Welding is the most common method for joining stainless steel. The resulting joints should have the same, if not better, corrosion-resistant properties. There is a perception that welding stainless steel is difficult, but actually, it’s just different.
Stainless steel is made up of a large family of grades and types, based on the main alloying elements of iron and chromium. All stainless steel grades can be welded but the weldability of each grade varies considerably, due to the different chemical compositions and crystal structures, and how they react to the different thermal cycles of welding.
Because stainless steel has a lower melting temperature than mild steel, less heat is needed to produce fusion. This is important to remember when swapping from welding mild steel to welding stainless steel.
Stainless steel can be welded using a variety of different processes, including arc, friction, electron and laser beam, brazing and resistance welding. If you use a MIG welder or wire feed, you have to use gas, as stainless steel isn’t available in flux-cored form.
The most popular method is arc welding, as it means low heat and low current can be used, which is perfect for welding thin materials while producing a smooth finished weld. Various types of gas can be used when arc welding stainless steel, including nitrogen, helium and hydrogen, although pure argon is the most popular.
Austenitic stainless steel - a type of steel alloy composed of iron, carbon, chromium, nickel and other minor alloys - make up more than 70% of steel production. It is one of the most commonly used stainless steels. The weldability of these grades of stainless steel are usually excellent, but it’s always a good idea when it comes to selecting the welding gases best suited for your application, to consult with your welding supplier for expert advice.
Careful matching of shielding gas to the welding operation is an important step to achieve world-class weld quality. This breakdown of the different welding gasses should get you on the right track.
MIG welding uses a solid wire with argon or argon/helium mixtures. A small amount of an oxidising gas such as carbon dioxide forms part of the welding gas composition and serves to stabilise the arc.
Cronigon 2 is a general-purpose gas mixture of argon and 2.5% carbon dioxide. This gas mixture produces a smooth weld, as it creates little to no splatter. Due to the low surface oxidation, it also requires less aggressive chemical cleaning. This mixture is best suited for welding stainless steels with a thickness of less than 6 mm. It is also an excellent mixture to begin with for those unfamiliar with welding stainless steel.
Cronigon 2 He38 is a three-component shielding gas that contains argon, helium and carbon dioxide. It’s best suited for spray and pulse welding on thicker materials. The helium component increases the welding speed and keeps distortion to a minimum. It produces high-quality welds with a good surface appearance and virtually eliminates the need for rework. This welding gas mixture is ideal for manual, robotic and mechanised welding and offers outstanding corrosion resistance.
Cronigon 2 He55 is another mixture of argon, helium and carbon dioxide and produces welds with excellent low-temperature toughness values, impressive corrosion resistance and low levels of porosity. It’s ideal for applications where weld quality is of utmost importance while keeping manufacture costs low. It can be used to weld a wide range of material thicknesses and works well in all transfer modes such as dip, pulse and spray.
TIG welding is the most popular process for welding stainless steels where a good surface finish and high-quality welds are important. However, not all welding gases are suitable for all material types. For duplex types of stainless steel nitrogen-containing mixtures are best, while hydrogen containing mixtures are better suited to austenitic types of stainless steel.
Argon 4.6 is generally suitable for all grades of stainless steel and produces a stable welding arc. However, as the thickness of the material increases, porosity and fusion problems can arise.
Varigon H2 is a two-component gas mixture of argon and hydrogen and is prefered for manual TIG welding of austenitic stainless steel grades. The weld surface is neater and the weld appearance more consistent, which minimises the need for post-weld cleaning. Fusion and porosity welding defect risks are significantly reduced and due to the increased weld speed, cutting down on manufacturing time, thus making components cheaper to produce.
Varigon H5 contains a higher hydrogen content than Varigon H2 and is generally used for welding thicker sections. This welding gas is best suited to automatic and orbital TIG welding of austenitic stainless steels. It increases weld speed and the more fluid weld pool gives good weld penetration and fusion, ensuring low defect levels and scrapping costs.
Varigon H10 is an argon and hydrogen mixture used primarily for plasma welding and automatic TIG welding of austenitic stainless steel. It is good for welding thicker materials and where speed is a priority. Thinner sections of stainless steel may pose a problem when using this welding gas.
Varigon N2.5 is a wedling gas mixture of argon and nitrogen, specifically designed for welding duplex stainless steels. This kind of stainless steels are used for their good corrosion resistance and a shielding gas can improve this feature and help maintain the life of the component.
For all your welding supplies, repairs and equipment contact Tru-Butt today.
For all your welding needs, including repairs, contact Tru-Butt today, for more information on their services.
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