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 more streamlined stamping and scrap reduction.

    DH steel basics

    Dual phase steels with high formability have a multiphase microstructure featuring a ferrite matrix with martensite, bainite — and a significant amount of retained austenite. As with more traditional dual phase steels, deformation of DH creates a high work-hardening rate. But unlike conventional DP grades, 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.

    Auto applications for DH steels

    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.

    • 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.

    Body in white
    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.

    streamlined stamping

    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 CR330Y590T DH GI T: 0.80 - 2.40 mm
      W: Up to 1400 mm
      SSAB

      Docol® 600DH

      Docol 800DH Docol CR440Y780T DH GI T: 0.80 - 2.00 mm
      W: Up to 1400 mm
      VDA 239-100

      Docol® 800DH

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      Comparison

        Forming Docol DH automotive 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.
        • 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.

        Forming Docol steel

        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.

        DH benefits for each department

        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.

        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.

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