Download - Hot Dip Galvanizing of TWIP Steels
![Page 1: Hot Dip Galvanizing of TWIP Steels](https://reader037.vdocuments.us/reader037/viewer/2022102513/56816868550346895dded0c5/html5/thumbnails/1.jpg)
Hot Dip Galvanizing of TWIP Steels
Sahar Ghafurian
Supervisor: Dr. J.R. McDermid
April 2012
Presentation for 702 Seminar I
![Page 2: Hot Dip Galvanizing of TWIP Steels](https://reader037.vdocuments.us/reader037/viewer/2022102513/56816868550346895dded0c5/html5/thumbnails/2.jpg)
2
Outline
Introduction
Background
Objectives
Experimental Procedure
Results and Discussion
Conclusions and Future Work
4/13/2012
![Page 3: Hot Dip Galvanizing of TWIP Steels](https://reader037.vdocuments.us/reader037/viewer/2022102513/56816868550346895dded0c5/html5/thumbnails/3.jpg)
3
Introduction
• TWIP Steels: high manganese (15-30wt%) fully austenitic AHSS
High energy absorptionCrash management applications in
automotive Structures
CharacteristicsTensile Strengths
as high as 1300MPa
Elongations of 60-75%
•Light weight body parts
•High stretch forming
Pros
•Expensive•Delayed
Hydrogen Cracking
•Needs Protection against corrosion
Cons
4/13/2012
![Page 4: Hot Dip Galvanizing of TWIP Steels](https://reader037.vdocuments.us/reader037/viewer/2022102513/56816868550346895dded0c5/html5/thumbnails/4.jpg)
4
Hot Dip Galvanizing
– Coating the steel strip by immersing it in a molten zinc bath
• Barrier Protection• Galvanic Protection
– Selective alloying element oxides (here Mn) created during annealing can adversely affect the wetting of the substrate by the molten zinc bath
http
://w
ww
.brit
anni
ca.c
omJORDAN & MARDER, MET&MAT. TRANS. A, VOL. 28A (1997) 2683
4/13/2012
EMF:
Anode(Corrosion)Zinc
Aluminum
Steel
…
Copper
Cathode (Protection)
Higher tendency for oxidation
![Page 5: Hot Dip Galvanizing of TWIP Steels](https://reader037.vdocuments.us/reader037/viewer/2022102513/56816868550346895dded0c5/html5/thumbnails/5.jpg)
5
Background
• Purpose of annealing for single phase steels– Reduction of iron oxides– Recrystallize microstructure
• Annealing furnace conditions:– N2/5-20%H2+ controlled water vapour– Times of 60 to 120 seconds– Temperatures of 550-850oC
Annealing Furnace
Zinc Pot
• Reduction of iron oxides• N2/5-20%H2
• Intercritical annealing/ recrystallization
• 0.14-0.2%Al• 4-6 seconds
Cooling Section
Alkaline/electrolytic cleaning section
4/13/2012
http://www.salzgitter-flachstahl.de
![Page 6: Hot Dip Galvanizing of TWIP Steels](https://reader037.vdocuments.us/reader037/viewer/2022102513/56816868550346895dded0c5/html5/thumbnails/6.jpg)
6
Background
• Define the partial pressure of water vapour:
• Dew Point:The temperature at whichFor this fixed pressure of water
vapour gas state liquid state
HHO
Annealing Furnace
N2/5%H2
Steel Strip
2 (l) 2 (g)H O =H O
4/13/2012
![Page 7: Hot Dip Galvanizing of TWIP Steels](https://reader037.vdocuments.us/reader037/viewer/2022102513/56816868550346895dded0c5/html5/thumbnails/7.jpg)
7
Fixed pO2
BackgroundTemperature, pH2 and
pH2O are fixed (N2-5%H2)
Fe 3O 4
Fe
FeOFe
ZnO
Zn MnO
Mn SiO 2
Si
Al 2O 3
Al
DP=-30oC
4/13/2012
![Page 8: Hot Dip Galvanizing of TWIP Steels](https://reader037.vdocuments.us/reader037/viewer/2022102513/56816868550346895dded0c5/html5/thumbnails/8.jpg)
8
Selective Oxidation: PROBLEM
