Hi, I have been doing some research about imapact toughness of steel and found a paper comparing toughnesses of 4 different steels using the Charpy impact test. The following is a link to the paper mentioned. https://drive.google.com/file/d/0B363OnUPK7-deGJDdkhwVU9SQ2s/view?usp=sharing At 24oC, SAE 4140 has the lowest impact energy, 13J. In the conclusion it is stated that fracture toughness of SAE 4140 is the largest of all at 68.61 MPa m1/2. How come the mentioned steel absorbed the least amount energy and ended up being the the toughest? Is it because it has a higher ultimate tensile strength? Could it be considered as being a ductile or brittle material? The high toughness suggests it is ductile but is surely did not deform as much as the other steels. Note: I am still unsure of how to calculate the impact toughness from a Charpy energy test although I understand how the energy to fracture the specimen is obtained.