Formability of sheared edges can have a critical role in forming high-strength hot-rolled steel components due to possibility of edge cracking. The most utilized method to investigate sheared edge formability is the ISO 16630 hole expansion (HE) test, however, the results do not describe the edge behavior in detail. Additionally, there has been interest in the industry to decrease the amount of required HE testing. Aim of this study was to investigate cut edge formability of high-strength hot-rolled steels in detail and to compare performance to various tensile testing results.

Five industrially hot-rolled low-carbon steels with 3 mm thickness were selected to have similar tensile strength (~840 MPa) and different microstructural constitutions. HE testing was performed according to ISO 16630, tensile tests were conducted in three different sheet directions, and r-values were determined to investigate anisotropy. Local ductility was evaluated by measuring thickness strains from tensile fracture surfaces. Due to challenges in digital image correlation (DIC) strain measurement during standard conical HE testing, evolution of strain in different sheet directions was additionally investigated with alternative expansion tool geometries for three selected steels.

The hole expansion ratios (HER) did not correlate with majority of the tensile test results, however, a positive correlation between HER and a lesser degree of anisotropy was observed. No clear correlation was found between HER and local ductility. With the DIC measurements, major strains around the holes were detected to localize in the sheet rolling and transversal directions. The material with the least amount of planar anisotropy showed higher mean strains and delayed strain localization. The results overall show that in addition to the microstructure, anisotropy has a significant influence on HE performance of hot-rolled steels with similar strength level.