A study on hot forged low carbon HSLA steels

Machinability characteristics, heat treatment response and mechanical prope rties of hot forged low carbon niobium containing HSLA steels (0.03-0.05%C, 0.85-1.25%Mn, 0.3%Cr, 0.2%Ni, 0.05-0.15%Nb) were investigated. Modificatio n of inclusions in the steels with a Fe-Si-2%Mg-4%Ca alloy - reduced tool w ear during turning experiments. These steels may be conveniently strengthen ed (410-500MPa Y.S., 460-600 MPa UTS, 24% E1) by forced air draft cooling f rom 1100 degreesC. Although the room temperature impact toughness of the he at treated steels was quire high (>200 J), a sharp drop in toughness (below 10 J) occurred at -40 degreesC. Interestingly, the steels air quenched fro m 950 degreesC retained good toughness even at -40 degreesC. A mild seconda ry hardening response was noted during tempering of the as air quenched ste els at 400-500 degreesC.