EN 10025-4 Standard Guide

Thermomechanical Rolled Weldable Fine Grain Structural Steels

1. SCOPE AND APPLICATION

1.1 Product Forms

This standard covers two main categories of hot rolled products:

Flat products: Hot rolled plates (≥3mm thick), sheet, strip, and wide flats
Long products: I and H sections, channels, angles, T sections, bars (flat, square, round, hexagon), and rod

1.2 Thickness Range

Maximum nominal thickness: 150mm

1.3 Intended Use

These steels are especially intended for use in heavily loaded parts of welded structures requiring superior toughness, such as:

Bridges and heavy construction
Flood gates and hydraulic structures
Storage tanks and pressure vessels
Water supply tanks and pipelines
Heavy machinery and mobile equipment
Offshore structures and marine applications
Mining and material handling equipment

Important: Suitable for service at ambient and low temperatures with enhanced toughness compared to normalized steels.

2. CLASSIFICATION AND DESIGNATION

2.1 Steel Grades

Five steel grades are specified: S275, S355, S420, S460, and S500

2.2 Quality Classes

Each grade is available in two quality classes based on impact test temperature:

M quality: Minimum impact energy values at temperatures not lower than -20°C
ML quality: Minimum impact energy values at temperatures not lower than -50°C (enhanced low temperature toughness)

2.3 Complete Steel Grades with Numbers

Steel Name	Steel Number	Description
S275M	1.8818	Thermomechanical rolled, -20°C impact
S275ML	1.8819	Thermomechanical rolled, -50°C impact
S355M	1.8823	Thermomechanical rolled, -20°C impact
S355ML	1.8834	Thermomechanical rolled, -50°C impact
S420M	1.8825	Thermomechanical rolled, -20°C impact
S420ML	1.8836	Thermomechanical rolled, -50°C impact
S460M	1.8827	Thermomechanical rolled, -20°C impact
S460ML	1.8838	Thermomechanical rolled, -50°C impact
S500M	1.8829	Thermomechanical rolled, -20°C impact
S500ML	1.8839	Thermomechanical rolled, -50°C impact

2.4 Designation System

The steel name consists of:

S: Symbol for structural steel
Number: Minimum yield strength in MPa for thickness ≤16mm (275, 355, 420, 460, 500)
M: Thermomechanical rolled delivery condition
L (optional): Enhanced low temperature toughness (-50°C)

Example: EN 10025-4 – S355ML

This designates a thermomechanical rolled structural steel with 355 MPa minimum yield strength and -50°C impact toughness.

2.5 Main Quality Classification

According to EN 10020:

S275M: Non-alloy quality steel
S355M, S420M, S460M, S500M: Alloy special steels

3. MANUFACTURING PROCESS

3.1 Steel Making Process

Any steel making process may be used except:

Excluded: Open hearth (Siemens-Martin) process

Note: Option 1 allows specification of steel making process details at time of order.

3.2 Deoxidation and Grain Structure

Steels of EN 10025-4 must meet the following requirements:

Fully killed steel: Complete deoxidation required
Fine grain structure: Ferritic grain size index ≥6 according to EN ISO 643
Nitrogen binding elements: Sufficient amounts to bind available nitrogen

Typical requirement: Minimum 0.020% total aluminium or equivalent nitrogen-binding elements

Guideline: Minimum aluminium to nitrogen ratio of 2:1 when no other nitrogen-binding elements are present. Other nitrogen-binding elements and their content must be reported in the inspection document.

3.3 Delivery Conditions

Products must be supplied in the thermomechanical rolled condition (M).

Definition: Thermomechanical rolling is a rolling process in which the final deformation is carried out in a certain temperature range leading to a material condition with certain properties which cannot be achieved or repeated by heat treatment alone.

Note: Thermomechanical rolling can include processes with an increasing cooling rate with or without tempering including self-tempering but excluding direct quenching and quenching and tempering. Also known as TMCP (Thermomechanical Control Process).

Important Distinction: EN 10025-4 steels achieve their properties through controlled thermomechanical rolling, whereas EN 10025-3 steels achieve properties through normalizing or normalized rolling. The thermomechanical process typically provides better toughness and weldability at equivalent strength levels.

