S355JR Structural Steel

Plain English is a quick buyer's guide. Engineer view adds the full property tables, composition and design-for-laser figures.

Overview

S355JR is a non-alloy structural steel to BS EN 10025-2, with a minimum yield strength of 355 MPa in thin sections. The "S" marks it as a structural grade, "355" the minimum yield in MPa, and "JR" a guaranteed Charpy impact value of 27 J at room temperature (+20°C). It is appreciably stronger than the more common S275JR for the same section, which means lighter or thinner parts at the same load. It welds readily, machines reasonably and is magnetic. Like all plain carbon steel it will rust, so outdoor or wet parts need painting, galvanising or another coating. It is a default choice for load-bearing brackets, base plates, frames and feeder parts for BS EN 1090 fabrication, particularly in thicker gauges.

Best for

Load-bearing brackets and base plates
Frames, gussets and structural connections
Feeder parts for BS EN 1090 fabrication
Thicker-gauge plate parts needing strength
Welded structural assemblies

Less ideal for

Outdoor parts left uncoated (it rusts)
Sub-zero impact duty (use a J0/J2 sub-grade)
Corrosive or hygienic settings (use stainless)
Lightweight parts where weight is critical (use aluminium)

Properties

BS EN 10025-2:2019

Physical

Density	7.85	g/cm³
Melting point	~1500	°C
Thermal expansion	12	×10⁻⁶/K
Modulus of elasticity	210	GPa
Thermal conductivity	~50	W/m·K
Carbon equivalent (CEV)	≤0.45	(≤16 mm)

Mechanical

Yield strength (≤16 mm)	355 min	MPa
Tensile strength	470–630	MPa
Elongation A (≥3 mm)	22 min	%
Charpy impact (+20°C)	27 min	J

Flat product (typical; yield falls as thickness rises)

Chemical Composition

BS EN 10025-2 · S355JR (1.0045), max % (ladle)

Fe Mn Si Cu C P S N

Element		% present
Iron	Fe	Balance
Manganese	Mn	0.0 – 1.60
Silicon	Si	0.0 – 0.55
Copper	Cu	0.0 – 0.55
Carbon	C	0.0 – 0.24
Phosphorus	P	0.0 – 0.035
Sulphur	S	0.0 – 0.035
Nitrogen	N	0.0 – 0.012

Formability & Fabrication

S355JR is supplied hot-rolled and is straightforward to fabricate. It welds excellently by all common processes thanks to its controlled carbon equivalent, though thicker sections may benefit from preheat to avoid cracking. It cold-forms and bends well for a structural steel, machines reasonably, and takes paint, zinc plating or galvanising readily. Being plain carbon steel it is fully magnetic.

Cold working

Good

Bending

Good

Gas welding

Good

Arc / MIG / MAG

Excellent

Resistance weld

Good

Galvanising

Good

Machinability

Fair

Hardenability

Poor

Recommended consumables: a low-hydrogen E/G 42 or 46 grade matching the steel — for example an ER70S-6 (G3Si1) MIG wire or a basic E7016/E7018 stick electrode. Use a matching or slightly over-matching filler and keep heat input controlled on thicker plate.

Corrosion Resistance

S355JR has no inherent corrosion resistance — it is plain carbon steel and will rust in damp or outdoor conditions. Indoors and dry it is stable, but any part exposed to weather, condensation or chemicals must be protected by paint, powder coat, zinc plating or hot-dip galvanising. For settings where coating is impractical, choose stainless steel or aluminium instead.

Environment	Suitability
Dry indoor / climate-controlled	Good
Atmospheric / outdoor (uncoated)	Poor
Painted or galvanised outdoor	Good
Marine / coastal (uncoated)	Avoid
Fresh water (uncoated)	Poor
Industrial / chemical	Avoid

Typical Applications

Load-bearing brackets Base & mounting plates Frames & gussets Structural connections BS EN 1090 feeder parts Machine bases & sub-frames Lifting & rigging components Heavy-gauge plate parts

Need a part in S355JR Structural Steel? Build it to your exact size for an instant price — or browse our ready-made laser-cut parts.

Build your part → Browse products

Laser Cutting & Ordering

at Metal Parts Direct

Thicknesses we cut

3 mm4 mm6 mm8 mm10 mm12 mm15 mm20 mm25 mm30 mm35 mm40 mm

Cut tolerance

±0.25 mm up to 20 mm, ±0.5 mm above

Max part size

1000 × 1000 mm

Max part weight

No maximum

Estimated delivery if ordered today

Friday 28th August 2026 – Monday 31st August 2026

UK-made Laser cut to your spec No minimum order Material certs on request

Design-for-laser quick reference

These are the exact minimums the Part Builder enforces as you design, relative to sheet thickness — so your part and your quote never disagree.

Feature	Minimum
Min hole / bore Ø	0.7 × thickness (min 1 mm)
Min slot / opening width	0.7 × thickness (min 1 mm)
Min web / wall between cuts	0.7 × thickness (min 1 mm)
Min cut-to-edge distance	0.7 × thickness (min 1 mm)

Frequently Asked Questions

What is the difference between S355JR and S275JR?

Both are weldable structural steels to BS EN 10025-2 with the same JR toughness (27 J at +20°C). The difference is strength: S355JR has a minimum yield of 355 MPa against S275JR's 275 MPa. That extra strength lets you use a thinner or lighter section for the same load, which is why S355JR is preferred for more demanding structural parts.

What does "JR" mean in S355JR?

The "JR" sets the impact toughness requirement — a Charpy V-notch value of 27 joules tested at +20°C (room temperature). Sub-grades J0 and J2 guarantee the same 27 J at 0°C and -20°C respectively, so choose J0 or J2 if the part must take impact loads in cold conditions.

Does S355JR need a coating outdoors?

Yes. S355JR is plain carbon steel with no built-in corrosion resistance, so any outdoor, damp or chemically exposed part will rust without protection. Paint, powder coat, zinc plate or hot-dip galvanise it for outdoor service, or pick stainless steel where coating is not practical.

Is S355JR easy to weld?

Yes — it is one of the most weldable structural steels, with a controlled carbon equivalent that suits all common arc processes. Use a matching low-hydrogen consumable. Thicker sections may need preheat to avoid hydrogen cracking, but for typical plate thicknesses it welds without fuss.

Why does the yield strength fall in thicker plate?

The 355 MPa minimum yield applies to sections up to 16 mm thick. As thickness increases the guaranteed minimum steps down — for example to 345 MPa over 16 mm and lower again in heavy plate — because thicker rolled sections cool more slowly and develop a coarser grain. Always check the minimum that applies to your actual thickness for structural calculations.

Equivalents

Also designated

S355JR 1.0045 BS 4360 50B (old) EN 10025-2

Cross-references are indicative and may not be exact equivalents — confirm against the certificate for critical work.

Build your part in S355JR Structural Steel

Pick a shape, set the size, choose S355JR Structural Steel — and get an instant price. Laser-cut to your spec and shipped, with no minimum order.

Build in S355JR → Browse products

This data is indicative and provided in good faith from recognised EN standards and industry references. It is not a substitute for the full specification or material certificate; mechanical properties in particular vary with temper, form and dimension. Material supplied will conform to the relevant applicable standards but may differ from these figures. No liability is accepted for actions taken in reliance on this guide. Confirm critical values against the certificate for your delivery.