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

Complex phase steels have a bainite-ferrite microstructure with small amounts of martensite and retained austenite and pearlite. The thermal cycles used to produce CP retards recrystallization while promoting different carbo-nitride precipitations, resulting in extreme grain refinements for excellent ductility, even for high (e.g., 1200 MPa or 174 ksi) tensile strength grades.

The carbo-nitride precipitations also increase complex phase steel’s ferrite strength; as a result, CP steels have higher yield strengths than dual phase (DP) steels at equivalent tensile strength levels. Complex phase steels’ high yield strengths are used by body-in-white designers for high crash-energy absorption for safety components, such as in frame rails, reinforcements, beams, and more.

• Up to 100% hole expansion ratios — significantly reduce or eliminate micro cracks and burrs on cut/sheared edges.
• Greatly increases local formability, providing ductility for deep-drawn components with complex geometries.
• Excellent for energy-efficient cold-forming and fineblanking of auto parts with complex, punched edges.
• Improved cleanliness and grain refinement provides tight radii bendability and stretch flangeability even at very high yield strengths.
• Excellent true fracture strain (local formability).
• High crash-energy absorption.
• Good fatigue resistance and durability.

To stretch or form cut edges that are crack-free can be a major challenge when working with advanced-high strength steels. To reduce the risk of cracked (raised) edges, SSAB is introducing two new versions of hot-rolled 800 megapascal steels with extremely high edge ductility.

Many of these steel properties should contradict one another: formability vs. high strength, high edge ductility vs. good crash performance. But these steels deliver all of these properties – and, especially, they deliver very high edge ductility.



These new high edge ductility AHSSs can step in as "problem-solvers". Or, they can be used on auto parts where you want higher confidence that you won't have cracked edges.

Hot-rolled Docol CP steels deliver good fatigue resistance and can be suitable for car parts subjected to dynamic alternating stress. For example, multilink suspensions, trailing arms, torsion beams and subframes.

Cold-rolled Docol CP applications include body-in-white applications, seat tracks and seat recliners.

Complex Phase (CP) steels have higher yield strength and lower work hardening effect, compared to DP steels for same strength level. The CP steels have good fatigue properties when it comes to low cycle fatigue. Compared to DP, the CP steels offer better flanging and ISO hole expansion performance and these steels are suitable for applications where high strength, good bendability and stretch-flange ability is required.

Docol^® Complex phase steel product offer:

• Outstanding ISO 16630 hole expansion ratios allow for crack-free forming of stretch flanging and stretch bending, as well as punched flanges.
• Improved cleanliness enables deep drawing and tight radius forming for complex part geometries.
• With exceptional bending properties and formability, these steels are suitable for cold forming of critical auto safety components.
• Ideal for fineblanking.
• Good weldability, including resistance spot welding and laser welding.

Do you have manufacturability questions about these grades? Our Technical Support can provide specific CP and HER steel forming guidance for your automotive component.

• Metal coatings for corrosion protection.
• Excellent uniform ductility (see our article about AHSS elongation and local formability).
• Bake-hardenable.
• Ideal for cold-forming crash relevant auto parts with complex shapes.
• Excellent for lightweighting critical structural car components without burrs or edge cracks.

Safety engineers: Complex phase’s high yield-to-tensile-strength ratio provides high crash energy absorption.

Lightweighting engineers: Achieve thinner and lighter parts by specifying higher strength grades of CP steels.

Production engineers: Deliver complex shape components – e.g., stretched flanges with punched holes and tight radii – with high repeatability. Fully leverage cold-forming operations to save energy and processing time while increasing production line flexibility.

Buyers: Buy less material as you greatly reduce the number of defective components due to cracked sheared edges.

Sustainability officers: SSAB’s iron-ore based steelmaking is so CO₂-efficient that our AHSS steels are equivalent to using recycled steel. And Fossil-Free Docol AHSS will be commercially available in 2026.

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.