Advantages of Using coated steels in Automotive Industryallaboutmetallurgy.com/wp/wp-content/uploads/2016/10/Saini... · Advantages of Using coated steels in Automotive Industry

Advantages of Using coated steels

in Automotive Industry

Avtar Singh Saini

Head, Product Application Group

Tata Steel

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This document is price sensitive and should not be reproduced

Agenda

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1.0 Introduction

2.0 Corrosion Warranties

3.0 The big Debate GI Vs GA

4.0 Recommendations to stamp GA

5.0 Automotive coated outlook for India


Agenda

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1.0 Introduction






We all Love our cars

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We all Love our cars

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Why Hot Dip Galvanising

Prevention of red rust

- aesthetic

- perforation


World Corrosion Map

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In India more than 5% of GDP is lost every year to corrosion

Indian Corrosion Map


Common places of Corrosion in Automobile


Agenda

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1.0 Introduction






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Auto Makers have warranties in place

Toyota

Honda


Agenda

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1.0 Introduction






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Region GA Usage GI Usage

North America

Europe

Japan 0

South Korea 0

India

GI Vs GA -‐ The Big Debate in Automotive

GI - Zero spangled Galvanised GA - Galvannealed

The Automotive world is divided GI vs. GA


GI versus GA

Flat & shiny Al% bath ≥ 0.16

Rough & dull Al% bath < 0.14

FeΓ (21-28%)

Γ1+δ (15%)

ζ (6%)δ (7-12%)

GI = galvanised GA = galvannealed

T=~500°C

~20 s

Zn!Fe2Al5!

Fe!

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GI versus GA

Delta 7-11% Fe

Zeta 6% Fe

Steel Gamma 23% Fe

Microstructure GA (optical microscope, etched)

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GI versus GA

Advantages GA: •  no stick during pressing

•  paint adhesion

•  weldable

Disadvantages GA:

•  cratering for ED-paint

•  powdering and flaking

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Powdering is the loss of small particles from the coating

under compressive forces.It is associated with high surface hardness, and promoted by high alloying

Flaking is the de-lamination of larger particles (but no necessary visible to naked eye) from the coating at the interface with the substrate. It is associated with insufficient surface hardness, and promoted by low alloying

Both defects may give dust pollution during press forming

Disadvantages of GA it its solutions

Process parameters to be controlled to minimize powdering & Flaking 1.Steel Chemistry 2. Line Speed 3. GA Electrical power 4. Coating Weight 5. % Al in bath 6. Heating rate • 

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substrat

dzétadelta 1gamma

substrat

dzéta

delta 1gamma

substrat

delta 1gamma

Friction properties

Powdering properties - - ++

Underalloyed GA Overalloyed GA IFTiNb target GA 60 g/m2

The product target defined on IFTiNb

(60g/m2, 8-10% iron, a few zeta crystals on the surface, resulting

powdering < 5g/m2)

Powdering and flaking can be overcome

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ð Powdering recommendations at the customer plant

l  Avoid the too low radii (typically less than 3 thicknesses) where the coating deformations are high, with risk of powdering and flaking, giving « pimples » on the stamped components

l  Use a blank washing/re-oiling machine before stamping to :

1.  Eliminate the dust from the previous process (storage, slitting, blanking…)

2.  Apply a specific stamping oil (Check periodically the oil filtration)


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l  Use surface treatment (hard Cr, hard bronze, TiCN, Cr N ) or inserts for active surfaces (first step)

l  Reinforced dies are required on all major parts because of the hard and abrasive GA coating

l  Dies for critical parts shall be regularly restored because GA coating wears

l  Have a special attention for draw-beads and blank holders surface


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l  Roughness of active surfaces must be in same order than sheet material (0.5 to 0.8 υm)

l  Use surface treatment also for the cutting blames to avoid GA dust prone to « pimples »

!


