EN 10025-6 Standard Guide

Technical Delivery Conditions for Flat Products of High Yield Strength Structural Steels in the Quenched and Tempered Condition

1. Scope and Application

This standard specifies technical delivery conditions for flat products of high yield strength alloy special steels supplied in the quenched and tempered (Q+T) condition. These steels are designed for applications requiring high strength combined with good toughness.

1.1 Product Forms

Hot-rolled plates
Wide flats
Sheet
Strip

1.2 Thickness Range

Minimum nominal thickness: 3 mm
Maximum nominal thickness:

– S460, S500, S550, S620, S690: 200 mm – S890, S960: 125 mm

2. Steel Grades and Qualities

EN 10025-6 includes seven steel grades differentiated by their minimum yield strength, with three impact toughness qualities for each grade.

2.1 Grade Classification

Grade	Min. Yield Strength (MPa)	Description
S460	460	Standard high strength grade
S500	500	Medium high strength grade
S550	550	High strength grade
S620	620	Very high strength grade
S690	690	Very high strength grade
S890	890	Ultra-high strength grade (max 125 mm)
S960	960	Ultra-high strength grade (max 125 mm)

2.2 Quality Designations

Quality	Impact Test Temperature	Typical Application
Q	-20°C	Standard toughness
QL	-40°C	Low temperature toughness
QL1	-60°C	Very low temperature toughness

2.3 Complete Grade List with Steel Numbers

Steel Name	Steel Number	Quality
S460Q	1.8908	Q
S460QL	1.8906	QL
S460QL1	1.8916	QL1
S500Q	1.8924	Q
S500QL	1.8909	QL
S500QL1	1.8984	QL1
S550Q	1.8904	Q
S550QL	1.8926	QL
S550QL1	1.8986	QL1
S620Q	1.8914	Q
S620QL	1.8927	QL
S620QL1	1.8987	QL1
S690Q	1.8931	Q
S690QL	1.8928	QL
S690QL1	1.8988	QL1
S890Q	1.8940	Q
S890QL	1.8983	QL
S890QL1	1.8925	QL1
S960Q	1.8941	Q
S960QL	1.8933	QL
S960QL1	1.8934	QL1

3. Manufacturing Process

3.1 Steel Making

Any steel making process is permitted except the open hearth (Siemens-Martin) process. Common methods include basic oxygen steelmaking (BOS) and electric arc furnace (EAF).

3.2 Deoxidation

Fully killed steel (completely deoxidized)
Fine grain structure required
Nitrogen binding elements in sufficient amounts (typically min. 0.020% total aluminum)

3.3 Delivery Condition

All products are supplied in the quenched and tempered (Q+T) condition:

Quenching: Rapid cooling from austenitizing temperature (more rapid than in still air)
Tempering: Reheating to specific temperature below Ac1 to achieve required properties

Note: Direct quenching after hot-rolling followed by tempering is considered equivalent to conventional quenching and tempering.

4. Chemical Composition (Heat Analysis)

Maximum chemical composition limits apply to all grades. The manufacturer may add alloying elements up to specified maximum values to achieve required properties.

Element	C	Si	Mn	P	S	N	B	Cr	Cu	Mo	Nb	Ni	Ti	V	Zr
Max %	0.20	0.80	1.70	0.025	0.020	0.020	0.0015	0.010	0.010	0.015	0.0050	1.50	0.050	0.12	0.15

Note: Nitrogen binding elements (Nb, Ti, V, Zr) shall be present in sufficient amounts to bind available nitrogen. Usual guideline: minimum Al:N ratio of 2:1 when no other nitrogen binding elements are present.

