“Ferritic Stainless Steels for Construction Applications”

Nancy Baddoo

Steel Construction Institute

UK

CHARLES HATCHETT SEMINAR 2015

CBMM ©

1

Ferritic Stainless Steels for

Construction Applications

Nancy Baddoo

15 July 2015

The Steel Construction Institute SCI

Established in 1986 to

develop and promote

the effective use of

steel in construction

Independent member-

based organisation

Staff of 28

Composite construction, Connections, Fire engineering, Sustainability,

Bridges, Light steel construction, Stainless steel, High strength steel….

Construction supply chainR

eg

ula

tio

ns

Architect Cost Consultant

Consulting Engineer Design team

General Contractor

Steelwork Contractors

Steel Producers

Mining Companies

Design standards

Construction

standards

Production standards

Owner

Specialist

manufacturerSCI

What do construction specifiers need?

Design standards & supporting guidance

Design examples & software

Information on product availability

Fabrication and erection specifications

Case studies

Market development strategy

Influence specifiers in favour of steel

Support the supply chain

• Make design in steel easier than in other materials

(e.g. standards development)

• Remove barriers

• Continuous improvement & innovation

• Communications (e.g. courses, webinars)

• Technical support (e.g. publications, software, Industry

Focus Groups)

Stainless steel in the built environment

18 August 2015

Stainless steel in industrial structures

18 August 2015

Cost considerations

Life cycle cost analyses show that stainless steel can be

the cheapest option compared to materials requiring more

maintenance.

Before

After

Stainless Structurals

Ferritic stainless steel structures

18 August 2015

Electrification mastsIndustrial support structures

3Cr12 structures in South Africa > 30 years old

Which grade of stainless steel?

Ferritics vs austenitics

Higher strength

Less non-linear yielding

Lower cost for a given corrosion resistance

Easier to roll-form and achieve flatness

Low coefficient of thermal expansion/higher

thermal conductivity less weld distortion

Magnetic

18 August 2015

18 August 2015

EN AISI Cr content (%) Other key alloying elements (%)

Standard grades

1.4003 ‘3Cr12’ 10.5 - 12.5 -

1.4016 430 16.0 - 18.0 -

Special or stabilised grades

1.4509 441 17.5 - 18.5 Niobium, titanium

1.4621 445 20.0 - 21.5 Niobium, copper

1.4521 444 17.0 - 20.0 Molybdenum, titanium and/or

niobium and/or zirconium

Future applications of ferritics?

Ferritic stainless steels

18 August 2015

Fujitsu Building, Brisbane

The Sentinel, Takapuna Beach, Auckland

University of New South Wales

Future applications of ferritics?

Substitute for galvanised steel (permanent formwork,

roof purlins, supports to services such as cable trays.

18 August 2015

Semi-enclosed unheated

environments (e.g.

railways, grandstands,

bicycle sheds etc.) and in

cladding support systems,

windposts, masonry

supports

18 August 2015

Future applications of ferritics?

Energy-efficient floors

Exposed soffit (lower face) of a concrete or composite floor thermal mass of the floor slab regulate the building temperature

• Floor slab absorbs heat (daytime) and releases it (night-time)

• Reduces the cost of heating and cooling the building

Future applications of ferritics?

Where galvanizing is not viable

Supporting structure for solar panels, particularly in desert

locations where the abrasive effect of the sand can be

harmful to galvanised steel

18 August 2015

Structural

applications of

ferritic stainless

steels (SAFSS)

18 August 2015

Ferritic stainless steels:

Low nickel alloys

cheaper and more cost-stable

than austenitic and duplex

alloys but…..

limited toughness & weldability

(t>3mm)

18 August 2015

Research Fund for Coal & Steel (RFCS) gives

funding of over €50 million every year to innovative

projects to enhance the safety, efficiency and

competitive edge of the EU coal and steel industries.

