The drawing says “S355J2+N”, the enquiry says “St52-3” and the inspection certificate says “1.0577”. Each of these carries specific information about the material — you just need to know how to read it. The European designation system for steels is set out in two standards: EN 10027-1 (steel names) and EN 10027-2 (steel numbers, also called material numbers).
This article explains the designations we see most often in machining enquiries: structural steels, steels for quenching and tempering, and stainless steels. We start with a cheat sheet; details and examples follow below.
Cheat sheet: steel designations at a glance
| Part of the designation | Meaning | Example |
|---|---|---|
| S, P, E, L, B at the start | application: S structural, P pressure purposes, E engineering, L line pipe, B concrete reinforcing steel | S355, P265GH, E295 |
| number after S, P, E… | minimum yield strength in MPa for the smallest thickness range | S355 → 355 MPa |
| J / K / L | required impact energy in the Charpy test: J = 27 J, K = 40 J, L = 60 J | S355K2 → 40 J at −20 °C |
| R / 0 / 2 / 3…6 after J, K, L | test temperature: R = +20 °C, 0 = 0 °C, 2 = −20 °C, 3…6 = −30…−60 °C | S355J2 → 27 J at −20 °C |
| +AR, +N, +M, +QT, +A, +C | treatment condition: +AR as rolled, +N normalized or normalized rolled, +M thermomechanically rolled, +QT quenched and tempered, +A soft annealed, +C cold work hardened | S355J2+N, 42CrMo4+QT |
| C + number | non-alloy steel (Mn below 1 %); number = average carbon content × 100 | C45 → approx. 0.45 % C |
| number + elements + numbers, e.g. 42 Cr Mo 4 | alloy steel with no element averaging 5 % or more; carbon × 100, alloying elements × factor, e.g. Cr, Mn, Ni, Si × 4; Mo, V, Cu × 10 | 42CrMo4 → approx. 0.42 % C, approx. 1 % Cr |
| X + number + elements + numbers | high-alloy steel (at least one element ≥ 5 %); carbon still × 100, alloying elements in % without factors | X5CrNi18-10 → low carbon, approx. 18 % Cr, approx. 8–10.5 % Ni |
| HS + numbers | high-speed steel; W-Mo-V-Co contents in % | HS6-5-2-5 → 6 % W, 5 % Mo, 2 % V, 5 % Co |
| 1.XXYY | steel number: 1 = steel, XX = steel group, YY = sequential number; the delivery condition is not included | 1.0577 = S355J2, 1.4301 = X5CrNi18-10 |
Note: the same letter can mean different things depending on its position. L at the start means line pipe steel, in the impact symbol it means 60 J, and at the end of a name such as S355NL it means low temperature. C at the start means non-alloy steel, while +C after the plus sign means cold work hardened.
Two ways of naming steels
EN 10027-1 divides steel names into two groups:
- by application and properties — the name tells you what the steel is for and its key property, usually the yield strength. Example: S355J2.
- by chemical composition — the name tells you how much carbon and which alloying elements the steel contains. Examples: C45, 42CrMo4, X5CrNi18-10.
A steel grade has a name from one of these groups and, in addition, a steel number. The name and the number identify the same grade: S355J2 is 1.0577, C45 is 1.0503.
S355J2+N — how to read a structural steel designation
- S — structural steel.
- 355 — minimum yield strength in MPa for the smallest thickness range. For S355J2 to EN 10025-2 this is 355 MPa up to 16 mm. Thicker products have lower values: 345 MPa for 16–40 mm, 335 MPa for 40–63 mm, and lower still above that.
- J2 — required impact energy in the Charpy test: at least 27 J at −20 °C.
- +N — delivery condition: normalized or normalized rolled.
Besides S, you will often see: P — steels for pressure purposes (e.g. P265GH), E — engineering steels (e.g. E295), L — steels for line pipe, B — steels for reinforcing concrete.
What is impact toughness?
