Material course- Ch1&2

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©Teaching Resource in Design of Steel Structures

IIT Madras, SERC Madras, Anna Univ., INSDAG 1

HISTORICAL DEVELOPMENT AND CHARACTERISTICS OF

STRUCTURAL STEELS

CORROSION, FIRE PROTECTION AND FATIGUE

CONSIDERATIONS





Layout of the Lecture

• Historical Development of Steel

• Metallurgy of steel

• Production Process

• Mechanical properties

• Special steels

• Corrosion aspects

• Fire Engineering of steel structures

• Fatigue considerations





Early constructions in

Steel

• Indus Valley, Greeks and

Egyptians (1000 BC)

• Wrought Iron as tie bars in

Haghia Sophia (6thCentury)

• Galleries for house of

Commons and railings for

St.Paul’s cathedral (17thCentury)

• 18th Century refractory

furnace - Coalbrookadale

bridge• 1855 Henry Bessemer

invented the modern steel

making





Iron & Steel Tradition of

India

• Our Great Epics

• Iron Pillar of Mehrauli

• Dwaja Stamba - a rustless

wonder for 1.5 millennia !

• Rabindra Sethu!

• Numerous Steel

monuments of colonial past

• Second Hooghly and

Jogighopa Bridges- Steel

intensive constructions

• Visionaries like Tata, Pandit

Nehru and Visweswaraya

have sown the seed for

development in Steel





Into the Lecture …...

• Historical Development of Steel

• Metallurgy of steel



• Special steels








What do we do in these situations? And Why

should we teach the students a little bit of

metallurgy?

• Bhai Sahib, I saw some pipes lying in your

back door, can I use them as purlins for your

shop floor extension shed?• A failure investigation report say “ …..the

bolts have matensitic structure in

microstructure analysis”.

• “After exposure to fire the steel member ahard ness value of 345 PHN”.





The world has become cramped ? ! !

• So do Engineering

disciplines

• No Single conventional

Eng. discipline can existon its own

• Structural Steel

Construction, Metallurgy

and Mechanical

• Engineering disciplines

crisscross each other !Air Crossing !





(b) Face centred

cube (fcc )

(a) Body centred

cub e (bcc )

Crysta l structure of Iron





Al lo t ropy o f Iron

200

400

600

800

1000

1200

1400

1600

Magnetic

Non-Magnetic

Heating Cooling

768 0C

910 0 C

1400 0 C

1539 0 C

bcc

fcc

bcc

0

Temp 0 C

Time





In terst i t ial so l id solut ion

of Carbon in Iron

Steel is al loy o f Iron and Carbon !

(Point to ponder)

--Carbon

-Ferrite

More Carbon morestrength? - Yes

But what happens to

ductility?

Adding Carbon - Is it the

only way to get strength?

Is there a limit for carbon

content in structural steel?

Carbon content inStructural steel- 0.12-.25%





I ron – Iron -Carbon phase diagram

Peritectic

point

1.0 2.0 3.0 4.0 6.05.0 6.67

910 0C

1147 0C

723 0C

14930C

0.02% ferrite

phase Austenite

+

Liquid

Liquid

Fe3C+

Liquid + Fe3C

Austenite +

Cementite

+ Fe3C

Ferrite +

Cementite

Cementite

Eutectoid

point

+

0.0

0.0

200

400

600

800

1000

1200

1400

1534 0C

0.1% ferrite

0.8% 4.3%

Eutectic

point

% Carbon





The Eutectoid s ect ion of th e Iron – Iron

Carbon phase diagram

Weight % of Carbon

Temp 0 C

0.0

200

400

600

800

1000

1200

0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

723 0 C

Austenite1147 0 C

Ferrite

Ferr ite + Pearl ite

Ferr ite + Austeni te

Austeni te + Cementi te

Hypo-Eutectoid steel

Eutectoid

Point

Cementite + Pearl ite

Hyper-Eutectoid steel

ba c d

i

j

k

l





Different stages of formation of Pearlite

Austenite Ferrite

nucleiFerriteAustenite Ferrite Pearlite

C

(a) (b) (c)




IIT Madras, SERC Madras, Anna Univ., INSDAG

14

Microstruc tures of steels

(a)100% Ferrite in extra

low carbon steel

(b)Ferrite+Pearlite

(c) 100% Pearlite inEutectoid steel

(d)Pearlite+Cementite in

hyper-Eutectoid steel

SOURCE: Thelning K.E., “Steel and its heat

treatment”, Butterworths, (1984).





15

d

k 0 f y f

Are there any their any parameters which

increases strength of steel? Yes, Grain s ize

•Using temperature control we can achieve small

grain size

•Using Mechanical pressure during rolling we can

get smaller grain size





16

0.

