With the development of HCT590Xxtend®, Salzgitter Flachstahl has created a new grade of steel for demanding applications in vehicle body manufacturing. This quality of steel offers increased formability when compared with HCT590X dual phase steel. The brand name xtend® derives from the Latin extendere (= stretch) and reflects the improved elongation of these steels. In common with the dual phase steels previously available, xtend® steels exhibit outstanding processing characteristics, including weldability.
To produce crash-critical strengthening elements for motor vehicle bodies, steels with are required which exhibit complex characteristics. On the one hand, a low yield point and excellent formability are required to reproduce complex geometries. Whereas on the other hand a high tensile strength and a substantial degree of strain-hardening through forming are needed in order to protect the vehicle occupants in case of a crash by absorbing much of the energy. Special dual phase steels with increased formability have been developed to meet demands not previously met by steels of this type.
In the case of many structural components, dual phase steels have in turn replaced micro-alloy steels, which has also resulted in weight savings relative to the previous method of construction. Another contributing factor has been the ability to exploit the bake-hardening effect achieved as part of the paint process. As a result the cost- and energy-intensive use of aluminum to reduce weight is frequently no longer required. And naturally, these grades of steel can be supplied with a hot-dip galvanized finish to protect against corrosion.
The corresponding characteristics are determined by the analysis of the steel and careful temperature control during manufacture. The deciding factor is the targeted inclusion of martensite pockets in the ferritic matrix of these steels, the proportion of which determines the material strength.
As a consistent continuation of this successful development, formability has been further increased, leading to the creation of a new group of DP steels known as DH steels. This has been achieved through improvements in technical processes and the associated inclusion of small proportions of retained austenite in the microstructure of the material (Figure 1). These steels are offered by Salzgitter Flachstahl under the brand name HCT…Xxtend® in hot-dip galvanized form. A new addition to this group of materials is HCT590Xxtend®. This grade of steel corresponds with a CR330Y590T-DH, which is included among the standards specified by many OEMs. It offers advantages similar to those of the established grade HCT780Xxtend® (CR440Y780T-DH), with even better formability and lower strength (Table 1, Figure 2).
In addition, dual phase steel of this strength is also available with guaranteed 50% hole expansion under the brand name HCT590Xxpand® (expandere=expand).
|Steel grade||Yield strength||Tensile strength||Fracture elongation||Hardening exponent||BH2-Wert|
|A80 mm||A50 mm||n4-6||n10-20/Ag|
|330 - 430||590 - 700||≥ 20||≥ 21||≥ 0.18||≥ 0.14||≥ 30 (20)|
|330 - 430||590 - 700||≥ 26||≥ 27||≥ 0.21||≥ 0.16||≥ 30 (20)|