Microstructure Property Correlation of Low Alloy Steel Processed through Heat Treatment

In the current study, an effort has been made to establish a relationship between the low alloy steel’s
microstructure and properties. Austenitizing temperature of for this low steel was taken at 1150˚C for
1-hour holding for annealing, normalizing, quenching in water and oil. Tempering was done (below
A1) at 550˚C for a two-hour holding period, and then quenched specimens were cooled by air. By using
optical microscopy and SEM, on base specimen ferrite, carbides and early austenite grains (PAG).
Microstructure of the annealing specimen was ferrite + pearlite. Microstructure of the normalizing
specimen was proeutectoid ferrite and fine carbide with bainite. Ferrite + tempered martensite +
carbide precipitates are observed in microstructure of quenched in water followed by tempering of low
alloy steel. Ferrite + bainite + carbide precipitates are observed in microstructure of quenched in oil
followed by tempering of low alloy steel. The mechanical properties of base alloy, annealing,
normalizing, water and oil quenching followed by tempering low alloy specimens are was tested by
Vickers macro hardness, Tensile test (UTS, Y.S, Elongation %) and Charpy impact test are 195.46
HV,150.19 HV, 289.90 HV, 337.33 HV and 289.71 HV; (610.82 MPa, 444.99 MPa, 823.28 MPa, 954.89
MPa and 916.73 Mpa; 492 MPa, 241.41 MPa, 604.74 MPa, 837.04 MPa and 788.15 MPa; 22.07 %,
18.94 %, 12.17 %, 11.84 % and 12.63 %); 85.5 J, 20.67 J, 32.67 J, 25.33 J and 22.67 J respectively.
Fractography of tensile specimens of base alloy and heat treated reveal ductile fracture.