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Different Steel Grades and Their Designation

The global economy has been severely disrupted over the past two years with the COVID pandemic, the logistics bottlenecks, the rising prices in energy and now the ongoing war in Ukraine. This has forced many companies to change the way they are procuring steel and other metals as their traditional procurement channels got impacted. But is it that easy to change a supplier overnight? Not really….

Different Steel Grades systems across Europe and other geographies can lead to confusion when buying or selling steel.

Let’s go through the most used steel grade classifications before providing you with a Steel Grade Equivalency Table.

A general explanation of steel grade standards and why they exist

In reality, the “problem” with the complexity of steel grades equivalence comes from the fact that almost every country has developed a different standardization system, which in turn gives different names to steels with similar composition and physical properties. Different standardization systems also use different designations in different editions. Aside from this, private producers and suppliers sometimes create their own standards, which add further confusion.

But first, what is a steel grade?

A steel grade is a classification of various steels based on their composition and physical properties. Two different grades of steel will behave differently and serve different purposes.

There are over 3,500 different grades of steel (75% of which did not exist 20 years ago). These grades can be split into four main material categories:

• Carbon Steel – Most commonly used steel. Consists of Mostly Iron (Fe), <1% Carbon (C), and trace amounts of other metals. Carbon is present in all steel and is the principal hardening element of it. More than 1% of carbon makes the material brittle. Generally, the higher the carbon content, the more difficult carbon steel is to machine.

• Alloy Steel – Alloy Steel is made by adding additional elements in the production. Most commonly Nickel (Ni), Copper (Cu), Chromium (Cr), and/or Aluminum (Al) are added. These elements change the physical and chemical properties of the metal.

• Stainless Steel – Stainless Steels (originally called rustless steels) are technically an Alloy Steel, consisting of 10-20% Chromium (Cr). The Chromium creates a protective coating, which prevents corrosion. This makes stainless steel perfect for outside constructions, electrical equipment, and materials used in customer-facing environments, because of its “clean” look.

• Tool Steel –  Tool Steels are used for drilling & cutting machines, knives and so on… These alloys typically have very high heat resistance and overall durability. Combined with their shape retention, this makes them suitable for heavy usage.

These four categories describe the most common types of steel, however, they are too broad for people that want to buy, sell and use steel for specific purposes. There are thousands of different types of each material category, and they all need their unique grade classification and name in order to be properly separated.

In this article, we have included the five most popular national standards, which you might come across when buying steel in Europe and Vanilla Steel: EN, DIN, AFNOR, UNI, SAE.

There are many other standards but the general rule of thumb is that each steel is marked with a unique combination of letters and numbers, usually starting with the abbreviation of the standard used. The following letters are describing the specific chemical and mechanical properties of the metal.

For example EN S235JR is the European standard for non-alloy general construction and machine steel with unique chemical composition (C≤0.17, MN≤01.40, P≤0.035, S≤0.035, N≤0.12, Cu≤0.55) and mechanical properties. If you want to sell this steel in Germany, it would be best to convert it to the German equivalent standard, which would be DIN St37-2. You can do this by using the table at the end of this article.

Sometimes overlaps in similar compositions occur. We advise you to use the following information as guidance and always double-check the properties of both standards when looking for very specific steel.

A short introduction to the standards and how they are used

We will use the following two steels as a comparison across the different grading standards:

 
Europe EN Germany DIN France AFNOR Italy UNI USA SAE/AISI
S235JR ST37-2 E24-2 FE360B SAE1015
S355MC QSTE360TM E360D FEE355 GR50
:

Europe EN

The EN Steel Standard is a European standard that specifies the requirements for a product or process.

The designation systems used in EN standards most commonly describe different properties of the metal with the following structure:

• S… means Structural Steel. E… is Engineering steel (P… – Pressure vessel, L… – Pipeline construction, B… – Reinforcing steel, Y… – Prestressing, R… – Steel for rails, H… – Cold rolled flat rolled steels with higher-strength drawing quality, D… – Flat products made of soft steels for cold reforming)

• .235…, .275… and so on notes the yield strengthin MPa (megapascals) for the smallest dimensional range

• …JR.., …J0.., …K2.., will describe the Longitudinal Charpy V-notch impacts (…J0.. would be 0°C, …N.. Means not lower than  -20°C, …NL.. Is not lower than  -50°C, etc.)

• Customer options include …C.. (grade suitable for cold forming), …Z..(Grade with improved properties perpendicular to the surface)

 
After Coating After Surface Treatment After Surface Protection
Hot-dip Aluminium (+A) Conventional surface (A) Without surface treatment (U)
Hot-dip Alusi (+AS) Improved surface (B) Oiled (O)
Hot Dip Zinc / Galvanized (+Z) Best surface (C) Chemically passivated (C)
Hot Dip Zinc Magnesium (+ZM) Bright (b) Chemically passivated and oiled (CO)
Galfan (+ZA) Semi-bright (g) Phosphated (P)
Electrogalvanized (+ZE) Normal (m) Phosphated and oiled (PO)
Galvannealed / Zinc-Iron (+ZF) Rough (r)
Normal spangle (N)
*coating thickness is described with numbers, which follow the letter combination Minimized spangle (M)
:

*Note that different letters have a different meaning, depending on their place in the designation.

