Recognizing the benefits of the concept, the firm has decided to expand to 600- and 1000-MPa Hyperform grades. “In fact,” Berkhout explains, “we now have started to upgrade one of our newest galvanizing lines to enable us to develop the HyperForm 1000-MPa grade. We see this grade family as falling between the DP steels and the extra-ductile (ED) quenched and partitioning (Q&P) grades in terms of formability. We’ll position it as a workhorse for future vehicles.”
How do these steels gain their extra formability and weldability? By fine-tuning the steel recipe and optimizing the annealing curve.
“The goal has been to make the grades lean in terms of composition—low silicon to ensure good weldability, and relatively low carbon content,” Berkhout says. “Then the annealing curve is optimized to enable us to develop a microstructure capable of very high work-hardening rate. At 600 MPa, for example, the elongation is at least 6 percent higher than a conventional DP600 steel. So, for example, replacing a 300-MPa HSLA grade with DP600-GI HyperForm we can reduce part weight by 10 to 15 percent.”
Nucor on the Move
Speaking of new galvanizing lines boosting steelmakers’ capabilities, Nucor, which has a large portfolio of automotive grades, recently completed a new galvanizing line at its facility in Gallatin, KY. That plant now can produce galvanized automotive products to 8.5 mm thick. The recent expansion of the mill nearly doubles its capacity, producing hot-rolled coated and uncoated steels to 1865 mm wide.
Ready for Viewing: Great Designs in Steel Agenda, Highlighting EV Architectures It's time to start planning your day for Great Designs in Steel 2023, coming May 24. A preliminary agenda now is available (tinyurl.com/ecxbc723), featuring keynote speakers Lourenco Goncalves, Cleveland-Cliffs chairman, president and CEO; and Chris Michaels, General Motors director of global body structures and integrated systems. Presentations are organized into three tracks—EV Architecture, Materials, and Welding/Joining/ Manufacturing. Among the presentations slated for the Materials Track:
It's time to start planning your day for Great Designs in Steel 2023, coming May 24. A preliminary agenda now is available (tinyurl.com/ecxbc723), featuring keynote speakers Lourenco Goncalves, Cleveland-Cliffs chairman, president and CEO; and Chris Michaels, General Motors director of global body structures and integrated systems. Presentations are organized into three tracks—EV Architecture, Materials, and Welding/Joining/ Manufacturing.
Among the presentations slated for the Materials Track:
In addition, Nucor’s new specialty cold-rolling complex, opened late in 2019 in Hickman, AR, increased the mill’s cold-rolling capacity by 500,000 tons, with a robust reversing mill capable of producing AHSS grades with far fewer passes and to lighter gauges, according to Nucor officials. That facility’s Flex galvanizing line can produce 3rd Gen AHSS grades, coated and uncoated. With an added galvanizing capacity of 500,000 tons/yr., it also has an over-aging section capable of producing Q&P grades.
Lastly, Nucor is building a new 3-million-ton sheet mill in Mason County, WV, capable of producing 2133-mm-wide hot band and 1930-mm-wide cold-rolled sheet on its tandem mill. It will have two galvanizing lines, MetalForming is told, one dedicated to automotive. This new mill is well-located, Nucor officials say, to serve the Midwest and Northeast regions, and will have one of the lowest carbon footprints of any steel facility in the world.
New DP Grade from Big River Steel (U.S. Steel) Earns Steelie Award Nomination
Earning a 2022 nomination for Innovation of the Year from worldsteel (the World Steel Association): the Big River Steel subsidiary of U.S. Steel, for its development of a single phase nano-precipitation strengthened batch-annealed SP590 sheet steel with reportedly outstanding formability and marketed as a low-cost, greener DP590 alternative. The high-strength highly formable sheet steel has been developed with very low-carbon lean alloying, the company reports, using an innovative fine-grained single-phase ferritic microstructure strengthened with TiC nano precipitates. It provides a hole-expansion ratio of 80 to 110 percent (a hole-expansion ratio of 90 percent and above has been registered for a sheet thickness of 1.2 mm) and tensile strength similar to DP 590, reportedly with formability properties far exceeding that of DP590 or any steels with similar strength. The steel has been commercially produced and successfully used in critical autobody structural components such as seat side supports.
