Galvanizing Symposium São Paulo, Brasil - · PDF fileGalvanizing Symposium São...

30/9/2009

1

essential

for life

Galvanizing Symposium

São Paulo, Brasil

September, 25, 2009

Dr. Frank E. Goodwin, IZA

Zinc

…essential

for life

30/9/2009

2

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for life

Session 1

• Zinc Alloys and Their Effects on the Steel

Coating

• Influence of Steel Alloying Elements on Al

Consumption and Fe Release into the

Zinc

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for life Consumption and Fe Release into the

Bath

• Methods of Control of Chemical

Composition of Steel Coating

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Iron and Steel Engineer, March 1962; From Data

Collected in 1911

Optimum “tightness” seen at 0.2% Al, regardless of Temperature

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Open literature data

� Mg addition strongly improves corrosion resistance of

zinc-coated steel (salt spray test, cyclic corrosion tests)

• 3 to 20 fold prolongation of time to red rust appearance• Undercreep significantly retarded (20 instead of 3–4 weeks),

delamination distance lower

�Two methods of manufacturing�Two methods of manufacturing

• Hot dipping• Physical vapor deposition

MagiZincTM of CORUS

Salt spray test, 10 µm coatings

ZnMg alloy 0.4-1.6 µm

PVD0.2-0.8 µm

Mg

Heat treatmentT>250 oC

GI or GE substrate

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Flange corrosion ofzinc coatings in thecyclical corrosiveEnvironment test

VDA 621-415 (glassflange SEP 1160/8)

Test Duration in hours until red rust occurs in the salt spray test (DIN 50021-SS)

New Zinc Alloy CoatingsZinc

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Micrograph of the coating

structure of the new

Zinc

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the new ZnMg and Fe-Zn coatings

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Session 1


Coating



Zinc

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Bath



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Influence of Steel Alloying Elements on Al Consumption and Fe Release into the Bath

• No organized examination of effects of steel grades has been found

• Effects of other line operating variables has been studied

Zinc

…essential

for life • The effect of steel composition on interface

structures produced in galvanized coatings has been studied

• These studies give us some idea of the effects of steel composition on release to the bath

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The coverage of the steel surface by the Al-Fe

inhibition layer happens very quickly

0.6

0.8

1

Cov

erag

e

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0 0.001 0.002 0.003 0.004 0.005 0.006 0.007

Time (s)

0

0.2

0.4

0.6

Cov

erag

e

SET 465 EAL 0.108

SET 465 EAL 0.16

SET 520 EAL 0.108

SET 520 EAL 0.16

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essential

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The diffusion of Fe from the strip surface into the bath before

the inhibition layer is formed

Iron Concentration Near Strip Before Inhibition

20

40

60

80

100

Fe

(w

t%)

Zinc

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0

20

0.00E+00 2.00E-06 4.00E-06 6.00E-06 8.00E-06 1.00E-05Distance (m)

The amount of iron that dissolves into the bath from the strip before theinhibition layer forms is equal to the area under the graphmultiplied by the area of strip that is not covered by the inhibition layer

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• For a line speed of 80m/min, a strip width of

1m, effective aluminium of 0.108wt% and a

strip entry temperature of 460°C the

Initial Fe dissolution into bathZinc

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for life

strip entry temperature of 460°C the

amount of iron dissolution that occurs

before the inhibition layer forms is 89.60

mg/m2 (of coil, not surface area), for a steel

with 100% Fe on the surface. The amounts

and identities of alloying elements affect

this result

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essential

for life

Effect of Strip Temperature

470

480

490

500

510

520

Tem

p (C

)

SET 465

SET 475 BT 500

SET 485

SET 495 1.2mm

SET 515

Zinc

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0 0.2 0.4 0.6 0.8 1

Time (s)

450

460

470 SET 515

Bath temperature 455°C unless indicatedStrip thickness 0.7 mm unless indicatedThere is a great variation in T, and therefore the amount of Fe that will be dissolved

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Variation of inhibition layer thickness

with Al and T

200

250

300

Thi

ckne

ss (

nm)

SET 465 EAL 0.108

SET 465 EAL 0.135

SET 465 EAL 0.2

SET 520 EAL 0.16

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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Time (s)

0

50

100

150

Thi

ckne

ss (

nm)

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Fixed Conditions for Fe dissolution

study of O’Dell

Parameters Value

Line Speed (m/min) 80

Gauge (mm) 0.7

SET (°C) 465

Zinc

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for life SET (°C) 465

Bath Temp (°C) 455

Effective Aluminium (wt%) 0.108

Simon O’Dell et al., “Modelling Of Iron Dissolution During The Hot Dip Galvanising of Strip Steel”, Institute of Metals (UK)

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essential

for life

Effect of strip entry T on Fe dissolution,

before and after inhibition

150

200

250

Iron

Dis

solu

tion

(mg/

m2)

Without Inhibition

With Inhibition

Total

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400 425 450 475 500 525 550 575 600

Strip Entry temperature (C)

0

50

100

150

Iron

Dis

solu

tion

(mg/

m2)

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Effective Al influence

60

70

80

90

100Ir

on D

isso

lutio

n (m

g/m

2)

Without Inhibition

With Inhibition

Total

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0.1 0.15 0.2 0.25 0.3

Effective Aluminium (wt%)

0

10

20

30

40

50

60

Iron

Dis

solu

tion

(mg/

m2)

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Effect of Bath T

400

600

800

1000

Iron

Dis

solu

tion

(mg/

m2)

Without Inhibition

With Inhibition

Total

Zinc

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for life

425 450 475 500 525 550

Bath Temperature (C)

0

200

400

Iron

Dis

solu

tion

(mg/

m2)

No effect of bath T on dissolution from uninhibited strip,it has no time to change its T

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for life

Increasing line speed decreases the

residence time in the bath

125

150

Iron

Dis

solu

tion

(mg/

m2)

Without Inhibition

With Inhibition

Total

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20 40 60 80 100 120

Line Speed (m/min)

0

25

50

75

100

Iron

Dis

solu

tion

(mg/

m2) Total

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Combining Al and Strip Entry T

200

Zinc

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0.11

0.15

0.19

0.23

0.27

0

50

100

150

I r o n D i s s o l u t i o n

( mg / m2 )

S t r i p E n t r y

T e mp e r a t u r e ( C )

E f f e c t i v e

A l u mi n i u m ( w t %)

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Effect of Steel Composition on

Intermetallic Layer Formation

• Zn-Al-Fe inhibition layer

• Fe-Zn phases forming after

• Thickness and composition of layer

influenced by steel compositions and

Zinc

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process variables

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Compositions provided by Suppliers 1,2,3Zinc

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Process Conditions from Suppliers 1,2,3Zinc

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Samples and Conditions from Supplier 4Zinc

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Co

mp

ositio

ns fro

m S

up

plie

r 5Zinc…essential

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Process Conditions from Supplier 5Zinc

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Ch

ara

cteriza

tion

s of S

am

ple

sZinc…essential

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Re

sults

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Session 1


Coating



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Bath



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Effect of a) line speed, b) coating weight and c)

bath Al level on the distribution of Al in the coating

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essential

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Session 2

• Processing of materials AHSS (DP and

TRIP)

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Production sequence for steel sheets • • • •

CASTING

HOT ROLLING — self annealing

PICKLINGPICKLING

COLD ROLLING

ANNEALING

TEMPER ROLLING

— softening to control properties

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Property Changes in Annealing

STRENGTHor

HARDNESSRECOVERY

.

