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 grade names you will often see on engineering drawings include “P20,” “1.2311,” “3Cr2Mo,” “H13,” “1.2344,” “SKD61,” “1045,” “C45,” and “S45C.”

These names are often treated as equivalents in daily shop-floor communication, but they come from different standard systems. AISI / ASTM is common in U.S. engineering drawings, DIN / EN / ISO is common in European procurement, JIS is common in Japanese and Asia-Pacific supply chains, and GB is common in Chinese material certificates.

A mold steel grade name is only the starting point. Procurement still needs to confirm the standard, chemistry, delivery condition, hardness, refining process, heat treatment, and inspection scope.

In Guda Machinery’s internal incoming-inspection records, most material disputes did not come from a completely wrong steel family. They came from small but important gaps: missing standard version, unclear delivery condition, missing ESR / UT requirement, hardness scale mismatch, or a substitute grade being treated as identical without chemical and process confirmation.

Standard Systems

AISI / ASTM / UNS

The American Iron and Steel Institute (AISI) four-digit naming system is widely used for carbon and alloy steels. In many AISI / SAE carbon steels, the 1xxx series denotes carbon steel, and the last two digits indicate approximate carbon content in 0.01%.

• 1045: medium-carbon steel with about 0.45% carbon.

• 4140: chromium-molybdenum alloy steel.

• 4340: nickel-chromium-molybdenum alloy steel.

Tool steels use letter prefixes such as A, D, H, S, O, W, and P.

• A: air-hardening cold-work tool steel

• D: high-carbon high-chromium cold-work tool steel

• H: hot-work tool steel

• S: shock-resistant tool steel

• O: oil-hardening cold-work tool steel

• W: water-hardening tool steel

• P: plastic mold steel

ASTM A681 covers wrought alloy tool steel products, including hot-finished or cold-finished bar, plate, sheet, strip, rod, wire, and forgings normally fabricated into tools, dies, or fixtures^[1].

That means ASTM A681 is relevant to mold and die steels such as P20 and H13, but it is not the right standard for 1045 medium-carbon engineering steel. If a drawing only says “1045,” the purchase order should add the applicable ASTM / SAE / regional standard, delivery condition, heat-treatment condition, hardness requirement, and inspection requirement.

The Unified Numbering System (UNS) is often used alongside AISI / SAE names in international documents.

• 1045 is commonly associated with UNS G10450.

• P20 is commonly associated with UNS T51620.

• H13 is commonly associated with UNS T20813.

Export MTCs may list both the common grade and the standard or UNS number, but the exact format varies by supplier. A clearer purchase order should ask for the standard, grade, heat number, chemistry, delivery condition, hardness scale, and inspection certificate.

DIN / EN / ISO

The German DIN W-Nr. material number system uses numbers such as 1.2311, 1.2344, and 1.2379 for tool and mold steels. These numbers are identifiers, not direct chemical formulas.

DIN W-Nr. names are still widely used in European mold shops. EN ISO 4957 is commonly referenced for tool steel procurement and covers wrought non-alloy cold-work tool steels, alloy cold-work tool steels, alloy hot-work tool steels, and high-speed tool steels^[2].

For practical material selection, cold-work tool steels are used for lower-temperature forming and cutting work, hot-work tool steels are used where the tool face is exposed to elevated temperature, and high-speed tool steels are selected where hot hardness must be retained during cutting.

European suppliers often quote both the DIN W-Nr. and the EN symbolic grade. For example, “1.2344” and “X40CrMoV5-1” usually refer to the same hot-work steel family, but procurement should still state which standard controls acceptance.

JIS

JIS tool-steel naming pairs a letter group with numbers to distinguish use.

• SKxx: carbon tool steel

• SKDxx: alloy tool steel, commonly used for die steels

• SKHxx: high-speed tool steel

• SKTxx: alloy tool steel for hot-work applications

• S45C: medium-carbon structural steel, not a tool steel

JIS SKD61 is a hot-work alloy tool steel commonly treated as a commercial equivalent to H13 and 1.2344. JIS SKD11 is commonly treated as a commercial equivalent to D2 and 1.2379. JIS S45C is commonly treated as a medium-carbon steel equivalent to 1045 and C45-family steels.

