316 Stainless Steel Sheet Fabrication

One addition, one capability

316 sheet is 304 sheet with molybdenum added, and everything that distinguishes it follows from that.

The austenitic base gives the same forming behaviour, the same weldability and the same non-magnetic-when-annealed characteristic. The molybdenum — roughly 2–3% — changes how the oxide film behaves when chlorides are present. Chloride ions break the film down at weak points, and because the breakdown is local the attack is local: a pit rather than general wastage. Crevices are the same problem with a head start, because oxygen cannot reach the metal to repair the film. Molybdenum makes the film more resistant to that breakdown.

That is why 316 is specified by environment rather than by strength — and it is also why the grade is often specified when it is not needed, since molybdenum is an expensive addition and there are no chlorides in most fabricated equipment.

Fabrication property	316 sheet	Compared with 304
Formability	Good	Slightly less — the material is stronger
Bend radius, annealed	~0.5–1× thickness	Essentially the same
Springback	Slightly greater	304 is marginally more forgiving
Weldability	Excellent	Same, with the same L-grade rule
Chloride resistance	Excellent	304 is not a chloride grade
Cost	Higher	Molybdenum is expensive

Forming: like 304, slightly stiffer

316 forms well in the annealed condition, with minimum bend radii of roughly 0.5 to 1 times the material thickness — close to 304’s.

The difference is in the springback. 316 is slightly stronger than 304 in the annealed condition, and stronger material springs back more when the bending force is released. Combined with the fact that austenitic stainless work-hardens as it is formed — so the material in the bend is springier at the end of the operation than at the start — the effect is real and worth planning for rather than correcting.

The practical handling is the same as for 304: overbend by a calculated amount, consider bottoming or coining where the angle matters, and agree the bend allowance and springback in DFM so the flat pattern accounts for both before the blank is cut.

Welding: the 316L rule

316 welds very readily, and a welded fabrication should still be specified as 316L.

The mechanism is the same sensitisation that governs 304: welding heats a band beside the joint into the range where chromium carbides form at the grain boundaries, and those carbides strip chromium from the surrounding metal, leaving a narrow band that corrodes first. 316L holds carbon below about 0.03%, low enough that the carbides cannot form.

This matters more on 316 than on 304, because 316 is usually chosen because the environment is aggressive. A sensitised band beside a weld in a chloride-exposed assembly is the single most likely place for the part to fail — and it is entirely preventable by the grade call-out. The 316 vs 316L article works through the mechanism.

Where the sheet is dual-certified 316/316L, the question settles itself.

Finishing: the sequence matters more here

Passivation is the standard step on any fabricated stainless assembly, and on a chloride-exposed 316 part the sequence is not a detail.

Heat tint must be removed before passivation, not after. Heat tint is a chromium-depleted oxide layer, and on a welded joint it sits exactly where the sensitisation risk already is. Leaving it on a 316 weld that will see sea air or bleach is the fastest way to make the part fail at the joint rather than in the panel.

Mechanical cleaning, pickling or electropolishing all serve to remove it; the order is clean first, passivate second.

Beyond that:

• Electropolishing — smoother, brighter surface for hygienic and pharmaceutical service
• Polishing and brushing — directional or reflective finishes for visible work
• A defined mill finish — 2B, BA or No. 4 as the starting point, which affects how much finishing the part needs

Formed-feature rules

The geometric rules around a bend apply on 316 as on any formed stainless.

Holes and slots must clear the bend. A hole inside the bend zone distorts as the material stretches around the radius. The working rule is to keep a hole at least a distance of roughly two-and-a-half times the material thickness plus the bend radius away from the bend line — measured from the edge of the hole, not its centre.

Flanges have a minimum length. A flange shorter than roughly four times the material thickness cannot be formed reliably, because the press brake tooling has nothing to grip.

Bend relief prevents tearing. Where a bend runs into a corner or up to an edge, a relief notch at the end of the bend line stops the material tearing as it is stretched. On an austenitic grade the hardened material in the bend has limited stretch left, so the relief is standard practice rather than optional.

Grain direction affects the achievable radius, and where a part has a tight radius the orientation of the flat pattern is worth agreeing rather than left to the press.

Plan for springback rather than correcting it. Correcting an angle after forming means re-bending already-hardened material, which risks cracking it — and on a 316 part in chloride service, a crack is a corrosion site as well as a defect.

Where 316 sheet is the right choice

• Marine and coastal fabrications — see marine parts
• Chemical process equipment, vessels, ducting and fittings
• Pharmaceutical and hygienic plant, usually electropolished
• Food equipment cleaned with chloride-based sanitisers
• Desalination and water-treatment components
• Coastal architectural and trim work
• Any welded assembly that has to survive chlorides

Where 316 sheet is the wrong choice

There are no chlorides in the duty. 304 does the same job for less money, and the molybdenum is doing nothing. This is the most common way to overspend on a stainless fabrication.

The part sees warm, concentrated or stagnant chlorides. 316 is the minimum grade for chlorides, not a solution to every chloride problem. Where the duty is beyond it, the answer is a higher-alloy grade outside our standard range, or a change to the geometry and operating conditions.

The part must be hard or wear resistant. Austenitic stainless cannot be hardened by heat treatment.

The part’s function is to store energy or hold tension. 316 does not work-harden enough to make a spring.

The weld will be left with heat tint and no cleaning step. A 316 assembly with heat tint on the welds will corrode at the joints — which defeats the reason for choosing the grade.

The part is heavily formed and must stay non-magnetic. Cold forming makes 316 slightly magnetic.

What to put on the drawing

Instead of	Write
Stainless sheet	316, or 316L for a welded fabrication
316, welded	Specify 316L, or check whether the stock is dual-certified
316, no chlorides in service	304 costs less and does the same job
316, warm or stagnant chlorides	Review the duty — 316 has limits here
316, bend radius and angle	State the angle and tolerance — springback is slightly greater than 304’s
316, welded and exposed	State the finish — heat tint comes off before passivation
316, crevice or trapped liquid	Say so — geometry drives the risk as much as the alloy
316, needs to stay non-magnetic	Heavy forming makes it slightly magnetic

The three lines that decide most 316 sheet parts are whether chlorides are genuinely present, whether the assembly is welded, and the bend radius and angle tolerance. The first decides whether 316 is needed or 304 will do. The second decides the L. The third is the forming review, which on an austenitic grade is where springback has to be planned.

Send the drawing through the request a quote form and the reply comes back within 24 hours with DFM feedback — including a note on the grade, the bend allowances, the weld route and the finishing sequence where any of them need settling.