HODGSON Peter Deakin University

Advanced High Strength Steels (AHSS) for the automotive industry and generally multiphase steels such as DP (dual phase) and TRIP. However, these steel types often have poor stretch flangeability due to the strength difference between the different phases. JFE in Japan developed a new class of ferritic AHSS with high levels of precipitation hardening through the combined effect of Ti and Mo. Using atom probe tomography (APT) we were able to show that these steels contained exceptionally fine interphase precipitates. The current work examines this class of steels in more detail using advanced TEM and APT to examine the effects of composition and transformation/holding time on the nature, size and composition of these precipitates. One of the major insights in this work was the clear evidence for cluster formation and strengthening in the final product, especially at very short holding times.