S275JR Mild Steel

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

Overview

S275JR is a hot-rolled, non-alloy structural steel to BS EN 10025-2 — the everyday mild steel of UK fabrication. It offers a guaranteed minimum yield of 275 MPa in thinner sections, good ductility and excellent weldability, which makes it the natural pick for brackets, base plates, frames and general structural parts. The "JR" denotes a minimum 27 J Charpy impact value tested at +20 °C. It is supplied either self-colour (with the dark mill scale left on) or descaled-and-oiled with the scale removed for a cleaner surface. Where you need higher strength step up to S355JR; where rust resistance or a bright surface matters, choose a stainless or aluminium grade instead — bare mild steel will corrode outdoors and needs paint, galvanising or another coating.

Best for

Brackets, base plates and gussets
Fabricated frames and weldments
General structural and machine parts
BS EN 1090 feeder parts and sub-assemblies
Folded and bent components (medium duty)

Less ideal for

Higher-load structural members (use S355JR)
Bare outdoor or wet use without a coating
Corrosive or hygienic environments (use stainless)
Lightweight parts where weight matters (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	~52	W/m·K
Magnetic	Yes	ferromagnetic

Mechanical

Yield strength (ReH)	275 min	MPa
Tensile strength (Rm)	410–560	MPa
Elongation A (≥3 mm)	23 min	%
Charpy impact at +20 °C	27 min	J

Hot-rolled (≤16 mm; yield falls as thickness rises)

Chemical Composition

BS EN 10025-2 · S275JR (1.0044) · product analysis, max %

Fe Mn Cu C P S N

Element		% present
Iron	Fe	Balance
Manganese	Mn	0.0 – 1.50
Copper	Cu	0.0 – 0.55
Carbon	C	0.0 – 0.21
Phosphorus	P	0.0 – 0.035
Sulphur	S	0.0 – 0.035
Nitrogen	N	0.0 – 0.012

Formability & Fabrication

S275JR cold-forms and bends well for general fabrication and tolerates the press-brake radii used on everyday brackets and folded parts. With a low carbon content it is very weldable by all common processes — MIG/MAG, MMA (stick) and TIG — usually without preheat in normal thicknesses. Machinability is fair, typical of a low-carbon mild steel. The self-colour finish carries loose mill scale that is best removed before painting; descaled-and-oiled stock is already clean for a better weld and paint surface.

Cold working

Good

Bending

Good

Gas welding

Good

Arc / MIG / MMA

Excellent

Resistance weld

Good

Brazing

Good

Soldering

Fair

Machinability

Fair

Recommended consumables: ER70S-6 wire for MIG/MAG and E7018 electrodes for MMA suit S275JR and match the parent strength. No preheat is normally needed at typical sheet and plate thicknesses; keep joints clean of mill scale, oil and any residual film on descaled-and-oiled stock.

Corrosion Resistance

S275JR is a plain carbon steel with no inherent corrosion resistance — left bare it rusts readily in damp air and outdoors, so it almost always needs a protective coating such as paint, powder coat, galvanising or plating. The self-colour finish wears a layer of mill scale that gives short-term cover but flakes and is no substitute for proper protection; descaled-and-oiled stock has a light oil film that guards against rust in storage only. For wet, marine or corrosive service choose stainless steel instead.

Environment	Suitability
Dry indoor (heated)	Good
Indoor (unheated / humid)	Fair
Atmospheric / outdoor (bare)	Poor
Fresh water	Poor
Marine / coastal (bare)	Avoid
Salt-water immersion	Avoid

Typical Applications

Brackets & gussets Base & mounting plates Fabricated frames & weldments Machine guards & bases BS EN 1090 feeder parts General structural parts Folded trays & enclosures Sub-assemblies for painting

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Laser Cutting & Ordering

at Metal Parts Direct

Thicknesses we cut

3 mm4 mm5 mm6 mm8 mm10 mm12 mm15 mm20 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 S275JR and S355JR?

Both are weldable structural mild steels to BS EN 10025-2 with similar chemistry and handling. S355JR is stronger — a minimum yield of 355 MPa against 275 MPa for S275JR — so it carries more load for the same section. Choose S275JR for general fabrication and step up to S355JR where the part is more heavily loaded.

What does the "JR" mean?

The letters give the impact (toughness) grade. JR means a minimum Charpy V-notch impact value of 27 J tested at +20 °C. Tougher sub-grades — J0 (0 °C) and J2 (−20 °C) — are tested colder for low-temperature duty.

What is the difference between the dry (self-colour) and descaled-and-oiled finishes?

Self-colour, or dry, steel keeps the dark blue-grey mill scale from hot rolling — fine for general work, but the scale should be removed before painting or critical welding. The descaled-and-oiled finish has had the scale acid-removed and a light protective oil applied, giving a cleaner, more uniform surface that paints and welds better.

Does S275JR need painting or coating?

Yes, for anything but dry indoor use. Bare mild steel rusts in damp conditions, so parts are normally painted, powder-coated, galvanised or plated. The mill scale and storage oil offer only temporary protection.

Is S275JR suitable for BS EN 1090 fabrication?

Yes — it is a CE/UKCA-markable structural steel covered by BS EN 10025-2 and widely used for EN 1090 work. We can supply laser-cut feeder parts; your fabricator handles the execution-class requirements and documentation for the finished assembly.

Equivalents

Also designated

S275JR 1.0044 BS 4360 43A BS 4360 43B Fe430B

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

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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.