Three alloys, three different jobs
In a workshop that cuts and welds stainless steel three items in the store are usually enough. 308L for chromium nickel steels of the 18/8 type, 316L for steels with molybdenum and 309L for typical joints of stainless steel with non alloy steel. Dissimilar joints outside that pattern, for example with high strength steels or working at high temperature, need a separate selection. The rest of the catalogue covers special cases.
The rule of selection is simple: the weld metal is to have a composition close to the parent material or richer, never poorer. A loss of chromium and nickel in the weld means that the joint will corrode first, even if the rest of the structure lasts twenty years.
Selection by steel grade
1.4301 and 1.4307, the classic 18/8
For 1.4301 (X5CrNi18-10, the equivalent of AISI 304) and 1.4307 (X2CrNi18-9, that is 304L) you use weld metal of the 308L type. This is the most common case in sheet metal work, on balustrades, water tanks and kitchen structures.
You recognise the form by the classification letter, not by the trade name: G is a solid wire for MIG/MAG, W is a rod for TIG. The same 308L alloy comes in both forms, and each of them also has a variant with raised silicon. In the catalogue of voestalpine Böhler Welding, Thermanit JE-308L Si appears both as the solid wire G 19 9 L Si and as the TIG rod W 19 9 L Si; both carry the AWS number ER308LSi.
1.4401 and 1.4404, the steels with molybdenum
For 1.4401 (X5CrNiMo17-12-2, AISI 316) and 1.4404 (X2CrNiMo17-12-2, that is 316L) you need weld metal 316L. Molybdenum in the composition raises the resistance to pitting corrosion, so this is the material for installations with chlorides, for the food industry with chemical cleaning and for structures by the sea.
Do not replace 316L with wire 308L, because you will lose the molybdenum in the weld and move the point of corrosion exactly into the joint. The opposite substitution, that is 316L for 1.4301, is technically acceptable but dearer for no reason.
Dissimilar joints and black steel
309L is a transition alloy. It has about 23 percent chromium and 12 percent nickel, so a reserve of ferrite forming and austenite forming elements compared with 308L. Thanks to that, after dilution with the parent material the weld more often falls within the austenitic ferritic range, where a few percent of delta ferrite lowers the risk of hot cracking. You use it where stainless steel meets non alloy steel.
Typical uses: welding a stainless flange to a black pipe, repair of linings, a buffer layer before surfacing with austenite, joining 1.4301 to steel S235.
What happens with 308L on such a joint: the weld diluted with iron from the black steel becomes poorer in chromium and nickel and moves towards the range in which martensite may appear. How far it moves depends on the share of the parent material in the weld, on the composition of both materials and on the welding parameters. This is a risk to be calculated, not a certainty: the direction is shown by the Schaeffler and WRC-1992 diagrams, but the result is settled by the actual dilution in your joint. That is why on dissimilar joints you take 309L with a reserve instead of counting on 308L to work out.
Matching table
| Parent material | Type of weld metal | EN ISO | AWS | Böhler product |
|---|---|---|---|---|
| 1.4301, 1.4307 (304, 304L) | 308L | G 19 9 L Si, TIG rod W 19 9 L Si | ER308LSi | BÖHLER EAS 2-IG (Si), Thermanit JE-308L Si |
| 1.4401, 1.4404 (316, 316L) | 316L | G 19 12 3 L Si, TIG rod W 19 12 3 L Si | ER316LSi | BÖHLER EAS 4 M-IG (Si), Thermanit GE-316L Si |
| Stainless steel to non alloy steel | 309L | G 23 12 L | ER309L | BÖHLER CN 23/12-IG |
| 1.4301 to 1.4404 | 316L | G 19 12 3 L Si | ER316LSi | BÖHLER EAS 4 M-IG (Si) |
| Repairs, dissimilar joints, buffer layers | 307 | G 18 8 Mn, TIG rod W 18 8 Mn | ER307 (mod.) | BÖHLER A 7 CN-IG |
What 307 can really do
The last row is the item that repair workshops reach for, but it is not a wire that settles every unknown material. The data sheet of BÖHLER A 7 CN-IG (edition 08/2024) gives a specific scope: repair and maintenance, dissimilar joints, buffer layers before surfacing, manganese steels, chromium steels of 13 to 17 percent and heat resistant steels up to 850 degrees, high carbon steels and quenched and tempered steels. For austenitic ferritic joints the manufacturer gives a maximum working temperature of 300 degrees, and tells you to match the preheating and the interpass temperature to the parent material. Gas: argon with an addition of CO2 up to 2.5 percent.
