What is the structure of stainless steel

Stainless steel and magnetism

Official names of the stainless steel types in the hardware area
(AISI = American Iren and Steellnstitute - American material identification)

Material number 1.430 I (X5CrNII8-I 0)
AISI 304 IV2A

Material number 1.440 I (X5CrNiMo 17-12-2)
AISI 3 16 IV4A

Why is stainless steel partially magnetic?

The stainless chromium steels have the same crystal structure as the normal ones
Steels (structure Alpha) and are magnetic.
The addition of nickel changes the structure. This makes it austenitic (structure gamma) and
non-magnetic.
Unfortunately, the chromium-nickel steel thus obtained does not have a stable structure. He has
There is a tendency to return to a structure of the alpha type, i.e. magnetic. This depends on his
chemical composition and the effects of various external influences (temperature;
Work hardening, deformation, etc.).
depending on the ratio of its components and from one melt to another, the stainless
Steel have a greater or lesser tendency towards magnetism.
Schaefller defines in a diagram the austenitic, non-magnetic structure of a steel, the
It should contain 17.5% chromium and I I, 4% nickel and is in a solution-annealed condition. This
corresponds to a steel of type 18/8. Unfortunately, the 18/8 type stainless steels are very
sensitive to cold hardening. As mentioned above, this phenomenon can lead to regression in the
Structure alpha, which explains why solution-annealed, non-magnetic material
hardens after drawing and can become partially magnetic, but magnetism is in no case
in terms of corrosion resistance.
The appearance of magnetism during work hardening is a phenomenon that occurs from a melt to the
others, according to the nature of the steel, despite identical analyzes, varies. These steels are
necessarily of good quality and have the normal rustproof properties
a non-magnetic steel is required, qualities with 25% chromium and 20% nickel must be used
The inconvenience of the magnetism occurring in the grades 18/8 can be due to
solution heat treatment or annealing at 1050 ° C and rapid cooling
become. In contrast to the hardenable steels, this treatment results in an undesirable one
reduction
the hardness. The throat fabric also dissolves, which leads to a return to the gamma structure,
so non-magnetic.

Hermat works almost exclusively with the stainless steel fittings
Stainless steel qualities V2A (AlSI 304) andV4 (AlSI 316). As mentioned above, cast stainless steel can
be magnetic.
However, magnetism is in no way related to the corrosion resistance of the stainless
Stainless steel material.