1

STAINLESS STEEL IN CONSTRUCTION

Cátia Maria Abbott Ferreira de Sousa

Instituto Superior Técnico, Lisbon

Abstract

The main purpose of this paper is to analyze the concept of stainless steel and how it can be

useful in construction, particularly in structural elements. To achieve this, its constitution is

analyzed throughout this article, the principal alloying elements, properties and behaviors

specified in European Norms (EN) and the North American Standards (ASTM), and evaluate

how this material, in certain situations, can offer more advantages than carbon steel commonly

used in reinforced concrete structures. This article will also discuss two experimental trials that

were done on two types of austenitic stainless steel. The first test analyzes the mechanical

characterization by tensile tests and the second test evaluates the susceptibility that stainless

steel has corrosion relative to carbon steel.

Key-Words: Stainless steel; Alloying element; Normative references; Structure durability;

Corrosion prevention; Mechanical properties; Economical availability.

1. Introduction

The oxidation of the steel caused by the phenomenon of corrosion leads to an increase volume

of reinforcement that causes delamination of the concrete in the coating zone damaging in this

way the reinforcement. In general, corrosion is caused by the physical-chemical interaction of a

metal with its environment that results in significant changes in the properties of metal and often

degradation thereof. This is therefore an electrochemical process usually spontaneous, which

ally or not the mechanical stress affects the durability and performance of materials (Louro,

2008).

There are numerous techniques for preventing corrosion of reinforcement in order to address

the mechanism of deterioration of the concrete such as, for example, the correct choice of the

thickness of the concrete coating. When the lifetime of the structures is very high, there are

several methods that can be applied directly to the concrete ensuring the durability thereof,

such as, for example, reducing the water/cement ratio of the concrete.

However, to use these solutions it necessarily implies paying for the high cost of maintenance

and repair, as these solutions do not entirely eliminate the occurrence of corrosion.

The replacement of carbon by reinforcement bars of stainless steel means greater longevity of

the structures and minimizes the impacts associated with the monitoring and maintenance of

concrete structures. Furthermore, although stainless steel appears as an alternative solution to

methods of prevention, they still have certain limitations, primarily related to economic

difficulties. According to (Tula and Helene, 2000), the stainless steel reinforcement is 4 to 13

times more expensive than carbon steel reinforcement, which directly affects the initial costs of

the works.

Stainless steel is a very versatile material, with excellent mechanical characteristics associated

with a high corrosion resistance. This is a 100% recyclable material, thus enabling sustainable

development and the preservation of the environment.

The durability of stainless steels is based on the principle that they are alloys of iron and

chromium or iron, chromium, nickel, and other elements, which contain enough quantity to

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ensure the presence of the passivation mechanism, this being responsible for the high corrosion

resistance of these steels, regardless of the pH of the concrete.

The term "steel" does not designate a particular material, but a remarkably diverse set of

materials, where hundreds of different alloys, which are different in terms of chemical

composition and crystalline microstructure properties and areas of application (Colaço, 2005).

Depending on the chemical composition and the temperature to which it is subjected during the

manufacturing process, the steel may have different microstructures, which correspond to

different mechanical properties.

The alloying element iron, from room temperature up to 912ºC, the iron atoms are arranged in a

cubic body-centered microstructure, which is designated as ferrite or phase-α. Since 912ºC up

1394ºC, iron undergoes a series of transformations and its crystalline microstructure changes to

face-centered cubic structure, also called austenite or phase-ɣ. From 1394ºC up to melting

point, the iron passes again having body-centered cubic microstructure (Colaço, 2005).

Given that the carbon is considerably smaller than the iron atom, the carbon atoms can occupy

the interstices formed by iron atoms, in this way giving greater yield strength and tensile

strength of the material (Colaço, 2005).

With respect to alloying elements, when used together these may lead to slightly different

properties of steel than if they had been used separately. However, the chromium is the most

important alloying element in stainless steel.

For a steel can be classified as stainless steel, this has to have in their chemical composition

minimum chromium content of 10.5% and maximum carbon content of 1.2%, in order to create

the necessary conditions for the formation of the protective chromium oxide layer which gives

this class of steels greater corrosion resistance (IMOA, 2009).