A high manganese content, typically 7 percent, lowers the tendency of the weld metal to crack and allows a larger dilution than 308L, but this is still a risk that depends on what the parent material really is. When repairing a part responsible for safety or working under pressure, establish the grade before welding: from the documentation, from the marking of the product, from the material certificate or from a composition test with a spectrometer. Without identification of the material there is no WPS and no basis for acceptance.
Stabilised grades
1.4541 (X6CrNiTi18-10, that is 321) and 1.4571 (X6CrNiMoTi17-12-2, that is 316Ti) contain an addition of titanium, which binds carbon instead of chromium. For them you use weld metal stabilised with niobium, type 347 for 1.4541 and type 318 for 1.4571, in the Böhler line SAS 2-IG and SAS 4-IG respectively.
The data sheet of Thermanit GE-316L Si gives this alloy also for steels stabilised with titanium, such as 1.4571, at a working temperature up to 400 degrees; above that the manufacturer requires weld metal stabilised with niobium, for example BÖHLER SAS 4-IG (Si). You do not jump over that limit with a workshop shortcut.
Ferrite in the weld metal and the risk of hot cracking
Weld metal that solidifies fully as austenite is more prone to hot cracking. During solidification sulphur and phosphorus gather at the grain boundaries, and with the shrinkage the weld can tear along the axis of the run. A few percent of delta ferrite in the structure reduces that risk, because ferrite dissolves sulphur and phosphorus and breaks up the continuous grain boundaries.
The risk is not constant. It grows with the content of sulphur and phosphorus in the parent material and in the weld metal, with the dilution, with a high heat input, with a high interpass temperature and with an unfavourable shape of the run, that is narrow and deep. It falls when you keep the heat input low, fill the craters and hold the share of ferrite.
That is why the weld metals 308L and 316L are set up to give a few percent of ferrite, and 309L more. The data sheet of Thermanit GE-316L Si gives an austenitic structure with 5 to 10 percent ferrite, a typical value of 7 FN to WRC-92, a heat input up to 2.0 kJ/mm and an interpass temperature up to 150 degrees. These are numbers of the manufacturer for a specific product, not a rule for all stainless steel: check the data sheet of your own consumable.
The practical sign of a lack of ferrite is a longitudinal crack in the middle of the face, usually in the crater at the end of the run. If you see it with the correct consumable, check first the dilution with the parent material, the heat input, the interpass temperature and the filling of craters.
What L means and what Si means
L, that is lowered carbon
The letter L means at most 0.03 percent carbon in the weld metal. There is one reason: during cooling through the range of about 450 to 850 degrees carbon binds chromium into carbides at the grain boundaries. Chromium then stops protecting the steel and the joint corrodes intergranularly, usually along the fusion line.
On thin sheet and a single run the problem is small. On multi run welds on thick material, where every next layer heats the previous one, the version without L is sometimes a mistake that is not seen through the first two years of the installation working.
Si, that is raised silicon
Si in the name and in the code means one thing: a raised content of silicon in the consumable. Silicon lowers the surface tension of the pool, so the weld metal is more fluid, wets the edges better, gives a flat face and less undercut. The price is more silicates on the face, which have to be removed before pickling or painting.
Si says nothing about the process. Variants with raised silicon come both in wires for MIG/MAG and in rods for TIG. In the catalogue of voestalpine Böhler Welding the same product is sometimes catalogued directly in both forms: Thermanit GE-316L Si appears as the solid wire G 19 12 3 L Si and as the TIG rod W 19 12 3 L Si, in both cases with the AWS number ER316LSi. The same goes for Thermanit JE-308L Si (G and W 19 9 L Si, ER308LSi) and Thermanit H-347 Si (G and W 19 9 Nb Si, ER347Si).
