How to read European steel names and numbers: EN 10027 (C45, 42CrMo4, S235JR, 1.4301)

Names by use and mechanical properties

Steels bought for strength are named by their application letter and a number. The number is the minimum yield strength in MPa for the smallest thickness range, because yield strength falls as sections get thicker.

Common letters are S for structural steel, P for pressure purposes, L for line pipe, E for engineering steel, B for reinforcing steel and R for rail. Extra symbols follow the number. For structural steels, J, K or L give the impact energy (27 J, 40 J or 60 J) and R, 0 or 2 give the test temperature (room temperature, 0 °C or −20 °C). Delivery conditions are added with a plus sign, as in S355J2+N.

• S235JR: structural steel, minimum yield 235 MPa, 27 J impact energy at room temperature.
• E295: engineering steel, minimum yield 295 MPa.
• B500B: reinforcing steel, characteristic yield strength 500 MPa; the final B is ductility class B (classes A, B and C follow Eurocode 2), as used in BS 4449.

Names by chemical composition

Non-alloy steels with less than 1% manganese are written C plus 100 times the mean carbon content: C45 has about 0.45% carbon. Extra letters can follow: C45E has a specified maximum sulphur content and C45R a specified sulphur range.

Low-alloy steels (and non-alloy steels with 1% manganese or more) start with the carbon figure, then the symbols of the characterizing elements in order of content, then figures for those elements multiplied by a factor. The figures belong to the elements in the order written; elements without a figure are simply present. In 42CrMo4 the 4 belongs to chromium: 4 ÷ 4 = about 1% Cr, and molybdenum is named without a figure.

High-alloy steels, where at least one element reaches 5%, start with X. Carbon is still 100 times the mean content, but the element figures are plain percentages separated by hyphens: X5CrNi18-10 has about 0.05% C, 18% Cr and 10% Ni.

Steel numbers (EN 10027-2)

Every European steel also has a material number in the form 1.yyzz. The 1 means steel. The next two digits are the steel group, and the last two are a sequence number assigned by the registration office (VDEh in Düsseldorf). Two further digits are reserved for future use.

The group tells you the broad class without reading the name. Groups 00–09 and 90–99 are non-alloy basic and quality steels, 10–19 non-alloy special steels, 20–29 tool steels, 40–49 stainless and heat-resisting steels, and 50–89 alloy structural, machinery and pressure-vessel steels grouped by alloy system. The number is easier to use in databases and order systems than the name, which is why EN 10027-2 was written for data processing.

• 1.0503 (C45): group 05, non-alloy quality steel in the medium-carbon band.
• 1.1191 (C45E): group 11, non-alloy special steel, the tighter-controlled version of C45.
• 1.7225 (42CrMo4): group 72, chromium-molybdenum steels with less than 0.35% Mo.
• 1.4301 (X5CrNi18-10): group 43, stainless steels with at least 2.5% Ni and no molybdenum; 1.4401 (316 type) is in group 44, with molybdenum.

Legacy DIN names and what replaced them

Before the European standards, German DIN standards used names such as St37 and Ck45. These still appear on older drawings and in stockists' catalogues. In the St names the figure was about one tenth of the minimum tensile strength in N/mm² (St 37 ≈ 370 N/mm²), so St 37 and St 52 named tensile classes rather than yield strengths.

DIN 17100 (structural steels) was replaced by EN 10025 and DIN 17200 (quenched and tempered steels) by EN 10083. The table gives the published successors.

Worked examples

Each row splits a European designation into its parts.