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Stainless Shines in Darling Harbour

Mirror finished stainless steel sign blades can be found scattered along the central boulevard of Sydney’s revitalised Darling Harbour.

Through a recent $3.4 billion transformation, Darling Harbour has become Australia’s largest entertainment and events precinct boasting world class facilities, including over 40,000 square metres of exhibition space. This urban rejuvenation builds on the success of Darling Harbour and in turn, will generate $200 million annually in economic benefit for the NSW economy.

The Harbour is ringed by attractions, entertainment and extraordinary waterfront restaurants. The Boulevard creates an active north-south pedestrian connection between Central Station and Cockle Bay. Its prime location is within walking distance of most points in the Sydney CBD therefore wayfinding signage is pivotal in navigating people through and around the precinct.

ASSDA Member and Accredited Fabricator Stoddart were engaged by Lend Lease to manufacture and install 19 stainless steel wayfinding sign blades for Darling Harbour’s ‘once in a generation’ re-development. The sign blades are featured in groups of two and three, each standing seven metres tall and two metres wide.

258 panels of grade 316 stainless steel were used for the sign blades in order to provide housing for LED display screens throughout the precinct. The structural stainless steel frame also mounts speakers and power outlets. All stainless steel used in this project was supplied by ASSDA Member, Fagersta Steels

Featuring a mirror profile finish, the stainless steel signs create a stunning visual effect through the reflection of the countless city lights and surrounds of the bustling tourist and entertainment mecca.

Stainless steel was specified by landscape architects, Hassell, for its aesthetic appeal and high-quality attributes. The Harbour’s salt water environment and location was also a consideration in the materials specification, being adjacent to the city centre.

It is only fitting for quality material such as stainless steel to be showcased in one of the world’s most desirable entertainment and event destinations.

This article featured in Australian Stainless magazine - Issue 64, Summer 2018/19.

Stainless Opulence

Exemplary stainless steel craftmanship has delivered a sophisticated and lavish cocktail lounge in the heart of the Gold Coast’s entertainment hub.

Cocktail connoisseurs have been flocking to Cherry, The Star Gold Coast to experience the designer drinks on offer in the grandeur of the lounge featuring a 22m long bar. Refurbished in 2017 as part of the first stage of the property’s major transformation, its upmarket look and feel was inspired by its sister venue at The Star Sydney.

Central to Cherry’s luxury design is the intricate, gold metalwork featured in the VIP booth screens, lounge surrounds and balustrades. ASSDA Member and Accredited Fabricator Minnis & Samson fabricated these elements using grade 316 stainless steel tube and flat bar supplied by ASSDA Member Australian Stainless Distributors

The stainless steel was mirror polished prior to the electrostatic application of a special coating to achieve the gold colour finish. Crystal hardware and lush red velvet furnishings complement the gold stainless steel to deliver the opulent design and vision of the cocktail lounge.

Stainless steel is a high quality and high strength material, and was specified for its longevity, hygienic properties and aesthetic appeal. In addition, stainless steel offered better weldability to achieve the detail in the metalwork’s curvature design.

This article featured in Australian Stainless magazine - Issue 63, Spring 2018

The Emerging Dragon

A stainless steel masterpiece

Michael Van Dam’s award-winning stainless steel dragon sculpture plays a major part in Chinese culture dating several thousand years. 

The dragon is a symbol of prosperity, strength, courage and resolve. The designer himself was born in the year of the Dragon (1964). As a result of welding thousands of stainless steel links together, alongside Van Dam’s creativity, a durable and aesthetically pleasing piece of art came to life – The ‘Emerging Dragon’. 

The Emerging Dragon has been showcased at various locations and shows on the Gold Coast. This stainless steel masterpiece was originally created for the 2015 Swell Sculpture Festival held on Currumbin Beach which attracted 250,000 visitors over ten days, winning both Kid’s and People’s Choice Awards. 

