Effect of Vanadium and Rare Earth on the Structure, Phase Transformation Kinetics and Mechanical Properties of Carbide-Free Bainitic Steel Containing Silicon

Carbide-free bainitic (CFB) steels with a matrix of ferrite and thin layers retained austenite, to reduce the manufacturing costs, usually do not contain alloying elements. However, few reports were presented regarding effect elements on properties these steels. Thus, this study evaluates effects vanadium rare earth (Ce-La) microalloying structure, phase transformation kinetics, mechanical carbide-free bainite steel containing silicon fabricated by casting austempering procedure. Optical scanning electron microscopy (OM SEM), backscatter diffraction (EBSD), X-ray (XRD) used microstructure structure. The kinetics examined dilatometry test. Hardness, tensile, impact tests evaluated properties. Due adding elements, fracture toughness change in phases relation was studied crack tip opening displacement (CTOD) test SEM fractography. added sample completely bainite. results showed helped CFB formation, even continuous cooling. primary austenite grain (PAG) size grew addition. EBSD map illustrates an increment percentage vanadium. In contrast, addition 0.03 wt% reduced content. confirmed that both critical cooling rate transformation. Vanadium leads earlier cessation transformation, while postpone Mechanical tensile strength strongly influenced morphology volume fraction austenite. Retained when transformed martensite during transformation-induced plasticity (TRIP) phenomenon, increased toughness, or film-like shape prevents growth cracks blinding tip. result CTOD exhibited plays leading role increasing resistance TRIP occurs.