9. Stainless steel structures 1 Introduction, realization of stainless steel structures, material and its properties, Note: In the following lectures are used some figures taken from References presented in the end of the lecture No. 10.

Annual trend growth 5.58 %

35.4 Mt

1 Mt

World annual stainless crude steel production 2C08 - 9

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Prof. Ing. Josef Macháček, DrSc.

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2012

2005

EU - 27

Americas

Asia excl. China

China

Rest of world

Regional stainless steel production 2C08 - 9

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Prof. Ing. Josef Macháček, DrSc.

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• Formerly: • Nowadays:

predominantly as planar, facade, aesthetical elements. more and more also load bearing elements.

Examples of some planar and facade elements:

Finland

Germany

Japan

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Prof. Ing. Josef Macháček, DrSc.

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Facades Stainless steel and glass Spider (point) holders – usually from austenitic steel. Example: Four-point holder (170x170 mm) produced as casting (lost wax casting), and later bead blasted (by glass beads) for satin finish. Example of canopy roofing, 1.4432, glass t = 25 mm

1 - pre-tensioned cable Ø 20 mm (1.4404) 2 - stainless steel cylinder Ø 60 mm (1.4404) 3 - stainless steel holder (1.4404) 4 - stainless steel fixing (1.4404) 5 – insulating glass (8 toughened, 15 cavity, 2x6 laminated safety glass, total 35 mm) 6 – black silicone seal

glass supporting tube

Photo: LindnerArchitectur, Baden

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Prof. Ing. Josef Macháček, DrSc.

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Chrysler Building (New York), 1930 Cladding of the steel structure (which is bricked up) is from the austenitic steel Enduro KA-2 ("Nirosta" - nichtrostender Stahl, Krupp). Height: initially 246 m, final design 282 m - required by Chrysler; but at the same year N.Y. Bank 283, therefore finally 319 m (using the additionally slid-up 56 m spire).

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Prof. Ing. Josef Macháček, DrSc.

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Gateway Arch (St. Louis), 1965

(designed by E. Saarinen)

The structure is covered by stainless steel sheeting in total weight of 804 t. Up to 91 m the arch was as assembled of 142 prefabricated triangular stainless steel sections 3.7 m long (width at base 16 m, at top 5.2 m) . Once in place, each section had its double-walled skin filled with concrete and prestressed with 252 tension bars. Up to peak the structure is from carbon steel. Inside is a unique tram system to take visitors to the top. Centroid height 191 m, width 182 m.

6 mm stainless steel 30÷90 cm concrete 9 mm structural steel

catenary shape

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Prof. Ing. Josef Macháček, DrSc.

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Residential houses in Hertogenbosch (Netherlands) Austenitic steel 1.4401: sheeting with thickness t = 1 mm on timber decking.

Building envelopes in stainless steel, Euro Inox 2004 2C08 - 9

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Prof. Ing. Josef Macháček, DrSc.

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Technology park in Venice (Italy) Austenitic steel 1.4401: 0,6 mm stainless steel sheeting of 500 mm width, connected by standing seam with height of 75 mm.

Building envelopes in stainless steel, Euro Inox 2004 2C08 - 9

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Prof. Ing. Josef Macháček, DrSc.

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Ski jump, Innsbruck (Austria), 2002 (Zaha Hadid Architects, London) Austenitic steel 1.4301: 1 mm stainless steel sheeting blind-riveted to supporting frame steel structure.

Building envelopes in stainless steel, Euro Inox 2004 2C08 - 9

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Prof. Ing. Josef Macháček, DrSc.

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Ministry of culture, Paris Austenitic steel 1.4301: 12 mm stainless steel facade cladding cut-up by laser.

Detail

Suspension of the facade

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Institut du Monde Arabe, Paris, 1987 (architect Jean Nouvel) 1600 panels from austenitic steel (in mushrabiyah style – Arab traditional latticed-wood windows to see out without being seen) with central and 21 side electronic photosensitive iris shutters to control light levels (already not in operation).