Grain Growth

RECRYSTALLIZATION

REX.START

REX.FINISH

Temperature

(REX)

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DEFINITIONS & TYPES OF ANNEALING

BATCH (OR BOX) ANNEALING

HEATING/COOLING

RATES TIME

Tightly wrapped coils stacked on annealing bases and

heated in large movable furnace covers with controlled

circulatory gas

• MULTIPLE STACKS V. Slow Days

• SINGLE STACKS Slow Days

Medium HoursOPEN COIL ANNEALING

CONTINUOUS ANNEALING

CONTINUOUS NORMALIZING

Medium Hours

Open wound coils single stacked and heated in moveable

furnace cover usually with a decarburizing atmosphere

Fast Minutes

Annealing of moving strand of sheet/strip through a

stationary furnace system having a controlled atmosphere

Fast MinutesHigher temperatures (austenite zone)

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Evolution of Modern CA

Characteristics of BA and old CA

BA CATemp.

2 – 20 hrs

25 to 50° F/hr.

10 – 120 secs.

15 to 60° F/s

• Grain Size Large (controlled) SmallDuctility High Low OK for CQ/DQ

(Grade1,2-SAE J2329)• Crystal texture Good Poor

Deep drawability High Low Not OK for DDQ(Grade 3,4-SAE J2329)

• Quench/Strain aging None YesStretcher – Strains None Yes

Time, days Time, mins.

Slow heat & cool/long soak Rapid heat & cool/short soak

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METALLURGICAL ASPECTS OF ANNEALING

� Specific mechanical properties— high ductility for stretch forming

— controlled crystallographic texture for • deep drawing• earing control (CR sheet & tinplate)

Requirements of the annealed sheet• • • •

• earing control (CR sheet & tinplate)• magnetic properties (CRMLS & NO electrical sheet)

— high strength— stable properties (no aging or controlled aging)

� Clean Surface

� Controlled surface texture (additional temper rolling)

� Flatness

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METALLURGICAL ASPECTS OF ANNEALING

� Steel Composition— C

— Solid solution elements (Mn, Si, P) — Carbo-nitrides

• Allll N, Ti (& Nb) CN affect crystallographic texture – hence, deep

drawability, /earing and strengths

Annealed sheet characteristics are affected by • • • •

drawability, /earing and strengths— Interstitial-free (IF) steels

� Hot rolling— Finishing and coiling temperatures affect crystallographic texture – deep

drawing /earing and strength

� Cold reduction— affects recrystallization temperature, grain size and crystallographic texture

� Annealing Process— effects of above may differ for BA and CA— cooling rates affect quench/strain aging

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Modern CA Process

CA for CR (EG coated) sheets

CA for hot-dipped products

— significantly expanded application in last 20 years• more flexibility• quicker throughput

— change has been facilitated by• new metallurgy (steel composition and processing)• new steelmaking• overaging section in-line

CA for hot-dipped products

— increased demand for HD products by automotive— new metallurgy and steelmaking has enabled

�� similar properties to CR BA for low strength high forming grades— no significant changes in annealing cycles

• trend to higher cooling rates before the pot• trend to modify cooling for AHSS

— no overaging sections

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Metallurgy of Modern CA for DDQ CR Sheets

CA Processing (continued)CA Processing (continued)

� Control of primary cooling rates

… significant impact on line length and investment costs.

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CA in Producing HSS/AHSS

CA – FOR CR

CAL CAPL

CA – FOR HD

HDGI HDGA

Schematic CA Cycles at ArcelorMittal

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Types of HSS/AHSS

� YS• ULSAB: > 207 MPa (30 ksi)• SAE J2340: > 180 MPa (26 ksi)

�� TS – AISI: >270 MPa (39 ksi)

� Solid Solution Strengthening

• C (including BH)• Mn• P

Definition of HSS

Four general categories

�� HSLA (Grain size/precipitation strengthening)

• V• Nb• Ti

�� Transformation strengthening

• Bainite• Martensite• Dual Phase• TRIP (TRansformation Induced Plasticity)• Complex Phase

�� Recovery Annealing

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Overview of Hardening Mechanisms for HSS/AHSS

Steel Grade Alloy Basis Hardening Mechanism Main Alloying Addition

Microalloyed grades LCPrecipitation,

grain refinement, solid solution

Ti, Nb and/or V

Mn

Rephosphorized LC grades

LCSolid solution,

grain refinementP, Mn, Si

HS IF grades IF (Ti, Nb or Ti + Nb)Solid solution,

grain refinement, precipitation

P, Mn, Si, B

BH grades (LC) LCSolid solution,

grain refinementP, Mn, Si

grain refinement

BH grades (ULC) ULC (Ti, Nb, V)Solid solution,

grain refinementP, Mn

DP/MP grades LC Transformation C, Mn, Cr, Mo

TRIP grades LC Transformation C, Mn, Si, Al, P

[Source: Pichler, et al; 44th MWSP Conf., 2002]

• • • •Used for CA/CR and ILA/HD

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CA for AHSS

Transformation Strengthening

Principle: Transform to complex (multiple)phases; bainite, martensite and retained austenite

Keys: • Composition control to produce Keys: • Composition control to produce required phases with a given CAcycle

• Low alloy steels (C, Mn, Si, Mo, etc.)

• Intercritical annealing to provide+ starting structure with

high C

γγ

α

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CA for AHSS

Benefits of Transformation Strengthening

� Unique structures

� Unique properties—high TS—low Yield/Tensile ratio—high work hardening—high work hardening—better ductility at

a given TS

� Automotive application—crash enhancement—weight reduction

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CA for AHSS

Transformation Strengthening

CR HD

√√√√ √√√√

� Ferrite - Martensite—better strength-ductility

relationship—low YS/TS ratio

Dual Phase

—low YS/TS ratio—high work hardening

� Proportions of martensite canbe changed by composition/primary cooling

� Growing demand for HDDPfrom automotive (crash improvement/weight reduction)

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Overaging/Tempering provides flexible properties for CR AHSS

T

Tempering

of Martensite

t

of Martensite

Hi Local Elong.

