Characterization of Solidification Cracking in 304HCu Austenitic Stainless Steel Welds

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ORIGINAL ARTICLE

Characterization of Solidification Cracking in 304HCu Austenitic Stainless Steel Welds R. Ravibharath1



V. Muthupandi2 • P. Bala Srinivasan3 • K. Devakumaran1

Received: 2 August 2019 / Accepted: 18 June 2020 Ó The Indian Institute of Metals - IIM 2020

Abstract Alloy 304HCu is an austenitic stainless, developed from TP304H with the addition of copper and niobium for power plant applications. Solidification cracking is major issue in welding of austenitic stainless steels. In this paper, solidification cracking behaviour of alloy 304HCu with three different fillers viz., nickel fortified near-matching alloy 304HCu, ER NiCrCoMo-1 and ER NiCrMo-3 using Varestraint weldability testing. The solidification cracking behaviour of the parent material and different welds were assessed under different strain rates and the mechanisms were discussed, addressing the microstructural evolution and compositional changes. The weld materials were characterized for their mechanical properties both at ambient conditions and at elevated temperature, highlighting their usefulness in the power sector. Keywords Alloy 304HCu  GTA welding  Weldability testing  Solidification cracking  Back-filling

& R. Ravibharath [email protected] 1

Welding Research Institute, BHEL, Tiruchirappalli, Tamil Nadu 620 014, India

2

Department of Metallurgical and Materials Engineering, National Institute of Technology, Tiruchirappalli, Tamil Nadu 620 015, India

3

School of Mechanical Engineering, SASTRA Deemed University, Thanjavur, Tamil Nadu 613 401, India

1 Introduction Alloy 304HCu (UNS S30432) was developed by Sumitomo Metal Industries Limited, Japan for boiler applications in the 1990s [1]. This is a modified version of the austenitic stainless steel grade TP304H, with the addition of copper and niobium. In recent times, this is a preferred material for the re-heater and super-heater tubings for the super-critical boilers owing to the superior creep-rupture properties up to 650 °C [2]. Aging of alloy 304HCu at the operating temperatures results in nano-sized copper precipitates and this is reported to enhance the stability of this material at these operating conditions. As is well known, there is significant welding associated with boiler tubings and the published information on the weldability of alloy 304HCu is limited. Solidification cracking in Alloy 304HCu has been highlighted in few published work [3–5]. The current work is an attempt to address the solidification cracking in 304HCu welds produced with different filler materials, in greater detail. Weldability of austenitic stainless steels depends on their solidification behaviour, the amount of delta ferrite and the level of impurities in the weld/base metal. The primary mode of solidification influences the propensity to cracking in austenitic stainless steels. Earlier studies indicate that the primary ferritic solidification mode reduces the cracking tendency in austenitic stainless steels [6–8]. Possible modes of solidification for alloy 304HCu from its nominal c

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