ABSTRACT
In the heat-affected zone (HAZ) significant changes in the microstructure and properties take place due to the transformations induced by the thermal cycles. The HAZ can be divided into several subzones, depending on the peak temperature that the material has experienced. For regions of the HAZ that achieve peak temperatures between 1100 to 1500°C, the steels transform to austenite, the grains of which can grow significantly during the high-temperature part of the thermal cycle. In the HAZ, the microstructure must obviously vary with the distance from the fusion line in correspondence with the fact that both the austenite grain size and the cooling rate are a function of this distance. The microstructure that develops in the different parts of the HAZ depends upon the chemical composition of the steel, the thermal cycle, and the austenite grain size. The chapter concludes with a discussion of some qualities of steel that are especially pertinent to the HAZ.
