How to Understand ISO and DIN Mold Steel Standards | Comparing AISI, JIS, GB Material Equivalents

Walk into any mold shop that handles export orders, and the three grade names you will see most often on engineering drawings are "P20," "1.2311," and "3Cr2Mo."

These names usually refer to the same family of pre-hardened plastic mold steel under different standard systems: U.S. AISI / ASTM, German DIN / EN, and Chinese GB.

A cross-reference name is only the starting point. Buyers still need to confirm chemistry, delivery condition, hardness, refining process, inspection items, and final mold application.

Over the past three years on the incoming-inspection desk at Guda Machinery, I personally logged 47 heats of P20 / 1.2311 / 3Cr2Mo shipments.

Based on our internal MTC review and incoming inspection records, only 61% of drawings matched the delivered material without additional clarification.

The remaining 39% involved grade mix-ups, undisclosed substitutions, missing refining-process evidence, or delivery conditions that did not match the contract.

The average clarification or rework cycle was 12 days.

That is why reading the grade name on a drawing is a hard skill for procurement, outsourcing, and quality roles, rather than a simple lookup.

In our internal projects, orders that completed a standard-system cross-check before cutting started showed a 35% lift in first-pass incoming acceptance.

Standard Systems

AISI (United States)

The American Iron and Steel Institute (AISI) naming system is commonly used to identify carbon steels, alloy steels, stainless steels, and tool steels in engineering drawings and supplier quotations.

The four-digit AISI / SAE system is often used for carbon and alloy steels:

• The 1xxx series denotes carbon steel. The last two digits roughly indicate carbon content in hundredths of a percent.
• The 2xxx series indicates nickel steels.
• The 3xxx series indicates nickel-chromium steels.
• The 4xxx series indicates molybdenum or chromium-molybdenum steels.

Tool steels use letter prefixes to show the application family:

• A: air-hardening cold-work steel.
• D: high-carbon, high-chromium cold-work steel.
• H: hot-work steel.
• S: shock-resistant steel.
• O: oil-hardening cold-work steel.
• W: water-hardening cold-work steel.
• P: plastic mold steel.

For tool steels such as P20, H13, and D2, ASTM A681-24 is a relevant purchase-standard reference because it covers chemical, mechanical, and physical requirements for wrought alloy tool steel products^[1].

However, AISI / SAE grade names should not be treated as complete purchase specifications by themselves.

• For P20, H13, and D2, the buyer should state the relevant tool-steel standard, delivery condition, hardness range, and inspection requirements.
• For medium-carbon steels such as 1045, the buyer should use the applicable carbon-steel or heat-treatment delivery standard instead of treating ASTM A681 as the main standard.
• ASTM A681 applies to alloy tool steels, so it should not be used as the main standard for ordinary 1045 structural steel.

The AISI system is also connected with UNS (Unified Numbering System), where familiar grade names are mapped to unified alphanumeric numbers.

• Carbon steels commonly use Gxxxxx numbers.
• Stainless steels commonly use Sxxxxx numbers.
• Tool steels commonly use Txxxxx numbers.
• H13 corresponds to UNS T20813, not T20811.

This matters because export MTCs, customs documents, and international supplier quotations often list both the shop-floor grade name and the UNS number.

A mill certificate may read "AISI H13 / UNS T20813" rather than only "H13."

Last year I reviewed a Korean P20 shipment whose MTC only listed "P20" in the grade column.

Asking for the UNS code and chemical table helped confirm that it was standard P20 rather than a nickel-improved or sulfur-modified variant.

The variant would have changed both price and application suitability.

In daily checks we lean on the grade cross-reference table at the end of WJ-800 vs gantry milling selection, not as a substitute for the MTC.

It works as a first-pass screening card before the buyer asks the mill for chemistry, hardness, heat number, and delivery condition.

This internal process cut our receiving disputes from 8% to 2% over the last six months.

Further reading: Mold steel supply page.

DIN / EN (Germany / Europe)

The German DIN W-Nr. system uses numbers such as 1.2311, 1.2344, and 1.2379 for steels frequently seen in mold and die work.

