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Dual Phase steels

Description

Dual Phase steels offer an outstanding combination of strength and drawability as a result of their microstructure, in which a hard martensitic or bainitic phase is dispersed in a soft ferritic matrix. These steels have high strain hardenability. This gives them good strain redistribution capacity and thus drawability as well as finished part mechanical properties, including yield strength, that are far superior to those of the initial blank. The yield strength of Dual Phase steels is further increased by the paint baking (also called Bake Hardening, BH) process.

High finished part mechanical strength lends these steels excellent fatigue strength and good energy absorption capacity, making them suitable for use in structural parts and reinforcements. The strain hardening capacity of these steels combined with a strong bake hardening effect gives them excellent potential for reducing the weight of structural parts and even – notably in the case of FullFinished 280 DP (FF 280 DP) – skin parts.

Applications

Given their high energy absorption capacity and fatigue strength, cold rolled Dual Phase Steels are particularly well suited for automotive structural and safety parts such as longitudinal beams, cross members and reinforcements.

 

FF 280 DP can be used to make visible parts with 20% higher dent resistance than conventional high strength steels, resulting in a potential weight saving of some 15%.

As a result of its mechanical strength, hot rolled Dual Phase 600 can be used to reduce the weight of structural parts by decreasing their thickness. Relevant automotive applications include:

  • wheel webs
  • longitudinal rails
  • shock towers
  • fasteners.

Bumper in Dual Phase 1180 (thickness: 1.35 mm)

B-pillar reinforcement in Dual Phase 980 LCE Y600 Extragal®

Wheel web in hot rolled Dual Phase 600 - Patented VersaStyle® wheel from Hayes Lemmerz International

ArcelorMittal has an extensive database on the forming and service characteristics of the entire range of Dual Phase steels. To integrate these steels at the design stage, a team of experts is available to carry out specific studies based on modeling and testing.

Designation and standard

 EuronormsVDA 239-100
FF 280 DPHCT500X (+Z)CR290Y490T-DP (-GI)
Dual Phase 450HCT450X (+ZE,+Z,+ZF)
Dual Phase 500HCT490X (+ZE,+Z)CR290Y490T-DP (-UNC,-EG,-GI)
Dual Phase 600HCT590X (+ZE,+Z,+ZF, +ZM)CR330Y590T-DP (-UNC,-EG,-GI,-GA,-ZM)
Dual Phase 780 Y450HCT780X (+ZE,+Z,+ZF)CR440Y780T-DP (-GI,-GA)
Dual Phase 780 LCE Y450HCT780X (+ZE)CR440Y780T-DP (-UNC,-EG)
Dual Phase 780 Y500
Dual Phase 780 LCE Y500
Dual Phase 980 LCE Y600HCT980X (+ZE,+Z,+ZF)CR590Y980T-DP(-UNC,-EG,-GI,-GA)
Dual Phase 980 LCE Y660
Dual Phase 980 Y700HCT980XG (+ZE)CR700Y980T-DP (-UNC,-EG)
Dual Phase 980 LCE Y700HCT980XG (+ZE,+Z, +ZF)CR700Y980T-DP (-UNC,-EG,-GI)
Dual Phase 1180HCT1180G2 (+ZE)CR900Y1180T-CP (-UNC,-EG)
Dual Phase 600HDT580XHR330Y580T-DP (-UNC)
Dual Phase 780
 

Euronorms
Uncoated (EN 10338 :2015): Steel grade name
Electrogalvanized (EN 10338 :2015 + EN 10152 :2009): Steel grade name+ZE
Galvannealed (EN 10346 :2015): Steel grade name+ZF
Extragal® (EN 10346 :2015): Steel grade name+Z
Zagnelis® (EN 10346 :2015): Steel grade name+ZM

VDA 239-100
Uncoated: Steel grade name-UNC
Electrogalvanized: Steel grade name-EG
Galvannealed: Steel grade name-GA
Extragal®: Steel grade name-GI
Zagnelis®: Steel grade name-ZM

 
 Hot rolled     Cold rolled

FF 280 DP (Full Finished): grade specially developed for skin parts.

LCE: Low Carbon Equivalent grade used to optimize properties in service.

The above indicative table summarizes the European and VDA standards corresponding to the ArcelorMittal product range.

