DUAL PHASE STEEL APPLICATIONS
IN TAILOR-WELDED BLANK
TECHNOLGY
Alex A. Konieczny
United States Steel Corporation
www.autosteel.org
Overview
• Introduction
ƒ Material Properties
ƒ Opportunities & Challenges
• DP Steel (Dual Phase) TWB (Tailor Welded
Blanks)
ƒ Quality
ƒ Micrographs
ƒ Fatigue Performance
• Dual Phase Steel TWB Rails
• DP Steel LW (Laser Welded) Tubular Blanks
• Conclusions
www.autosteel.org
Introduction
• Small heat input in laser welding
– Due to small heat input, LW is a favorable joining
technology for fabrication of DP steel TWB
• Industrial applications/advanced trials:
– TWBs composed with DP600, DP800, DP1000
Rails
A & B-pillars
Body side inner, etc.
DP LW hydroformed engine cradles, etc.
www.autosteel.org
Opportunities
• Range of gauge and grade combinations
(DQ, DP600, DP800, DP1000, etc.)
• Unique opportunities to reduce cost and
improve performance:
ƒ Optimize strength and mass distribution
over the vehicle body
ƒ Optimize vehicle crash and structural
performance
ƒ Reduce part count and overall assembly cost
www.autosteel.org
Challenges
• Challenges:
ƒNeed to optimize laser welding processes
ƒNeed to optimize part geometry and stamping
process for springback control
ƒHigher press tonnage/pressure requirements
ƒImpact on tool’s durability
ƒDifferences in material strength, work
hardening rate, and resulting heat generation
in stamping
www.autosteel.org
Tested Materials
Example of Typical Mechanical Properties
GRADE
YS
(MPa)
UTS (MPa)
El (%)
t (mm)
n-value
(10%-UE)
n-value (4-6%)
IF
163
282
49.0
-
0.240
-
DDQ
183
314
42.9
1.6
0.230
-
DQ
214
323
37.5
2.8
0.192
-
HSLA340
387
438
30.8
1.6
0.170
-
C-Mn440
375
484
16.0
2.8
0.180
-
HSLA480
487
604
28.0
2.2
0.128
-
HSLA550
641
672
13.5
2.0
0.040*
-
DP600
386
607
25.5
1.2&1.6
0.168
0.208
T600
390
618
35.1
1.6
0.230
-
DP800
459
838
17.2
1.2&1.6
0.115*
0.168
T800
475
822
28.0
1.6
0.240
-
DP1000
726
1003
10.8
1.2
0.060*
0.08
www.autosteel.org
Tested Materials, Cont’d
True Stress – True Strain Curves
Comparison of Yield Strength, Tested As Delivered, L-dir.
DP800
1200
HSLA340
DDS
HSLA550
DP1000
DP600
600T
Work hardening rate
Stress,MPa
MPa
TrueTrue
Stress,
1000
800
600
400
200
0
0
0.05
0.1
0.15
True Strain
www.autosteel.org
0.2
0.25
Dual Phase Steel
Tailor Welded Blanks
www.autosteel.org
TWB Welding Process Parameters
Laser Welding
Batch
1
Laser: YAG
Power: 4kW, 2 beams
Speed: 6.1 – 7.1 m/min
Focus: Part surface
Batch
2
Laser: YAG
Power: 3kW
Speed: 5.25m/min
Focus: 0.5mm from
bottom of part
Mash Seam Welding
Current: 18kA
Force: 12kN DP600
Overlap: 2.5 mm
Speed: 4m/min
www.autosteel.org
-
Weld Seam Quality and Hardness
YS, MPa TS, MPa
1.2mm
DP600
427
638
Welded
429
646
1.5mm
DP600
432
683
93.6%
Quality
Performed test:
- Tension test
- Olsen test
- Geometry evaluation
- Microhardness
DP600 1.2mm + DP600 1.5mm
Microhardness Traverse
500
HV 100
400
300
200
100
0
3.0
4.0
5.0
Distance, mm
6.0
7.0
High quality laser weld seam
geometry for dissimilar gages of
TWB is not an issue.
