Microstructure and mechanical properties of TLP-bonded 9CrMoCoB heat-resistant steel with Ni–Cr–B interlayer

Abstract

Abstract 9CrMoCoB heat-resistant steel was transient liquid phase (TLP) bonded by using a Ni–Cr–B amorphous filler metal. Results indicated that the TLP-bonded joint was composed of three feature regions, and the precipitates in the diffusion affected zone (DAZ) were M23(C,B)6-type carboborides and M3B2-type borides with different morphologies and locations. Fine granular Fe2Mo-type Laves phases and MX-type carbides that existed in the original base metal were found in the grain. The carboborides and borides in the DAZ that grew with the increase in bonding time and temperature were reduced or completely dissolved after post weld heat treatment (PWHT). The joints without PWHT showed high strength and low elongation due to the high hardness and high hardenability of the matrix. The initiation of cracks occurred on borides in the athermal solidification zone and carboborides in the Ni-DAZ and passed through in the bonded seam, resulting in the reduction in the tensile strength of the bonded joints. The hardness of the joints was obviously reduced, and their toughness was obviously improved after PWHT. The highest tensile strength reached to 744 MPa when the TLP joints were bonded at 1150 °C for 30 min, which was comparable with the original base metal.