The 3m high by 5m long sculpture was created from more than 4000m of 4mm 316 stainless steel chain and weighs an impressive 700kg. Following fabrication the sculpture was electropolished. All stainless steel chain used for Michael’s sculptures is supplied by ASSDA Member BRIDCO

Van Dam’s stainless steel art pieces are well equipped to face the rigours of outdoor display. This led to grade 316 stainless steel chain being his choice of material for all his sculptures. He believes the use of stainless steel for his pieces makes for a unique use of the material, it feels great to the touch, can withstand various environments and will outlast most other materials. 

This article featured in Australian Stainless magazine - Issue 63, Spring 2018

Stainless and Sand Go Hand-In-Hand

With the use of stainless steel, indigenous artist Kylie Graham’s interest in Whadjuk Noongar customs and culture has helped bring a symbolic sculpture to life at Perth’s recently revitalised Scarborough beach. 

The people of Whadjuk Noongar are the traditional owners of Perth. The Ethereal Welcome Hand sculpture represents a hand casting sand which acknowledges the custodians, the people of Whadjuk and their enduring spiritual connection to the land and sea. 

In respect to Noongar cultural customs, visitors are to throw a handful of sand into the water as an introduction of themselves to the spirits and ancestors. It was only fitting for the 3D sculpture to cast its presence near water and is primarily constructed from grade 316 stainless steel supplied by ASSDA Members Midway Metals and Stirlings Australia

The 6.5m tall sculpture uses 5mm stainless steel plate throughout the entire wire frame hand spanning 4m long. The finish is 2B and all the welds are TIG welded, cleaned and passivated. The four support columns are also fabricated from 316 stainless steel. 

Illustrated in the palm of the stainless steel hand, pouring down to the ground is gold anodised aluminium cladding, with perforations backlit with LED lights which can be programmed for multiple occasions.

At the back of the hand, the design of a dolphin and three fish is laser cut through the stainless steel, to reflect the importance of the relationship between Noongars and mammals.

Stainless steel was chosen as the main sculptural material for its durability, excellent corrosion resistance and aesthetically-pleasing properties. This stunning work-of-art was designed, fabricated and installed by local art consultant Forever Shining.

The Ethereal Welcome Hand is one of six pieces of artwork along the redeveloped foreshore and can be found between the surf club and swimming pool. It has been welcoming the public since March 2018 and will continue to do so for many years to come thanks to the durable life span of stainless steel.

This article featured in Australian Stainless magazine - Issue 62 Winter 2018.

Ferritic Stainless Steels

Ferritics account for approximately 25% of stainless steel use worldwide. The name arises because these alloys have similar properties to carbon steels when they are bent or cut and, unlike the well-known 304 and 316 austenitic grades, ferritics are strongly attracted to a magnet.

There is a major misconception that ferritic stainless steels are less corrosion resistant than austenitic alloys. On the contrary, for any required level of corrosion resistance (or Pitting Resistance Equivalent [PRE]), you can select a specific stainless steel from either the austenitic or ferritic family depending on the physical properties desired. Another similarity of these two families of stainless steel is that neither can be hardened by heat treatment. However, a significant difference is that, in common with carbon steels, ferritic stainless steels become brittle when used in sub-zero temperatures. The actual transition temperature depends on the specific alloy, but it increases for welded fabrications.

Often regarded as the simplest stainless steel alloy, ferritics are steels (iron and a small addition of carbon) with at least 11% chromium added to produce the passive chromium oxide film. This self-repairing chromium oxide layer gives stainless steel its corrosion resistance. The first stainless steels developed in 1913 were ferritics with a high carbon content. Today, those alloys are called martensitics and are used for high hardness blades or wear resistant surfaces. The alloys now known as ferritic stainless steels have been used commercially for many decades, primarily as sheet cladding up to about 3mm that do not require welding. The Fujitsu building in Brisbane for example is clad in profiled ferritic stainless steel sheet, and the use of perforated and solid ferritic stainless steel sheeting is featured in the ceiling and fascia paneling in Sydney’s Wynyard Walk.

