AISC Live Webinars

Practical Steel Metallurgy for the Structural Steel User AISC SteelDay Live Webinar 9/23/2011

AISC Live Webinars AISC Live Webinars

Thank you for joining our live webinar today. Today’s audio will be broadcast through the internet.
We will begin shortly. Please standby. Alternatively, to hear the audio through the phone,
Thank you. dial 888 227 6699.
Need Help? International callers, dial 00+1 303 223 2680.
Call ReadyTalk Support: 800.843.9166 For additional support, please press *0 and you will be
connected to a live operator.
AISC Live Webinars
Practical Steel Metallurgy
Today’s live webinar will begin shortly. for the Structural Steel User
Please standby.
As a reminder, all lines have been muted. Please type any What you need to know about Steel Metallurgy
questions or comments through the Chat feature on the left
portion of your screen. Doug Rees-Evans
Today’s audio will be broadcast through the internet. Steel Dynamics, Inc.
Alternatively, to hear the audio through the phone, dial Structural and Rail Division
888 227 6699. Columbia City, IN 46725
International callers, dial 00+1 303 223 2680.
For additional support, please press *0 and you will be American Institute of Steel Construction 1
connected to a live operator.

D. Rees-Evans (c) 2011

Practical Steel Metallurgy for the Structural Steel User AISC SteelDay Live Webinar 9/23/2011

Practical Steel Metallurgy for Welcome
the Structural Steel User
Audience :

 Engineers / Architects

 Fabricators

 Steel Users / Purchasers

 Students

 General Interest
 Metallurgists

Approach :

• “Hit the High-Points”

 Additional information given in slides for self-study.

• Practical Focus

Doug Rees-Evans 5 6

Steel Dynamics, Inc.
Structural and Rail Division
Columbia City, IN 46725

Questions Iron – Steel: What is the Difference ?
Steel
• Iron – Steel: What is the Difference ?
• Why are there multiple Grades of Steel ? Isn’t Steels can be classified in a
number of ways:
steel, steel ?
• How can a mill control chemistry ? Isn’t it • major alloying element(s),
• microstructural makeup,
dependent upon what scrap is used ? • processing method(s),
• intended application(s).
o How does a mill control the properties of a steel product ?
8
• If I retest a product, will I get the same results
as in the MTR? American Institute of Steel Construction 2

7

D. Rees-Evans (c) 2011

Practical Steel Metallurgy for the Structural Steel User AISC SteelDay Live Webinar 9/23/2011

Iron – Steel: What is the Difference ? Iron – Steel: What is the Difference ?
Steel Iron

Our discussion will be limited • a magnetic, silvery-grey
to Carbon-Steels metal

Aka: • 26th Element in the
• Carbon steel Periodic Table

– Mild Steel ( %C ≤ .25%) • Symbol : Fe
– Medium Carbon Steel ( .25% > %C ≥ .45%) (Latin: Ferrum)
– High Carbon Steel ( .45% > %C ≥ 1.5%)
• Carbon – Manganese steel (C-Mn) • 4th most abundant
• High Strength – Low Alloy Steel (HSLA) naturally occurring
terrestrial surface
– HSLA = C-Mn Steel + micro-alloy (eg. V, Nb) in low concentrations element

9 10

Iron – Steel: What is the Difference ? Iron – Steel: What is the Difference ?
Iron Iron-based Building Materials

• Very reactive (O, S, Cl), 26 • Mixtures (Alloys) of other elements in Iron

thus not found naturally Fe • Iron-based Alloys commonly classified by the
major alloying constituent(s).
occurring in the metallic Iron
56  Carbon
state.
 Carbon Steel
• Found in nature as (ores):  Cast Iron
 Wrought Iron
• Oxides Ironmaking  Pig Iron (Hot Metal)

• Sulfides  Other than carbon (Ni, Cr, Mo, W, …)

• Carbonates  Stainless Steel
 Alloy Steel
• Chlorides

• Ores also include impurity

elements: S, P, Mn, Si, …

• ‘pure’ metallic Iron of 12

little commercial use.

11

D. Rees-Evans (c) 2011 American Institute of Steel Construction 3

Practical Steel Metallurgy for the Structural Steel User AISC SteelDay Live Webinar 9/23/2011

Iron – Steel: What is the Difference ? Iron – Steel: What is the Difference ?
Short Answer: Short Answer:

<< based upon the chemical makeup of the material >> << based upon the chemical makeup of the material >>

• Iron: An element metal. • Wrought Iron : the metallic product of the Puddle
Furnace
• (Carbon) Steel : a series of alloys that has more Iron
(by mass) than any other element, and a maximum o Can be considered the precursor of modern low - mild carbon steels
Carbon content of less than 2 wt%. o OBSOLETE

o Secondary alloying element is typically Manganese (Mn) • Pig Iron: the solid metallic product of the Blast
Furnace (typically 3.5 – 4.5 wt% C, with 1 – 2.5 wt% (ea.) of Mn, and Si).
• Cast Iron: a series of alloys that has more Iron (by
mass) than any other element, and a minimum o In the liquid state is commonly known as “Hot Metal”
carbon content of 2 wt% (typical max: 4 wt% C). o No “structural” uses. Manufactured as the feed-stock for Steelmaking

o Secondary alloying element is typically Silicon (Si) and Cast Ironmaking.

13 14

Iron – Steel: What is the Difference ? Metallurgy Basics
4 Carbon Content Chemistries
Phase Diagram
wt% Carbon Content 2 - 4% : Cast Iron CAST IRONs A graphical representation of composition and temperature limits for
the existence of different phases within an alloy system (at equilibrium).
Q. Why separation @ 2 wt% ?  A. Phase • Temperature vs. Composition
2 Diagram. • Solid Lines delineate Phases
• Crossing a phase line (@ constant composition) results in a phase
1 – 2% : Ultra High Carbon Steel change. {LS, L  L + S (mushy), S  S’, S  S’ + S”, etc.}

1 .60 – 1% : High Carbon Steel CARBON STEELs 1

0.6 .30 - .60% : Medium Carbon Steel Example:

0.3 .15 - .30% : Mild Steel 2
Hypothetical Chocolate- Vanilla Phase Diagram
0.15 Cooling of a composition (green arrow)
0.05 •Temp 1: Homogeneous Liquid (HC)

0 .05 - .25% : Wrought Iron 3 •Temp 2: Solidification of Solid (CC) from the
liquid
.05 - .15% : Low Carbon Steel •Temp 2 – 3 : Mushy (Liquid VM + Solid CC)
<.05% : Ultra-Low Carbon Steel •Temp 3: Solidification of Liquid VM : Duplex
Structure = Ripple
Common Structural Applications: Shapes, Bars, 15 Upon Heating, reactions are reversible.
Bolts, Plates, etc.
100
D. Rees-Evans (c) 2011
16

American Institute of Steel Construction 4

Practical Steel Metallurgy for the Structural Steel User AISC SteelDay Live Webinar 9/23/2011

Iron – Steel: What is the Difference ? Fe- C Phase Diagram Iron – Steel: What is the Difference ?
Long Answer:
Q. Why separation between L
Cast Iron and Steels @ 2 wt% C ? The properties of Iron – Carbon
(Liquid) alloys are controlled by the
δ-Iron 2800 °F
microstructure of the material,
2540 °F which consequentially are

Homogeneous, single γ γ+L determined by the chemistry and
Phase: “Austenite” austenite processing of the material.
2100 °F
2.01% C 18

1625 °F α+γ γ + Fe3C Basic Metallurgy

Duplex Phases: 1340 °F Nature of Metals
“Austenite” + Fe3C
Temperature α + Fe3C α + Graphite • crystalline : in the solid state, a metal’s atoms are arranged in
or Eutectoid
“Austenite” + Graphite an orderly repeating 3-D pattern (crystal lattice).
• smallest symmetric
α-Ferrite arrangement of atoms =

.008 unit cell

.4 .8 1.0 % Carbon (wt%) 6.67

Hypoeutectic Hypereutectic 17

STEELS CAST IRON

Iron – Steel: What is the Difference ?
Iron - Carbon Alloys

One of the most important
properties of Iron is its’
allotropic nature.