Impact toughness describes how well a material resists fracture under a sudden blow. Yield strength tells you the stress at which steel starts to deform permanently under a slowly applied load. The impact test shows something else: whether a notched specimen deforms and absorbs energy when struck, or breaks in a brittle way.
It is measured in the Charpy pendulum impact test to EN ISO 148-1. A 55 mm long specimen with a 10 × 10 mm cross-section and a V-notch is broken by a single blow from a swinging pendulum. The result is the energy absorbed by the specimen when it breaks — the absorbed energy KV, in joules. In everyday use, this value is also loosely called impact toughness.
For structural steels the test temperature matters. Below a certain temperature they become brittle and the absorbed energy drops sharply. That is why the symbol always states two things: the required energy and the temperature at which it must be reached. Austenitic stainless steels such as 1.4301 do not show this ductile-to-brittle transition. The choice of quality (JR, J0, J2, K2…) matters most for welded structures, thick members and low service temperatures; for steel structures it is covered by EN 1993-1-10.
Impact symbols: JR, J0, J2, K2 and others
The symbol consists of a letter and a character after it. The letter gives the required impact energy, the character after it — R or a digit — gives the test temperature.
| Letter | Required impact energy |
|---|---|
| J | 27 J |
| K | 40 J |
| L | 60 J |
| Character | Test temperature |
|---|---|
| R | +20 °C |
| 0 | 0 °C |
| 2 | −20 °C |
| 3 / 4 / 5 / 6 | −30 / −40 / −50 / −60 °C |
So JR means 27 J at +20 °C, J0 27 J at 0 °C, J2 27 J at −20 °C and K2 40 J at −20 °C. The lower the test temperature and the higher the energy, the stricter the requirement for resistance to brittle fracture.
Watch out for fine-grain steels. In S355NL the letters are part of the name, not an addition after the plus sign: N stands for normalized or normalized rolled, and L for low-temperature service. This is a different L from the one in the impact scale.
What the suffix after the plus sign means
Symbols after the “+” describe the product. They can indicate special requirements or the type of coating, but in machining enquiries they usually give the treatment condition. The most common condition symbols in EN 10027-1:
- +AR — as rolled, without any special rolling or heat treatment conditions,
- +N — normalized or normalized formed (rolled),
- +M — thermomechanically formed (rolled),
- +QT — quenched and tempered,
- +A — soft annealed,
- +C — cold work hardened,
- +SR — stress relieved.
Careful with +A: on coated flat products the same symbol means a hot-dip aluminium coating, not annealing. The product standard determines which meaning applies.
The condition matters for machining. The same steel machines differently in the +A and +QT conditions, and the finished part has different mechanical properties. That is why the enquiry should give the full designation, including the part after the plus sign.
C45, 42CrMo4, X5CrNi18-10 — designations by chemical composition
Non-alloy steels: letter C. The letter C is used for non-alloy steels with an average manganese content below 1 %. In C45 the number is 100 × the average carbon content, i.e. approx. 0.45 % C (the range for C45 is 0.42–0.50 %). Additional letters specify requirements, e.g. C45E has a specified maximum sulphur content. C45E is a separate grade with its own number, 1.1191.
Alloy steels where no element averages 5 % or more: number, elements and factors. In 42CrMo4, 42 is 100 × the carbon content (approx. 0.42 % C). Then come the alloying elements in decreasing order of content. The numbers at the end, separated by hyphens, are the contents of those elements in the same order, multiplied by a factor:
| Elements | Factor |
|---|---|
| Cr, Co, Mn, Ni, Si, W | 4 |
| Al, Be, Cu, Mo, Nb, Pb, Ta, Ti, V, Zr | 10 |
| Ce, N, P, S | 100 |
| B | 1000 |
The 4 in 42CrMo4 therefore means about 1 % chromium (4 / 4 = 1). There is no number for molybdenum — for alloy steels the standard allows some digits or symbols to be omitted where there is no risk of confusion with a similar grade. 42CrMo4 contains 0.15–0.30 % molybdenum. An example with two numbers: 13CrMo4-5 contains approx. 1 % chromium and approx. 0.5 % molybdenum.