Apart from the 12% chromium utility alloys, the sheet thickness limits for the supply and welding of ferritics are due to its metallurgical structure. Unlike austenitic stainless steels, the microstructure does not transform during welding, and so the initially microscopic ferrite grains can grow and embrittle the metal.

Ferritics have gained wider acceptance since changes in its alloy design and production methods allowed welding. The adoption of the Argon Oxygen Decarburisation (AOD) refining process in the 1970s also assisted, allowing both the reduction of impurity levels and, critical for welding, good control of both carbon and nitrogen content.

Table 1: Selected Ferritic Alloys

Common name

UNS

C%

Cr%

Mo%

Others

PRED

Main uses

409

S40900

0.03

11

-

0.3Ti

11

Car exhausts

4003, 3/5Cr12A

S40977

0.02

11

-

0.5Ni

11

Rail wagons, non-cosmetic structures

430B

S43000

0.03

17

-

-

17

Cladding – not marine

444

S44400

0.02

18

2

0.4(Ti+Nb)

25

Instant hot water units

446

S44600

0.15

24

-

-

24C

High temperature

447

S44700

0.01

29

3.8

0.1Cu,0.1Ni

42

Seawater tubing

Notes:
A. Balance of composition important to avoid welding corrosion issues
B. Also derivative grades with low carbon and Ti/Nb to allow welding
C. Not good indicator of corrosion resistance especially if welded because of high carbon
D. For comparison, the PRE of 304 is ~18.5 and 316  ~23.5.

Available Ferritic Alloys and Applications
The Ferritic Solution (TFS), published by the International Stainless Steel Forum, lists 71 ferritic alloys in ASTM, EN and JSA standards, although most are in sheet form. For example, A240 lists 26 alloys as flat product while ASTM A276 only has nine alloys listed as bar or shape. TFS classifies ferritic alloys into five groups based on chromium content:

- Chromium (10.5% to 14%)
- Chromium 14% to 18%)
- Titanium and/or niobium added to avoid sensitisation with welding
- Molybdenum additions for corrosion resistance
- Weldable group of alloys with higher corrosion resistance and chromium >18%, added molybdenum and low impurity content.  

Table 1 lists common names, UNS numbers, typical compositions and applications of representative alloys. There are also families of alloys derived from the same root UNS numbers. In addition, a growing number of proprietary ferritic alloys have been and are being developed especially in Japan. The PRE column is a measure of corrosion resistance based on composition, i.e. PRE = %Cr + 3.3% Mo. The 16%N term used for austenitic and duplex grades is omitted because nitrogen is virtually insoluble in ferritic alloys. 

Corrosion and Heat Resistance
These are not the same. Oxidation (or scaling) resistance of stainless steels in air depends on the stability of the oxide layer (or scale) on the surface. This is not the thin (nanometres) passive film formed in water but the thicker, high temperature oxide formed above about 250oC. Its protective properties depend on its bond to the metal surface below. In turn, this depends on the relative expansion of the oxide and the metal surface. 

As shown in Table 3, ferritic alloys have low thermal expansion compared to austenitics, which means the adhesion of their protective scale is better in thermal cycling conditions. In practical terms, this means that ferritic alloys have higher scaling temperature limits for intermittent service than in continuous service, whereas the reverse is true for austenitic alloys.

At temperatures in the high hundreds (oC), the relatively low strength of most ferritic alloys limits their use, although the niobium-treated ferritics have similar strength to the austentic alloys. Ferritic (and duplex) grades should not be used in the band around 475oC as metallurgical phase transformations cause embrittlement during extended exposures.

In oxygen-rich environments, the simple wet corrosion resistance of ferritic, austenitic and duplex alloys is well-described by the PRE index as given in Table 1. The predictions are for a passive surface and will be unreliable if the surface has been contaminated by carbon steel or if welding heat tint has not been removed.

