The generally held view for stainless steels is characterized by some erroneous conceptions that can easily be attributed to widespread ignorance. One misconception is that stainless steel does not have iron, when this is actually its primary constituent (around 70 %). Another incorrect view is the one that considers stainless steel (usually grade 304) as a solution to any kind of corrosion, and thus when a corrosion issue arises, then people accuse the steel that it is not stainless. However, we saw earlier that we have the possibility of choosing among a great variety of stainless steel grades. What one must do is the study and understanding of the conditions prevailing during the material's application and functioning and the consultation with a credible supplier. At the same time, the final user must certainly take a decision for the relation he accepts between the material's cost and its life cycle (there are "everlasting" types that yet cost dearly). Of utmost importance for preserving stainless steel in good condition is its regular cleaning, as well as the procedure of chemical cleaning (pickling/passivation) Chemical cleaning refers to the procedures of pickling and passivation. Pickling is the removal of a thin layer of metal from the surface of the stainless steel. Mixtures of nitric and hydrofluoric acids are usually used for pickling stainless steels. Passivation usually occurs naturally on the surfaces of stainless steels, but it may sometimes be necessary to assist the process with oxidizing acid treatments. Solutions of nitric or citric acid are used for passivating stainless steel surfaces. If the metal's surface is contaminated with grease, oil or inorganic contaminants, then a cleaning operation prior to acid treatment should be carried out. The two operations can be applied to all stainless steel types. with the completion of the construction.

Finally, a widely held misconception is that because ferritic and duplex types are magnetic they are not real stainless steels and will rust like carbon steel. This is wrong. Purely for reasons of atomic structure, some stainless steels are magnetic and some are not. Corrosion resistance is not a matter of atomic structure but one of chemical composition. Magnetism has nothing to do with it. Reference was made earlier to the PRE formula which is used to state each type's resistance to pitting corrosion. Studying the PRE number of both magnetic and non-magnetic types we easily find out that there exist magnetic grades with higher PRE, and thus move resistant, to non-magnetic. Below we present a table with the PRE number of the most popular grades.

Typical chemical composition, % by wt.
AISI EN Cr Ni Mo N others PRE
ferritic stainless steels

430 1.4016 16,5 - - -
441 1.4509 18 - - - Nb, Ti 18
444 1.4521 17,8 - 2.1 0.01 Ti 25
austenitic stainless steels

304L 1.4307 18,1 8.1 - - - 18
316L 1.4404 17,2 10.1 2.1 - - 24
904L 1.4539 20 25 4.3 - 1.5 Cu 34
duplex stainless steels

S32101 1.4162 21,5 1.5 0.3 0.22 5Mn 26
S32304 1.4362 23 4.8 0.3 0.10 - 26
S32205 1.4462 22 5.7 3.1 0.17 - 35

PRE = % Cr + 3.3 x % Mo + 16 x % N


Concluding, stainless steel's main properties can be summarized as follows

corrosion resistance
aesthetic appeal
heat resistance
low lifecycle and maintenance cost
full recyclability
biological neutrality (meets EU RoHS requirements)
ease of fabrication and durability

* The present text has been registered at a notary office for the intellectual rights' protection.
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