Development of Nb-V-Ti Hot-Rolled High Strength Steel With Fine Ferrite and Precipitation Strengthening

A hot-rolled steel with high yield strength of 700 MPa, good elongation of about 20% and low ductile-brittle transition temperature (DBTT) lower than -70 degrees C has been developed in laboratory. The results show that adopting finishing rolling temperature of around 800 degrees C is rational. and coiling temperature is between 400 and 500 degrees C. The strength of developed 700 MPa hot-rolled high strength steel is derived from the cumulative contribution of fine grain sized dislocation hardening and precipitation hardening. The fine grain strengthening and precipitation hardening are the dominant factors responsible for such high strength, and good elongation and toughness are predominantly due to fine grain ferrite.