High-alloy steels: letter X. When the average content of at least one alloying element is 5 % or more, the designation starts with X. It is followed by 100 × the carbon content, and the numbers at the end are the element contents in percent, without factors. X5CrNi18-10 is a widely used austenitic stainless steel (comparable to AISI 304). The numbers in the name are nominal. According to EN 10088 it contains max. 0.07 % carbon, 17.5–19.5 % chromium and 8–10.5 % nickel.
High-speed steels: HS. The numbers, e.g. in HS6-5-2-5, are the contents of tungsten, molybdenum, vanadium and cobalt in percent, rounded to whole numbers.
Steel number: 1.0577, 1.0503, 1.4301
The number to EN 10027-2 has the form 1.XXYY. The 1 stands for steel, the next two digits for the steel group and the last ones for the sequential number within the group. Each number refers to exactly one grade.
- 1.0577 — S355J2, non-alloy structural steel,
- 1.0503 — C45, non-alloy steel for quenching and tempering,
- 1.7225 — 42CrMo4, chromium-molybdenum alloy steel,
- 1.4301 — X5CrNi18-10, stainless steel. Groups 1.40 to 1.49 cover stainless, heat-resisting and creep-resisting steels.
The number is short and convenient in documents and stock systems. It does not include the delivery condition, though: S355J2 and S355J2+N share the number 1.0577. So in an order the number alone is not enough.
Check your designation straight away. The steel grade equivalents tool breaks the name down into its parts and gives the steel number, the product standard and comparable grades in DIN, AISI/SAE, JIS and BS — enter e.g. S355J2+N, St52-3 or 1.4301. It runs in your browser and sends nothing to a server.
Old designations still found on drawings
Older drawings and enquiries still use names from former national standards, especially German DIN. The most common ones and their approximate equivalents:
- St37-2 (DIN 17100) — comparable to S235JR,
- St52-3 (DIN 17100) — depending on the variant: St52-3 U (1.0553) ≈ S355J0, St52-3 N (1.0570) ≈ S355J2G3, today S355J2+N,
- Ck45 (DIN 17200) — corresponds to C45E (1.1191),
- S355J2G3 (number 1.0570) — designation from the 1993 edition of EN 10025. G3 meant fully killed steel delivered in the normalized condition. In today’s EN 10025-2 it corresponds to S355J2+N (number 1.0577).
These are approximate equivalents, not one-to-one substitutes. The old standards had different requirements for composition and toughness. If a drawing shows an old designation and the part is safety-critical, it is best to agree the current grade with whoever issued the drawing.
What this means for your enquiry
- Give the full designation, including the impact symbol, delivery condition and product standard, e.g. S355J2+N to EN 10025-2 — not just “S355”.
- If the drawing shows an old name, add the current equivalent or ask which one to use.
- If you need a 3.1 inspection certificate to EN 10204, say so in the enquiry.
For guidance on choosing a grade, see Material Selection for CNC Machining, and what we make from steel is described on the CNC steel machining page.
Frequently asked questions
What does S355J2+N mean?
A structural steel with a minimum yield strength of 355 MPa (up to 16 mm thickness) and an impact energy of at least 27 J at −20 °C, delivered normalized or normalized rolled.
What is the difference between S355J2 and S355K2?
The test temperature is the same, −20 °C, but K2 requires a higher impact energy: 40 J instead of 27 J.
What does the number in C45 mean?
It is 100 × the average carbon content. C45 contains about 0.45 % carbon.
What is the material number of S355J2?
1.0577. C45 is 1.0503, 42CrMo4 is 1.7225 and X5CrNi18-10 is 1.4301.
Is St52-3 the same as S355J2?
Not exactly. St52-3 N corresponds roughly to S355J2+N, St52-3 U to S355J0. The steels are comparable, but the old DIN 17100 had different requirements. New orders should use the current designation.
Not sure about the material on your drawing? Send it with your enquiry — if anything is unclear, we will ask before quoting. Request a quote.
