Beware of Incomplete Steel Specifications

Knowing how to heat treat a component begins with knowledge of the base composition or grade of steel. But one often stops short of having a complete understanding. One item that is routinely ignored is grain size. Because grain size has a direct influence on hardenability and toughness, it is important to have more complete compositional information and/or mill certifications. Some examples are given to show how differences in grain size will influence the depth of hardening and potential for quench cracking. Mixed heat lots especially will cause significant difficulty for the heat treater. Grain size through its influence on hardenability also influences heat treat distortion. It also influences toughness of the finished product.