Examination of Phase Transformations andMicrostructural Changes on Medium Carbon Steel DIN۱.۵۰۲۵ under One-step Quenching and Partitioning HeatTreatment Conditions

Third-generation advanced high-strength steels serve as advanced engineering materials in variousindustries, including land, air, rail, and maritime transportation, with expanding applications. In thepresent study, a sample of low-alloy steel with medium carbon content (۰.۵۲۹ wt%) and high siliconcontent (۱.۶۷۰ wt%) was selected and subjected to one-step quenching and partitioning heat treatmentat temperatures of ۱۴۰ and ۱۸۰ oC for different partitioning times. Phase transformations andmicrostructural investigations were conducted using dilatometry, laser microscopy, and ElectronBackscatter Diffraction (EBSD) analysis. Dilatometry results indicated that the formation of initialmartensite occurs at a temperature of ۲۷۵ oC, and during a holding time of ۳۶۰۰ s, only carbonpartitioning into retained austenite takes place at temperatures of ۱۴۰ and ۱۸۰ oC, yet martensiteformation occurs during the final cooling. Additionally, considering the changes in specimen widthduring isothermal holding, tempering of the initial martensite can be anticipated. Microstructuralexaminations also confirmed the formation of microphasic structures, including initial martensite,retained austenite, and final martensite

Keywords:

Low alloy steel , Advanced high strength steels , Quenching and partitioningheat treatment , Phase transformation , Dilatometry test.