The Stainless Steel Experts - MSTAINLESS

BUSINESS DIVISION
Industrial components
made of stainless steel
18
Material analysis
Austenitic stainless steel
These type of stainless steel grades
presently dominate the market
and cover the most commonly
used qualities, such as material no.
1.4301 or 1.4404 and also material
nos. 1.4539 and 1.4529 with a
Structure of austenitic steel
higher alloy content. Characteristic
of this steel is the high content of
austenite-forming substances, in
particular nickel.
Further alloy elements are chromium,
molybdenum as well as sometimes
copper, titanium, niobium and
nitrogen. Adding nitrogen increases
the steel's stretch resistance. The application
areas for austenitic steel are
extremely varied. This type of steel is
used in the chemical industry as well
as the foodstuffs industry.
Moreover, molybdenum-free steel
performs well within the high temperature
range, which explains why
it is frequently used in the construction
of furnaces and heat exchangers.
Its high resistance to impact at
low temperatures is taken advantage
of, for example, in producing containers
for deep-frozen fluids.
In the lower alloy range (e.g. 1.4301
or 1.4404) austenitic steel is rela-
tively susceptible to stress corrosion
cracking, in particular chloride and
hydrogen-induced versions.
Hardening by means of heat
treatment is not possible. It is normally
supplied in a lumenized state
(quenched and tempered), is soft
and therefore highly formable. Its
strength can be improved with cold
forming. That's why some grades
are supplied cold-drawn (coldstretched)
or hard-rolled.
With the austenitic steel grades
the modulus of elasticity is subject
to major fluctuations due to the
increased strain hardening tendency.
That's why for attachment
systems in the construction sector
the German Institute for Construction
Engineering in Berlin (DIBT)
has reduced the value from 200 to
170 kN/mm². Tests have shown that
major strain hardening reduces the
modulus of elasticity. In terms of
the structure, high strength values
achieved through strain hardening
may not be applied to welded constructions.
In such a case, the yield
point value Rp0.2 must be based on
the strength of the metal in the annealed
state (green strength). Refer
to the latest version of the General
Technical Approval Z-30.3-6, “Products,
Connectors and Structural
Components in Stainless Steel”.
As a rule, austenitic steel grades are
not magnetic in the annealed state.
However, this can change due to
cold forming and the martensite
formation associated with it. In such
a case a magnet will also adhere to
the metal sheet or profile in the
strain hardened area. For example,
it is frequently the case that this
causes die-cut washers to be slightly
magnetic.The worldwide market for
the austenitic steel grades and their
fields of application are presently in
stark decline due to the relatively
expensive alloy content Ni=nickel
und Mo=molybdenum.Other types,
e.g. ferritic steel grades and stainless
steel duplex grades, have caught up
significantly in terms of their technical
possibilities, and are in some instances
considerably less expensive.
We will be happy to advise you.
Ferritic stainless steel
This steel is always ferritic regardless
of the temperature. This is achieved
through a reduced number of
austenite-forming elements (primarily
nickel) combined with a high
degree of ferrite-formers (mainly
chromium).
Structure of ferritic steel
The older qualities, such as material
no. 1.4016, were mainly used for
household articles and in application
areas where the demand for
corrosion-resistance was not particularly
high. The current ferritic stainless
steel grades, such as material
no. 1.4521 with an extremely low
carbon and nitrogen content is pref-