Microstructure and Mechanical Properties of Transient Liquid Phase Bonded Joints of CB2 Ferritic Heat Resistant Steels with Amorphous BNi-2 Interlayer

Abstract

Microstructure and mechanical properties of transient liquid phase (TLP) bonded joints and the post bonding heat treatment (PBHT) for CB2 heat resistant steel using BNi-2 insert alloy were investigated. The Cr-rich borides and Cr-Mo borides generated in the transition region (TZ) and diffusion-affected zone (DAZ) reach the peak values in size and quantity when the isothermal solidification is completed. Subsequent elevation in bonding temperature and increment in bonding time result in gradual disappearance of such Cr-rich and Cr-Mo borides, as well as increased percent of BN precipitates. After PBHT the Cr-rich borides almost disappear while the size and amount of BN precipitates rise. The maximum tensile strength reaches to 934 MPa for the joint bonded at 1150 °C for 1800 s with elongation of only 5.3%. PBHT result in significant improvement in ductility of the joint as elongation of 20% is achieved with a decreased strength of 720 MPa, while the fracture takes place at base materials.