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DUAL-TEN®
(DUAL PHASE) STEEL
DUAL-TEN®
(dual phase) steels are quickly becoming one of the most popular and versatile materials in today's automotive industry. Currently these steels are most commonly used in structural applications where they have replaced more conventional HSLA steels. They offer a great opportunity for part weight reduction. The improved formability, capacity to absorb crash energy, and ability to resist fatigue has driven this substitution. Today's applications include front and rear rails, crush cans, rocker reinforcements, b/c pillar reinforcements, cowl inner/outer, back panels, cross members, bumpers, and door intrusion beams. Recently
DUAL-TEN® (dual phase) steels are gaining popularity in automotive closures.
DUAL-TEN®
(dual phase) steels are made in the following grades. You can find more specific material property information about these grades by following the links provided.
In general, DUAL-TEN® (dual phase) steel is a mixture of ferrite matrix and martensite islands decorating grain boundaries with possible addition of bainite. Formable
DUAL-TEN® (dual phase) steels contain approximately 5 - 15% martensite. Refer to
Figure - 1.
- Ferrite - soft phase, offers ductility
- Martensite - hard phase, offers strength
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Figure - 1. Example of DUAL-TEN® 600 (dual phase) steel structure, 1000x
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Characteristics of DUAL-TEN® (dual phase) steels:
Figure - 2.
Yield point elongation - Tested DUAL-TEN® 590/600 and DUAL-TEN® 780
steels show no yield point elongation. Refer to
Figure - 3.
Formability - Due to higher work-hardening rate and absence of
YPE, DUAL-TEN® (dual phase) steels behave predictably in stamping processes (i.e. resistance to necking, plastic instability, and kinking).
FLD curves - For the needs of forming feasibility analysis, FLD can be approximated with sufficient accuracy by the conventional ASM-FLD calculated from n-value and thickness. Refer to
Table - 1
and
Figure - 4
and
Figure - 5.
Springback - As compared to conventional HSLA steels, springback is easier to control due to consistent behavior during stamping. Refer to
Figure - 6.
Bendabilty -
DUAL-TEN® (dual phase) steel has very good bendability.
Refer to Figure - 7.
Bake hardening - DUAL-TEN®
(dual phase) steels have an excellent bake-hardening capacity. The increase in the yield strength resulting from typical paint baking cycle is approximately 5-10 ksi (35-70 MPa). Refer to Figure
Figure - 8 and
Figure - 9.
In-part strength -
DUAL-TEN® (dual phase) steels have a high ultimate tensile strength (UTS). UTS ranges from 72 -175 ksi (500 - 1200 MPa) for available grades.
Shelf life -
DUAL-TEN® (dual phase) steel displays no room temperature aging.
Mass reduction capability - These steels have high potential for part downgaging and weight reduction (up to
25% as compared to equivalent conventional HSLA steels).
Crash energy management -
DUAL-TEN® (dual phase) steels have a higher yield to tensile ratio as compared to conventional HSLA steels (0.5 - 0.6). This results in a higher capacity to manage vehicle crash energy.
Fatigue performance -
DUAL-TEN® (dual phase) steels have a higher fatigue strength than equivalent conventional HSLA steels.
Weldability - DUAL-TEN®
(dual phase) steel meets automotive application weldability needs.
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Figure - 2. Example of Work-Hardening Rate for DUAL-TEN®
590/600 steel: Instantaneous n-value as a function of engineering strain. Note the characteristic high n-value in the low plastic deformation range.
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Return to DUAL-TEN® (dual phase)
steel Characteristics.
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Figure - 3. Examples of Stress-Strain Curves for DUAL-TEN® Steels as Compared with Various Grades.
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Return to DUAL-TEN® (dual phase)
steel Characteristics.
Table - 1: Comparison of mechanical properties for DUAL-TEN® 590 and HSLA 340
steels
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Material
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Yield Strength
(ksi)
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Tensile
Strength
(ksi)
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YPE
(%)
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Elongation
(%)
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n-value
10%-UE
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| DUAL-TEN® 590
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375
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640
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24.5
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0.170
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| HSLA 340
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378
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458
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2.8
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30.0
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0.170
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Return to DUAL-TEN® (dual phase) Characteristics.
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Figure - 4: Experimental Forming Limit Curve for Material Thickness of
1.8mm. A conventional ASM FLC calculated from n-value and thickness can be used for
DUAL-TEN® steel with sufficient accuracy.
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Return to DUAL-TEN® (dual phase) Characteristics.
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Figure - 5. Experimental Forming Limit Curve for Material Thickness of 1.2mm. A conventional ASM FLC calculated from n-value and thickness can be used for
DUAL-TEN® (dual phase) steel with sufficient accuracy.
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Figure - 6: Springback. Results of Bending Under Tension Test. Various back tension forces at constant ratio of bending radius to material thickness,
R/t = 2.14. For the top samples back tension is 85% YS, the middle is 75% YS and the bottom is 50% YS. Two samples are shown in the picture for each case. Note consistent geometry for
DUAL-TEN® 590. Dimensional accuracy of parts made of DUAL-TEN®
(dual phase) steel can be controlled easier due consistent material behavior in plastic deformation.
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Return to DUAL-TEN® (dual phase) Characteristics.
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Figure - 7. Bendability in a free-bending test. Results of bendability test for
DUAL-TEN® 590 steel: a) inner radius close to zero, b) inner radius close to the half of the material thickness. Note material folding tendencies in the inner radius area. Bending with inner radius close to zero can be performed successfully without fracture on the outer bend line.
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Return to DUAL-TEN® (dual phase)
steel Characteristics.
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Figure - 8. Bake Hardening in Paint Baking Cycle. Increase in Yield Strength due to Bake Hardening for
DUAL-TEN® 590 (dual phase) Steel at Various Pre-strain Levels.
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Return to
DUAL-TEN>® (dual phase)
steel Characteristics.
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Figure - 9. Combine Effect of Work Hardening (WH) and Bake Hardening (BH). Yield strength of
DUAL-TEN® 600 steel increases more than 260 MPa after deformation to 5% and baking in a typical paint baking cycle. |
Return to
DUAL-TEN® (dual phase) Characteristics.
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