Characterizing Spatial Distributions of Microstructure and Notch Toughness in Modern Structural Steel Weldments Using Numerical and Physical Simulations

Abstract

Heterogeneity of material properties in structural weldments resulting from steep gradients in material microstructure is one of several factors that complicates the prediction of their full mechanical response up to and including fracture. Conventional material test coupons typically sample material volumes far greater than those over which these properties vary and consequently indicate effective material responses aggregated over multiple microstructures, which are unsuitable for use within continuum finite element–based frameworks that rely on estimates of local material properties. In this study, a method is validated for measuring the spatial distribution of mechanical properties in weldments that circumvents this issue. The method uses a combination of numerical and physical simulation to reproduce the microstructures that form over short length scales ( ∼ 0.75    mm ) in the weld heat affected zone (HAZ). The microstructures are produced uniformly over the gauge length of a coupon that can be later tested to determine mechanical properties. Once validated, the method is used to make quantitative assessments of the connection between the notch toughness of individual HAZ regions, their measured volume fractions along the crack plane, and the resulting energy absorbed in a Charpy V-notch (CVN) test. The results, which shed light on the scatter common to HAZ CVN data, are used to examine the merits of CVN sampling locations required in weld qualification testing by current welding codes and to make recommendations for alternate sampling locations tailored to better identify low toughness regions in modern weldments.