4. CHEMICAL COMPOSITION

4.1 Heat Analysis Requirements

The chemical composition determined by heat analysis shall comply with the values specified in the table below. For elements not defined in the table, limit values of Table 1 of EN 10020:2000 shall apply as maximum values.

Table: Maximum Chemical Composition (Heat Analysis) in % by mass

Grade	C max	Si max	Mn max	P max	S max	Nb max	V max	Ti max
S275M/ML	0.13	0.50	1.50	0.025	0.025	0.05	0.08	0.05
S355M/ML	0.14	0.50	1.60	0.025	0.025	0.05	0.10	0.05
S420M/ML	0.16	0.50	1.70	0.030	0.025	0.05	0.12	0.05
S460M/ML	0.16	0.60	1.70	0.030	0.025	0.05	0.12	0.05
S500M/ML	0.16	0.60	1.70	0.030	0.025	0.05	0.12	0.05

Notes on Chemical Composition:

For long products, P and S content can be 0.005% higher
Minimum 0.020% total Al required (or equivalent N-binding elements)
Maximum Cr: 0.30%, Ni: 0.50%, Mo: 0.10%, Cu: 0.55%
Maximum N: 0.015% (S275), 0.015% (S355), 0.025% (S420/S460/S500)
For long products S275/S355: C max can be 0.15% and 0.16% respectively
For long products S420/S460/S500: C max can be 0.18%

4.2 Carbon Equivalent Value (CEV)

The maximum CEV values based on heat analysis are specified to ensure weldability:

CEV Formula (IIW): CEV = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15

Grade	≤16mm	>16-40mm	>40-63mm	>63-150mm
S275M/ML	0.34	0.34	0.35	0.38
S355M/ML	0.39	0.39	0.40	0.45
S420M/ML	0.43	0.45	0.46	0.47
S460M/ML	0.45	0.46	0.47	0.48
S500M/ML	0.47	0.47	0.47	0.48

Hot-Dip Zinc Coating (Option 5): When products are supplied with controlled Si content for hot-dip zinc coating, the maximum CEV values shall be increased:

For Si ≤ 0.04%: Increase CEV by 0.02
For Si ≤ 0.25%: Increase CEV by 0.01

5. MECHANICAL PROPERTIES

5.1 Tensile Properties at Room Temperature

The mechanical properties determined under standard inspection and testing conditions shall comply with the following values:

Table: Tensile Properties for Nominal Thickness ≤16mm

Grade	ReH min (MPa)	Rm (MPa)	A min (%)
S275M/ML	275	370-530	24
S355M/ML	355	470-630	22
S420M/ML	420	520-680	19
S460M/ML	460	540-720	17
S500M/ML	500	580-760	15

Notes:

ReH = Upper yield strength (if yield phenomenon not present, use Rp0.2)
Rm = Tensile strength
A = Minimum elongation after fracture (L₀ = 5.65√S₀)
For flat products with width ≥600mm, transverse direction applies
For all other products, longitudinal direction applies
Yield strength decreases with increasing thickness (see full tables in standard)

Stress Relief Warning: Stress relieving at more than 580°C or for over 1 hour may lead to deterioration of mechanical properties. If stress relief at higher temperatures or longer times is intended, minimum values should be agreed upon at time of order.

5.2 Impact Properties

Impact energy values are specified for Charpy V-notch test pieces (2mm striker) according to EN ISO 148-1:

Quality	Test Temp	KV min (J)	Direction	Acceptance
M quality	-20°C	40	Longitudinal	Avg ≥40J
ML quality	-50°C	27	Longitudinal	Avg ≥27J

Acceptance Criteria:

The average value of three test results shall meet the specified requirement
One individual value may be below the minimum average value, provided it is not less than 70% of that value
Three additional test pieces shall be tested if requirements not met
For subsized specimens, minimum values reduced in direct proportion to cross-sectional area

Test Piece Exemptions:

Flat products: No impact test required for thickness <6mm
Sections: No impact test required for thickness <6mm
Bars/rods: No impact test required for diameter <16mm (round) or thickness <12mm (rectangular)

Optional Requirements:

Option 24: Other impact test temperature can be agreed
Option 30: Transverse test pieces (minimum values: 20J for M, 16J for ML)
Option 13: Impact test on each parent plate/coil
Option 14: Impact and tensile test on each parent plate/coil

5.3 Through-Thickness Properties (Option 4)

If agreed upon at time of order, flat and long products shall comply with one of the requirements of EN 10164 for improved deformation properties perpendicular to the surface (Z15, Z25, or Z35).