0

200

400

600

800

Temp 0

C

Variat ion o f m icrostru cture as a

funct ion of cool ing

Time in Seconds 1 10 100 100 0 10 4 10 5

Eutectoid temperature

MantensiteM antensite+

Pearlite Fine PearliteCourse Pearlite

Full

annealing

NormaliseOil

quenchWater

quench





17

Subst i tut ion sol id so lut ion of Manganese in Iron

-Manganese

-

Ferrite

Are there any their any parameters which increases

strength of steel? Yes, Add it ive metals

How much can we add? It Shou ld not exceed C eq

(0.45)

Ceq =%C + % Mn/6 + (% Cr + % Mo + % V)/5+(% Ni + % Cu)/15

What happens then (C eq >0.45) ? Welding becomes a prob lem !!





18

Points to Ponder about

steel!

• More carbon : more strength; but

negatively affect the important property

of ductility!• Smaller the grain size greater the

strength (Production control)

• Smaller additive metals also increasesthe strength of steel - HSLA steels





19


• Historical Development of Steel• Metallurgy of steel


• Mechanical properties• Special steels








20

• Iron ore, Limestone and

coal is fed into the BF

• Liquid pig iron collects at

the bottom of BF(C-

4.0%;Mn-.5%;P-0.12%;S-0.05%)

• Hot metal is charged into

Steel making vessel.

Oxygen is blown in a

controlled manner to

reduce carbon and

impurities like silicon,

manganese, phosphorous

and sulphur . Final steel is

produced. (C-0.1-.25%;Mn-

.4-1.2%;P-0.05%;S-0.05%).• Oxygen less than 30 ppm -

fully killed steel; 150 ppm

semi-killed steel.Source: Adams P.F., Krentz H.A. and Kulak G.L.,

“Limit state design in structural design – SI

Units”, Canadian Institute of Steel Construction

(1979).





21

Ingot slab bloom Billet

Basic shapes and their relative proportions

Primary rolls for plates Primary rolls for structural shapes

Molten steel





22












23

F

Standard tensi le

test specimen

F

rt

d

Lc

Area=S 0-

L

Tensi le streng th of s teel

F

Deformed

regions

Moving edges of

Luder’s band

Luder‟s bands in

tensi le test s pecimen

Tensi le test

specimen before

rupture F

Area=S -

L

F

F





24

f

y

y

sh 10 y

f y

Elastic

range

Plasticrange

Strainhardenin

g range

E sh

Stress s tra in curvefor sharp yie ld ing

structu ra l steels

Variation

due to

Luder’s

bands

Stress stra in cu rve for

cont inuous ly y ield ing

structu ra l steels

f

y

f y

0.2%

strain

Uniform

plastic

Non-uniform

plastic

Elastic

0.2% proof

stress





25

Hardness

Hardness is regarded as the resistance of a material to

indentations and scratching. This is generallydetermined by forcing an indentor on to the surface.

(a) Brinell hardness Square based

diamond pyramids

of 135O included

angle

(b) Vickers Hardness Diamond core with

120

O

includedangle





26

h1

h2 c

Experimental

set up for

notch

tough ness test

Test specimen for no tch

tough ness test

Temperature

Strain rate

Energy absorbed

Region of

Cleavage(brit

tle) failure

Region ofShear

(Ductile)

failure

Transition

Temperature

Effect of temperature on notch

tough ness of steel

Ductile to

brittle

transition curve





27

1.2

1.1

10 -5

1.0

10 -4 10 -3 10 -2 10 -1

Strain rate in

seconds-1

)410 x2@( y f

y f

33.0.45.0973.0

)410 x2@( y f

y f

Effect of strain rate on the yield strength of

steel





28

Yield strength(Mpa)

Thickness (mm)

Type of steel

Design-ation

UTS(MPa)

<20 20-40

>40

Elongation

Gauge

Charpy V -notchvalues

Joules(min)

Fe

410A

410 250 24

0

230 23 27

Fe

410B

410 250 24

0

230 23 27

Standard

structural steel

Fe

410C

410 250 24

0

230 23 27

St58HT 580 360 0.0

5

1.00 20 -High

tensilestructural steel

ST55-HTW

550 360 .05 1.00 20 -

Some Mechanical properties of structural Steel





29












30

Special steels

• Stainless steels

Stainless Steel grades and their usage

Grade of stainless steel

Usage

316 (18% Cr) Profiled roofing, cladding, gutters,

facades and hand railings—inhighly polluted environments304 (18% Cr-

(% Ni)Decorative elements in areas nearcoast line. Also for kitchen andsanitary wares—coastal and lesspolluted areas

430 (17% Cr) Roofing, gutters, decorative walltiles, hallow structural sections—non-polluted environments

409 (11% Cr) Painted roofing-- non-pollutedenvironments





31

Cold rolled steel and cold forming of

steel

• Unheated slabs are rolled at ambient temperature

into thin sheets (.3mm-8mm)

• Results in smooth surface and improved

mechanical properties

• Cold forming of hold /cold rolled sheets

• CF sheets are basically low carbon steels which

are reheated to 6500C to recrystalise ferrite to get

finer grain size





32

TMCP steels and HSLA steels

• Thermo-Mechanically Controlled Process (TMCP)

steels are becoming popular in obtaining high

strength steels of yield strength of 800 MPa and

thickness even beyond 40 mm.