Allotropic = Has different crystal structures unit cell

at different temperatures.

.

19 crystal lattice 20

D. Rees-Evans (c) 2011 American Institute of Steel Construction 5

Practical Steel Metallurgy for the Structural Steel User AISC SteelDay Live Webinar 9/23/2011

Basic Metallurgy Basic Metallurgy

Crystal Space Lattices Nature of Metals

• 14 different types of crystal “space lattices”. • intersection of crystal lattices of differing spatial
orientations create grain boundaries
• 3 most common (favored by metals)

BCC FCC metallographic
appearance of
Body-Centered Cubic Face-Centered Cubic grain boundaries

{ Cr, Mo, Nb, V } { Al, Cu, Ni } Each grain will have
a different
2-D schematic
“crystallographic”
orientation than its

neighbor

HCP 21 22

Hexagonal Close-Packed

{ Co, Ti }

Iron – Steel: What is the Difference ? Basic Metallurgy
Iron Allotropism the existence of two
Carbon in an Iron Crystal Lattice
or more different Atomic radii (Angstroms)

physical forms

Phase Diagram of “Pure” Iron 2 “BCC” Allotropes (Phases) Carbon : 0.7 FCC - Austenite

•δ-Iron (2541 - 2800°F)
•α-Iron (≤ 1670°F)

Modified and used under GNU Free Documentation License, V1.2 1 “FCC” Allotrope (Phase) Defect in Crystal Structure: C: Dislocation (planar) Iron : 1.4
Original source: A: Interstitial Solute D: Vacancy
http://en.wikipedia.org/wiki/File:Pure_iron_phase_diagram_(EN).png •γ-Iron (1670 - 2541 °F) B: Substitution Solute

D. Rees-Evans (c) 2011 23 24

American Institute of Steel Construction 6

Practical Steel Metallurgy for the Structural Steel User AISC SteelDay Live Webinar 9/23/2011

Basic Metallurgy Basic Metallurgy

Iron Allotropism Austenite to Ferrite Phase Transformation

γ-Iron (FCC) “Austenite” α-Iron (BCC) “Ferrite” γ-Iron Max Carbon Solubility: “New Phase”
≤ 1670°F 2.01%(wt%) •C-rich
> 1670°F
Carbon diffusion Morphology ?
3.57 Unit Cells 2.57
Volume % and
(Angstroms) spacing
Dependent upon:
2.01% Max Carbon 0.02% •Wt% C
•Other alloying
Solubility α-Iron elements
•Cooling rate.
(wt%) Max Carbon
Solubility: Upon Heating:
Problem upon Cooling: 0.02%(wt%) α→γ

Carbon Solubility Difference Fully reversible
α←γ
(2 orders of magnitude)
Upon cooling

25 BASIS OF THE HEAT-TREATMENT 26
OF Fe-C ALLOYS

Basic Metallurgy Basic Metallurgy

Austenite to Ferrite Phase Transformation Equilibrium Microstructures

At equilibrium in Steel Typical Metallographic Varying Carbon 0.02 wt% C ~ 0.20 wt% C
Appearance of Pearlite content yields
Fe3C | Cementite : varying
microstructures
• 6.67 wt% C γ-Iron
• Strong α-Iron Fully Ferritic predominately Ferritic, small volume fraction
• Hard of pearlite
• Wear-Resistant ~ 0.80 wt% C
• Brittle ~ 1.00 wt% C
• Un-Weldable

α-Iron | Ferrite : ~ 0.40 wt% C
• 0.02 wt% C
• Weaker Dark = Cementite
• Soft Light = Ferrite
• Ductile
• Weldable Pearlite: a two-phased, lamellar structure approx. 50-50 ferrite - pearlite 100% pearlitic (eutectic) predominately pearlitic, small volume fraction
composed of alternating layers of ferrite of ferrite along grain boundaries.
and cementite. 27
28
“technically: is a colony – not a “grain”.

D. Rees-Evans (c) 2011 American Institute of Steel Construction 7

Practical Steel Metallurgy for the Structural Steel User AISC SteelDay Live Webinar 9/23/2011

Basic Metallurgy Basic Metallurgy
Austenite to Ferrite Phase Transformation
Austenite to Ferrite Phase Transformation
Non-equilibrium in Steel
Carbon Solubility: γ (2.01%) → α (0.02%)
γ-Iron TTT Diagram for Eutectic Steel • Curve shapes shift and
Carbon Diffusion Diffusion:
change shape in response
Temperature • Time Reaction to alloying additions

α-Iron If insufficient Time or Temperature is provided (ie. Rapid
cooling), carbon will be “trapped” in a non-equilibrium position

Non-Equilibrium Steel Phases:
• Upper & Lower Bainite

- Highly variable microstructures (dependent
upon alloy content and cooling rates)

+ (low C): low temp toughness, improved
strength, weldability.

• Martensite

- Low: ductility, & fracture toughness
+ Very: strong, hard, & wear resistant

Used under the GNU Free Documentation License v1.2
Author: Metallos
Source: http://en.wikipedia.org/wiki/File:T-T-T-diagram.svg

29 30

Basic Metallurgy Cast Iron

Austenite to Ferrite Phase Transformation Historic Structural Uses

At equilibrium in Cast Iron Static / Compressive

Gray Iron Ductile / Nodular Iron

• 3D network • addition of elements
of graphite (Mg) result in
flakes in formation of
Pearlitic graphite nodules
matrix instead of flakes.

× Graphite = soft, low strength, acts like a “void”.
× Flakes morphology = stress risers
× Low Strength
× Low Ductility

× LOW NOTCH TOUGHNESS

 Excellent machinability
 Good compressive strength
 Excellent “castability”

31 32

D. Rees-Evans (c) 2011 American Institute of Steel Construction 8

Practical Steel Metallurgy for the Structural Steel User AISC SteelDay Live Webinar 9/23/2011

Cast Iron Cast Iron

Historic Structural Uses Historic Structural Uses

“Iron Bridge” After example of the 1781 “Iron Bridge” :
1830’s – 1840’s: 1,000’s of Cast Iron based bridges put into RR service.
across the River Severn
Cast Iron Bridge Experiences: 1830 - 1891
Coalbrookdale, Shropshire, UK
Dee Bridge, Chester, Cheshire, UK
1st CAST IRON BRIDGEWORK Opened to Rail traffic: Sept 1846.
Failure: 24 May 1847. 5 fatalities. Fracture of CI beam
Opened: 1781
Closed to traffic: 1934, still standing Wootton Bridge, Wootton, UK
UNESCO “World Heritage Site” Failure: 11 June 1860. 2 fatalities. Fracture of CI beam
Length: 60m,
Longest Span: 30.5m, Bull Bridge, Ambergate, UK
Clearance: 18m Failure: 26 Sep 1860. 0 fatalities. Fracture of CI beam
800+ casting : 379 tons of iron
built on carpentry joinery principles Ashtabula River Bridge, Ashtabula, OH
(mortise and tenon, blind dovetails) Failure: 29 Dec 1876. 92 fatalities, 64 injuries.
Cost (in 1781): £6,000 Fatigue (?) of CI beam.

Tay Rail Bridge, Dundee, Scotland 11 June 1860  Wootton Bridge Collapse

Failure: 28 Dec 1879. 75 fatalities.

Wind load - Failure of CI to wrought Iron connections. After 2nd Norwood Junction Rail Bridge “incident”, UK

Norwood Jnct Rail Bridge, Norwood, UK “Board of Trade” issues circular recommending gradual

Fracture & Repair of CI beams due to derailment replacement of CI bridgework.
(impact ?): Dec 1876 fatalities.
Failure: 1 May 1891. 0 CAST IRONS not suitable for Tension nor Cyclic

Failure of CI beams. Loading

33 ×Graphite = soft, low strength, acts like a “void”. 34
×Flakes morphology = stress risers
×Low Strength, Low Ductility
×LOW NOTCH TOUGHNESS

Iron – Steel: What is the Difference ? Iron – Steel: What is the Difference ?

