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7/27/2019 Lunchtime Seminar by ChiewSP (7Aug12) v3
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Lunch-time seminar on
Material Selection and Qualit Assurance
-
School of Civil and Environmental Engineering,
7 August 2012
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Material Desi n & Execution
Desi nBS 5950
BS EN 1993
Material Executions on y BS EN 1090
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ni uel in a ore!
Desi nBS 5950
BS EN 1993
Material Executions on- s
(ASTM/JIS/AS/NZS/GB)BS EN 1090
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Material Issues ?
Steel material production standards aresubstantial documents covering mechanical,
One piece of steel is not necessary the same
We are not the only ones using steel e never uy s ee y weg Testing a batch of steel from different parents
is meaningless Material failure can be sudden and disastrous
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Performance Re uirements for Structural
Applications
Strength ability to carry load
Ductility ability to sustain permanent
without fracture
Weldability ability to transfer load
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Strength Toughness
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The performance of structural steel can beenhanced through three basic mechanisms, i.e.
the introduction of interstitial and
the generation and concentration ofdislocations at the grain boundaries (work or
strain hardenin
the formation of additional grain boundaries.
7
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any ypes o ruc ura ee
Carbon (non-alloy) steel
Alloy (fine grain) steel
-
-
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Steel Structure at Macro, Micro and Nano
Level
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molecules
The scanning tunneling
possible to image the electron
cloud associated individualatoms at the surface of amaterial. Right is an STM
showing the regular alignmentof atoms.
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Linear Defects (Dislocations) - Source of
Plasticity
the crystal structure. The movement of dislocations when a
.
Discovered by Taylor, Orowan& Polyani in 1934 with the aid
of TEM
Dislocation as seen under TEM (transmission electron microscope)
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-
Pure iron is soft and weak. By dissolvingcarbon and othe elements into molten iron,
steel with much superior engineering propertiesove pure ron can e ac eve .
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Carbon steel: carbon and manganese the maininterstitial alloys, with Mn (< 1.65%), Si (< 0.6%) & Cu
< . . improving strength with addition of carbon andmanganese.
Alloy steel: essentially low carbon-manganese steelalloyed with addition of strong carbide or nitrideforming elements, e.g. Nb, Ti or V.
increasing strength by grain refinement andprecipitation hardening.
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ymaximum content specified for alloying elements does
- . , - . , -0.60%; (2) the specified minimum for Cu does not.
Carbon steel differ from low-alloy and alloy steel in that.
alloying elements are not specified.
ncreas ng e percen age o car on ra ses e yestrength and hardness but reduces ductility and
.
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Hi h Stren th Low-Allo Steel
HSLA steel have moderate amount of alloying elementsother than carbon. The term low-alloy is used to describesteel for which the total of all the alloying elements does
not exceed 5% of the total composition. These steel have been develo ed as a com romise
between the convenient fabrication characteristics of the
low cost mild carbon steel and the high cost of heat-treatedalloy steel.
HSLA steel have ield stresses ran in from 275 to 460
MPa, and well-defined yield points like mild carbon steel.They are used in the as-rolled or heat-treated in thenormalized conditions.
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Work Hardening -
Work hardening also known as strain hardening or
cold workin is a wa of stren thenin b lasticdeformation
dislocations at the grain boundaries.
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deformation
(b)
(a)
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Dislocation Pile-ups at Grain Boundaries
-further dislocation motion.
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Theory of Work Hardening
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-
Cold forging for rebars Cold for in for headin s
o at ro ng o ro en ng
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Cold-Reduced Steel Wires
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Cold-Reduced Steel Wires
HotHot--rolled Wire Rodrolled Wire Rod
YS : 300 N/mmYS : 300 N/mm22
Profiling RollersProfiling Rollers-- Dia. ReductionDia. Reductione.g. 8mm > 7mme.g. 8mm > 7mmFinished Wire CoilsFinished Wire Coils
Dia. 5mm to 13mm,Dia. 5mm to 13mm,YS : 500 N/mmYS : 500 N/mm22
22
Welded Mesh (Fabric)
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Welded Mesh (Fabric)
Computerised Machine
Wires in coil / re-cut
form
ColdStraightening & Cutting
Resistance WeldingRolledWire
Welded Mesh 23
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Heat Treatment -
Improving the properties through control of grain size
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Heat Treatment Although the properties of steel are greatly affected
,
furnace can also affect the mechanical properties
Most of these treatments involve changing the
,treatment is used generally to cover all these
.