The alloying elements can be divided between gamagenes and alphagenes, depending on the

swelling of the austenitic or ferritic field area, respectively (Colaco, 2005). Gamagenes alloy

elements, such as nickel, manganese and nitrogen have the function of stabilizing the austenite

of the steels thus enabling the microstructure centered cubic crystal faces. They are elements

that provide good corrosion resistance and good mechanical properties. Alfagéneos alloy

elements, such as silicon, aluminum, molybdenum and tungsten, whose function is to decrease

the hardenability of the steel and gives them a better mechanical strength when worked at high

temperatures. In the case of molybdenum and tungsten, these also have the function of

improving the flow of the steels and improve corrosion resistance by stabilizing the protective

passive layer of the stainless steels, especially in rich environment of chloride

The standard EN 10088-1: 1995 "Stainless Steels - Part 1: List of stainless steels" [n1] asserts

that stainless steels can be grouped into five main categories, according to their microstructure:

ferritic steels, martensitic steels, percipitation steel-hardening, austenitic steels and austenitic-

ferritic steel which generally designate as duplex.

The ferritic stainless steels, they are characterized by having very low contents of carbon and

chromium contents always higher than 16%, where the steels end up with a degree of

resistance relatively low. The corrosion resistance of this class of steels is higher than that of

martensitic but lower than that of austenitic and duplex steels. The martensitic stainless steels

contain carbon levels a little higher with respect to ferritic steels, reflecting into higher strength.

The mechanical strength of martensitic steel can be increased by heat treatment, giving rise to

a class of hardened stainless steels by precipitation. The austenitic and duplex stainless steels

have good corrosion resistance and high strength, which makes this type of steel in a good

choice for the building industry, namely in buildings structural part [n1].

When we talk about stainless steels it is very important that you understand the definition of the

phenomenon of corrosion. In the case of metals, corrosion is their oxidation and this is an

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electrochemical phenomenon. However, corrosion can happen in many ways, in which the

correct identification of the type of corrosion is essential to assess the mechanism and the

correct application of protective measures or treatment. However, there are some corrosive

processes that are beneficial and of great importance in the metal industry, such as the case of

oxidation of stainless steel which is responsible for the formation of the protective chromium

oxide film process (Gentil, 1996). Stainless steel can suffer six distinct processes of corrosion:

uniform corrosion, pitting, crevice corrosion, intergranular corrosion, stress corrosion and

galvanic corrosion.

2. Standardization and application

2.1. European norms (EN)

All European Standards relating to stainless steel supports, in general, the physical, chemical

and mechanical properties, allowable dimensional tolerances, the information that the buyer

must provide, tests, certifications, a precise description of all products and standards quality.

The aim of the European Standards is to make the market of stainless steel throughout Europe

easier and more intuitive, to minimize errors during the ordering process.

The publication EN 10088-1: 1995 "Stainless Steels - Part 1: List of stainless steels" [n1], lists

and describes the various existing classes of stainless steel, providing its chemical composition,

various physical and mechanical properties. The publication EN 10088-2: 1995 "Stainless

Steels - Part 2: Technical delivery conditions for sheet/plate and strip for general purposes" [n2],

describes the properties and terms of delivery for products in sheet form and contains 68 types

of stainless steel. This standard refers essentially to the layout application that companies

should do to the metallurgical enterprises. It also refers to the permitted tolerances. The

publication EN 10088-3: 1995 "Stainless Steels - Part 3: Technical delivery conditions for semi-

finished products, bar, rods, and section for general purposes" [n3], describes the technical

conditions of delivery of semi-finished products, plates / strips rolled sheets and hot or cold, as

well as bars, wire and rolled profiles processed hot or cold, made in stainless steel.

2.2. North American Standard (ASTM)

The ASTM A955, “Standard Specification for Deformed and Plain Stainless Steel Bars for

concrete Reinforcement” [n4] covers deformed and plain stainless steel bars for concrete

reinforcement proposed to be used in applications requiring corrosion resistance or controlled

magnetic permeability. For each specimen, one tension test, one bend test, if required, and one

set of dimensional property tests shall be made.

The publication ASTM A276 - 13, "Standard Specification for Stainless Steel Bars and Shapes"

[n5] refers to the chemical composition of stainless steels and the respective mechanical

requirements.

The ASTM A240, "Standard Specification for Chromium and Chromium-Nickel Stainless Steel

Plate, Sheet and Strip for Pressure Vessels and for General Applications" [n6] refers to

chromium, chromium-nickel and chromium-manganese-nickel in stainless steel with the form of

plates and sheets for general applications. The standard indicates that the steel must conform

to the chemical composition requirements specified in this standard. Beyond the chemical

composition requirements, the material must also comply with specified mechanical properties.

