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DUAL PHASE STEEL APPLICATIONS DUAL PHASE STEEL APPLICATIONS IN TAILORIN TAILOR--WELDED BLANK WELDED BLANK
TECHNOLGYTECHNOLGY
Alex A. Alex A. KoniecznyKoniecznyUnited States Steel CorporationUnited States Steel Corporation
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Overview
•• DPDP Steel (Steel (DDualual PPhase)hase) TWB TWB ((TTailorailor WWeldedeldedBBlanks)lanks)
QualityQualityMicrographsMicrographsFatigue PerformanceFatigue Performance
•• IntroductionIntroductionMaterial PropertiesMaterial PropertiesOpportunities & ChallengesOpportunities & Challenges
•• Dual Phase Steel TWB Rails Dual Phase Steel TWB Rails
•• DP Steel DP Steel LWLW ((LLaser aser WWelded) Tubular Blankselded) Tubular Blanks
•• ConclusionsConclusions
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Introduction
•• Small heat input in laser weldingSmall heat input in laser welding–– Due to small heat input, LW is a favorable joining Due to small heat input, LW is a favorable joining
technology for fabrication of DP steel TWBtechnology for fabrication of DP steel TWB
•• Industrial applications/advanced trials:Industrial applications/advanced trials:–– TWBsTWBs composed with DP600, DP800, DP1000composed with DP600, DP800, DP1000
Rails Rails
A & BA & B--pillars pillars
Body side inner, etc. Body side inner, etc.
DP LW DP LW hydroformedhydroformed engine cradles, etc.engine cradles, etc.
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•• Range of gauge and grade combinations Range of gauge and grade combinations
(DQ, DP600, DP800, DP1000, etc.)(DQ, DP600, DP800, DP1000, etc.)
Opportunities
•• Unique opportunities to reduce cost andUnique opportunities to reduce cost and
improve performance:improve performance:Optimize strength and mass distribution Optimize strength and mass distribution
over the vehicle bodyover the vehicle body
Optimize vehicle crash and structuralOptimize vehicle crash and structural
performanceperformance
Reduce part count and overall assembly costReduce part count and overall assembly cost
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Challenges
•• Challenges:Challenges:
Need to optimize laser welding processesNeed to optimize laser welding processes
Need to optimize part geometry and stampingNeed to optimize part geometry and stamping
process forprocess for springbackspringback controlcontrol
Higher press tonnage/pressure requirementsHigher press tonnage/pressure requirements
Impact on toolImpact on tool’’s durabilitys durability
Differences in material strength, work Differences in material strength, work
hardening rate, and resulting heat generationhardening rate, and resulting heat generation
in stampingin stamping
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Tested Materials
Example of Typical Mechanical PropertiesExample of Typical Mechanical Properties
UTS (UTS (MPaMPa)) El (%)El (%) nn--value value (10%(10%--UE)UE) nn--value (4value (4--6%)6%)
323323 37.537.5 0.1920.192 --
438438 30.830.8 0.1700.170 --
607607 25.525.5 0.1680.168 0.2080.208
838838 17.217.2 0.115*0.115* 0.1680.168
GRADEGRADE
DQDQ
HSLA340HSLA340
DP600DP600
DP800DP800
YS YS ((MPaMPa))
214214
387387
386386
459459
t (mm)t (mm)
2.82.8
1.61.6
1.2&1.61.2&1.6
1.2&1.61.2&1.6
282282 49.049.0 0.2400.240 --
314314 42.942.9 0.2300.230 --
484484 16.016.0 0.1800.180 --
604604 28.028.0 0.1280.128 --
672672 13.513.5 0.040*0.040* --
618618 35.135.1 0.2300.230 --
822822 28.028.0 0.2400.240 --
10031003 10.810.8 0.060*0.060* 0.080.08
IFIF
DDQDDQ
CC--Mn440Mn440
HSLA480HSLA480
HSLA550HSLA550
T600T600
T800T800
DP1000DP1000
163163
183183
375375
487487
641641
390390
475475
726726
--
1.61.6
2.82.8
2.22.2
2.02.0
1.61.6
1.61.6
1.21.2
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Comparison of Yield Strength, Tested As Delivered, L-dir.
