Upper shelf energy region

When welding, you have to keep an eye on the transition temperature, i.e. the range where the material changes from tough to brittle fracture behavior. If you put too much heat in or cool down incorrectly, the structure can open up and you get stresses or cracks, especially with higher-strength steels. Keep the interpass temperature low enough and don't let the part cool too quickly, then the notch impact toughness stays in the green range.