The austenitic steel designated 1.4307 belongs to the commonest stainless-steel type containing about 18% chromium and 9% nickel. The carbon content is low, at most 0.03%, which means that the risk for corrosive attack in the vicinity of welds is minimised.
In the form of welded tubes, 1.4307 is standardised in EN 10296-2. Tibnor’s stock-standard programme covers tubes with outside diameters in the range 20-254 mm and wall thicknesses between 1.5 and 3.2 mm. The tube manufacturing process starts from sheet that has been annealed, pickled and cold rolled (usual finish is 2B) which after slitting is bent into a round shape and longitudinally welded. The welding process can vary but for thin-walled tubes, resistance butt welding is the usual method.
Grade 1.4307 exhibits good resistance to corrosion in neutral water both indoors and outdoors. The steel is also fairly immune to atmospheric corrosion. However, the material is less suitable if the environment is acidic or contains chlorides. In such instances, higher alloyed grades will be needed.
1.4307 has good formability and weldability and these favourable characteristics are retained even when the product form is a welded tube. In the context of cold formability, welded tubes are subjected to extensive testing in order to ensure that there is no risk for cracking at or in the vicinity of the weld in the event the tubes need to be processed via cold forming.
Welded tubes that are stocked in grade 1.4307 have after welding been annealed and pickled once again or bright annealed. The surface finishes in these instances, which are designated in EN 10296-2 as W2A or W2R respectively, are metallically clean/bright and without oxide but with the weld still discernible. It is permitted that the weld bead is raised somewhat. The tolerances on outer diameter (D) and wall thickness (T) are stipulated in detail in EN 10296-2 and EN-ISO 1127 but are at most ±1% of D and ±10% of T. Straightness is good with the allowed height of arc at most 0.002 times length.