Precipitation Behavior and Its Strengthening Effect of X100 Pipeline Steel

Using TEM (transmisson electron microscopy), electron diffraction, EDX (energy dispersive X-ray) analysis and physicochemical phase analysis, the morphology, crystal structure, size distribution and chemical composition of precipitates in the microstructure of high strength Nb-microalloyed X100 pipeline steel were investigated, and the strengthening effect of precipitation was quantitatively calculated with Ashby-Orowan correction model. The precipitates obtained in X100 pipeline steel can be divided into two kinds, complex and single particles by morphology. The EDX analysis of single precipitates reveals that the chemical composition matches well with particle dimensions, especially the Nb to Ti ratio regularly decreases with the increase of particle size. The yield strength increments in the way of precipitation strengthening of X100 pipeline steel reached about 52 MPa, suggesting that the precipitation strengthening is not the dominative strengthening mechanism for X100 pipeline steel.