Electroslag welding is a single-pass welding process that uses a molten slag to generate heat and melt the filler metal and workpiece edges. An electric current is passed through the slag, which reaches temperatures over 1930°C. This melts the consumable electrode and forms a slag bath that extinguishes the arc and allows the melted electrode to sink into the weld pool. Electroslag welding is efficient for joining thick steel plates over 25mm in a single pass and produces low residual stresses. It is commonly used for welding thick sections and plates of low-carbon, high-strength, stainless, and nickel alloys.

1. ELECTROSLAG WELDING (ESW)
Electro-slag Welding is the welding process in which the
heat is generated by an electric current passing between the
consumable electrode (filler metal) and the work piece
through a molten slag, which covers the weld surface
Electro slag welding is a very efficient, single pass process carried out
in the vertical or near vertical position and used for joining steel
plates/sections in thicknesses of 25mm and above

6. # Prior to welding, the gap between the two work pieces is filled
with small amount of welding flux
# Welding is initiated by an arc between the electrode and the
starting plate
# Heat, generated by the arc, melts the fluxing powder and forms
molten slag
# The slag, having low electric conductivity, is maintained in liquid
state due to heat produced by the electric current
# The slag reaches a temperature of about 3500°F (1930°C)
# Unlike other high current fusion processes, electro slag welding is
not an arc process. Heat required for melting both the welding
wire and the plate edges is generated through a molten slag's
resistance to the passage of an electric current.

7. # This temperature is sufficient for melting the consumable
electrode and work piece edges
# Additional flux is added which melts forming a flux bath which
rises and extinguishes the arc
# The added wire then melts into this bath sinking to the bottom
before solidifying to form the weld
# For thick sections, additional wires may be added and an even
distribution of weld metal is achieved by oscillating the wires
across the joint
# As welding progresses, both the wire feed mechanism and the
copper shoes are moved progressively upwards until the top of
the weld is reached
# Electroslag Welding is used mainly for steels

9. PROCESS VARIABLES
# Welding current
# Welding voltage
# Welding current is directly responsible for the
electrode melt rate
# Voltage influences the base metal penetration
and weld bead width

10. Optimum condition Poor condition
w/h > 2 w/h < 1
FORM FACTOR

11. ESW FLUXES
# Electroslag welding fluxes are invariably fused, rather than
agglomerated
# Compared with the arc welding fluxes, fluxes for ESW are
higher in resistivity, because the arc is extinguished soon after
the process becomes stable
# Sometimes, an agglomerated starting flux with high
conductivity is used to initiate the process and form the weld
pool
# After that, a running flux of high resistivity is added to generate
heat for melting the filler metal and to maintain steady welding
operation
# In fact, for high-current welding the use of starting flux is often
omitted.

12. CONSTITUENT CONTENT, WT%
SiO2 25
MnO 10
CaF2 15
Al2O3 25
CaO 15
MgO 10
A typical running flux for low-carbon steels

13. Electrodes and Guides
The electrodes can be
Solid wires
Tubular flux-cored wires
Large-section solid electrodes
Large-section cored electrodes
The guides or nozzles can be
Consumable – Stationary electrode feed mechanism
Nonconsumable (snorkels) – Mobile electrode feed mechanism

14. (A) SINGLE FLUX-COVERED TUBE.
(B) CLUSTER OF RODS TAPED
TOGETHER.
(C) FLUX-COVERED WING NOZZLE.
(D) FLUX-COVERED WING OR WEB
NOZZLE WITH TWO TUBES

15. Welding current
# DCEP
Constant Voltage machine
# AC
# A = 400 – 800 Amps
V = 25 – 55 V

16. ADVANTAGES
 Joint preparation is often much simpler than for other welding
processes.
 Much thicker steels can be welded in single pass and more
economically. Thicknesses up to 450 mm in plain and alloy steels
can be welded without difficulty.
 Electroslag welding gives extremely high deposition rates.
 Residual stresses and distortion produced are low.
 Flux consumption as compared to that in submerged arc welding
is very low.
 During the electro slag process, since no arc exists, no spattering
or intense arc flashing occurs.

17. DISADVANTAGES
 Submerged arc welding is more economical than electroslag
welding for joints below 60 mm
 In electroslag welding, there is some tendency toward hot cracking
and notch sensitivity in the heat affected zone.
 It is difficult to close cylindrical welds.
 Electroslag welding tends to produce rather large grain size with
large HAZ
 Welding is carried out in vertical uphill position.

18. Applications
(i) Heavy plates, forgings and castings can be butt welded.
(ii) Where plates or castings of uniform thickness are involved or if
they taper at a uniform rate, electroslag welding has virtually
replaced thermit welding, being much simpler.
(iii) Following alloys can be welded:
Low carbon and medium carbon steels.
High strength structural steels
High strength alloy steels such as stainless steel and nickel
alloys.