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• Stainless steel is a family of iron-based alloys that contain a minimum of approximately 11% chromium
• The chromium oxide layer creates resistance to corrosion and staining, as well as providing heat-resistant properties.
• As stainless steel is hygienic, low maintenance and has aesthetic appeal it is rarely coated.
• Different types of stainless steel include the elements carbon, nitrogen, aluminium, silicon, titanium, nickel, copper, selenium, niobium, and molybdenum.
• There are four categories of stainless steel:
• Austenitic stainless steel
• Ferritic stainless steel
• Martenitic stainless steel
• Duplex stainless steel
• Typical applications range from installations in the pharma/chemical industries to offshore and from food applications to road tankers and more.
Pure argon or argon/carbon dioxide mixtures are commonly used for MIG/MAG welding stainless steel. Additional benefits can be gained from the inclusion of helium into the mixture. For TIG welding stainless steel a small addition of hydrogen reduces surface oxidisation. Use our interactive welding gas selector to identify the most suitable gas for your welding application.
There are some core materials required to MIG weld – welding machine, filler wire, welding gas and PPE. There are also some core safety rules that need to be observed and surface preparation required before welding can commence.
In summary, an electric motor continuously feeds consumable filler wire through the welding torch into the arc, and the power source keeps the arc length at a pre-set value. This allows the welder to concentrate on ensuring a complete fusion of the joint. Most power sources for MIG/MAG welding processes are known as constant voltage machines.
Stainless steel can be difficult to weld as the metal conducts heat slower than carbon steel increasing the risk of distortion, burn-through and oxidisation. A clean workplace is essential as stainless steel is vulnerable to ferrous contamination. Likewise, spatter should be kept to a minimum to avoid damaging the protective chromium oxide layer.
Inert gases such as argon or helium can be used for welding stainless steel. However, argon mix gases provide optimal weldability and weld quality. If you are looking for an ideal all-rounder for MIG/ MAG welding stainless steel, Inomaxx® 2 welding gas with 2% oxygen in argon, provides optimal heat, even with thin materials, to prevent burn-through. It is suitable for pulsed arc transfer and offers superior mechanical properties.
Stainless steel can be sluggish to weld – for increased weldability there is Inomaxx® Plus with 35% helium and 2% carbon dioxide in argon. The low addition of carbon dioxide eliminates the risk of carbonisation and any mechanical property interference and the optimum helium addition allows for faster weld travel speeds and better control.
One of the advantages of TIG welding is that it allows you to weld a wide range of materials. Modern power sources combine constant current and constant voltage characteristics and deliver excellent arc stability. Machines ranging from 5A (micro-TIG) to over 500A are available.
In manual welding the operator points the electrode in the direction of welding and uses the arc to melt the metal at the joint. Arc length is controlled by the welder and is usually between 2mm and 5mm. Note – stainless steel is vulnerable to ferrous contamination so it is important that the workspace is clean.
Filler metal is added to the leading edge of the weld pool. Travel speed is adjusted to match the time needed to melt the joint and keep a constant weld pool size. Stainless steel can be sluggish as it conducts heat slower than carbon steel so welder needs to be mindful of oxidisation and/or burn-through.
Often the gas is argon, but helium by itself, or mixed with argon, may be used for special applications. Argon-hydrogen mixtures can be used for exceptional results when welding austenitic stainless steel.
Air Products recommends Inomaxx® TIG welding gas (2% hydrogen in argon) for TIG welding stainless steel as the hydrogen reduces surface oxidisation which reduces the post-weld cleaning as well as reducing the amount of ozone produced in the fume.
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