APFIM AND TEM INVESTIGATIONS OF PRECIPITATION IN RAPIDLY SOLIDIFIED 316-STAINLESS-STEEL

316 stainless steel has been rapid solidification-processed (RSP) by g as atomization and hot extrusion of the powder with the intent of impr oving the mechanical properties through fine-scale precipitation. Vana dium, nitrogen and oxygen have been introduced intentionally as alloyi ng elements for this purpose. The yield strength after solution heat t reatment of the RSP alloy is 450 MPa. By ageing at 600 degrees C for 1 000 h, the yield strength increases to 615 MPa with little loss of duc tility (53% reduction of area). The ultimate tensile strength after co ld work and ageing is 922 MPa. The morphology and composition of the p recipitates in this steel have been investigated using APFIM and TEM t echniques in order understand the origin of the high strength. A high numbered density (approximate to 2x10(21) m(-3)) of 25 nm plate-like p recipitates was observed with TEM in an aged specimen. The composition of these precipitates was analyzed using APFIM techniques, and was fo und to be a complex nitride of Cr, V, Fe, Ni and Mo. This nitride prec ipitate was not found in an unaged specimen of this alloy. These preci pitates are responsible for improving mechanical properties by dispers ion strengthening. (C) 1998 Elsevier Science S.A. All rights reserved.