Hi Total Elong.

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Effect of Overaging/Tempering on Elongation of CR-980 MPa sheet

Overaging/Tempering

Temperature

Yield

Strength

(MPa)

Tensile

Strength

(MPa)

Total

Elongµ

Hole Exp.(ג)*

Low 660 1010 17 25

Intermediate 720 1010 15 35Intermediate 720 1010 15 35

High 790 1080 13 50

[Source: Kobe Steel]

ג* = DF – D I

DI

D I = initial hole diameter

DF = final hole diameter

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Effect of Alloying on AHSS Transformation Strengthening Products

Schematic TTT Behavior

[Source: Ehrhardt, et al; AHSS Proceedings 2004]

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Temperature ‘hold’ for HD AHSS Dual Phase

Value: Temperature equalization in strip

Control of pot-entry temperature

+

Austenite stabilization

~470°C

20–60 secs

After Hoydick and Haezebrouck; 45th MWSP Conf. 2003

But …… danger

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Transformation to Bainite can occur – undesirable for DP

Must control composition,

soak temp, hold temp.

& time

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Effect of C Austenite/Martensite % on Tensile Strength

Base Steel

Mn: 1.6-2.2%

Cr & Mo: ~ 0.4%Cr & Mo: ~ 0.4%

Aℓ: 0.04%

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Zinc Quenching Can Provide Flexibility for AHSS

For 0.1C – 2.1Mn steel

MPaYS TS

Total Elong. %

Zincquench ® 330 750 17

Conventional 400 610 23

Zincquench Technology® Conventional HD Process

Higher cooling rates (100ºC/s) from snout temperature (600-480ºC) can provide:

– either higher TS– or same TS from leaner composition

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Summary of HD Dual Phase 500-1000 MPa- Effect of Composition and Processing

National Steel Corp/NKK Corp*

Steel Grades C Si Mn P S Cr V Nb Ti Aℓ

DP 500 / DP 600 0.07- 0.30 1.00- 0.02 0.01 0.10- 0.02- 0.05 0.05 0.06

DP 800 / DP 1000 0.20 max 2.50 max max 1.00 0.10 max max max

Lab Heats – all gradesCommercial Heats – DP 600 and DP 800

Variables Studied

�� Steel composition�� Hot mill coiling temperature�� Annealing temperature�� Line speed (DP 500)�� Leveler and Temper Extension

(DP 600)

[*Source: Rege, et al, 44th MWSP Conf. 2002]

Annealing simulation

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Schematic Summary of ICA on Tensile Properties – DP 600

[Source: Rege, et al, 44th MWSP Conf. 2002]

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Summary of ICA on Tensile Properties – DP 500-1000

Steel Grade Production

Yield

Strength,

MPa

Tensile

Strength,

MPa

Total

Elong.

%

װ value(4-6%)

װ value(10-15%)

Yield

Ratio, %

DP500 Commercial 350 580 29 0.23 0.19 60

DP600 Commercial 350 610 28 0.21 0.17 57DP600 Commercial 350 610 28 0.21 0.17 57

DP800 Commercial 530 890 17 0.16 0.12 60

DP1000 Laboratory 590 1030 14 0.14 0.10 57

[Source: Rege, et al, 44th MWSP Conf. 2002]

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Principles for AHSS Transformation Strengthened TRIP

Schematic TTT Behavior

[Source: Ehrhardt, et al, AHSS Proc. 2004]

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Composition and Annealing Optimization for TRIP

Tailor composition to CA cycle (e.g., 0.2C/1.5Mn/V5 Si) – C+ Mn prevent pearlite.

Hold to form bainitic ferrite (promoted by Si and Aℓ).

growth of ferrite

prevent pearlite formation

promote bainitic ferrite formation

prevent precipitation of cementite

(pearlite)

bainitic ferrite is very low in C.

C in ɤ is maximized resulting in retained ɤ (RA) after post pot cooling

• • • •

[After Pichler, et al, 44th MWSP Conf. 2002]

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Classic Bainite versus Bainitic Ferrite

[Source: Ehrhardt, et al: AHSS Proceedings, 2004]

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Carbon Diffusion and Microstructure – DP and TRIP(CR and HDG)

DP

[After Ehrhardt, et al., AHSS Proceedings, 2004]

Carbon content of ɤ Process time

DP

RA (TRIP)

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Importance of Overaging Temperature – HD TRIPYS, TS [MPa]

Eℓ u, Eℓ T

[%]

YS TS

Eℓu EℓT

[Source: Pichler, et al, 44th MWSP Conf. 2002]

• • • • Suggests TOA >460 for maximum elongation

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Typical Tensile Properties – TRIP 600 to 800(C – MN – Si base)

Steel GradeYield

Strength(MPa)

TensileStrength(MPa)

TotalElong.

%

n value(4-6%)

n value(10-15%)

TRIP 600 380 640 30 0.18 0.22

TRIP 700 460 720 28 0.18 0.20

TRIP 800 490 810 22 0.20 0.18

[After Pichler, et al, 44th MWSP Conf. 2002]

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Tensile Properties of C– Mn - Aℓ TRIP Steels

[After Ehrhardt, et al, AHSS Proceedings, 2002]

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Challenges for TRIP Steels

Production� Rich compositions (0.2 C/1.5 Mn/1.5 Si or 1.5 Aℓ)

―Steel making ―Hot-mill processing/surfaces

―CR surface for CA or HD processing

�� Critical tailoring of composition/processing to specific CAL or HDL

―Interaction of composition, annealing temperature andoveraging temperatureoveraging temperature

Application� Rich compositions

―Welding�� Benefit for cost/price�� Fatigue durability

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Strengthening Mechanisms - AHSS

Complex Phase Steels

� Many phases

-upper & lower bainite

-martensite / retained ɤ

• • • •

-ferrite

� Fine precipitates

-micro alloys (Nb, Ti, V)

� Very fine grains

� Better ductility

than martensite steels

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Typical Composition/Microstructure of CP Steels

Composition, wt % C Mn Si Aℓ Cr V/Nb/Ti ~0.1 1.5-1.70 0.3-0.6 0.03 0.1-0.30 Yes

Microstructure

• • • • More widely available as HR and CR products than HD

[Source: Ehrhardt, et al, AHSS Proceedings, 2004]

(Bainite)

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Complex Phase (Bainite rich) Steels

―Lower total elongation than DP or TRIP

―Better hole expansion due to finer multi-phase structure

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AHSS – Transformation Strengthened Steels - Martensite Grades

Characteristics …...