CAST Steel ≠ CAST Iron Low C / Mild Steel vs. WROUGHT Iron
• Steel – Bessemer, Open Hearth, BOF, EAF (from the liquid)
Cast Steels Cast Iron
• Wrought Iron = Puddling (not fully liquid – “pasty”)  Rolling  Slitting 
• Any “steel” composition • Pearlite + Stacking  Reheating  Forging/Re-Rolling (Merchant Bar)

• Variable Cast Graphite • Chemistry (typical – wt%): C ≤ .25, Mn ≤ .05, S ≤ .03, P .10 - .12, Si .10 -.15
Grain Structures
 Period literature reports: .05 - .15 wt% C as usual analysis
Surface
Chill Zone (equiaxed) • Mechanical Properties (typical – wt%):

Columnar • Strength: Yield – 23ksi Tensile – 46ksi

Equiaxed Zone • Elongation (in 8”): 26% Oxide Inclusions

 High fraction (typ. 2-3% volume fraction) of oriented slag inclusions

Period literature claims slag content benefits ductility and malleability – more likely due to very low C / Mn.

 OBSOLETE – (quality and manufacturing cost)

Core Steel Wrought Iron

• Ferrite Microstructure: Ferrite + Pearlite Microstructure: Ferrite + Slag

• Pearlite

35 36

D. Rees-Evans (c) 2011 American Institute of Steel Construction 9

Practical Steel Metallurgy for the Structural Steel User AISC SteelDay Live Webinar 9/23/2011

Iron – Steel: What is the Difference ? Iron – Steel: What is the Difference ?

WROUGHT Iron “Long Answer”: The difference is…..

The Eiffel Tower • Iron is an Element;

Paris, France  Steel is a series of alloys based on the element Iron
Built 1889
Designer: Gustave Eiffel • If referring to “Cast Irons” as “Iron” :
Material: Puddle (Wrought) Iron
 Cast Irons differ greatly from steel in chemistry (carbon content),
“Heated and Hammered Bars” and microstructure.

From:  Cast STEEL ≠ Cast IRON.

Sir Henry Bessemer, F.R.S • If referring to “Wrought Iron” as “Iron” :
AN AUTOBIOGRAPH,Y WITH A CONCLUDING CHAPTER.
• Although similar in carbon content to low carbon / mild steels,
Universal Press, London 1905. Wrought Iron differs greatly in bulk chemistry, method of
manufacture, and microstructure (large slag volume content);
“Mild” Bessemer Steel Puddle (Wrought) Iron and consequently applicability.

Wrought Iron = prone to “delaminate” 37 38

Questions Why Multiple Grades?

Iron – Steel: What is the Difference ? What is a Grade ?
Why are there multiple Grades of Steel ? Isn’t
Webster’s
steel, steel ?
• How can a mill control chemistry ? Isn’t it Grade \ ‘grad \ n (1659) 1: to arrange in a scale or series

dependent upon what scrap is used ? (1796) 2a: a position in a scale of rank or
qualities.
o How does a mill control the properties of a steel product ?
b: a standard of quality
• If I retest a product, will I get the same results
as in the MTR? Examples of Structural Steel Grades } definition 1, 2a

39 A572 - Grades 42,50,60,65 } Standard loosely definition 2b
A588 - Grades ‘A’,’B’,’C’,’K’
D. Rees-Evans (c) 2011 A36, A992

40

American Institute of Steel Construction 10

Practical Steel Metallurgy for the Structural Steel User AISC SteelDay Live Webinar 9/23/2011

Why Multiple Grades? Why Multiple Grades?

What is a Grade ? What is a Grade ?

Classification / systematic arrangement / division of steels into groups based upon Metal classifications, other than Carbon and Alloys Steels, are generally made by:
some common characteristic(s).
Characteristics: • Grade: denotes chemical composition

• Composition / Chemistry • Type: denotes deoxidation method
• Principle alloying element :
• C-Steels, Ni-Steels, Cr-Steels, Cr-V-Steels, etc. Our industry, however, tends to use grade, type and
• Quantity of principle alloying element: class interchangeably.
• Low-C, Mild, Med-C, High-C, etc.
Eg: ASTM A572 grade 50 (A572-50): “50” is a strength level (min 50ksi fy).
• Manufacturing / processing method(s) “A572” = “Standard Specification” | “ASTM” = Specification Issuing/Controlling body
• Rimmed / Capped / semi-killed / killed
• Hot Rolled / Cold rolled Grade: Specification detailing chemical and mechanical
• Heat treated property requirements/restrictions

• Product Form 42
• Bar, plate, sheet, strip, tubing, structural shape, etc.

41

Why Multiple Grades? Why Multiple Grades?

Specification Issuing Bodies The different Specification Issuing Organizations
may adopt & adapt different “grades”
Focus
Example: AASHTO M270M/M270 vs ASTM A709/A709M vs ASTM A572/A572M
AASHTO Association of American State Highway  Bridge & Highway • ASTM controls and issues Specification A572
ABS Transportation Officials  Ship Building • ASTM A572 has various strength levels: eg. 50 [345] (ksi [MPa]).
• ASTM A572 = riveted, welded, bolted structures (general applications).
American Bureau of Shipping • AASHTO has incorporated ASTM A572 gr 50 into their M270M/M270

API American Petroleum Institute  Petroleum Industry specification for use in bridge construction (M270M gr 345).
• By agreement, the AASHTO M270M/M270 specification is republished by ASTM
ASTM ASTM International  General/Specific
CSA as specification A709/A709M.
SAE Canadian Standards Association  For use in Canada Thus:

Society of Automotive Engineers  Automotive ASTM A709-50 ≈* AASHTO M270M-345 ≈* ASTM A572-50

+ many others. ∗ some differences may exist due to committee activity and publishing cycles
and actual intended applications.
43
44
D. Rees-Evans (c) 2011
American Institute of Steel Construction 11

Practical Steel Metallurgy for the Structural Steel User AISC SteelDay Live Webinar 9/23/2011

Why Multiple Grades? Why Multiple Grades?

Specific Product Application Specific Product Application

Example : ASTM A709-50 vs ASTM A709-50Tx vs ASTM A709-50Fx Example : ASTM A709-50 vs ASTM A709-50Tx vs ASTM A709-50Fx

* “x” = 1, 2, or 3 – represents specific “zone” / minimum service temperature A709 CVN Testing Requirements Minimum Average Energy
(ft-lbf)
• A709-50 = “base grade” – “general” bridge (≤ 2” Shape)
• Due to SPECIFIC product application, SPECIFIC additional requirements (CVN
Fracture "Condition" Zone 1 Zone 2 Zone 3
Testing) is required. Non- Critical (T) 15 @ 70°F 15 @ 40°F 15 @ 10°F
• Non-Fracture Critical: (Grade designation: A709-50Tx) Critical (F) 25 @ 70°F 25 @ 40°F 25 @ 10°F

• main load carrying member Service Temperature (°F) 0°F >0°F to -30°F >-30°F to -60°F
• Has redundancy or failure not expected to cause collapse
• Fracture Critical: (Grade designation: A709-50Fx) A709-50T1 = A709-50 + T1 CVN requirements (min 15 ft-lbf @ 70°F)
• main load carrying tension member or tension component of bending
•Redundant main load carrying member (non-fracture critical) for use at or above 0°F
member
• Failure expected to lead to collapse A709-50F3 = A709-50 + F3 CVN requirements (min 25 ft-lbf @ 10°F)

45 •Non-Redundant main load carrying tension member (Fracture Critical) for use
between -30 to -60°F
Why Multiple Grades?
46
Additions / Restrictions
Why Multiple Grades?
Example : ASTM A572-50 vs ASTM A992 (Structural Shapes)
• ASTM A572-50 vs ASTM A992 = both 50ksi [345 MPa] min fy Different Products
• ASTM A572-50
Pancakes:
• Originally published by ASTM 1966
• Predominately OH and BOF mills, limited EAF mills (domestic production) 2 Cups Baking Mix 2 Tbsp. sugar
• HSLA (Nb-V) C-Mn Steel
• Low residuals (Cu, Ni, Cr, Mo) - $$ to add 1 1/3 cups milk 1 egg Same “chemistry”

•Stir ingredients together until blended. Similar processing
Different product
• Bake on hot, lightly greased griddle …

Waffles:

2 Cups Baking Mix 2 Tbsp. sugar

1 1/3 cups milk 1 egg

•Stir ingredients together until blended.

