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.
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.