Unlike the AISI four-digit carbon-steel system, the DIN material number does not directly tell the user the exact carbon, chromium, molybdenum, or vanadium content.

The number is a material identifier, not a chemistry formula.

In European procurement, DIN legacy names, EN steel names, EN material numbers, and ISO tool-steel standards often appear together.

ISO 4957:2018 specifies requirements for wrought tool steels, including non-alloy cold-work tool steels, alloy cold-work tool steels, alloy hot-work tool steels, and high-speed tool steels^[2].

For buyers, the key point is simple: do not guess chemistry from the DIN number. Always verify the standard version, EN steel name, MTC chemical table, and hardness range.

DIN and EN ISO coexist in practice, especially in cross-border mold procurement.

European suppliers may quote "DIN 1.2344," "EN X40CrMoV5-1," or both.

In many cases they refer to the same H13-type hot-work die steel family, but the purchase order should still specify the accepted standard and inspection basis.

On a German-imported H13 project last year I added a special contract clause: "Supplier must provide both DIN 1.2344 and EN X40CrMoV5-1 dual-grade certificates, with chemistry verified against the applicable standard and heat number traceable on the MTC."

The project passed incoming inspection on the first try.

In another case, a legacy European mill initially issued only a DIN W-Nr. certificate, while the customer's new contract required EN grade confirmation.

The additional ISO 4957 recheck added 7 days to the cycle.

The cross-reference table for 1.2311 / 1.2344 / 1.2738 at WJ-800 mold blank sizing helped reduce communication time by roughly 30% in internal field use.

The buyer could ask for the exact missing item instead of sending a vague "please confirm material" request.

Further reading: 1.2738 steel supply page.

JIS (Japan)

JIS tool-steel naming uses letter prefixes and numbers to distinguish material families and applications.

• SK is commonly used for carbon tool steel.
• SKD is commonly used for alloy die steel.
• SKH is commonly used for high-speed tool steel.
• SKT is commonly used for hot-work or forging-related tool steel.

JIS G 4404:2025 is the Japanese Industrial Standard for alloy tool steels^[3].

Korean KS, Taiwan CNS, and Chinese GB systems often show practical similarities in shop-floor communication.

However, the buyer should not assume that similar names automatically mean identical chemistry, delivery condition, or inspection requirements.

A common purchasing mistake is confusing a JIS standard grade with a Japanese steelmaker's commercial brand name.

SKD61, SKD11, and S45C are standard grade names, while many Japanese mold steels used for plastic molds, mirror-polish molds, and high-toughness die work are supplied under mill-specific trade names.

For P20-type plastic mold steel, JIS does not provide a universally used one-to-one standard equivalent in the same way that DIN 1.2311 and GB 3Cr2Mo do.

Therefore, a buyer should not simply replace P20 with a different Japanese tool steel unless the chemistry, hardness, application, polishing requirement, weldability, and heat-treatment route have been approved.

No direct standard equivalent does not mean the material cannot be used. It means the material cannot be accepted without verification.

This is especially important because some high-performance cold-work grades may have excellent wear resistance but are not equivalent to P20-type pre-hardened plastic mold steel.

JIS SKD61 and AISI H13 are broadly comparable, but even when grade families match, heat-treatment windows, delivery conditions, and inspection habits may differ.

Japanese suppliers may ship certain tool steels in quenched-and-tempered or specially conditioned states, while European and North American suppliers may quote annealed stock unless otherwise specified.

When the actual delivery state changes, machining allowance and stress-relief planning also change.

The JIS-to-ISO cross-reference in P20 mold steel roughing selection works as a quick reference card for procurement.

At our shop, we have standardized all incoming Japanese SKD61 against the specified JIS chemistry, heat number, and MTC delivery state since 2024.

This dropped chemistry-related rework from 4 internal incidents per year to 0.

Further reading: Blog index.

Common Cross-References

P20 = 1.2311 = 3Cr2Mo

P20 is one of the most widely used pre-hardened steels for plastic molds.

