Effect of Proeutectoid Ferrite Morphology on the Microstructure and Mechanical Properties of Hot Rolled 60Si2MnA Spring Steel

Abstract

The hot rolled 60Si2MnA spring steel was transformed to obtain different proeutectoid ferrite morphologies by different cooling rates after finish rolling through dynamic thermal simulation test. The coexistence relationship between proeutectoid ferrite and pearlite, and the effect of proeutectoid ferrite morphology on mechanical properties were systematically investigated. Results showed that the reticular proeutectoid ferrite could be formed by the cooling rates of 0.5–2 °C/s; the small, dispersed and blocky proeutectoid ferrite could be formed by the increased cooling rates of 3–5 °C/s; and the bulk content of proeutectoid ferrite decreased. The pearlitic colony and interlamellar spacing also decreased, the reciprocal of them both followed a linear relationship with the reciprocal of proeutectoid ferrite bulk content. Besides, the tensile strength, percentage of area reduction, impact energy and microhardness increased, which all follow a Hall–Petch-type relationship with the inverse of square root of proeutectoid ferrite bulk content. The fracture morphologies of tensile and impact tests transformed from intergranular fracture to cleavage and dimple fracture, and the strength and plasticity of spring steel were both improved. The results have been explained on the basis of proeutectoid ferrite morphologies–microstructures–mechanical properties relationship effectively.

Keywords

• 60si2mna spring steel
• cooling rate
• proeutectoid ferrite morphology
• microstructure
• mechanical property
• hall–petch relation