Republic of Iraq
Ministry of Higher Education
And Scientific Research
University of Diyala
College of Engineering
Ferritic stainless steel
By :
‫كاظم‬ ‫انيس‬
‫تايه‬
Supervisor by
‫أ‬
.
‫خليل‬ ‫عادل‬ ‫د‬
1

Introduction
 Ferritic steel is a grade of stainless steel alloy that
contains over 12% chromium.
 It differs from other forms of stainless steel in two
critical regards: its molecular grain structure and its
chemical composition.
 Ferritic stainless steel is actually defined as a straight
chromium non-hardenable class of stainless alloys that
have chromium contents ranging from 10.5% to 30% and
a carbon content of less than 0.20%.
 These steels are non-hardenable by heat treatment, and
only marginally hardenable by cold rolling.
2

Ferritic Stainless Steels
• Advantages
– Relatively Cheap
– Low Corrosion rate – pitting & SCC
– Low tendency of sensitization
• Limitations
– High ductile to brittle transition temperature.
– 475oC Embrittlement
– Formation of undesirable intermetallics such as
Sigma, Chi and Laves phases.
– Low Weld Ductility with increase in Cr Content
– Sensitization
– Limitation of Strength at higher temperature
3

Grade C Mn Si Cr Mo P S Comments/Applications
405 0.08 1.0 1.0 11.5-14.5 - 0.04 0.03 0.1-0.3 Al
409 0.08 1.0 1.0 10.5-11.75 - 0.045 0.045 (6xC) Ti min
429 0.12 1.0 1.0 14.0-16.0 - 0.04 0.03
430 0.12 1.0 1.0 16.0-18.0 - 0.04 0.03
446 0.20 1.5 1.0 23.0-27.0 - 0.04 0.03 0.25 N
Composition of Important Ferritic Stainless steels
4

Effect of Cr Concentration on the impact properties of Fe-Cr Alloys
5

Fe-Cr equilibrium Diagram
6

Pseudo Binary Phase Diagram of Fe-18Cr Alloy
7

Mechanism of Sensitization
8

Pseudo binary Phase Digram Fe-18Cr-8Ni SS with C
C solubility limit in Fe-18Cr-8Ni SS
9

Sensitization Curves for 304 and 347 SS
347 S
Effect of Mo on sensitization
Effect of N on Sensitization
10

PRE = %Cr + 3.3 x %Mo + 16 x %N
Pitting of Stainless Steels
11

Super Ferritic/Austenitic Stainless Steels
• To enhance further the Pitting corrosion,
Chloride Stress Corrosion cracking, super
ferritic, super-austentic Stainless Steels
are made :
• They have Mo – upto 6%
• Nitrogen from 0.1-0.2%
• Mostly used in Offshore structure, ships
and marine applications
• Very costly compared to conventional SS
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Effect of ferrite content on the pitting rate of duplex SS steel Welds of
varying N levels – exposed to 6% FeCl3 + 0.05N HCl solution
13

Cr concentration profile around austenitic-Ferrite interface
Containing M23C6 carbide
Pseudo binary phase diagram of 65Fe-Cr-NiAlloy
14

IC378 - The darker etching phase is
ferrite and the remainder is austenite
Microstructures of some Duplex SS
IC381 (dark phase is ferrite).
IC381 (dark phase is ferrite
A219 The austenite is yellow and ferrite is
dark brown, with the sigma phase white.
15

Effect of C addition on the gamma loop in Fe-Cr alloys
16

The properties of ferritic
stainless steel
 Ferritic stainless steels are characterised by their body-
centred cubic (BCC) crystal structure, and they contain
11% to 27% chromium and small amounts of ferrite
stabilisers, such as niobium and titanium.
 Ferritic alloys exhibit ferromagnetic behaviour up to a
temperature known as the Curie point (650 °C – 750
°C), beyond which materials lose their permanent
magnetic properties.
 The BCC grain structure of ferritic alloys, which is the
same as that of pure iron at room temperature, is the
reason for its magnetic nature.
 Ferritic stainless steels, similar to austenitic stainless
steels, cannot be strengthened by heat treatment.
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18
ferritic stainless steel

The applications of ferritic stainless
steel
 The magnetic properties of ferritic grades is a major advantage
and enabler for many of their applications.
 Fastening parts and induction heating, for example, both make
use of this property in the production of induction cookers and
magnetic fasteners.
 Ferritic alloys also have a lower thermal expansion coefficient and
higher thermal conductivity than austenitic grades, which makes
them particularly suitable for heat transfer applications such as
cooking utensils.
 The corrosion resistance of some ferritic stainless steels is
sufficient to replace austenitic steel 304, and they can be used in
the production of dishwashers, kitchen sinks and food processing
equipment.
 Some specialty grade ferritic stainless steels have additional
molybdenum and higher chromium content, which makes them
useful in corrosive seawater applications. 19

Uses of Ferritic stainless
steels.
 Ferritic steels are chosen for their resistance to
stress corrosion cracking,
 which makes them an attractive alternative to
austenitic stainless steels in applications where
chloride-induced SCC is prevalent.
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References
1. Lacombe, P.; Baroux, B.; Beranger, G., eds. (1990). Les Aciers
Inoxydables. Les éditions de Physique. pp. Chapters 14 and 15.
ISBN 2-86883-142-7.
2. The ferritic solution. 2007. ISBN 978-2-930069-51-7.
3. The International Nickel Company (1974). "Standard Wrought
Austenitic Stainless Steels". Nickel Institute. Archived from the
original on 2018-01-09..
4. "304 vs 430 stainless steel". Reliance Foundry Co. Ltd.
5. "Frederick Mark Becket American metallurgist". Encyclopaedia
Britannica.
6. Cobb, Harold M. (2012). Dictionary of Metals. ASM International. p.
307. ISBN 9781615039920.
7. Charles, J.; Mithieux, J.D.; Santacreu, P.; Peguet, L. (2009). "The
ferritic family: The appropriate answer to nickel volatility?". Revue
de Métallurgie. 106: 124–139. doi:10.1051/metal/2009024.
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