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Dual phase with high formability/ductility for crack-free cold deep drawing

Dual phase with high formability/ductility (DH) steels are TRIP-assisted, 3rd Generation automotive steels with high global and local formability and good resistance to edge cracking. DH steel have excellent energy-absorbing properties, included reserved ductility during crash impact. DH grades are ideal for complex geometries, including cold deep drawing. DH steel's FLDs and HERs are superior to DP steels, enabling scrap reduction and more streamlined stamping.

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    What is dual phase with high ductility steel?

    Dual phase steels with high formability (DH) use a multiphase microstructure with a ferrite matrix holding martensite, bainite and retained austenite. Unlike conventional dual phase steels, DH steel’s hardening rate persists at higher strains levels. This is because DH’s larger quantity of retained austenite is transformed into martensite at a progressively increasing rate of work hardening under higher strains.


    With its substantially higher strain hardening rate (n-value), TRIP-assisted 3rd Gen steels like DH provide distinctly improved formability in stretch deformation compared to DP grades. TRIP-assisted DH steels provide high ductility for manufacturing automotive safety components with complex geometries. Plus DH steels supply superb and progressive crash-energy absorption — via high strain hardening — during crash deformation.

    Steel properties

    • High global and local formability, with higher elongation and higher resistance to edge cracking than conventional DP.
    • Stellar crash performance, with ductility left in the steel for additional energy absorption.
    • Greater design flexibility: enables deep drawing of complex geometries with secondary forming.
    • Highly resistant to compression failure.
    • UHSS strength levels with improved FLD and HER performance compared to conventional DP.
    • 3rd Gen AHSS allows for simplified, cost-effective, cold forming of complex auto parts.
    • Very good RSW weldability, comparable to conventional DP grades.
    • Enables lighter, more complex BIW components — with less risk of edge cracking compared to DP.

    What problems do Duel Phase steels with high formability solve?

    Designs at, or near, their stamping limits can benefit from Docol DH steels. DH’s higher “reserve” ductility can also be a problem solver when a design needs additional energy absorption for crash performance.

    • A-pillars, upper B-pillars, and pillar reinforcements
    • Cross members and cross beams
    • Dashboard panels
    • Floors, sills, and reinforcements
    • Passenger safety cage
    • Rails: roof, side, front and rear; frame rails; and reinforcements
    • Seat frames

    Find more DP steels here.

    Additional application ideas
    Dual phase steel with high formability for automotive applications
    Customer case story

    Streamlined stamping of high flanges with near 0% defects

    In 2018, a well-known Tier 1 automotive parts manufacturer had two new designs featuring lightweight-yet-strong stamped vertical links. The UHSS parts’ high flanges, however, increased the risk of cracked edges — and the Tier 1 wanted the lowest possible scrap rate.

    The manufacturer approached the SSAB team, requesting a highly formable, highly consistent steel in 1.5 mm and 2.2 mm thicknesses. The new Docol 600DH-GI, a 3rd generation steel, delivered high formability for the stretched edges, with an almost 0% cracked edge/scrap rate due to SSAB’s highly consistent mechanical properties from coil to coil.

    “The Docol DH grades have higher FLDs compared to our conventional DP steel and they perform better in the plane strain,” notes Matti Säily, Product Manager for metal-coated products at SSAB.

    Read more about this near-flawless AHSS forming
    Stamping of dual phase steel with high formability

    Grades and mechanical properties

    Metal coated Docol® 600DH-GI and 800DH-GI are two of the steel grades now avaliable and more are on the way.

    DA special heat treatment producing mainly two-phase structure makes Docol® 600DH-GI and 800DH-GI suitable where an improved formability is requested compared to conventional dual-phase steel grades with the same tensile strength level.

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      Product Family Product name Coating Dimensions Standards Datasheet
      Docol 600DH Docol CR​330Y​590T-​DH GI T: 0.80 - 2.40 mm
      W: Up to 1400 mm      T: 0.031 - 0.0945 in
      W: Up to 55.12 in             		SSAB

      Docol 600DH
      Docol 800DH Docol CR​440Y​780T-​DH GI T: 0.80 - 2.00 mm
      W: Up to 1400 mm      T: 0.031 - 0.0787 in
      W: Up to 55.12 in             		VDA 239-100

      Docol 800DH
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      Comparison

        What forming operations can you use for dual phase with high ductility steel?

        • Excellent cold forming, using either roll forming or conventional equipment.
        • Cold deep drawing and secondary forming, like stretched edges, are possible because of DH’s higher elongation.
        • Stamping is more efficient during roll changes due to Docol DH’s high homogeneity.
        • Good RSW weldability, similar to our DP steels.
        • Improved FLP and elongation compared to conventional DP steels.
        • More resistant to edge cracking on stretched formed edges on complex shapes.

        Do you have forming questions about DH grades and how they compare to Docol DP grades? Our Technical Support can provide specific DH steel stamping, drawing, and forming guidance for your automotive component.