JIS SKD61 and AISI H13 are close equivalents, but heat-treatment practice may vary by supplier, section size, furnace control, and target hardness. Substitution should not stop at the grade name; the heat-treatment sheet and acceptance criteria still need to be confirmed.

GB

Chinese GB grade names often describe approximate composition. For example, “3Cr2Mo” means about 0.3% carbon, about 2% chromium, and molybdenum addition. It does not mean 3% chromium and 2% molybdenum.

GB/T 1299-2025 “Tool and mould steels” was issued on 2025-10-31 and implemented on 2026-05-01. It supersedes GB/T 1299-2014 and GB/T 33811-2017 according to the national standard notice^[3].

For current procurement, new purchase orders should refer to GB/T 1299-2025 when ordering Chinese tool and mould steels. If an older MTC or inventory certificate uses GB/T 1299-2014, the buyer should confirm whether the old certificate is acceptable for the project.

Common Cross-References

P20 = 1.2311 = 3Cr2Mo

P20 is one of the most widely used pre-hardened steel families for plastic molds. It is used for plastic injection molds, compression molds, mold plates, holders, backers, and general mold structures.

Standard P20 under ASTM A681 is commonly associated with UNS T51620. A typical P20 chemical range is C 0.28–0.40%, Mn 0.60–1.00%, Si 0.20–0.80%, Cr 1.40–2.00%, and Mo 0.30–0.55%^[4].

DIN / EN 1.2311, also known as 40CrMnMo7, is a close European plastic mold steel equivalent. A typical 1.2311 chemical range is C 0.35–0.45%, Mn 1.30–1.60%, Si 0.20–0.40%, Cr 1.80–2.10%, and Mo 0.15–0.25%^[5].

Chinese GB 3Cr2Mo is the corresponding GB mold-steel grade. Under GB/T 1299-2025 material data, 3Cr2Mo can be supplied in annealed condition or pre-hardened condition. A common pre-hardened reference range is HRC 28–36^[6].

P20, 1.2311, and 3Cr2Mo are close commercial equivalents, but they are not automatically identical in every heat. The exact acceptance should be based on the ordered standard, chemical range, hardness range, delivery condition, and inspection certificate.

P20’s advantage is that it can be supplied pre-hardened and machined directly, reducing the deformation risk from post-machining heat treatment. Welded areas still need a controlled repair procedure and suitable post-weld heat treatment according to the actual steel condition.

When the drawing says “P20+Ni,” “P20 + Ni,” or “1.2738,” it usually means the nickel-improved plastic mold steel family. The nickel addition improves through-hardening behavior, toughness, and hardness uniformity in larger plastic molds.

When the drawing says “P20+S” or “1.2312,” it usually means a sulfur-added version of the P20 / 1.2311 family. The sulfur addition improves machinability, but it reduces suitability for high-polish or high-texture cosmetic mold surfaces.

H13 = 1.2344 = SKD61 = 4Cr5MoSiV1

H13 is the representative chromium-molybdenum-vanadium hot-work die steel. It is widely used for aluminum die-casting dies, magnesium die-casting dies, zinc die-casting dies, extrusion dies, hot forging dies, and high-temperature tooling.

AISI H13 commonly lists C 0.32–0.45%, Mn 0.20–0.50%, Si 0.80–1.20%, Cr 4.75–5.50%, Mo 1.10–1.75%, and V 0.80–1.20%^[7].

DIN / EN X40CrMoV5-1 / 1.2344 is a close European equivalent. A common reference range is C 0.35–0.42%, Si 0.80–1.20%, Mn 0.25–0.50%, Cr 4.80–5.50%, Mo 1.20–1.50%, and V 0.85–1.15%^[8].

JIS SKD61 is also close to H13 and 1.2344. Material data for JIS G 4404 SKD61 lists it as an alloy tool steel and places it in the same hot-work steel family^[9].

