Indian Welding Journal

M. Vinoth Kumar ¹, V. Balasubramanian ¹

Affiliations
1 Centre for Materials Joining & Research (CEMAJOR), Department of Manufacturing Engineering, Annamalai University, Annamalai Nagar- 608 002, Tamil Nadu, IN

Abstract

The SUS 304HCu austenitic stainless steel is used in superheater / reheater of ultra super critical boilers for their high temperature oxidation and corrosion resistance. Cu addition to steels can have adverse effects on the mechanical properties during fusion welding as it can form low temperature eutectic phases that preferentially segregate to the grain boundaries and embrittle the alloy. Friction welding is a solid state welding process where the bonding takes place well below the melting temperature of the alloy, combined with the autogenous nature of this welding process minimizes the adverse effects of low temperature eutectics segregation. Hence, in this investigation an attempt has been made to develop an empirical relationship to predict the tensile strength of the friction welded SUS 304HCu tubes of 57.1 mm outer diameter and 3.5 mm thick using statistical tools such as design of experiments, analysis of variance and regression analysis. Response surface methodology was used to optimize the process variables and maximum joint efficiency of 99% was achieved using the optimized friction welding variables.

Keywords

SUS 304HCu, Friction Welding, Design of Experiments, Tensile Properties.

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M. Vinoth Kumar ¹, V. Balasubramanian ¹, A. Gourav Rao ²

Affiliations
1 Department of Manufacturing Engineering, Annamalai University, Annamalai Nagar, Tamil Nadu - 608002, IN
2 Naval Material Research Laboratory (NMRL), Ambernath, Mumbai - 421506, IN

Abstract

AISI 304HCu austenitic stainless steel containing 2.3 to 3 (% wt) of Cu is mainly used in superheaters and reheater of ultra super critical (USC) boilers which operates over 600°C of steam temperature. Austenitic stainless steels welded by gas tungsten arc welding (GTAW) alters the phase composition, and microstructure of the steel in the fusion zone of welds and may affect the mechanical properties. In our previous investigation, it is found that autogenous welding of AISI 304HCu tubes resulted in segregation of alloying elements in the weld metal and resulted in joints with inferior tensile strength. Hence, in this study the high temperature tensile properties of filler added GTA welded AISI 304HCu tube joints were evaluated and correlated with the microstructural features. The tensile strength of the filler added GTA weld joints was higher than the parent metal at all test temperatures and the weld joint with filler addition was recommended for application in USC boilers.

Keywords

AISI 304HCu, Gas Tungsten Arc Welding, High Temperature Tensile Properties, Ultra Super Critical Boilers.

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