TLP Bonding of AISI 4340 Steel Under Two-Stage Heating
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TECHNICAL ARTICLE
TLP Bonding of AISI 4340 Steel Under Two‑Stage Heating R. Bakhtiari1 · M. Hoseinabadi2 Received: 23 March 2020 / Revised: 22 September 2020 / Accepted: 29 September 2020 © ASM International 2020
Abstract In this study, transient liquid phase (TLP) bonding was investigated for AISI 4340 steel, a heat-resistant and low-alloy steel, due to the benefits compared to conventional joining methods. Single-stage and two-stage TLP bonding was conducted for this steel using FE830250 interlayer with a thickness of 25 μm. Samples were heated at 1300 °C for less than 4 min, and a second heating stage was performed at 1270 °C for 5, 12, 20, 30, 120, and 210 min. The microstructure studies showed higher degree of microstructural homogeneity, including reduction of intermetallic compounds at the joints, for the two-stage bonded samples. The optimum TLP bonding temperature and time for this steel were obtained as 13 min initial heating at 1300 °C and 210 min for secondary heating at 1270 °C. Therefore, the austenite phase is expected to have a high homogeneity at temperatures between 1270 and 1300 °C. Also, diffusion of the interlayer alloying elements into the base metal was conducted more effectively that the isothermal solidification could be completed. At this condition, the highest joint’s shear strength achieved was 252 MPa. Keywords Transitional liquid phase bonding (TLP) · AISI 4340 steel · Two-stage heating
Introduction 4340 steel is a heat-treated and low-alloy steel containing chromium, nickel, and molybdenum. This type of steel is often used in power shafts and gears, aircraft landing gears. 4340 steel is usually bonded through fusion and resistance welding methods. However, solving problems caused by pre-heating and post-heating processes to reach a desirable permanent bonding is still a matter of discussion. The welding problem concerning this type of steel when conventional methods are put to practice is the formation of a heat-affected zone (HAZ), which reduces the service life of the parts. Therefore, alternative bonding methods should minimize HAZ without altering the microstructure of the steel. Transient liquid phase (TLP) is a bonding method in which the base metals do not melt. This method potentially preserves the microstructure and physical and mechanical * R. Bakhtiari [email protected]; [email protected] 1
Department of Materials and Textile Engineering, Faculty of Engineering, Razi University, Kermanshah, Iran
Department of Metallurgical Engineering, College of Engineering, Kermanshah Branch, Islamic Azad University, Kermanshah, Iran
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properties of the base metal. Furthermore, it is a composite process best suited for brazing (short bonding time and a very little local melting) and intrusive bonding (low bonding temperature and structure uniformity) [1]. A new twostage heating of TLP process has been employed to achieve a homogeneous bonding with no intersection in carbon steels. This process is an innovative method that creates a non-flat interface. This method in
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