Critical Assessment of Techniques for the Description of the Phase Composition of Advanced High-Strength Steels

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.