Study on Microstructure and Strengthening Mechanism of 700 MPa High Strength Low Alloy Steel

Through comparing Q345B low-carbon steel and 700MPa high strength steel produced by compact strip production,the strengthening mechanism of 700MPa high strength steel was studied. The results show that 700 MPa high strength steel has higher tensile strength and yield strength than Q345B. The strength increment from grain refinement,solution and dislocation strengthening of high strength steel is 69,36,17MPa,respectively. The size of TiC with less than 20 nm is the main phase of precipitation hardening which precipitate in the ferrite during phase transformation. There is 22.3% [Ti] precipitating from the ferrite in the form of TiC in the high strength steel,which result in an increase of 117 MPa to the yield strength. Consequently,the grain refinement and precipitation hardening are the dominant factors to increase the yield strength in the steels.