planes — not surface readings only | Directly proves through-hardening was achieved in full cross-section |
| Heat Treatment Record | Time-temperature curves for austenitizing, quench, and temper with actual measured data | Validates that Ni was utilized in the correct HT cycle |
| Forging Route Card | Ingot reduction ratio (minimum 3:1 recommended), forging temp range, press tonnage | Confirms grain refinement via sufficient thermomechanical work |
| Third-Party Inspection | Buyer-nominated inspector or independent agency (e.g. SGS, BV, TÜV, Intertek); scope and access agreed before production start | Independent verification eliminates supplier self-certification risk |
Jiangsu Liangyi supplies EN 10204 3.1 material test certificates as standard with all 1.2738 forged products. Third-party inspection is available at buyer's cost with no exclusive agency affiliations. Our complete production chain — EAF melting → vacuum degassing → open die forging → heat treatment → rough machining → NDT — operates under one facility in Jiangyin with no subcontracting at any stage.
Full specifications, available forms, size ranges, and online inquiry: our full specifications and inquiry page.
Section 12
Frequently Asked Questions: 1.2738 vs P20
Is 1.2738 always better than P20 steel?
No. 1.2738 (40CrMnNiMo8-6-4) is significantly better than P20 for mold blocks with cross-sections exceeding 300 mm, for high-polish applications (VDI 9 or finer), and for production volumes above 1 million shots. For molds with all cross-sections consistently under 250 mm, standard surface finish requirements, and short production runs, P20 performs comparably at lower material cost. Specifying 1.2738 everywhere adds 15–30% material cost without proportional performance benefit in small-section molds.
What is the exact chemical difference between 1.2738 and P20?
The sole critical chemical difference is nickel content. 1.2738 contains Ni: 0.85–1.15% (typically ~1.0%). P20 (1.2311) contains Ni: ≤0.25% (residual level only). Carbon (0.35–0.45%), chromium (1.80–2.10%), and manganese (1.30–1.60%) are essentially identical in both grades. The nickel addition extends 1.2738's hardenability to blocks up to 600 mm cross-section versus P20's practical limit of approximately 300 mm.
What is the standard pre-hardened hardness of 1.2738 steel?
Standard 1.2738 is pre-hardened to 280–320 HB (Brinell), equivalent to approximately 29–35 HRC. The 718H variant is pre-hardened to 330–370 HB. Custom hardness ranges and annealed supply (~230 HB) are available to order. For any large-section block, always request a core hardness survey — not just surface hardness — as part of the incoming inspection.
Can 1.2738 steel be gas nitrided for additional surface hardness?
Yes. 1.2738 responds well to gas nitriding, achieving surface hardness of 900–1,050 HV at a nitrided case depth of 0.1–0.3 mm. This is commonly applied to cavity surfaces in molds processing glass-fiber reinforced thermoplastics (PA66+GF30, PBT+GF) where abrasion resistance is critical. The 1% nickel content does not inhibit nitriding and positively contributes to core toughness supporting the brittle nitrided case under cyclic load.
What is the difference between 1.2738 and 718H steel?
718H is a commercial trade name (originally ASSAB/Uddeholm) for a higher-hardness variant of 1.2738, pre-hardened to 330–370 HB versus standard 1.2738 at 280–320 HB. Both have essentially identical chemical composition (40CrMnNiMo8-6-4 chemistry with Ni ≈ 1.0%). 718H delivers improved cavity wear resistance at the cost of approximately 5–8% reduced machinability and slightly lower toughness.
Does forged 1.2738 outperform rolled 1.2738 plate?
For blocks above 200 mm thickness, open die forged 1.2738 is significantly superior to rolled plate. Rolled plate has anisotropic mechanical properties and retains rolling-direction compositional segregation. Open die forged blocks have isotropic mechanical properties with no preferred grain direction — critical for mold blocks where machined features exist in all three axes. Below 150 mm, the performance difference narrows and certified rolled plate may be acceptable if properly tested.
How long does it take to receive custom 1.2738 forged blocks from Jiangsu Liangyi?
Lead times: under 500 kg: 3–5 weeks; 500 kg to 5,000 kg: 5–8 weeks; above 5,000 kg: 8–12 weeks. Sea freight to European ports is approximately 25–35 days. Air freight is 3–5 days. EN 10204 3.1 MTCs and UT test reports are included as standard. Provide your drawing and inspection requirements at inquiry stage for a confirmed lead time and quote within 24 hours.
What is the minimum order quantity (MOQ) for 1.2738 forged blocks?
The minimum order quantity is 1 piece with no minimum weight or value requirement. We accept single-piece prototype orders as well as full production batches. Pricing is provided within 24 hours of receiving your drawing or dimensional specifications.
Conclusion
The Bottom Line: 1.2738 vs P20
Summary for Engineers and Procurement Teams
1.2738 (40CrMnNiMo8-6-4 / P20+Ni / 718) is the correct specification when mold block cross-section exceeds 300 mm, when surface finish must be VDI 9 or finer, or when production volume exceeds 1 million shots. The nickel addition is not a marketing feature — it is an engineering solution to a hardenability physics problem that P20 cannot overcome in large sections.
P20 (AISI P20 / DIN 1.2311 / 3Cr2Mo) remains the correct specification for molds with cross-sections consistently under 250 mm, budget-constrained projects, short-run or prototype molds, and applications where in-situ weld repair without preheat is required. Its lower cost and easier weldability are genuine engineering advantages within its specification range.
The most common procurement error is not choosing the wrong grade — it is failing to verify through-section hardness uniformity on delivery. Always require a core hardness survey as part of the incoming inspection protocol, regardless of grade or supplier.
For custom 1.2738 forged blocks, bars, flat plates, and seamless rolled rings, Jiangsu Liangyi Co., Ltd. has supplied mold makers in Germany, the Netherlands, the United States, South Korea, Italy, Australia, and Southeast Asia for over 25 years. ISO 9001:2015 certified. MOQ 1 piece. EN 10204 3.1 certificates standard on all orders.
Ready to Source 1.2738 for Your Next Mold?
Send us your drawing, cross-section dimensions, and hardness requirement. Free quote with EN 10204 3.1 MTC, UT scope, and delivery lead time — within 24 hours.
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JL
Jiangsu Liangyi Technical Engineering Team
Metallurgical and Forging Process Engineering · Jiangyin, Jiangsu, China
Jiangsu Liangyi Co., Ltd. was established in 1997 in Jiangyin, Jiangsu Province, China. Over 25 years, we have specialized in 1.2738 (40CrMnNiMo8-6-4) open die forgings and seamless rolled rings, serving 200+ long-term global clients across 50+ countries. ISO 9001:2015 certified. All technical content on this page is reviewed by our in-house metallurgical engineering team.