Estimation of local properties in welded joints using samples with simulated microstructure

Abstract

Purpose

The purpose of this paper is to determine local properties in a coarse grain zone of 10 mm thick butt welded joints made of structural S355 and high strength S960 steels. Metallographic analyses showed that the width of the investigated zone for both S355 and S960 weldments was too small for direct sampling. Therefore, samples with reproduced microstructure were manufactured by heat treatment taking into account chemical composition and cooling conditions of weldments.

Design/methodology/approach

The basis for the heat treatment was the time-temperature-transition (TTT) curve, whose shape is defined by welding and cooling parameters. In this study the TTT curve was determined experimentally during welding as well as numerically simulated using SYSWELD program. The work pieces were heat-treated according to the TTT curves using thermomechanical treatment simulator and evaluated in terms of microstructure and micro hardness distribution. Finally, the secondary specimens were manufactured and investigated in monotonic tensile tests.

Findings

The presented approach allows for the determination of the local properties of welded joints. In this study mechanical properties (stress-strain curves) of heat affected zone (HAZ) were successfully estimated using samples with reproduced microstructure. Furthermore, it was found out that the chemical composition in the HAZ was not influenced by the welding process. Thus, the HAZ microstructure can be successfully reproduced using base material. Additionally, the paper contains recommendations for simulation of the local microstructure and suggestions for the evaluation of the obtained results.

Originality/value

The advantage of the proposed approach is the enlargement of the material volume with homogeneous microstructure so that different local properties like toughness, fatigue behavior, crack propagation or crashworthiness can be analyzed, what is technically infeasible for the weldments with small HAZ.

Citation

Kucharczyk, P. and Münstermann, S. (2016), "Estimation of local properties in welded joints using samples with simulated microstructure", International Journal of Structural Integrity, Vol. 7 No. 6, pp. 739-747. https://doi.org/10.1108/IJSI-10-2015-0047