TWI Industrial Member Report Summary 178/1982
By S B Dunkerton
Tensile and Charpy impact tests have been carried out on diffusion bonded joints in a medium carbon, low alloy steel to BS 910:708M40 (En19). Tensile strengths similar to the quench and tempered parent material are readily achieved on bonding at temperatures above the Ac3 (~810°C), whilst bonding below the Ac1 (~125°C) gives joints with significantly lower tensile strengths, but greater ductility when failure occurs away from the bond interface. Increasing bonding temperature and/or time generally increases the incidence of parent metal failure.
Impact properties of as-bonded joints are very poor as a result of the microstructure imparted to the material by the bond thermal cycle. Heat treatment improves the impact strength of the bonds but not to the same level as unbonded control specimens in parent material. Limited work on the use of interlayers gave no improvement to the impact strength of the bonded joints.
Metallographic and fractographic examination give information on the joint structure and extent of bonding for the bonding conditions and heat treatments investigated.