• C-Mn Steels

• Continuous normalizing (CN)

or high ILA temperatures

(CR CA) followed by rapid

coolingcooling

• High strengths

(600 to 1000 MPa TS)

• Limited forming

-bumper reinforcements

-side impact structures

• • • • Corrosion resistance addedby electrogalvanizing

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Martensite Steels compared with DP Steels

[Martensite Steel information source: Arcelor Mittal brochure]

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Unique class of UHSS – Recovery Annealed Steels

CR HD

Availability: √√√√ √√√√

� C and HSLA steels

� Limit annealing

conditions to recovery stage only

STRENGTHor

RECOVERY

Recovery annealed (500-1000 MPa TS)

recovery stage only(prevent recrystallization)

� Only small recovery of

ductility

� Low forming applications

— roll forming— stamping of simple

shapes— bumper reinforcements,

side impact structures

.

Grain Growth

orHARDNESS

RECRYSTALLIZATION

REX.START

REX.FINISH

Temperature

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92

Elo

ngati

on

(%

) 50

60

70 Low Strength

Steels (<270MPa)

Ultra High Strength

Steels (>700MPa)

High Strength

Steels

IF Conventional HSS

Ductility – Strength of HSS and AHSS

CA Processes

Reviewed for HSS/AHSS

Elo

ngati

on

(%

)

Tensile Strength (MPa)

0

10

20

30

40

0 600 1200300 900 1600

DP, CP

TRIP

AHSS

MART

HSLA

IF

Mild

IF-HS

BH

CMn

ISO

Conventional HSS

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93

Availability of HSS/AHSS

General

Category Type Tensile Strength, MPaContinuous

CRAnnealed

HD

HSS

Solid solution strengthened- P- IF- BH- C-Mn

270 - 600√√√√

√√√√

HSLA 350 - 800 √ √

AHSS Dual Phase 500 – 1000 √ √

TRIP 600 – 850 √ Limited

Complex Phase 600 – 1000 √ Limited

Martensitic 900 – 1600 √ No

Specific Example

Recovery Annealed 500 - 1000 √ √

[ThyssenKrupp Stahl (Ehrhardt, et al, AHSS Proceedings, 2004]

AHSS Dual Phase 500 min600 min

√√

√√

TRIP 600 min700 min780 min

√√√

No√√

Complex Phase 780 min √ No

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94

essential

for life

Session 3

• On line measurement of Fe in the bath

• Influence of chemical composition of GA

coating on powdering defect

• GA material with zeta free

Zinc

…essential

for life • GA material with zeta free

30/9/200995

essential

for life

Zinc…essential

for life

30/9/200996

essential

for life

Zinc…essential

for life

30/9/200997

essential

for life

Zinc…essential

for life

30/9/200998

essential

for life

Zinc…essential

for life

30/9/200999

essential

for life

Zinc…essential

for life

30/9/2009

100

essential

for life

Zinc…essential

for life

30/9/2009

101

essential

for life

Zinc…essential

for life

30/9/2009

102

essential

for life

Zinc…essential

for life

30/9/2009

103

essential

for life

Analytical Techniques

Zinc…essential

for life

30/9/2009

104

essential

for life

Zinc…essential

for life

30/9/2009

105

essential

for life

Teck

Al S

en

sor P

rincip

les

Zinc…essential

for life

30/9/2009

106

essential

for life

AlS

en

sor™

an

d A

lVie

we

r™Zinc…essential

for life

30/9/2009

107

essential

for life

Al Sensor in Field ApplicationZinc

…essential

for life

30/9/2009

108

Teck Electrochemical Sensor

30/9/2009

109

essential

for life

BACKGROUND OF LIBS

• LIBS principle of measurement

• On-line LIBS measurement of aluminum and

iron content in zinc bath of Sorevco plant

Zinc

…essential

for life iron content in zinc bath of Sorevco plant

• Comparison with Teck Cominco probe

30/9/2009

110

essential

for life

Principle of LIBS analysis of molten metalZinc

…essential

for life

30/9/2009

111

essential

for life

LIBS components

Spectrometer

Detector Controller PC

Pulse energy, duration,spot size, wavelength

Échelle spectrometer,Czerny-Turner

IPDA, ICCD,Interline CCD, gated CCD

PMs

Zinc

…essential

for life

Surrounding atmosphere,pressure, composition

Target

Laser Dichroic mirror

Lenses

Plasma

spot size, wavelength

Reflectivity, heat capacity, melting and boiling point,thermal conductivity etc.

Czerny-TurnerRowland circle

30/9/2009

112

essential

for life

Problems and difficulties

• Problems related to the laser-liquid interaction– Splashing of the liquid caused by powerful laser

pulses

– Generation of waves perturbing the surface

Zinc

…essential

for life

– Generation of waves perturbing the surface

– Aerosols and particles ejected

• Difficulties related to the molten metal– Surface is not representative of the bulk

– Diffusion of some elements to the surface

– The sensor should be sufficiently rugged for plant

use

30/9/2009

113

essential

for life

Problems and difficulties

• Problems related to the LIBS technique when compared with conventional techniques

Zinc

…essential

for life

– Reproducibility is poorer than conventional techniques

– LIBS sensitivity is in the range of ppm which is poorer than conventional techniques

30/9/2009

114

essential

for life

lens

Laser pulse

Laser-liquid interactionZinc

…essential

for life

bubbleaerosol

lens

waves

liquid

splashing

30/9/2009

115

essential

for life

Approaches to analyse molten metal by LIBS

De Saro and WeisbergUS6784429, 2002Apparatus and method for in situ, real time measurements of properties of liquids

Singh et al US6762835, 2002

Fiber optic laser-induced breakdown spectroscopy sensor for molten material analysis

Zinc

…essential

for life

30/9/2009

116

essential

for life

LIBS of molten zinc

Principle

Laser head+

light collection optics

Laser head+

light collection optics

Dynamic approach:Bubbles ensurethat a frequentlyrenewed surface

is analysed

Dynamic approach:Bubbles ensurethat a frequentlyrenewed surface

is analysed

Zinc

…essential

for life

Zinc bathZinc bath

GasflowGasflow

LaserbeamLaserbeam

PlasmaPlasma

Probetube

Probetube

BubblesBubbles

is analysedis analysed

Slag

30/9/2009

117

essential

for life

LIBS on molten zinc

Laser head+

Light collection

Zinc

…essential

for life

Light collection

To spectralanalysissystem

100 kg zinc bath

Probe tubewith probe gas

30/9/2009

118

essential

for life

LIBS

of m

olte

n zin

c

Typ

ical LIB

S sp

ectru

mLIB

S o

f mo

lten

zinc

Typ

ical LIB

S sp

ectru

m

(4 eV)

Al 308.22 (4 eV)

Zn 307.59 (4 eV)

Zn 303.58 (8 eV)

Zn 307.21 (8 eV)

Al 309.27 (4 eV)

Zn 301.84 (8 eV)

Spectrum

for zinc bath with 0.12%

Al and 0.04%

Fe (nom

inal)S

pectrum for zinc bath w

ith 0.12% A

l and 0.04% F

e (nominal)

Zinc…essential

for life

Fe 302.06 (4 eV)

Al 308.22

Zn 307.59 (4 eV)

Zn 303.58

Zn 307.21 (8 eV)

Al 309.27 (4 eV)

Zn 301.84 (8 eV)

30/9/2009

119

essential

for life

Al 3

08.2

2 / Z

n 30

7.59

4

5

6

Analysis of aluminum and

iron in molten zinc for the

galvanizing processA

l 308

.22

/ Zn

307.