• Pour onto hot waffle iron…

 Same chemistry
 Deviation in Processing – Different Product

 Might or Might Not be in same specification.

47 48

D. Rees-Evans (c) 2011 American Institute of Steel Construction 12

Practical Steel Metallurgy for the Structural Steel User AISC SteelDay Live Webinar 9/23/2011

Why Multiple Grades? What is Why Multiple Grades?
the
Multi-Certification Multi-Certification
W16x36’s
“. . .” denotes no requirement(s) MTR First Name: Doug
Grade Last Name: Rees-Evans
? Nicknames: “Reesy” (grade school)

You can call me:

… only if you’re my mother. • Doug Whatever you call me;
… I won’t answer ! • Douglas does not change who I am.
• Mr. Rees-Evans
• Reesy

Which name/title is used = f ( CONTEXT )

Whichever Grade is used = f ( CONTEXT )

* Requirements assuming: (1) Shape, (2) Flange Tested, (3) tf ≤ 2”, 49 50
(4) no “footnoted” alternatives used.

Why Multiple Grades? Questions

A. The difference is due to….. Iron – Steel: What is the Difference ?
Why are there multiple Grades of Steel ? Isn’t
• Different specification bodies
• Different products and/or product steel, steel ?
How can a mill control chemistry ? Isn’t it
applications
• Cross adaption / adoption dependent upon what scrap is used ?

• Same Material  Different Grade(s) / o How does a mill control the properties of a steel product ?
{Name(s)} “multi-certification”:
due to “Application Context” • If I retest a product, will I get the same results
as in the MTR?
51
52
D. Rees-Evans (c) 2011
American Institute of Steel Construction 13

Practical Steel Metallurgy for the Structural Steel User AISC SteelDay Live Webinar 9/23/2011

Process Design Ironmaking Blast Furnace

Chemistry Cont“roSl teelmaking” Process Diagram Fe3O4 Important Historical Developments:
Fe2O3 • antiquity: precursor = “Bloomery”
Raw Materials Iron FeO • Late 1300’s – mid 1400’s: beginning of Tonnage Ironmaking
Making Fe(l) “Shaft” Blast Furnace blow by water driven wheel.
ChCeomnitsrtoryl • 1768 - 1777: Watt Steam engine replaces water wheels
Steel Casting • Late 1700’s: use of coke rather than charcoal
Making • 1828: Neilson employs “Hot” blast (air preheated by waste off-gasses)

Re- “Hot” Finished Purpose: transformation (smelting) of iron-oxides (ores) to metallic iron
Heating Rolling Products
(Hot Metal / Pig Iron)
Process Flow Cold
Finishing Inputs (charge): prepared Iron Ore, limestone, coke

Product Design consideration flow Process:
counter to the “Process Flow” 53
• preheated air blow through alternating layers of charge materials
• Progressive reduction of iron oxides to metallic iron

Fe3O4 → Fe2O3 → FeO → Fe (l)
• secondary reductions: SiO2 → Si, MnO → Mn
• Liquid Iron dissolves carbon from coke

Outputs: Hot Metal / Pig Iron
• Typ: 3.5 – 4.5 wt% C, 1 wt% Mn, 1-2 wt% Si

54

Process Design Ironmaking “Alternate Iron”

Chemistry Control Reduction of Iron Oxides to Metallic Iron

Oxygen Map of Iron and Steel Making

Iron Ore (Fe304, Fe203)

30% O
LOW  OXYGEN POTENTIAL  HIGH without melting (solid state)

Oxidation Reactions Direct Reduced Iron (DRI) – Hot Briquetted Iron (HBI) – Sponge Iron
Solid Metallic for use in Melting

“Ironmaking” Reduction Reactions Alternative to Blast Furnace

C + O → CO • Shorter furnace campaign cycles
Fe3O4 → Fe2O3 →
• Can operate in an on/off manner
FeO → Fe (l)
• Similar “chemistry” to Hot Metal / Pig Iron

Tap O : depends on Tap C Deoxidation Example Processes:
Steelmaker controls via Alloying
• Pre 1980’s : MIDREX / HYL Process / FINMET
“Steelmaking” Final O : depends on • :1990’s Iron Carbide (Nucor) / Iron Dynamics* (SDI)
Deox. Level (typ 1-50 ppm)
C + O → CO → CO2 *DRI melted in submerged Arc Furnace
Mn + O → MnO Tap: Hot Metal / Pig Iron / Alt. Iron
Si + O → SiO2 1-5ppm O • :2000’s ITmk3 / Mesabi Iron Nuggets
Al + O → Al2O3

55 56

D. Rees-Evans (c) 2011 American Institute of Steel Construction 14

Practical Steel Metallurgy for the Structural Steel User AISC SteelDay Live Webinar 9/23/2011

STEELMAKING Puddling STEELMAKING Important Historical Developments: Bessemer
• 1856: Bessemer demonstrates his “converter”
Heat Puddling Important Historical Developments: • 1865: 1st US Production of “Bessemer” Steel
Source Hearth • 1613: Reverberatory Furnace Invented • 1879: Thomas Process / Basic Bessemer Steel
• 1760: Puddling Process Invented • 1949: Last “New” Bessemer Converter installation in US
• 1890’s: Wrought Iron for structural applications largely replaced by steel • 1966: Last commercial production Bessemer Steel in US
• 1925: Aston Process: Bessemer “iron” replaces pig iron + reverberatory furnaces
route. – Puddling OBSOLETE. [1st “tonnage” Steelmaking]

• Last commercial production of “true” wrought iron : USA 1969; UK 1973 Inputs : Hot Metal, Air

Inputs (charge): Pig Iron, Heat (fuel – coke / coal) Process :

Puddling Furnace Process : • Hot Metal teemed into converter
• Air (78% N2, 21% O2) blown (20psig) from bottom of vessel through Hot Metal.
Heat Size: 750 – 1500 # • Pig iron melted in the hearth of a reverberatory furnace • Preferential oxidation of dissolved elements:
Tap-Tap:
(typical) • Liquid stirred with a pole to expose to air. • Si, Mn  C  Fe =  TEMPERATURE

4 – 6 hr Outputs : (liquid) Steel – carbon level controlled by duration of the “blow”

Partial, High-Temp Fe-C Phase Diagram • Dissolved C oxidizes (surface liquid) reducing raises temp. Advantages : (over Puddling)

carbon content. Liquid composition moves ( not hot enough to Heat Size: 15 -20 ton • Speed: 20 tons in 30 mins vs ¾ tons in 4-6 hrs
into γ+L phase (“mushy” puddle). reach “steelmaking” Tap-Tap: • Autogenous : – no external heat / energy required
(typical) • Cost: price of finished steel in 1865 (converted to 2010 USD).
• Dissolved Si, Mn oxidize (slag) temps )
20 – 30 min Puddle Iron: $5,000/ton | Bessemer Steel: $800/ton
• Comes “of nature” when C & temp reaches γ(solid) phase.
Difficulties :
• “pasty ball” removed from furnace and hammer/rolled to
• Cannot remove Sulfur nor Phosphorous (no slag)
“squeeze-out” slag • Process speed too rapid for real-time chemical analysis
• Rolled/hammered pieces are sheared, stacked, reheated and • Cannot use scrap

