Cold working
Excellent
01
Overview
Pre-galvanised steel is ordinary low-carbon mild steel that has been hot-dip zinc coated as a continuous coil before it reaches us, so every flat face arrives with built-in corrosion protection. The usual substrate is DX51D, a soft forming grade chosen for how well it bends and folds rather than for high strength, and the common coating is Z275 — 275 g/m² of zinc spread across both sides, roughly 20 µm per face. That coating is the whole point: it lets parts live outdoors or in damp conditions without painting or plating. It is a workhorse for ducting, electrical enclosures and outdoor brackets. Where you need higher strength choose a structural grade such as S275JR or S355JR; where the cut edges must never show any rust, a fully galvanised or stainless option is better, because laser-cut edges are bare steel.
Best for
- Ducting, trunking and ventilation parts
- Electrical enclosures and back-boxes
- Outdoor and damp-location brackets
- Cable trays, baskets and trays
- Folded parts that need rust protection without painting
Less ideal for
- Highly-stressed structural members (use S275JR / S355JR)
- Parts where bare cut edges must never rust (use stainless)
- Cosmetic, paint-grade visible surfaces without preparation
- Food-contact or hygienic surfaces (use stainless 304/316)
02
Properties
BS EN 10346:2015Physical
| Density | 7.85 | g/cm³ |
| Melting point (steel) | ~1450 | °C |
| Thermal expansion | 12 | ×10⁻⁶/K |
| Modulus of elasticity | 210 | GPa |
| Thermal conductivity | ~50 | W/m·K |
| Zinc coating thickness | ~20 | µm/side |
Mechanical
| Tensile strength | 270–500 | MPa |
| Proof stress (Re) | 140–300 | MPa |
| Elongation A80 | 22 min | % |
| Coating weight Z275 | 275 | g/m² |
DX51D+Z substrate (forming grade; figures indicative)
03
Chemical Composition
BS EN 10346 · DX51D substrate (steel; zinc coating is a surface layer)
Fe
C
Mn
Ti
P
S
| Element | % present | |
|---|---|---|
| Iron | Fe | Balance |
| Carbon | C | 0.0 – 0.18 |
| Manganese | Mn | 0.0 – 1.20 |
| Titanium | Ti | 0.0 – 0.30 |
| Phosphorus | P | 0.0 – 0.12 |
| Sulphur | S | 0.0 – 0.045 |
04
Formability & Fabrication
Pre-galvanised steel forms very well cold — the DX51D substrate is a dedicated forming grade, so it bends and folds cleanly and tolerates tight radii without cracking. The zinc coating flexes with the steel on normal bends, keeping its protection on the formed face. It welds readily, though the zinc burns off around the weld and gives off fumes, so weld in good ventilation and re-protect the bare zone afterwards. Machinability is fair, as for mild steel generally.
Bending
Excellent
Gas welding
Good
Arc / MIG / MAG
Good
Resistance weld
Good
Brazing
Good
Soldering
Good
Machinability
Fair
Recommended filler: standard mild-steel wire such as ER70S-6 (G3Si1) for MIG/MAG work. Clean the zinc back from the weld line first, weld in good ventilation as the coating produces zinc fumes, and re-coat the bare weld zone with a zinc-rich paint to restore protection.
05
Corrosion Resistance
The zinc coating gives pre-galvanised steel good resistance in normal outdoor and damp conditions without any further treatment — the zinc weathers slowly and also protects the steel sacrificially, so small scratches and the bare laser-cut edges are guarded for a time by the surrounding coating. It is not stainless, however: in salt spray, constant immersion or aggressive chemical conditions the zinc is consumed faster and the part will eventually rust. For long outdoor life the coating can be over-painted; for the harshest service choose stainless.
| Environment | Suitability |
|---|---|
| Dry indoor / sheltered | Excellent |
| Atmospheric / outdoor | Good |
| Damp / condensing | Good |
| Industrial / polluted air | Fair |
| Marine / coastal salt | Fair |
| Salt-water immersion | Poor |
06
Typical Applications
Ducting & ventilation parts
Electrical enclosures & back-boxes
Cable trays & baskets
Outdoor brackets & fixings
Trunking & cable management
Roofing & cladding sub-frames
Folded trays & chassis parts
General sheet-metal fabrication
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07
Laser Cutting & Ordering
at Metal Parts DirectThicknesses we cut
0.9 mm1.2 mm1.5 mm2 mm2.5 mm3 mm4 mm5 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) |
08
Frequently Asked Questions
Will the laser-cut edges rust?
The cut edge is bare steel — the laser burns through both the steel and its zinc coating, so the freshly cut edge has no zinc on it. In practice the surrounding coating gives that edge some sacrificial protection for a while, so light indoor or sheltered use is usually fine. For long outdoor life, exposed edges should be painted or treated with a zinc-rich primer.
What is the difference between pre-galvanised and hot-dip galvanised after cutting?
Pre-galvanised (or pre-galv) steel is zinc-coated as a flat coil before it is cut, so the faces are protected but the cut edges are bare. Dipping a finished part in molten zinc after cutting (batch hot-dip galvanising) coats every surface including the edges, but it is a separate post-process — pre-galv sheet is the ready-coated material we cut from.
Is pre-galvanised steel the same as Zintec?
No — they are related but different. "Zintec" is an electro-galvanised steel with a thin, even zinc layer mainly for indoor use and painting. The pre-galv sheet here is hot-dip coated (typically Z275), which puts down a thicker zinc layer and gives better outdoor corrosion resistance.
Does the Z275 coating need painting?
Not for normal use — Z275 means 275 g/m² of zinc across both faces, roughly 20 µm per side, and that is enough to protect parts outdoors or in damp conditions on its own. Painting is optional: it extends the life further and is worth doing on cut edges or in harsher, salty or polluted environments.
Is it magnetic?
Yes. It is mild steel with a zinc coating, so it is fully magnetic and works with magnetic clamps, sensors and fixings.
Can I weld pre-galvanised steel?
Yes, but the zinc burns off around the weld and produces fumes, so weld in good ventilation and clean the zinc back from the joint first. After welding, re-protect the bare weld zone with a zinc-rich paint to restore corrosion resistance.
09
Equivalents
Also designated
DX51D+Z
1.0226
Z275
BS EN 10346
Galv / pre-galv
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.