Four Steel Naming Systems, Four Philosophies: EN, ASTM, JIS and GB

One steel can carry four unrelated names. This guide compares the logic behind the European, American, Japanese and Chinese designation systems: who names a steel by its chemistry, who by its strength, and who by a specification number.

Two basic philosophies

Every designation system answers one of two questions. Composition-based systems describe what the steel is made of: carbon content and alloying elements. Property-based systems describe what the steel guarantees: usually a minimum yield or tensile strength. Most real systems mix the two, but each leans one way — and that lean explains most cross-standard confusion.

EN (Europe): properties for structural, chemistry for alloy

EN structural steels are property-based: S355 is a structural steel (S) with a minimum yield strength of 355 MPa. No chemistry is visible in the name at all. EN alloy and specialty steels flip to composition logic: 42CrMo4 states roughly 0.42% carbon with chromium and molybdenum, and stainless grades carry descriptive names too (X5CrNi18-10 ≈ 0.05% C, 18% Cr, 10% Ni). Behind both sits the numeric Werkstoff number (1.0570, 1.4301), a pure registry code that encodes neither.

AISI/SAE (USA): chemistry in four digits

The American system for carbon and alloy steels is composition-based: in 4140, the 41 identifies the chromium-molybdenum family and 40 the nominal carbon content (0.40%). Stainless uses a parallel three-digit code (304, 316, 430) in which the first digit marks the family, not an element. Alongside it, ASTM designations such as A36 or A516 Grade 70 are specification numbers: they identify a product standard plus a strength grade, and say nothing directly about chemistry at all.

JIS (Japan): letters for the family, numbers for the recipe

JIS names combine a family prefix with a composition or strength number. Carbon and alloy steels are composition-based (S45C = 0.45% carbon steel; SCM440 = chromium-molybdenum steel at 0.40% carbon), while structural grades are property-based — and, a classic trap, the number is usually tensile strength rather than yield: SS400 and SM490 are named for 400 and 490 MPa minimum tensile strength. Stainless simply borrows the AISI numbers (SUS304).

GB (China): a systematic hybrid

Chinese GB designations are the most rule-driven of the four. Structural steels are property-based on yield strength (Q355, where Q comes from the Chinese word for yield point). Carbon and alloy steels are composition-based, spelling out carbon in hundredths of a percent and each alloying element with its approximate percentage (42CrMo, GCr15). Stainless uses explicit element figures (06Cr19Ni10). A single GB name usually lets you reconstruct the nominal recipe without a table.

Why this matters

System	Structural grades named by	Alloy grades named by
EN	Yield strength	Composition (plus registry number)
AISI/SAE	— (ASTM uses specification numbers)	Composition
JIS	Tensile strength	Composition
GB	Yield strength	Composition

Because the philosophies differ, equivalents are found by matching chemistry and guaranteed properties — never by matching the digits. A "355" in Europe, a "490" in Japan and a "Grade 70" in an ASTM specification all measure different things, and a name that looks familiar can quietly belong to the other philosophy.