Investigation On Preparation, Microstructure And Mechanical Properties Of14Cr Oxide Dispersion Strengthened Ferritic Steel

14Cr Oxide dispersion strengthened (ODS) ferritic steels, which are the leading candidate structural materials for fusion first wall application, were investigated in this thesis. Supersaturated Fe-14Cr-2W-0.3Ti-0.3Y2O3(wt%) alloy powders were prepared by mechanical alloying (MA). Effects of mechanical alloying process on powder morphology, particle size, composition and grain size were studied by scanning electron microscopy (SEM), Energy Dispersive Spectrometer (EDS), X-ray diffraction analysis (XRD) and laser particle size analysis. MA powders were consolidated by hot isostatic pressing (HIP) to produce14Cr ODS ferrtic steel with extremely high density of nano-scale oxide dispersion strengthened precipitates. Microstructure of hipped ODS steel was studied by transmission electron microscope (TEM) and mechanical properties were investigated after HIP. The main conclusions are shown as follows:(1) After2h milling, MA powders have serious cold welding phenomenon and mean particle size increases to a maximum of47.74μm. After12h, the average particle size decreases rapidly and the peak of particle size distribution curve gradually shifts to the left side. In the range of40～70h, the morphology of MA powders trends to be spherical, the mean particle size is refined gradually and reaches the minimum value of12.21μm.(2) With the increasing of milling time, W and Cr dissolve gradually in α-Fe matrix, grain size of MA powders decreases and lattice distortion increases. During0.05～20h milling, grain size of powders reduces to10.3nm quickly and then there is not obvious change of grain size. After70h milling, W and Cr dissolve completely in α-Fe, the composition of MA powders is uniformly and mechanical alloying process is completed. Up to80h, mean particle size begins to increase due to powder agglomeration. So the optimal milling time is70h.(3)14Cr ODS ferritic steel is obtained by hot isostatic pressing of70h MA powders. The density of ODS steel is up to99.6%of the theoretical density.(4) The characteristical microstructure of14Cr ODS ferritic is extremely high density of nano-scale clusters/precipitates, high density of dislocations and the grains in the range from hundreds of nanometers to several microns. Three precipitates are found by TEM:①High density of non-stoichiometric fine Y-Ti-O rich clusters, which are coherent with the matrix. The density of clusters is1.875×1024/m3. After heat treatment, the density is1.7×1024/m3;②A few precipitates of Y2Ti2O7(face-centered cubic, a0=1.009nm) with the density of2×1020/m3;③A complex Cr-, Ti-,Y-rich precipitates, Cr/Ti ratio is close to2:1, which is a unknown phase. The clusters are very stable after1250℃/8h heat treatment. YaTiO7distrbute heterogeneous after HIP, while distribute dispersion in the grain after heatrement.(5)14Cr-ODS ferritic steel shows high strength at room temperature and high temperature tensile test. Tensile strength at room temperature,700℃and750℃are1150MPa,370MPa and265MPa respectively. So, odixe dispersion particles can improve high temperature strength. By means of optimization HIP pressing to improve high temperature plastic of14Cr-ODS ferritic steel in further.