The ASTM A480, “Standard Specification for General Requirements for Flat-Rolled Stainless

Steel and Heat-Resisting Steel Plate, Sheet and Strip” [n7] covers general requirements for flat-

rolled stainless and heat-resisting steel plate, sheet, and strip.

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The ASTM A555, “Standard Specification for General Requirements for Stainless Steel Wire

and Wire Rods” [n8] covers general requirements that shall apply to stainless wire and wire

rods. The material may be furnished in one of the conditions detailed in the applicable material

specification, that is, annealed, bright annealed, or cold worked.

The ASTM A564/A564M – 10, “Standard Specification for Hot-Rolled and Cold-Finishes Age-

Hardening Stainless Steel Bars and Shapes” [n9] covers bars and shapes of age-hardening

stainless steels. Hot-finished or cold-finished rounds, squares, hexagons, bar shapes, angles,

tees, and channels are included.

The ASTM A580-13a, “Standard Specification for Stainless Steel Wire” [n10] covers stainless

steel wire, except the free-machining types. It includes round, square, octagon, hexagon, and

shape wire in coils only for the more commonly used types of stainless steels for general

corrosion resistance and high-temperature service.

The ASTM standards, such as European Standards, these are indispensable tools in the

classification, chemical and mechanical evaluation and definition of the metallurgical properties

of different types of stainless steel. These standards serve only to guide laboratories, producers

and buyers to ensure the quality and safety of the product.

2.3. Application

Architects and engineers are, increasingly, enjoying the various benefits offered by the unique

combination of properties of stainless steels for a large number of applications in construction.

Nowadays, the market of metallurgical stainless steels offers a wide range of sizes and various

kinds of resistance, which allows this to be easily used in all kinds of works.

There are currently numerous examples of bridges that were built with stainless steel elements.

An example is the Helix pedestrian bridge in Singapore.

For environments such as those prevailing in Singapore, it was essential that the chosen stainless steel had excellent long-term corrosion resistance. Several alloys could achieve this requirement but grade EN 1.4462 (S31803) provides more than adequate resistance while meeting other requirements of good availability, cost effectiveness, ease of fabrication and the structural/architectural requirements. It also provides good fatigue strength as well as high resistance to stress corrosion cracking [s1].

Currently, Stainless steel is commonly used in building roofs. An example for this type of work is

the most coverage constructed with stainless steel, which is located in the New Doha

International Airport, Qatar and came into operation in 2012. The wavy roof was built with

duplex stainless steel enriched with molybdenum (S32003) [s2].

There are many other applications in which the stainless steel has an essential role as it is the

case of units of flue gas desulfurization and desalinization plants. These are environments that

present one of the most demanding challenges for materials due to them being highly

aggressive environments. For this type of works it is often used duplex stainless steel due to its

high mechanical strength, high corrosion resistance and high toughness [s2].

Stainless steel is a material that is able to combine an extraordinary mechanical capacity at high

corrosion resistance, however, for certain environments and under certain conditions, there

must be some measures that should be taken to avoid of structures collapsing.

In 1985, a concrete cover of a pool collapsed in Uster, Switzerland. The structure had 13 years

of use. The roof was supported by pillars of stainless steel EN 1.4301 (AISI 304), which had

collapsed due to corrosion phenomena. Investigations following the tragedy came to

demonstrate that the collapse was due to the hot and humid environment rich in chlorides

associated with tension steel [s3].

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The stress corrosion cracking occurs when the steel is subjected to tension in a specific

corrosive environment. In the case of pools, the products used for disinfection of water

containing large amounts of ammonia and chlorine. These elements, when evaporated and

condensed on the steel surface, form a highly corrosive film, which can lead to stress corrosion

cracking. This type of corrosion can be controlled through the preparation of a project that

facilitates the inspection and maintenance of the structure, provided that the risk analysis

structure can provide and through more careful selection of the type of stainless steel used in

the structure [s4]. This collapse has not been the only one registered in structures of stainless

steel due to stress corrosion cracking. In the Netherlands, in 2001, a false ceiling supported by

elements of AISI 304 stainless steel in a pool fell. Two other similar accidents occurred, one in

Finland in 2002 in a hotel pool and another in the UK, also with a pool cover in 2003, where

steel was used AISI 304.

3. Experimental work

3.1. Description

To answer one of the objectives of the work, which corresponded to look to proceed for a

comparative analysis of the mechanical performance and corrosion resistance of stainless

steels and carbon steels, we proceeded to the development of an experimental campaign. The

developed experimental campaign included two parts, the mechanical characterization and

evaluation of corrosion susceptibility, carried out on steels used in the performance of

structures.

