LAUSR

The heat affected zone (HAZ) formed due to vigorous heat treatment and recrystallization during welding is the most critical zone. Failure at the HAZ has been reported to be as a result of change in microstructure and reduction of mechanical properties [1]. Variation in preheating temperature and cooling rate has a significant effect on microstructure and mechanical properties of the HAZ of welded pearlitic rail steel and formation of martensite at higher cooling rates has been reported [2]. Slow cooling rates increased both the grain size and interlamellar spacing of the pearlite colony in the HAZ of welded rail [3]. Narrow interlamellar spacing resulted in higher hardness as more of the cementite phase was present there. However, toughness depends only on grain size, with a smaller grain size producing higher toughness [4]. For these reasons, retention of the pearlitic structure in the HAZ after gas metal arc weld (GMAW) finishing is highly desirable and understanding the effect of cooling rate on microstructure needs attention.