Steel and auto collaboration: What's to come using 3rd generation AHSS

April 6, 2018
AHSS is the fastest growing material in automotive applications according to a 2015 report by Ducker Worldwide. Over the past five years, the amount of AHSS used each year in automotive applications has been 10 percent higher than forecasted. 

Lately within the repair industry, there has been conversation about all of the innovations regarding material applications for lightweighting new vehicles. With an increased use of mixed materials, the repair industry faces the challenge of establishing robust repair procedures for a wide range of body materials. One material that has gained a lot of attention and interest is advanced high-strength steel (AHSS). AHSS is the fastest growing material in automotive applications according to a 2015 report by Ducker Worldwide. Over the past five years, the amount of AHSS used each year in automotive applications has been 10 percent higher than forecasted.   

Steel’s evolution

Today there are more than 200 steel grades available (Figure 1), allowing automakers to use the right grade for the right application. This is a result of the collaborative efforts between the steel and automotive industries working together to develop innovative technology. Compared to a decade ago, today’s steel grades are as much as six times stronger. The added strength of AHSS allows automakers to deliver performance and safety benefits with lightweight products using their existing manufacturing infrastructure, eliminating major manufacturing costs associated with the introduction of alternative materials.  

A significant portion of steel innovation is in AHSS. Several categories of AHSS grades are possible through small changes in alloying elements combined with thermal-mechanical processing to deliver various mircostructures and properties. These distinct generations and classifications include: 

  • First-generation AHSS include dual phase (DP), ferritic-bainitic (FB), complex phase (CP), martensitic (MS), transformation-induced plasticity (TRIP) and hot-formed (HF). They offer significantly higher strengths as compared to conventional steels and some have improved formability as well. 
  • Second-generation AHSS have mainly austenitic microstructures and include austenitic stainless steel and twinning-induced plasticity (TWIP). They are extremely strong and formable and can be used to provide extraordinary mass reduction for difficult-to-form parts.  
  • Third-generation AHSS (3rd Gen AHSS) are currently being introduced commercially. These grades will mainly be multi-phased (MP) steels with high strength and increased formability compared to first-generation AHSS. 
Figure 1: There are more than 200 steel grades available, ranging from 200 to 2000 MPa.

3rd Gen AHSS 
To bridge the properties gap between the already developed first-generation AHSS and second-generation AHSS, as show in Figure 1, 3rd Gen AHSS are being developed to provide automakers a high-value steel solution. This new generation of steel shares the high-strength properties of AHSS, while also having a higher total elongation similar to high-strength steels. This also allows automakers the continued use of their current stamping and assembly infrastructures.  

There are many opportunities for 3rd Gen AHSS applications in vehicles, including: lightweighting through direct material substitution and thickness reduction, improved energy absorption through enhanced strength/elongation, and optimized geometries and part consolidation enabled by enhanced formability. Potential applications identified for maximum performance and weight reduction benefit include a- and b-pillars, roof rails, roof bows and underbody reinforcements to name a few. 

As with first- and second-generation AHSS, 3rd Gen AHSS applications will require different repair techniques. The automotive and steel industries are fully committed to working with the repair industry to inform these professionals on where AHSS are being applied within vehicles and the best ways to work with those steels based on their properties. Partnering with repair professionals will continue as 3rd Gen AHSS becomes more prominent in vehicle design. 

Integrated Computational Materials Engineering (ICME) Project

A testament to the industry’s interest in 3rd Gen AHSS, the United States Automotive Materials Partnership LLC (USAMP), a wholly owned subsidiary of the U.S. Council for Automotive Research LLC representing FCA US LLC, Ford Motor Company and General Motors, completed a four-year project in 2017. This project worked to develop an Integrated Computational Materials Engineering (ICME) model for 3rd Gen AHSS, shown in Figure 2.  

Figure 2: Volume elements (RVEs for 3rd Gen AHSS

The project, managed in collaboration with the Auto/Steel Partnership, was funded in part by a competitively solicited $6 million award from the U.S. Department of Energy (DOE) in 2012. The project’s goal was to create an ICME computer model to aid the steel industry in developing 3rd Gen AHSS used in manufacturing lightweight steel components to meet automotive mass savings, performance and safety requirements. The project was supported by five universities, three steel companies, two engineering firms, three automotive OEMs, and one national laboratory. 

