SS Square Tubes EN 1.4404/4571
The austenitic steel with designation 1.4404 contains about 2% molybdenum in addition to chromium and nickel. The difference against 1.4301 and 1.4307 apart from the presence of molybdenum is that the nickel content is greater. This type of stainless steel is often referred to as acid resistant which is to some degree a misnomer since the material resists attack only by weak acids. 1.4404 has low carbon content which means that it can be welded without risking impairment of corrosion resistance in the vicinity of the weld. In terms of strength, 1.4404 is more or less equivalent to the lower-alloyed grades 1.4301/1.4307.
In relation to the base steel, hollow sections of 1.4404 are standardised in EN 10088-2 and 10088-4 while tolerances and section properties are as stipulated in EN 10219-2. Tibnor’s programme covers sections with width 25-100 mm, height 25-100 mm and thickness 2-5 mm. The starting material for manufacture of hollow sections is cold-or hot-finished strip (annealed and pickled, surface 1D or 2B) which is slit, shaped to a square or rectangular format and welded longitudinally. Welding methods vary, examples being plasma/TIG, laser or butt resistance welding. As a final operation, the appearance of the welded area is improved by grinding.
The presence of molybdenum along with chromium renders 1.4404 resistant to corrosion in weak acids and water containing chlorides so long as the chloride concentration is not too high; an example of an environment where the steel works well is salt-laden coastal atmosphere.
1.4404 is characterised by excellent formability and weldability so that if needed, welding, bending or other cold-forming of hollow sections is seldom an issue. Extensive testing guarantees weld quality so that risk for cracking in the vicinity of the weld in connection with bending or cold forming is minimal.
Hollow sections in grade 1.4404 are offered with two surface executions: untreated with the welded area ground to remove oxide but the weld still completely visible, or with the entirety of the flat faces ground (grit 220, Ra 1.0-1.4 µm). Tolerances are stipulated in detail in EN 10219-2 but are at most ±0.6-1.0% for width and breadth (depending on dimension) and ±10% or ±0.5 mm for thickness. Straightness is good with the allowed height of arc at most 0.0015 times length.