Microstructure and mechanical properties of transient liquid phase diffusion bonding zone of low carbon steel Cu foil 304 stainless steel composite pipe

Composition, microstructure and performance of the transient liquid phase(TLP) diffusion bonding zone of low carbon steel/stainless steel using Cu interlayer were examined by means of SEM and OM, EDS analysis, microhardness test and shear test. The results show that the metallurgical bond of low carbon steel and stainless steel is obtained by the process of cold-draw and TLP diffusion bonding using Cu as interlayer, and compression shearing strength of the bonding zone is over 300 MPa. At the copper/stainless steel interface, liquid copper diffuses along austenite grain boundary and forms isolated-island austenite distributed in copper matrix. On the other hand, microstructure of continuous island-form iron-rich phase forms and grow to copper matrix as pinetree form at carbon steel/copper interface. Within a specific range of temperature and time, the amount of iron-rich phase, hardness and shearing strength of bonding zone increase with increasing diffusion bonding temperature and time.