Effect of Preheating Temperature on Microstructure and Mechanical Properties of Friction Stir Welded DMR249A HSLA Steel Joints

The purpose of this research is to examine the influence of temperature of preheating on mechanical performance and microstructure of FSW joints of DMR249A steel. The FSW joints were produced with no preheating and preheating at 100, 150, 200 and 250 degrees C respectively. Tensile properties and toughness of FSW joints were reduced when the temperature of preheating was raised from 100 to 250 degrees C. This is primarily related to an increased input of heat that results in inclusions of tungsten due to the wear of W99 tool and grain coarsening in stir zone (SZ) of FSW joints. The FSW joints produced with no preheating and preheating at 100 degrees C displayed greater tensile properties and toughness compared to the FSW joints produced with preheating at 150, 200 and 250 degrees C. This refers to the greater refinement of SZ microstructure of FSW joints which is made up of greater bainite regions and acicular ferrite.