Precipitation Behaviors of Second Phase in Er-containing Stainless Steel Shielding Material

The precipitation behaviors of the second phase in Er-containing stainless steel were investigated by means of optical microscope（OM） and scanning electron microscope（SEM）.The second phase in stainless steel is mainly Ni-Er system,there are two second phases with the same elements but showing obviously different content,and the molar fraction ratio of Ni and Er in the two second phases is 2∶1.Most of the second phases in stainless steel are rod-like and precipitate along the grain boundaries,their amounts increase linearly with increasing the Er content.When the mass fraction of Er increases from 1.62% to 7.45%,the area percentage of the second phase increases from 7.0% to 24.5%.The plasticity of the second phase is worse than that of the matrix,thus the two phases cannot deform synergistically.Consequently the external force causes the second phase to break and fracture,which leads to the initiation and development of micro-cracks.