0
200
400
600
800
1000
1200
0 0.05 0.1 0.15 0.2 0.25
True Strain
True
Str
ess,
MPa
DP800 HSLA340 DDS HSLA550 DP1000 DP600 600T
True
Str
ess,
MPa
True Stress True Stress –– True Strain CurvesTrue Strain Curves
Tested Materials, Cont’d
Work hardening rateWork hardening rate
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Dual Phase SteelDual Phase SteelTailor Welded BlanksTailor Welded Blanks
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TWB Welding Process Parameters
--
Laser: YAGLaser: YAGPower: 3kWPower: 3kWSpeed: 5.25m/minSpeed: 5.25m/minFocus: 0.5mm from Focus: 0.5mm from
bottom of partbottom of part
Batch Batch 22
Current: 18kACurrent: 18kAForce: 12kN DP600Force: 12kN DP600Overlap: 2.5 mmOverlap: 2.5 mmSpeed: 4m/minSpeed: 4m/min
Laser: YAGLaser: YAGPower: 4kW, 2 beams Power: 4kW, 2 beams Speed: 6.1 Speed: 6.1 –– 7.1 m/min7.1 m/minFocus: Part surfaceFocus: Part surface
Batch Batch 11
Mash Seam WeldingMash Seam WeldingLaser WeldingLaser Welding
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Weld Seam Quality and Hardness
DP600 1.2mm + DP600 1.5mm Microhardness Traverse
0
100
200
300
400
500
3.0 4.0 5.0 6.0 7.0
Distance, mm
HV
100
Performed test:Performed test:-- Tension testTension test-- Olsen testOlsen test-- Geometry evaluationGeometry evaluation-- MicrohardnessMicrohardnessHigh quality laser weld seam High quality laser weld seam geometry for dissimilar gages of geometry for dissimilar gages of TWB is not an issue.TWB is not an issue.Acceptance criterion: Minimum Acceptance criterion: Minimum 85% of theoretical cross85% of theoretical cross--section.section.
93.6%93.6%
6836834324321.5mm 1.5mm DP600DP600
QualityQuality
646646429429WeldedWelded
6386384274271.2mm 1.2mm DP600DP600
TS, TS, MPaMPaYS, YS, MPaMPa
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7867864074071.6mm 1.6mm DP800DP800
93.0%93.0%Weld Weld QualityQuality
648648433433WeldedWelded
6476474084081.2mm 1.2mm DP600DP600
TS, TS, MPaMPa
YS,YS,MPaMPa
DP600 1.2mm + DP800 1.6mm Microhardness Traverses
0
100
200
300
400
500
3.0 4.0 5.0 6.0 7.0
Distance, mm
HV
100
DP600 1.2mm + DP800 1.6mmDP600 1.2mm + DP800 1.6mm
2982981681681.6mm 1.6mm DQDQ
95.5%95.5%Weld Weld QualityQuality
307307170170WeldedWelded
6396394044041.2mm 1.2mm DP600DP600
TS, TS, MPaMPaYS,YS,MPaMPa
DP600 1.2mm + DQ 1.6mm Microhardness Weld Traverse
0
100
200
300
400
3.0 4.0 5.0 6.0 7.0
Distance, mm
HV
100
DP600 1.2mm + DQ 1.6mmDP600 1.2mm + DQ 1.6mm
Weld Seam Quality and Hardness, Cont’d
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7957954184181.6mm 1.6mm DP800DP800
92.4%92.4%Weld Weld QualityQuality
870870502502WeldedWelded
8668664924921.2mm 1.2mm DP800DP800
TS, TS, MPaMPa
YS, YS, MPaMPa
DP800 1.2mm to DP800 1.6mmMicrohardness Traverse
0.0
100.0
200.0
300.0
400.0
500.0
3.0 4.0 5.0 6.0 7.0
Distance, mm
HV
100
DP800 1.2mm + DP800 1.6mmDP800 1.2mm + DP800 1.6mm
3003001601601.6mm 1.6mm DQDQ
97.4%97.4%Weld Weld QualityQuality
306306168168WeldedWelded
8518514704701.2mm 1.2mm DP800DP800
TS, TS, MPaMPa
YS,YS,MPaMPa
DP800 1.2mm + DQ 1.6mmMicrohardness Traverse
0.0
100.0
200.0
300.0
400.0
500.0
3.0 4.0 5.0 6.0
Distance, mm
HV 1
00
DP800 1.2mm + DQ 1.6mmDP800 1.2mm + DQ 1.6mm
Weld Seam Quality and Hardness, Cont’d
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DP600 1.2mm to DP600 1.2mmMicrohardness Traverse
0.0
100.0
200.0
300.0
400.0
500.0
2.0 3.0 4.0 5.0 6.0
Distance, mm
HV
100
Fatigue testing Fatigue testing results for this case results for this case are presented laterare presented later
Laser welding is Laser welding is moremore difficult for difficult for similar gagessimilar gages
632632401401Right BarRight Bar
91.8%91.8%Weld QualityWeld Quality
635635408408WeldedWelded
640640407407Left BarLeft Bar
TS, TS, MPaMPaYS, YS, MPaMPa
DP600 1.2mm + DP600 1.2mmDP600 1.2mm + DP600 1.2mm
Weld Seam Quality and Hardness, Cont’d
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Mash Weld DP600 1.2mm to DP600 1.2mmMicrohardness Traverse
0.0
100.0
200.0
300.0
400.0
500.0
2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0
Distance, mm
HV
100
Weld Seam Quality and Hardness, Cont’d
