Cooling Induced Segregation of Impurity Elements to Grain Boundaries in Fe--3 wt.% Ni Alloys, 2.25 wt.% Cr--1 wt.% Mo Steel and Submerged Arc Weld Metal

• Published in: Acta metallurgica et materialia Vol. 42; no. 10; pp. 3309 - 3320
• Main Authors: Vorlicek, V, Flewitt, P E J
• Format: Journal Article
• Language: English
• Published: 01.10.1994
• ISSN: 0956-7151

Previous theoretical and experimental studies demonstrate that small bulk concentrations of impurity and solute elements can segregate to grain boundaries in ferritic steels during cooling from high temperatures. This results from solute-vacancy pair formation and their subsequent diffusion to the grain boundary sinks. The grain boundary segregation which results from cooling at three different rates from fixed temperatures of 1273 and 1323K respectively, have been measured on ferritic (in wt.%) Fe--3Ni alloys and 2.25Cr--1Mo steel containing additions of either phosphorus or tin. In addition, a C--Mn submerged arc weld metal subject to a complex thermal cycle has been investigaed. The composition of the grain boundaries have been measured on thin foil specimens using both conventional and high resolution STEM-EDS X-ray microanalysis techniques. Segregations of both P and Sn have been observed in the Fe--3Ni alloys and 2.25Cr--1Mo steel and P segregations in the weld metal. The measured grain boundary segregations of both P and Sn are discussed with respect to previous theoretical predictions for the cooling rates investigated and interactive role of other elements present.