The selected materials are austenitic stainless steels of the type AISI 304 and AISI 316 The

chemical compositions percentage of both stainless steels according to EN 10088-1: 1995

"Stainless Steels - Part 1: List of stainless steels" [n1] are presented in Table 3.1.

Table 3.1 - Nominal chemical composition of austenitic stainless steel type AISI 304 and AISI 316 according to EN 10088-1: 1995 [n1].

Designation AISI/ASTM

Chemical composition [%]

C Si Mn P S N Cr Mo Ni

304 ≤0,07 ≤1,00 ≤2,00 ≤0,045 ≤0,015 ≤0,11 17,00 a 19,50 - 8,00 a 10,50

316 ≤0,07 ≤1,00 ≤2,00 ≤0,045 ≤0,015 ≤0,11 16,50 a 18,50 2,00 a 2,50 10,00 a 13,00

Carbon steels selected were the A400NR and the A500NR. The chemical compositions of the

steels A400NR and A500NR are similar, according to the specification LNEC 449-2010 [n11]

and 450-2010 [n12], Table 3.2.

Table 3.2 - Chemical composition of carbon steel A400NR and A500NR, second specifications LNEC E449-2010 [n12] and E450-2010 [n13].

Designation Chemical composition [%]

C P S N Cu

A400NR 0,240 0,055 0,055 0,014 0,850

A500NR 0,240 0,055 0,055 0,014 0,850

3.2. Mechanical Resistance

The tensile test is often used to provide basic design information on the strength of materials.

The tensile test involves subjecting a test piece to a growing and continuous axial load, while

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simultaneously registering the stretching that it is subjected to. Tensile tests were performed

according to EN 10002-1: 2006: "Metallic materials - Tensile testing" [n13].

The Table 3.3 identifies all steel and shows the number of specimens submitted to mechanical

tensile test with the objective to study their mechanical behavior. All test pieces tested had a

length (Lo) of 200 mm, Figure 3.1.

Table 3.3 - Tensile test (Part 1) - Identification of steels and the number of specimens tested.

Ø

[cm]

Steel type

Carbon steel Stainless steel

A400NR A500NR AISI 304 AISI 316

Ø 8 2 - 2 2

Ø 16 - 1 - 1

Ø 20 - 2 2 -

The Table 3.4 presents all samples analyzed of the trial and their respective identification

number, steel type, length (Lo) and the diameter (nominal and measured).

Table 3.4 - Identification of the test pieces used in the first part of the mechanical tests.

Test pieces Steel type Lo [mm] Ønominal [mm] Ømeasured [mm]

Carbon steel C1 A400NR 200 8 8,0 C2 A400NR 200 8 8,0 C3 A500NR 200 16 16,0 C4 A400NR 200 20 20,0 C5 A400NR 200 20 20,0

Stainless steel I1 AISI 316 200 8 8 I2 AISI 316 200 8 8 I3 AISI 304 200 8 8 I4 AISI 304 200 8 8 I5 AISI 316 200 16 16 I6 AISI 304 200 20 20 I7 AISI 304 200 20 20

3.2.1. Tested materials and methods

For the tests an INSTRON machine was used. This test equipment is in the Laboratory of Civil

Engineering at Instituto Superior Técnico. The tests were performed according to standard EN

10002-1: 2006 [n14] at room temperature and at a speed of 0.2 mm/s.

The testing of traction permit making diagrams Force-Displacement that, after taking into

account each section of the tested test pieces and the difference in initial and final length, we

obtain a diagram Tension-Extension.

3.2.2. Results

The INSTRON machine used for the tensile test provides diagrams Force-Displacement. It is

necessary to determine the respective diagrams Tension-Extension. For this, it was considered

that:

Figure 3.1 - Test pieces of Part 1 of the tensile test.

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The INSTRON machine Laboratory of Civil Engineering at Instituto Superior Técnico does not

contain extensometers, we considered the following calculation,

The Lfree is the free distance between claws. It is known that the length calculated here is not the

actual extension, however is the solution adopted for the calculation thereof.

The Figures 3.2 and 3.3 show the Tension-Extension diagrams of specimens of carbon steel and

stainless steel, respectively.

Figure 3.2 - Carbon Steel - Diagrams Tension-Extension.

Figure 3.3 - Stainless Steel - Diagrams Tension-Extension.