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Microstructure
High strength, high
tou hness, low ducti li t
c anges ur ng
heat treatment
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,structures
emper ng: re nng e mcros ruc ures an par a yrelieving residual stresses
Annealing: stress relieving, a treatment opposite to
hardening Normalizing: refining grains which have been
deformed through cold work
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anywhere to 815 to 9000C for most steel and thensuddenl coolin it in water brine oil o molten lead.
The rapid cooling causes the formation of fine grained
fabricating steel, it is most commonly used to harden
steel b introducin martensite a ver hard bu brittlemicrostructure.
,
residual stresses and distortion. Besides, the
problemwith rapid quenching.
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emper ng
To refine the microstructures and partially relieveresidual stresses, quenching is normally followed by
emperng. Tempering consists of normally reheating the steel to
370-6500C and cooling it in ai .
As a result, the internal stresses are partially relievedand the ductility as well as toughness are improvedremarkably, without great reduction in the strength.
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Annealing
Annealing, also called stress relieving, is a treatmentopposite to hardening (quenching).
It is achieved by heating the steel to a temperatureabove the transformation ran e (hi he thantempering), and after maintains the specific
temperature for a sufficient time, cooling the steelvery slowly in the furnace.
This rocess im roves the ductilit of the steel and
decreases residual stresses but on the other hand,reduces the yield strength, tensile strength andhardness accordingly.
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orma z ng
Normalizing includes heating a ferrous alloy to asuitable temperature above the transformation
temperature range and cooling in ai . It is used to refine rains which have been deformed
through cold work. During normalizing, small grains
are formed which lead to a tough metal with normalstrength, but it is not so ductile as steel achieved byannealing.
Strictly speaking, normalizing is an annealing process.
32
Difference between Tempering, Normalizing
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p g, g
an nnea ng
Tempering To toughen previously hardened steel.
The steel is heated uniforml below lower critical tem erature
and then cooled in air.
To relieve stresses and increase ductility.
.temperature, and then cooled in the furnace.
orma z ng
To remove coarse grained structures in forgings or castings.
The steel is heated to 37.8-93.30C above upper criticaltemperature, and then cooled in air.
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ea rea e ow- oy an oy ee
Heat-treated steel, mainly quenched and tempered (QT)steel differ from alloy-steel in that they have a higher
percen age o a oyng e emen s an ey re y on eatreatment to develop high strength and improvemec anca proper es.
They have very high strength (620~690 MPa) and pooruct ty compare to car on or a oy stee an are onyavailable in plates.
QT steels do not exhibit well-defined yield points. Theyare generally weldable but special welding techniquesare usually required.
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-
35
Thermo Mechanical Controlled Process
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Thermo-Mechanical Controlled Process
(TMCP)TMCP combines controlled rolling with accelerated coolingfor grain refinement.
The decrease in strength due to less alloy elements arecom ensated b accelerated coolin rocess
Improved weldability thanks to lower CEV
TMCP steel cannot be normalized (or annealed)
After hot rolling the deformed structure
prevented from growing by precipitation ofextremely small carbides and nitrides.
36Controlled Rolling
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37
TMCP Steel Plate by OLAC
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Facility Layout HotLevelerFinisherRougher Cooling
Accelerated Water-cooling
Furnace
ee
On-Line Accelerated CoolingHot Rolling
Fine grain
50m50m
High strengthExcellent toughness
Coarse grain
50m50m
38(1) Advanced TMCP
(2) Conventional process
Low strengthPoor toughness
Com arison of DQT RQT and TMCP
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Com arison of DQT RQT and TMCP
Steel Plates
DQT: rolling=> cooling => rolling twice => quenching => tempering => cooling in aiRQT: rolling => quenching => reheating => quenching => tempering => cooling in air
TMCP: rollin => coolin => rollin twice => accelerated coolin (without tem erin )
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Comparison of Production Process
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Temperature As-RolledControlled Rolling
(Normalized)
TMCP
Water-cooled TypeDirect Quenched & Tempered
Slab reheating
RollingRolling
Rolling
Off-lineheat treatment
QuenchingRolling
Rolling
+Rolling
(Ar3) WaterCooling
Tempering
Strength: TS 400-500(MPa) 400-500(MPa) 500-590(MPa) 550-800(MPa)
Thickness: t max. 50mm max. 50mm max. 100mm max. over 100mm
Toughness
Weldability
Product Costt>50mm: Decrease Strength
Countermeasure: Increase Carbon
On-line heat
treatedOff-line heat treated
40
Increase Strength
Decrease Toughness & Weldabili ty
and
low-alloy steelalloy steel
So many different Steel Products!
