Heat-Affected Zone in Multipass Welding

Traditionally, the heat-affected zone (HAZ) of welded joints of low-carbon steels of the type under study is divided into four main zones [9, 10]: 1) the grain coarsened zone, in which the temperature of metal during welding is increased above 1100-1200 °С (depending on the chemical composition of the steel), designated as GCHAZ; 2) the fine grain zone, in which complete recrystallization occurs, and the temperature of metal increased above 1100÷1200 °С (Ac3), designated as FGHAZ; 3) the intercritical zone, in which partial recrystallization occurs (Ac3 -to Ac1), designated as ICHAZ; and 4) the subcritical zone, in which the temperature of metal during welding is not increased above Ac1, designated as SCHAZ.

However, in multipass welding, the above zones can be repeatedly layered on top of each other [ 11], thereby forming alternating microstructural states at distances which are equidistant from the central axis of the weld.

When examining thick-walled welded joint in detail, it is possible to distinguish more than 10 zones, including actual critical and conditional critical areas.

These include: 1 – columnar weld metal, 2 –subcritical grain coarsened zone in the presence of influence from other zones, 3 – intercritical grain coarsened zone resulting from overlapping of heat-affected zones, 4 – conditional line Ас3, 5 – conditional line Ас1, 6 – isolated intercritical zones in the absence of influence from other zones, 7 – unit subcritical zone in the absence of influence from other zones, 8 – actual nonvisible boundary of the heat-affected zone, 9 –base metal, 10 – fine-grain zone, 11 – grain coarsened zone, 12 – fusion line