Metallurgical transformations of high strength low alloys steels 450 EMZ type II in the heat affected zone during multipass submerged arc welding

A considerable number of crack tip opening displacement tests in the heat affected zone (HAZ) of multipass welds, performed in accordance with standards BS 5762 and EEMUA, are rejected since the crack is not inside the coarse grain region at 0.5 mm from the fusion border, as well as the quantity of the crack length in percentage, that the crack goes through the intercritical region instead of in the grain coarse region as it would correspond. This circumstance make advisable to carry out a metallographic study of the intercritical zone in the HAZ as well as the corresponding tests, in order analyze the intercritical region brittleness reasons. The study is performed on a HSLA 75 mm thick panel 450 EMZ type II, welded under a SAW process with heat input and welded parameters controlled, without any cost weld heat treatment