Acceptance criterion: Minimum
85% of theoretical cross-section.
www.autosteel.org
Weld Seam Quality and Hardness, Cont’d
YS,
MPa
TS,
MPa
1.2mm
DP600
408
647
Welded
433
1.6mm
DP800
407
Weld
Quality
YS,
MPa
TS, MPa
1.2mm
DP600
404
639
648
Welded
170
307
786
1.6mm
DQ
168
298
Weld
Quality
93.0%
95.5%
DP600 1.2mm + DP800 1.6mm
DP600 1.2mm + DQ 1.6mm
DP600 1.2mm + DP800 1.6mm
Microhardness Traverses
DP600 1.2mm + DQ 1.6mm
Microhardness Weld Traverse
400
400
HV 100
HV 100
500
300
200
300
200
100
100
0
0
3.0
4.0
5.0
6.0
7.0
3.0
4.0
Distance, mm
www.autosteel.org
5.0
Distance, mm
6.0
7.0
Weld Seam Quality and Hardness, Cont’d
YS,
MPa
TS,
MPa
1.2mm
DP800
492
866
Welded
502
1.6mm
DP800
418
Weld
Quality
YS,
MPa
TS,
MPa
1.2mm
DP800
470
851
870
Welded
168
306
795
1.6mm
DQ
160
300
Weld
Quality
92.4%
DP800 1.2mm + DP800 1.6mm
DP800 1.2mm + DQ 1.6mm
DP800 1.2mm + DQ 1.6mm
Microhardness Traverse
DP800 1.2mm to DP800 1.6mm
Microhardness Traverse
500.0
500.0
400.0
400.0
HV 100
HV 100
97.4%
300.0
200.0
300.0
200.0
100.0
100.0
0.0
0.0
3.0
4.0
5.0
6.0
7.0
3.0
4.0
Distance, mm
www.autosteel.org
5.0
Distance, mm
6.0
Weld Seam Quality and Hardness, Cont’d
YS, MPa
TS, MPa
Left Bar
407
640
Welded
408
635
Right Bar
401
632
Weld Quality
91.8%
DP600 1.2mm + DP600 1.2mm
Laser welding is
more difficult for
similar gages
DP600 1.2mm to DP600 1.2mm
Microhardness Traverse
500.0
HV 100
400.0
300.0
200.0
100.0
0.0
2.0
3.0
4.0
Distance, mm
5.0
6.0
Fatigue testing
results for this case
are presented later
www.autosteel.org
Weld Seam Quality and Hardness, Cont’d
YS, MPa
TS, MPa
Left Bar
398
632
Welded
412
634
Right Bar
398
633
Weld Quality
n/a
DP600 1.2mm + DP600 1.2mm
Mash welding results
in “added material”
Mash Weld DP600 1.2mm to DP600 1.2mm
Microhardness Traverse
500.0
HV 100
400.0
300.0
200.0
100.0
0.0
2.0
3.0
4.0
5.0
6.0
Distance, mm
7.0
8.0
9.0
Fatigue testing
results for this case
are presented later
www.autosteel.org
DP 600 TWB Fatigue Test
Specimen as a cantilever beam with constant controlled stress
δ
F
Fl 3
δ =
2EI
3
bt
I =
12
M = Fl
2
Sbt
l=
6F
b
L
t
l
www.autosteel.org
strain gage
DP 600 TWB Fatigue Test, Cont’d
Experimental setup for
constant stress bending
fatigue test
www.autosteel.org
DP 600 TWB Fatigue Test, Cont’d
1000
Laser-welded
Mash-welded
~6.5
Weld
1.5
3.0
Fatigue test performed in
fully reversed bending
mode; R = -1 at frequency
of f = 7 - 15 Hz using
constatnt stress specimens.
Variable speed, LFE-550
fatigue testing machine was
used. Tests performed in
lab environment; T = 23 oC,
RH = 30 %.