• Reactive Wetting– Relative surface tensions between
interfaces: wetting angle– Reactive wetting: If a reaction product
is formed, the surface tension between liquid and solid can decrease
4/13/2012
vapour(V)
Liquid(L)
Solid(S)
LV
SLV
γγγcosθ
S
γSV γSL
γLV θ
Fe- Al Interfacial Layer: Intermetallic compound (η-Fe2Al5Znx) enhances reactive wettingSelective oxides can result in spots over which this layer is not created, and consequently adversely affect reactive wetting
![Page 9: Hot Dip Galvanizing of TWIP Steels](https://reader037.vdocuments.us/reader037/viewer/2022102513/56816868550346895dded0c5/html5/thumbnails/9.jpg)
9
Selective Oxidation: PROBLEM
Morphology Chemistry Mode
Gong et al, ISIJ International, vol. 49, pp. 557-563, 2009
TRIP Steel+5oC DP- N2/10H2870oC0.11 % C, 1.53 % Mn1.46 % Si
4/13/2012
![Page 10: Hot Dip Galvanizing of TWIP Steels](https://reader037.vdocuments.us/reader037/viewer/2022102513/56816868550346895dded0c5/html5/thumbnails/10.jpg)
10
Selective Oxidation: PROBLEM
• Oxidation Mode• Above a critical
amount of alloying element M, oxidation mode changes from internal to external
M
M
M
M
M
Oxygen
Oxygen
Oxygen
Oxygen
M
M
M
M
Oxygen
Oxygen
Oxygen
Oxygen
Oxygen
Oxygen
Oxygen
4/13/2012
![Page 11: Hot Dip Galvanizing of TWIP Steels](https://reader037.vdocuments.us/reader037/viewer/2022102513/56816868550346895dded0c5/html5/thumbnails/11.jpg)
11
Selective Oxidation: PROBLEMFe/FeO
DP = -30
oC
DP = +5
oC
At 700oCD
P = -50oC
4/13/2012
![Page 12: Hot Dip Galvanizing of TWIP Steels](https://reader037.vdocuments.us/reader037/viewer/2022102513/56816868550346895dded0c5/html5/thumbnails/12.jpg)
12
Selective Oxidation: PROBLEM
• For most of the cases an external layer of MnO is created on the surface:
• The Aluminothermic Reduction of MnO layer has been shown by Kavitha and McDermid to take place for high Mn Steels*
4/13/2012
Y. F. Gong et al., Materials Science Forum Vols. 654-656(2010)
* Kavitha and McDermid, Galvatech, Houston, Genova(Italy), 2011
![Page 13: Hot Dip Galvanizing of TWIP Steels](https://reader037.vdocuments.us/reader037/viewer/2022102513/56816868550346895dded0c5/html5/thumbnails/13.jpg)
13
Selective Oxidation: PROBLEM
4/13/2012* Kavitha and McDermid, Galvatech, Houston, Genova(Italy), 2011
0 2 4 6 8 10 12 14 16 18 20
-250
-200
-150
-100
-50t
MnO
(nm
)
immersion time (s)
r2 = 0.97
T=770°CT=600s
![Page 14: Hot Dip Galvanizing of TWIP Steels](https://reader037.vdocuments.us/reader037/viewer/2022102513/56816868550346895dded0c5/html5/thumbnails/14.jpg)
14
Objective
• Successfully galvanizing two grades of TWIP steels under CGL conditions– Find annealing time and temperatures to achieve a fully
recrystallized microstructure via a minimum energy route– Investigating the effect of selected time, temperature and
process dew points (pO2) on the selective oxidation– Evaluating the interaction of the selective oxides on the
surface with the molten metal for reactive wetting– Defining the proper amount of bath Al, immersion times
and bath temperatures, to obtain a well developed interfacial layer and a high quality galvanized coating
4/13/2012
![Page 15: Hot Dip Galvanizing of TWIP Steels](https://reader037.vdocuments.us/reader037/viewer/2022102513/56816868550346895dded0c5/html5/thumbnails/15.jpg)
