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E: ssas@bssa.org.uk
Welding austenitic stainless steels to carbon and low alloy steels are established methods in the process and construction industries. including TIG (Tungsten Inert Gas) and MIG (Metal Inert Gas).
A colour chart is shown for guidance on exposure temperatures on 1.4301 (304) type. The factors affecting the degree or depth of colours formed are outlined. These include steel composition, atmosphere, time and surface finish.
Citric and nitric acid based treatments
Fume is generated by arc welding processes used for welding stainless steels, both the flux-shielded processes (manual metal arc and flux cored arc) and the gas-shielded processes (tungsten inert gas and metal inert/active gas). Plasma arc cutting also produces fume.
The composition of stainless steel welding consumables is matched with the base or parent material. The chemical analyses (composition) of the consumables used are usually balanced to optimise the welding process and avoid hot cracking.
Duplex stainless steels differ significantly from austenitic stainless steels in the following important respects: 1) Chemical composition 2) Mechanical properties 3) Formability 4) Weldability
The table shows both current and obsolete standards (where these may be of current interest) in the 'Status' column. 'C' is current and 'W' is withdrawn. The 'date' is the original publication year. Use the 'Ctrl' and 'F' keys to 'find' the standard you are looking for. These lists cannot be guaranteed as
Although classed as readily weldable, the austenitic stainless steels can be prone to distortion during and after welding. This is due mainly to their specific combination of physical properties, mainly their relatively high thermal expansion rate and low thermal conduv
This is the most widely used process due to its versatility and high quality as well as the aesthetic appearance of the finished weld. The ability to weld at low current, and hence low heat input, plus the ability to add filler wire when required, make it ideal for thin materials and root runs in one sided welding of thicker plate and pipe. The process is easily mechanised and the ability to weld with or without the addition of filler wire (autogenous welding) make it the process for orbital welding of pipe. Pure argon is the most popular shielding gas, but argon rich mixtures with the addition of hydrogen, helium or nitrogen are also employed for specific purposes. Inert backing gas protection of the weld under-bead is employed with single-sided welding to prevent oxidation and the loss of corrosion resistance.
Intermittent fillet welds and intermittent partial penetration butt welds should only be used where crevice corrosion is unlikely to occur. Furthermore, continuous partial penetration butt welds should be used with care in marine or very heavily polluted onshore environments, particularly where capillary action might occur.
Ferrite is important in avoiding hot cracking in during cooling from welding of austenitic stainless steels. 'Constitution diagrams' are used to predict ferrite levels from the composition by comparing the effects of austenite and ferrite stabilising elements. The Schaeffler and Delong diagrams are the original methods of predicting the phase balances in austenitic stainless steel welds.
Methods for post fabrication and welding clean-up of stainless steel are well documented. One issue is whether the heat tint discolouration in the heat-affected zone of stainless steel welds should be removed.
Stainless steels are designed to naturally self-passivate whenever a clean surface is exposed to an environment that can provide enough oxygen to form the chromium rich oxide surface layer, on which the corrosion resistance of these alloys depends.