Matching the consumable to the parent material
The chemical composition of stainless steel welding consumables is matched with the base or parent material. The chemical analysis (composition) of the consumables used are usually balanced to optimise the welding process and avoid hot cracking.
Austenitic stainless steel
Low carbon levels are normally used to reduce the risks of intergranular corrosion (intercystalline) following cooling through temperatures from around 850 down to 450 C after weld solidification. Corrosion mechanisms in stainless steel. Consumables such as 19 9 and 19 12 2 with higher carbon levels should give higher strength welds, more suited for high service temperatureapplications.
The titanium stabilized steel, 321 and 316Ti are welded with consumables containing niobium, rather than titanium. The very high melting point titanium carbides that would be present in the consumable would be unlikely to melt during the welding process, whereas the niobium carbo-nitrides in the niobium type consumables have lower melting points and are a better choice.
Ferrite levels of austenitic consumables are normally balanced between 4 and 12 %, to reduce the risk of hot cracking at temperature just below the solidification point of the weld metal. For welding the special low / zero ferrite grades, intended for special corrosion resistant, cryogenic temperature or low magnetic permeability service conditions, matching low /zero ferrite consumables, such as 18 15 3 L, should be used.
Ferritic, martensitic and precipitation hardening stainless steel
Generally, either matching consumables, or an austenitic filler with matching chromium and molybdenum contents, can be used. Austenitic fillers are used where good weld toughness is essential, but these are not a good idea where the weld appearance (colour), mechanical strength (in the case of welds between martensitic and precipitation hardening parent material) and physical properties (thermal expansion) need to be matched with the parent material.
In contrast to the austenitic consumables, duplex fillers, such as 22 9 3 N L are balanced to produce more austenite in the weld than in the parent metal. This is done to optimise weld mechanical properties and corrosion resistance and is achieved by adding more nickel and usually nitrogen to the consumable than is present in the matched base metal.
Compositions of consumables
The consumable alloy symbols are common in the European standards. The compositions can vary, however, for the various consumable types between EN 1600, EN 12072 and EN 12073 for the same ‘Alloy symbol’ used in each standard. For each specific consumable type the particular standard should be consulted.
As a guide the table below gives the compositions in EN 1600. For these coated electrode types, the type of covering determines to a large extent the usability characteristics of the electrode and properties of the weld metal.
Two symbols are used to describe the type of covering: R for Rutile covering and B for Basic covering. A description of the characteristics of each of the types of covering is given in Annex A of BS EN 1600. (See also paragraph 4.3 of the standard)
|Alloy symbols||Chemical composition (% by mass – max unless stated)|
|19 9 L||0.04||1.2||2.0||0.030||0.025||18.0/21.0||9.0/11.0||–||–|
|19 9 Nb||0.08||1.2||2.0||0.030||0.025||18.0/21.0||9.0/11.0||–||Nb-8x%C min, 1.1%max|
|19 12 2||0.08||1.2||2.0||0.030||0.025||17.0/20.0||10.0/13.0||2.0/3.0||–|
Suggested consumables for welding stainless steel
Euro Inox publication ‘Welding of Stainless Steels’ tabulates suggested consumables for welding a range of stainless steel base or parent grades. This publication can be viewed or down loaded in pdf format from the Euro Inox web site, www.euro-inox.org by selecting the Materials and Applications sub menu.
Only the steel number is shown. The original Euro Inox table also has the steel name.
AISI is the American Iron and Steel Institute
Wire electrodes covered by EN 12072 may use the following prefixes G for GMAW (MIG), W for GTAW (TIG) P for PAW (plasma arc), or S for SAW (submerged arc).
Tubular cored electrodes are sometimes referred to as flux cored electrodes.
- Welding of Stainless Steels
- Euro Inox, Materials and Applications Series, vol.3
- Welding of Stainless Steels and Other Joining Methods
- The Nickel Institute, AISI Designers Handbook Series No 9002
Source: Zhejiang Yaang Pipe Industry Co., Limited (www.yaang.com)