Red line (right to left) approximates composition rerolled (wrought) into merchant bar

Outputs :and temperature changes during Puddling Wrought Iron

• Typ: .10 – .20 wt% C (max .05 - .25)

• Extremely variability in C content between “batches”57 58
• Negligible Mn, Si

STEELMAKING “ACID” VS “BASIC” Process Design “Refractories” & “Slags”
STEELMAKING

One of the early MAJOR problems with implementation of the Refractories Material(s) of very high melting point that are suitable for
Bessemer Process was the inability to CONTROL :
Slag: the use as linings for steel - making, handling, reacting, and
SULFUR and PHOSPHOROUS
Argon Stir in Ladle @ LMF transfer vessels. eg: CaO, MgO, Al2O3, SiO2, MnO

1879: Thomas discovered that Sulfur and A mixture of non-metallics that is liquid at steelmaking
Phosphorous could removed from liquid steel
by the use of “BASIC” slags and refractories. temperatures. • Lower density than steel (floats on top of steel).

ACID Slag / Refractory = Silicate (SiO2) based. Refractory Lining • Capable of absorbing and retaining
BASIC Slag / Refractory = Lime (CaO2) / Dolomitic (CaO2, MgO) based. “impurities” (usually as oxides / sulfides) from
liquid steel.

Molten Slag • Acts as a thermal blanket (reduces radiant temp
loss from liq. Steel).

ACID “practice” uses ACID refractories  BASIC “practice” uses BASIC refractories • Acts as a re-oxidation barrier (prevents direct
air  liq. Steel contact).

* In Europe, due to high P-bearing ores, the “Basic” Bessemer Process was wide used. More commonly Molten Steel • Chemical Equilibrium: steel Slag
referred to as the “Thomas Process”. “don’t make steel – make slag”
(~ 2900 F)
* In NA, due to ores with lower P-content, and the higher cost of Basic refractories (at the time), the “Acid” * Sustainability:
Bessemer Process was more predominate.
• Metallics recovered from used refractories and slag. Returned
to melting processes.

• Used refractories: crushed, classified – used as slag modifiers.

• Used Slag: crushed, classified – used as concrete aggregate,

59 road-base, RR ballast, etc. 60

D. Rees-Evans (c) 2011 American Institute of Steel Construction 15

Practical Steel Metallurgy for the Structural Steel User AISC SteelDay Live Webinar 9/23/2011

STEELMAKING Important Historical Developments: Open Hearth STEELMAKING Basic Oxygen Furnace
• 1860: Seismen’s (OH) Process invented
Important Historical Developments:
• 1870: 1st US production of Open Hearth Steel (Boston, MA) • ~1940 - 1945: “bulk” liquid Oxygen generation (Germany)
• 1949 - 1952: Development & Commercialization of LD/BOF (Voest-Alpine, Linz & Donawitz, Austria)
• 1888: 1st US “Basic” Open Hearth furnace (US Steel – Homestead Works) (Seismen’s Process) • 1954: 1st commercial US - BOF steelmaking (McLouth Steel)
• 1967: Last commercial OH steel production - USA Acid / Basic
• 2001: Last commercial world-wide OH steel production – (China)

Inputs : Hot Metal, Fuel, Air, Slag Formers, Scrap &/or Pig Iron Several different configurations

Process : Top-Blown, Bottom-Blown, combination

• Solids (scrap/Pig Iron) + slag formers charged Inputs : • PRIMARY INPUT
• Hot combustion product gases passed over top of slag and molten bath.
• “Iron Units” - Scrap, Pig Iron, Alt. Iron, Hot Metal
Waste gases heat regeneration chambers for the preheating of combustion air •
Slag Formers and Fluxes
• When solids were molten, Hot Metal charged (teemed) Process :
• Preferential oxidation of dissolved elements (refining): Si, Mn  C Energy(chemical) – Supersonic O2

Outputs : (liquid) Steel – carbon level controlled at tap by sampling Charge Solids  Charge Hot Metal  Blow  Tap

Advantages : Preferential oxidation of dissolved elements: Si, Mn  C : Heat

• Large heat size : 50 – 300 tons Heat Size: 200 -250 ton Outputs : (liquid) Steel
• Process speed allows for chemical sampling Tap-Tap:
• S & P control (typical) Advantages :
• Can charge solid Pig Iron and/or Scrap
30min – 1 hr • Autogenous (REQUIRES NO EXTERNAL ENERGY SOURCE)
• Dilution of “residual” elements
Difficulties :
Difficulties :
• Long process times (4-6 hrs).
• Needs Hot Metal source • Requires continual Hot Metal supply

• Needs fuel (Bessemer = autogenous). Heat Size: 50 -300 ton Tap-Tap: 4 – 6 hr

(typical – 150 – 300 ton)

61 62

STEELMAKING Electric Arc Furnace Process Design “Metallics” Input to Furnace
STEELMAKING
Heat Size: 30 – 400 ton Important Historical Developments: Domestic Use
• 1808: Carbon Arc discovered (Humphrey Davis)
(80 – 180 most common) • 1899: 1st commercial EAF steelmaking (Le Praz, France)
• 1909: 1st commercial US - EAF steelmaking (US Steel – Southworks, Chicago, IL)
Tap-Tap: 30min – 1 ½ hr
Many different styles and configurations of EAFs
(assuming 80 – 180 heat size)
Many different methods and mode of EAF practice/operation

Inputs : • PRIMARY INPUT (1909) US Steel, Southworks 1865 - 1966

• “Iron Units” - Scrap, Pig Iron, Alt. Iron, Hot Metal
• (~2000’s) IDI @ SDI – Flat Roll Div.
Slag Formers and Fluxes

Energy – Electricity(primary), Supersonic O2, Nat. Gas, Carbon add.

Process : 1870 - 1967

Charge  Melt  Refine  Tap

 Desired chemistry (C) & temperature

Outputs : (liquid) Steel

Advantages : 1909 - current

• Flexibility - charge materials (variety, not reliant upon constant source of Hot Metal)
- Operations : On/Off quickly
Difficulties :

• Non-autogenous 1954 - current
• “residual” element control (“high” scrap content in feed stock) 64

63

D. Rees-Evans (c) 2011 American Institute of Steel Construction 16

Practical Steel Metallurgy for the Structural Steel User AISC SteelDay Live Webinar 9/23/2011

Process Design Scrap Selection How can a mill control chemistry ? Isn’t it
dependent upon what scrap is used ?
Steelmaking
A.
“graded” and segregated by: size, source(past history), expected chemistry
• Scrap has had a long history of use in steelmaking
Plate & Structural #2 Heavy Melting Scrap Bushelling Shredded
• Open Hearth (1860 – 2001)
Blended into charge: • Basic Oxygen (1952 – current)
• Electric Arc (1909 – current)
• Cost
• Density • Careful selection and blending of Scrap
• Melting Efficiency
• Chemistry (inc. anticipated “residual” content) {Grade Requirements}
• yield • Melting Characteristics
• melting characteristics • Cost
• Chemistry
• Chemical Energy • Dilution
• Residual Elements (Cu, Ni, Cr, Mo, Sn)
66
65

How can a mill control chemistry ? Isn’t it Process Design Process Design Influences
dependent upon what scrap is used ?

