MaX – stainless steel for automotive applications

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To meet increasingly stringent environmental regulations, automobile manufacturers are focusing on reducing a vehicle’s overall weight. They do this via product redesign and an extensive use of advanced lightweight materials – including such high-strength stainless steels as Aperam’s MaX product.

High-strength steel formed by hot stamping, when used in conjunction with a lighter structure, has proved to be a good candidate for achieving better in-use performance. The automotive industry uses hot stamping to produce complex parts with large in-use properties, allowing for a significant reduction in vehicle mass of between 15 to 50 %. This reduction can be achieved in both body-in-white (BIW) for structural panels (e.g. floors, wheel houses, dash panel) and chassis components (e.g. Lower Control Arms, rear beams).

Although martensitic boron carbon steels are well adapted to hot stamping, the industry is looking for new materials. Specifically, they are looking for a material that will allow for the use of very thin parts for structural panels, along with complex geometry - all at an extremely competitive price.

MaX, Aperam’s martensitic stainless steel (MSS), is well-positioned to answer this demand. As MaX contains between 11 and 14% Cr, which considerably enhances its oxidation and corrosion resistance, it is not necessary to add expensive coatings for oxidation protection - making MaX compatible with fast heating processes. Furthermore, MaX’s high chromium content gives it excellent quench hardenability – making the product insensitive to cooling rates between 100°C/s and 1°C/s. The low oxidation kinetics, together with MaX’s high quench hardenability, makes the hot stamping process extremely flexible. Last but not least, MaX is nickel free, meaning it is one of the most stable and competitively priced stainless steels currently on the market.

MaX’s differentiator is its unique suitability for both direct and indirect hot stamping processes. Its thickness is far below the most advanced high-strength stainless steels available today. Compared to the competition, only MaX can reach 0.55 mm, enabling manufacturers to reduce a vehicle’s overall weight by up to 30%. Available in either MaX 1.2 for chassis (1200MPa tensile strength) or MaX 1.6 for BIW (1600MPa tensile strength), both versions’ excellent fatigue properties make it an ideal choice for such automotive chassis parts as lower control arms and engine cradles. The product’s elevated crash performances also makes it suitable for BIW applications, such as the structural panels, where energy absorption is key. Furthermore, as steel can be readily recycled, MaX has a unique environmental advantage over other metals.

The MaX advantage
  • Can be hardened by hot stamping up to a tensile strength of up to 1.6 GPa.
  • Ability to be air quench hardened.
  • Oxidation resistance with no coating needed.
  • Outstanding fatigue behaviour.
  • Compatibility with fast heating (joule or induction).
  • Ability to make the hot stamping process more flexible (leading to cost savings).
  • Can be formed on either a single- or multiple-step process.

Looking down the innovation pipeline, Aperam is currently developing a new process for producing MaX 1.6. Branded as MaX 1.6 CRYO, instead of heating the material before stamping it will be cooled down after stamping. Offering the same level of strength as MaX 1.6, MaX 1.6 CRYO represents an innovative breakthrough to anything currently found on the market.