Structure-Property Correlation of Quenching and Partitioning Heat Treated Silicon-Manganese Steel

The present investigation deals with the effect of varying quenching and partitioning parameters on microstructure and mechanical properties of American Iron and Steel Institute 9255 steel. The specimens were fully austenitised at 900 ∘C for 45 min and then quenched at 190 ∘C and followed by partitioning at various temperatures 280, 320, 360 and 400 ∘C and partitioning times 15, 30, 45, 60 and 90 min for each temperature. Post heat treatment includes microstructural analysis that was carried out by using scanning electron microscope (SEM) along with electron back scattered diffraction (EBSD) and x-ray diffraction (XRD) and then correlated to the mechanical properties i.e. tensile properties and hardness of the steel. Results indicate that the specimens quenched at 190 ∘C and partitioned over a temperature range 280 to 400 ∘C generates multiphase microstructures containing major fraction of martensitic structure (lath and plate-type), transitional ε-carbides in tempered martensite matrix and retained austenite (RA) for all the conditions. At higher partitioning temperatures i.e. 360 and 400 ∘C reveals some bainitic ferrite laths along with martensite and RA. Superior tensile strength, % elongation and modulus of toughness values of 1860 MPa, 12% and 207 MJ/m3 respectively was attained at partitioning time of 15 min at 280 ∘C.