• Chemistry = more than just scrap 1. Steelmaker decides:
• Why is Chemistry important ?
 What product(s)
Product Mechanical Properties (MP)  Target Market
 Where
• Strength (Yield, Tensile) • Weldability
• Elongation • Hardness / Wear-resistance 2. External Influences:

• Impact Resistance • Etc…  Product “demands”

MP = f (chemistry , microstructure) Requirements / limitations

Re-defined question:  Available Technology(s) Process Design Flow
 Raw Material
How does a mill control the 1 + 2 → which technology
Cost / Availability / Suitability solution to employ
properties of a steel product ?
 CO$T$ !! 68

67

D. Rees-Evans (c) 2011 American Institute of Steel Construction 17

Practical Steel Metallurgy for the Structural Steel User AISC SteelDay Live Webinar 9/23/2011

Process Design Output of Furnace Chemistry “Types” of Elements
STEELMAKING
Control

• Oxidizable Elements
can be removed from liquid steel by adding Oxygen (O)

Tap Secondary – Aluminum (Al) and Titanium (Ti)  Order of
Steelmaking Removal
– Silicon (Si) and Vanadium (V) “lost” during
– Carbon (C) and Phosphorous (P) Melting Operations

– Manganese (Mn) and Iron (Fe)

During “Steelmaking” “Secondary Steelmaking” • Reducible Elements
•C + ½O2 → CO •Tailor to desired chemistry can be removed from liquid steel by removing Oxygen (O)
•Mn + O → MnO – Sulfur (S)
•Si + O2 → SiO2
 Oxygen can be removed from steel by adding oxidizable elements
Desirable elements removed
Most commonly Si, Al, Mn, C

69 70

Chemistry “Types” of Elements Process Design Secondary Steelmaking
STEELMAKING
Control
Ladle Metallurgy Furnace
• Other Elements • Desulfurization (slag treatment)

can not be removed from steel by adding or removing Oxygen (O) • Build Chemistry

Level controlled by dilution (adding clean material) (scrap or iron product) (add elements to obtain desired chemistry – C, Mn, Si, Al,
Cu, Ni, Cr, V, Nb, etc.)
– Copper (Cu)
• Inclusion Control (deox / deS products)
– Chrome (Cr) Controlled through the careful
– Nickel (Ni) selection of type and quantities of • Temperature Control
– Molybdenum (Mo) raw materials.
– Tin (Sn)

– *Antimony (Sb)

– *Arsenic (As) Element wt% = as melted (casting consideration, segregation)

* commonly a residual • Homogeneity

from iron ores.

• When purposefully added, known as: Alloying Elements (chemistry, temperature)

• When arriving from raw material stream (eg. Scrap, Ore), Degassing (DH, RH, Tank, etc…)
Known as : Residual Elements

•Control level of dissolved gasses

71 ( H, O, N ) 72

D. Rees-Evans (c) 2011 American Institute of Steel Construction 18

Practical Steel Metallurgy for the Structural Steel User AISC SteelDay Live Webinar 9/23/2011

Process Design Mechanical Properties Metal Crystal Defects

Microstructure Theory

MP = f (chemistry, microstructure)

How Does Chemistry
Influence Mechanical

Properties?

Strengthening Mechanisms

• Solution Strengthening
• Precipitation / Dispersion Strengthening

Contribute collectively to observed A: Interstitial Solute C: Edge Dislocation
mechanical properties
SOLUTE ATOM DOES NOT OCCUPY LATTICE POSITION OF SOLVENT AN EXTRA PARTIAL PLANE OF ATOMS WITHIN THE LATTICE
73 (Solid-state diffusion via interstitial pathways) Local lattice is distorted/stretched at edge of dislocation.

B: Substitution Solute D: Vacancy

SOLUTE ATOM OCCUPIES LATTICE POSITION OF SOLVENT AN UNOCCUPIED LATTICE LOCATION
(Solid-state diffusion via Vacancy Migration)
74

Metal Dislocation Slip Metal Crystal Anisotropy

Theory Theory

Dislocations (may be “Edge” or “Screw”) within the 3-D crystal unit cell / lattice there are

AN EXTRA PARTIAL PLANE OF ATOMS WITHIN THE LATTICE Post-stress planes with differing atoms “packing” efficiencies.
Local lattice is distorted/stretched at edge of dislocation.

Pre-stress

(100) Plane in BCC Iron (111) Plane in BCC Iron
Easy slip  “Weak” Difficult slip  “Strong”

Plastic Deformation = Dislocation Slip  Original Dislocation Slip Location different planes offer different resistances to dislocation motion

• When under stress, dislocations break existing bonds with neighbors and re- @ Macro Level:
randomly oriented grains
establish bonds with other neighbors. May progress rapidly through crystal. exhibit “average” behavior

• Net effect, the dislocation plane moves through the bulk crystal and shape has @ Grain Level :
Steel = ANISOTROPIC
permanently changed.
<< Different strengths in different
• Stress require to slip dislocations is on the order of x102 less than is required to directions >>

cause slip of entire (full) plane of atoms. Permanent Shape Change.

75 76

D. Rees-Evans (c) 2011 American Institute of Steel Construction 19

Practical Steel Metallurgy for the Structural Steel User AISC SteelDay Live Webinar 9/23/2011

Strengthening Solution Strengthening Metal Solid State Diffusion

Mechanism(s) Theory • Given sufficient time and energy
(temperature), solute atoms can
A: Interstitial Solute B: Substitution Solute A: Interstitial Solute B: Substitution Solute diffuse through the crystal

• Unless involved in forming a precipitate or other phase, all alloying element atoms will occupy Vacancy Migration Interstitial Solute: diffuse through
either an Interstitial or Substitution Position within the lattice. interstitial “pathways” between iron atoms.

(Elements that can not reside in either position are immiscible / insoluble) Substitutional Solute: diffuse via “Vacancy
Migration”
• Presence of solute atoms create a “localized” strain on the iron lattice.
• Interstitial solutes (low concentrations) can “Pin” dislocations. (Increases strength) Solid-state Substitution Solute diffusion –
akin to getting from the back of the
• Substitution solutes interfere with / block dislocation slip. (Increases strength) platform on to the car.

• For Substitution Elements with atomic diameters greater than iron: Strengthening Effect “red” atom “breaks” bond with neighbor, moves one
increase with increasing atomic diameter. atomic unit left and re-establishes bonds

Net effect: Vacancy Migration to the right

77 78

Process Design Mechanical Properties Process Design Grain Boundaries

Microstructure Microstructure • Grain Boundaries =

MP = f (chemistry, microstructure) intersection of lattices differing in orientation (random)

How Does • Mismatch = strained lattice = un-satisfied bonds
Microstructure Grain Boundaries = high potential chemical energy
Influence Mechanical
“NATURE TENDS TO THE LOWEST ENERGY STATE”
Properties? In a fixed volume:
 Small grains = more grain boundaries
Strengthening Mechanisms  Large grains = more grain volume
 Large grains = lower overall energy
• Solution Strengthening
• Precipitation / Dispersion Strengthening Given the impetus (temperature + time); large grains
will grow larger by consuming smaller grains.
Contribute collectively to observed
mechanical properties • Dislocation and Vacancies do not cross, but “pile-
up” at Grain Boundaries.
79
• Larger grains offer more unimpeded volume for dislocation to
move with.
• Smaller (finer) grain size = stronger.

