Abstract: The effect of hot galvanizing processes on the mechanical properties and microstructure of non-Si and P-added TRIP steel was studied by using optical microscopy,transmission electron microscopy,X-ray diffraction and tensile test.It is shown that the steel with tensile strength over 780 MPa and percentage elongation after fracture over 24% can be obtained.The temperatures of intercritical annealing and isothermal bainitic transformation(IBT) have little influence on the mechanical properties,while IBT time plays significant contribution to them.When the IBT time prolongs from 20 s to 60 s,the sample reaches the best performance.Its yielding strength rises by 65 MPa,tensile strength decreases by 45 MPa,and elongation increases obviously from 23.01% to 27.56%,respectively.The microstructure of non-Si and P-added TRIP steel consists of ferrite,bainite,retain austenite and martensite.As the IBT time shortens,the amount and stability of austenite get decreased,the content of martensite increases markedly,and the mechanical characteristics of the steel transform from TRIP steel's to dual-phase steel's gradually.