Advanced High-Strength Steels (AHSS) definitions, nomenclature and evolving categories

Some of the most popular metallurgical types of steels capable of achieving AHSS tensile strengths include:

• Martensitic (M)
• Press Hardening Steel (PHS, aka hardenable boron steel, aka “hot stamped” steel)
• Complex Phase (CP)
• High Edge Ductility (HE)
• Dual Phase (DP)
• Dual Phase with High Formability (DH)
• Ferritic Bainitic (FB)

The original nomenclature for advanced high-strength steels included their metallurgical type and minimum tensile strength; e.g., “DP500” for dual phase 500 MPa. For brevity, strength numbers can be “rounded up” when discussing a group of steels with similar characteristics.  

To determine a specific grade’s actual value, look at its full steel grade name: for example, “CR290Y490T-DP” describes a DP500 steel with an actual minimum tensile strength of 490 MPa (the “490T”), as well as its minimum yield strength of 290 MPa (the “290Y”).

In any case, automakers buy steels to meet either their own custom AHSS specifications, or specific national or international AHSS standards, and they clearly delineate the AHSS properties, including the minimum yield and tensile strengths.

Also note that AHSS steels’ predecessor – high-strength, low-alloy steels (or HSLA) – used designations, for example HSLA 430, that referenced the grade’s minimum yield strength and not its tensile strength.

An additional nomenclature consideration is that HSLA steels (which are sometimes further abbreviated to just “LA” in their product names) have progressed to the point where their minimum tensile strengths exceed the 440 MPa level, qualifying them for the AHSS designation.

As steel manufacturers use increasingly sophisticated processes to develop new AHSS steels, including 3rd generation AHSS steels, the old metallurgical categories don’t always fit. For example, some new grades exhibit attributes from more than one of the traditional metallurgical categories. Or the new steels don’t fit neatly into the current international standards’ definitions of metallurgical categories.

To counter this, some steelmakers are coming up with new AHSS designations based on AHSS properties such as formability or usability, such as High Edge (HE) ductility or Dual Phase with High Formability.

Another change in AHSS terminology is the increased use of the phase “ultra-high strength steel”. UHSS has become useful shorthand to mean AHSS steels that have (depending on who you’re speaking to) two or three times higher minimum tensile strength levels than the original AHSS level of 440 MPa.

Visit our UHSS page to learn about the highest strength steels, as well as how AHSS/UHSS steels in general can make your vehicles stronger, lighter, safer, and more sustainable.