: The standard defines different quality classes (typically Classes 1 through 4) based on the size and frequency of detectable internal defects. Class 4 represents the highest level of stringency. Testing Techniques
The standard defines permissible levels of carbon (C), manganese (Mn), silicon (Si), phosphorus (P), sulfur (S), and optional alloying elements (chromium, vanadium, boron). These elements determine the hardenability and final mechanical properties after heat treatment. en 10306 pdf