Transient liquid phase bonding of nitrogen containing duplex stainless steel UNS S31803 using Ni-Cr-Fe-Si-B insert metal

Abstract

Microstructural evolution during transient liquid phase (TLP) bonding of nitrogen containing duplex stainless steel UNS S31803 has been investigated. In order to evaluate mechanical property of joint, tensile strength test was carried out at room temperature. TLP bonding was conducted at the temperature range 1283-1353 K for 0-1000 s under a vacuum of 6.7 mPa using Ni-7.mass%Cr-3 mass%Fe-4.5 mass%Si-3.2 mass%B amorphous insert metal. The results show that the volume fraction of austenite (γ) decreased with increasing bonding temperature and holding time. Particularly, in the case of prolonged holding time, the depleted area of γ phase was observed in the base metal adjacent to joints. There were linear correlations between the width of the remaining liquid phase and square root of holding time at each bonding temperature. In this investigation, the secondary phases formed in the joint area were (Cr, Mo) borides dominantly. For the specimen bonded for longer time up to 1000 s, boron nitride formed at the center and interface of joint area, on the other hand, the amount of borides decreased compared with the case of shorter bonding time. Tensile strength increased with holding time, and the bonding efficiency was ∼94% for the specimen held for 1000 s at 1353 K. Tensile strength of joint depended on, for a short holding time, brittle eutectic and borides, and after completion of isothermal solidification, depended on the boron nitride formed at the joint interface.