Strengthening and Toughening of a Heavy Plate Steel for Shipbuilding with Yield Strength of Approximately 690 MPa

Interpretation of cryogenic-temperature Charpy fracture initiation and propagation energies by microstructural evolution occurring during dynamic compressive test of austenitic Fe–(0.4,1.0)C–18Mn steels

“…4(a) through (d) presents instrumented Charpy impact load-time (P-t) curves of the 4C and 10C steels tested at 25°C and À196°C. Fracture initiation energy (E I ) and fracture propagation energy (E P ) were obtained by measuring areas below these curves on the basis of peak load (P max ) [20][21][22][23], as summarized in Fig. 5 (a) and (b) and Table 2.…”

“…4(b) and (d)). When the load is dropped after the P max point, the unstable crack growth starts to form the E P part, and the crack propagation rate is approximately proportional to slope of P-t curve [21][22][23]. The slope is much steeper in the 4C steel than in the 10C steel, which implies that the 4C steel shows the lower E P than the 10C steel.…”

On the determining role of acicular ferrite in V-N microalloyed steel in increasing strength-toughness combination

“…Advanced medium and heavy steel plates with high strength and excellent low temperature toughness are preferred as structural materials for ship hull, bridges, building, pressure vessels, and offshore structures [1][2][3][4][5]. To obtain good toughness and weldability, carbon-content is generally reduced.…”

“…Moreover, Nb is added during controlled rolling to inhibit austenite recrystallization, and Ti is added to avoid extensive austenite grain coarsening during the welding process [6][7][8][9]. To enhance the homogeneity of Nb-Ti microalloyed steels through thickness, expensive microalloying elements, such as Ni, Cr, Mo, and Cu, are added [1][2]. Recently, the focus has been toward developing as-hot rolled steels to replace conventional quenched and tempered steels from the viewpoint of production cost, energy, and efficiency considerations.…”

“…Quenched and tempered steels can be substituted by microalloyed steels with equivalent strength and toughness [7,10]. But during thermo-mechanically controlled processing (TMCP) of advanced medium and heavy steel plates, deformation and cooling are rarely uniform across the thickness, because of which unfavorable microstructures such as coarse granular bainite and Widmanstatten ferrite are obtained at small reduction and low cooling rate in the center of the steel plate, and toughness is severely deteriorated [1,11]. Acicular ferrite is of considerable practical significance in the case of plates because it is characterized by relatively high strength and toughness [12].…”