Steel Grade Designation Systems: EN, GB/T, ASTM, DIN, GOST Compared

A 4140 bar in the United States is the same steel as 42CrMo4 in Europe, 1.7225 in the old DIN Werkstoff-Nummer system, SCM440 in JIS and 38ХМ under GOST. None of these is "wrong" — they are the same alloy with five different names. But once you start writing purchase orders across markets, the question becomes: which designation do you write on the PO, and how do you translate when the supplier only knows one of them? This article walks through the five most-used grade designation systems — EN 10027, GB/T 221, ASTM/AISI, DIN Werkstoffnummer and GOST — and gives a conversion method that does not depend on a single look-up table.

Why Five Systems Still Coexist

Each system grew out of its own industrial base:

• ASTM/AISI dominates North American steel procurement.

• EN 10027 (and the older DIN system it absorbed) is the European reference.

• GB/T 221 is the Chinese system, used by every Chinese mill.

• DIN Werkstoffnummer is a 7-digit material number that survives inside the EN system as the secondary designation.

• GOST is the Russian/Commonwealth of Independent States system.

Each designates the same metallurgy in a different way: ASTM/AISI by chemistry family, EN 10027-1 by application + composition, GB/T 221 by composition + application, GOST by composition in Cyrillic letters, and the Werkstoffnummer as a numeric key. The trick is knowing how each works.

EN 10027-1 and EN 10027-2

EN 10027-1 ("Designation systems for steels — Part 1: Steel names") defines the alphabetic name. The first letter marks the application:

The application letter is followed by a number (yield or tensile in MPa, or carbon × 100), then optional letters for impact test temperature (J0, J2, K2), heat delivery condition (N = normalised, M = thermomechanically rolled, Q = quenched and tempered, T = tempered), and alloy code. So S355J2W+N reads as "structural steel, 355 MPa yield minimum, J2 impact at -20 °C, weathering grade, normalised".

EN 10027-2 is the numeric designation — the "Werkstoffnummer" or WNr., a 7-digit number like 1.0570 for S355J2(+N) or 1.7225 for 42CrMo4. Format: "1.XXXX" where the first group after the dot identifies the alloy family (1.0xxx = carbon, 1.2xxx = stainless, 1.7xxx = alloy, 1.9xxx = tool). The Werkstoffnummer is the cleanest key for cross-system conversion because it is unique per chemistry.

GB/T 221 (China)

GB/T 221 ("Notation of steel grade") is the Chinese designation system. It uses one of three approaches depending on the steel family:

By composition (most carbon and alloy steels): two digits for carbon × 100, then Latin letters for the alloying elements, then percentage numbers for the alloying content. Example: 42CrMo = 0.42% C, ~1% Cr, ~0.2% Mo. The convention is the same as the older DIN name (42CrMo4) minus the multiplier digit on each alloy. The carbon figure is the upper limit of the spec range.

By yield strength (structural and pressure plate): the prefix Q + yield in MPa, then impact test grade. Q355B, Q355C, Q355D, Q355E are the four impact grades of the GB/T 1591 structural steel — B (20 °C), C (0 °C), D (-20 °C), E (-40 °C). The new GB/T 1591-2018 renamed Q345 to Q355 to align yield strength reporting with EN 10025.

By application prefix:

• Q = yield-strength designation (structural, pressure, ship)

• ML = cold-heading steel (e.g., ML20MnTi)

• Y = free-machining steel (e.g., Y15, Y45)

• ZG = cast steel (e.g., ZG230-450)

• H = weldable structural steel (H-shaped)

GB/T designations are usually shortened in trade speech. "45#" or "45 steel" means 0.45% carbon plain steel, equivalent to AISI 1045 / EN C45. "40Cr" is the 1% Cr alloy steel, equivalent to AISI 5140 / EN 41Cr4 / 1.7035 — see our 40Cr alloy forged bar product.

ASTM/AISI

The American system uses ASTM specifications (product standards like A29, A681, A516) that reference AISI/SAE grade numbers. The AISI/SAE system is a 4-digit code:

• 1xxx — carbon steels. 10xx = plain carbon (1045 = 0.45% C); 11xx = resulfurised free-machining; 12xx = resulfurised + rephosphorised.

