Welding stainless steel correctly

Welding stainless steel is not entirely unproblematic. In addition, there are the special properties of each type of stainless steel. Therefore, in the following guide, we focus in particular on stainless or. stainless steel when welding. The information can of course be understood as instructions for welding stainless steels.

Differentiation from stainless steels

Stainless steels are standardized according to DIN EN and also typified. The typifications relate to the specific composition of the respective alloys contained in the stainless steel. In this way, completely different properties can be set for each type of stainless steel. Of course, this has a massive influence on the welding of stainless steels, which is why we focus here in particular on stainless and non-rusting stainless steels.

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Alloys of rustproof and rustproof stainless steels

In the case of rustproof and non-rusting stainless steels, the following alloys in particular play an important role:

  • chrome
  • nickel
  • niobium
  • molybdenum

Important distinguishing features according to the structure

Without going into more detail on the structure properties, because that would go too deep into the matter, the following types of structure must be differentiated according to steel types:

  • Austenitic steels (chrome-nickel steel with a nickel content of at least 8 percent)
  • ferritic steels (two groups with a chromium content between 11 and 13 and around 17 percent)
  • ferritic-austenitic steels (duplex steel)
  • martensitic steels (chromium content 12 to 18 percent, carbon content from 0.1 percent, specially processed)

Depending on the steel used, there are also different properties during welding. With ferritic stainless steels, for example, there is a lower elongation at break and toughness, which can be seen if incorrect welding techniques, welding consumables, etc. leads to the fact that cracks can easily develop. Austenitic stainless steels, on the other hand, have a high risk of cracking when the material is still hot.

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Welding consumables and electrodes for stainless steel welding

Stainless and non-rusting stainless steels require special attention with regard to their ability to corrode. You surely know that rustproof or rustproof stainless steel can also rust. Welding consumables are usually used in welding in order to be able to better join two stainless steels. An example of this would be fusible electrodes for the electric welding device or for certain inert gas welding techniques.

Various ingredients are added to this welding additive. In addition to substances (carbon, for example) that influence a chemical reaction, there are also alloys such as chromium or nickel in a certain proportion. This means you have to choose the welding consumables you need based on the exact type of stainless steel you want to weld.

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Make sure that the welding consumables are selected correctly

You should therefore only purchase such products where you can get competent specialist advice, i.e. in specialist shops or in online shops that deal intensively with welding. In the online shops you can get exact descriptions of the exact composition and the steels for which the respective product is suitable for every electrode and welding wire.

In specialist shops you can ask the seller which welding wire or electrodes you need. Keep in mind that austenitic stainless steels are the most common. Sellers who do not know very much about stainless steels therefore tend to recommend welding materials that are precisely suitable for such austenitic steels.

The welding process for stainless steel

Almost any welding process can be used to weld stainless steel. Below is a summary of the most common welding techniques that are suitable for welding stainless steel:

  • Tungsten gas shielded arc welding, especially TIG welding
  • Gas-shielded metal arc welding, MIG, MIG and MAG welding
  • Electric arc welding (EH) for electric manual arc welding or electric welding

Of course there are other welding processes for welding steel and stainless steel. However, these methods are rather unsuitable for do-it-yourselfers and even numerous craftsmen.

Electric welding for welding stainless steel

When it comes to electric welding, choosing the right electrode is fundamental. With the exception of non-rusting ferritic stainless steels, rutile-coated and not basic electrodes should be used. The weld seam becomes smoother with the rutile-coated electrodes, and the slag is much more difficult to remove with basic burn-off electrodes. We explain the problem behind this in the section "Corrosion from welding stainless steel".

The electrodes

Also make sure that the electrodes are absolutely dry (especially if electrodes have been stored for a longer period of time). Moisture can worsen welding, but it can also worsen slag removal considerably. Since the core consists of highly alloyed rods, the welding wire should be lower than that of conventionally used electrodes for welding steel (structural steel, for example).