15
Experimental Procedure
• Alloy composition:
PAT
20oC/s
5oC/s 10oC/s
20oC/s
Holding+ Immersion
E.M. Bellhouse, PhD thesis, October 2010
4/13/2012
22%Mn-0.6%C
12%Mn+0.7%C+1.5%Cu+1%Al+0.25%Si
![Page 16: Hot Dip Galvanizing of TWIP Steels](https://reader037.vdocuments.us/reader037/viewer/2022102513/56816868550346895dded0c5/html5/thumbnails/16.jpg)
16
Experimental Procedure
• The Recrystallization Experiments:– To define the times and temperatures needed for
recrystallization– Fraction Recrystallized was assessed using microhardness
• Full Recrystallization was obtained– ~700oC + 60 seconds– ~675oC + 120 seconds
4/13/2012
![Page 17: Hot Dip Galvanizing of TWIP Steels](https://reader037.vdocuments.us/reader037/viewer/2022102513/56816868550346895dded0c5/html5/thumbnails/17.jpg)
17
Experimental Procedure
• The Selective Oxidation Experiments:
• The Reactive Wetting Experiments
4/13/2012
Alloy PAT (oC) pO2 (atm) Dew Point (oC) Annealing time (sec)
22%Mn-0.6%C 7002.44486E-27 -50 60,1201.50981E-25 -30 60,1204.29035E-23 +5 60,120
12%Mn+0.7%C+1.5%Cu To obtain after Recrystallization experiments -50, -30, +5 60,120
Bath temperature (oC)
Bath dissolved Al content (%)
Immersion time (sec)
460 0.20, 0.30 4,6470 0.20, 0.30 4,6
![Page 18: Hot Dip Galvanizing of TWIP Steels](https://reader037.vdocuments.us/reader037/viewer/2022102513/56816868550346895dded0c5/html5/thumbnails/18.jpg)
18
Results and Discussion
• The recrystallization experiments:
4/13/2012Bracke et al., Acta Materialia, vol. 57, pp. 1512-1524, 2009.
![Page 19: Hot Dip Galvanizing of TWIP Steels](https://reader037.vdocuments.us/reader037/viewer/2022102513/56816868550346895dded0c5/html5/thumbnails/19.jpg)
19
Conclusions
– A recrystallized microstructure of the 22%Mn-0.6%C was obtained at ~700oC for 60 seconds and ~675oC for 120 seconds
– Based on the results of recrystallization experiments, the matrix for oxidation experiments for this alloy was constructed
– The combination of bath dissolved Al, immersion time and bath temperature was designed to investigate reactive wetting
4/13/2012
![Page 20: Hot Dip Galvanizing of TWIP Steels](https://reader037.vdocuments.us/reader037/viewer/2022102513/56816868550346895dded0c5/html5/thumbnails/20.jpg)
20
Future Work
• Carry out oxidation experiments to investigate the effect of several annealing conditions on oxide morphology, thickness, and composition
• Select a series of annealing conditions to investigate the reactive wetting
• Testing of selected mechanical properties; namely tensile tests and cup tests to evaluate delayed hydrogen cracking
4/13/2012
![Page 21: Hot Dip Galvanizing of TWIP Steels](https://reader037.vdocuments.us/reader037/viewer/2022102513/56816868550346895dded0c5/html5/thumbnails/21.jpg)
21
Acknowledgment– My Supervisor: Dr. McDermid– My Supervisor Committee: Dr. Kish and Dr Zurob– John Thomson– Mariana Budiman– All my friends in CAMC (Centre for Automotive
Materials and Corrosion) and Steel Research Centre– Doug Colley– Ed McCaffery– CCEM Staff– Feihong Nan
4/13/2012
![Page 22: Hot Dip Galvanizing of TWIP Steels](https://reader037.vdocuments.us/reader037/viewer/2022102513/56816868550346895dded0c5/html5/thumbnails/22.jpg)
Thanks for your time