"What Really Sank the Titanic: New Forensic Discoveries Solve One of History's Deadliest Mysteries"
by Jennifer Hooper McCarty and Tim Foecke
A scanning electron microscope image of a broken wrought iron sample, pulled along the direction of the slag fibers. Note the very large piece of slag, and how much bigger is the hole it formed than those around the small pieces. The big pieces are the ones causing the loss in strength.