Sheared Edge Stretchability of Steels Suitable for Automotive Applications

In recent years, dual phase (DP) Advanced High Strength Steels (AHSS) and Ultra High Strength Steels (UHSS) are considered as prominent materials in the automotive industry due to superior structural performance and vehicle weight reduction capabilities. However, these materials are often sensitive to trimmed edge cracking if stretching along sheared edge occurs in such processes as stretch flanging. Another major issue in the trimming of UHSS is tool wear because of higher contact pressures at the interface between cutting tools and sheet metal blank caused by UHSS’s higher flow stresses and the presence of a hard martensitic phase in the microstructure. The objective of the current paper is to study the influence of trimming conditions and tool wear on quality and stretchability of trimmed edge of DP980 steel sheet. For this purpose, mechanically trimmed edges were characterized for DP980 steel and compared with other steels such as HSLA 350 and BH210. Sheared edge stretchability of these materials was analyzed by performing the tensile tests. Local elongations were measured by grid analysis and digital image correlation (DIC) in the area adjacent to fracture and outside the localization zone. Wear of cutting inserts was an additional factor which played an important role in the condition of the sheared edge of studied materials. Measurements of burnished area and burr height were performed in addition to stretchability analysis.