Influence of tempering on the microstructure and mechanical properties of HSLA-100 steel plates

The influence of tempering on the microstructure and mechanical properties of HSLA-100 steel (with C-0.04, Mn-0.87, Cu-1.77, Cr-0.58, Mo-0.57, Ni-3.54 , and Nb-.038 pct) has been studied. The plate samples were tempered from 3 00 degreesC to 700 degreesC for 1 hour after austenitizing and water quench ing. The transmission electron microscopy (TEM) studies of the as-quenched steel revealed a predominantly lath martensite structure along with fine pr ecipitates of Cu and Nb(C, N). A very small amount of retained austenite co uld be seen in the lath boundaries in the quenched condition. Profuse preci pitation of Cu could be noticed on tempering at 450 degreesC, which enhance d the strength of the steel significantly (yield strength (YS)-1168 MPa, an d ultimate tensile strength (UTS)-1219 MPa). though at the cost of its notc h toughness, which dropped to 37 and 14 J at 25 degreesC and -85 degreesC. respectively. The precipitates became considerably coarsened and elongated on tempering at 650 degreesC, resulting in a phenomenal rise in impact toug hness (Charpy V-notch (CVN) of 196 and 149 J, respectively, at 25 degreesC and -85 degreesC) at the expense of YS and UTS. The best combination of str ength and toughness has been obtained on tempering at 600 degreesC for 1 ho ur (YS-1015 MPa and UTS-1068 MPa, with 88 J at -85 degreesC).