Touted as U.S. Steel’s most advanced AHSS grade: 980 XG3, a 980-MPa tensile-strength 3rd Gen grade touted as a potential replacement for press-hardenable steels with reportedly identical crash performance and part weight. 980 XG3 has an excellent combination of strength and ductility, say company officials, excellent weldability, a low yield-to-tensile ratio (< 0.7) and total elongation consistently above 20 percent. Applications include A- and B-pillar outers and inners, roof headers, rear rails and hinge pillars.
Hyundai Steel’s New 1.8-GPa Hot-Stamped Steel Also Earns worldsteel Recognition
Also earning a worldsteel 2022 Steelie Award nomination for Innovation of the Year: Hyundai Steel, for its development of a 1.5-GPa hot stamping steel. Early in 2022 the firm announced its ability to mass-produce what it says is the world’s first 1.8-GPa hot stamping steel, developed in association with the Hyundai Kia Namyang R&D Center. According to the firm’s press release, it is supplying the new steel product for Hyundai Motor’s new-generation Genesis G80 electric vehicle (G80EV) and the new Genesis G90.
The company started supplying the new steel to Hyundai Motor Co. in 2021 and it plans to supply as much as 145,000 sheets of steel every year, sufficient to produce about 30,000 EVs.
3rd Gen Grades from ArcelorMittal
Not to be outdone on the hot stamping front, ArcelorMittal, reportedly the first steelmaker to offer the automotive industry a coated press-hardened steel (Usibor 1500 and Ductibor 500), recently has introduced Usibor 2000 and Ductibor 1000.
Usibor and Ductibor have aluminum-silicon pre-coating, developed to protect the steel from oxidation (scale) and decarburization during hot stamping, company officials note. The pre-coating is applied to the coils in a continuous process, similar to zinc coatings. Usibor 1500-GI galvanized Zn, Usibor 1500 and Usibor 2000-GA galvannealed ZnFe also are available.
For the last couple of years, ArcelorMittal has been bringing 3rd Gen steels to the automotive industry under the Fortiform brand. It offers the grades with tensile-strength levels ranging from 980 to 1470 MPa. From a datasheet issued in May 2022:
“The Fortiform/FortiformS/Gen 3 grades extend ArcelorMittal’s range of AHSS and UHSS steels. In comparison to first-generation DP steels (and first-generation TRIP steels), these steels exhibit higher formability at equivalent strength levels. They maintain a high level of bake-hardenability, which in combination with high strain hardening results in a substantial increase in the yield stress. These materials are particularly suitable for automotive safety parts with requirements for energy absorption at high strength levels. They can be used for front and rear rails, shotguns, sled runners and various cross-members that require shapes too complex for higher-strength DP grades and at strength levels lower than or comparable to press-hardenable steels. In particular, the hole-expansion characteristics supported by these grades make them suitable for applications with higher local formability (edge stretch) than can be typically supported by DP or TRIP grades.”
Posco, Kobe Focused on Multi-Material Solutions
The Posco (Pohang Iron and Steel Co.) Steel Solution Research Center, Automotive Material Research Center and Automotive Material Marketing Office are spurring the development of steel-centered multi-material technologies combining conventional materials such as steel, aluminum, stainless steel and plastic. According to a presentation in the firm’s online newsroom, it expects multi-material solutions to fit nicely into several EV applications, including battery packs and closures (aluminum for the outer panel of the closure and ultra-thin steel for inner panels).
South Korea-based Posco also has been focusing efforts on producing nonoriented electrical steel sheet used in EV motor cores, and in July 2022 it began the construction of a new plant in Coahuila, Mexico, its first North American factory. MF
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