A818-06(2016) refers to a specific standard for a steel grade. In this case, the standard number is A818-06(2016). The chemical composition of this steel grade refers to the specific elements and their respective proportions present in the steel. The mechanical properties of the steel grade refer to its physical characteristics, such as strength, hardness, and ductility. Understanding the composition and mechanical properties of a steel grade is essential for determining its suitability for various applications.