The composition of stainless steel welding consumables is matched to the base metal or parent material. The chemical analysis (composition) of the consumables used is usually balanced to optimise the welding process and avoid thermal cracking.
Austenitic stainless steels
A low carbon content is often used to reduce the risk of intergranular (intergranular) corrosion after the weld has cooled from about 850 to 450 C after solidification.
Titanium stabilised steels 1.4541 (321) and 1.4571 (316Ti) are welded with welding consumables containing niobium instead of titanium. The very high melting point of titanium carbide present in the consumables is unlikely to melt during welding, whereas the niobium carbon-nitride present in niobium-based consumables has a lower melting point and is a better choice.
Austenitic welding consumables are usually balanced with a ferrite content of between 4 and 12 per cent to reduce the risk of thermal cracking at temperatures slightly below the freezing point of the weld metal. For welding special low/zero ferrite grades for special corrosion-resistant, low-temperature or low permeability working conditions, matched low/zero ferrite welding consumables should be used.
Ferritic, martensitic and precipitation-hardening stainless steels
In general, matched consumables, or austenitic fillers with matched chromium and molybdenum content, can be used. Austenitic fillers are used where good weld toughness is a must, but where weld appearance (colour), mechanical strength (in the case of a weld between a martensitic and precipitation-hardening base metal) and physical properties (thermal expansion) are required, it is not a good idea to match the base metal.
Duplex Stainless Steel
In contrast to austenitic consumables, duplex fillers are balanced to produce more austenite in the weld than the base metal. This is done to optimise weld mechanical properties and corrosion resistance and is achieved by adding more nickel (usually nitrogen) to the consumables than in the matching base metal.
Dissimilar metal welding
The welding of two steels with different chemical compositions is called dissimilar metal welding. In dissimilar metal welding, the choice of welding consumables needs to be based on the combination of the base materials with due consideration of crack resistance, corrosion resistance, mechanical properties, etc. Basically, should be used to meet the joint at least one parent metal mechanical properties of the welding material
Notes: ① Carbon steel and austenitic stainless steel welding, generally use the higher Cr, Ni content of the 309 type welding consumables. This is because, when using Type 308 welding consumables, Cr and Ni are diluted by the carbon steel base metal, resulting in the formation of martensitic organisation (brittle organisation) in the weld metal. ② When welding carbon steel with austenitic stainless steel, due to the large difference in the coefficient of thermal expansion of the two metals, when the weldment is subjected to intense thermal cycling at high temperatures, a high nickel-chromium-nickel-iron alloy type of welding consumables with a medium coefficient of thermal expansion should be used. ③ In welding carbon steel to Cr stainless steel, any of the Cr stainless steel type, austenitic stainless steel type and high nickel type welding consumables may be used, taking into account the following advantages and disadvantages of each type. Cr stainless steel type consumables are suitable for applications in intense thermal cycling or nickel-sensitive corrosive environments. However, proper preheating and post-weld heat treatment is required to prevent delayed cracking. Austenitic stainless steel consumables offer good weldability, but can cause thermal stress problems in environments where the weldment is exposed to intense thermal cycling. High-nickel type welding consumables are costly and susceptible to thermal cracking; on the other hand, since they can withstand intense thermal cycling, they are suitable for weldments that are difficult to treat after welding and are used in an environment with intense thermal cycling. ④ For welding of dissimilar metals, welding processes with large dilution ratios such as submerged arc welding are not recommended. ⑤ When welding dissimilar metals using MIG and TIG welding processes, the melt depth of carbon steel should be as small as possible.