AHSS Repairability
Repairability of Advanced High Strength
Steel (AHSS) Structural Components
Blake K. Zuidema
National Steel Corporation
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AHSS Repairability
Acknowledgements
Leadership/
Mentors :
Brian Dotterer
Jim Fekete
General Motors Corporation
Experimental:
Steve Kelley
Bethlehem Steel Corporation
Nassos Lazaridis
Ispat Inland, Inc.
Blake Zuidema
National Steel Corporation
Dave Hoydick
United States Steel Corporation
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AHSS Repairability
Background
Common Collision Repair Processes:
•Bolt off, bolt on
•Cold straightening
•Cut-off, weld on
•Flame (hot) straightening
The latter two require application of heat, which
could affect steels that gain their strength by
thermal processing
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AHSS Repairability
Thermal histories of welds, flame straightening were
determined previously by GM using thermocoupled coupons*
Temperature
(oC)
Simulated Flame Straightening Thermal Cycle
1000
850
750
650
<
80 sec
> <5-90 sec> <
80 sec
>
Time
*Stevenson, et. al, SAE Technical Paper No. 910292
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AHSS Repairability
Materials
(note: all steels ~1.5 mm gauge)
Steel
IF Grade 4
GM Grade
GMW2M-ST-S
Grade 4
Description
HDGI IF mild steel
HSLA 340
GMW3032M-ST-S
CR340
HDGI 340 MPa YS
HSLA steel
DP 600
GMW3032M-ST-S
CR 340 DP
HDGI 340 MPa YS, 600
MPa UTS DP steel
Mart 1300
GMW3399M-ST-S
1300T/1030Y M
Uncoated (bare) 1300
MPa UTS martensitic steel
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AHSS Repairability
Experimental Procedure
•Test as-produced mechanical properties
•Strain 8% uniaxial tension, bake 170 oC/20 sec
•Test as-fabricated mechanical properties
•Apply simulated flame straightening thermal cycles
•Test as-repaired mechanical properties
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AHSS Repairability
Notes on Experimental Procedure
•Martensitic steel was baked only, not pre-strained
•All tensile tests ASTM longitudinal
•n-values calculated in 10%-UE range (YS-UE for mart.)
•Zinc stripped from GI steels before thermal treatment
•750 oC condition included 3x30sec interrupted heating
•AC1, AC3 temperatures provided by steel suppliers
For all steels tested:
•650 C was high in α phase field
•750 C was low in α + γ phase field
•850 C was high in α + γ phase field
•1000 C was in γ phase field
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AHSS Repairability
Results - HDGI IF Grade 4 Steel
IF Grade 4 Mild Steel
IF Grade 4 Mild Steel
As Received
50
400
As Received + 650C/90s
8% Strain + Bake
5sec
10sec
30sec
60sec
90sec
30x3sec
300
As Received
200
As Received + 650C/90s
100
AC1
0
0
200
AC3
400
600
800
1000
IF Grade 4 Mild Steel
Hold Temperature, C
40
30
20
10
AC1
0
0
1200
0.25
400
As Received
As Received +650C/90s
5sec
10sec
30sec
60sec
90sec
30x3sec
200
100
AC3
AC1
0
0
200
400
600
800
Hold Temperature, C
1000
200
400
600
800
1000
IF Grade
4 Mild Steel
Hold
Temperature,
C
0.2
1200
5sec
10sec
30sec
60sec
90sec
30x3sec
0.15
0.1
0.05
AC1
0
1200
AC3
As Received + 650C/90s
As Received
8% Strain + Bake
300
5sec
10sec
30sec
60sec
90sec
30x3sec
8% Strain + Bake
0
200
400
600
AC3
800
Hold Temperature, C
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1000
1200
AHSS Repairability
Results - HDGI HSLA 340 Steel
HSLA 340 Steel
HSLA 340 Steel
40
600
35
8% Strain + Bake
500
5sec
10sec
30sec
60sec
90sec
30x3sec
As Received + 650C/90s
400
As Received
300
200
100
AC1
0
As Received
As Received + 650C/90s
30
25
20
8% Strain + Bake
15
10
5
AC1
0
AC3
0
0
200
400
600
800
1000
200
1200
0.2
600
500
400
5sec
10sec
30sec
60sec
90sec
30x3sec
300
200
100
AC1
0
0
200
400
600
Hold Temperature, C
1000
600
800
1000
1200
As Received + 650C/90s
As Received
0.15
5sec
10sec
30sec
60sec
90sec
30x3sec
0.1
0.05
8% Strain + Bake
AC1
AC3
800
400
AC3
Hold Temperature,
C
HSLA 340 Steel
