Iron-phosphorus-carbon system Part 2 - Metallographic behaviour of Oberhoffer's reagent

An investigation of the microstructures found in phosphoric irons has been carried out as part of a larger archeometallurgical investigation. Oberhoff er's reagent has been used traditionally to display the macroscopic distrib ution of phosphorus in steels but in order to determine the microscopic res ponse of the reagent with certainty, a systematic study of its action has b een undertaken. The reagent is in current use in the metallographic analysi s of archeological iron artefacts and its action needed to be clarified bef ore further use in the current work. A series of specimens with controlled microstructures and solute profiles has been examined when etched with nita l and also with Oberhoffer's reagent. The solute distribution in some of th e specimens has been confirmed using wavelength dispersive X-ray microanaly sis. It has been shown that Oberhoffer's reagent responds to microstructura l as well as macrostructural segregations of phosphorus and also to nickel and arsenic. The etch does not deposit copper at a significant rate on carb ide or phosphide particles so that they remain bright after etching. In fer ritic microstructures, there may be a slight response due to variation in g rain orientation. MST/4364. (C) 2000 IoM Communications Ltd.