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Welding of stainless steel

Oerlikon provides complete solutions for stainless steels welding & cutting applications

Stainless steels in industry are used almost everywhere: equipment for the manufacture of food products and pharmaceuticals, plants for the treatment of water, chemical and petro-chemical plants, components for automotive and aero engines, fuel and chemical tankers, buildings, transportation…

Due to their highly remarkable properties stainless steels are widely used in several fields of industrial and day to day activities.
The term stainless steel applies to alloys of iron and a minimum of 10.5 % of chromium that gives a bright shiny gloss and makes steel highly resistant to tarnishing and rusting. This corrosion resistance is what sets stainless steel apart from most other forms of steel.

Apart corrosion resistance  other features are to be noticed : heat resistance, aesthetic appearance, strength, high toughness as well  from elevated temperatures to far below freezing, making the stainless steels particularly suited to cryogenic applications. With addition of other alloying components (Ni, Mo, W, N, Cu, C, Ti, Nb, Zr, S, Si, Mn…) the properties are modified.

Categories of stainless steels

The stainless steel family is often differentiated by the metallurgical phases present in their microscopic structures: ferritic, martensitic, austenitic and duplex steels.

Stainless steel family Alloying elements Features
Austenitic

Fe
C ≤ 0.10%
Cr = 16% to 28%
Ni = 3-5% to 32%
(Mo≤ 7%)

 These alloys are the most popular grades of stainless steels because of their excellent formability,
corrosion resistance and weldability. All are non-magnetic in the annealed condition.
Ferritic

Fe
C ≤ 0.08%
Cr = 10.5% to 30%
(Mo≤ 4-5%)

 Ferritic stainless steels have a low carbon content, with Chromium (and Molybdenum) as major alloying elements.
They are non-hardenable by heat treatment and are always magnetic. They show superior corrosion resistance and
good oxidation resistance. Ferritic steels are readily welded in thin sections but loss their properties when welded
in thicker sections
Duplex
(austenitic-ferritic)

Fe
C ≤ 0.03%
Cr = 21% to 26%
Ni = 3-5% to 8%
(Mo≤ 4-5%)
N ≤ 0.35%

 The microstructure of duplex stainless steels consists of a mixture of austenite and ferrite. They exhibit characteristics
of both phases with higher strength and ductility. Nitrogen is added to provide strength and improve pitting and crevice
corrosion resistance. They are magnetic and non-hardenable by heat treatment
Martensitic

Fe
C ≤1.2%
Cr = 11.5% to 17%            
(Ni ≤ 6%)
(Mo≤ 1.8%)
(V ≤ 0.2%)

 These alloys can be heat treated to a wide range of useful hardness levels. The martensitic structure obtained is magnetic

Working stainless steels

Thermal cutting of stainless steels can be performed only by the plasma cutting process (CITOCUT for manual application and NERTAJET HP for automatic cutting on tables (OPTITOME, OXYTOME...). Oxyfuel cutting should be prohibited.

The assembly by welding of the stainless steels is possible with almost all the arc welding processes and the required equipment are described above in the unalloyed steel section.
Several points has to be taken in account :

  • Cr > 12% is necessary for the proper corrosion resistance to generate a solid Cr-oxide layer.
  • If Cr > 22%, between 550 °C and 900 °C there is -phase segregation.
  • Poor thermal conductivity, high thermal expansion coefficient.
  • Very easily become overheated and deformed.
  • Straightening can cause stress corrosion. To reduce distortion is necessary to use tack welding more frequently than used for mild steels.
  • During welding the cleanliness is very important.
  • The root side of the weld should be protected either with shielding gas (back purge) or use ceramic backing.
  • Arc striking and stopping only in the weld joint preparation with controlled shielding, otherwise these points behave as a corrosion starting points.
  • Right choice of shielding gases is primordial (in MIG/MAG –solid wire or Flux Cored Wire- and TIG processes).

Take advantage of new possibilities of modern MIG/MAG power sources

SPEED SHORT ARC (SSA) is a patented arc transfer from Oerlikon available on CITOPULS and CITOWAVE power sources ideal for root pass welding.
It is an extension of the short arc area due to a very dynamic regulation of the current. SSA extends energy, but avoids globular arc transfer mode.

SOFT SILENCE PULSE (SSP) is an Oerlikon patented pulsed mode available on CITOPULS and CITOWAVE power sources producing a hotter arc than pulse mode, giving better wetting of weld pool than conventional pulse. In addition SSP reduces the arc noise by 50%.

COLD DOUBLE PULSE (CDP) is a specific cycle (sequencer) available on CITOPULS and CITOWAVE power sources, avoiding overheating, mainly for thin stainless steel sheets (< 2 mm). This is an alternative phase of wire speed (cold and hot) in pulse or short arc transfer. Using this cycle the deformation is limited because the reduction of heat input. The weld bead gets the same perfect appearance as a TIG bead.

Categories of stainless steels filler materials

The right selection of the filler metal is critical to obtain good weld quality.
A large number of filler metals are available in the Oerlikon range of welding consumables please contact our service engineers to help you to choose the right one.

Oerlikon can provide a wide range of consumables  for

  • Martensitic and Ferritic stainless steels
  • Austenitic stainless steels
  • Heat resisting stainless steels
  • Duplex stainless steels
  • Stainless steels filler materials for heterogeneous joints and for austenitic buffer layers

A complete range of consumables for the various arc welding processes are also available for the heterogeneous welding and buffer layers.
Filler material grades : 307, 308Mo, 309L, 309LMo, 309LNb, 312.

Solutions for aluminium and alloys welding and cutting applications

Solutions for low alloyed steels welding and cutting applications

Solutions for hardfacing applications