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Chapter 9: Comments on the Standards for Stainless Steel
All the given data in the table are according to the new Euro Norm (EN), which, roughly, is the
same as the old, German Werkstoff Nummer (W.Nr.). To the far right, the closest parallel AISI and
SS numbers are given, however, take note that 100 % correlation is rarely seen. The “translation” in
between the systems is merely approximate.
In addition, jumping from W.Nr. to EN may cause some confusion. As a rule of the thumb, it’s quite
safe to “translate” directly from W.Nr. to EN and use EN 1.4307 instead of the W.Nr. 1.4307 showed
on the blueprint. Admittedly, EN 1.4307 has a lower limit for the chromium content (Cr) which happens
to be 0.5 % above that of the W.Nr., however, Cr just benefits the corrosion resistance, so we
actually get a small improvement. In short: “Don’t worry, be happy”, and use the new EN numbers
without problems.
Low-Carbon vs. ”Common” Grades
Another common source of confusion is the carbon content of the steels.. For all austenitic, ferritic
and the ferritic-austenitic (duplex) grades, carbon is an unwanted impurity, and for that reason the
carbon content of all standards is given as an upper limit. In parallel with the increasing efficiency
of the mills, this limit has gradually moved down. In the good old days, just 20 years ago, the state
of the art was a carbon content of 0.07 or 0.08 %, however, nowadays the low-carbon grades with
maximum 0.03 % C are much more common – in particular for European made stainless steel.
On many blueprints, one may still see lots of old high-carbon steel grades, such as W.Nr. 1.4301,
AISI 304, or AISI 316, but nowadays, the steel is frequently marked EN 1.4307, AISI 304L or AISI
316L, respectively. The only chemical difference between an AISI 304 and a 304L is the carbon content,
however, don’t worry about that. An AISI 304L always fulfills the chemical requirements of the
“old” 304 and can easily be used as a substitute. Similarly, the 4307 or 4404 can replace the highcarbon
4301 or 4401, respectively.
In short: It’s almost always possible to replace a “normal” alloy with max. 0,07 or 0,08 % C with
the corresponding low-carbon with max. 0.03 %. The only exception occurs when the mechanical
strength is critical at temperatures above 4-500 °C. For other purposes, the easy switch may be
made. Fortunately, both sheets and tubes tend to be double-certified showing both 4301 and 4307,
in which case all doubt should be erased.
For further information regarding the standards, the carbon content and the possibilities of
changing in between the steel grades, we refer to the book ”Stainless steel and Corrosion” (Claus
Qvist Jessen, Damstahl, October 2011). The book can be ordered via www.damstahl.dk.
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01.2013