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y
Hot-rolled coils Cold-rolled coils Coated coils Slitted coils
Plates Sheet piles Hot-rolled sections Rail sections
Reinforcing bars Wire rods UOE pipes Spiral-welded pipes
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Some Current Material Issues -
Boron-treated Steel
TMCP, DQT & RQT Steel Plates
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oron ar ena y n ancemen
Boron is a potent alloy for hardenability enhancement,-
the other more expensive alloying elements (e.g..
ea treate ow a oy stee wt oron extreme yhigh strength, e.g. quenched and tempered boron steela o ve c es w ye s reng o - a.
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Influence of Weldin in Boron-treated Steel
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(HAZ)
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C Mn Cu P S Al Ti Si Cr Mo V Ni B
B 0.19 0.53 0.002 0.035 0.007 0.026 0.001 0.23 0.012 0.006 0.005 0.008 0.0014
BW 0.19 0.51 0.003 0.033 0.007 0.026 0.001 0.22 0.009 0.004 0.003 0.008 0.0014
C 0.21 1.6 0.6 0.04 0.04 - - - - - - - -
FG 0.18
0.5-
0.55 0.03 0.025 0.02 0.05 0.40 0.30 0.10 0.05 0.30 -.
RQT-S690
0.2 1.6 0.20 0.025 0.01 0.06 0.04 0.50 0.25 0.20 0.08 0.70 0.005
B: Boron steel, S275BW: Boron steel after welding, S275 Welding will not change thechemical composition
C: BS EN 10025-2, carbon steel, S275FG: BS EN 10025-3, normalized fine grain low alloy steel, S275RQT-S690: Reheated, quenched and tempered steel, S690
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Tensile Test Results
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600 Obvious necking
500+0.0%
300
400
200
+12.3%-9.4%
Almost no necking
100Boron steel
Boron steel - welding affected
0 5 10 15 20 25 30 35 40
46
Im act Test Results
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B B-W hr hr-w cf cf-wmpac
Value (J )228 228 280 245.8 255.4 265.7
Average228 262.9 260.6
Boron steel Boron steel - welded
- -
47
-
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800Boron steel
hot-formedRQT: Extremely high strength& low ductility
500
600
RQT-S690
Boron -> little influence
300
400
Typical mild steel:
o m s ee
100
200average strength & good ductility
0
0 5 10 15 20 25 30 35 40
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y , yheat-treated quenched and tempered steel to enhance
.
There is no product standards for Boron-treated carbonor a oy s ee , m s crea e e r own s an ar ssuch as ASTM A36B or A36 Modified because it is NOT
.
We do NOT have Boron-treated welding electrodes andwe o no un ers an su c en y e e avor o oron-
treated carbon or alloy steel (HAZ) under the influence.
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2. Form-Square Weld-Square Process
1. Electric Resistance Welding Process 3. Submerged Arc Weld Process
50
Hot-Formed vs. Cold-Formed
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Hot-Formed Cold-Formed
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Re-Forming into Square/Rectangular Section
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Usually comprises 4 conventional squeeze-roller stands
52
Re-Forming Stage Hot vs. Cold Formed
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Hot-Formed-
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Question - Which one is Hot ?
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Answer Both are hot!
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Hot-Formed Hot-Finished
55
Cold-Formed Circular Hollow Section
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Hot-formed & Hot-finished Cold-formed
BS EN10210: 2006
BS EN10219: 2006
and heat treated and welding
same in BS/EN design codes)
Similar in appearance,Hot-formed / hot-finished: 180mm x 180mm x 12.5mm
Cold-formed: 200mm x 200mm x 12.5mm
57
different in properties
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The cold-formed hollow section had the largest corneradii, followed by hot-finished and hot-formed hollowsections.