• 2xxx — nickel steels (3.5–5% Ni).

• 3xxx — nickel-chromium steels.

• 4xxx — molybdenum steels (40xx = 0.2% Mo, 41xx = Cr-Mo, 43xx = Ni-Cr-Mo).

• 5xxx — chromium steels.

• 6xxx — chromium-vanadium steels.

• 8xxx — nickel-chromium-molybdenum (e.g., 4340 is technically 4xxx but classed Ni-Cr-Mo; 8620 is the classic Ni-Cr-Mo carburising grade).

• 9xxx — silicon-manganese and other specials.

The first digit is the alloy family; the second is the approximate percentage of the major alloy; the last two are the carbon content × 100. So 4140 = 4xxx (Cr-Mo family), 1 (≈1% Cr), 40 (0.40% C). 4340 = Ni-Cr-Mo, ~1.75% Ni and ~0.8% Cr combined, 0.40% C.

The ASTM product standards (A29 for alloy bar, A108 for carbon bar, A516 for PV plate, A681 for tool steel, A961 for fasteners, etc.) define the chemistry and properties; the AISI number identifies the grade within them. ASTM also runs a separate UNS (Unified Numbering System) — G10450 for 1045, G41400 for 4140, T20813 for H13 — which is unique per alloy and serves the same role as the European Werkstoffnummer.

DIN Werkstoffnummer (Germany, now in EN)

The German Werkstoff-Nummer (material number) is a 7-digit numeric designation defined by DIN EN 10027-2. The format is 1.XXXX where:

• The leading "1" means steel.

• The next two digits (XX) identify the alloy group:

• 1.00xx–1.09xx — plain carbon and low-alloy carbon-manganese.

• 1.10xx–1.19xx — free-machining carbon.

• 1.20xx–1.29xx — stainless, heat-resisting (1.4301 = 304, 1.4401 = 316).

• 1.40xx–1.49xx — stainless (alloy additions).

• 1.70xx–1.79xx — alloy structural (1.7225 = 42CrMo4 = 4140; 1.6582 = 34CrNiMo6).

• 1.90xx–1.99xx — tool steels (1.2344 = H13, 1.2379 = D2).

• The last three digits are sequential within the alloy group.

The Werkstoffnummer is the most useful key for cross-system conversion. If you know the WNr., you can usually find every other designation; if you know the AISI number, the WNr. is one look-up away.

Note: the old DIN alphabetic names (C45, 42CrMo4, X40CrMoV5-1) are now formally EN names, but the trade still calls them "DIN names" and the designations are unchanged. The 1.7225-style WNr. survives inside the EN system.

GOST (Russia / CIS)

GOST uses two parallel systems: an alphabetic name in Cyrillic, and a numeric GOST standard number that defines the chemistry.

The alphabetic name is composition-based, similar in spirit to the old DIN/EN system but in Cyrillic. The alloying element letters are:

The first two digits are carbon × 100. So 38ХМ = 0.38% C, ~1% Cr, ~0.2% Mo = AISI 4140 = 42CrMo4 = 1.7225. The trailing "А" letter (Cyrillic A) means "high-purity" (low sulfur and phosphorus) — so 38ХМА is the high-quality variant of 4140.

A more complex example: 30ХГСА = 0.30% C, ~1% Cr, ~1% Mn, ~1% Si, high-purity. This is a Ni-free medium-alloy structural steel, used in airframe and gear applications. The GOST standard that defines the chemistry is GOST 4543.

Equivalence Table — Common Engineering Steels

Two warnings. First, GOST and GB/T equivalents are not always exact chemistry matches — the carbon or alloy figure may differ by 0.02–0.05% from the AISI/EN window. For most applications this is metallurgically equivalent; for tight heat-treat windows it can shift the response. Second, the WNr. and the EN name are sometimes inconsistent for older grades — some mills still use 1.7227 (50CrMo4) and call it "4140-equivalent" in their literature, which it is not (50CrMo4 has 0.50% C).