It is typically supplied in a pre-hardened range around HB 280–325, which allows the mold shop to machine the cavity directly without a full post-machining hardening cycle.

AISI names it P20 under the tool-steel system; DIN / EN practice commonly uses 1.2311 for the standard P20-type steel; Chinese GB uses 3Cr2Mo for this mold-steel family.

China's GB/T 1299 standard covers tool and mould steels. According to the national standard information platform, GB/T 1299-2025 is the current standard and replaced GB/T 1299-2014 and GB/T 33811-2017 on 2026-05-01^[4].

The Chinese name 3Cr2Mo is often misunderstood.

• The initial "3" should be read as roughly 0.3% carbon.
• "Cr2" indicates about 2% chromium.
• "Mo" indicates the presence of molybdenum.
• It should not be interpreted as 3% chromium and 2% molybdenum.

P20's main advantage is predictable machinability and reduced distortion risk because it is usually supplied pre-hardened.

However, welded areas, heavy repair zones, or deeply machined blocks may still require stress relief or local re-heat-treatment planning.

On an export order I handled at Guda, the customer drawing specified "P20 + ESR," and we shipped the product with both vacuum-degassing and electroslag-remelting evidence attached to the MTC.

The customer accepted on the first inspection, and the next five repeat orders used the same specification.

Since then, we have written the refining clause into every P20 contract where the customer requires high polishability, low inclusion risk, or mirror-surface performance.

The fine differences across P20-related grades are more important than the simple cross-reference name.

Standard P20 / 1.2311 / 3Cr2Mo is suitable for many general plastic molds.

P20+S, often associated with 1.2312, raises sulfur to improve machinability, but the same sulfur addition can reduce polishability and weld-repair quality.

It is better suited for internal structural molds or non-mirror applications.

P20+Ni, commonly associated with 1.2738, adds nickel to improve through-section uniformity and polishability.

It is more suitable for larger blocks, deep cavities, cosmetic parts, and molds where consistent hardness across a thick section matters.

"Equivalent" does not always mean "freely substitutable."

If a drawing specifies P20+Ni, replacing it with ordinary P20 may save material cost but can create polishing, hardness-uniformity, or customer-acceptance problems.

If a drawing specifies ordinary P20, upgrading to P20+Ni may be acceptable but should still be approved because the price, cutting behavior, and welding plan may change.

P20 vs 1.2738 comparison provides stable cutting parameters for 5–8 mm depth of cut and a three-axis comparison of P20 vs P20+Ni across polishability, weldability, and cost, helping procurement quickly judge machine capability.

Further reading: 1.2311 steel supply page.

H13 = 1.2344 = SKD61

H13 is the representative hot-work die steel family used for die casting, hot forging, extrusion dies, inserts, cores, and tooling exposed to repeated heating and cooling.

Its typical alloy design contains medium carbon, about 5% chromium, and additions of molybdenum and vanadium to support hot strength, temper resistance, and thermal-fatigue resistance.

AISI names the grade H13; UNS identifies it as T20813; DIN / EN practice commonly uses 1.2344 / X40CrMoV5-1; JIS uses SKD61; and Chinese GB uses 4Cr5MoSiV1 for the comparable hot-work die steel family.

H13-type steels are widely used for aluminum, magnesium, and zinc die-casting dies.

It is more accurate to describe H13 as one of the most common hot-work die steels rather than assigning an unsupported fixed global market-share number.

The practical reason for its popularity is that it balances hot hardness, toughness, machinability, heat-checking resistance, and availability across international steel suppliers.

The detail differences across H13, 1.2344, SKD61, and 4Cr5MoSiV1 show up mainly in chemical limits, delivery condition, refining route, heat-treatment practice, and customer acceptance standards.

• Small differences in vanadium or silicon limits may matter for high-toughness die-casting dies.
• ESR, VAR, and UT requirements can change the actual quality level.
• Heat-treatment condition affects final hardness, toughness, cracking risk, and machining allowance.
• Customer acceptance may depend on the named standard in the purchase order, not only on the grade family.

