The grade of the hook depends on the mechanical properties of the finished hook. The rated lifting weight and grade are defined by the rated lifting weight and test load, which are expressed by the letters M, P, S and T respectively.
The basic design load of the hook is equal to the test load (Fe).
Requirements for steel for four grades of hooks M, P, S and T:
1) Steel products shall be made from open hearth, electric furnace and oxygen top-blown converter.
2) The steel should be killed steel with good malleability and can meet the mechanical properties specified in the standard after proper heat treatment.
Note: S and T grade hooks require more steel.
Alloy steel for class S hooks shall contain at least one of the following elements: nickel, chromium, molybdenum or elements with the same properties.
Alloy steel for grade T hooks shall contain at least two of the following elements: nickel, chromium, molybdenum, boron or elements of the same properties.