Microstructure and mechanical properties of 750 MPa grade Nb-Ti-Mo microalloyed square tube steel
In order to achieve lightweight of automobile body frame,750 MPa grade Nb-Ti-Mo composite microal-loyed square pipe steel was developed.The microstructure and properties of 750 MPa grade Nb-Ti-Mo composite microalloyed square tube steel were analyzed by OM,SEM and TEM.The results show that the microstructure of the 750 MPa grade Nb-Ti-Mo composite microalloyed square steel is full of total ferrite and a large number of dis-persed nanoscale precipitates,and the material has excellent comprehensive mechanical properties by adopting the low C,low Mn,Nb,Ti and Mo composite microalloyed composition system and optimizing the coiling process.The properties of 750 MPa grade Nb-Ti-Mo composite microalloyed square pipe steel are similar to those of the base ma-terial after direct square forming process.When the tube is made by the round to square process,with the decrease of pipe diameter,the strength is obviously increased,the plasticity is gradually decreased,and the elongation is still greater than 14％.When 750 MPa grade Nb-Ti-Mo composite microalloyed square pipe steel is instead of traditional Q235,345C,510L and other low strength steel to apply to the body skeleton,the weight reduction ratio is as high as 30％,the weight reduction effect is remarkable.
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