59 5

6

7

Zinc

…essential

for life

Concentration nominale d'aluminium (ppm)

0 200 400 600 800 1000 1200 1400

Al 3

08.2

2 / Z

n 30

7.59

0

1

2

3

4

r = 0.99987

Concentration nominale d'aluminium (ppm)

0 200 400 600 800 1000 1200 1400

Al 3

08.2

2 / Z

n 30

7.59

0

1

2

3

4

Aluminum nominal concentration (ppm )Aluminum nominal concentration (ppm )

N2 bubbling Ar bubbling

30/9/2009

120

essential

for life

LIBS of molten zinc

Experimental sequence of bath

additionsZinc

…essential

for life

30/9/2009

121

essential

for life

LIBS of molten zinc

Effect of solid particles

0

2

4

6

8

Al /

Zn

inte

nsity

rat

io

(a)

(b)250

0.0505 wt.%Al0.0505 wt.%Al

0.1839 wt.%Al0.1839 wt.%Al

Spikes are related to non-melted fragments, oxides skins and

intermetallic particles

Spikes are related to non-melted fragments, oxides skins and

intermetallic particles

Al/Zn intensity ratio of 1200 consecutive pulsesAl/Zn intensity ratio of 1200 consecutive pulses

Zinc

…essential

for life

(240 s)

Al /

Zn

inte

nsity

rat

io

0

2

4

6

Shot number

0 200 400 600 800 1000 12000

2

4

6

(b)

(c) dross added

Fre

quen

cy

0

50

100

150

200

250

Al / Zn intensity ratio

0 1 2 3 4 5 6

Fre

quen

cy

0

50

100

150

200

(d)

(e)

0.1839 wt.%Al0.1839 wt.%Al

0.2108 wt.%Al0.2108 wt.%Al

30/9/2009

122

essential

for life

LIBS of molten zinc


• Analytical depth of LIBS is

small : 50 nm.

• FeZn and FeAlZn

intermetallic particles are Plasma

Ablated thickness

Zinc

…essential

for life

intermetallic particles are

always wetted by molten

zinc.

• Larger particles can rise

the molten surface

Solid particles

Small particles Large particles

30/9/2009

123

essential

for life

LIBS of molten zinc


Fe

/ Zn

inte

nsity

rat

io

0.04

0.05

0.06

0.07

ICP-AESICP-AES LIBS resultsLIBS results

Zinc

…essential

for life

Al / Zn intensity ratio

0.0 0.2 0.4 0.6 0.8 1.0F

e / Z

n in

tens

ity r

atio

0.00

0.01

0.02

0.03

Fe/Al obtained with LIBS does not follow the trendobserved with total-Fe/total-Al

Fe/Al obtained with LIBS does not follow the trendobserved with total-Fe/total-Al

30/9/2009

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essential

for life

LIBS of molten zinc

LIBS vs. ICP-AES

0.00 0.01 0.02 0.03 0.04

LIB

S: F

e / Z

n in

tens

ity r

atio

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

liquid (6.7 g cm−3)liquid + FeZn7Al (7.2 g cm−3)

liquid + Fe2Al5Zn (4.5 g cm−3)

(a)

0.00 0.05 0.10 0.15 0.20 0.25

LIB

S: A

l / Z

n in

tens

ity r

atio

0.0

0.2

0.4

0.6

0.8

1.0

liquid (6.7 g cm−3)liquid + FeZn7Al (7.2 g cm−3)

liquid + Fe2Al5Zn (4.5 g cm−3)

(c)

FeFe AlAl

Zinc

…essential

for life

LIBS data treatment leads to Al and Fe in solutionLIBS data treatment leads to Al and Fe in solution

ICP analysis: [Fe] total (%)

0.00 0.01 0.02 0.03 0.04

ICP analysis: [Fe] effective (%)

0.00 0.01 0.02 0.03 0.04

LIB

S: F

e / Z

n in

tens

ity r

atio

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

(b)

ICP analysis: [Al] total (%)

0.00 0.05 0.10 0.15 0.20 0.25

ICP analysis: [Al] effective (%)

0.00 0.05 0.10 0.15 0.20 0.25

LIB

S: A

l / Z

n in

tens

ity r

atio

0.0

0.2

0.4

0.6

0.8

1.0

(d)

30/9/2009

125

essential

for life

LIBS of molten zinc

Sensitivity and reproducibility

LIB

S: F

e / Z

n in

tens

ity r

atio

0.00

0.01

0.02

0.03

0.04

0.05

LIB

S: A

l / Z

n in

tens

ity r

atio

0.0

0.2

0.4

0.6

0.8

1.0

(a) (b)

Calibration

curves

Calibration

curves

Zinc

…essential

for life [Fe] effective (%)

0.000 0.005 0.010 0.015 0.020 0.025 0.0300.00

[Al] effective (%)

0.00 0.05 0.10 0.15 0.200.0

Time

13:35 13:39 13:43 13:47 13:51

Al /

Zn

inte

nsity

rat

io

0.0

0.2

0.4

0.6

0.8

1.0

RSD (n=10) : 0.9%

Time

13:35 13:39 13:43 13:47 13:51

Fe

/ Zn

inte

nsity

rat

io

0.00

0.01

0.02

0.03

0.04

RSD (n=10) : 3.1%

(a) Fe (b) Al

Reproducibility

over 17 minutes

Reproducibility

over 17 minutes

“Analytical sensitivity” of LIBS for zinc baths (~500 ppm Fe, ~2000 ppm Al) =Standard deviation / calibration slope = 6 ppm Fe, 16 ppm Al“Analytical sensitivity” of LIBS for zinc baths (~500 ppm Fe, ~2000 ppm Al) =Standard deviation / calibration slope = 6 ppm Fe, 16 ppm Al

