Ultra High Tensile Strength Steel with High Formability

Vehicle weight and size have been increasing in recent years with the pursuit of safety and comfort. Weight reduction is an unavoidable path for auto manufacturers, in order to improve fuel consumption and reduce CO2 emissions. Nissan has dedicated itself to developing new materials to reduce a vehicle’s overall weight. In order to simultaneously clear the two issues of “reducing vehicle weight to reduce environmental impact” and “improving collision safety”, Nissan has focused on using high tensile strength steel in their vehicle body structures. The results are body structures that are not only strong but also highly formable.

In 2013, Nissan succeeded in developing a 1.2 Gpa ultra high tensile strength, high-formability steel that was stronger than conventional high tensile steels. This new material was first used in the Infiniti Q50 midsize sedan.

In 2018, Nissan developed and introduced a 980 MPa ultra high tensile strength, high-formability steel that featured further improvements to collision energy absorption performance. This material was used in the Infiniti QX50 premium midsize SUV.

Research and development efforts such as Ultra High Tensile Strength Steel have resulted in further reducing vehicle weight and improving collision safety.

• As a general rule, when the strength of high tensile steel is increased, its elongation capacity decreases. A decrease in elongation capacity can cause cracking during cold-press forming. Because prior high tensile strength steels were unable to withstand cold-pressing into complex shapes, they were used only for a limited number of parts.
• The advantage of 1.2-GPa Ultra High Tensile Strength Steel with High Formability is to have both high strength and elongation capacity. By precisely controlling the material’s structure on the sub-micron level through a new heat treatment process, it can be utilized for many more body structure parts than previously possible.
• A spot welding method suitable for 1.2-GPa Ultra High Tensile Strength Steel with Formability has also been developed. The new welding method makes it possible to use this steel for “Safety Zone” structure parts, such as the center pillar reinforcement, front roof rails, and side roof rails, meant to protect vehicle occupants in the event of a collision.
• For the newly developed 980-MPa Ultra High Tensile Strength Steel with High Formability, a more finely tuned heat treatment process that gives the material high energy absorption performance was achieved. As a world-first, Nissan began using this material on the front side members, rear side members, and other “crushable zone” frame parts that require high collision energy absorption. This material has the same level of formability as conventional 590-MPa steel, and can be used for parts with more complex shapes.

Nissan has established a target of using Ultra High Tensile Strength Steel with High Formability in 25% or more of the gross weight of body parts. Nissan is actively moving forward with the development of technologies for applications of high strength steel and expands its use in the Nissan model line-up.