Microstructural examination of two experimental high-strength bainitic low-alloy steels containing silicon

Theoretical design and advanced microstructure in super high strength steels

“…In previous research carried out by Bhadeshia and Edmonds [6,7] and Miihkinen and Edmonds [14][15][16], it was found that carbide free bainite is in principle an ideal microstructure from many points of view. In particular, the steel has a high resistance to cleavage fracture and void formation due to the absence of carbides.…”

“…Steels with different carbon content will exhibit the same T 0 o curve [4][5][6][7][8][9][10][11][12][13][14][15][16][17]. The driving force for the formation of new plates decreases as the carbon concentration in the untransformed austenite approaches the T 0 o composition at which the free energy of ferrite and austenite phases of the same composition become identical.…”

The bainite transformation and the carbide precipitation of 4.88% aluminium austempered ductile iron investigated using electron microscopy

“…examination at this austempering time indicated that the matrix of Al-alloyed ductile irons is without carbides after 40 min isothermal heat treatment. Bhadeshia and Edmonds [19] also reported a similar microstructure for bainite in silicon steels austempered at 340 • C. In addition, the bainitic transformation of two silicon-containing low-alloy steels indicated that bainitic ferrite laths, interwoven thin films of retained austenite and possibly coarser granular regions of retained austenite instead of cementite are present in the upper bainite microstructure [20].…”

Advanced Ultrahigh Strength Bainitic Steels

“…A minimum ductility of 12% elongation and 50% reduction of area were also required. Previous research, carried out by Bhadeshia and Edmonds [6,7] and Miihkinen and Edmonds [8][9][10], on two silicon-containing steels, nominally, Fe-0.2C-2Si-3Mn wt.% and Fe-0.4C-2Si-4Ni wt.% showed that these alloys hold promise. The Fe-0.2C-2Si-3Mn wt.% alloy exhibited excellent fracture toughness (K Ic = 160 MPa √ m) in a strength range of 1375-1440 MPa as isothermally heat-treated at 250 C. This fracture toughness is better or equal than that of quenched and tempered AISI 300 M and AISI 4340 steels at equivalent strength levels and approaches that of the 18 wt.% Ni maraging steel [10].…”