Steel doesn’t usually fail because someone picked the wrong grade. More often it fails because nobody ran a charpy impact test at the temperature the part would actually see in service. A batch of plate can pass every check on the shop floor, machinable, weldable, tensile numbers sitting comfortably within spec, and still snap like glass months later on a platform through a cold winter. Nothing about the material changed between those two moments. The temperature did. The problem with testing at room temperature only Most mechanical properties don’t swing wildly with a shift in temperature. Toughness is different. A…