6. TECHNOLOGICAL PROPERTIES

6.1 Weldability

All steel grades specified in EN 10025-4 shall be suitable for welding. General requirements for arc welding are given in EN 1011-2.

Cold Cracking Risk: With increasing product thickness and strength level, cold cracking can occur. Cold cracking is caused by the following factors in combination:

The amount of diffusible hydrogen in the weld metal
A brittle structure of the heat affected zone (HAZ)
Significant tensile stress concentrations in the welded joint

Important Advantage: Due to their favorable chemical composition in comparison to normalized steel at the same yield strength level, thermomechanically treated steels according to EN 10025-4 exhibit enhanced weldability compared to EN 10025-3 steels.

6.2 Formability

Hot Forming: Hot forming shall not be undertaken.

Note: Products ordered and supplied in the thermomechanical rolled condition are not suitable for hot forming as this would destroy the specially developed microstructure.

Cold Forming: Cold forming leads to reduction in ductility. Furthermore, it is necessary to draw attention to the risk of brittle fracture in connection with hot-dip zinc coating. Recommendations regarding cold forming are laid out in CEN/TR 10347.

6.3 Flangeability (Option 11)

If specified at time of order, plate, sheet, strip and wide flats with nominal thickness ≤12mm shall be suitable for flanging without cracking with the following minimum bend radii:

S275M/S355M: 2 × t (transverse), 2.5 × t (longitudinal)
S420M/S460M/S500M: 4 × t (transverse), 5 × t (longitudinal)

where t = nominal thickness

6.4 Roll Forming (Option 12)

If specified at time of order, plate, sheet and strip with nominal thickness ≤8mm shall be suitable for the production of sections by cold rolling (e.g., according to EN 10162), with the same minimum bend radii as given in 6.3. Products suitable for roll forming are also suitable for the manufacture of cold-finished square and rectangular hollow sections.

6.5 Hot-Dip Zinc Coating (Option 5)

EN ISO 14713-2 provides guidance on hot-dip galvanizing, including information on the influence of various factors, including steel chemical composition, on coating formation.

Option 5 can be used to order steels with a chemical composition required for hot-dip zinc coating. When Option 5 is implemented, the purchaser and manufacturer shall agree to a steel composition (heat analysis) of silicon and phosphorous according to either:

Category A: Si ≤ 0.03% AND Si + 2.5P ≤ 0.09%
Category B: 0.14% ≤ Si ≤ 0.25%
Category D: 0.25% < Si ≤ 0.35%

Note: The maximum carbon equivalent shall be increased by 0.02 or 0.01 (see Section 4.2).

Warning: In some cases steels above S460 may be sensitive to cracking during galvanizing and therefore special care should be taken.

7. SURFACE PROPERTIES

7.1 Strip

The surface condition should not impair an application appropriate to the steel grade if adequate processing of the strip is applied.

7.2 Plates and Wide Flats

EN 10163-1 and EN 10163-2 shall apply for the permissible surface discontinuities and for the repair of surface defects by grinding and/or welding.

Default: Class A, subclass 1 of EN 10163-2

Option 15: Class B regarding grinding or subclasses 2 or 3 regarding repair by welding can be agreed upon at time of order

7.3 Sections

EN 10163-1 and EN 10163-3 shall apply for the permissible surface discontinuities and for the repair of surface defects by grinding and/or welding.

Default: Class C, subclass 1 of EN 10163-3

Option 16: Class D regarding grinding or subclasses 2 or 3 regarding repair by welding can be agreed upon at time of order

7.4 Bars and Rods

EN ISO 9443 applies for the permissible surface discontinuities and for the repair of surface defects by grinding and/or welding.

