FLUXES FOR WELDING
JABIN MATHEW BENJAMIN
DEPT. OF METALLURGICAL ENGINEERING
NEED FOR FLUXES
Sources of O2
Reduces hardenability of weld
NEED FOR FLUXES
Sources of inclusions
Mechanical entrapment of nonmetallic slag
Reactions between metallic alloy elements and nonmetallic
Added to the welding environment to improve arc stability
The flux, by providing easily ionized atoms, plays an important
role in welding by improving arc stability.
To provide a slag and with low density
Covers the hot weld metal and protects it from the atmosphere.
To add alloying elements
To improve weld metal properties
Refine the weld pool (deoxidation and desulfurization)
To avoid formation to oxide and sulphide inclusions
Types Of Fluxes
•Used for Al and Ti
•Low-carbon or low alloy steels
K2O, Na2O, CaO, MgO
SiO2, TiO2, P2O5
Al2O3, Fe2O3, Cr2O3
•Donors of free
•Lower non metallic
•High toughness of
to absorb moisture
not be very good
•Acceptors of oxide
•Improves weld bead
•High deposition rate
•High welding speed
Functions of flux components
Lower content increases the width to depth ratio.
Slag a mixture of glass and crystalline structure
Melt below the melting temperature of base metal
Density less than base metal to reduce slag entrapment
Must possess proper viscosity in the temperature range of
1450 to 1550 °C
Easily detach from the weld deposit
Solidify on the weld deposit to protect the surface from
oxidation during cooling.
Shielded Metal Arc Welding
Electrode is covered with flux material which performs the functions.
Flux-cored Arc Welding (FCAW)
Uses a hollow wire filled with flux reagents and ferro-additions.
High CO2 content as carbonates
Low CO2 content
Submerged Arc Welding
The flux is supplied from a hopper, which travels with the torch. No
shielding gas is needed because the molten metal is separated
from the air by the molten slag and granular flux.
Non metallic and ferro additions with low temperature
Similar to bonded but used with ceramic glass binder
cured at high temperature
Homogeneous glass mixture of proper flux mixture into
Fluxes and Weld Penetration
Confine the molten weld pool
Increases the heat input for a given area
Affects arc stability
More ionized particles more stable arc
A more stable arc will produce deeper penetration
Increases weld penetration.
Finally a welding flux must also..
Stabilize arc and control arc resistivity
Permit use of different types of current and polarity
Promote slag detachability
Produce smooth weld contour
Reduce spatter and fume
Jackson, C. E., "Fluxes and Slags in Welding," W. R. C Bulletin, 190,
Janzen, H. E„ "An Investigation of the SiO-MnO-CaO/CaF2 Welding
Flux System, "Thesis, Colorado School of Mines,T-1970, (1977).
ASM handbook, Vol. 6.