Enhanced edge ductility through exceptional fracture toughness  

As the automotive industry is always in search of lightweight solutions, part designers tend to upgrade to higher strength levels, such as 800 MPa where weight savings of around 15% are achievable over HR420LA. That’s why they are constantly pushing the boundaries with more advanced and creative designs.
In the case of chassis parts, this entails complex shapes with deeper holes and more intricate flanges, compensating for the use of thinner material in terms of stiffness and durability. These innovative designs place substantial demands on the material, posing increasing challenges for manufacturability. In particular, edge-cracking is one of the most common pain points of press shops when forming chassis parts.

Therefore, there is a pressing need for further enhanced, so-called, ‘edge ductility’. Dr. Arjan Rijkenberg, Principal Scientist - high strength strip steels at Tata Steel Nederland, explains, "Current high ductile steels rely upon their very high hole-expansion capacity (HEC), but they can still encounter edge failures during forming, implying that there is a critical factor for the required edge ductility beyond HEC: fracture toughness. Understanding the pivotal role of fracture toughness in achieving true edge ductility, we conducted a research into the relationship of HEC and fracture toughness. Our findings have played a pivotal role in the development of HyperFlange."

Recognising the importance of fracture toughness, Tata Steel has developed two highly effective and practical in-house tests which assess crack susceptibility and offer a means of measuring the fracture toughness of steels.Their tests have shown the exceptional fracture toughness of CP800 HyperFlange compared to standard HSLA HR700LA. In combination with its outstanding typical HEC of 70%, this results in superior edge ductility for the new chassis steel, as proven through extensive deep drawing tests, indicating that CP800 HyperFlange demonstrates significantly higher resistance to crack growth than HSLA HR700LA. Moe Ziaran, Marketing Manager – Automotive Chassis & Components, adds, "Through our HyperFlange products, we have optimised our steels to enhance edge ductility. This translates to fewer edge cracks, minimised material wastage, and reduced production line interruptions, all contributing to heightened productivity and efficiency in the car makers' press shop. As a result, chassis engineers can have confidence that their advanced lightweight designs will not only pass simulations but can also be reliably manufactured."

Availability and future developments

Tata Steel has started offering its CP800 HyperFlange in large width and thickness ranges, with an upcoming GI (galvanised) variant in development. With continued support from Tata Steel’s expert team, the company ensures seamless integration into production lines.

For more information, or to inquire about availability, please contact Tata Steel’s HyperFlange experts.