Mash welding results Mash welding results in in ““added materialadded material””
Fatigue testing Fatigue testing results for this case results for this case are presented laterare presented later
633633398398Right BarRight Bar
n/an/aWeld QualityWeld Quality
634634412412WeldedWelded
632632398398Left BarLeft Bar
TS, TS, MPaMPaYS,YS, MPaMPa
DP600 1.2mm + DP600 1.2mmDP600 1.2mm + DP600 1.2mm
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DP 600 TWB Fatigue Test
δ = Fl3
2EI
I = bt3
12
l = Sbt2
6F
F
δ
M = Fl
L
b
t
l
Specimen as a cantilever beam with constant controlled stressSpecimen as a cantilever beam with constant controlled stress
strain gage
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Experimental setup for Experimental setup for constant stress bending constant stress bending
fatigue test fatigue test
DP 600 TWB Fatigue Test, Cont’d
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DP 600 TWB Fatigue Test, Cont’d
10
100
1000
10 4 10 5 10 6 10 7
Summary plot for laser-welded, mash-welded, and base metal sheet steel
No
min
al te
nsio
n s
tre
ss, S
n(M
Pa
)
Fatigue life, N (cycles)
3.0
7.0
1.25 0.5
3.0
1.5
3.19
Weld
~6.5
~3.0
1.2
5
Laser-weldedMash-welded
Base metal
Fatigue test performed in fully reversed bending mode; R = -1 at frequency of f = 7 - 15 Hz using constatnt stress specimens. Variable speed, LFE-550fatigue testing machine was used. Tests performed in lab environment; T = 23 oC, RH = 30 %.
16
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1 5 0
2 0 0
2 5 0
3 0 0
3 5 0
4 0 0
-2 -1 0 1 2
1 5 0
2 0 0
2 5 0
3 0 0
3 5 0
4 0 0
-2 -1 0 1 2
[Micrograph of Hybrid Laser Weld]
Sample N°: AS 33Material: DP 600Process: Laser/MAG HybridFocus: Twin SpotTraces Speed: 4.5 m/min
Sample N°: AS 40BMaterial: DP 600Process: Laser onlyFocus: Mono SpotTraces Speed: 4.5 m/min
[Vickers-Micro Hardness Traverse]
Vickers (HV)
0 1-1150
200
250
300
350
400[Micrograph of Laser Welded DP 600]
[Vickers-Micro Hardness Traverse]
Vickers (HV)
0 1-1150
200
250
300
350
400
Distance /mm Distance /mm
Hybrid Laser/MAG Welding
Hybrid Laser Welding for TWB production: Tolerates gaps up to 1.Hybrid Laser Welding for TWB production: Tolerates gaps up to 1.00mm00mm
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Dual Phase Steel Dual Phase Steel Tailor Welded Blank RailsTailor Welded Blank Rails
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Laser Weld Seam LocationLaser Weld Seam Location
Heavy gauge side Heavy gauge side
Stamping of DP TWB Rails
Example of DP600 TWB Front Rail Example of DP600 TWB Front Rail
Heavy gauge side Heavy gauge side
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Stamping of DP TWB Rails, Cont’d
SpringbackSpringback for DP600 and HSLA280 TWB railsfor DP600 and HSLA280 TWB rails
HSLA280, 2mmHSLA280, 2mmOriginal DesignOriginal Design
94°
85° 84°
94°
88°88°
75°76°
DP600, 2mmDP600, 2mmDirect SubstitutionDirect Substitution
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•• Various grades combinations: from DQ to DP800, and gagesVarious grades combinations: from DQ to DP800, and gagesfrom 1.2mm to 1.6mmfrom 1.2mm to 1.6mm
•• 5% stretch across weld seam5% stretch across weld seam•• All combinations stamped without failure in industrial conditiAll combinations stamped without failure in industrial conditionsons•• No No springbackspringback related issues even though UTS varied related issues even though UTS varied
by 500MPa within the partby 500MPa within the part
AHSS – TWB: Part geometry designed for springback control
Stamping of DP TWB Rails, Cont’d
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Stamping of DP TWB Rails, Cont’d
View from the end of DQ,1.6mmView from the end of DQ,1.6mm
500 500 MPa MPa difference in UTSdifference in UTS
Product Geometry Designed Product Geometry Designed for for Springback Springback ControlControl
View from the end of DP800,1.2mmView from the end of DP800,1.2mm
Dimensional Accuracy/Dimensional Accuracy/SpringbackSpringback Control Solution for DP TWBControl Solution for DP TWB
90o
90o
Designed forDesigned forspringbackspringback
ConventionalConventionalapproach approach
