Comparison of the welding behavior of P/M borated and I/M borated stainless steel

Tanniru Rajesh Babu; Sadayan Rajendra Boopathy; Sajja Rama Koteswara Rao; Guttikonda Raja Kumar; Gabbita Durga Janaki Ram

doi:10.3139/120.111065

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Comparison of the welding behavior of P/M borated and I/M borated stainless steel

Tanniru Rajesh Babu , Sadayan Rajendra Boopathy , Sajja Rama Koteswara Rao , Guttikonda Raja Kumar und Gabbita Durga Janaki Ram

Veröffentlicht/Copyright: 28. August 2017

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Abstract

Borated stainless steels are being used to control neutron criticality in reactors as control rods, shielding material, spent fuel storage racks and transportation casks. Borated stainless steels fabricated via powder metallurgy (P/M) route (grade A) exhibit superior neutron absorption, enhanced toughness and ductility compared to cast ingot metallurgy (I/M) steels (grade B), due to fine and uniform dispersion of borides. In this study, welds were made using both 304B grade A and grade B materials by gas tungsten arc welding and activated gas tungsten arc welding processes. The effect of the activated flux on the bead geometry, microstructure and mechanical properties was investigated and compared. The heat input required for P/M steel material to produce full penetration welds has been found to be significantly higher compared to I/M steel, while all welds exhibited high joint efficiencies. Metallographic examinations revealed that no porosities and shrinkage cracks have been observed either in the fusion zone or in partially melted zone of the weldments. The fusion zone structure of 304 P/M type consists of a higher amount of eutectics with less number of austenite dendrites compared to I/M type. Both P/M and I/M steel welds exhibited partially melted zones adjacent to fusion zone. P/M steel welds were found to fracture in the partially melted zone, where a significant loss in hardness was noticed due to irregular boride eutectics, while in case of I/M steel welds, failure occurred in base material. It has been concluded that the P/M steel 304B grade A exhibits good GTA weldability compared to grade B material.

Kurzfassung

Borierte hochlegierte Stähle werden verwendet, um die Neutronenkritikalität in Reaktoren zu kontrollieren, so werden sie als Kontrollstücke, Schutzwerkstoff, Lagergestelle für verbrauchte Brennelemente und Transportgebinde verwendet. Borierte Stähle, die mittels Pulvermetallurgie (P/M) hergestellt wurden (Güte A), weisen eine sehr gute Neutronenabsorption, eine verbesserte Zähigkeit und Duktilität im Vergleich zu metallurgisch vergossenen (Cast Ingot Metallurgy (I/M)) Stählen (Güte B) auf, und zwar aufgrund der feinen und gleichmäßigen Verteilung der Boride. In der diesem Beitrag zugrundeliegenden Studie wurden Schweißungen aus beiden Stählen des Typs 304B, Güte A und Güte B, mittels des Wolfram Inertgas und mittels des Wolfram Aktivgas Prozesses hergestellt. Die Auswirkungen des Aktivgases auf die Schweißnahtgeometrie, die Mikrostruktur und die mechanischen Eigenschaften wurden untersucht und verglichen. Der erforderliche Wärmeeintrag für den P/M-Stahl zur Herstellung voll durchgeschweißter Verbindungen stellte sich im Vergleich zum I/M-Stahl als signifikant höher heraus, während alle Schweißungen eine hohe Verbindungseffizienz aufwiesen. Metallografische Untersuchungen zeigten, dass keine Porosität und keine Schwindungsrisse auftraten, und zwar weder im Schweißgut noch in der Wärmeeinflusszone. Das Schweißgutgefüge des Stahles 304 P/M enthält eine höhere Anzahl an Eutektika mit einer geringeren Anzahl austenitischer Dendriten im Vergleich zum I/M-Typ. Beide Stahlschweißungen, P/M und I/M, zeigten partiell aufgeschmolzene Zonen neben der Schmelzzone, wo ein signifikanter Härteverlust beobachtet wurde, und zwar aufgrund der irregulären Borid-Eutektika, während im Fall der I/M-Stahlschweißungen ein Versagen im Grundwerkstoff auftrat. Daraus wurde geschlossen, dass der Stahl 304B des Typs P/M (Güte A) im Vergleich zum Werkstoff Güte B eine gute Schweißbarkeit mittels Aktivgas aufweist.

*Correspondence Address, Asst. Prof. T. Rajesh Babu, Tagore Engineering College, Rathinamangalm, Melakottayiur Post, Chennai 600127, E-mail: rajesh_babu999@yahoo.com, boopathy@annauniv.edu, sajjarkr@yahoo.com, rajkumardotcom@yahoo.com, jram@iitm.ac.in

Assistant Prof. Tanniru Rajesh Babu, born in 1984, completed his ME in Manufacturing Systems and Management at Anna University, Chennai, India. He is working as Assistant Professor in the Department of Mechanical Engineering, Tagore Engineering College, Chennai, India. He is pursuing his PhD in the Faculty of Mechanical Engineering at Anna University, Chennai under the guidance of Prof S. Rajendra Boopathy and Prof. S. R. Koteswara Rao.

Prof. Dr. Sadayan Rajendra Boopathy, born in 1961, received his PhD in Mechanical Engineering from Anna University, Chennai, India. He has published more than 15 papers in international journals. He has around 29 years of professional experience in teaching and research. Presently, he is working as Professor in the Department of Mechanical Engineering, Anna University, Chennai.

Prof. Dr. Sajja Rama Koteswara Rao, born in 1966, received his PhD in Metallurgical and Materials Engineering from IIT Madras, Chennai, India in 2005. He has published more than 25 papers in international journals. He has around 20 years of professional experience in teaching and research. Presently, he is working as Professor in the Department of Mechanical Engineering, SSN College of Engineering, Kalavakkam, Chennai, India.

Associate Prof. Dr. Guttikonda Raja Kumar, born in 1980, received his PhD in Mechanical Engineering from Anna University, Chennai, India. He has published more than six papers in international journals. He has around 13 years of professional experience in teaching and research. Presently, he is working as Associative Professor in the Department of Mechanical Engineering, Swarna Bharathi Institute of Science and Technology, Khammam, Telangana, India.

Associate Professor Dr. G. D. Janaki Ram, born in 1968, received his PhD in Metallurgical and Materials Engineering from IIT in Madras, Chennai, India in 2005. He completed his post-doctoral studies at Utah State University, USA. He has published more than 53 papers in international journals. He has around 20 years of professional experience in teaching, industry and research. Presently, he is working as Associate Professor in the Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai, India.

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Published Online: 2017-08-28

Published in Print: 2017-09-01

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https://doi.org/10.3139/120.111065