Example:

 
S235JR S355MC
S… – Structural Steel S… – Structural Steel
.235.. – Minimum yield strength of 234( Reh) in MPa @16mm .355.. – Minimum yield strength of 355( Reh) in MPa (megapascals) @16mm
…JR Longitudinal Charpy V-notch impacts 27 J @ +20°C …M. – Thermomechanically rolled
….C – Special cold forming,
:

Germany DIN

DIN steel specifications are German standards developed by the “Deutsches Institut für Normung”, meaning “German Institute for Standardization”.

DIN specifications are a combination of letters and numbers most often (but not always) showing chemical composition. In some cases suppliers use old designations or the DIN standard includes serial numbers. When this is not the case the the structure of the steel is the following:

• N… – normalizing, TS…. – tensile strength, U… -without heat treatment, TM… – thermomechanically-rolled and others..

• The second combination of symbols shows the alloying element(s) and their quantity. For example, .Mo6… means Molybdenum Alloy, .B… – Boron Alloy, and so on..

*The numbers are not exact representations. To get exact representation you need to multiply the average content by the coefficient of the element, described below:

 
Alloying Element Coefficient
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
:

*Note that different letters have a different meaning, depending on their place in the designation.

Example:

 
ST37-2 QStE360TM
St… – Structural Steel Q … – Quenched
37-2 – Serial Number .St.. – Structural Steel
..E360. – Minimum yield strength of 360( Reh) in MPa (megapascals)
…TM – thermomechanically-rolled
:

France AFNOR

The French AFNOR steel standard is used mainly in French-speaking countries and companies working with them.

The standard uses a unique combination of letters and numbers to name each steel grade. When a serial number is not used the most common structure is:

• The first letter represents the type of steel (For example Z means stainless steel).

• The numbers afterward express 100 times the carbon content, then the letters showed the main alloying elements (C for Cr, N for Ni, etc.)

• Тhe following figure expressed 4 times the percentage content of the first material in the list

• Mechanical properties include A – Minimum elongation, J – Notch impact test, etc.

• Heat treatment designations include +AR – As rolled, +CR – Cold rolled, +N – Normalized, +M – Thermo mechanical rolling, +U – Untreated, etc.

*Note that different letters have a different meaning, depending on their place in the designation.

Example:

 
ST37-2 QStE360TM
St… – Structural Steel Q … – Quenched
37-2 – Serial Number .St.. – Structural Steel
..E360. – Minimum yield strength of 360( Reh) in MPa (megapascals)
…TM – thermomechanically-rolled
:

Italy UNI

UNI stands for Ente Nazionale Italiano di Unificazione, it is an association that performs regulatory services in Italy. UNI’s designation for steel and aluminum alloys is similar to EN and ISO designations. This body, therefore, uses chemical composition for the designation of steel and alloys.

Example:

 
ST37-2 QStE360TM
St… – Structural Steel Q … – Quenched
37-2 – Serial Number .St.. – Structural Steel
..E360. – Minimum yield strength of 360( Reh) in MPa (megapascals)
…TM – thermomechanically-rolled
:

USA SAE/AISI

SAE(Society of Automotive Engineers) was working in parallel with AISI  towards the standardization of steel grades. The systems were united into a joint system designated the AISI/SAE steel grades.

Carbon Steels and Alloy Steels are most often designated a four-digit number, whereby the first digit indicates the main alloying element(s), the second digit indicates tg (top grade) element(s), and the last two digits indicate the amount of carbon, in hundredths of a percent (basis point) by weight. For example, a 1060 steel is a plain-carbon steel containing 0.60 wt% C.

Carbon Steels Description 
Grade Description
10xx non-resulfurized, 1.00 manganese maximum
11xx resulfurized
12xx rephosphorized and resulfurized
15xx non-resulfurized, over 1.00 manganese maximum
:
Alloy Steels Description 
Grade Description
13xx 1.75 manganese
40xx 0.20 or 0.25 molybdenum or 0.25 molybdenum and 0.042 sulfur
41xx 0.50, 0.80, or 0.95 chromium and 0.12, 0.20, or 0.30 molybdenum
43xx 1.83 nickel, 0.50 to 0.80 chromium, and 0.25 molybdenum
46xx 0.85 or 1.83 nickel and 0.20 or 0.25 molybdenum
47xx 1.05 nickel, 0.45 chromium, 0.20 or 0.35 molybdenum
48xx 3.50 nickel and 0.25 molybdenum
51xx 0.80, 0.88, 0.93, 0.95, or 1.00 chromium
51Xxx 1.03 chromium
52xx 1.45 chromium
61xx 0.60 or 0.95 chromium and 0.13 or 0.15 vanadium minimum
86xx 0.55 nickel, 0.50 chromium, and 0.20 molybdenum
87xx 0.55 nickel, 0.50 chromium, and 0.25 molybdenum
88xx 0.55 nickel, 0.50 chromium, and 0.35 molybdenum
92xx 2.00 silicon or 1.40 silicon and 0.70 chromium
50Bxx 0.28 or 0.50 chromium
51Bxx 0.80 chromium
81Bxx 0.30 nickel, 0.45 chromium, and 0.12 molybdenum
94Bxx 0.45 nickel, 0.40 chromium, and 0.12 molybdenum

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