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Load bearing stainless steel structures Grande Arche, Paris (1989) Prestresses concrete frame 1989, arch. J. O. Spreckelsen

La Défense Barrias 1883

Duplex stainless steel X2CrNiMoCu22-6-3-2 fy ≈ 500 MPa

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Prof. Ing. Josef Macháček, DrSc.

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La Défense

Grande Arche: Lift made from stainless steel. (arch. Francois Deslaugiers) • brushed finish of tubes, • electrolytically polished sand-blasted cast elements.

Stainless steel colonnade

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Monastery Santa Maria de Carracedo in Spain arch. Salvador P. Arroyo Stainless steel spiral staircase.

New Meets Old Euro-Inox, 2007 2C08 - 9

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Prof. Ing. Josef Macháček, DrSc.

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Porto airport (2003-6) Francisco Sá Carneiro Airport Stainless steel props.

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Prof. Ing. Josef Macháček, DrSc.

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Glasshouse Prague Castle 1999, arch. E. Jiřičná Grade 1.4301. Connections with 1 bolt, however insufficiently rigid, finally welded.

New Meets Old, Euro-Inox, 2007 2C08 - 9

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Prof. Ing. Josef Macháček, DrSc.

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Former bunker in Vreeland, Netherlands arch. UNStudio Stainless steel sheeting (1.5 mm) over steel frame structure, Grade 1.4404. Bunker used as a multifunctional meeting space facing National polo centre.

New Meets Old, Euro-Inox, 2007 2C08 - 9

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Prof. Ing. Josef Macháček, DrSc.

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Innovation centre in Montceau-les-Mines, France arch. Francis Soler The reflective façade of panels with stainless steel sheeting 1.5 mm. Grade 1.4301.

New Meets Old, Euro-Inox, 2007 2C08 - 9

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Prof. Ing. Josef Macháček, DrSc.

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Arch bridge in Andrésy (near to Paris) 2000, arch. M. Roy L = 32 m, all from stainless steel Grade 1.4401

t = 15 mm

tie rods 2x φ 36 mm

Pedestrian bridges in stainless steel Euro-Inox, 2004 welded cross beam with bracings 2C08 - 9

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Prof. Ing. Josef Macháček, DrSc.

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Arch bridge in York (GB) • arch L = 80 m: hollow cross section 600x200 mm (t = 20 and 80 mm), tilted at 50º to the vertical, duplex stainless steel 1.4462, • hangers: φ 19 mm, stainless steel 1.4401, • balustrade on both sides (incl. mesh at arch bottom) stainless steel Grade 1.4401. _________________________________________________ • longitudinal girder (welded box girder) from common steel plates with t = 10÷125 mm, • travelled surface 6 mm epoxy resin (non-slip coating).

Pedestrian bridges in stainless steel Euro-Inox, 2004 2C08 - 9

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Prof. Ing. Josef Macháček, DrSc.

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Helical Bridge, near Paddington, London Spiral pedestrian bridge, 1989, arch. J. O. Spreckelsen L = 7m, spiral from stainless steel tubes 140x6 mm, Grade 1.4401, laminated safety glass, t = 15 mm.

The bridge was originally designed to retract to one bank (to open for water traffic). With bridge moving, the spiral started a rotary movement giving the impression the bridge is being corkscrewed into bank. Nowadays the movement does not work.

Pedestrian bridges in stainless steel Euro-Inox, 2004 2C08 - 9

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Prof. Ing. Josef Macháček, DrSc.

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Prof. Ing. Josef Macháček, DrSc.

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Stress-ribbon pedestrian bridge in the Viamala Gorge, Switzerland 1996, Conzett, Bronzini, Gartmann L = 40 m; B = 0,85 m The structure form two ribbons from duplex stainless steel (60x15 mm), Grade 1.4462 and stone slabs acting after post-tensioning of ribbons as a monolithic slab.

Grade 1.4435, 10x40 mm Grade 1.4435, φ 16 mm

strips from duplex steel 1.4462

stone slabs 1100x250x60 mm (joint insert 3/60/1100 mm from aluminium) 2C08 - 9

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Prof. Ing. Josef Macháček, DrSc.