While the ArcelorMittal grades conform perfectly well to the indicated EN standards, ArcelorMittal grades generally offer tighter mechanical properties (see table below).

Technical characteristics

Mechanical properties
Guaranteed for 20x80 mm ISO tensile specimens (uncoated sheet)

ST - Transverse direction (perpendicular to the rolling direction) / SL - Rolling direction

 YS (MPa)UTS (MPa)ef (%)
L0 = 80 mm
th < 3 mm
Ef (%)
L0 = 5,65 √S0 (mm)
th ≥ 3 mm
nBH2 (MPa)Direction
 FF 280 DP*300 - 380≥ 490≥ 250,1530ST
 Dual Phase 450280 - 340450 - 530≥ 270,1630ST
 Dual Phase 500300 - 380500 - 600≥ 250,1530SL
 Dual Phase 600330 - 410600 - 700≥ 210,1430SL
 Dual Phase 780 Y450450 - 550780 - 900≥ 150,1030SL
 Dual Phase 780 LCE Y450450 - 550780 - 900≥ 150,1030SL
 Dual Phase 780 Y500500 - 600780 - 900≥ 130,1030SL
 Dual Phase 780 LCE Y500500 - 600780 - 900≥ 130,1030SL
 Dual Phase 980 LCE Y600600 - 750980 - 1100≥ 1030ST
 Dual Phase 980 LCE Y660660 - 830980 - 1100≥ 1030ST
 Dual Phase 980 Y700700 - 850980 - 1100≥ 830SL
 Dual Phase 980 LCE Y700700 - 850980 - 1100≥ 830SL
 Dual Phase 1180900 - 1100≥ 1180≥ 530SL
 Dual Phase 600330 - 460580 - 670≥ 22≥ 2430SL
 Dual Phase 780*≥ 450≥ 750≥ 15≥ 1830SL
 
 Hot rolled     Cold rolled

* The guarantees for this grade are subject to change.

FF 280 DP (Full Finished): grade specially developed for skin parts.

LCE: Low Carbon Equivalent grade, used to optimize properties in service.

Chemical Composition (%)

 CMnSi
 MaxMaxMax
FF 280 DP0,141,60,40
Dual Phase 4500,081,60,40
Dual Phase 5000,141,60,40
Dual Phase 6000,142,10,40
Dual Phase 780 Y4500,172,20,60
Dual Phase 780 LCE Y4500,102,00,40
Dual Phase 780 Y5000,172,20,60
Dual Phase 780 LCE Y5000,102,00,40
Dual Phase 980 LCE Y6000,112,90,70
Dual Phase 980 LCE Y6600,112,90,70
Dual Phase 980 Y7000,182,40,60
Dual Phase 980 LCE Y7000,112,90,70
Dual Phase 11800,182,40,60
Dual Phase 6000,091,00,25
Dual Phase 7800,091,00,30
 
 Hot rolled     Cold rolled

FF 280 DP (Full Finished): grade specially developed for skin parts.

LCE: Low Carbon Equivalent grade, used to optimize properties in service.

Dual Phase 600

Dual Phase 980 Y700

The service properties of Dual Phase steels are guaranteed by the controlled manufacturing process. The controlled (temperature, cooling speed) annealing cycle in particular ensures achievement of the Dual Phase microstructure and reproducibility of mechanical properties.

Available coatings and surface conditions

 UncoatedElectrogalvanizedExtragal®GalvannealedZagnelis®Jetgal®
 EURNAMSAMRSACHIEURNAMSAMRSACHIEURNAMSAMRSACHIEURNAMSAMRSACHIEURNAMSAMRSACHIEURNAMSAMRSACHI
Dual Phase 450                          
FF 280 DP / Dual Phase 500                       
Dual Phase 600               
Dual Phase 600 Y420                   
Dual Phase 780 Y450                    
Dual Phase 780 LCE Y450, Y500                         
Dual Phase 780 Y500                        
Dual Phase 980 Y600                             
Dual Phase 980 LCE Y600                 
Dual Phase 980 LCE Y660, Y700                    
Dual Phase 980 Y700                           
Dual Phase 1180                    
Dual Phase 600                           
Dual Phase 780                             

 Hot rolled     Cold rolled

Available in non-visible part quality Undergoing customer testing Under development Available in visible and non-visible part quality (Z)

EUR : Europe Region - NAM : North America Region - SAM : South America Region - RSA : South Africa Region - CHI : China

X available / O under development

FF 280 DP (Full Finished): grade specially developed for skin parts.

