Evaluation of Microstructure, Microhardness, and X-Ray Elastic Constants for Simulated Heat-Affected Zones in Q1N Steel

摘要

Reliable assessment of residual stresses in critical structures using x-ray diffraction techniques requires determination of an accurate x-ray elastic constant (XEC) to accurately calculate residual stress state from measured crystallographic elastic strain. Experimental derivation of the XEC is the most reliable approach. This study examines whether experimental XECs derived for quenched and tempered Q1N steel are still accurate to quantify stress in the heat-affected zones (HAZ) of welded joints. A Gleebl thermal simulator is used to generate coarse-grained, fine-grained and intercritical HAZ microstructure in Q&T Q1N steel. Thermal simulation conditions (grip separation, thermal cycles and cooling rate) were optimized to produce the desired coarse-grained HAZ microstructure at a peak temperature of 1300 degrees C in large Q1N steel samples. While thermal conditions produced HAZ microstructure and microhardness values that were characteristic of real weld HAZs, there is no measurable effect on bulk elastic properties or the XECs. The bulk elastic modulus has an average value of 204.0 +/- 1.3 GPa for the base metal and the selected peak temperatures used for the three different HAZ regions. The XECs have an average value of 176.6 +/- 3.6 GPa for the {211} crystallographic planes of bcc Fe for all samples. Results instil confidence in use of base metal XECs for residual stress analysis within actual or real weld HAZ of Q&T Q1N steel on submarine pressure hulls.