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Bridge in the Viamala Gorge (from above) Stainless steel used due to de-icing spray from a nearby road.

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Prof. Ing. Josef Macháček, DrSc.

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Sports hall in Quart (near Girona, Spain) 2001, arch. Luis Sánchez Cuenca 48x34,5 [m], outer space truss structure (double layer), constant depth is 1.2 m; roof decking is suspended, stainless steel Grade 1.4301 (30 t in total), only 3 tubes dimensions: 35x1,5, 53x1,5 a 70x2 [mm], simple joint using 1 bolt ø 22 mm, totally 10456 tubes with average length of 1.45 m.

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Prof. Ing. Josef Macháček, DrSc.

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Stonecutters Bridge, Hong Kong (China), 2009 (Design: Ove Arup & Partners + COWI A/S) - The third longest span in the world (3/2013). - 2000 t of duplex stainless steel 1.4462 (the upper part of composite steel and concrete pylons). - Shot peened surface finish to reach optimal day and night light reflection.

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Prof. Ing. Josef Macháček, DrSc.

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New Doha International Airport, Katar, 2009 (Completion of all construction expected in 2015, company Takenaka) - The airport will be able to handle 29 million annual passengers. - The largest stainless steel roof in the world (195 000 m2, 1600 t ). - Requirement: to resist heat and humidity, salt, favourable strength-to-weight ratio: → special AL 2003™ lean duplex stainless steel (21.5% Cr, 3.7% Ni, 1.8% Mo, 0.17% N).

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Prof. Ing. Josef Macháček, DrSc.

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New Doha International Airport Contractor: Metal Resources, USA (using InvariMatte® matte finish).

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Prof. Ing. Josef Macháček, DrSc.

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Stainless steel material and its properties Stainless steels belong into alloyed steels and have: min. 10,5% Cr max. 1,2 % C Grades (according to EN 10027, EN 10088): material name:

alloying elements, [%]

e.g.

X5CrNi18-10

means highly alloyed (> 5 % of one alloying element)

content of C [100 × %] - here 0.05%

particular steel in the group

material number: the same steel („Grade“) steel

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Prof. Ing. Josef Macháček, DrSc.

1.4301 stainless steel with ≥ 2.5 % Ni (has no Mo, Nb, Ti). E.g. group 44 includes molybdenum.

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Work hardening condition is very important in design. Due to cold rolling or other fabrication process increased both the yield strength fy and ultimate strength fu may be adopted. Grades for work hardened steels: CP350, CP 500, CP700 (for fu corresponding C700, C850, C1000) increased yield strength fy (0,2 % proofed stress) in [MPa] (Common Eurocode design is permissible only for grade CP350 (C700).

These Grades must be guaranteed by fabricator (e.g. for tubes), or by testing laboratory. According to principal properties (EN 10088: Stainless steels): a) Steels resistant to corrosion: Chromium forms corrosion-resisting self-repair oxide film on the steel surface. (Steels 1.40××, 1.41××, 1.43××, up to 1.46××: e.g. common 1.4301, 1.4401, 1.4462)

b) Steels resistant to fire: Steels with good resistance to oxidation and gases in temperatures > 500 ºC. (Steels 1.47××, 1.48××)

c) Heat-resistant steels: Retain strength, are resistant to deformations under loading and temperatures > 500 ºC. (Steels 1.49××) 2C08 - 9

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Prof. Ing. Josef Macháček, DrSc.

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Reduction factors under fire: comparison of carbon and stainless steel Ea,θ / Ea

1,0 0,8

modulus of elasticity

stainless steel

0,6

at 800 ºC: 7x higher for stainless steel

0,4 0,2

carbon steel

0 20º 200º

fy,θ / fy

yield stress

400º

1,0

600º 800º 1000º 1200ºC T [º C] carbon steel

0,8

stainless 1.4404

0,6

stainless 1.4529

0,4 0,2

stainless 1.4362

at 800 ºC: 2x higher for stainless steel

stainless 1.4003 stainless 1.4462

0 20º 200º

400º

600º 800º 1000º 1200ºC

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Prof. Ing. Josef Macháček, DrSc.

