Development of shielded metal arc welding electrodes to achieve carbide-free bainitic weld microstructures
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RESEARCH PAPER
Development of shielded metal arc welding electrodes to achieve carbide-free bainitic weld microstructures Sudharsanan Sundaram 1 & G. D. Janaki Ram 2 & Murugaiyan Amirthalingam 1 Received: 28 July 2020 / Revised: 1 September 2020 / Accepted: 2 September 2020 # International Institute of Welding 2020
Abstract Carbide-free bainite (CFB) microstructures containing a mixture of nano-sized retained austenite laths and bainitic ferrite exhibit a good combination of strength, ductility, and toughness. In this work, an attempt was made to identify welding electrode compositions with a carbon content of about 0.35 to 0.5 wt.% to achieve carbide-free bainite microstructures in multi-pass shielded metal arc welds. Suitable alloy compositions were designed using a commercial neural network–based database, considering thermodynamic parameters such as allotropic phase boundary (XTo), ΔGɣ-ɑ (driving force for transformation) and martensite start temperatures. Three different alloy compositions were identified using this approach. Shielded metal arc welding (SMAW) electrodes were fabricated with the compositions identified and the samples extracted from the weld deposits were used for dilatometer studies, metallurgical characterisation, and mechanical property evaluation. Based on the results, an optimised electrode composition and welding parameters were identified to stabilise the carbide-free bainitic microstructures in weld metal. Keywords Carbide-free bainite . SMAW electrode . Weld microstructure
1 Introduction Steel microstructures containing bainitic ferrite and nanosized retained austenite laths are known to offer a good combination of tensile strength (up to 1.8 GPa), total elongation (up to 30%), and toughness up to 40 MPa m1/2 [1]. These high-strength steels are currently considered candidate materials for balliest resistance armour tank bodies, construction of heavy-duty cranes, and load bearing members in earthmovers. This combination of properties is achieved by the presence of fine bainitic ferrite plates and filmy inter-lath retained Recommended for publication by Commission II - Arc Welding and Filler Metals * Sudharsanan Sundaram [email protected] G. D. Janaki Ram [email protected] Murugaiyan Amirthalingam [email protected] 1
Indian Institute of Technology Madras, Chennai, TN, India
2
Indian Institute of Technology Hyderabad, Yeddumailaram, TS, India
austenite. This microstructure is stabilised by suppressing nucleation of cementite while austenite is transforming to bainite [1, 2]. The suppression of cementite during the transformation of austenite to bainite is possible by the addition of silicon (about 1.5 wt.% or higher) [3–5]. Carbide-free bainitic (CFB) microstructures are also known to provide adequate resistance against hydrogenassisted cold cracking [6, 7]. The retained austenite present in CFB structure delays hydrogen-assisted cold cracking in three ways: (i) dissolving atomic hydrogen in the austenite matrix, as the solubility of hydrogen is more in austenite than in f
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