The Table 3.5 presents all the results obtained from the tensile test.

Table 3.5 - Results obtained from the tensile test.

Carbon Steel

Designation Steel type Ønominal [mm]

Re [MPa]

Rm [MPa]

lu [mm]

lo = 5Ø [mm]

C1 A400NR 8 532 600 99 80 0,24 C2 A400NR 8 535 600 * * * C3 A500NR 16 545 659 196 160 0,23 C4 A400NR 20 479 589 271 200 0,35 C5 A400NR 20 474 582 268 200 0,34

Stainless Steel

Designation Steel type Ønominal [mm]

Rp0,2 [MPa]

Rm [MPa]

lu [mm]

lo = 5Ø [mm]

I1 AISI 304 8 630 684 108 80 0,35 I2 AISI 304 8 577 693 110 80 0,38 I3 AISI 316 8 632 772 102 80 0,28 I4 AISI 316 8 716 772 104 80 0,3 I5 AISI 316 16 782 872 * * * I6 AISI 304 20 521 738 270 200 0,35 I7 AISI 304 20 494 732 271 200 0,36

0

100

200

300

400

500

600

700

800

900

0,0

0

0,0

4

0,0

8

0,1

2

0,1

6

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0

0,2

4

0,2

8

0,3

2

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6

0,4

0

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4

0,4

8 0

100

200

300

400

500

600

700

800

900

0,0

0

0,0

4

0,0

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2

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6

0,2

0

0,2

4

0,2

8

0,3

2

0,3

6

0,4

0

0,4

4

0,4

8

[MPa]

ε

Ø16 – A500NR

Ø8 - A400NR

Ø20 - A400NR

[MPa]

ε

Ø16 – AISI316

Ø8 – AISI 316

Ø20 – AISI 304

Ø8 – AISI 304

8

* It was not possible to measure lu due to rupture of the specimen occurred along the clutches of the INSTRON

machine.

3.3. Corrosion susceptibility

This experimental component was to study the corrosion susceptibility of austenitic stainless

steel, AISI 304 and AISI 316, relative to carbon steel, A400NR and A500NR, when exposed to a

saline solution at constant temperature and see how far the corrosion influenced or not their

mechanical performance.

After selected types of steel to make the study of corrosion and to compare the properties

chosen, proceeded to demand the necessary standards for the purpose. The corrosion test

developed corresponds to an adaptation of the procedure described in ASTM B117-11:

"Standard Practice for Operating Salt Spray (Fog) Apparatus" [n15]. Thus, there was a solution

prepared of 5% by weight sodium chloride (NaCl) and 95% distilled water, as described to this

standard.

3.3.1. Tested materials and methods

The protocol for testing susceptibility to corrosion of stainless steel involves exposing test pieces to a corrosive environment for 110 consecutive days. Then, the specimens were placed permanently to a level approximately 1 cm above the salt solution.

The test was performed in various test pieces of carbon steel and stainless steel identified in

Table 3.6, with the objective of comparing the evolution of the corrosion of stainless steels

relatively to carbon steel. All test pieces tested had a length (Lo) of 200 mm, except the two

pieces of stainless steel AISI 316 with Ø8, Figure 3.6.

Table 3.6 - Identification of steels and the number of test pieces used in the testing of susceptibility to corrosion.

Ø [cm]

Steel type

Carbon steel Stainless steel

A400NR A500NR AISI 304 AISI 316

Ø 8 4 - 5 2

Ø 12 4 - 2 -

Ø 16 - 4 - 1

The Table 3.7 shows all the samples analyzed in this test and their respective identification

number, steel type, length (Lo) and the diameter (nominal and measured).

Table 3.7 - Identification of the test pieces used in corrosion testing.

Carbon Steel

Designation Steel type Lo [mm] Weight [g] ΔM [%] Ønominal [mm] Ømeasured [mm]

C1 A400NR 200 76,77 -0,16 8 8,0 C2 A400NR 200 76,59 -0,12 8 7,9 C3 A400NR 200 77,29 -0,10 8 8,0 C4 A400NR 200 77,32 -0,08 8 8,0 C5 A400NR 200 174,60 -0,07 12 12,0 C6 A400NR 200 178,14 -0,07 12 12,0 C7 A400NR 200 169,24 -0,12 12 12,0 C8 A400NR 200 175,28 -0,06 12 12,1 C9 A500NR 200 316,11 -0,05 16 16,0

