Relation between Slack-Quenched Homogeneous Structure and Mechanical Properties of Spring Steel

Abstract

Effects of microstructure on mechanical properties of C (SUP 3), Si-Mn (SUP6) and Mn-Cr (SUP9) spring steels were investigated.
Specimens prepared from each spring steel were first heat-treated to produce various asquenched structures: namely, martensite, fine pearlite or bainite.
These specimens were then tempered to the spring hardness H_B 300-500 before testing.
Specimens heat-treated as above were subject to twisting, bending, fatigue or repeated impact tests.
Results obtained were summerized as follows.
1. The proportional limit of twisting or bending for sorbite specimens was the same without regard to the kind of steel.
2. The ratio of proportional limit of sorbitic structure to that of fine pearlitic or bainitic structure for the alloy spring steels was slightly higher than that for the carbon spring steel.
3. The results indicated also that the endurance limit or repeated impact value of each steel were nearly the same for sorbitic, fine pearlitic and bainitic structures.
4. Spring properties of steel with sorbitic structure were not always superior to that of a steel having fine pearlitic or bainitic structure.