TWI Industrial Member Report Summary 10/1976
By N Bailey and M L E Davis
The first part of this survey dealt with the role of welding fluxes, their manufacture and their physical properties and associated weldability. This second part discusses the effects of flux on weld properties and on weld defects.
Fluxes exert a primary influence on the properties which are related to weld cleanliness with respect to non-metallic inclusions, namely upper shelf toughness, ductility and possibly creep rupture behaviour. Weld metals low in oxygen and sulphur are promoted by basic fluxes, although the degree of basicity required for practical applications is a matter for discussion. Other properties, such as cleavage resistance, yield and tensile strength, hardness and stress corrosion resistance depend principally on the weld metal microstructure. This is a function of weld composition, which is partially influenced by the flux, and also the weld cooling rate and heat treatment. Fatigue resistance is principally dependent on weld shape but there appears to be no systematic work relating it to flux type.
Weld shape defects, porosity and slag entrapment are principally controlled by the welding parameters, although the flux can have a secondary influence. Solidification cracking is influenced by weld composition, solidification pattern and strain across the solidifying weld. The flux influences cracking principally through its effects on weld composition, particularly carbon content. Hydrogen cracking is influenced by flux in two important ways; together with wire the flux is a major source of hydrogen to the weld whilst its influence on weld metal composition helps to determine the susceptibility of the weld metal to cracking.
Later parts of this survey will include sections on the chemistry of fluxes and their classification and and will conclude with summaries of each section highlighting problem areas.