C10 A500NR 200 318,27 -0,04 16 16,0 C11 A500NR 200 314,66 -0,05 16 16,0 C12 A500NR 200 315,55 -0,04 16 16,0

Figure 3.6 - Test pieces of Part 2 of the tensile test

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Stainless Steel

Designation Steel type Lo [mm] Weight [g] ΔM [%] Ønominal [mm] Ømeasured [mm]

I1 AISI 316 150 59,70 0,00 8 8,0 I2 AISI 316 150 58,92 0,00 8 8,0

I3 AISI 304 200 78,59 0,00 8 8,0

I4 AISI 304 200 78,94 0,00 8 8,0 I5 AISI 304 200 78,94 0,00 8 8,0 I6 AISI 304 200 79,42 0,00 8 8,0 I7 AISI 304 200 78,92 0,00 8 8,0 I8 AISI 304 200 178,06 0,00 12 12,0 I9 AISI 304 200 177,96 0,00 12 12,0 I10 AISI 316 200 309,58 0,00 16 16,0

During the experimentation multiple weighings were carried out to test pieces. These were

made and reported two weighings per week, one on Monday and one on Friday.

In order to enable more expeditious analysis of the results of the experimental campaign, the

percentage mass loss was calculated for each of the test samples using the following formula:

Where Mi refers to the mass of the test piece at time i, and M0 is the initial mass of the test

piece.

After the test pieces were subjected to 110 days a corrosive environment, they were subjected

to a test of mechanical characterization. The Table 3.10 identifies the steel and shows the

number of test pieces used in this test. All test pieces had an initial length of 20 cm, except for

the two test pieces of AISI 316 with Ø8, which had an initial length of 15 cm, Figure 3.7.

3.3.2. Results

Next is shown the result of experimental campaign for determining susceptibility to corrosion in

graphs with the percentage of mass loss related to time in days, in order to be able to determine

the susceptibility to corrosion of various steels tested, Figure 3.7 to 3.9.

Figure 3.7 - Results obtained in the test of susceptibility to corrosion in test pieces with Ø8.

Figure 3.8- Results obtained in the test of susceptibility to corrosion in test pieces with Ø12.

-0,16

-0,14

-0,12

-0,10

-0,08

-0,06

-0,04

-0,02

0,00

0

7

14

21

28

36

43

64

71

78

85

92

99

10

6

-0,16

-0,14

-0,12

-0,10

-0,08

-0,06

-0,04

-0,02

0,00

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14

21

28

36

43

64

71

78

85

92

99

10

6

AISI 316 -1

AISI 316 – 2

AISI 304 – 3

AISI 304 - 4

AISI 304 - 5

AISI 304 - 6

AISI 304 - 7

A400NR - 1

A400NR - 4

A400NR - 2

A400NR - 3

t (days)

ΔM (%)

t (days)

ΔM (%)

AISI 304 – 8

AISI 304 -9

A400NR - 8

A400NR - 5

A400NR - 3

A400NR - 2

10

Figure 3.9 - Results obtained in the test of susceptibility to corrosion in test pieces with Ø16.

After completion of testing of susceptibility to corrosion, the samples were submitted to

mechanical tests with the aim to assess possible changes in mechanical properties due to

corrosion. Figures 3.10 and 3.11 show the tension-extension diagrams of the specimens of

carbon steel and stainless steel, respectively.

Figure 3.10 - Carbon Steel - Diagrams Tension-Extension.

Figure 3.11 - Stainless Steel - Diagrams Tension-Extension.

The results for the mechanical tests are described in Table 3.8.

Table 3.8 - Results obtained from the tensile test.

Carbon Steel

Designation Steel type Ønominal [mm]

Re [MPa]

Rm [MPa]

lu [mm]

lo = 5Ø [mm]

C1 A400NR 8 523 592 1,1 * * * C2 A400NR 8 517 580 1,1 99 80 0,24 C3 A400NR 8 514 581 1,1 * * * C4 A400NR 8 506 578 1,1 99 80 0,24 C5 A400NR 12 440 574 1,3 147 120 0,23 C6 A400NR 12 436 564 1,3 152 120 0,27 C7 A400NR 12 495 626 1,3 155 120 0,29 C8 A400NR 12 460 596 1,3 152 120 0,27 C9 A500NR 16 542 662 1,2 202 160 0,26