80

D. Rees-Evans (c) 2011 American Institute of Steel Construction 20

Practical Steel Metallurgy for the Structural Steel User AISC SteelDay Live Webinar 9/23/2011

Grain Size Rolling MillImportant Historical Developments: Process Design Grain Size Control
Control • 1590 : 1st slitting and cutting of cast iron bar (by rolls) for nail mfg.
Purpose: Microstructure
Worked Grains Austenitic Temperature Range
•transformation a solid cast shape into a desired Coarse Grains
(Plastically Deformed)
“finished product” shape/form
•Product possesses desired mechanical properties/characteristics Fine (recrystallized) Grains

Process :

• Material is plastically deformed by passing between counter-
rotating rolls

• In Austenitic Temp range A0 Force (time & temp) Grain Growth
<< Hot Rolling >> A1 Re-crystallization

• In Ferritic Temp range L0 L1 Conservation of
<< Cold Rolling >> Matter
Force • Ideal Grain shape: Equiaxed
• plastically deformed austenitic grains will re-crystallize
Material AL00 = LA11 • Austenitic Temperature range, given time: grain coarsening
Flow <
82
• Myriad of Roll shapes, sizes, and configurations.
• f (product shape, as-cast size / shape)

81

Process Design Grain Size Control Process Design Grain Size Control

Microstructure Microstructure

theoretical shape attributes ▪ hypothetical mill ▪ Grade: A992

Austenite  Ferrite Transformation: Austenitic Temperature Range GmraoinreStizoCehScteormennitsgrtitrbhyuttheadn

• Ferrite nucleates at defects in Austenite (grain boundaries, precipitates, second phases)

L0/L1: L0/L1: W14x398 :
High Reduction Ratio
A0 Low Reduction Ratio thicker flange
A0 A1
A1 W16x36 W14x398 *lower rolling reduction

Thickness (in) Flange .430 2.845

L0 L1 “fine” recrystallized L0 L1 Chemistry (wt%) C .08 - .12 .08 - .12 W14x398 :
Mn .80 - .90 1.20 - 1.30 “more”
grain size “coarse” recrystallized V .01 - .02 .05 - .06 chemistry

grain size

Greater reduction  Finer recrystallized grains Strength (ksi) Yield 60 - 65 50 - 55 W14x398 :
Tensil 65 - 70 “less”

e 75 - 80 strength

Fine Austenite Grain Size  Fine Ferrite Grain Size fy/fu .75 - .80 .80 - .85 W14x398 :
coarse grain size
Grain Size (Ferritic - core) 9 – 10 5-6

83 “fine” “coarse” 84

* Actual analysis and properties will vary from mill to mill.

D. Rees-Evans (c) 2011 American Institute of Steel Construction 21

Practical Steel Metallurgy for the Structural Steel User AISC SteelDay Live Webinar 9/23/2011

Process Design Grain Size Control Metal Precipitation Strengthening
Thermal History
Microstructure Theory
Air Cool
Selective Cooling Precipitates form, upon cooling / during transformation
• section size from a supersaturated solid solution.
• localized • mill pace
• Fine particles or second phase
Center of Thermal Mass
 Carbides
Quench & Self-Temper • Fine particles: VC, Nb4C3, TiC,
• Second Phase: Fe3C (Cementite: laths as part of pearlite)
• ASTM A913
Microstructure:  Nitrides
• Fine particles: VN, NbN, AlN, TiN,
• (U-Bainite Shell + Ferrite Core)
• Grain Size Control  Carbonitrides

85 Some elements will form both carbides and nitrides which are mutually soluble (C,N).

• Fine particles: V(C,N), Nb(C,N)

 Strengthening Mechanism(s):
• γ → α nucleation site – promotes fine α grain size
• “macro” block to dislocation

86

Process Design Mechanical Response Process Design Mechanical Response

Remove stress, will return to Young’s / Elastic Modulus Yield
original shape
{ Ferritic State } Point / Strength / (Lüder’s) Plateau
ELASTIC BEHAVIOR
“constant” characteristic of a polycrystalline metal Elastic behavior ends and yielding begins when
Governed by inter-atomic binding forces sufficient stress is applied to result in “sudden”:
NOT ALTERED unless basic nature of metal is changed •dislocation slip along “weak” crystal axes
•creation of new dislocations
Eg. Add enough alloy to become something different:
Ni +Cr +Fe => stainless steel; Interstitial Solutes (C,N) pinning dislocations, preventing slip.

Carbon steels: NOT SENSITIVE TO STRUCTURE “sharp” Yield Point : present in lower strength steels (lower C, N concentrations) = activation energy
Unaffected by Grain Size / Alloy content to un-pin dislocations and allow slip.
** ISOTROPIC BEHAVIOR **
strain rate sensitive.  Strain Rate =  Yield Point
<< same mechanical behavior regardless of direction >>
Yield (Lüder’s) Plateau: stress level required for plastic
Important when yielding is a design consideration deformation (un-pinned dislocations –
w(poelayckryasxtaellsin)e. )D–u“epsllaipteianur”anisdnoomcatnlaygi“ovuerinveainrqiatuebeidli”tygsirntar“iernessssults” due .2% offsets
Temperature Dependent
Yield Strength: If no shalerpvepl oint, virtually impossible to determine exact point when plastic
87 deformation occurs: Yield Strength = occurs at .2% deformation (offset from elastic modulus).

88

D. Rees-Evans (c) 2011 American Institute of Steel Construction 22

Practical Steel Metallurgy for the Structural Steel User AISC SteelDay Live Webinar 9/23/2011

Process Design Mechanical Response Process Design Mechanical Response

Strain Hardening UTS to Failure

{ Ferritic State } { Ferritic State }

As dislocations slip through the Ultimate Tensile Strength
grains, they will encounter:
Maximum stress that the material can bear without the onset
•Grain Boundaries of non-uniform elongation across the member.
•Substitution Solute Elements
•Precipitates, Second Phases, Inclusions

1. Dislocations will accumulate at Grain Boundaries and Precipitates, Second Phases, & Inclusions Accumulation of many multiple dislocations at Grain Boundaries and Precipitates, Second Phases,
& Inclusions ultimately lead to microscopic cracking.
<< remove from further slip >>
• Reduction of stress carrying cross-section
2. Dislocations pinned by solute atoms • Localized Plastic Deformation (necking)
• Coalescence of micro-cracks accelerates necking
<< remove from further slip >> • Granular Cleavage

Increasing Stress required to create new dislocations ultimately leads to Fracture
and slip on multiple crystal “packing” axes (not only the weak axis)
90
Uniform Cross-Sectional Volume Reduction / Elongation

89

Process Design Mechanical Response How does a mill control the properties of
a steel product ?
Equal Ferrite & Pearlite Eutectic C : 100% Pearlite Alloying Content (C)
contributions {chemistry & microstructure}
Pearlite lath spacing influences
increasing carbon
• Strong ( Cementite)
• Very poor ductility / elongation

o Ductility due to ferrite

3 Eg: T-Rail, bearing

Carbon Steel Microstructure: Med C : Ferrite  Pearlite Ferrite & Cementite contributions “STRUCTURAL STEELS” A.
• Stronger • varying degrees of control on process variables
Ferrite : (.02%C), Ductile, Weak o Interstitial Strength. • an improvement in one property can not be made without
Pearlite : laths (Ferrite, Cementite) o Cementite influence upon other properties
Cementite : (6.67%C), Brittle, Strong • seek to optimize ‘total package’ of properties in a cost
• Reduction in vol% of effective manner to meet grade requirements.
Ferrite = reduced ductility
92
• Pearlite lath spacing has
American Institute of Steel Construction 23
2 moderate influence

Low C : Ferrite, Pearlite

Ferrite Governs

• Weak ( YS / UTS)
• Ductile ( Elongation)

1

an improvement in one property can not be made

without influence upon other properties 91

D. Rees-Evans (c) 2011

Practical Steel Metallurgy for the Structural Steel User AISC SteelDay Live Webinar 9/23/2011

Questions If I retest a product, will I get the same results
as in the MTR?
Iron – Steel: What is the Difference ?
Why are there multiple Grades of Steel ? Isn’t A. (short Answer)

steel, steel ? • Exactly Same Values ?
How can a mill control chemistry ? Isn’t it
 No
dependent upon what scrap is used ?
• “Nominally” Same Values ?
 How does a mill control the properties of a steel product ?
 Yes
If I retest a product, will I get the same results
as in the MTR (Mill Test ?Report) 94

93

MTR Variability Chemical Analysis General Metallurgy CO2 (g) “Killed”
“Soda” Analogy
Removed from system
(degassed)

Casting Method(s) strongly influence variability in “Product Check” • As steel cools  solidifies, dissolved gases H, O, N

come out of solution.

