Influence of heat input on microstructure and mechanical properties of gas tungsten arc welded HSLA S500MC steel joints

Kornokar, K., Nematzadeh, F., Mostaan, H., Sadeghian, A., Moradi, M., Waugh, D.G. and Bodaghi, M. ORCID: 0000-0002-0707-944X, 2022. Influence of heat input on microstructure and mechanical properties of gas tungsten arc welded HSLA S500MC steel joints. Metals, 12 (4): 565. ISSN 2075-4701

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Abstract

High-strength low alloy (HSLA) S500MC steel is widely used for chassis components, structural parts, and pressure vessels. In this study, the effects of heat input during automatic gas tungsten arc welding (GTAW) on microstructure and mechanical properties of thermomechanically controlled processed (TMP) S500MC steel were investigated. A butt joint configuration was used, and welding was performed in autogenous mode. Six different levels of heat input namely 1.764 kJ/mm, 1.995 kJ/mm, 2.035 kJ/mm, 2.132 kJ/mm, 2.229 kJ/mm, and 2.33 kJ/mm were considered. Microstructural investigations revealed a different microstructure than base metal in the fusion zone (FZ) of all welded joints which was most likely due to a lath martensitic microstructure surrounded by retained austenite. With increased heat input, the amount of retained austenite and the size of packets increased. In the heat-affected zone (HAZ), two distinct regions of coarse grain (CG-HAZ) and fine grain (FG-HAZ) were observed. Due to the presence of carbides in the HAZ, mostly a martensitic microstructure with smaller packets, compared to FZ, was formed. By increasing the heat input and through the dissolution of carbides, the dimension of packets increased. Due to microstructural changes and grain growth, in both the FZ and the HAZ, the mechanical properties produced by TMP were lost in these regions. However, failure occurred in the base metal of all samples with a maximum tensile strength of 690 MPa. Thus, tensile strength in the weld zone and HAZ were higher than the base metal even for the highest heat input indicating the formation of a good joint between S500MC plates with GTAW, regardless of heat input.

Item Type: Journal article
Publication Title: Metals
Creators: Kornokar, K., Nematzadeh, F., Mostaan, H., Sadeghian, A., Moradi, M., Waugh, D.G. and Bodaghi, M.
Publisher: MDPI AG
Date: 27 March 2022
Volume: 12
Number: 4
ISSN: 2075-4701
Identifiers:
NumberType
10.3390/met12040565DOI
1533667Other
Rights: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).
Divisions: Schools > School of Science and Technology
Record created by: Laura Ward
Date Added: 30 Mar 2022 10:48
Last Modified: 30 Mar 2022 10:48
URI: http://irep.ntu.ac.uk/id/eprint/46002

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