30/9/2009

126

essential

for life

LIBS probe inserted into zinc bath at Sorevco

plantZinc

…essential

for life

30/9/2009

127

essential

for life

Isometric view of Sorevco bathLIBS probe Teck Cominco probe

Zinc

…essential

for life

30/9/2009

128

essential

for life

Ingot addition in Sorevco zinc bath

LIBS probe

Zinc

…essential

for life

30/9/2009

129

essential

for life

Plan view of Sorevco bath

LIBS probe

Teck Cominco probe

Zinc

…essential

for life

Ingot

30/9/2009

130

essential

for life

Online monitoring of Al and Fe in molten zinc

1500

2000

2500

Co

ncen

trati

on

Al (p

pm

)

500

600

700

800

900

Co

ncen

trati

on

Fe (

pp

m)

Zinc

…essential

for life

0

500

1000

00:00 06:00 12:00 18:00 00:00 06:00 12:00

Time 4-5 Febuary 2005

Co

ncen

trati

on

Al (p

pm

)

0

100

200

300

400

Co

ncen

trati

on

Fe (

pp

m)

LIBS Aluminium Al in solution Sorevco Al in solution CEZinc

LIBS Iron Fe in solution Sorevco Fe in solution CEZinc

30/9/2009

131

essential

for life

Comparison of realtime measurements of

aluminum in zinc bath of Sorevco obtained by

LIBS and Teck Cominco probe

1500

2000

2500

Co

nc

en

tra

tio

n A

l (p

pm

)

Zinc

…essential

for life

0

500

1000

00:00 06:00 12:00 18:00 00:00 06:00 12:00


Co

nc

en

tra

tio

n A

l (p

pm

)

LIBS Aluminium Al in solution Sorevco Al in solution CEZinc TeckCominco

Each point of LIBS corresponds to an average of 5 minutes

30/9/2009

132

essential

for life

1500

2000

2500C

on

ce

ntr

ati

on

Al

(pp

m)







Zinc

…essential

for life

0

500

1000

00:00 06:00 12:00 18:00 00:00 06:00 12:00


Co

nc

en

tra

tio

n A

l (p

pm

)

LIBS Al 10 min Al in solution Sorevco Al in solution CEZinc TeckCominco


30/9/2009

133

essential

for life







2000

2500

Co

nc

en

tra

tio

n A

l (p

pm

)

Zinc

…essential

for life


0

500

1000

1500

00:00 06:00 12:00 18:00 00:00 06:00 12:00


Co

nc

en

tra

tio

n A

l (p

pm

)

Libs Al 30 min Al in solution Sorevco Al in solution CEZinc TeckCominco

30/9/2009

134

essential

for life

Zoom showing the additions during the transition from GA to

GI. The bath was containing 100 tonnes of molten zinc

1000

1500

2000

2500

Co

nc

en

tra

tio

n A

l (p

pm

)

150

200

250

300

350

400

Co

nc

en

tra

tio

n F

e (

pp

m)

Co

nce

ntr

ati

on

Fe

(pp

m)

Zinc

…essential

for life

B= Blue Jumbo (1 tonne with 4.5% Al) W= White Jumbo (1 tonne with 1% Al)

B

0

500

05:00 06:00 07:00 08:00 09:00 10:00 11:00

Time 4 Febuary 2005

Co

nc

en

tra

tio

n A

l (p

pm

)

0

50

100

150

Co

nc

en

tra

tio

n F

e (

pp

m)

LIBS Aluminium Al in solution Sorevco Al in solution CEZincLIBS Iron Fe in solution Sorevco Fe in solution CEZinc

Co

nce

ntr

ati

on

Fe

(pp

m)

30/9/2009

135

essential

for life

Zoom showing the additions during the transition from GA to

GI. The bath was containing 100 tonnes of molten zinc

1000

1500

2000

2500

Co

ncen

trati

on

Al (p

pm

)

200

250

300

350

400

Co

ncen

trati

on

Fe (

pp

m)

Co

nce

ntr

ati

on

Fe

(pp

m)

Zinc

…essential

for life

0

500

1000

11:00 12:00 13:00 14:00 15:00 16:00 17:00

Time 4 Febuary 2005

Co

ncen

trati

on

Al (p

pm

)

0

50

100

150

Co

ncen

trati

on

Fe (

pp

m)

LIBS Aluminium Al in solution Sorevco Al in solution CEZincLIBS Iron Fe in solution Sorevco Fe in solution CEZinc

Co

nce

ntr

ati

on

Fe

(pp

m)

B=Blue Jumbo (1 tonne with 4.5% Al) W=White Jumbo (1 tonne with 1% Al)

B

WW W

W

30/9/2009

136

essential

for life

Conclusions

• Simultaneous on line measurements of dissolved (effective)Al and Fe

content in the Sorevco galvanizing bath using the LIBS system and the

Teck Cominco probe for Al composition.

• Successful, long duration trial during galvannneal to galvanize

transition.

• The LIBS system shows excellent sensitivity to changes in bath

Zinc

…essential

for life

• The LIBS system shows excellent sensitivity to changes in bath

composition following ingot additions.

• Excellent agreement between the Al measurements from the two

methods of measurements and the analytical results obtained by ICP.

• Analysis of results on composition variations is still in progress.

• Numerical modeling using new data in progress.

30/9/2009

137

essential

for life

Zinc…essential

for life

30/9/2009

138

essential

for life

Zinc…essential

for life

30/9/2009

139

essential

for life

Zinc…essential

for life

30/9/2009

140

essential

for life

Zinc…essential

for life

30/9/2009

141

essential

for life

Zinc P

roductsZinc…essential

for life

30/9/2009

142

essential

for life

Zinc…essential

for life

30/9/2009

143

essential

for life

10% vs. 5%

barsZinc…essential

for life

30/9/2009

144

essential

for life

Brightener Bar MicrostructuresZinc

…essential

for life

30/9/2009

145

essential

for life

Session 3


• Influence of chemical composition of GA

coating on powdering defect


Zinc

…essential

for life • GA material with zeta free

30/9/2009

146

Hot Dip Galvanized Steel Sheet

Item

Zinc (GI) Zinc Alloy (GA) One& Half (G90/A01)

Zn Zn-Fe Alloy Zn

Film Composition

13.8 µm

6.3 µm

13.8 µm

98 g/m^2 45 g/m^2 98 g/m^2

Steel Sheet Steel Sheet Steel Sheet

Zn-Fe Alloy

Coating Weight (per

side) (oz/ft^2)

<g/m^2>

0.12-1.00

<35-300>

0.12-0.30

<35-90>

0.12-0.33

<35-90>

Thickness (Inch)

<mm>

0.009-0.177

<0.23-4.5>

0.016-0.177

<0.4-4.5>

0.016-0.126

<0.4-1.6>

30/9/2009

147

Electrogalvanized Steel Sheet

EG EGA Zn Multi ZnO

Coating Weight(per side)

(oz/ft2)