T [º C] 31

Distribution according to microstructure: • ferritic steels • martensitic steels

(C < 0,8 %, magnetic, poorly weldable), (C < 1,0 %, magnetic, hard – use for bearings etc.),

• precipitation-hardening steels (additional temperature hardening of martensite), ________

• austenitic steels

(Cr 17-19 %, Ni 8,5-14,5 %, Mo 2-2,5%) non-magnetic, in civil structures the most common, • austenitic-ferritic (duplex) steels (Cr 21-23 %, Ni 4,5-6,5 %, Mo 2,5-3,5 %, N 0,1-0,22 %) better, higher strength, higher corrosion resistance, more expensive, bridges. Ni [%] 20

austenitic steels

15 austenitic-ferritic steels 10 precipitationhardening steels 5

feritic steels

martensitic steels 0

10

15

20

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30

Cr [%] 32

Grades in EN 1993-1-4: Grade

according AISI/ASTM (American Iron and Steel Institute)

Chromium-nickel austenitic

1.4318 1.4301 1.4306, 1.4307 1.4311 1.4541

301LN 304 304L 304LN 321

Chromium-nickel-molybdenum austenitic

1.4401 1.4404, 1.4432, 1.4435 1.4406 1.4571 1.4439 1.4539

316 316L 316LN 316Ti 317LN 904L

Super austenitic

1.4529 1.4547

925 „6 % molybdenum“

Duplex

1.4362 1.4462

2304 2205

Ferritic

1.4003 1.4016 1.4512

„weldable 409“ 430 409

(improved corrosion properties, say 25%Cr, 7%Ni, 3,5%Mo, N)

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Significance of chemical elements Chromium

Forms a passive film with oxygen that prevent the further diffusion of oxygen into the surface. Composition needs to contain at least 10.5% to be a stainless steel.

Nickel

Increases ductility and toughness. Increase corrosion resistance to acids. In addition creates non-magnetic structure.

Molybdenum

Increases pitting and crevice corrosion resistance. Increases resistance to chlorides.

Copper

Increases corrosion resistance to sulphuric acid.

Manganese

Substitutes for nickel.

Titanium/Niobium

Ties up carbon and prevents inter-granular corrosion in welded zone of ferritic grades.

Nitrogen

Increases strength and corrosion resistance in austenitic and duplex grades.

Silicon

Improves resistance to high temperature scaling.

Sulphur

Usually kept low except for "free-machining" grades.

Carbon

Usually kept low. Used in martensitic grades to increase strength and hardness.

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New grades of stainless steels for structural engineering (low-cost): 1. Lean duplex grade: 1.4162

= Outokumpu LDX 2101 Acc. to ASTM S32101

Composition: 0,03% C; 21 ,5 % Cr; 5% Mn; 1,5% Ni; 0,3% Mo; 0,22% N Properties: • high strength (fy ≥ 450 MPa; fu ≥ 650 MPa; δ ≥ 30%; KV20º C ≥ 60 J; α = 0,0000135), • good weldability (similar as for other duplex steels), • corrosion resistance as for austenitic steels, • good fatigue resistance.

2. Ferritic steels: 1.4509

Acc. to ASTM 441: X2CrTINb18 Alloys improve weldability and workability (stabilized with titanium and niobium), oxidation resistance up to 950°C.

1.4521

Acc. to ASTM 444: X2CrMoTi18-2 Alloys (Ti, Nb, Mo) improve corrosion resistance. 2C08 - 9

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Mechanical properties of stainless steels: • non-linear stress-strain diagram

• different properties in tension, compression, transversal and

(Ramberg-Osgood’s model)

longitudinal direction σ [MPa]

σ [MPa]

stainless steels

compression - transversal tension - transversal compression - longitudinal tension - longitudinal

carbon steels

ε

ε

Note: Eurocode permits to calculate with single design values received for longitudinal tension. 2C08 - 9

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Common design according to Eurocode EN 1993-1-4:

• E = 200 000 MPa

(G = 77 000 MPa)