C10 A500NR 16 552 671 1,2 201 160 0,26 C11 A500NR 16 567 684 1,2 * * * C12 A500NR 16 537 657 1,2 * * *

-0,16

-0,14

-0,12

-0,10

-0,08

-0,06

-0,04

-0,02

0,00

0 7 14 21 28 36 43 64 71 78 85 92 99 106

0

150

300

450

600

750

900

0,0

0

0,0

4

0,0

8

0,1

2

0,1

6

0,2

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4

0,2

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0,3

2

0,3

6

0,4

0

0,4

4

0,4

8 0

150

300

450

600

750

900

0,0

0

0,0

6

0,1

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0,2

4

0,3

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0,3

6

0,4

2

0,4

5

0,4

7

0,4

9

AISI 316 – 10

A500NR - 9

A500NR - 12

A500NR - 10

A500NR - 11

ΔM (%)

t (days)

ε

[MPa]

ε

Ø16 – A500NR

Ø8 – A400NR

Ø12 – A400NR

Ø8 – AISI 304

Ø16 – AISI 316 [MPa]

Ø12 – AISI 304

Ø8 – AISI 316

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Stainless Steel

Designation Steel type Ønominal [mm]

Rp0,2 [MPa]

Rm [MPa]

lu [mm]

lo = 5Ø [mm]

I1 AISI 316 8 562 687 1,2 109 80 0,36 I2 AISI 316 8 594 686 1,2 110 80 0,38 I3 AISI 304 8 697 771 1,1 102 80 0,28 I4 AISI 304 8 696 772 1,1 104 80 0,30 I5 AISI 304 8 697 768 1,1 107 80 0,34 I6 AISI 304 8 554 668 1,2 109 80 0,36 I7 AISI 304 8 686 764 1,1 108 80 0,35 I8 AISI 304 12 592 732 1,2 166 120 0,38 I9 AISI 304 12 552 722 1,3 172 120 0,43

I10 AISI 316 16 699 910 1,3 * * *

* It was not possible to measure lu due to rupture of the specimen occurred along the clutches of the INSTRON

machine.

The Figures 5.12 and 5.13 show the comparison between the values of the mechanical

characterization, Rm, carbon steels and stainless steels that were not and they were subjected to

the test of susceptibility to corrosion.

Figure 3.12 – Carbon Steels – Rm values in samples submitted and not submitted to corrosion testing.

Figure 3.13 – Stainless Steels – Rm values in samples submitted and not subjected to the corrosion test.

Analyzing the results in the graphs of Figures 3.7 to 3.9 is concluded that the corrosion

resistance of stainless steel is considerably higher than that presented by carbon steels. It was

verified that at 110 days of testing, the test pieces of stainless steel suffered no corrosion.

The study of the mechanical behavior of steel without undergoing the corrosion test after

undergoing the corrosion test, behavior revealed the following aspects:

After rupture, the test pieces of stainless steel there was considerably more heat than

carbon steels, which means that a large part of the mechanical energy produced during

the test is dissipated by the form of heat;

The rupture of stainless steel is much more violent than that seen in carbon steels;

The Stainless steels has no level of yield, contrary to what happens with carbon steels,

as can be seen in the graphs presented in the previous section.

0

150

300

450

600

750

900

0

150

300

450

600

750

900

Ø8 Ø12 Ø16 Ø20

Rm [MPa]

Aft

er

co

rro

sio

n

A400NR

Aft

er

co

rro

sio

n

No

co

rro

sio

n

A400NR A500NR A400NR

Aft

er

co

rro

sio

n

No

co

rro

sio

n

No

co

rro

sio

n

Rm [MPa]

AISI 304 AISI 316 AISI 304

AISI 316

AISI 304

No

co

rro

sio

n

Aft

er

co

rro

sio

n

No

co

rro

sio

n

Aft

er

co

rro

sio

n

Aft

er

co

rro

sio

n

No

co

rro

sio

n

Aft

er

co

rro

sio

n

No

co

rro

sio

n

Ø8 Ø12 Ø16 Ø20 Ø8

12

Analyzing the ductility of several samples that had previously been subjected to the corrosion

test, it is concluded that the corrosion process expressed a negative influence. The majority of

tested steels expressed reducing the extent of rupture after having undergone the corrosion test.

4. Conclusions

We conclude that there is a combination of properties that make stainless steel a desirable

material in a large number of applications in architecture and construction.

According to Tula and Helene, 2000, the total cost of the life cycle, together with the direct

operating costs over the useful life, armed with stainless steel structures, have huge

advantages. The total cost for the cycle of life of these structures, which employ this "protection

method", is often lower than the total cost of the traditional reinforced concrete structures, more

so lower if the rate of economic inflation in the country were lower too.

