Abstract
The phase composition and portion of individual phases in advanced high-strength steels (AHSS) CP1000 and DP1000 was studied by complementary microscopic and diffraction techniques. CP1000 and DP1000 steel grades have a high strength-to-density ratio and they are used in many applications in the automotive industry. The microstructure of the CP1000 “complex phase” steel consists of ferrite, bainite, martensite and a small amount of retained austenite. DP1000 is a dual phase steel, which has a structure of a ferritic matrix with islands of martensite and a minor amount of retained austenite. The influence of selected etchants (Nital, LePera, Beraha I, Nital followed by metabisulfite, Nital followed by LePera, and Nital followed by Beraha I) on the microstructure image is described. X-ray diffraction, neutron diffraction and light optical, scanning and transmission electron microscopy were used in this work for advanced characterization of the microstructure and phase composition. The information provided by each technique is critically compared.
Highlights
Over the last decades, the automotive industry has searched for new materials with improved mechanical properties in combination with low density
Neutron diffraction enabled distinguishing the martensite from ferrite based on small differences in the lattice parameters, but the amount of bainite was impossibleMaterials to quantify because its main constituent is ferrite
Identification and quantification of the phases in CP1000 and DP1000 advanced high-strength steels was achieved by combining data from several complementary techniques:
Summary
The automotive industry has searched for new materials with improved mechanical properties in combination with low density. Advanced high-strength steels (AHSS) offer higher strength and better formability compared to conventional steels, which is given by improved phase composition [1,10,11,12]. Their tensile strength ranges from 500 to 1600 MPa, which makes them attractive for application in various car components [13,14]. Dual-phase steel (DP, ferritic-martensitic) is characterized by low yield strength, high work hardening, high tensile strength, continuous yielding [21], as well as high uniform and fracture elongation due to the martensite phase islands present in the microstructure [22,23,24,25]. The aim of this work was to determine phase compositions of CP and DP AHSSs and compare available metallographic and diffraction techniques in view of their applicability for these materials
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