5. Carbon Equivalent Values (CEV)

CEV is calculated using the IIW (International Institute of Welding) formula: CEV = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15

Grade	≤50 mm	>50-100 mm	>100-125 mm	>125-200 mm
S460Q, S460QL, S460QL1	0.47	0.48	0.50	0.50
S500Q, S500QL, S500QL1	0.47	0.70	0.70	0.70
S550Q, S550QL, S550QL1	0.65	0.77	0.83	0.83
S620Q, S620QL, S620QL1	0.65	0.77	0.83	0.83
S690Q, S690QL, S690QL1	0.65	0.77	0.83	0.83
S890Q, S890QL, S890QL1	0.72	0.82	0.83	–
S960Q, S960QL, S960QL1	0.82	0.85	0.85	–

Note: For products with controlled Si content for hot-dip zinc coating, CEV values shall be increased as specified in the standard.

6. Mechanical Properties

6.1 Tensile Properties

Tensile properties vary by grade and nominal thickness. Values shown are minimum requirements at room temperature.

Grade	Min. Yield Strength ReH (MPa)				Tensile Strength Rm (MPa)				Min. Elong. %
Thickness (mm)	3-50	50-100	100-125	125-200	3-50	50-100	100-125	125-200	Min. Elong. %
S460Q, S460QL, S460QL1	460	440	–	400	550-720	550-720	–	500-670	17
S500Q, S500QL, S500QL1	500	480	–	440	590-770	590-770	–	540-720	17
S550Q, S550QL, S550QL1	550	530	–	490	640-820	640-820	–	590-770	16
S620Q, S620QL, S620QL1	620	580	–	560	700-890	700-890	–	650-830	15
S690Q, S690QL, S690QL1	690	650	630	630	770-940	760-930	760-930	710-900	14
S890Q, S890QL, S890QL1	890	830	830	–	940-1100	880-1100	880-1100	–	11
S960Q, S960QL, S960QL1	960	850	850	–	980-1150	900-1100	900-1100	–	10

6.2 Impact Properties (Longitudinal Test Pieces)

Minimum average impact energy values in Joules for standard 10mm x 10mm V-notch test pieces. For subsized specimens, values are reduced in direct proportion to cross-sectional area.

Quality	Test Temp.	S460-S690	S890	S960
Q	-20°C	30 J	30 J	30 J
QL	-40°C	30 J	30 J	30 J
QL1	-60°C	30 J	30 J	30 J

Testing Requirements: • Average of three test results must meet specified requirement • One individual value may be below minimum average, but not less than 70% of that value • No impact tests required for nominal thickness < 6 mm

7. Technological Properties

7.1 Weldability

These steels do not have unlimited suitability for all welding processes. Weldability depends on material properties, dimensions, shape, and manufacturing/service conditions. General requirements for arc welding are given in EN 1011-2.

Important welding considerations: • Cold cracking risk increases with product thickness and strength level • Cold cracking is caused by combination of: diffusible hydrogen, brittle HAZ structure, and tensile stress concentrations • Proper preheating and welding procedures essential for higher strength grades • Consult EN 1011-2 for detailed welding recommendations

7.2 Formability

7.2.1 Hot Forming

Hot forming is not recommended for quenched and tempered steels, as the necessary heat treatment after hot forming is very difficult to reproduce.

7.2.2 Cold Formability

Cold forming is possible but leads to reduction in ductility. Special care should be taken regarding brittle fracture risk, particularly in connection with hot-dip zinc coating. Flangeability specifications available for products ≤16 mm nominal thickness.

7.2.3 Flame Straightening

Recommendations for flame straightening are provided in CEN/TR 10347.

7.3 Hot-Dip Zinc Coating

When hot-dip zinc coating is required, special chemical composition control is necessary (Option 5). Agreement between purchaser and manufacturer required for silicon and phosphorus content. Note: Products quenched in water may be susceptible to stress corrosion cracking after hot-dip zinc coating. Special care needed for grades above S460.

7.4 Stress Relief Treatment

If stress relief treatment is intended, the maximum temperature should be at least 30°C below the tempering temperature and not held for more than 1 hour. Contact steel producer before stress relief treatment, as tempering temperature is normally not known in advance.