How to Convert Between Systems

A practical method, in order of preference:

• 1. Use the Werkstoffnummer (WNr.) as the key. Every European mill test certificate lists both the EN name and the WNr. If you have the WNr., look it up in a cross-reference (the EN 10027-2 standard, or a recognised database like WinSteel/Eurocode 2) to get the AISI, JIS, GB/T and GOST equivalents.

• 2. If you only have the AISI number, use the AISI-to-EN cross-reference tables published by ASTM in E527 (Standard for Numbering Metals), or the SAE J406 document. For the most common grades the AISI → WNr. → GB/T → GOST chain is one query away.

• 3. If you only have a GB/T or GOST name, work out the chemistry from the digits (carbon × 100, then alloy letters and percentages) and match against the EN 10020 alloy classification tables. This works for ~80% of common engineering grades.

• 4. If the grade is ambiguous or modified (e.g., 4140 + Pb, or 42CrMo4 mod with restricted S), do not rely on the cross-reference table. Specify the chemistry window directly in the PO.

Specification Advice for Export Trade

If you are buying steel for cross-border delivery, write the PO with two designations plus the chemistry:

Grade: AISI 4140 / 42CrMo4 (EN 1.7225); C 0.38–0.43, Mn 0.75–1.00, Cr 0.80–1.10, Mo 0.15–0.25.

This protects you against three real problems:

• The mill runs to the loose end of one window and the tight end of another.

• A customer's notified body (PED, ASME, GB 150) only recognises one designation.

• A dispute over grade identity ends up being resolved by chemistry, not by name.

For plate going to European pressure equipment, lead with the EN name and put ASTM in brackets. For North American forging work, lead with ASTM and put EN in brackets. For Chinese domestic work, lead with GB/T and put EN in brackets. The mill will quote to its native system; the customer will inspect to theirs.

FAQ

Q: Is 42CrMo4 the same as 4140?
Practically yes — the chemistry windows overlap by about 80%. The EN 42CrMo4 carbon window is 0.38–0.43% and the AISI 4140 is 0.38–0.43%; the chromium and molybdenum windows are slightly different (EN 0.90–1.20% Cr vs AISI 0.80–1.10% Cr) but in practice the same heats satisfy both. For PED work, lead with 42CrMo4.

Q: Why does my mill cert say 1.7225 but the customer asked for 4140?
Because 1.7225 is the Werkstoffnummer for 42CrMo4, and 42CrMo4 ≈ 4140. Most European mills issue dual-spec certs that list both. If the customer insists on a 4140 stamp on the cert, ask the mill for an ASTM A29 dual-spec certificate.

Q: Is Q355 the same as S355?
Close but not identical. Q355 (GB/T 1591-2018) and S355 (EN 10025-2) have similar yield strength targets (355 MPa at ≤16 mm) but slightly different impact and chemistry windows. Q355B is roughly comparable to S355J0; Q355C to S355J2. Most Chinese mills will dual-certify Q355B/S355J0 on request.

Q: What is the GOST equivalent of 4340?
40ХН2МА (40KhN2MA) under GOST 4543. The "А" suffix means high-quality (low S and P).

Q: How do I convert a GOST name when I don't know Cyrillic?
Read the first two digits as carbon × 100, then map the Cyrillic letters to Latin element symbols (Х → Cr, Н → Ni, М → Mo, etc.), then match the chemistry against EN 10020. The mapping table above covers the common letters.

Talk to Qilu Metal

Qilu Metal supplies forged and hot-rolled bar in AISI 4140 / 42CrMo4 / 1.7225, AISI 4340, AISI 4130 / 25CrMo4, 40Cr / 41Cr4 / 1.7035 and DIN 34CrNiMo6 / 1.6582, with dual-spec mill test certificates to ASTM, EN and GB/T. If you need help matching a customer's grade designation to a Chinese mill's standard offer, send the spec and the chemistry — our metallurgy team will confirm the equivalence and issue a quotation with the designations written both ways. Email enquiry@qilumetal.com.