Stainless Steel Round Bar Machined EN 1.4539
1.4539 (Outokumpu 904L) is a high-alloyed austenitic steel with very good resistance to corrosion in aggressive environments such as sea water and acids, especially sulphuric acid. The steel is alloyed with 20% chromium, 25% nickel and 4,5% molybdenum and 2% or so of copper. The carbon content is low, at most 0,02%. The strength level is somewhat higher than for 1.4307 or 1.4404 but not so high as for 1.4547.
Rounds in 1.4539 are standardised in EN 10088-3. This standard covers cold-finished round bars with diameters up to and including 160 mm. Tibnor’s programme comprises machined bars up to 150 mm in diameter.
1.4539 was originally developed to provide good resistance to attack by sulphuric acid but its range of application has been extended thanks to its generally good resistance to aggressive chemicals as well as a high degree of immunity to pitting and crevice corrosion in chloride-containing environments, such as sea water. Furthermore, the high nickel content promotes resistance to stress-corrosion cracking in the presence of chlorides to which lesser-alloyed austenitic grades like 1.4307 and 1.4404 are prone. The material finds use in the chemical industry as well as in the marine and offshore segments. In the form of bars, 1.4539 is suitable for machine parts subjected to aggressive environments like sea water and acids.
The steel is quite weldable so long as the heat input is not too high and a suitable consumable is chosen. Cold-forming operations can usually be carried out without any difficulty. 1.4539 is quite troublesome to machine since the material works hardens appreciably, which must be taken into consideration when deciding upon machining parameters like depth of cut. Machining is facilitated through the use of bespoke tooling.
The surface finish of machined 1.4539 as stocked is 2B as defined in EN 10088-3. Machining, usually peeling, is carried after hot-rolled bars have been annealed; machining marks are evened out by the burnishing action of subsequent straightening. This procedure eliminates any remaining surface defects. The diameter tolerance of machined bars is k12 as stipulated in ISO 286 - 2 which is a zero-plus tolerance. In other words, the actual diameter is marginally larger than the nominal one. In addition, machined bars of stainless steel are rather straight with height of arc less than 0.001 x length.