The detail differences across standards show up mainly in chemistry limits, heat-treatment requirements, cleanliness requirements, ultrasonic testing, and the specified refining route.

• AISI H13 commonly sets V at 0.80–1.20%.

• DIN / EN X40CrMoV5-1 commonly uses V around 0.85–1.15%.

• JIS SKD61 is close to the H13 / 1.2344 family, but acceptance should be checked against the ordered JIS standard and MTC.

• GB 4Cr5MoSiV1 is generally treated as the Chinese H13-family grade, but the GB/T version should be confirmed.

If a supplied H13-family heat shows V around 1.35%, it should not be casually accepted as standard H13 / 1.2344 / SKD61. That level is outside the common H13 and 1.2344 reference ranges and should require written customer concession, a special mill specification, or corrected supply.

Another procurement key point is the difference between conventional H13, H13 ESR, and H13 VAR. ESR and VAR are secondary remelting routes, but final quality still depends on mill process control, ingot size, reduction ratio, heat treatment, and inspection requirements.

• ESR is commonly specified to improve cleanliness, structure consistency, toughness, and reliability in demanding hot-work tooling.

• VAR is commonly specified where vacuum remelting, gas control, and high-integrity structure are required.

• When the drawing does not specify ESR, VAR, VD, or UT, mills may quote a lower-cost route that only meets the minimum written requirement.

For H13-family steel, the purchase order should state the exact grade, standard, standard version, refining route, hardness, ultrasonic testing class, heat-treatment condition, and MTC requirement.

1045 = C45 = S45C = 45 Steel

1045 is medium-carbon engineering steel, not a tool steel. It is used for shafts, gears, pins, plates, mold bases, backing plates, support structures, and general mechanical components.

AISI 1045 is commonly supplied in black hot-rolled or normalized condition. A typical reference range is 570–700 MPa tensile strength and HB 170–210, depending on delivery and heat-treatment condition^[10].

In mold manufacturing, 1045 / S45C / C45 / 45 steel is commonly used for mold bases, backing plates, and support structures. It is normally not used for production cavity surfaces where wear resistance, polishability, corrosion resistance, or long mold life is required.

This is different from P20 / 1.2311 / 3Cr2Mo, which is a plastic mold steel family, and different from H13 / 1.2344 / SKD61 / 4Cr5MoSiV1, which is a hot-work die steel family.

The key parameters across standards are close but not identical:

• AISI 1045 commonly sets C around 0.42–0.50% and Mn around 0.60–0.90%.

• DIN / EN C45-family steels commonly sit around the medium-carbon range, with details depending on the exact C45 / C45E / C45R route.

• JIS S45C is commonly treated as a Japanese equivalent in shop-floor communication.

• GB 45 steel is commonly treated as the Chinese equivalent, but the exact GB/T 699 requirement should be checked.

If the drawing only says “45 steel,” procurement needs to clarify whether it means GB 45, S45C, C45-family steel, or AISI 1045. The names are close in daily shop-floor communication, but deoxidation practice, S / P limits, delivery condition, heat treatment, and internal stress can affect machining and welding behavior.

1045 / S45C / 45 steel also requires controlled welding procedures, especially for thick sections. Its carbon level is high enough that preheat, interpass temperature, filler selection, cooling control, and post-weld treatment should not be ignored.

Procurement Skills

How to Read the Grade on the Drawing

When reading the grade on a drawing, first confirm three things. Each item should be backed by at least one standard clause, drawing note, or purchase-order line.

1. Which standard system the grade belongs to: AISI, ASTM, DIN, EN, ISO, JIS, GB, or UNS.

2. The steel’s delivery condition: hot-rolled, forged, annealed, normalized, quenched-and-tempered, or pre-hardened.

3. Any additional requirements: ESR, VAR, VD, UT, hardness range, surface quality, polishing class, or inspection certificate.

For example, “P20 ESR” means P20 plus electroslag remelting. “1.2738 + ESR + UT” means the P20+Ni family, with electroslag remelting and ultrasonic testing required.

When these extras are not written clearly, suppliers may quote the lowest product that still appears to match the short grade name. The problem often surfaces during machining, polishing, welding repair, or final inspection.

