abstract no. 62 2015 - stahl- · pdf fileabstract no. 62 control of ... in galvanising...

Abstract No. 62

Control of galvanizing process thanks to oxidation thickness measurement inside furnace

G.Moreas, P.Albart, L.Bordignon, G.Monfort, V.Tusset, X.Vanden Eynde

CRM Group, Liege, Belgium

Abstract The market of galvanised high strength steels, with high Mn, Cr, Al and Si content has significantly increased these last years. Although good mechanical properties are achieved with these grades, the alloying elements significantly reduces the reactivity during hot dipping, resulting in galvanising problems like bad zinc wetting and coating adherence. To solve these problems, the chosen solution consists in the oxidation of the strip during heating or during the rapid cooling, followed by the reduction of formed iron oxide, resulting into the formation of a pure metallic iron at the surface level. The iron oxide layer must be thick enough to avoid the alloying oxide formation and sufficiently thin to avoid roll picking inside the furnace and to ensure complete reduction just before entering the zinc bath. CRM has developed a sensor, based on reflectance spectroscopy that allows the continuous control of this iron oxide formation for all HSS on industrial lines, resulting in a better product quality. Key words: HSS; dual phase; continuous annealing, industrial sensor, thickness measurement

CETA

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Control of galvanizing process using oxidation thickness

measurement inside furnace

G. Moreas, P. Albart, L. Bordignon, G.Monfort, V. Tusset, X. Vanden Eynde

2Control of galvanizing process thanks oxidation thickness measurement inside furnace

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OTTM: online measurement of Oxide Thickness and Temperature

Developed in particular for the Galvanizing of High Strength Steels

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State of art-High Strength Steels (1)

Thinner and thinner strips for automotive applications

to lighten the weight of the cars

Production of more and more high strength steels (HSS)with high Mn, Cr, Al and Si content

(Dual Phase and TRIP steels)


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Solution: induced strip oxidation

1. Oxidation of the strip during heating or during rapid cooling

Heating rate:40°C/s up to 650°C - 1s

0

1

2

3

0 0.1 0.2 0.3 0.4 0.5 0.6

%Vol O2 or %Vol CO2 (/100) in N2

FeO

thic

knes

s (g

/m²)

IF 0.1%Mn Ti/Nb

C-1.1%Mn-0.2%Si

C-1.5%Mn-0.4%Si

C-1%Mn-0.5%Cr

C-1.5%Mn-1.4%Si

C-1.5%Mn-1.2%Al

With CO2

(steel 0.5%Cr)

WithO2

2. Reduction in the radian tube furnace or in the overaging section

Pure metallic iron at the surface level

Iron oxide to avoid alloying oxides

Improved zinc wettability during galvanisingCETA

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Strip oxidation

During Heating During Rapid Cooling

Influence of the steel grade on the oxidation rate during heating in O2 /N2 or

CO2 /N2 mixtures

Influence of the dew point during soaking and the oxygen injection

during rapid coling on surface chemistry (Al-Si TRIP steel).


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Need to control the iron oxide formationfor all HSS on industrial lines

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CrOx

SiOx

AlOx

STRIP

Bare spots on DP Cr (0.5%) Si(0.2%)

CET

AS 1

6-18

May

200

6Steel oxidation control for galvanisation of steels


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STRIP FeO

CrOx

SiOx

AlOxOXIDISING

ATMOSPHERE

Oxidation give pure FeO oxide

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STRIP

REDUCING

ATMOSPHERE

Fe

Porous MetallicIron

CrOx

SiOx

AlOx

Then reduction before galvanisation


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Strip oxidation

During Heating

Influence of the steel grade on the oxidation rate during heating with O2 /N2 or CO2 /N2 mixtures injectionCETA

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Aims for OTTM sensors

Online characterisation of coatings

Measurement of thickness of thin transparent films and in particular FeO

Online temperature measurement of the oxidized strip


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For which applications ?

In the galvanising process, improve the wettability of AHSS steels by controlling its pre-oxidation:

FeO oxide layer thickness measurement

Strip temperature measurementCETA

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Principle

Thin film thickness measurement:White light illumination

Spectroscopic reflectance

Interference peaks detection

Temperature measurement:Thermal radiation measurement with same instrument and optic


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λ

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CE

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Principle of the sensor

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Spectrometer

t = k. λ / 4n

• t : layer thickness• λ : wavelength of the peak• n :refractive index of the oxide layer • k : order of the peak

(e.g. k=1 1st minimum)

White light reflectance measurement


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Temperature measurementTemperature calculation

IR radiation measured, blackbody calibration

emissivity = f(thickness) to determine

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Implementation

Halogen/UV lighting with shutter

1 or 2 spectrometers to cover UV-VIS-NIR

Fiber bundle and optic to couple emission and reception

Optic inserted into a cooled pyrometric tube

Diameter: 170mm

Height: 200mm


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CE

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Measurement layout

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Validation

OTTM thickness measurement in good agreement with offline lab reference methods (GDOES, SEM)

Good correlation between injected oxygen and measured thickness

Different steel grades successfully tested


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Correlation with GDOES measurements

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Correlation with SEM measurements

0

30

60

90

120

150

180

0 30 60 90 120 150 180

SEM m

easurement (nm)

Oxide sensor measurement (nm)

IF Ti

DP600


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Relation with injected oxygen

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Industrial tests

0

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100

120

0

30

60

90

120

150

180

12:17:00 12:22:00 12:27:00

Tem

p. c

han

ge (

°C)

O

2in

ject

ion

(x0

.1%

)

Oxi

de

thic

kn

ess

(nm

)

O2 injection(x 0.1%)

Oxide thickness

Strip temp

IF steel


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Specifications (1/2)

ThicknessRange: 30nm to more than 250nm

Repeatability: 1nm

Accuracy: +/-10nm

TemperatureRange: 500-1000°C

Repeatability: 5°C

Accuracy: +/-15°CCETA

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Specifications (2/2)

Optical spot diameter: 8mm-24mm (for a distance of 185mm-1500mm)

Working distance to steel sheet: from 185mm to 1500mm (device must be located outside the furnace)

Typical measurement period: 1s (shorter possible)

Max temperature of steel sheet: 800°C


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CE

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Pilot lines and industrial testsLine Furnace Control Distance

Pilot TKS Induction Power + O2 270mm

Pilot CRM DFF, RTF Power + O2 270mm, 1500mm

Galva2 VoestAlpine

DFF Air / Gas 1200mm

TataSteelIjmuidenRhesca

Lamp furnace O2 300mm

Multidipsimulator

Lamp furnace O2 165mm

ARCEO NA NA ~500mmCETA

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For a customer application

Oxide thickness range to measure ?

Oxide type and homogeneity (Feo, selective oxidation) ?

Distance between product and optic ?

Presence of a pyrometric tube ?

Temperature of the product ?

Type of furnace and location on the line ?CETA

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CRM Group Sensors Diffusion

OTTM

WOW technology is in charge of the industrial diffusion

SRM : industrial on-line topography measurement (roughness, peak count, …)

-industrial diffusion by AMEPA Germany

LIBS(Laser Induced Breakdown Spectroscopy):On-line measurement of the hot metal temperature and composition in the blast furnace runners

-industrial diffusion by TMT G.D.Luxemburg

Thank you for your attention !CETA

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abstract no. 62 2015 - stahl- · pdf fileabstract no. 62 control of ... in galvanising...

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