Microstructure and Mechanical Properties of Reheated Zones in the Multi-pass Weld Metal of High-Strength Steel

Abstract

The influence of thermo-mechanical cycling on the microstructure and strength in the weld coarse-grained heat affected zone (CGHAZ) of Ti-Nb added low carbon HSLA steel was explored through Vickers hardness tests, nanoindentation experiments, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis. Undeformed and deformed CGHAZs were simulated using Gleeble simulator with different heat inputs of 30kJ/cm and 300kJ/cm. At high heat input of 300kJ/cm, the CGHAZ consisted of ferrite and pearlite and then their grain sizes were not affected by deformation. At low heat input of 30kJ/cm, the CGHAZ consisted of lath martensite and then the sizes of prior austenite grain, packet and lath width decreased with deformation. In addition, the fraction of particle increased with deformation and this is because the precipitation kinetics was accelerated by deformation. Meanwhile, the Vickers and nanoindentation hardness of deformed CGHAZ with 30kJ/cm heat input were higher than those of undeformed CGHAZ, which are due to the effect of grain refinement and precipitation strengthening.

Characterization of the local brittle layer formed in electro-gas weld metals

“…These are different from the as-deposited microstructures to a varied extent depending on the peak temperatures of weld thermal cycles given by the subsequent passes and their cooling rates [15]. This, in turn, can render local changes in mechanical properties and especially in the impact toughness of the weld metals [16][17][18][19]. Accordingly, for a better understanding of the relationship between microstructure and mechanical properties, researchers often prefer to employ the as-deposited weld metals made via one-pass welding techniques [10,20,21].…”