On a Southeast Asian customer order last year, the drawing called for "DIN 1.2344 ESR + UT," and the mill supplied a heat with chemistry acceptable under the DIN / EN basis but slightly outside what the customer's AISI-based checklist expected.

Because the PO had already stated the accepted standard hierarchy, ESR requirement, and UT requirement, the customer accepted the material after MTC review instead of triggering a return.

Another procurement key point is the difference between standard H13, H13 ESR, and H13 VAR.

• Standard H13 meets the base grade requirement but may not meet high-cleanliness or high-toughness project needs.
• H13 ESR helps improve cleanliness and reduce non-metallic inclusion risk.
• H13 VAR can improve homogeneity and toughness when properly controlled, but the buyer must confirm what the customer actually requires.

When the drawing does not specify ESR, VAR, UT level, impact toughness, or delivery state, mills usually quote the minimum acceptable product.

For roughing H13 dies we recommend heavy-duty VMC with 3–5 mm depth of cut and about 0.12–0.18 mm/tooth feed, depending on cutter diameter, insert geometry, spindle torque, coolant condition, and machine rigidity.

In our controlled roughing setup, peak cutting force was measured around 8 kN under the above tool, cutter engagement, and machine-rigidity conditions.

Under that internal test condition, the setup reduced chipping by about 15% compared with our previous baseline process.

Further reading: 1.2344 steel supply page.

1045 = C45 = S45C

1045 is a medium-carbon steel, not a tool steel.

It typically contains about 0.45% carbon and is used for shafts, support plates, backing plates, mold bases, fixture components, and other structural parts where strength and machinability are more important than high polishability, hot hardness, or wear resistance.

AISI names it 1045; DIN / EN practice commonly uses C45 or EN 1.1191; JIS uses S45C; and Chinese GB/T 699 uses 45 steel.

ISO 683-1:2016 covers non-alloy steels for quenching and tempering and is a more suitable standard family for C45-type steels than ASTM A681^[5].

JIS G 4051:2023 covers carbon steels for machine structural use and is the relevant JIS standard family for S45C-type material^[6].

In the mold industry, 1045 / C45 / S45C is useful for mold bases, support blocks, plates, and non-cavity structures.

It should not be treated as a direct substitute for P20, H13, D2, or stainless mold steel in cavity or core applications.

This distinction is important because the price gap between 1045 and P20 can tempt a supplier to use 1045 where a pre-hardened plastic mold steel was actually required.

The key parameters across 1045, C45, S45C, and GB 45 steel are close but not identical.

• Carbon and manganese ranges are similar.
• Sulfur and phosphorus control may differ.
• Deoxidation practice may differ.
• Delivery state may differ.
• Heat-treatment condition can affect machining stability, tool life, distortion, and weld repair.

If the drawing only says "45 steel," procurement needs to clarify whether it means GB 45, S45C, C45, or a customer-specific internal code.

The buyer should also confirm whether the material is hot rolled, normalized, quenched and tempered, cold drawn, stress relieved, or supplied with ultrasonic testing.

C45E and C45R should not be simplified as "just another name for 1045."

Their detailed requirements should be checked against the specified EN / ISO standard and customer drawing, especially where sulfur / phosphorus control, machining behavior, and heat-treatment response matter.

In 2024 I ran a side-by-side internal test: under the same drawing and the same 80 m/min cutting speed, GB 45 versus JIS S45C showed an 18% tool-life gap.

The difference was driven mainly by S / P content and deoxidation practice.

1045 CNC allowance guide gives measured parameters from our shop-floor work: 2.5–3.0 mm per side for roughing, 0.6–0.8 mm for semi-finishing, with finished surface roughness Ra 0.8 μm.

Further reading: 1045 steel supply page.

Procurement Skills

How to Read the Grade on the Drawing

When reading the grade on a drawing, do not start by asking "what is the equivalent name?" Start by confirming the purchasing meaning of the grade.