8. Tolerances and Surface Properties

8.1 Dimensional Tolerances

Tolerances shall be in accordance with:

EN 10029 for hot rolled plates (Class A thickness tolerance unless otherwise agreed)
EN 10048 for hot rolled narrow strip
EN 10051 for continuously hot-rolled strip and plate cut from wide strip

8.2 Surface Properties

Permissible surface discontinuities and repair of surface defects by grinding and/or welding shall be in accordance with EN 10163-1 and EN 10163-2. Class A, subclass 1 applies unless otherwise agreed at time of order.

8.3 Internal Soundness

Ultrasonic testing may be specified at time of order in accordance with EN 10160 for flat products with nominal thickness ≥6 mm (excluding hot rolled strip and plate cut from strip).

9. Inspection and Testing

9.1 Standard Tests

The following tests shall be carried out:

Heat analysis: Once per cast
Tensile test: One per test unit (60 tonnes or part thereof)
Impact test: One per test unit for products ≥6 mm thickness

9.2 Test Unit Definition

Test unit shall be 60 tonnes or part thereof, containing products of same form, grade, and thickness range. Nominal thickness within test unit shall not deviate more than 5 mm from sample product thickness.

9.3 Sample Location

Tensile test pieces: Longitudinal for width ≥600 mm, transverse for width <600 mm
Impact test pieces: Longitudinal with axis at 1/4 thickness for plates ≥40 mm
For nominal thickness >40 mm: Impact test pieces from 1/4 thickness position

9.4 Optional Tests

Additional tests available by agreement at time of order:

Product analysis (chemical composition verification)
Impact testing at other temperatures
Impact testing on transverse test pieces
Testing for each heat treatment unit
Improved deformation properties perpendicular to surface (Z-grade)
Ultrasonic testing
Flangeability verification (≤16 mm thickness)

10. Grade Selection Matrix

This table helps select appropriate grades based on application requirements:

Requirement	Recommended Grades	Quality	Application Examples
High strength, standard toughness	S460-S690	Q	General structural applications
Low temperature service	S460-S690	QL, QL1	Cold climate structures, offshore
Ultra-high strength	S890, S960	Q, QL, QL1	Heavy mobile equipment, cranes
Weight reduction critical	S620-S960	Q, QL, QL1	Transport vehicles, mobile cranes
Good weldability needed	S460-S550	Q, QL, QL1	Welded structures, bridges
Thick sections (>125mm)	S460-S690	Q, QL, QL1	Heavy machinery, large structures

11. Important Notes and Warnings

11.1 Safety Considerations

Brittle fracture risk: Cold forming and hot-dip zinc coating increase brittle fracture risk
Stress corrosion: Products quenched in water may be susceptible after hot-dip zinc coating
Cold cracking in welding: Risk increases with thickness and strength level

11.2 Processing Limitations

Hot forming generally not recommended (heat treatment difficult to reproduce)
Cold forming causes ductility reduction
Stress relief treatment requires coordination with steel producer
Grades above S460 require special care for hot-dip galvanizing

11.3 Ordering Requirements

When ordering, specify:

Product form and dimensions
Steel designation (grade and quality)
Type of inspection document required
Any optional requirements (see Section 9.4)
Special requirements for hot-dip coating if applicable

12. Reference Standards

This guide is based on BS EN 10025-6:2019. For complete technical requirements and detailed specifications, always refer to the full standard. Related standards:

EN 10025-1: General technical delivery conditions
EN 10027-1: Steel designation systems – Steel names
EN 10027-2: Steel designation systems – Numerical system
EN 10029: Hot-rolled steel plates – Tolerances
EN 10160: Ultrasonic testing of steel flat products
EN 10163-1, 10163-2: Surface condition requirements
EN 10164: Improved deformation properties perpendicular to surface
EN 1011-2: Welding recommendations for ferritic steels
EN ISO 14713-2: Hot-dip galvanizing guidelines
CEN/TR 10347: Guidance for forming of structural steels