<g/m2>

0.12-0.33

<3-100>

0.033-0.13

<10-40>

0.033-0.13

<10-40>

20+3.5 g/m2

<0.4-1.6>

20 g/m2 + l um

(30)

Thickness

(in)

<mm>

0.016-0.126

<0.4-3.2>

0.016-0.126

<0.4-3.2>

0.016-0.126

<0.4-3.2>

0.016-0.063

<0.4-1.6>

0.016-0.063

<0.4-1.6>

30/9/2009

148

Comparison of Weldability Lobesfor GI & GA Material

30/9/2009

149

Paint Delamination at Scribes

30/9/2009

150

Galvannealing & Coating Morphology

GALVANNEALING

• Galvanneal coatings are diffusion coatings that exposed galvanized steel to an annealing temperature around 500C to produce a fully alloyed

COATING MORPHOLOGY• Type O-under alloyed coating

containing mostly zeta phase.• Type 1-optimum alloyed

coating with less than a 1 micron gamma layer and a top layer of delta phase mixed with

500C to produce a fully alloyed coating of Fe-Zn phases.

layer of delta phase mixed with a small amount of zeta phase.

• Type 2-over-alloyed coating with gamma layer greater than 1 micron and overlay of delta phase containing basal plane cracks.

30/9/2009

151

Galvanneal Growth Sequence

• Formation of Fe2Al5 (Zn) inhibition layer in galvanizing bath.• Diffusion of Zn into Fe as inhibition layer breaks down.• Formation of zeta and delta phases as outbursts.• Gamma phase saturates quickly near 1 micron.• Zeta phase grows quickly and eventually disappears.• Delta phase continues to grow at the expense of other phases:

• at short times delta has extended solubility for Fe and Al compared with equilibrium

• Delta phase growth from zeta and eventual cracking of delta phase.

30/9/2009

152

Characteristic of Fe-Zn Intermetallic Compound

Phase Compoun

d

% Fe Hardness (Hv 0.01 kp/mm2)

Gamma Fe3Zn10 21 ~ 28 496

Delta 1* FeZn7 7 ~ 12 Delta 1k 355Delta 1 p 263-320

Zeta FeZn13 5 ~ 6 192-231

Eta Zn 0.03 35

Base steel Fe 100 ~100

30/9/2009

153

GalvannealedGalvannealedTypical GA Structures

η ξ

δ

ζ

δ

Fe-Flash

δδδ

Γ Γ Γ

Steel Steel Steel

Under-AlloyedMarginal Alloying

(Fe-Flash option)

Fully Alloyed

30/9/2009

154

Effect of Al & BathTemperature onGalvanneal Growth

30/9/2009

155

GALVANNEAL COATING WEIGHTS

• Hot Dip Galvanized Coating

• ~35~60 g/m2 per side, some up to 90 g/m2 per • ~35~60 g/m2 per side, some up to 90 g/m2 per side

• Fully alloyed with iron

30/9/2009

156

Galvannealed Current Production Method

30/9/2009

157

30/9/2009

158

Alloy phase layerthickness as a function of reactiontemperature and

Delta ( δδδδ ) & Zeta ( ζζζζ ) Growth OnAl-Free Baths

temperature andtime

30/9/2009

159

Growth of Alloy Phase Layers at 450ºC

30/9/2009

160

SUBSTRATE COMPOSITION

• Grain boundary reactivity solutes increase alloying rate:– Ti added to ensure clean grain boundaries for

increased reactivity of Zn with Fe to form galvanneal phases.phases.

– IF steels containing Ti and/or Nb that form carbides at high temperature prevent segregation of C to grain boundaries at lower temperatures.

– Grain boundary segregants decrease alloying rate and prevent Zn from diffusing down grain boundaries and reacting with Fe (C and P).

30/9/2009

161

BATH COMPOSITION

• EFFECTS:– Low Al-reaction is continuous with a planar

interface between all phase layers because of diffusion.diffusion.

– High Al (0.2%)-reaction is discontinuous due to outburst reactions.

30/9/2009

162

Reaction curves for the transformation of Fe2Al5 to delta phase at various Al contents

in the bath.

30/9/2009

163

Fe content in the coating decreases withincreased levels of phosphorus in the base steel.

30/9/2009

164

Influence of alloying elements in steel on theincubation time for galvannealing.

Incubation time at 773K, s

30/9/2009

165

Influence of base steeltypes on Galvannealing

rates.

Influence of base steel types on amount of

ΓΓΓΓ-phase

30/9/2009

166

Woodgrain Coating Appearance Analysis

30/9/2009

167

Effect of 0.06% P in ULC steel on Alloying Behavior During Galvannealing

30/9/2009

168

Effect of Si in Steel on Alloying Rate

30/9/2009

169

GALVANNEAL SURFACE STRUCTURE

• Surface roughness effects formability and paintability.

• Craters form on the surface from solidification • Craters form on the surface from solidification shrinkage.

• High Al bath composition causes more outbursts.

30/9/2009

170

Effects of Temperature and Soaking Time onPowdering Resistance.(After Lucas etal., 1989)

30/9/2009

171

Effects of δδδδ1 and ΓΓΓΓ Phases on Powdering Resistance(After Lucas etal., 1989).

30/9/2009

172

Schematic illustration of a crater crosssection

(from Carless, etal., 1998)

30/9/2009

173

Metallographic presentation of galvannealedcoating with and without craters

(from Hamers, etal., 1998)

30/9/2009

174

Powder rank plotted vs. crater density.Individual points are labeled by sampling &

coating weight in gm/m2

30/9/2009

175

Friction rank plotted against powder rank

30/9/2009

176

Stone Chipping Simulation

30/9/2009

177

Chipped Samples

30/9/2009

178

Paint System Format

30/9/2009

179

Stone Chip Data

30/9/2009

180

Stone Chipping Test Performance as a Function of

Crater Density

30/9/2009

181

Effect of Substrate Roughness on As-ProducedGalvanneal Roughness

30/9/2009

182

Relationship Between Temper Extension& Surface Roughness – Galvannealed

Steel Sheet

30/9/2009

183

Relationship Between Bath AluminumContent and Roughness

30/9/2009

184

Relationship Between Roughness & FrictionGalvannealed Steel

30/9/2009

185

Expanded Region of the Iron-Zinc Phase Diagram Showing the Four Main Phases &

the Samples Studied

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Session 3


• Influence of chemical composition of GA coating on powdering defectGA coating on powdering defect


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Processing to make zero zeta GA

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Bath Al=0.12%

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60° V-bend testbath Al=0.12%

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Variation in the ratio of XRD peak intensities from zeta and delta phase of GA coatings on low carbon steel with

coating weight. Bath Al=0.12%

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Variation in the ratio of XRD peak intensities from zeta and delta phase of GA coating on AI-killed low carbon steel with Fe

content. (Bath Al 0.12 %, gavannealing T=520°C

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Time potential curves of the coatings on AI-killed low carbon steel with different bath AI content.

