Determination of Mechanical Property Gradients in Heat-Affected Zones of Ferritic Steel Weldments by Shear-Punch Tests

摘要

The heat-affected zone (HAZ) of 2.25 Cr-1 Mo ferritic steel weldments consists of coarse-grained bainite, fine-grained bainite and intercritical structures. In the case of a 2.25 Cr-1 Mo/9 Cr-1 Mo dissimilar weld joint formed with 9 Cr-1 Mo weld metal, the HAZ on the 2.25 Cr-1 Mo base metal side consists of a soft decarburized zone and a carburized zone in the adjacent weld metal. In welded structures of these ferritic steels, a high percentage of failure has been reported to occur in the HAZ of the weldment. The mechanical properties of these individual regions of HAZ are difficult to determine by conventional methods because of the practical difficulties of making mechanical test pieces of adequate dimensions with entirely individual microstructures from the very small regions in HAZ. This paper describes the use of shear punch tests to determine the mechanical properties of the individual regions of HAZ formed in 2.25 Cr-1 Mo (similar) weldments and 2.25 Cr-1 Mo/9 Cr-1 Mo (dissimilar) weld joints. A linear correlation established between the tensile properties and the corresponding properties obtained from the shear punch test of various heat-treated structures has been used to characterize the mechanical properties of individual regions of the HAZ of actual weldments.