Default: Class A of EN ISO 9443

Option 17: Other class can be agreed upon at time of order

8. INTERNAL SOUNDNESS (OPTIONAL)

Ultrasonic testing may be agreed upon at time of order for verification of internal soundness:

Option 6: Ultrasonic testing for flat products in nominal thicknesses ≥6mm, except for hot rolled strip and plate cut from strip, in accordance with EN 10160
Option 7: Ultrasonic testing for H beams with parallel flanges and IPE beams in accordance with EN 10306
Option 8: Ultrasonic testing for bars in accordance with EN 10308

9. DIMENSIONS, TOLERANCES, AND MASS

9.1 Applicable Standards

Dimensions, tolerances on dimensions and shape shall be in accordance with the requirements given in the order by reference to the following standards:

Flat Products:

Hot rolled plates: EN 10029 (Class A default, Option 18 for other)
Plates cut from strip: EN 10051 (Option 34 for EN 10029)
Strip: EN 10051
Patterned strip: EN 10363

Long Products:

I and H sections: EN 10034, EN 10365
Channels: EN 10279, EN 10365
Angles: EN 10056-1, EN 10056-2
T sections: EN 10055
Flat bars and wide flats: EN 10058
Square bars: EN 10059
Round bars: EN 10060
Hexagon bars: EN 10061
Bulb flats: EN 10067
Taper flange I sections: EN 10024
Rod: EN 10017

9.2 Nominal Mass

The nominal mass shall be determined from the nominal dimensions using a volumetric mass of 7850 kg/m³.

10. TESTING AND INSPECTION

10.1 Type of Inspection Document

Products shall be delivered with specific inspection and testing to indicate compliance with the order and this standard. The manufacturer shall obtain from the purchaser which of the inspection documents specified in EN 10204 is required:

Type	Description
Type 2.2	Test report – issued by manufacturer
Type 3.1	Inspection certificate – issued by manufacturer’s authorized inspection representative
Type 3.2	Inspection certificate – issued by manufacturer’s authorized inspection representative and independent body

Note: Unless otherwise agreed upon, steel grades of this standard are delivered with CE marking and shall fulfill not only these technical delivery conditions but also the requirements of EN 10025-1. Option 33 allows abstaining from CE-marking for products not covered by the Construction Product Regulation.

10.2 Tests to be Carried Out

The following tests shall be carried out:

Heat analysis (once per cast)
Tensile test (per test unit)
Impact test (per test unit, with thickness limitations per Section 5.2)

Additional tests can be agreed upon:

Product analysis (Option 2)
Impact test at another temperature (Option 24)
Impact test on transverse test pieces (Option 30)

10.3 Frequency of Testing

For verifying the mechanical properties, the following test unit shall apply:

Standard: 60 tonnes or part thereof
Heavy sections (>200 kg/m): 80 tonnes or part thereof
Large casts (>200 tonnes): 80 tonnes or part thereof for all sections

The test unit shall contain products of the same form, grade and quality and of the same thickness range as specified in the tensile properties tables.

10.4 Test Methods

Chemical Analysis: EN 10315, EN ISO 15350, or CR 10320

Tensile Test: EN ISO 6892-1 (method A or B)

Impact Test: EN ISO 148-1 (V-notch, 2mm striker)

11. MARKING, LABELING, AND PACKAGING

11.1 Required Marking

Products shall be legibly marked with the following information:

The grade, quality, and delivery condition (abbreviated designation)
A number by which the cast and, if applicable, the sample can be identified
The manufacturer’s name or trademark

11.2 Marking Methods

Marking may be applied using methods such as:

Painting
Stamping (die stamping)
Laser marking
Bar coding
Durable adhesive labels
Attached tags

Option 10: Special type of marking may be specified at time of order

Option 31: No die stamping or stamping at special position can be specified

11.3 Marking Location

Marking shall be at a position close to one end of each product or on the end cut face at the manufacturer’s discretion.

Where products are supplied in securely tied bundles, the marking shall be on a label attached to the bundle or on the top product of the bundle.

Note: When Option 5 for hot-dip galvanizing is chosen, the marking methods and materials used can be agreed upon to avoid interference with preparation for hot-dip galvanizing (see EN ISO 14713-2).

12. AVAILABLE OPTIONS

The following options may be specified at the time of enquiry and order. In the event that the purchaser does not indicate a wish to implement any of these options, the supplier shall supply in accordance with the basic specification.