• fy (yield strength, (nominal stress, 0.2% proof stress) • fu (ultimate tensile strength)

acc. to Grade and thickness t

e.g. for most common steels with t ≤ 6 mm (or ≤ 75 mm): 1.4301 (austenitic)

fy = 230 (210) MPa

fu = 540 (520) MPa

1.4401 (austenitic)

fy = 240 (220) MPa

fu = 530 (520) MPa

1.4462 (duplex)

fy = 480 (460) MPa

fu = 660 (640) MPa

• great elongation to fracture (40 ÷ 60 %), • great thermal expansion (α = 0.000 017, common carbon steel 0.000 012), • impact strength and fracture toughness excellent up to - 40º C. 2C08 - 9

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More demanding calculations (in accordance with EN 1993-1-4): Ramberg-Osgood’s model:

ε=

σσ σ0.2 = ffye

⎛σ + 0.002 ⎜ ⎜ E ⎝ fy

σ

n

R-O coefficient

⎞ ⎟ ⎟ ⎠

σ

σ

fuf max σ0.2= fyf p

E0.2

EE

ε o,e

ε

ε

ε

max εmax

e ε0.2 = 0.002

Common model:

E E11

EE ε

p εε0.2

ε εεumax

a)

However, better model valid for stresses σ ≥ f (excellent up to ε ≤ 10 %, proposed by Gardner y and Nethercot, 2004) is recommended in Eurocode 1993-1-4 Annex C:

ε = 0.002 +

fy E

+

σ − fy E

⎛ σ − fy + εu ⎜ ⎜ ⎝ fu − fy

m

⎞ ⎟ + ε 0.2 ⎟ ⎠

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Prof. Ing. Josef Macháček, DrSc.

m = 1 + 3.5

fy fu 38

Suggested grades for atmospheric applications (acc. to EN 1993-1-4): Type of environment and corrosion category Grade to EN 10088

N

S

V

N

S

V

N

S

V

N

S

V

1.4006 1.4016

indoor only

-

-

indoor only

-

-

-

-

-

-

-

-

yes

yes

yes

yes

yes

the best

the best

the best

the best

often to clean

often to clean

often to clean

-

yes

the best

the best

often to clean

-

1.4362 1.4401 1.4404 1.4406 1.4571

can be used

can be used

can be used

can be used

yes

yes

yes

yes

yes

yes

the best

the best

the best

the best

often to clean

the best

the best

often to clean

1.4439 1.4462 1.4529 1.4539

can be used

can be used

can be used

can be used

can be used

can be used

can be used

can be used

yes

can be used

can be used

1.4301 1.4311 1.4541 1.4318

Rural

Urban

Industrial

Marine

the best

yes the best

N – low corrosive conditions (low humidity or low temperatures), S – typical for that type of environment, V – corrosion higher than typical (high humidity, high temperatures or aggressive air pollutants). 2C08 - 9

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Examples of use of stainless steel in structural engineering: • Austenitic steels (lower fy, α ≈ 0.000 016 ÷ 0,000 018): 1.4301 (X5CrNi18-10)

- low corrosion resistance demands (low-cost),

1.4401 (X5CrNiMo17-12-2)

- higher corrosion resistance, sheeting and profiles with sandblasted and electrobrightened finishes,

1.4404 (X2CrNiMo17-12-2) 1.4432 (X5CrNiMo17-12-3)

- higher corrosion resistance, roof sheeting, ties in bridges, - pressed profiles with satin finish, spider (point) holders of glass panes etc.,

spec. (X2CrNiMoCu22-6-3-2)

- high yield strength (fy = 500 MPa), used in Grande Arche, α ≈ 0.000 014,

1.4435 (X2CrNiMo18-4-3)

- higher corrosion resistance, bridge handrail.

• Austenitic-ferritic (duplex) steels (high fy, α ≈ 0.000 013): 1.4362 (X2CrNiN23-4)

- exposed load-bearing parts of structures,

1.4462 (X2CrNiMoN22-5-3)

- high corrosion resistance (also against chlorides, SO2 , ...), exposed load/bearing bridge parts. 2C08 - 9

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