• High Strength Low Alloy(HSLA) also are very

popular which requires very good process

control.





33

Chem ical composi t ion of f i re resistant steel

C Mn Si S P Mo+Cr

FRS 0.20

%

1.50

%

0.50

%

0.04

0%

0.04

0%

1.00

%

MildSteel

0.23%

1.50%

0.40%

0.050%

0.050%

-

Fire resistant steels

•Very cost effective compared to structural steel

•FRS are available in India

•Very popular and cost effective - Japanese

experience





34








Metal Con nect ion





35

Electrolyte

C

Mechanism of co rros ion as a

m iniature battery

A

Anode

Drop of water

Metal bar

CA

Cathode

Mechanism o f Corrosion in steel





36

Drop of Water

A

C

Mechanism of c rev ice corros ion

F

C

A

F

Mechanism of stress

corros ion

The mechanism of fret ting corros ion

AC

Galvanic corrosion

Hydrogen

embritlement

Bacterial corrosion

Types of co rros ion





37

Simple or ientat ion of members

Methods of prevention corrosion - Simple

procedures

Detai l ing to enhance air

mo vement between

jo in ts

Simple rule:

•Eliminate the electrolyte

•Avoid simultaneous

presence of water and oxygen





38

Is Corrosion a real Problem?

• Indian designers feel that steel corrodes most in

India. Is it true?

• Steel corrodes all over the world! But they are

better managed in the western countries!

• Excellent protective coatings which retain their

life even up to 20 years are available!

• Corrosion-where does it matter? Normal inland

there is no problem! Exposed conditions

ofcourse do need attention.

• Corrosion is no more a disincentive for not usingsteel in housing sector!





39












40

Positive points of steel as a

construction material under fire

• Damage to strength of steel due to fire is

reversible in most of the cases

• Using the principle “ if the member is straight

after the fire - the steel is O.K” many of themembers could be salvaged.

• Up to about 2150C steel retains its strength

• In the case of concrete, at 2350C turns pink;

5900

C turns red and irreversible damage after6000C

• Steel exposed to 6000C could be strengthened

and reused.





41

Examples of fire load in various structuresType of steel structure Kg wood / m

2

School 15

Hospital 20Hotel 25Office 35Departmental store 35Textile mill show room >200

Typical fire loads and behaviour of steel

under fire





42

Typical fire loads and behaviour of steel

under fire

Time (Minutes)

1000

500

0

0 C

30 60 90

Furnace

temperature

Unprotected steel

Fire protected steel

temperature





Mechan ical propert ies of s teel at elevated

temperatures

0.5

1.0

1.5

200 400 600 800 1000

Young‟s modulus

ratio

Coeff. of thermalexpansion (x 10 5 )

Yield stress ratio

Temperature 0 C





High Hp / A

Value

Low Hp / A

Value

The sect ion factor

conceptSome typical values of H P o f

f i re pro tected steel sect ions

B

D t H p

=2D+3B-2tH p =2D+B

H p =2D+2B H p =2D+4B-2t

Fire Engineering o f steel stru ctu res- very well

developed in the l i terature





Methods of fire protection

• Spray protection

• Board protection

• Intumescent coatings

• Concrete encasement?









• Special steels








d

mn

Stress

con centrat ions in

the presence of

notches and

holes

Hole

m n

Notch

>

Stress

concentration

Crack growth

and fat igue

fai lure un der

cycl ic load

Number of cycles

Crack length

12

3

4

Crack length

Fatigue

crack

+

-

Applied cyclic stress





S-N diagram for fat igue l i fe assessment

140170

200

260

230

290

103 104 105 107

Cycles of stress for failure (N)

Stress

range

in MPa (S)

106

Endurance Limit

S-N

Curve





Modif ied Goodman diagram for fat igue resistant

design o f steel structures

Point of stressFillet Weld





Schematic stress

diagram

concentration

Stress

concentrat ionat the weld toe

FF

F

>F

Class „F‟

detai l ing

accord ing to

IS:1024 (1968)Weldement

Direction of applied stress





THANK YOU VERY

MUCH !

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Material course- Ch1&2