Enabled significant research on all topics related to steel in construction

(fire, light gauge, bridges, cellular beams, composite, sustainability,

renovation, stainless…)

18 August 2015

Objective: Generate performance data design guidance

for a group of ferritic stainless steels with potential for

structural applications (focus on t<6 mm)

Background to SAFSS

WP1: Material Performance

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Characterisation of

stress-strain behaviour

- 120 tests (tens + compr,

various t)

- slightly anisotropic

(transverse values 12% higher

than longitudinal)

Fracture toughness- CVN impact tests: -130°C to +240°C

- Dependence of DBTT & upper shelf

energy on grade, t and direction

(longit. or transverse)

WP2: Structural Members

Model calibration tests on

RHS & top-hats:

- Bending tests (10 no.)

- Internal & external

support tests (10 no.)

WP3: Composite

floor systems

Production feasibility study

Cofraplus 60 profile

Decking tests at the

construction stage:

- simply supported tests

- continuous tests

- rotation tests

- web crushing tests

Comparison with tests on

galvanised decking

WP3: Composite floor

systems

18 August 2015

Composite slab tests4 long and 4 short span tests(4.3 m and 2.5 m)Lower resistance to first slip, but similar ultimate resistance to galv. steel

Shear connection testsThrough deck weldingPush tests

Thermal massTemperature regulation performance of composite floor with exposed deck

Fire performanceEffect of strength & stiffness retentioncharacteristics

18 August 2015

WP4: Fire Resistance

WP5: Welded Connections MIG/MAG, MMA, TIG weld processes

Common austenitic filler metal 308LSi as a reference, less

common ferritic filler metals 409LNb, 430LNb, 430Ti

Mechanical tests & metallographic examination of welds:- Tensile tests on transverse weld specimens

- Impact toughness tests on sub-size specimens

- Vickers hardness tests

- Metallographic observations: optical microscopy & SEM

- Sensitisation with standard and modified Strauss corrosion tests

WP6: Bolted & Screwed Connections

18 August 2015

Shear Lap Bolted connections

Single & double shear tests

Net-section, bearing, block

tearing

Equal angle tests

Net-section, bearing

Screw connections

Self-drilling screws

Single shear

Generally bearing failure

(hole elongation, out of

plane curling)

WP7: Corrosion Resistance

18 August 2015

Pollutants at locations characterised

Plain, welded, bolted, different finishes

Samples were collected & evaluated after

12 and 18 months exposure

Field Trials

WP7: Corrosion Resistance continued

18 August 2015

Accelerated corrosion tests

To measure relative

performance of

different grades and

finishes

Electrochemical

corrosion tests

To evaluate pitting &

uniform corrosion

resistance

Samples inside climatic

chamber after 504 hours

WP7: Corrosion

Resistance

(441) (441)

(445)(445)

(444) (444)

WP8: Exploitation

of results

Submission to EN

1993-1-4 WG- new grades

- design material values

- buckling curve

- durability info

- material modelling

- strength & stiffness retention

- thermal properties

www.steel-stainless.org/ferritics

Public web site:

- all WP deliverables

- Final Report

- Brochure

www.steel-

stainless.org/designmanual

- Guidance

- Commentary

- Design examples

Design Guidance to Eurocodes

1st Edition 1993

2nd Edition 2002

3rd Edition 2006

4th Edition 2016?

Eurocode 3: Part 1-4 (EN 1993-1-4)

Design of steel structures.

Supplementary rules for stainless steels (2006)

Modifies and supplements rules for carbon steel given in other parts of Eurocode 3

Applies to buildings, bridges, tanks etc

Austenitics, duplexes & ferritics

EU Research: Innovative steel glass composite

structures for high performance building skins

Ferritic stainless steel in high performance

glazing units (grade 471)

Steel framed, adhesively bonded to glass

plated structures

18 August 2015

Material Coefficient of

thermal expansion

10-6 K-1

Glass 9

Aluminium 24

Carbon steel 12

Ferritic stainless 10

Thank you…