Answer
Laser-Cut Stainless: 304 vs 316 and How It Is Finished
Same laser, same edge, one alloying difference: how to pick the grade and write the finish on the print.
304 and 316 stainless laser cut the same way and look alike off the sheet; the difference is molybdenum. 316 carries 2-3% molybdenum, which resists pitting from chlorides, so it is the grade for marine, washdown, food and medical parts, while 304 covers indoor, dry and cost-sensitive work. Name the material and thickness on the print. A finish called out on the print is quoted with the part. Send the print for a quote in 24-48 hours.
Updated October 2026
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What separates 304 from 316: 2-3% molybdenum
The composition gap is small and the corrosion gap is not. 304 runs about 18-20% chromium and 8-11% nickel. Wikipedia’s 316 page (en.wikipedia.org/wiki/SAE_316L_stainless_steel) lists 16-18% chromium, 10-12% nickel and 2-3% molybdenum, and states that the molybdenum "provides greater corrosion resistance than 304, with respect to localized corrosive attack by chlorides." Both are austenitic and both cut on the same fiber laser with the same edge. On a print the grade is written with its sheet spec: "316L per ASTM A240".
ASTM A240/A240M (store.astm.org/a0240_a0240m-26.html) covers "chromium, chromium-nickel, and chromium-manganese-nickel stainless steel plate, sheet, and strip for pressure vessels and for general applications," and it is the specification stainless sheet is bought against. Naming it on the print settles what "stainless" means. The grade pages here, 303 and 304 and 316, cover the machined-bar side; the stainless steel hub ties the grades together.
When 304 is enough and when to pay for 316
304 is enough when the part stays indoors, dry, and away from salt and bleach. Its published limit is plain: it is subject to pitting and crevice corrosion in warm chloride environments and to stress corrosion cracking above about 60 °C (140 °F), and it is rated resistant to pitting in water up to about 400 mg/L chlorides at room temperature, falling to about 150 mg/L at 60 °C. Brackets, panels, guards and enclosures inside a building sit well within that, and 304 is the grade laser suppliers stock in the most thicknesses.
316 is the grade to write where chlorides live: marine hardware, washdown food equipment, chemical splash, and anything wiped down with chlorine-based cleaners. The same Wikipedia page lists food processing, pharmaceutical equipment, medical devices and marine applications among its common uses, which is why medical and lab parts tend to be drawn in 316 or 316L. The L grades matter for welded parts: ASTM A240 holds 304L to 0.030% carbon maximum, which prevents sensitization during welding, and 316L is the low-carbon version of 316. If a laser-cut part will be welded to the print, write the L grade.
Thickness: name it on the print
Stainless sheet is stocked in fewer thicknesses in 316 than in 304, and that gap is the practical reason a 304 quote often comes back with more options. Both grades are covered for sheet and plate by ASTM A240, which is why the grade, the spec and the thickness all belong on the print. Write the thickness as a decimal (0.125 in) rather than a gauge number, so there is only one way to read it.
Build-to-print work is not limited to a stock list: the print names the grade and thickness, and the quote covers getting that sheet, including a thickness no menu carries. Profile tolerances are covered on laser-cut tolerances; the short version is that the quote states the tolerance used on the cut, thickness follows the mill tolerance on the sheet, and anything tighter is a machined feature. Tapped holes, reamed holes and a machined edge on a stainless blank are quoted on the same order, see laser-cut, tapped and machined as one order.
The edge after laser cutting, and the magnet test
A laser-cut stainless edge is bright when cut under nitrogen and colored when oxygen gets in. Nitrogen assist keeps oxygen away from the molten edge, and yellow or brown discoloration at the edge is the sign that oxygen reached the cut. Cut edges on 304 and 316 may show gold or blue coloring, so a print that needs a clean edge says so and is quoted that way: nitrogen cutting, deburr, or passivation after the cut.