        Contact our tech support
        Forming of dual phase steel with high formability

        More benefits from Docol dual phase with high ductility

        • Improved strength-to-weight ratios.
        • Extremely consistent mechanical properties from coil to coil for streamlined stamping.
        • Superior formability means less edge cracking and the potential for near 0% scrap rate.
        • Ideal for deep-drawn, high-flanged, complex shapes used in your innovative crash components.
        • Two cold-rolled “strength families” commercially available now: Docol 600DH-GI and Docol 800DH-GI.
        • Docol 1000DH-GI is in development.

        OEM-specific dual phase with high formability steels

        Individual Docol DH steel grades can be modified to OEM specifications or made to globally recognized standards, such as VDA 239-100:2016, or SSAB’s own high internal standards. For optimal component production efficiency and crash performance, we encourage you contact our team early in your design process.

        Custom AHSS for automotive OEMs

        What are the advantages of DP with high ductility steel?

        Safety engineers: Outstanding energy-absorption, with “reserved ductility” providing progressively higher amounts of absorption at higher impacts.

        Lightweighting engineers: With higher strength grades, BIW components can be made lighter with a low risk of cracked edges.

        Production engineers: Realize near defect-free stamping, even for complex geometries with stretched edges, high flanges, deep drawing, etc. Excellent consistency, from roll-to-roll, of mechanical properties.

        Buyers: Downgauging with higher strength DH grades means you buy less material — and that material is more efficiently stamped, with greatly reduced scrap rates.

        Future-proof your life cycle assessment

        Lessen your CO2 content

        Docol dual phase steel with high formability is "future-proofed".
        TRIAL MATERIAL STOCK

        DH steel samples

        With our Trial Material Stock Center, you can get AHSS samples for most of our commercially available steels – as well as samples for our newest but not yet commercially released grades. Unique to the industry, we ship coils, sheets and custom lengths of any size. In 1 to 2 weeks, your material is ready for dispatch to anywhere in the world.

        Request trial material
        Expand all

        What is dual phase with high ductility steel?

        Dual phase steels with high formability/ductility have a multiphase microstructure featuring a ferrite matrix with martensite, bainite, and a significant amount of retained austenite. But unlike conventional DP Grades, DH steel’s hardening rate persists at higher strain levels.

         

        Why use dual phase with high ductility steels?

        These 3rd Generation, TRIP-assisted advanced steels have hardening rates that persist at higher strain levels, providing excellent crash performance. Their high global and local formability and resistance to edge cracking make DH steels ideal for complex geometries.

        Where is dual phase with high formability steel used?

        Docol DH steels can be a problem-solver for designs at, or near, their stamping limits, or when higher “reserve” ductility is needed for additional energy absorption for crash performance.

         

        What is the formability of dual phase with high ductility steels?

        • Excellent cold formability, using conventional equipment or roll forming.
        • DH’s higher elongation provides for cold deep drawing, including secondary forming operations like stretched edges.
        • Highly homogenous from roll to roll – improves stamping efficiencies during roll changes.

        FAQ

        Other steel categories

        • martensitic steel coil

          Martensitic steel: excellent formability-to-strength ratio

          Martensitic steel combines tensile strengths up to 1700 MPa with good ductility, making it highly efficient for both vehicle lightweighting and improved crash protection — especially in anti-intrusion zones.

        • Press hardening steels (PHS) for complex shapes

          Press hardening steels have four major advantages: they can be formed into very complex shapes, their ultimate tensile strength ranges up to 2000 MPa (290 ksi), there is little or no springback, and, with tailored tempering, you can combine “full hard zones” and “soft zones” for multi-function crash performance within a single part.

        • Docol complex phase steel

          Complex phase (CP) steels for the highest hole expansion ratios

          Complex phase steels have the highest — up to 100% — hole expansion ratios available from advanced high strength steels. Their high HER values provide excellent cold-forming properties for punched and stretched edges/flanges, as well as deep-drawn shapes. CP steels’ superior yield strengths are used for high crash-energy absorption, while their elevated UTS levels enable thinner walls for significant automobile weight reductions.

        • Dual phase (DP) steel: excellent ductility and energy absorption

          Dual phase automotive steels have an excellent balance of ductility, high tensile strengths, easy cold formability, and very good crash energy-absorption. Its high early-stage strain hardening (n-value) makes DP steel resistant to local necking due to strain redistribution — providing highly uniform elongation. Dual phase steel’s low yield-to-tensile-strength ratio creates high global formability for deep-drawing and high-stretching capacities — all with good weldability.

        • Docol High Edge ductility

          High edge (HE) ductility HSLA steel

          High edge ductility HSLA steel with greatly improved local formability and high hole expansion ratios – ideal for challenging auto components with complex designs on sheared stretched edges.

        • High strength, low alloy (HSLA) steels for cost-effective automotive lightweighting

          High strength, low alloy steels are a cost-effective choice for increasing strength-to-weight ratios when compared to conventional mild carbon steels. HSLA steels also have excellent bendability and weldability and can increase the strength and/or decrease the weight for a variety of body-in-white and chassis automotive components, including suspensions, beams, and subframes.

        • Ferritic-Bainitic steel: stretch edge flangeability for cold-forming

          Ferritic-Bainitic are multi-phased steels with high hole expansion ratios and good edge stretch capabilities. FB steels are suited for cold-formed and punched flanges when lightweighting automotive components such as wheels, cross members, and other structural parts.