Comparison of microstructure and formation of intermetallic phases on F82H-mod. and MANET II

This paper describes investigations on the formation and transformation of aluminde phases on F82H-mod. steel and for comparison on MANET II, as reference materials. In order to achieve the desired mechanical properties of both steels, a fully martensitic microstructure has to be adjusted by a special heat-treatment. For the improvement of the microstructure of the Al based permeation barrier, a heat treatment after hot dip aluminising is necessary as well. To meet both requirements, heat treatments at different temperatures (700 degrees C/100 h or 1075 degrees C/0.5 h for MANET II and F82H-mod.) were performed for comparison after hot dipping, followed by a subsequent annealing at 750 degrees C for 2 h. At the highest temperature, the perfectly adhering aluminide scale can be subdivided into an upper FeAl phase, an intermediate band of pores and a lower part of alpha-Fe(Al) solid solution phase. Differences in microstructure and phase composition between MANET II and F82H-mod. are described by microanalytical techniques. (C) 1998 Elsevier Science B.V. All rights reserved.