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Structural
applications of ferritic
stainless steels Katherine Cashell
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14 December 2012
About the project
60% funded by EC RFCS
40% funded by stainless steel industry
3 year project (July 2010 – July 2013)
8 European partners
• Co-ordinated by SCI
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Overview: today’s discussion
Background and objectives of the project
Key findings to date
• Material response
• Member response
• Connections
• Corrosion
What next?
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A little about ferritics…
Compared to carbon steel
• Good corrosion-resistance
Compared to typical stainless steel
• Low-cost
• Price-stable (no nickel!)
As well as….
• Durable, strong, good impact-resistance
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Objective of the project
Generate & provide technical information
so ferritics can be specified in buildings
• Structural performance
• Fire resistance
• Atmospheric corrosion resistance
• Guidance on connections
Investigate and highlight the advantages
of this steel (economic, environmental…)
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14 December 2012
WP9
Project Co-
ordination
WP1
Material
Properties
WP2
Member
performance
WP3
Composite
structures
WP4 Fire
performance
WP5 Welded
Connections
WP6 Bolted
Connections
WP7
Corrosion
WP8
Dissem-
ination
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WP1: End user requirements (Arup)
Unknown in the construction industry
Provide data on:
• Corrosion and durability
• Mechanical properties
• Welding procedures and joining
• Toughness
• Grade selection
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WP1: Material properties
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WP1: Material properties
14 December 2012
Typical
cold-rolled
ferritic
Typical
austenitic
fy 350N/mm2 280N/mm2
fu 500N/mm2
650N/mm2
εu
(A80)
27% 55%
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WP1: Material properties
Relatively low fu/fy ratio (by SS standards)
n value = under review
• Look to be relatively high (like CS)
• Annealed/cold formed
Es = under discussion
• Around 200 N/mm2
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WP1: Toughness properties
1. Charpy tests
• -40 to +20°C
• Results: OK toughness for stabilised.
• Need to do fracture toughness tests
2. Fracture toughness tests
• Happening early 2013
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WP2: Member performance
Aim: to develop efficient design methods for
ferritic thin-walled members
• Numerical analysis: Based on GMNIA and use
ABAQUS
• Experimental validation: Thin walled top-hat and
hollow sections
Design expressions developed
Recommendations for the use of DSM
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Key findings (to date):
Existing stainless steel buckling curve can
be used in all cases
• except cold-rolled hollow sections which
should use carbon steel curves
Higher “n” factor of ferritic steels can be
taken into account for open sections
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WP3: Composite performance
Ferritic stainless steel decking
• Decking tests (construction stage)
• Composite slab tests
• Stud welding trials
• Push-out tests
• Thermal performance
• Fire performance
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WP3: Thermal Modelling
Utilisation of inherent thermal mass in
comp. slab for efficient low-carbon solution
Detailed FE analysis used to understand,
quantify and compare behaviour
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Temperature distribution (night)
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Thermal flux for various profiles
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WP4 Fire tests: Columns
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WP4 Fire tests: Columns
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WP4: Column analysis
-30
-20
-10
0
10
20
30
0 100 200 300 400 500 600 700 800
Axia
l d
ispla
cem
ent
(mm
)
Furnace temperature ( C)
80x80x3-3000
Test
FE
-30
-20
-10
0
10
20
30
0 100 200 300 400 500 600 700 800
Ax
ial
dis
pla
cem
ent
(mm
)
Furnace temperature ( C)
120x80x3-2500
TestFE
-30
-20
-10
0
10
20
30
0 100 200 300 400 500 600 700 800
Ax
ial d
isp
lace
men
t (m
m)
Furnace temperature ( C)
80x80x3-2500
Test
FE
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WP4 Fire tests: Beams
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WP5: Welded joints
Mechanical tests and metallographic
examination of welds
Design guidance
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WP5: Key findings
Cold-rolled materials have adequate toughness
down to temperatures around 0°C.
HAZ toughness is reasonable
Susceptible to grain growth at temperatures
above 950 °C - decreased toughness
Welding heat input should be kept low
Use austenitic welding consumables
Stabilised ferritics are readily weldable
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WP5: Design rules welded joints
The strength rules in EN 1993-1-8 can be
applied to stainless steels in conjunction with
the rules in EN1993-1-3
No experiments have been carried out on
ferritic stainless steel tubular joints to date
The level of design guidance that can be
offered is limited
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WP6: Bolted connections
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WP7: Corrosion
Develop a comprehensive understanding of
the durability of the ferritic grades
Base material + welded + bolted
Exposure field tests, Accelerated tests,
Electrochemical tests
Design guidance
Comparative study of the service life of
building components
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In conclusion
Very successful consortium
Results & findings are starting to emerge
Toughness & durability are the key issues
What next for ferritics?
• Watch this space…
Questions?
14 December 2012
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