2025 PRODUCT GUIDE-INTERACTIVE - Flipbook - Page 152
Fastener Solutions
GRADES AND NOMENCLATURE OF STAINLESS STEELS
It is very important that readers of this document
understand the differences between grades of stainless
steels and the implications of using different grades in
different applications.
There are four main types of stainless steel, which serve to
classify the crystalline grain structure of the stainless-steel
alloy. It is critical that we acknowledge that stainless steels
are not homogenous in nature like a pure element (such as
aluminium or iron, etc), but are made up of a lattice
structure of crystals (also known as grains) which contain
the various alloying elements in the stainless steel.
THE FOUR TYPES OF STAINLESS STEELS ARE:
AUSTENITIC:
Given the name due to the iron in the grains turning to its allotropic
gamma phase, which is known materially as “austenite”. These grades
are non-magnetic and cannot be readily hardened by heat treatment like
carbon steels or even other types of stainless-steels. They can only be
hardened to a very limited degree by cold-working. These stainless teels
generally give the very best resistance to oxidation.
MARTENSITIC:
Given the name due to the presence of martensite, which itself is created by
the rapid cooling of austenite before it could form into cementite. These
grades are extremely hard and the resistance to oxidation varies wildly
between grades, but are almost universally less than that of austenitic grades.
FERRITIC:
Given the name due to the presence of ferrite, which is simply the iron in the
grains remaining in their allotropic alpha phase. These grades of stainless steel
harden extremely well at the cost of resistance to oxida琀椀on, indeed many ferri琀椀c
grades of stainless will rust as quickly as carbon steels.
DUPLEX:
Duplex stainless steels generally contain equal parts of an austenitic
stainless steel and a ferritic stainless steel in an attempt to give the
benefits of both alloying grades.
Grades of Steel Used by Evolution Fasteners UK Ltd
SAE
UNS
ISO 3506-1
EN 10088-3
TYPE OF ALLOY
304
S30400
A2-70
1.4301
Austenitic chromium-nickelmanganese alloy
316
S31600
A4-50
1.4401
Austenitic chromium-nickelmanganese alloy
316L
S31603
A4-50
1.4404
Austenitic chromium-nickelmanganese alloy
904L
N08904
A5-70
1.4539
Austenitic chromium-molybdenum
alloy
152
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