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Hilti X-CR / X-BT stainless steel
fastener (CR500 material)
Tests carried out by independent authorities
(FMPA Stuttgart ([5], RWTH Aachen [6]) clearly
indicate the superior properties of the
CR500 material when compared to AISI 316
(A4) or AISI 304 (A2). The superior properties
with regard to pitting potential are mainly due
to the higher molybdenum, nickel, chromium
and nitrogen content of the steel. Consequently,
CR500 material can be classified in
the same corrosion category as AISI 316
(A4).
Contact corrosion
Contact corrosion, where stainless steels
are concerned, is not a matter of concern.
Stainless steels are higher in the galvanic
series, i.e. more noble, than most generally
used materials such as aluminum, zinc and
steel. Stainless steel in contact with these
materials thus benefits from cathodic pro-
Heavily corrosive environments
In some heavily corrosive environments, e.g.
in road tunnels in the alps (salt and air pollution)
and in applications in the chemicals
industry in particular, where chlorides and
acid compounds are combined and the
fastening has a high safety relevance, use of
X-CR steel is not permissible.
This combination of “maritime” environment
as well as more acidic and oxidizing active
constituents in the electrolyte film are the
reason why conventional stainless steels of
the AISI 304 and AISI 316 grades can suffer
Corrosion
On the basis of results from field tests carried out, for
example, in industrial atmospheres, road tunnels and
in sea water over many years, it has been concluded
that AISI 316 (A4) grade steel provides adequate corrosion
resistance for use in “corrosive conditions in
industrial and marine air”. CR500 also provides this
resistance with great certainty.
tection. This type of contact therefore generally
has a favorable effect on the corrosion
properties of stainless steels.
The “noble” stainless steel fastener has a
very much lower rate of corrosion than the
“less noble” base material, and the material
of the component fastened, due to electrochemical
effects.
pitting corrosion and stress corrosion cracking
as a further consequence. This is one of
the most dangerous forms of corrosion. This
corrosion-induced failure can only occur if
particular media and a tensile stress are
present. Existing residual stress may be sufficient
to induce stress corrosion cracking.
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