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Home » Stainless and Acid-Proof Steel Chains » Corrosion |
Corrosion |
Corrosion is the chemical or electrochemical reaction of
metals with the environment, resulting in the impairment of
material properties. Fundamentally, there are 3 different
forms of corrosion:
Surface corrosion affects the entire surface evenly but an
irregular progress can result in the formation of trough-shaped
indentations. An early recognition is possible. Pitting develops
in local indentations which are either crater-shaped or in a
pin hole form, these eroding the surface. The most dangerous
form of corrosion is the corrosion cracks which as with pitting
are difficult to detect. The stress concentration of the crack
opening under mechanical load results in excessive tension
being applied and this together with the reduction in the
cross-section resulting from the crack can in turn result in
breakages occurring. This problem especially exists with
regard to chains due to the fact that chains are subjected to
heavy mechanical loads.
The standard non-alloy and low-alloy steels are practically
unstable when used in a corrosive environment. A chromium
content which exceeds the resistance threshold of
min. 12% produces extremely thin (approx. 5 ì), tenacious,
adhesive oxide films on the surface of the steel when
subjected to oxidizing conditions: the steel is passivated,
i.e. resistant against oxidizing media. Additional alloy
elements such as nickel (increases the impact value),
molybdenum (reduced susceptibility to pitting) or titanium
(stabilisation against granular corrosion) increase the
resistance against corrosion , result in a simplified
processing, increase the solidity and improve the thermal
behaviour. Fundamentally speaking, with stainless steels,
differentiations are made between ferritic steels, martensitic
steels, austenitic steels and austenitic-ferritic steels. Only
the austenitic chain steels are used for the manufacture of
chains due to their improved weld ability and cold
formability. These include approx. 16 -26% chromium,
3,5-32% nickel and up to 7% molybdenum. The steels
most widely used here are X 5 CrNiMo 17 12 2 (1.4401), X 2
CrNiMo 17 13 2 (1.4404), X 6 CrNiMoTi 17 12 2 (1.4571).
The tensile strength of these steels amounts to approx. 500-
800 N/mm. The impact value is extremely high even when
subjected to extreme cold. These steels also do not oxidize
even when subjected to high temperatures. Stainless steel
chains are fundamentally suitable for use in the food industry,
chemicals industry, pharmaceutical industry, textile industry,
use in cold forming technology, etc.
This situation is also valid for the oxygen corrosion, the
most well-known form being the iron and steel corrosion.
Hydrogen corrosion also exists. Hydrogen corrosion is only
of interest in acidic solutions (Ph value < 7). This also
includes acid attacks on metals (acidic corrosion). The alloy
elements described above retain their properties even when
subjected to hydrogen corrosion. For this reason, steels
containing these alloy elements are not only resistant to
oxygen corrosion (rust) but also to hydrogen corrosion,
meaning that they are also resistant to acid. |
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