Development of Advanced High Strength Steels (AHSS) for Automobiles: A Review on Design Criteria

Abstract

Improved fuel economy and emissions, leads to a growing trend to produce steels with high specific strength in vehicles. The high-strength, high-ductility characteristics of AHSS come from the metals’ unique microstructures. Where most steels have primarily one microstructural phase, like ferrite, AHSS typically has a combination of martensite, bainite, austenite and ferrite phases. Each microstructural phase has a different crystalline or molecular structure. For instance, ferrite has a body-centered-cubic (BCC) structure, and martensite has a body-centered-tetragonal structure. Each structure has its own set of physical properties due to the forces within the crystals and the densities with which atoms are packed in a crystal cell. Various research studies have shown that proper application of AHSS can cut a vehicle’s weight between 10 and 25%. When fuel economy is paramount, the 5% fueleconomy boost a 10% reduction in weight provides is a nice carrot.