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

Abstract

The influence of tempering on the microstructure and mechanical properties of HSLA-100 steel (with C-0.04, , and Nb-.038 pct) has been studied. The plate samples were tempered from 300 ЊC to 700 ЊC for 1 hour after austenitizing and water quenching. The transmission electron microscopy (TEM) studies of the as-quenched steel revealed a predominantly lath martensite structure along with fine precipitates of Cu and Nb(C, N). A very small amount of retained austenite could be seen in the lath boundaries in the quenched condition. Profuse precipitation of Cu could be noticed on tempering at 450 ЊC, which enhanced the strength of the steel significantly (yield strength (YS)-1168 MPa, and ultimate tensile strength (UTS)-1219 MPa), though at the cost of its notch toughness, which dropped to 37 and 14 J at 25 ЊC and Ϫ85 ЊC, respectively. The precipitates became considerably coarsened and elongated on tempering at 650 ЊC, resulting in a phenomenal rise in impact toughness (Charpy V-notch (CVN) of 196 and 149 J, respectively, at 25 ЊC and Ϫ85 ЊC) at the expense of YS and UTS. The best combination of strength and toughness has been obtained on tempering at 600 ЊC for 1 hour (YS-1015 MPa and UTS-1068 MPa, with 88 J at Ϫ85 ЊC).

High-Strength Low-Carbon Ferritic Steel Containing Cu-Fe-Ni-Al-Mn Precipitates

“…[1][2][3][4] HSLA-100 possesses similar strength and toughness values as HY-100, but because of the reduced nominal carbon content, it is weldable without preheat, thereby reducing fabrication costs. [3][4][5] To compensate for the decrease in strength on reducing the C concentration, Cu was added to HSLA-100 for precipitation strengthening, whereas Cr, Ni, and Mo were added to increase hardenability.…”

“…[1][2][3][4] HSLA-100 possesses similar strength and toughness values as HY-100, but because of the reduced nominal carbon content, it is weldable without preheat, thereby reducing fabrication costs. [3][4][5] To compensate for the decrease in strength on reducing the C concentration, Cu was added to HSLA-100 for precipitation strengthening, whereas Cr, Ni, and Mo were added to increase hardenability. [2][3][4][5][6][7] The thermal processing of HSLA-100, a solutionizing (austenitizing) and quenching step followed by tempering at 620°C to 690°C, produced a tempered martensitic steel containing Cu precipitates.…”

“…[2][3][4][5][6][7] The thermal processing of HSLA-100, a solutionizing (austenitizing) and quenching step followed by tempering at 620°C to 690°C, produced a tempered martensitic steel containing Cu precipitates. [2][3][4] Studies by Foley et al [8,9] have demonstrated that tempering of HSLA-100 overages the Cu precipitates, thereby reducing their strengthening contribution.…”

Evaluation of the transformation mechanisms and mechanical properties of ferrite: martensite microalloyed steels

“…The improvement in impact energy of the samples after 60 minutes can be attributed to the coarsening of the carbide particles that became pronounced during this period of holding. Dhua SK et al 9 also attributed the phenomenal improvement in impact toughness to the over aged microstructure of partially recovered matrix and coarse precipitates. They suggest that these might have helped in arresting the propagation of cleavage cracks.…”

“…Dhua SK et al 9 in their work attributed decrease in impact energy to both the negative effect of matrix strengthening and impurity segregation at the grain boundaries. Matrix strengthening occurred as a result of the increasing volume fraction of martensite and also as result of the precipitation of carbide particles at prior austenite grain boundaries.…”