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Adapt quality control at the end of press line : - immediate stop if problem

Adapt frequency and method of cleaning during production : Typically two per hour

l  Stamping tools cleaning


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ð Degreasing recommendations at the customer plant

l  To remove oil (stamping, and some times rust protection) and all pollution accumulated between the press shop and the surface treatment

l  The alkaline solution needs to be adapt to the oils to remove (to check with the degreasing supplier)

l  Check periodically the degreasing efficient ness (water droplet wetting)


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ð Phosphatation recommendations at the customer plant

l  Use a tri-cation (Zn, Mn, Ni) process with addition of free fluorine to complex the aluminium of the GA coating to deposit Hopeite : Zn3(PO4)2 + 4H2O

l  Free fluorine: 0.22-0.25 g/l coating time: 3 min- coating weight: 2-3g/m2

Good Phosphatation criteria

Shape: needles

Size: <10µm

Coverage: 100%


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Cratering is a big hole in the E-coat. It results from the still going water de-sorption of the Hopeite when the E-coat solidifies. The GA high specific surface area makes the de-sorption time quiet long

Pinholes are some holes in the E-coat. They result from the H2 de-sorption inducing sparks when the E-coat solidifies. The GA high specific surface area produces high H2 volumes during the E coating

ð Cratering (and pinholes) during painting

1 cm Cratering + Pinholes


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ð E coating recommandations at the customer plant

l  Voltage :

l  Reduce it typically (200 / 260 V) with GA, versus more than 340 V for bare steel

l  Adapt a complex multi step voltage process

l  Baking : Adapt the process to release the gas before solidification

l  E coat painting :

l  Decrease the viscosity

l  Increase the flow performance

Agenda

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1.0 Introduction





TWO MAJOR RULES

POLLUTION DEGRADATION

AT ALL STAGES OF PRODUCTION

²1° Transport / Storage

² 2° Cutting / Palletization blanks

² 3° Loading press / Stamping blanks

² 4° Storage finish stamped parts

1 2

AVOID ANY SOURCE OF

Recommendations to stamp Galvannealed

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Galvannealed can be spot welded without productivity loss

Recommended conditions : - Transformers able to deliver a current intensity up to 13kA - Equipment able to progressively increase current intensity during

production ( Step up Transformers) - Automatic dressing of electrodes ( accuracy and Productivity Example of data : Nb of spots requested between 2 redressings @ 1000 Nb of redressings with 1 electrode 17-20 Nb of welding spots before electrode replacement 17000 to 20000

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Recommendations for surface treatment of Galvannealed BIW

Rinsing Activating Phosphatation Degreasing Rinsing

Alcaline degreasing : removal of all or part of Al oxides

- Tri cation phosphate (Zn, Ni, Mn) - F addition for aluminium complexation (fluosilicic acid) - Phosphatation bath in stainless steel 316L

BIW with Galvannealed parts

Reinforcement of anti corrosion protection. This step is not necessary if the phosphate layer is homogeneous and covering the surface. A rinsing step is necessary to avoid pollution of cataphoresis bath.

Passivation + rinsing

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Equivalent paint appearance can be achieved on GA as on EG

Surface quality requirements for exposed panels :

zero defect + paint appearance Limited waviness to optimise paint appearance

Waviness is controlled at the steel plant by set up parameters at rolling mill and in the galvanising line (temper rolling)

The waviness / paint appearance compromise is the

same for GA and EG

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Agenda

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1.0 Introduction





165 300

400 60

120

180

60

215

320

15

85

120

2014 2020

>= 590

340 - 440

270 (Exposed)

270 (Internal)

All figures in ‘000 MT

Key Trends

1.  Significant growth expected in demand of hi-tensile (33%)

2.  HT demand will follow the trend of CR

3.  GI will gain ground as Ford is likely to shift to GI for its future models; VW will continue to use GI.

4.  GI demand is expected to be ~13% of the total coated demand

.

300

720

Total

Hi-Tensile demand in coated products will follow the trend of CR

2024

1020

END OF PRESENTATION

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Advantages of Using coated steels in Automotive Industryallaboutmetallurgy.com/wp/wp-content/uploads/2016/10/Saini... · Advantages of Using coated steels in Automotive Industry