HSD^® Steel: Properties

Major efforts have been committed to the development of high- and highest-strength steels in order to expand or improve the range of properties both in terms of strength and forming capabilities. The aim is to enable the production of weight reduced vehicles, offering fuel savings, while guaranteeing high crash safety at the same time.
HSD^® steel (High Strength and Ductility Stahl) by Salzgitter Flachstahl is precisely such a steel product, impressing with reduced density, high ductility and highest strength. Thanks to its mechanical technological properties, HSD^® steel is by far superior to standard high- and highest-strength steel materials. HSD^® steel features a tensile strength level of 1000 MPa, which is combined with an elongation at tear of more than 50 percent and a uniform elongation of 45 percent, while its density is reduced by five percent. The difference to standard steels is clearly demonstrated in the diagram of elongation at tear as a function of yield strength below (Fig. 1). Moreover, HSD^® steels even feature improved mechanical technological properties  compared to known austenitic, stainless steels.

HSD^® steel is an Fe-Mn-Al-Si steel with single-phase, austenitic microstructure. This austenitic microstructure retains its stability in the forming process. The TWIP (TWinning Induced Plasticity) effect is the primary strengthening mechanism. HSD^® steel normally has a grain factor of approximately 10-11 (to ASTM).

Table 1 provides a view of the mechanical properties of HSD^® steel compared to a modern dual-phase steels (HCT780XD) and a micro-alloyed steel (HC340LAD), while Fig 2 highlights a comparison of corresponding flow trends and the enormous energy absorption capability of an HSD^® steel.

Table 1:  Mechanical properties, overview.

	HSD® steel cold-rolled strip	HCT780 XD	HC340LAD
Rp0.2 [MPa]	620	450-560	340-420
Rm [MPa]	1000	780-900	410-510
Elong. to tear A80 [%]	50	≥14	≥21
Density [g/cm3]	7,35	7,8	7,8

      

These extraordinary properties of HSD^® steel offer enormous weight reduction potentials, especially for components that are subject to crash stress. These lightweight construction potentials can also be utilized for the development of fuel-saving automobiles. HSD^® steel delivers its maximum potential if its extraordinary properties are utilized in a component design that is based on the suitable materials.

HSD® steel offers additional potentials under the following aspects:

• HSD^® steel with increased yield strength (Rp0.2: > 1100 MPa, A80: > 16 %) can substitute press-hardened components
• The extraordinary ductility of the HSD^® steels allows for a high degree of functional integration pressed parts and enables the integration of two or multiple part components in order to produce a single part.
• HSD^® steels facilitate the reduction of necessary steps in the forming technological process
• HSD^® steels enable the substitution of a hardening processes by utilizing the enormous structural strengthening potentials during the forming process.