Over the years, catastrophic failures of die materials have become less common with advancements in steel making, heat treatment and technical advancements associated with the die casting process. NADCA has been a driving force for most, if not all, of these advancements. However, ongoing issues associated with tool life are still occurring. The range of failures is not associated with a particular die caster, material producer or a heat treatment facility. Impact toughness has been a focus of the North American die casting industry for several years, but how do these improvements relate to improved heat check resistance? This article will review additional mechanical and physical steel properties, besides toughness, that address the most common failure mode associated with thermal fatigue.