Laser Cutting Stainless Steel

Fiber laser vs CO2 on stainless

Fiber lasers have largely replaced CO2 for stainless steel cutting in production shops. A 6kW fiber laser cuts 0.250" 304SS at 100–150 IPM. A 6kW CO2 laser cuts the same material at 40–60 IPM. On thin material (18 ga and under), the speed advantage is 3–5x. The fiber also has lower operating cost — no laser gas consumption, higher electrical efficiency, and less maintenance.

CO2 lasers still have an edge on thick stainless (0.500"+) where beam quality matters for edge finish, and on highly reflective alloys where older fiber systems had back-reflection problems. Modern fiber lasers (IPG, TRUMPF TruDisk, Amada) have solved the reflection issue with optical isolators, but some shops still prefer CO2 for thick stainless finishing work.

Maximum thickness by laser power

These are production-realistic maximums — not lab demonstrations. Production means the shop can run this thickness reliably at acceptable speed with good edge quality, not that the laser can technically pierce it once.

304/316 stainless steel with nitrogen assist:

4kW fiber: 0.375" max (10 mm). Speed at max: 20–35 IPM.

6kW fiber: 0.500" max (12 mm). Speed at max: 15–25 IPM.

10kW fiber: 0.750" max (20 mm). Speed at max: 10–20 IPM.

12kW fiber: 1.000" max (25 mm). Speed at max: 8–15 IPM.

15kW+ fiber: 1.250" max (30 mm). Speed at max: 5–12 IPM.

With oxygen assist (changes the process): oxygen-assisted cutting is an exothermic reaction — the oxygen burns the iron in the steel, adding energy to the cut. This allows cutting 20–30% thicker material at a given laser power. A 6kW fiber can cut 0.625–0.750" stainless with oxygen assist. But oxygen leaves an oxide layer on the cut edge that must be removed before welding or finishing. Nitrogen cutting produces an oxide-free edge.

Cut speed by thickness

6kW fiber laser, 304 stainless, nitrogen assist (production speeds, not maximum capability):

18 ga (0.048"): 600–800 IPM. 16 ga (0.060"): 450–600 IPM. 14 ga (0.075"): 300–450 IPM. 12 ga (0.105"): 200–300 IPM. 10 ga (0.135"): 150–220 IPM. 3/16" (0.188"): 80–130 IPM. 1/4" (0.250"): 50–90 IPM. 3/8" (0.375"): 25–45 IPM. 1/2" (0.500"): 12–22 IPM.

The speed drop from 18 ga to 1/2" is roughly 40:1. This is why laser cutting is dramatically cheaper on thin material and gets expensive fast as thickness increases. A part with 100" of cut length takes 8 seconds in 18 ga and 5+ minutes in 1/2".

Edge quality by thickness

Thin (18–12 ga): Clean, smooth, oxide-free edges with nitrogen assist. Minimal dross (solidified metal on bottom edge). Parts often go directly to brake press forming or welding with no secondary edge prep. Edge perpendicularity within 1°. Surface roughness Ra 60–120 µin.

Medium (10 ga – 1/4"): Good edges with minor dross that can be knocked off by hand or with a belt sander. Edge taper starts to appear — the top of the cut is wider than the bottom by 0.002–0.005". This is the kerf taper inherent to laser cutting and it increases with thickness. Surface roughness Ra 100–200 µin.

Thick (3/8" – 1/2"): Visible striations on the cut face. Dross on the bottom edge requires grinding or deburring. Edge taper of 0.005–0.010". The heat-affected zone (HAZ) extends 0.005–0.010" from the cut edge — for 304SS this causes carbide precipitation (sensitization) that reduces corrosion resistance in the HAZ. If corrosion resistance matters, specify solution annealing after cutting or use 304L (low carbon, resistant to sensitization).

Above 1/2": Edge quality degrades rapidly. Heavy striations, significant dross, edge taper exceeding 0.010", and a HAZ of 0.010–0.020". At this point, waterjet or plasma with a machine torch produces comparable or better edges at lower cost per inch of cut.

Nitrogen vs oxygen assist gas

Nitrogen (N₂): The default for stainless steel. Produces an oxide-free, bright, clean edge. Critical for food/pharmaceutical equipment (where oxide contamination is unacceptable), parts going directly to welding (oxide-free edges weld cleaner), and visible/architectural surfaces. Nitrogen consumption is high — a 6kW laser cutting 1/4" stainless uses 400–600 CFH of nitrogen at 250–350 PSI. Shops running significant stainless volume install bulk nitrogen tanks or nitrogen generators to reduce gas cost from $0.50–1.00/ft of cut to $0.10–0.20/ft.

Oxygen (O₂): Produces a faster cut but leaves an iron oxide layer (dark discoloration) on the cut edge. The oxide must be removed by grinding, pickling, or passivation before welding or use in corrosive environments. Oxygen assist is appropriate when: the parts will be ground or machined after cutting, the edge finish doesn't matter aesthetically, or you need to cut thicker material than your laser power supports with nitrogen alone.

Shop air / clean dry air: Some shops use compressed air (78% nitrogen, 21% oxygen) as a cheaper alternative. Edge quality falls between pure nitrogen and pure oxygen. Acceptable for non-critical work where slight oxidation is tolerable.

Stainless grades and their quirks

304/304L: The standard. Cuts well on laser. No special considerations for thin material. Use 304L for thick sections where HAZ sensitization matters.

316/316L: Slightly slower cut speeds than 304 due to molybdenum content — about 5–10% slower. Edge quality is comparable. Same nitrogen/oxygen considerations as 304.

430 (ferritic): Easier to cut than 304 — lower nickel content means better thermal conductivity and faster heat extraction. Cuts 10–15% faster. Edge quality is excellent.

410/420 (martensitic): Cuts well but the HAZ will harden. If the part will be bent after cutting, the hardened HAZ can crack at the bend line. Anneal before forming, or position bends away from the cut edge.

Duplex (2205, 2507): Cuts 15–20% slower than 304. The mixed austenite-ferrite microstructure produces more dross. Increase nitrogen assist pressure by 20–30% to improve bottom-edge quality.

When to switch processes

Waterjet instead of laser when: thickness exceeds 1/2", no HAZ is acceptable at any thickness, the part requires tight tolerances on thick material (waterjet holds ±0.003" on 1" stainless), or the part has features that would overheat with laser (small tabs, narrow peninsulas).

Plasma instead of laser when: thickness exceeds 3/4", tolerances are ±0.010" or looser, high production volume on thick plate (plasma is 2–3x faster than laser above 1/2" and the machines cost less to operate), or edge quality is secondary to speed.

Laser stays competitive when: thickness is under 1/2", tolerances are ±0.005" or tighter on thin material, hole quality matters (laser produces cleaner holes than waterjet in thin material), or nitrogen-clean edges are required for welding or hygiene.