(Galvannealing temperature: 520°C)

(a) 0.12% AI (b) 0.16% AI

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XRD Analysis of GA

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Influence of light prephosphating on forming load

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Cup Test Formability Results for Bare, Light &Heavy Prephosphated Galvannealed Steel.

Average and One Standard Deviation are Shown.

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Cup Test Powderability Results for Bare, Light& Heavy Prephosphated Galvannealed Steel.

Average & One Standard Deviation are Shown.

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Session 4

• Galvanizing wire: defects and coating control

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Two basic groups of galvanized wire:

• Mild steel wire: C<0.25%. 343MPa<UTS<686MPa,

• used for barbed wire, netting, fencing• used for barbed wire, netting, fencing

• Hard Steel wire: C>0.25%, normally 0.40%<C<0.70%, 1176MPa<UTS<1961MPa

• used for springs, ropes, cables

Mild steel wires require in-line annealing, hard steel grades require heating to zinc temperature

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Recent Developments

• Increase speed of operation and number of wires on each line

• Total line length<120m• Total line length<120m• Galvanizing bath length<8 m• Galvanizing bath capacity<50 tonnes Zn• Immersion heaters increasing in use• Use of Pb-free patenting: replaced by hot

gas fluidized beds

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Typical Line Capabilities

Wire diameter: 1.5~3.8mm Power of product line: 371k W Power of product line: 371k W Speed of product line: 5~30m/minProducing ability (daily output): max.12T (3.8mm), min. 5T(1.5mm)Daily work time: 24h Size of product line: 70m x 3m Weight of product line: about 30T

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Heat Treating of Mild Steel

• Pb patenting still widely used but is being replaced by fluidized bed furnaces. The bed is normally alumina particles that are suspended in the particles that are suspended in the gas burner stream.

• The length of the patenting or fluidized bed determines the hardness of the wire

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Basic Process Steps

• Cleaning: can be degreased in Pb patenting bath or by use of hot alkaline degreaser

• Pickling: H2SO4 (10-14%) is • Pickling: H2SO4 (10-14%) is cheaper but requires heating, is quicker than HCl (14%)

• Inhibitors prevent attack on base metal after removal of scale

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Pretreatment Section

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Acid Rinse Tank

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Recycling of Pickling solutions

• H2SO4: precipitate Fe salts by cooling, return purified acid to pickle tanktank

• HCl: Add NH4OH and H2O2 to oxidize Fe+2 to Fe+3 and precipitate Fe(OH)3

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Fluxing

• Wet process: blanket of molten zinc ammonium chloride flux on top on bath.

• Dry process: immerse in tank of flux • Dry process: immerse in tank of flux before drying and immersing in zinc bath. Zinc ammonium chloride used with strength of 30% at T=80°C, wetting agent added, then dry at T<150°C

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Defects from Pretreatment Section

• Incomplete removal of drawing lubricants- problem with alkalinity of cleaning solution-consider brushing of heavy deposits-consider brushing of heavy deposits

• Incomplete removal of oxide scale-dilution of acid by carryover from rinsing section-too much oxidation from heat treatments

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Defects from Pretreatment Section

• Burn marks from overheating of flux- Maximum T ~=180°C

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Thermal Profile of Wire Galvanizing

TRADITIONAL PROCESS

Annealing process Galvanizing process

Steps of process

Annealing Lead Water Acid Water Flux Drier Zinc Water

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Dipping into the Zinc Bath

• Guide Rolls or ceramic sinker skids used to guide wire through bath

• Guide rolls can be pure Fe or 316L stainless steel

• Skids are made of a castable refractory

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Entry to Zinc Bath

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Sinker Skid in Zinc Bath

Section through the

plant showing the

mounting & positioning

of the sinker

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Defects from Coating Section

• Bare Spots-Usually from problems in pretreatment section-Dross pickup from bath surface can also -Dross pickup from bath surface can also cause problems – use of top flux can help

• Rough Spots- From drawing problems, overpickling or low Al in the zinc bath

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Exit from the Zinc Bath and Coating Control

• For heavy coatings, exit through a charcoal bed can be sufficient

• For thinner coatings (40-100 g/m²), this is traditionally followed by pad wiping, but gas wiping increasingly used to increase line speeds.

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Gas Wiping Apparatus

US Patent 3,707,400

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Defects from Coating Control

• Bamboo effect-Too heavy of coating to support before solidification – improve with oxygen-free exit, lowering of height of coating control exit, lowering of height of coating control device, increase cooling (mist)

• Poor concentricity-Vibration of exiting wire – low line tension-Poor condition of wiping device

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Adherence Defects

• Poor Al control in the bath: try to keep >0.14% dissolved Al (not including dross)

• Temperature and mixing of the bath are importantimportant

• Pretreatment of Surface to remove dirt and oxides

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Immersion HeaterFor Zinc Bath

Material: C-Bonded SiC

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SiC Sheath& Gas

Diverter

www.morganmms.com

Typical melting capacity: 720 kg.hr

Typical efficiency: 65%

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Treatments after Galvanizing

• Traditional: Cr+6 passivation• Developing: Cr-free treatments • Developing: Cr-free treatments

including silicates, thin organic films• Phosphates with fluorides of Mn,Mo

and Ti (Henkel)• Polycarboxylate dissolved in acid

(BASF)

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Wire Take-Up

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Galfan® Wire

• Better ductility and corrosion resistance than normal galvanized wire

• Used in fishing and mining ropes, • Used in fishing and mining ropes, ACSR wire, utility strand, springs, fence wire, gabions, animal cages

• Requires double-dip process

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Galfan Wire

Gabions

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Double-Dip Process for Galfan

• Normal galvanizing process performed, most of normal zinc coating wiped off

• Wire goes immediately to dipping in • Wire goes immediately to dipping in Zn-5%Al bath. The Fe-Zn intermetallic is transformed to Al-Fe-Zn and the Zn-5% coating is solidified over this. Gas wiping is used to control the thickness.

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Assessing Quality

1 2 3

Nominal diameter of zinc coated wire mm

Minimum mass per unit area of zinc

coating g/m2

Approximate equivalent average

thickness µm

1.20-1.50 215 30

1.51-1.80 230 32

1.81-2.20 245 34

2.21-2.50 260 36

2.51-3.50 275 38

3.51-5.00 290 40

Mass per unit area of the zinc coating for SABS 675

& SABS 935 class 1. (Heavy galvanized wire)

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Coating Adherence

Dimensions in millimeters

1 2 3

Mandrel Diameter

Wire diameter d Mandrel

Over Up to & including

Diameter

- 3.8 4d

3.8 5.0 5d

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