• If sufficient O: O reacts with C in liquid forming CO(g)

Ingot Casting Continuous Casting Δ vol. CO2 (g) bubble. Results in local reduction in carbon content +
voids / bubbles trapped in solid steel. ( UNKILLED )

KILLED STEEL:

- dissolved oxygen content low enough to

“green caffeine” (l) “green caffeine” (l) prevent CO(g) evolution during solidification.
+ CO2
“Killing” accomplished by removing / “tying-up” dissolved
 loss of CO2 solubility  oxygen through reaction with metals possessing a high
Ingot Casting chemical affinity for oxygen.

2Al + 3O = Al203 (s) | Si + 2O = SiO2 (s)

Killed Nature Ingot Continuous Cast unkilled “Gross” gas
MUST BE FULLY KILLED evolution
Solidification Rate Unkilled - to -fully killed
Segregation FAST during
Rimming & Capped 45 - 60 min solidification
“Heat”/Batch Separation CO evolution (local changes in C levels) 80 - 120 tons

SLOW Minimal
8 hrs - 2 days Sequenced Heats
10 - 40 tons
can be significant (C, S, P)
Single Heat in Mold

95 96

D. Rees-Evans (c) 2011 American Institute of Steel Construction 24

Practical Steel Metallurgy for the Structural Steel User AISC SteelDay Live Webinar 9/23/2011

General Metallurgy “Segregation” MTR Variability Chemical Analysis

In alloy systems, during solidification, the higher melting point constituent(s) freeze first. Sequence (Continuous) Casting
(Slow cooling):
A 1. Heat “1” (chemistry “1”) teemed from ladle [A] to tundish
•Lower melting point constituent(s) will be “rejected” by the advancing solidification front. [B]. Tundish distributes steel to casting mold(s) [C].
•Remaining liquid becomes enriched in lower melting point constituents. B
C 2. When ladle is empty, ladle removed. Tundish retrains steel
•Upon complete solidification: Regions of “Composition Fluctuation”  SEGREGATION of Heat “1”.

<< different chemistry in different regions >> 3. new ladle of Heat “2” (chemistry “2”) substituted, and
teemed to tundish.
Analogous Example: Traffic Jam = Solidified Alloy. ( Cars = Iron Atoms, Motorcycles = Sulfur Atoms )
4. For period of time, tundish chemistry = decreasing % of
Fast Cooling: Low (microscopic) Segregation Slow Cooling: High (macroscopic) Segregation Heat “1” and increasing % of Heat “2”; after which
Chemically Homogeneous Chemically Inhomogeneous chemistry = Heat “2”

5. When ladle “2” is empty, steps 3 & 4 repeated

Product of Heat “2” will possess a changing mix of Chem “1” to Chem “2” on one end, a
changing mix of Chem “2” to Chem “3” on the other, and chem “2” throughout the “middle”

• Heats 1, 2, 3 must be of nominally same chemistry (Grade Separation)
• Compliance to spec: eg. ASTM A6 Table A – Permitted Variations in Product Analysis

• ‘MTR’ Chemistry = average of samples taken during casting of the Heat

97 98

MTR Variability Tension Test Results MTR Variability “Thick” W Shapes
ASTM A6/A6M – 10a
Center of Thermal Mass
Appendix X2. Variation of Tensile Properties in Plates and Shapes

X2.1

• “tension testing requirements … are intended only to characterize the tensile
properties of a heat of steel …”.

• “not intended to define … tensile properties at all possible test locations…” bar leaving “hot” side of mill, entering cooling bed
SDI-SRD, Columbia City, IN
• “it is well known and documented that tensile properties will vary within a heat or Core
individual piece of steel as a function of chemical composition, processing, testing Area Residual Heat: variable thermal profile across thickness
procedure and other factors.” o leads to variable grain size across thickness (grain growth)

• “incumbent on designer and engineers to use sound engineering judgment when Region of low reduction ratio

using tension test results shown in mill test reports.” o coarse grain size

X2.2 Region of potential high segregation {C, S, P} (ingot cast)

• Expected variability: “one standard deviation equals approximately 4% of required • S,P dramatically reduces strength, elongation toughness
tensile strength, 8% of required yield strength, and 3% of required elongation.”.
Core Area (thickness: ASTM: + 1 ½”; AISC: +2”):
X2.1 : “testing procedures ... Have been found to provide structural o Coarsest Grain Size / potentially most segregated
o Lowest Toughness
products adequate for normal structural design criteria.”
100
99

D. Rees-Evans (c) 2011 American Institute of Steel Construction 25

Practical Steel Metallurgy for the Structural Steel User AISC SteelDay Live Webinar 9/23/2011

MTR Variability Coupon Type / Location MTR Variability Coupon Type / Location

tw 1 tw
Full Thickness Plate Specimen (MTR)
1/3 ASTM A6/A6M -10a
Mill Testing (MTR Values) use: 1/3 •Average of “discrete point” strength(s)
across flange thickness
2/3 • 2⁄3 of the way from the flange centerline to
the flange toe 2/3 •Expected in-service response

•Full thickness tw

•8” gage

•ASTM A370 – 1½” Wide “Plate-Type”

Coupon (Fig 3) 23

tw 2” gage length coupon 0.500” Round Coupon
gives better % (more)
ASTM A370 – 0.500” Round Coupon (Fig 4) •“localized properties”
elongation vs. 8” gage •≠ Plate Specimen values
•2” gage
•Can be tested on small / lower cap. Test Frame 101 o (microstructural, chemical differences)
•Commonly found in use by 3rd Party Testers
•Difference exaggerated by

o thickness
o QST (A913) / surface treatment / case hardening

102

If I retest a product, will I get the same results Questions
as in the MTR?
Iron – Steel: What is the Difference ?
A. (Long Answer) Why are there multiple Grades of Steel ? Isn’t

• Exactly Same Values ? steel, steel ?
How can a mill control chemistry ? Isn’t it
 No
dependent upon what scrap is used ?
• “Nominally” Same Values ?
 How does a mill control the properties of a steel product ?
 Yes – within allowable variations
If I retest a product, will I get the same results
o Mech. Prop’s: Same coupon and location(s) as in the MTR?

103 104
104
D. Rees-Evans (c) 2011
American Institute of Steel Construction 26

Practical Steel Metallurgy for the Structural Steel User AISC SteelDay Live Webinar 9/23/2011

For more information or answers CEU/PDH Certificates
to other Steel questions Within 1 business day…
contact: • You will receive an email on how to report attendance from:
[email protected].
AISC Steel Solutions Center • Be on the lookout: Check your spam filter and junk folder!
• Completely fill out online form. Don’t forget to check the boxes
866.ASK.AISC (866-275-2472) next to each attendee’s name!
• OR…
[email protected].
AISC Seminars
THERE’S ALWAYS A SOLUTION IN STEEL
Fall Schedule has started!
105 22 cities, 4 different seminars including
The NEW 14th Edition Manual/2010 Specification Seminar
CEU/PDH Certificates
Access available in 24 hours… www.aisc.org/seminars

• Go to:
http://www.wynjade.com/aiscfall11/webinarCEU.
Username: Your Web ID (found on your registration receipt)
Password: Your Last Name

• Completely fill out online form. Don’t forget to check the boxes
next to each attendee’s name!

• Questions? Please email us at [email protected].

D. Rees-Evans (c) 2011 American Institute of Steel Construction 27

Practical Steel Metallurgy for the Structural Steel User AISC SteelDay Live Webinar 9/23/2011

AISC Steel Camp AISC eLearning

2 day, 4 topics, 15 hours of Continuing Education, Over 80 hours of presentations available anytime,
One low price. online.

Charlotte, NC – October 6,7 CEUs/PDHs are available.
www.aisc.org/steelcamp www.aisc.org/elearning

AISC Live Webinars Please give us your feedback!
www.aisc.org/cesurvey
More live webinars coming soon including
December 8, 2011: New Composite Design Provisions Thank You!

www.aisc.org/webinars American Institute of Steel Construction 28

D. Rees-Evans (c) 2011