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Dual Phase Steel Dual Phase Steel Laser Welded Tubular BlanksLaser Welded Tubular Blanks
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050
100150200250300350400450
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0Location, mm
Mic
roha
rdne
ss,H
v
ERW LW
DP600 DP600 ERWERW((EElectriclectric
RResistanceesistanceWWelded) Tubeelded) Tube
DP600 DP600 LWLW((LLaser aser
WWelded)elded)TubeTube
Microhardness & Micrograph
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Die for Die for hydroforminghydroforming expansionexpansion
Tubular Laser Welded DP600 Blanks
-- Free expanded LW DP 600 tubesFree expanded LW DP 600 tubes-- Various end feed rateVarious end feed rate-- No failure up to 65% expansionNo failure up to 65% expansion
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Conclusions
•• DP Steels are excellent candidates for TWBDP Steels are excellent candidates for TWBcomponent applicationscomponent applications
•• As demonstrated,As demonstrated, springbackspringback in stamping in stamping of DP TWB can be controlled even though UTSof DP TWB can be controlled even though UTSvaries up to 500MPa varies up to 500MPa
•• DP TWB display good fatigue performanceDP TWB display good fatigue performance
•• Similar to other welded joints, fatigue performance Similar to other welded joints, fatigue performance for LW joints is geometry driven. for LW joints is geometry driven. Note: Weld seam area Note: Weld seam area in TWB components are located by the designer in TWB components are located by the designer in the in the ““protected zonesprotected zones””
•• DP600 LW tubular blanks are suitable DP600 LW tubular blanks are suitable for for hydroforminghydroforming applications with expansion applications with expansion up to 65%up to 65%
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Conclusions, Cont’d
•• Laser welding is the only recommended process Laser welding is the only recommended process for manufacture of DP 800 and DP1000 TWBfor manufacture of DP 800 and DP1000 TWB(after M.(after M. UchiharaUchihara & K. Fukui)& K. Fukui)
•• Industrial laser welding processes allow for good Industrial laser welding processes allow for good quality production DPquality production DP TWBs TWBs
•• Adding material in welding process (e.g. mashAdding material in welding process (e.g. mashwelding) results in improved fatigue performancewelding) results in improved fatigue performanceof TWB (almost as good as of substrate material)of TWB (almost as good as of substrate material)
•• In case of welding similar or heavy gauges In case of welding similar or heavy gauges of DP steels, other blank welding technologies of DP steels, other blank welding technologies could be applied, e.g. hybrid laser weldingcould be applied, e.g. hybrid laser welding
•• Further study is needed to optimize Further study is needed to optimize TWB technologies for AHSSTWB technologies for AHSS
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Presented in cooperation with:Presented in cooperation with:Tailor Welded Blank Technologies Tailor Welded Blank Technologies
Committee of AutoCommittee of Auto--Steel PartnershipSteel Partnership
Acknowledgments
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References
••M. M. UchiharaUchihara, K. , K. KiyoyukiKiyoyuki, Tailored Blanks of High , Tailored Blanks of High Strength Steels Strength Steels –– Comparison of Welding Processes, Comparison of Welding Processes, SAE 2003SAE 2003--0101
••A. A. KoniecznyKonieczny, , X.M. Chen, D.A. X.M. Chen, D.A. WitmerWitmer, M.F. Shi, Y. , M.F. Shi, Y. HayashidaHayashida and Y. and Y. OmiyaOmiya, , HydroformingHydroforming Performance Performance of Laser Welded and Electric Resistance Welded of Laser Welded and Electric Resistance Welded High Strength Steel Tubes, SAE 2004High Strength Steel Tubes, SAE 2004--0101--0830 0830
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DUAL PHASE STEEL APPLICATIONS DUAL PHASE STEEL APPLICATIONS IN TAILORIN TAILOR--WELDED BLANK WELDED BLANK
TECHNOLGYTECHNOLGY
Alex A. Alex A. KoniecznyKoniecznyUnited States Steel CorporationUnited States Steel Corporation
Q & AQ & A