Microstructure transformation of continuous cooling of Nb-Ti micro-alloyed low alloy steel

Through the thermal simulation test of the Nb-Ti micro-alloyed steel austenite cooling process and microstructure observation & microhardness test, the tests indicate cooling rates have effect on the phase transition and microstructure of tested steel, the critical quenching speed of Nb-Ti micro-alloyed steel is about 23 degrees C/s with very good hardenability. With the increasing of the cooling rate, the beginning and ending temperature of phase transformation decrease and the ferrite structure content was decreased at room temperature. It's easy to happen Bainite transformation at the beginning, and make the M block or flake M fine, which is to increase the strength and toughness of the steel.