With the experimental campaigns it was concluded that the corrosion has a negative effect on

ductility of rods, reducing the extension at break and energy absorption capacity with increasing

corrosion. It was also found that the austenitic stainless steels of the type AISI 304 and AISI 316,

have better performance in terms of mechanical characteristics as compared with the revealed

by A400NR A500NR and carbon steels.

References

(Colaço, 2004) Colaço, Rogério; “Engenharia e Vida – Engenharia civil, construção e desenvolvimento”;

Ano I, N.01, Abril 2004.

(Colaço, 2005) Colaço, Rogério; “Materiais de construção – Aços – Guia de utilização”, Loja da Imagem;

Outubro de 2005.

(Gentil, 1996) Gentil, Vicente; ”Corrosão” Rio de Janeiro; Livros Técnicos e Científicos Editora, S. A., 3ª

edição, 1996.

(IMOA, 2009) “Practical Guidelines for the Fabrication of Duplex Stainless Steel”; IMOA – The International

Molybdenum Association, Second Edition, London, 2009.

(Louro, 2008) Louro, A. S. M. da Silva; “Comportamento de vigas de betão armado com aço inoxidável”;

Dissertação de Mestrado, Universidade Técnica de Lisboa, Instituto Superior Técnico; Lisboa,

2008.

(Souza, 1982) Souza, S. A.; “Ensaios mecânicos de materiais metálicos”; 5ª Edição, Edgard Blucher, São

Paulo, 1982.

(Tula e Helene, 2000) Tula, Leonel; Helene, Paulo; “Contribuição ao estudo da resistência à corrosão de

armaduras de aço inoxidável”; Boletim Técnico da Escola Politécnica da USP, Departamento

de Engenharia Civil de Construção Civil – Série BT/PCC; São Paulo, 2000.

Normative references

[n1] EN 10088-1:1995 “Stainless Steels – Part 1: List of stainless steels”.

[n2] EN 10088-2:1995 “Stainless Steels – Part 2: Technical delivery conditions for sheet/plate and strip for

general purposes”.

[n3] EN 10088-3:1995 “Stainless Steels – Part 3: Technical delivery conditions for semi-finished products,

bar, rods, and section for general purposes”.

13

[n4] ASTM A955, “Standard Specification for Deformed and Plain Stainless Steel Bars for concrete

Reinforcement”.

[n5] ASTM A276 – 13: “Standard Specification for Stainless Steel Bars and Shapes”.

[n6] ASTM A240: “Standard Specification for Chromium and Chromium-Nickel Stainless Steel Plate, Sheet

and Strip for Pressure Vessels and for General Applications”.

[n7] ASTM A480, “Standard Specification for General Requirements for Flat-Rolled Stainless Steel and

Heat-Resisting Steel Plate, Sheet and Strip”.

[n8] ASTM A555, “Standard Specification for General Requirements for Stainless Steel Wire and Wire

Rods”.

[n9] ASTM A564/A564M – 10, “Standard Specification for Hot-Rolled and Cold-Finishes Age-Hardening

Stainless Steel Bars and Shapes”.

[n10] ASTM A580-13a, “Standard Specification for Stainless Steel Wire”

[n11] Especificação LNEC 449-2010 “Varões de Aço A400 NR para armaduras de betão armado –

Características, ensaios e marcação”.

[n12] Especificação LNEC 450-2010 “Varões de Aço A500 NR para armaduras de betão armado –

Características, ensaios e marcação”.

[n13] EN 10002-1:2006 “Tensile testing of metallic materials. Part 1: Method of test at ambient

temperature”.

[n14] ASTM B117-11: “Standard Practice for Operating Salt Spray (Fog) Apparatus”.

Websites

[s1] ISSF – International Stainless Steel Forum; http://www.worldstainless.org/architecture

_building_and_construction_applications/, visited in November, 2013.

[s2] ISSF – International Stainless Steel Forum; “Stainless Steel in Sewage Treatment Plants”; available

in: http://www.worldstainless.org/Files/issf/non-image-

files/PDF/ISSF_Stainless_steel_in_sewage_treatment_plants.pdf, visited in November, 2013.

[s3] http://www.drydenaqua.com/archives/2877, visited in January, 2014.

[s4] http://www.bssa.org.uk/cms/File/Baddoo%20Swimming%20Pools%20(3p).pdf, visited in November,

2013.