AHSS: Advanced High Strength Steels
Definition:Group of steels that is characterized by a mulitphase microstructure and an excellent strength-ducitility ratio.
Explanation:There is a general trend in sheet steel development towards an improved balance of formability and strength. AHSS show outstanding yield strength without the compromise of ductility loss. The physical background of this development is mainly that their microstructure is designed to contain constituents with strong distinction in mechanical properties. The final material behavior is affected by the coexistence of the different microstructure components, their different mechanical behavior and their mutual interactions.

Multiphase high strength steels with a ferrite matrix are addressed as AHSS 1. Generation. The term AHSS 2. Generation or 2.G is used for single phase austenitic high Mn steels which microstructure characteristically develops throughout plastic forming either by transformation induced plasticity due to strain induced martensite formation (→TRIP) by continuous microstructure refinement due to twinning induced plasticity (→TWIP) or by pronounced microband formation (→MRIP). Recently, AHSS 3.G is used as a term for medium Mn steels with a multiphase microstructure containing a high austenite fraction.

It is possible to vary the mechanical properties by adjusting type, morphology and orientation and above all volume fraction, size and distribution of the different phases. These transformations improve the formability by significant strain hardening and prolonging the uniform straining behavior. This effect can be seen in the ECO-index as (ultimate tensile strength)×(total elongation), which delivers a rough indicator for the overall performance.

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Classification of AHSS. Grades, ECO-index, and volume fraction of austenite (γ) are shown as well.
SFB-Link:The investigated materials show a multiphase microstructure and cover the range of TRIP and TWIP deformation mechanisms.

Components of the known industrially used AHSS are suitable especially for automobile light weight construction parts as pillars and beams or for crash relevant parts as bumpers.
References:Bleck, W.; Prahl, U.; Suwanpinij, P.: Microstructure Development in Hot-Rolled Advanced High Strength Steels. Rolling Conference, June 10.-12.2013, Venice, Italy