Please inquire about the availability of products shown as being under development or left blank in the table.

LCE: Low Carbon Equivalent grade, used to optimize properties in service.

Recommendations for use and secondary processing

Forming
Dual Phase steels offer an excellent combination of strength and drawability as a result of their good ductility and strain hardening capacity from the beginning of deformation, which ensure homogeneous strain redistribution and reduce local thinning. For example, in Dual Phase 500, the yield strength increases by about 120 MPa after 2% of plastic strain in uniaxial tension (a phenomenon known as work hardening or WH2). The yield strength can be further increased through bake hardening (BH2) after paint curing.

 

FF 280 DP can also be used to manufacture skin parts, as a result of its excellent biaxial and uniaxial stretch formability.

 

Dual Phase steels can be drawn on conventional tools, provided the settings are properly adjusted. For example, drawing pressure should be increased by approximately 20% for a Dual Phase 600, compared to a micro-alloyed (HSLA) type steel of the same thickness. It should be noted that these steels, especially the highest grades, are sensitive to the so-called springback phenomenon. Component geometry must be carefully studied during design (small die radius, reinforcement perpendicular to bends to stiffen open parts, etc.) and drawing sequence definition (overbending, calibration tool, punch stroke, increased blank-holder force, etc.).

ArcelorMittal has developed expertise in controlling springback by means of part and drawing tool design (OUTIFO method).

Forming limit curves for the cold-rolled Dual Phase family of steels (typical data)

For more information about the forming of Dual Phase steels in special thicknesses and with special coatings, please consult us.

Welding

Although Dual Phase steels are more highly alloyed than HSLA steels, they can be readily welded using conventional resistance spot welding processes, provided the parameters used in industrial conditions are adjusted. The table below gives indicative examples of spot weld properties for homogeneous Dual Phase steel joints complying with the ISO 18278-2 standard.

 CoatingThickness (mm)Nugget diameter (mm)Pure tensile (kN)Weld diameter (mm)Tensile-shear (kN)
Dual Phase 500-1.5814.28.818.4
Dual Phase 600Extragal®1.57.713.19.522.3
Dual Phase 780Extragal®1.58.910.59.425.6
Dual Phase 780 LCE-1.57.614.36.622.7
Dual Phase 980 LCEExtragal®1.58.413.210.130.4
Dual Phase 600-311.632.611.246.7
 
 Hot rolled     Cold rolled

For coated (galvanized and alloy galvanized) products, electrode life tests show values characteristic of the type of coating considered, with no significant modification due to the Dual Phase substrate.

 

In butt or lap MAG (Metal Active Gas) arc welding, maximum hardness in the fusion zone does not exceed 300 HV for a Dual Phase 600, whatever the parameters. The weld seams meet ISO 25817 Class B requirements. Recommended welding consumables are:

  • Filler: G3Si1 NF EN 440;
  • Protective gas: Ar + 8% CO2.

Dual phase steels have excellent mechanical strength in laser lap welding. Based on long shop-floor experience in characterizing its products, ArcelorMittal can provide technical assistance in adjusting the welding parameters for steels in the Dual Phase range.

Fatigue strength

As a result of their high mechanical strength, Dual Phase steels have good fatigue properties. Examples of Wöhler curves for a variety of Dual Phase steels are given in the two graphs below. The curves plot maximum stress versus number of cycles to failure. They are calculated for two loading ratios: tension-compression R=-1 and tension-tension R=0.1.

Wöhler curves or S-N curves for a variety of Dual Phase steels

The graph below shows the low-cycle fatigue or E-N curves for the same steels. The curves plot strain amplitude versus number of reversals to failure (one cycle corresponds to two reversals). Other high and low cycle fatigue data can be provided on request.

ArcelorMittal can make a Dual Phase steel fatigue database available to its customers.

Impact strength

As a result of their very high tensile strength, Dual Phase steels are particularly suitable for parts designed to absorb energy during an impact.

 

Dual Phase steels have been characterized in dynamic axial compression tests using an top hat structure with a spot-welded closure plate at an impact velocity of 56 kph. These tests have demonstrated the good impact behavior of these steels.

Mass reduction potential compared to that of an HSLA 380 steel (reference)

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