HSLA 340 Steel
Hold Temperature,
C
8% Strain + Bake
As Received
As Received + 650C/90s
5sec
10sec
30sec
60sec
90sec
30x3sec
AC3
0
1200
0
200
400
600
800
Hold Temperature, C
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1000
1200
AHSS Repairability
Results - Mart 1300 Steel
1300 MPa UTS Martensitic Steel
1300 MPA UTS Martensitic Steel
1600
40
1400
35
Bake
As Received
1200
1000
5sec
10sec
30sec
60sec
90sec
30x3sec
800
600
400
200
AC1
0
25
20
15
As Received
10
5
AC3
5sec
10sec
30sec
60sec
90sec
30x3sec
30
Bake
AC1
0
0
200
400
600
800
1000
1200
0
200
Hold
Temperature,
C Steel
1300
MPa
UTS Martensitic
1600
5sec
10sec
30sec
60sec
90sec
30x3sec
1000
800
600
400
AC1
0
800
1000
1200
0.25
1200
200
600
Hold Temperature, C
1300 MPa UTS Martensitic Steel
Bake
As Received
1400
400
AC3
0.2
5sec
10sec
30sec
60sec
90sec
30x3sec
0.15
0.1
0.05
As Received
Bake
AC3
AC1
AC3
0
0
200
400
600
800
Hold Temperature, C
1000
1200
0
200
400
600
800
Hold Temperature, C
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1000
1200
AHSS Repairability
Interpretation - Mart 1300 Steel
•Heating martensitic steel to lowest practical flame
straightening temperature (650 oC) for even short
time caused tempering of martensite phase and
reduction in strength
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AHSS Repairability
Results - HDGI DP 600 Steel
DP 600 Steel
DP 600 Steel
800
As Received + 650C/90s
30
8% Strain + Bake
25
5sec
10sec
30sec
60sec
90sec
30x3sec
600
As Received + 650C/90s
400
As Received
200
AC1
200
400
600
800
DP 600 Steel
Hold Temperature, C
1000
5sec
10sec
30sec
60sec
90sec
30x3sec
20
15
8% Strain + Bake
10
5
AC1
AC3
AC3
0
0
0
As Received
0
1200
200
400
600
800
1000
1200
DP 600 SteelC
Hold Temperature,
0.2
800
8% Strain + Bake
As Received + 650C/90s
As Received
600
5sec
10sec
30sec
60sec
90sec
30x3sec
As Received + 650C/90s
400
200
AC1
As Received
0.1
0.05
AC3
AC1
0
0
0
200
400
600
800
Hold Temperature, C
1000
1200
5sec
10sec
30sec
60sec
90sec
30x3sec
0.15
0
200
400
600
AC3
800
Hold Temperature, C
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1000
1200
AHSS Repairability
Metallography - HDGI DP 600 Steel
As-received
8% strain + bake
650 oC/60 sec
8% strain + bake
750 oC/90 sec
Un-tempered martensite
All specimens etched in LePera’s reagent
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AHSS Repairability
Interpretation - HDGI DP 600 Steel
•Heating the HDGI DP 600 steel to the lowest
practical flame straightening temperature (650 oC)
reduced strength by:
1.) Tempering the hard martensite phase, and
2.) Promoting recovery of cold work in the softer
ferrite phase.
•Heating to the higher 750 oC temperature
transformed the martensite to austenite which,
upon cooling, formed fresh, untempered martensite
and restored DP properties
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AHSS Repairability
Conclusions
1.) IF Grade 4 mild steel and HSLA 340 can be
repaired by flame straightening. Temperature
should be limited to no more than 650 oC
(1200 oF, or dull cherry red color) for short
duration.
2.) DP 600 and Mart 1300 steels should not be
repaired by flame straightening.
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AHSS Repairability
Recommendations
1.) The nature and suitability of repair
procedures for AHSS components will depend
highly on the nature and location of damage.
2.) AHSS response to repair thermal cycles
should be used in developing procedures
tailored to specific AHSS components.
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AHSS Repairability
Future Work - Phase 2 Underway (3/2003 completion)
1.) Four additional AHSS grades:
•TRIP 590
•TRIP 780
•DP 500/780
•DP 700/980
2.) MIG welds on both Phase 1 and Phase 2 materials
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AHSS Repairability
Repairability of Advanced High Strength
Steel (AHSS) Structural Components
Blake K. Zuidema
National Steel Corporation
www.autosteel.org