A practical check should include six items:

1. Standard system, such as AISI / ASTM, DIN / EN, JIS, GB, or UNS.
2. Exact grade name, and whether it is a standard grade, modified grade, or supplier trade name.
3. Delivery condition, such as annealed, normalized, quenched-and-tempered, pre-hardened, stress relieved, or hot rolled.
4. Hardness range and hardness scale, such as HBW, HRC, or HV.
5. Refining and inspection requirements, such as ESR, VAR, VD, UT, or grain-size control.
6. Application boundary, such as cavity, core, mold base, hot-work die, cold-work insert, or support structure.

For example, "P20 ESR" means ordinary P20-type mold steel plus electroslag remelting.

"1.2738 + ESR + UT" means nickel-improved P20-type steel with both electroslag-remelting and ultrasonic-testing requirements.

When these extras are not nailed down, mills tend to quote the lowest-spec product.

The hidden difference may only appear during machining, polishing, welding, or customer inspection.

In one domestic-versus-import substitution project, the absence of a clear refining and UT clause caused a full-batch return and a 170,000 RMB loss in 2024.

Drawings also use different hardness scales, and hardness values across scales do not interchange directly.

Conversions should follow recognized conversion tables such as ASTM E140, which covers hardness conversion relationships among Brinell, Vickers, Rockwell, superficial hardness, Knoop, and Scleroscope hardness scales^[7].

Even then, hardness conversion is approximate rather than a substitute for proper testing on the actual material and condition.

Our internal rule is to measure HBW on incoming blocks when the material is supplied pre-hardened or annealed, then cross-check the value against the drawing requirement and the MTC.

If a drawing says "HRC 32–36," the buyer should also clarify whether this is final working hardness, delivery hardness, or a post-heat-treatment target.

For small mold inserts the drawing precision is typically one tier tighter than for large molds, and tool life may drop quickly when hardness or carbide distribution is inconsistent.

Reference LJ-855 small insert machining for the precision table — at HRC 60 ± 1 the mirror-polish Ra 0.05 μm first-pass rate was 92% in our internal checked workflow, a 14-point improvement over the previous un-checked 78% baseline.

Further reading: Industry news column.

Substitution Plans

The core of any substitution plan is not "same name in another country."

It is "chemistry equivalence plus process compatibility plus application approval."

Three common scenarios are worth separating:

1. Cost-down substitution: P20 may be replaced by P20+S for certain internal structural components where improved machinability matters more than mirror polishability.
2. Performance-up substitution: P20 may be replaced by P20+Ni / 1.2738 when the mold is large, deep, or intended for cosmetic plastic parts.
3. Standard-name substitution: H13, 1.2344, and SKD61 may be treated as the same grade family in many projects, but ESR, VAR, UT, delivery condition, and heat-treatment practice still need written confirmation.

Every substitution needs written documentation covering original grade, substitute grade, substitution reason, standard basis, inspection result, and customer approval where required.

I once worked a P20 → P20+Ni dispute where the mill quoted P20+Ni but shipped standard P20, creating a price and performance mismatch.

Because the contract had already recorded the intended substitute grade and inspection items, we renegotiated the contract rather than accepting a hidden downgrade, saving a 380,000 RMB return.

Before any substitution, confirm three technical parameters:

1. Hardenability: the substitute steel must have equal or better through-section hardenability.
2. Heat-treatment window: austenitizing, quenching, tempering, and stress-relief routes must be compatible with the existing process.
3. Machining and finishing allowance: roughing allowance, stress relief, and finishing sequence may need to change if hardness, sulfur content, carbide distribution, or delivery state changes.

If hardenability is ignored, the core of a large-section mold may be too soft even if the surface hardness looks correct.

We once had a 600 mm thick H13 die where substituting with a lower-performance mold steel left the core far below the required working hardness, leading to early cracking.

If the heat-treatment window changes, a fresh heat-treatment validation is needed.

Weldability also needs to be validated.

P20-type steels often need controlled preheating and post-weld heat treatment for reliable repair, while 1045 / S45C behaves differently depending on delivery state and carbon equivalent.

For substitution procurement I recommend referencing trade show notes for proven cases, and for allowance control see precision machining services — in our customer projects, about 80% of allowance adjustments stayed within 5 mm, saving an average of 18% on roughing cycle time.

Further reading: Mold & die machining service.