Two more things a buyer notices on receipt. The 2B mill finish on the flat faces is the rolled surface, and published sheet pages state it will not be preserved through deburring, tumbling or bead blasting, so a part that must keep 2B is drawn with a light edge break only. And a magnet may stick lightly at the edges. Austenitic grades are usually non-magnetic but can be made slightly magnetic through work hardening, and when the sheet is cut or bent magnetism appears along the edge. That is not a wrong grade; it is cold work at the cut and the bend.
Finishes and how to write them on the print
Passivation does not change how a stainless part looks. ASTM A967/A967M (store.astm.org/a0967_a0967m-25.html) covers "several different types of chemical passivation treatments for stainless steel parts," names immersion in nitric acid, immersion in citric acid and electrochemical treatment, and requires that passivated parts "show no etching, pitting, or frosting." The treatment removes free iron picked up in cutting and handling and lets the chromium oxide layer re-form. Name passivation per ASTM A967 on the print; name citric or nitric only if your spec requires one. It is quoted with the part; see the passivation page.
Cosmetic finishes are written by number. A #4 is a brushed finish polished with roughly 150-180 grit; a #8 is a mirror polished out to 320-600 grit that is non-directional and virtually free of grain lines. A #4 has a grain, so the print shows an arrow for grain direction relative to the part’s long edge; a mirror needs no arrow. Bead blast gives a uniform matte that hides rolling marks, and tumble deburr rounds the laser edge on small parts. The finish hub explains how finishes are called out.
Inspection on receipt and what to send
Every part is inspected against your print before it ships: the profile and hole positions, the edge for burr and color, and the finish against its callout, threads bare where masked. Passivation cannot be seen, so it is confirmed against the print callout on the order rather than by eye. A part that misses any callout does not ship.
To quote, send a DXF or STEP of the profile and a PDF that carries the grade (304, 304L, 316 or 316L), the ASTM A240 reference, thickness, general tolerance, the finish by name or number, grain direction if brushed, and any masked areas. Any file type is accepted; those callouts are what turn a stainless quote around in 24-48 hours with no questions back. Start at the quote form or the laser-cut parts hub: no minimum, one piece to production runs of 10,000, lead time quoted per job with rush available.
Questions
Before you send a job.
01 Is 316 harder to laser cut than 304?
No. Both are austenitic stainless and cut on the same fiber laser to the same profile tolerance with the same edge. The difference a buyer sees is stock and price: 316 sheet is carried in fewer thicknesses than 304, and the molybdenum makes it cost more.
02 Does laser cutting hurt the corrosion resistance of stainless?
It can at the edge. Oxygen in the cut leaves an oxide tint, and cutting and handling can leave free iron on the surface. Passivation per ASTM A967, in citric or nitric acid, removes the free iron and lets the chromium oxide layer re-form without changing the look of the part. Write it on the print and it is quoted with the part.
03 Why is my 304 part slightly magnetic at the edges?
Cold work. Austenitic stainless is usually non-magnetic, but work hardening can make it slightly magnetic, and a laser cut or a bend does exactly that along the edge. A magnet sticking lightly at a cut edge or bend line on a 304 or 316 part does not mean the wrong grade was used. Grade is confirmed against the print callout, not with a magnet.
04 Should I specify 304L or 316L instead of 304 or 316?
For a welded part, yes. ASTM A240 holds 304L to 0.030% carbon maximum, which prevents sensitization during welding, and 316L is the low-carbon version of 316. Sheet is often stocked to meet both the standard and L-grade limits, so asking for the L grade rarely changes the price of a laser-cut blank.
05 How do I call out a brushed finish on a laser-cut stainless part?
Write the finish number and the grain direction. "#4 brushed, grain parallel to long edge" with an arrow on the drawing view is enough; that tells every reader of the print which way the grain runs. A #8 mirror has no grain and needs no arrow. Say whether the finish is one side or both, and whether protective film stays on.
06 Which grade for food or washdown equipment?
316 or 316L. Washdown means chlorides from cleaners and sanitizers, and 304 is subject to pitting and crevice corrosion in warm chloride environments. Pair it with passivation per ASTM A967, specified on the print and quoted with the part, plus any cosmetic finish the print calls out.
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