The “metallographic structure” of automotive leaf springs is classified into 7 grades, with grades 1 to 5 being qualified and grades 6 to 7 being unqualified. The specific standard map is as follows:
Grade 1: Fine tempered Troostite
Grade 2: Medium-fine tempered Troostite
Grade 3: Tempered Troostite distributed in a band-like pattern
Grade 4: Coarser tempered troostite
Grade 5: Tempered troostite + a small amount of upper bainite
Grade 6: Tempered troostite + upper bainite + a small amount of ferrite
Grade 7: Tempered troostite + banded distributed ferrite