Rutile-coated and basic electrodes

There are exceptions for non-rusting ferritic stainless steels. If rutile-coated electrodes are used, these can tend to form pores with the result of cold cracks. A basic electrode should therefore be used with non-rusting ferritic steels. Rutile-coated electrodes can also be welded with direct current and alternating current, while basic electrodes can only be welded with direct current (positive pole on the rod electrode). The arc is kept short with both electrodes used.

Weld stainless steel with shielding gas

First of all, the differences in gas-shielded welding. Inert MIG, TIG) and active (MAG) gases are used. TIG welding is also known as TIG (Tungsten intert Gaswelding). Inert gases such as helium, argon or nitrogen are used to protect the melt from oxygen.

Explicitly in TIG welding argon (ferritic stainless steel) or a mixture of argon and hydrogen (austenitic stainless steel) in machine welding to increase the speed. In MAG welding with active gases, either pure CO2 or a mixed gas consisting of CO2, argon and corgon is used.

Stainless steel TIG welding

TIG welding (tungsten inert gas welding WSG) differs somewhat from MIG / MAG welding. It is a tungsten electrode that does not melt. TIG welding only uses direct current.

In addition, an oxide layer like on aluminum can also be broken through, the electrode then being the positive pole. Overall, TIG welding results in a higher quality weld seam and is particularly suitable for stainless steel welding.

The welding of stainless steel with the TIG process

When welding stainless steel, however, the negative pole is on the electrode. In contrast to MIG / MAG welding, the electrode does not burn off with TIG welding, which is why the filler metal must be added manually.

However, this has the advantage that the current intensity and the additional supply are decoupled from one another. This makes TIG welding particularly suitable when welding has to be carried out in out of position (a stainless steel pipe, for example). But even a thin stainless steel sheet can be welded better with the TIG process due to the decoupling of the two processes.

Use of welding consumables

For the following types of stainless steel with a maximum thickness of stainless steel sheet or stainless steel pipe of 3 mm, a welding filler is not absolutely necessary:

  • 1.4301
  • 1.4401
  • 1.4541
  • 1.4571

On the other hand, the use of a filler metal is preferable for the following types:

  • 1.4435
  • 1.4439
  • 1.4462
  • 1.4539

Stainless steel MAG welding

The MAG welding process is also often used for stainless steel. Welding is also carried out with direct current, here too the electrode is at the positive pole. The wire feed enables high melting rates to be achieved. Solid and cored wire electrodes with a diameter between 0.8 and 1.6 mm are used for the welding wires.

If you want to work with solid welding wire, a mixture of argon with 1 to 3 percent oxygen is primarily used as the shielding gas. However, a high percentage of oxygen can increase the risk of corrosion. This method is rather unfavorable in difficult situations, for example overhead on a stainless steel pipe. The weld bead must also not get too high.

The peculiarities of cored wire

This is where cored wire shows its advantages. The caterpillars become flat and low, the surface smooth. In addition, cored wire can be selected to form slag. There is more information on this under Corrosion during welding in the next paragraph.

Corrosion when welding stainless steel

Corrosion is always a problem that must be taken into account, especially when welding rustproof or stainless steels. First of all, a slag-forming filler metal has the advantage that there is protection against corrosion during welding. However, the slag must be removed later so that the passive layer (oxide layer) can or. can be trained. If not all slag residues are removed, pitting can occur.

The risk of corrosion is kept low through an optimal selection

The choice of the right welding technology and welding consumables is also important so that no cracks (crevice corrosion and stress cracks) can form (during welding or cold cracks). Here, too, corrosive material can quickly deposit and damage the stainless steel. You must also note that if a more noble and a less noble metal come into contact, the less noble metal will corrode. Such metals must be isolated from one another accordingly.

Tips & Tricks You will find numerous other guides and instructions for processing stainless steel in the company journal. There are also instructions for anodizing stainless steel (actually correctly expressed, black oxidizing) in order to reliably protect the welded stainless steel workpiece again against corrosion.