Which Stainless Steel to Choose?
- I prefer 304, a low-carbon, austentic stainless steel for stainless steel sculptures. 304 is the primary stainless steel used for sculptures, architecture, manufacturing, etc. 304’s composition provides a better structural advantage and durability over 316, in most cases, as well as being less expensive.
- I am usually planning to weld the stainless steel and choose 304L, the low carbon version of 304. 304 and 304L are both 18-8, i. e. 18% chromium and 8% nickel. 304L has a lower carbon content (.03% maximum) than 304 which minimizes carbide precipitation occuring when welding. Consequently, 304L can be used ‘as welded’ in severe corrosion environments and eliminates the need for annealing the metal
- I usually choose the 2B finish. The 2B finish is a mill finish, which is smooth and not the brushed finish commonly seen on kitchen appliances. I do a lot of shaping, hammering and welding of the metal, which mean I have to repair the surface and create my own finish.
- 316 looks exactly like 304 but has 2-3% molybdenum added for even greater resistance to oxidation and corrosion. 316 is the preferred metal for food preparation, breweries, pharmaceuticals, laboratory use, etc. and any containers or objects that require resistance to extreme environmental conditions such as salt water, halides and acids.
- Occasionally I will use the 201 alloy of stainless steel for non-fountain, indoor sculptures. 201 is 4.5% nickel, 7% manganese and 16.3% chromium – it looks the same as 304 but is less expensive. It has a lower level of chromium and nickel than 304 but more manganese. It’s about 30 percent stronger than 304 but has less corrosion resistant and is more difficult to form and weld than 304.
Working with Stainless Steel
- Keep everything steel away from the stainless steel, including
• all steel grinding media, steel tools, steel tables, steel brushes, drills, etc
• all sparks and dust from grinding steel – keep the stainless isolated from steel sparks & dust
• A stainless steel sculpture can pick up iron particles from the forks on a forklift or steel banding or a steel roller and show rusted areas later.
- if something steel does come in contact with the metal, use a dedicated flap wheel to clean it, plus a nitric acid wash
- to remove the white plastic protecting the finish from the stainless steel
• roll it up with a dowel, adding heat with a heat gun
• for small pieces, warm water works great
- Cut with cnc-guided laser, water jet or plasma cutter. A cutting wheel on a grinder works well. Use a variable speed controller with your band saw and bi-metallic blades. I buy my 163″ band saw blades from MSC.
- for 13 gauge and thinner, I use the Makita JS3201 for hand cutting stainless steel.
- you can drill it, but go slow, back the bit out frequently and use drilling fluid. Keep the drill bit from smoking!
- Never use a grinding or polishing pad that you’ve previously used for another metal
Welding a Stainless Steel Sculpture
- First of all, choose the thickest stainless that suits your purpose! Stainless steel will warp much more than steel, bronze or aluminum. Clamp on thick heat sinks of copper or aluminum. Clamp on thick steel plates and keep them on until the weld is fully cooled. Weld braces under base tops to keep them flat.
- Welding Gas for Mig welding
• Many people use straight Argon, but this may cause globular transfer
• My favorite is Star 44 (Praxair) this is 1% CO2, 8% He and 71% Ar
• Be sure to keep CO2 less than 2%
• C25 (25% CO2 will cause rust formation after being outside for a while – the high carbon content tends to cause carbide precipitation
• Weldreality.com recommends 2% CO2, 98% Argon but this is hard to find here in Southwestern Michigan
- Use 100% Argon for Tig welding – generally, my practice is to do initial joins with Mig, repair any defects with Tig
- MIG and TIG Wire – use 308L or 308Lsi for 304 and 201 SS. The added silicon (‘si’) helps the puddle flow out better.
• Use 316L wire for 316 stainless steel
- Rapidly cool stainless steel through the 1600F – 800F range to avoid chromium carbide precipitation
• You can usually see that the hot weld has sunk – when it is cooled it pops back up to be level with the plane again. I use spray bottles for the cooling water and wet paper towels. Wet paper towels work well, hold a lot of water and you can just leave it there while you are welding elsewhere
- For stainless steel vertical welds, consider pulsed
- Use manual pulse/puddle-freeze technique when welding – don’t overheat! Manually on-off, on-off
- What I use – for 304L metal, Lincoln Electric Power Mig 300 with the push-pull python gun. I use 308Lsi wire, 100% Argon or Tri-Blend, Mode 62 setting for Spray/ Pulse, Trim = 0.50, Stall Factor = 30 and Pressure at 3 with the .030 wire. The wire feed speed varies with the thickness of the metal, from 150 up to 700 ipm, and the thickness of the wire – I am usually using .030. Mode 62 is spray mode with a very rapid on-off function. I prefer the python’s smallest 3/8″ nozzle, to see the puddle better. I do a 1-3 inch long bead with a rapid zig-zag weave then immediately cool the weld with lots of water on a wet towel, repeat until it stops sizzling. Then I move somewhere else to weld in order to balance out the heat and distortion. I brace the metal and clamp it to keep it from distorting. I stop occasionally to get any splatter off the nozzle and to clean out the tip.
- ]With Mig – when I am repairing a hole, I use a trim of 1.3 to get more penetration. Otherwise, there is a tendency for the weld to go over the hole. You grind it smooth and the hole is still there! The 1.3 trim solves that problem.
Stainless Steel Sculptures – Grinding & Finishing
- Grind asap after welding and cooling. This may have something to do with the regeneration of the chromium oxide coating. It is much easier to grind a weld you’ve done today than a weld you did yesterday. Try it and you’ll see what I mean.
- In general, Tig welds are softer than Mig welds. However, this doesn’t seem to apply to welds that are ground the same day. They seem to be about the same.
- Grinding – use 3M’s 982C Cubitron ll – this stuff if amazing. I buy it from Enco #337-1083
• it makes grinding stainless steel as easy as grinding steel.
- Don’t overheat when grinding!
• Blue color indicates overheating and a thin oxide layer
• use a variable speed grinder and drop the speed. 3500 rpm is about the fastest you want to go
• Underneath the blue oxide layer is a chromium depleted layer which can allow rust to form
• Grind it clean – don’t overheat this time – or remove the blue chemically – see your Welding Supplier
- Stainless steel cleaning and rust removal
• A sculpture friend says 1/3 muriatic acid + 2/3 water – I am skeptical – keep that chloride ion away from the iron!
• Why not use phosphoric acid aka Naval Jelly? H3PO4
• Oxalic acid with nitric might be good – that’s what I use to clean copper
• Internet says use a blend of nitric and fluoric acids to clean, then rinse – I’m skeptical – hydrofluoric acid is very dangerous, if it gets on your skin it will eat right through – you can’t wash it off – causes nerve damage
Hot Shaping Stainless Steel
Trying to roll some 3/8″ stainless and it’s too stiff? Heat it up with the oxy-acetylene torch – not red hot, just hot. It will shape nicely when warm. More on this later.
Alternatives to Welding Stainless Steel
- Nuts & Bolts
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