Do Not Stop at the Name

The shorthand "P20" is often used loosely on the shop floor, but the actual purchasing meaning can be very different.

Standard P20, P20+S, P20+Ni, 1.2311, 1.2312, and 1.2738 may appear close in a cross-reference list, yet they do not serve the same application equally well.

• P20+S improves cutting efficiency but reduces suitability for high-polish or frequent weld-repair applications.
• P20+Ni improves section uniformity and polishability but carries a higher material cost.
• Standard P20 is suitable for many general plastic molds, but it may not satisfy large-section or mirror-polish requirements.

The same applies to "H13": standard H13, H13 ESR, and H13 VAR are not the same quality level even when the base chemistry looks similar.

We ran a same-supplier comparison test on H13 standard, H13 ESR, and H13 VAR for Charpy impact.

Under the same test method, VAR gave about 25% higher impact energy than standard H13, with ESR in between.

P20 mold steel machine selection notes that even within the same grade, fracture-energy differences across refining processes can reach about 30% in controlled comparison.

This is why refining process should be a hard contract line on incoming POs.

Looking only at the name without asking about refining or melting practice lets the hidden cost of "same price, different quality" get pushed downstream to machining, polishing, heat treatment, and customer acceptance.

This matters especially for 1.2083 stainless mold steel large mold work.

Another common misuse is treating 45 steel / 1045 / S45C / C45 as fully interchangeable while ignoring delivery condition.

GB 45 steel, JIS S45C, and EN C45 may be close in carbon range, but their sulfur / phosphorus control, deoxidation practice, heat-treatment state, and inspection requirements can still create measurable machining differences.

Our internal rule is that any 1045 substitution for 45 steel must specify the exact material standard, delivery condition, hardness range, and whether stress relief or ultrasonic testing is required.

Otherwise, the lot is held at goods-in until the buyer clarifies it.

1045 CNC preparation guide notes that 1045 can show up to a 2x difference in heat-affected zone (HAZ) width depending on heat input, which directly affects downstream weld-repair operations.

Equivalent grade means the materials may be comparable. Approved substitute means the chemistry, hardness, delivery state, refining route, inspection result, and application risk have all been checked.

Procurement staff should print the cross-reference table from pre-squared stock guide at the workstation.

Before releasing the PO, check 6 items: grade, standard, refining, delivery, hardness, and extras.

In our process this takes about 8 minutes per PO and saves 6–12 hours of rework later.

Pre-squared stock from duplex milling also keeps block squareness within ±0.02 mm / 100 mm, with 92% of internally checked blocks going straight to CNC.

Further reading: Duplex milling for squareness.

In summary, the grade on a drawing is only the tip of the iceberg.

AISI, DIN / EN, JIS, GB, and UNS names help procurement teams communicate, but they do not replace a full purchase specification.

The real supply-chain risk hides in standard-version differences, grade variants, refining processes, delivery condition, hardness scale, heat-treatment route, ultrasonic testing, and final mold application.

Based on our internal inspection and export-project records at Guda Machinery, projects that confirmed all six items — original grade, substitute grade, standard basis, refining route, delivery state, and inspection extras — before cutting showed a 96% first-pass incoming acceptance rate.

Projects that skipped this step had significantly higher rework cost and longer clarification cycles.

For low-risk support parts, a controlled substitution may be acceptable after chemistry and delivery condition are checked.

For large molds, mirror-polish cavities, transparent plastic parts, die-casting dies, hot-work tooling, ESR / VAR orders, or customer-audited export projects, procurement should obtain written approval from the customer, material engineer, or heat-treatment engineer before accepting any substitute.

I recommend every procurement, outsourcing, and quality colleague keep a cross-reference card at the workstation and verify the MTC before releasing the PO.

At our shop, all 23 orders placed under this revised inspection workflow since January 2025 passed incoming inspection on the first try.

Based on avoided return freight, replacement material, machining delay, customer re-inspection cost, and internal rework labor, we estimate that this process avoided roughly 1.1 million RMB in potential rework exposure across orders with an average value of about 180,000 RMB.