PRE does not influence the spidery cracking that occurs in austenitic alloys that are stressed and exposed to warm or hot chloride solutions. Ferritic and duplex grades are effectively immune to this stress corrosion cracking attack and it is the reason why instant hot water tanks used in kitchens are ferritic alloys, usually 444.

Left: Fujitsu Building in Brisbane is clad in profiled ferritic stainless steel sheet. Right: Ferritic stainless steel sheeting featured in the ceiling and fascia paneling in Sydney's Wynyard Walk.

Mechanical and Fabrication Properties
Because of their microstructure, ferritic stainless steels behave very similarly to carbon steels in bending, roll forming, spinning and shaping. Fabricators can use the same techniques for ferritics when forming roofs or couplings.

Ferritics do not cold-work like austenitics and so, for the same thickness, they have less springback. Although deep drawing is easier for ferritics than austenitics, the higher chromium ferritics can suffer from ridging, so there are not many deep drawing applications. Stretch forming can only be to about 50% of that achieved with austenitics, as might be expected from the difference in ductility. Table 2 compares the mechanical properties of several ferritics with 304 and carbon steel. In broad outline, ferritic stainless steels have a higher yield (or strictly 0.2% proof stress) than austenitic stainless steels, lower tensile strength and about half the elongation at fracture. The modulus of elasticity is similar to carbon steels, so deflections under loading will be comparable.

Table 2: Typical room temperature mechanical properties

Common name

Yield MPa

Tensile

MPa

Elongation at break %

Modulus

GPa

409

170

380

20

220

4003, 3/5Cr12

L:320

T:360

480

18

220

430

205

450

22

220

444

275

415

20

220

304

270

650

57

200

Carbon steel

300

430

25

215

Welding

With the exception of the 12% chromium utility grades, welding of ferritics requires more skill than welding austenitics because of their sensitivity to impurities, which may cause cracking in the heat-affected zone. Very thorough attention to cleanliness is required as well as the use of high purity shielding gas and care in gas shielding – particularly outside the workshop where drafts can be a problem. Because of the risk of grain growth (and consequent low toughness) with extended periods at high temperatures, low heat input is required and pulsed welding equipment is a useful tool. This metallurgical sensitivity is the reason why ferritics are rarely available in thicknesses greater than 3mm. However, the low thermal expansion and better thermal conductivity of ferritics compared to austenitics means that welding distortion is less critical for all ferritics (refer to Table 3).

Like all stainless steels, the corrosion resistance of welded ferritics is restored if all heat tint is removed after welding, preferably by pickling. Mechanical abrasion is a good second best provided the surface roughness is not excessive.

The 12% chromium utility ferritics are widely used in welded thick structural sections in coal wagons, heavy vehicle chassis, high temperature exhaust ducting, fire proof fencing, low corrosion wear locations and multiple structures where aesthetics are not the primary consideration, i.e. where a brown adherent cosmetic haze is not considered a problem. The 12% utility ferritics are discussed in more detail in Australian Stainless #52 (available at www.assda.asn.au).

SUMMARY

Some ferritic grades have been in large scale commercial production for many years, but the variety of grades now available has only been possible because of new melting and refining technologies. A large number of grades now exist, and a great deal of active research and alloy development is continuing.

Ferritic stainless steels offer:
- Formability similar to carbon steels and can be readily bent, roll formed, pressed to shape or spun
- Higher yield strength and lower ductility than austenitics
- Comparable range of corrosion resistances to other stainless steel families
- A wide range of possible applications.

Table 3: Physical properties of Ferritic and Austenitic stainless steels

Property

Ferritic

Austenitic

Density (kg/m3)

7700

7900

Thermal expansion

(0-100oC μm/m/oC)

10.5

16.0

Thermal conductivity

(20oC, W/m.oC

25

15

Specific heat

(0-100oC, J/kg.oC

430-460

500

Electrical resisivity

(nΩ.m)

600

750-850

 

This article featured in Australian Stainless magazine - Issue 62 Winter 2018.