In Pursuit of Optimum Steel Weld Microstructure

A priori design of optimum steel weld microstructure, for high- or low-temperature application, with minimal experimental work remains as a challenge. With rapid progress in integrated computational materials science and engineering (ICME) models, it is quite possible to design new generation of steels with targeted mechanical properties. 

For example, Blast resistant steels [BA-160] for naval applications with high strength (yield strength > 1000 MPa), good toughness (CVN > 115 J at -60°C) and ballistic performance had been developed using ICME models [1], without experimental trial and error optimization.  In contrast, welding system design, i.e., optimization of heat-affected-zone (HAZ) and weld metal (WM) properties, requires experimental trial and error research. The seminar will provide highlights of the research on HAZ microstructure development in BA-160 steel using ex-situ [dilatometry, analytical electron microscopy, local electrode atom probe (LEAP) microscopy] and in-situ [local scanning confocal microscopy and time-resolved X-ray diffraction using Synchrotron radiation] characterizations.  Using these data, the softening and hardening in the HAZ regions were rationalized [2].  However, the design of filler metal for achieving comparable WM properties remains elusive. 

Use of integrated modeling is considered as a pathway to arrive at generic welding system solutions.  However, based on recent publications, arguments are made that generic solutions are not viable. This is due to inability of these models to consider complex and transient boundary conditions imposed by field welding conditions. In lieu of generic solutions, design of invariant microstructure is suggested as an alternative approach [3].

References

(1) A. Saha, G. B. Olson, J Computer-Aided Mater Des, 2007, Vol. 14, pp. 177-200

(2) X. Yu, et al., Acta Materialia, 2010, Vol. 58, pp. 5596 – 5609

(3) S. S. Babu, Science and Technology of Welding and Joining, 2011, Vol. 16, pp. 306 – 312