Production and several properties of single crystal austenitic stainless steels

The single crystal austenitic stainless steels Type 316L and 304L were grow n in order to improve the resistance to stress corrosion cracking (SCC) usi ng a unidirectional solidification method which can provide the large size single crystals. The mechanical properties and the chemical properties were examined. The orientation and temperature dependence of tensile properties of the single crystals were measured. The yield stress of the single cryst al steels are lower than those of the conventional polycrystal steels becau se of the grain boundary strength cannot be expected in the single crystal steels. The tensile properties of the single crystal austenitic stainless s teel Type 316L depend strongly on the orientation. The tensile strength in [111] orientation are about 200 MPa higher than those in the [100] and [110 ] orientations. The microstructure of the single crystal consists of a mixt ure of the continuous gamma-austenitic single crystal matrix and the delta- ferrite phase so that the effects of the gamma/delta boundaries on the chem ical properties were studied, The effects of the delta-ferrite phases and t he gamma/delta boundaries on the resistance to SCC were examined by the cre viced bent beam test (CBB test), No crack is observed in all the CBB test s pecimens of the single crystals, even at the gamma/delta boundaries. The be havior of the radiation induced segregation (RIS) at the gamma/delta bounda ries in the single crystal austenitic stainless steel Type 316L was evaluat ed by the electron irradiation test in the high voltage electron microscope (HVEM). The depletion of oversized solute chromium at the gamma/delta boun dary in the single crystal austenitic stainless steel Type 316L is remarkab ly lower than that at the grain boundary in the polycrystalline-type 316L.