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

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.

• 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.

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.

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.

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.

• 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.

• 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.

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.

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.