Hollowsections
bm(mm) tm (mm)
ro,m(mm)
ri,m(mm) b/t r o,m/tm ri,m/tm
Cold-formed 200.53 12.76 30.00 21.75 15.72 2.35 1.71
Hot-formed 180.27 12.72 25.00 12.13 14.17 1.97 0.95Hot-finished 180.34 12.88 26.75 14.00 14.00 2.08 1.09
58
-
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- -cold-formed zone, provided:
- the cold-formed zones are normalized after cold-forming but before
welding;- the r/t ratio satisfy the relevant values below.
-
BS EN1993-1-8 Table 4.2
r forming (%) (mm)
>3.0 2.0
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ress ra n urves
600a)
400
500
tress(M
300
S
100
Cold-Formed
Hot-Formed
0
0 5 10 15 20 25 30 35
-
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Residual Stress in the Hollow Sections
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Residual Stress in the Hollow Sections
Cold-formed
200mm 210mm
Hot-formed
180mm 180mm
Hot-finished
180mm 186mm
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1/fy
Cold-formed SHSHot-finished and cold-formed:
0.8
f
Hot-formed SHS
Hot-finished SHSSimilar !!!
0.4
.
0.2
-0.2
0 45 90 135 180 225 270 315 360
-0.4
Angle ()
62
ompar son o esu s
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p
Residual stress distributions in cold-formed section.
The amount of residual stress:
co - orme o - ns e o - orme
The hot-finished section also has very high residual
stress
The hot-finished section is not fully-annealed as ahot-formed section
63
onc u ng emar s
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g
The cold-formed section contains the highest residualstress with the biggest variance while the hot-formed
contains the least. The residual stress distribution of the hot-finished
section is similar to the cold-formed section.
Treatin hot-finished as the same as hot-formedhollow sections in current BS5950 / EC3 steel designcodes needs to be revisited ur entl .
The restrictive Table 4.2 of EC3 Part 1.8 needs to berevised ur entl .
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High strength lowHigh CEV
Alloyelements
alloys
High strengthCarbon steel
Fe + C
Low alloy
mild steelGood ductility
Heat
treatment Heat-treated steel
(TMCP, QT)
Extremely high strength
Low CEV
Plates onlyVulnerable to heat
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800.0
.
ress(Mpa)
25C
300C
600.0
.St
450C
500CStrength drops rapidlyfrom 300 to 700C
400.0
500.0600C
700C
200.0
300.0
Ductility is improveddramaticall
0.0
100.0
. . . . . . . .
Elongation (%)
66
Weldin of Hi h tren th T and TM P teel
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Loss of strength
and ductil ity in the
HAZ region
Strength
Ductility
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A36 (Most common)
g reng ow oy
A242, A572 (Co-V HSLA steel), A588 (Thicker weatheringsteel), A945 (Low carbon and restricted sulphur), A992(Rolled wide flange shape steel)
Heat Treated Carbon and Low Alloy Steel
A913 QT low allo sha e steel , A1066 TMCP late
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BS EN 10025-1 General technical delivery conditions
BS EN 10025-2 Non-allo structural steel
BS EN 10025-3 Normalized / normalized rolled weldable
BS EN 10025-4Thermo-mechanical rolled weldable fine
BS EN 10025-5 Structural steel with improved
BS EN 10025-6 Flat products of quenched and tempered
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-
on use of Alternative
Structural Steel to
71
Conclusions
A huge variety of steel microstructures, hence different
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engineering behavior and properties can be obtained byusing and combining various strengthening and heattreatment processes.
Boron-treated carbon and alloy steel should not be usedbecause it is not possible to be certified. Be more careful with hot-finished rectangular hollow
sections.
Select your steel from the list of certified steel materials inBC1: 2012.
, s ee pa es are cer e or e.g.
ASTM A1066, BS EN10025-4). or qua y assurance, ensure your cer e s ee
materials can be classified as CLASS 1 under BC1: 2012.
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Thank You for your Kinden on
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