To validate the ICME model, the team successfully produced small volume heats of two 3rd Gen AHSS alloys with mechanical properties meeting those targeted by the DOE for an exceptional-strength, high-ductility 3rd Gen AHSS and a high-strength, exceptional-ductility 3rd Gen AHSS. The team produced sufficient quantities of the two 3rd Gen AHSS alloys for testing, model calibration and model validation.   

The first, a medium manganese (10 weight percent) 3rd Gen AHSS alloy, achieved 1,200 megapascal (MPa) ultimate tensile strength and 37 percent tensile elongation, which exceeded DOE targets for a high-strength/exceptional-ductility steel. The second 3rd Gen AHSS alloy of a three percent manganese steel achieved 1,538 MPa tensile strength and 19 percent tensile elongation, which exceeded the strength target and was within the ductility target range for the DOE’s exceptional-strength/high-ductility steel.   

The project simulated the application of both 3rd Gen AHSS into a baseline automotive side structure shown in Figure 3. The side structure design was optimized to take advantage of the better mechanical properties of the 3rd Gen AHSS, which resulted in a final design that achieved a 30 percent mass savings while still achieving vehicle crash (pole intrusion, side impact, rear impact, roof crush) and stiffness (torsional and bending) requirements. This is especially significant considering the steel gauges for the components that made up the side structure ranged from 0.5 to 2 mm. Even with this reduced gauge, the optimized final side structure design showed improved crash performance versus the baseline design.  

Figure 3: A cut-out view of the left- and right-hand of the baseline side structures used to demonstrate the potential of 3rd Gen AHSS in lightweighting automotive assemblies.

As demonstrated by this project, these 3rd Gen AHSS both provide higher strength and enhanced formability, offering the automotive designer an additional suite of grades to help reduce mass and continue to keep steel a preferred material in future vehicles. This project reinforces why the steel and automotive industries must continue to work together, as further development and availability of 3rd Gen AHSS will provide an excellent economical path forward in meeting 2025 Corporate Average Fuel Economy standards and greenhouse gas regulations. While this project focused on material, design and forming, one of the next steps in this work includes modeling and validating joining technologies which would provide valuable input to the repairability of these grades. 

Auto/Steel Partnership

A/SP is a 30-year collaboration of auto companies and steel makers that leverages the intellectual and technical resources of the automotive, steel and related industries and organizations to develop pre-competitive lightweight steel solutions to meet the current and future needs of automakers. The consortium has proven to be a long-time leader in delivering mass-efficient, high-performing and cost-effective solutions for body and chassis applications as evident by numerous applications on the road today. 

The Partnership is committed to addressing fundamental technologies to speed up the implementation of 3rd Gen AHSS. As a result, A/SP projects have been expanded to evaluate the formability, optimized tooling solutions, corrosion, weldability, and repairability of 3rd Gen AHSS.  This work is evident in the A/SP’s Technology Roadmap, shown in Figure 4, which details technical areas of research and new development project opportunities for the automotive and steel industries over the course of the next four years. The opportunities presented in the roadmap illustrate how the steel and automotive industries will continue to work hand-in-hand to overcome the challenges and to advance the global automotive industry while driving innovation. 

Figure 4: Focus areas for the A/SP Technology Roadmap highlight 2018 through 2021 include materials, modeling, joining, forming and other/crosscutting areas.


As the automotive industry works to meet increasingly stringent fuel economy and safety regulations, the steel industry continues to collaborate with automakers to innovate and implement 3rd Gen AHSS into new vehicle designs. This next generation of steel opens automakers’ doors to the ability to continue to lightweight their vehicles with steel. It will provide higher strength and formability choices, increasing the value of steel as a weight reduction solution. It’s safe to say steel will remain a strong material of choice in the automobile for years to come, especially as 3rd Gen AHSS is implemented into more and more vehicles.

About the Author

John Catterall

John Catterall is executive director of the Auto/Steel Partnership (A/SP). In this role, he is responsible for maintaining and enhancing the partnership between auto and steel investors and executing strategic projects to develop lightweight steel solutions to meet the current and future needs of automakers.

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