Option	Description
1	Details of manufacturing process shall be indicated
2	Product analysis shall be carried out; frequency as agreed
4	Products shall comply with improved deformation properties perpendicular to surface (EN 10164: Z15/Z25/Z35)
5	Chemical composition for hot-dip zinc coating (Categories A, B, or D)
6	Ultrasonic testing for flat products ≥6mm per EN 10160
7	Ultrasonic testing for H/IPE beams per EN 10306
8	Ultrasonic testing for bars per EN 10308
10	Special type of marking required
11	Flangeability without cracking (≤12mm): S275/S355: 2×t (trans), 2.5×t (long); S420/S460/S500: 4×t (trans), 5×t (long)
12	Roll forming for flat products ≤8mm (same bend radii as Option 11)
13	For flat products: impact properties only verified on each parent plate or coil
14	For flat products: impact and tensile properties verified on each parent plate or coil
15	Other surface class for plates and wide flats (Class B or subclass 2/3)
16	Other surface class for sections (Class D or subclass 2/3)
17	Other surface class for bars and rods
18	For plates: other thickness tolerance than Class A (EN 10029)
24	Agreement on another impact test temperature
30	Impact properties verified on transverse test pieces (20J for M, 16J for ML)
31	Die stamping not allowed or at special position
32	Maximum S content 0.010% for heat analysis, 0.012% for product analysis (e.g., railways)
33	No application of CE-marking for products not covered by Construction Product Regulation
34	For plates cut from strip: thickness tolerances according to EN 10029

13. QUICK REFERENCE SUMMARY

13.1 Most Popular Grade Selections

S355M – Most Widely Used Thermomechanical Fine Grain Steel

355 MPa yield strength with excellent toughness (-20°C)
Ideal for bridges, offshore structures, cranes, and heavy machinery
Enhanced weldability compared to normalized steels
Cannot be normalized or hot formed after delivery

S355ML – Enhanced Low Temperature Performance

355 MPa yield strength with superior toughness (-50°C)
Arctic applications, LNG tanks, cryogenic vessels
Offshore platforms in cold climates
Best choice for extreme low temperature service

S460ML – High Strength for Weight-Critical Applications

460 MPa yield strength with low temperature toughness (-50°C)
Long-span bridges, offshore platforms, mobile cranes
Weight savings over lower strength grades
Requires more care in welding (higher CEV)

S500M/ML – NEW Ultra-High Strength (2019)

500 MPa yield strength – highest in EN 10025-4
Maximum weight optimization
Heavy machinery, mining equipment, advanced structures
Specialized welding procedures recommended

13.2 Key Advantages of Thermomechanical Rolling

Enhanced Weldability: Lower CEV values compared to normalized steels at same strength
Superior Toughness: Better impact properties through controlled rolling process
Fine Grain Structure: Grain size ≥6 ensures excellent mechanical properties
Reduced Alloying: Achieves high strength with lower alloy content
Cost-Effective: No normalizing heat treatment required after rolling

13.3 Critical Points to Remember

NO HOT FORMING: Products cannot be hot formed – destroys microstructure
NO NORMALIZING: Cannot be normalized after delivery
Delivery Condition: Thermomechanical rolled (M) – essential for properties
Fully Killed: Complete deoxidation with nitrogen binding required
Fine Grain: Grain size ≥6 mandatory (ferritic grain index)
Minimum Al: 0.020% total aluminium or equivalent N-binding elements
Impact Testing: Mandatory except thickness <6mm or diameter <16mm
ML Quality: 27J minimum at -50°C (exceptional low temperature toughness)
Cold Forming: Reduces ductility – flangeability options available
Stress Relief: Max 580°C for >1 hour to avoid property deterioration
Excellent Weldability: Cold cracking risk increases with thickness and strength
CE Marking: Typically required (Option 33 to exclude for non-CPR)
Part 4 Stand-Alone: Complete standard with all test methods and requirements

13.4 EN 10025-4 vs EN 10025-3 Comparison

Feature	EN 10025-3	EN 10025-4
Delivery Condition	N/NR (Normalized)	M (Thermomechanical)
Weldability	Good	Enhanced
Toughness	Good	Superior
Can be Normalized	Yes, after delivery	No
CEV Levels	Higher	Lower
Typical Applications	General structures	Heavy/critical structures