Friction Stir Welding of HT9 Ferritic-Martensitic Steel: An Assessment of Microstructure and Properties.

摘要

This thesis explores the processing-microstructure-property relationships in friction stir welded (FSW) HT9A ferritic-martensitic steel. HT9 has previously been studied as a structural component for fusion/fission based reactors; however, the changes in material microstructure and properties after friction stir welding have not been considered. HT9A steel plate was friction stir welded with a series of increasing heat inputs. The microstructure of this welded material was characterized using optical and electron microscopy. The mechanical properties of the welded material were determined using nanoindentation and microhardness measurements. In addition, electrochemical impedance spectroscopy (EIS) in molten lithium fluoride was used to assess the high temperature corrosion resistance of the welded material in the harsh environments found in fusion reactors. The quality of the friction stir welds was excellent, and the basic ferritic-martensitic microstructure was maintained for all of the conditions used. Some reduction in hardness was observed in the welded material, particularly in the heat affected zones. The high temperature corrosion response of the welded material was comparable to, or slightly better than, the base plate material.