Drawings also use different hardness scales, and the scale matters.

Hardness values across scales do not interchange directly. For Chinese procurement, GB/T 33362-2016 is the current standard for metallic material hardness conversion. ASTM E140 is also widely used for hardness conversion among Brinell, Vickers, Rockwell, superficial hardness, Knoop, and related scales^[11][12].

A practical incoming-inspection workflow is to measure the scale specified on the drawing whenever possible. If the shop uses HBW for incoming blocks while the drawing specifies HRC, the conversion should follow the correct standard table and should be treated as approximate unless the standard or customer allows it.

Substitution Plans

The core of any substitution plan is chemistry equivalence plus process compatibility.

Three common scenarios appear repeatedly in mold-steel procurement:

1. Cost-down substitution: P20 replaced by P20+S / 1.2312 where added sulfur improves machinability, but polishability and texturing suitability may be reduced.

2. Performance-up substitution: P20 replaced by P20+Ni / 1.2738 to improve hardenability, toughness, and hardness uniformity in larger plastic molds.

3. Process substitution: H13 replaced by SKD61, where the steel family is close, but the naming system, chemistry range, heat-treatment sheet, and inspection requirements still need confirmation.

Every substitution needs written documentation covering original grade, substitute grade, substitution reason, standard, chemistry, hardness, delivery condition, and incoming inspection result.

Before any substitution, confirm three parameters:

1. Hardenability: the substitute steel must have equal or better through-section hardenability for the actual section size.

2. Heat-treatment window: the substitute’s austenitizing and tempering temperatures should fit the existing process route, or a fresh heat-treatment validation is needed.

3. Machining allowance: if delivery hardness, internal stress, heat-treatment route, or section size changes, roughing allowance should be revalidated according to stress-relief plan and finishing tolerance.

A high-risk mistake is using P20 for an application that actually requires H13-family hot-work die steel. P20 / 3Cr2Mo is often supplied around HRC 28–36 in pre-hardened condition, while many H13 hot-work applications require a much higher working hardness after quenching and tempering. The result can be early cracking, thermal-fatigue failure, heat checking, or poor die life.

Also validate weldability. P20-family steel needs a controlled repair procedure, suitable preheat, filler selection, and post-weld treatment depending on hardness and steel condition. 1045 / S45C / 45 steel also requires controlled welding, especially for thick sections, because medium-carbon steels have a higher risk of hard heat-affected zones and cracking than low-carbon steels.

Do Not Stop at the Name

The shorthand “P20” is often used loosely on the shop floor, but the actual steel may be different.

Looking only at the grade name without asking about refining practice, melting route, hardness, UT, delivery condition, and surface requirement allows hidden quality differences to move downstream into machining, polishing, welding repair, and final mold trial.

Another common misuse is treating 45 steel / 1045 / S45C / C45 as fully interchangeable while ignoring delivery condition. The chemistry is close, but the real machining behavior can still change because of S / P limits, deoxidation practice, heat-treatment state, and internal stress.

Before releasing the PO, the check should cover six items:

1. Grade

2. Standard and standard version

3. Refining or melting process

4. Delivery condition

5. Hardness and hardness scale

6. Extras such as UT, VD, ESR, VAR, polishing class, or surface requirement

The grade on a drawing is only the visible part of the material requirement. The real procurement risk often hides in standard-system differences, refining process, hardness, heat treatment, delivery condition, and inspection scope.

For export mold-steel procurement, the safest method is to treat P20 / 1.2311 / 3Cr2Mo, H13 / 1.2344 / SKD61 / 4Cr5MoSiV1, and 1045 / C45 / S45C / 45 steel as close commercial families, not automatic one-word replacements.

At Guda Machinery, every mold-steel PO should confirm the grade, standard, standard version, delivery condition, hardness, refining process, and inspection certificate before cutting starts. This simple check reduces receiving disputes and prevents avoidable machining, welding, and polishing rework.

For procurement, outsourcing, and quality teams, the practical rule is simple: verify before releasing the PO, not after the steel arrives.