Ultra-High Strength Steels (UHSS): what are they and how they improve vehicles

Historically, WorldAutoSteel used the following definitions based on minimum tensile strength:

≥ 550 MPa TS: advanced high-strength steels (AHSS)
≥ 780 MPa TS: ultra-high strength steels (UHSS)
≥ 1000 MPa or 1 GPa TS: GigaPascal steels

However, WorldAutoSteel’s 2021 AHSS Application Guidelines puts the minimum tensile level for AHSS steels at 440 MPa, while acknowledging no agreed-upon level for UHSS steels. It could be that the less frequently used term “GigaPascal” will become more popular because there is no ambiguity regarding its definition: steels with tensile strengths of 1000 MPa or greater.

The metallurgical types of steels capable of achieving UHSS strengths can include:

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

If there is no generally accepted definition for ultra-high strength steel, why even use the term? The answer is that “UHSS” is useful for both steelmakers and automakers as shorthand for designating stronger AHSS steel grades.

And as UHSS steels continue to increase in strength, more thought has to go into how they are formed into car parts, including anticipating issues such as springback. That said, most of these forming issues can be addressed through the proper selection of UHSS steel properties, advanced forming simulations, correct tooling parameters, and car part design.

AHSS/UHSS steels enable automakers to optimize their body-in-white designs several ways: better impact protection, enhanced lightweighting and energy efficiency, increased vehicle capacity and performance, and improved sustainability when from highly CO₂-efficient steel mills or recycled sources.

Higher strength steels do require more design and pre-production planning. That’s why our AHSS/UHSS experts can help you optimize your designs by modeling product performance, forming, and joining.

And we have in-house steel production technicians to advise you every step of the way, whether your AHSS/UHSS fabrication includes cold forming, 3D roll forming, tailor welding blanks or coils, or hot-stamping of PHS steels.

Joining conventional steels to AHSS steels? Have questions about spot resistance welding or laser welding of AHSS? Check out our AHSS/UHSS Welding Guidebook.

Looking to use mixed materials, and possibility structural adhesives, with AHSS/UHSS steels? We can help with all of your AHSS/UHSS joining needs.