So the form of the product is told by the letter at the start of the code: G is a solid wire for MIG/MAG, W is a rod for TIG. The trade name and the Si suffix do not settle it. In TIG raised silicon makes sense as well, because a more fluid pool is easier to spread, only the benefit is smaller than in MIG/MAG, where the wetting of the edges happens by itself from the arc parameters.
Watch one detail: BÖHLER CN 23/12-IG is classified as G 23 12 L and ER309L, without the Si symbol. Variants 309LSi exist in other lines, so if your WPS says ER309LSi, check the code on the label and not the trade name alone.
The shielding gas without which the rest does not matter
| Process | Gas | Notes |
|---|---|---|
| MIG/MAG, spray and pulsed arc | argon with a small addition of CO2, roughly 2 percent (group M12) | stable arc, minimal carburising of the weld |
| MIG/MAG, alternative | argon with an addition of oxygen, roughly 2 percent (group M13) | smoother face, darker discoloration to be pickled |
| TIG | argon (I1) | purity at least 99.99 percent |
| Root shielding | argon or a mixture with nitrogen | without it the root oxidises and loses corrosion resistance |
| What not to use | pure CO2 (C1) | carburises the weld metal and destroys the effect of lowered carbon |
Welding stainless steel in pure CO2 is the most common mistake in workshops that move over from black steel. The consumable can be right, the code on the label in line with the documentation, and the joint will still lose its resistance. Set up a separate cylinder and a separate regulator, so that nobody mixes them up at a change. The data sheet of the consumable gives the permitted gas directly: for the rod Thermanit GE-316L Si the manufacturer points to argon, argon with 20 to 30 percent helium or argon with 1 to 5 percent hydrogen.
Diameters and currents
MIG/MAG wires for stainless steel are made mainly in 0.8, 1.0 and 1.2 mm, in thicker variants also 1.6 mm for mechanised welding. The TIG rod Thermanit GE-316L Si is given by the manufacturer in 1.0, 1.2, 1.6, 2.0, 2.4 and 3.2 mm. Rods BÖHLER CN 23/12-IG you get in 1.6, 2.0, 2.4 and 3.2 mm.
For sheet of 1.5 to 3 mm take 0.8 mm and a current of roughly 60 to 130 A. For 4 to 8 mm take 1.0 mm and 120 to 220 A. Above 8 mm and on multi run welds take 1.2 mm and 180 to 300 A. Stainless steel carries heat away worse than black steel, so stay with lower values than on the same thickness of non alloy steel.
Choose the liner according to the manual of your torch: the manufacturer states which liner goes with which wire and which diameter. For stainless steel these are usually liners of plastic (PTFE, polyamide) or steel liners in a version meant for stainless wires. The problem is not that the spiral is made of steel, but that a liner with remains of wire for black steel carries iron particles onto the face, where they rust as spots. If you weld both materials at one station, keep a separate set of consumables for stainless steel. The same goes for the brush: for stainless steel only a stainless wire brush.
Three mistakes that cost the most
- The same gas as for black steel: a carburised weld corrodes despite the correct consumable.
- No root shielding on pipes and tanks: an oxidised root is a ready seat of pitting corrosion.
- Welding a material whose grade nobody has established: without that the choice of consumable is guesswork, and when repairing a responsible part that guesswork costs the most.
All three come out after months, not straight after welding. That is why at the acceptance of stainless steel jobs the procedure counts, not the face of the weld alone.
We will match the consumable to your grade
Write to us what material, thickness, process and gas you have, and we will point to a specific item from the Böhler Welding line, for which we are an authorised distributor. Wires for MIG/MAG you find in the category solid MIG/MAG wires, the rods in the category TIG rods. If you are also looking for a machine for thin stainless steel, look into the category used TIG, where every unit is checked in our service workshop.