Shielded Active Gas Forge Welding of an L80 Steel in a Small Scale Shielded Active Gas Forge Welding Machine

Vinothkumar Palanisamy,Jan Ketil Solberg,Per Thomas Moe

doi:10.3390/jmmp5010016

Abstract

The Shielded Active Gas Forge Welding (SAG-FW) method is a solid-state welding technique in which the mating surfaces are heated by induction heating or direct electrical heating before being forged together to form a weld. In this article, an API 5CT L80 grade carbon steel alloy has been welded using the SAG-FW method. A small-scale forge welding machine has been used to join miniature pipes extracted from a large pipe wall. The welding was performed at three different forging temperatures, i.e., 1300 °C, 1150 °C and 950 °C, in some cases followed by one or two post weld heat treatment cycles. In order to qualify the welds, mechanical and corrosion testing was performed on miniature samples extracted from the welded pipes. In addition, the microstructure of the welds was analysed, and electron probe microanalysis was carried out to control that no oxide film had formed along the weld line. Based on the complete set of experimental results, promising parameters for SAG-FW welding of the API 5CT L80 grade steel are suggested. The most promising procedure includes forging at relative high temperature (1150 °C) followed by rapid cooling and a short temper. This procedure was found to give a weld zone microstructure dominated by tempered martensite with promising mechanical and corrosion properties. The investigation confirmed that small scale forge welding testing is a useful tool in the development of welding parameters for full size SAG-FW welding.

Highlights

Several solid-state welding techniques exist, e.g., cold forming, friction welding, diffusion bonding, explosive welding and forge welding, and several of these techniques have been used for joining steels for various applications [1,2,3]
There are advantages related to the absence of filler material and to the narrow heat affected zone (HAZ) that is normally obtained during fusion welding
The high temperatures alter the base material microstructure, so challenges exist for these welding methods, the absence of filler material eliminates some of the metallurgical problems associated with welding

Summary

Introduction

Several solid-state welding techniques exist, e.g., cold forming, friction welding, diffusion bonding, explosive welding and forge welding, and several of these techniques have been used for joining steels for various applications [1,2,3]. Local formation of intermetallic components, carbides, nitrides and other brittle constituents in HAZ have been reported to reduce the fracture toughness of fusion welds [1,4,5,6,7,8]. Many of these reactions occur in the heat affected zone adjacent to solid state welds, but the problem is less there than in fusion welds because during solid state welding, the highest temperatures near the melting temperature are avoided. The high temperatures alter the base material microstructure, so challenges exist for these welding methods, the absence of filler material eliminates some of the metallurgical problems associated with welding

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Conclusion