The Effect of Tensile Strength on the Formability Parameters of Dual Phase Steels
The importance of dual phase (DP) steels in the automotive industry was continuously spreading in the last decade. With their special microstructure—containing ferrite and martensite in particular ratio—high strength and increased formability is available. That’s the reason why the application of DP steels is providing to exceed the 50% in a modern car body structure, according to the European program of Ultra-Light Steel Auto Body Advanced Vehicle Technology. This paper presents the experimental results of hemispherical dome tests and uniaxial tensile tests of three types of DP steels: DP 600, DP 800 and DP 1000. The effect of the tensile strength on the formability was investigated. It was described by the total and the ultimate tensile elongation, the average anisotropy and the limiting dome height (LDH). Based on our results it can be concluded that both the total and the uniform elongations are nearly linearly decreasing as the tensile strength is increasing. The slope of total elongation is more sensitive to the strength growth. However, it is no longer true for the plastic anisotropy. The reduction rate of average anisotropy stops over 800 MPa, and does not change until 1100 MPa. According to the dome tests results, the formability is also influenced by the sample geometry—through the deformation path—besides the tensile strength. The LDH values in biaxial stretch strain conditions are less dependent on the tensile strength. They are within a 3 mm interval for all three strength classes. In plane or stretch-press strain conditions, higher reduction can be observed. The characteristics of dome height curves are similar for all samples, regardless of their strength.
KeywordsTensile Strength Dual Phase Steel Dual Phase Uniform Elongation Blank Holder
The presented research work was supported by Ministry of Human Resources, in the program of National Talent Program NFTÖ-16—scholarships to provide individual development.
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