1.25
100
1.25
16
Nominal tension stress, S
n
(MPa)
Base metal
0.5
3.0
3.19
~3.0
7.0
10
10 4
10 5
10 6
Fatigue life, N (cycles)
Summary plot for laser-welded, mash-welded, and base metal sheet steel
www.autosteel.org
10 7
Hybrid Laser/MAG Welding
[Micrograph of Hybrid Laser Weld]
400
Vickers (HV)
350
4
3
300
2
200
-2
150
5
3
250
1
Sample N°: AS 33
Material: DP 600
Process: Laser/MAG Hybrid
Focus: Twin Spot
Traces Speed: 4.5 m/min
0
5
Distance /mm
1
1
2
[Vickers-Micro Hardness Traverse]
-2
150
0 0
5
3
2
200
0
0
0
3
250
0
0 0
5
4
300
0 0
2
-1
-1
[Micrograph of Laser Welded DP 600]
400
Vickers (HV)
350
0 0
0
0 0
5
2
0
0 0
Distance /mm
1
-1
-1
Sample N°: AS 40B
Material: DP 600
Process: Laser only
Focus: Mono Spot
Traces Speed: 4.5 m/min
5
0
0
0
1
1
[Vickers-Micro Hardness Traverse]
Hybrid Laser Welding for TWB production: Tolerates gaps up to 1.00mm
www.autosteel.org
2
Dual Phase Steel
Tailor Welded Blank Rails
www.autosteel.org
Stamping of DP TWB Rails
Example of DP600 TWB Front Rail
Heavy gauge side
Laser Weld Seam Location
Heavy gauge side
www.autosteel.org
Stamping of DP TWB Rails, Cont’d
Springback for DP600 and HSLA280 TWB rails
85°
84°
HSLA280, 2mm
Original Design
94°
94°
76°
75°
DP600, 2mm
Direct Substitution
88°
88°
www.autosteel.org
Stamping of DP TWB Rails, Cont’d
AHSS – TWB: Part geometry designed for springback control
• Various grades combinations: from DQ to DP800, and gages
from 1.2mm to 1.6mm
• 5% stretch across weld seam
• All combinations stamped without failure in industrial conditions
• No springback related issues even though UTS varied
by 500MPa within the part
www.autosteel.org
Stamping of DP TWB Rails, Cont’d
Dimensional Accuracy/Springback Control Solution for DP TWB
Product Geometry Designed
for Springback Control
90o
90o
Designed for
springback
Conventional
approach
View from the end of DP800,1.2mm
View from the end of DQ,1.6mm
500 MPa difference in UTS
www.autosteel.org
Dual Phase Steel
Laser Welded Tubular Blanks
www.autosteel.org
Microhardness & Micrograph
DP600 ERW
(Electric
Resistance
Welded) Tube
Microhardness,Hv
ERW
LW
450
400
350
300
250
200
150
100
50
0
DP600 LW
(Laser
Welded)
Tube
0.0
0.5
1.0
1.5
2.0
2.5
Location, mm
3.0
3.5
www.autosteel.org
4.0
Tubular Laser Welded DP600 Blanks
Die for hydroforming expansion
- Free expanded LW DP 600 tubes
- Various end feed rate
- No failure up to 65% expansion
www.autosteel.org
Conclusions
• DP Steels are excellent candidates for TWB
component applications
• As demonstrated, springback in stamping
of DP TWB can be controlled even though UTS
varies up to 500MPa
• DP TWB display good fatigue performance
• Similar to other welded joints, fatigue performance
for LW joints is geometry driven. Note: Weld seam area
in TWB components are located by the designer
in the “protected zones”
• DP600 LW tubular blanks are suitable
for hydroforming applications with expansion
up to 65%
www.autosteel.org
Conclusions, Cont’d
• Laser welding is the only recommended process
for manufacture of DP 800 and DP1000 TWB
(after M. Uchihara & K. Fukui)
• Industrial laser welding processes allow for good
quality production DP TWBs
• Adding material in welding process (e.g. mash
welding) results in improved fatigue performance
of TWB (almost as good as of substrate material)
• In case of welding similar or heavy gauges
of DP steels, other blank welding technologies
could be applied, e.g. hybrid laser welding
• Further study is needed to optimize
TWB technologies for AHSS
www.autosteel.org
Acknowledgments
Presented in cooperation with:
Tailor Welded Blank Technologies
Committee of Auto-Steel Partnership
www.autosteel.org
References
• M. Uchihara, K. Kiyoyuki, Tailored Blanks of High
Strength Steels – Comparison of Welding Processes,
SAE 2003-01
• A. Konieczny, X.M. Chen, D.A. Witmer, M.F. Shi, Y.
Hayashida and Y. Omiya, Hydroforming Performance
of Laser Welded and Electric Resistance Welded
High Strength Steel Tubes, SAE 2004-01-0830
www.autosteel.org
DUAL PHASE STEEL APPLICATIONS
IN TAILOR-WELDED BLANK
TECHNOLGY
Q&A
Alex A. Konieczny
United States Steel Corporation
www.autosteel.org