Advantages of AHSS steels of the third generation

12.03.2024 | Initiative Automotive

Salzgitter Mannesmann Forschung presented the third generation of AHSS steels at the "WerkstoffPlus Auto" conference in Stuttgart. As part of the presentation on February 21, 2024, research and development activities relating to the third generation of AHSS steels were presented using the example of CR440Y780T-FH and CR590Y980T-DH. These are aimed at the increasing customer requirements in formability and energy absorption.

Increasing demands on improved formability and energy-absorbing properties of AHSS for automotive applications have been met by introducing special multiphase steels that offer, inter alia, greater elongation compared to conventional steels at equivalent strength levels. Such 3rd Gen AHSS include CH-, DH-, FH-steels, etc., being offered as uncoated, hot-dip galvanized and electrogalvanized steel strip. DH-steels have established themselves as an excellent solution to substitute DP-steels for complex geometries, lightweight construction and as a general problem-solver.

Improving the global ductility (i.e. total elongation), without sacrificing tensile strength, can be achieved by increasing the content of retained austenite in the final microstructure, thus utilizing the TRIP effect upon straining. Notably, for this purpose, alloying strategies often employ elements such as Si with up to 1.5 wt.% in such steel grades, greatly improving mechanical properties but adversely impacting weldability due to liquid metal embrittlement. Thus, novel alloying and processing strategies are needed to achieve enhanced ductility and overall balanced materials characteristics, while retaining compatibility with current welding techniques as well as resistance to hydrogen embrittlement, even at Gigapascal strength level.

The presentation discussed material concepts that aim at substituting and lowering the number of elements such as Si and Al, while still achieving a high fraction of retained austenite, thus, improving global formability. Examples of industrially produced galvanized steel grades that utilize these concepts in the strength classes of 800 and 1000 MPa are showcased to not only reach the same level of elongation vis-à-vis DH-steels but to surpass DH800 and DH1000 requirements by a substantial margin in terms of total elongation. By virtue of improved ductility and focus on thermal joining suitability these steel grades therefore offer a high potential for automotive safety components, complex parts, and component integration. Application examples are presented and discussed.

If you have any questions about our third generation AHSS steels, please contact our technical customer service and sales department.