6. Welding of Cast Materials
6.
Welding of Cast Materials
6. Welding of Cast Materials 77
Figure 6.1 provides
a summary of the
different cast iron
materials. In this
connection it is only
referred to cast iron,
cast steel and mal-
leable steel, as
special cast materi-
als, due to their
poor weldability, are
of no importance in
welding.
Figure 6.2 shows the designation of
the cast material in accordance with
DIN EN 1560. A distinction is made
between the designation “according to
the material code” and the designa-
tion “according to the material num-
ber”. In Figure 6.2, examples of two
materials are specified.
Figure 6.1
Designation according to the material number
e.g.: EN- J L 1271
1 2 3 4,5,6
Position 1: EN - standardised materialPosition 2: J - cast materialPosition 3: L - graphite structure (lamellar graphite)Position 4: 1 - number for the main characteristicPosition 5: 27 - material identification numberPosition 6: 1 - special requirement
Designation of Materials
© ISF 2004br-er07-02e.cdr
Designation according to the material code (DIN EN 1560)
e.g.: EN-GJ L F – 150
1 2 3 4 5
Position 1: EN -Position 2: GJ -Position 3: L -Position 4: F -Position 5: 150 - (R = 150 N/mm )
-Position 6: -
m
2
standardised materialcast materialgraphite structure (lamellar graphite)microstructure (ferritic)mechanical properties
chemical composition (high alloyed)optionally
Figure 6.2
6. Welding of Cast Materials 78
Figure 6.3 depicts a survey of the mechanical properties and the chemical composi-
tions of several customary cast materials. As to its analysis and mechanical proper-
ties which are very different from other cast materials, cast steel constitutes an
exception to the rule.
In Figure 6.4 the stable and the metastable iron-carbon diagram are shown. The dif-
ferences between
the cast material
are best explained
this way. Cast iron
with lamellar and
spheroidal graph-
ite has carbon
contents of be-
tween 2,8 and
4,5%. Through the
addition of alloying
elements, above
all Si, these mate-
rials solidify follow-
ing the stable sys-
tem, i.e., the car-
bon is precipitated
in the form of
graphite. Malleable
cast iron shows
similar C-contents,
the solidification
from the molten
metal, however,
follows the metast-
able system. The
C-contents of cast
steel, on the other
EN/ GJL/300 - lamellar graphite cast iron
EN -GJS -400 -15 - nodular graphite cast iron
EN -GJMW -400 -12 - decarburizing annealed malleable cast iron
(former : white -heart malleable cast iron)
GS 38 - cast steel
Iron Cast Material
Rp0,2 Rm A C Si Mn P S
N/mm2
N/mm2
% % % % % %
EN-GJL-300 300 ˜ 2,8 ˜ 1,4 ˜ 1,0 < 0,2 < 0,12
EN-GJS-400-15 250 400 15 ˜ 3,7 ˜ 2,2 ˜ 0,5 ˜ 0,05 ˜ 0,01
EN-GJMW-400-12 200 380 12 ˜ 3,2 ˜ 0,5 ˜ 0,3 < 0,12 ˜ 0,25
GS 38 190 380 25 0,15 0,47 0,35 0,045 0,054
MechanicalProperties Chemical Analysis
Characteristics and Analysesof Cast Materials
© ISF 2004br-er-07-03e.cdr
Figure 6.3
Figure 6.4
6. Welding of Cast Materials 79
hand, comply with those of common
structural steels, i.e., they are, as a
rule, below 0,8% C.
The structure of a normalised cast iron
which is composed of ferrite (bright)
and pearlite (dark) is shown in Figure
6.5. Since the properties are similar to
those of structural steels these materi-
als are weldable, constructional weld-
ing is also possible. It is recommended
to normalise the cast steel parts before
welding. Through this type of heat
treatment, on the one hand the trans-
formation of the cast structure is ob-
tained, the residual stresses inside the
workpiece are, on the other hand, re-
duced.
From a C-content in the steel cast of
0,15% up, it is recommended to carry
out preheating during welding, the
preheating temperature should follow
the analysis of the material, the work-
piece geometry and the welding
method. After welding the cast work-
pieces are subject to stress-relief an-
nealing.
Figure 6.6 shows the structure of cast
iron with lamellar graphite (grey cast
iron). Apart from their carbon content,
these materials are characterised by
increased contents of S and P which
Microstructure ofNormally Glowed Cast Steel
© ISF 2002br-er07-04e.cdr
Figure 6.5
Microstructure ofLamellar Graphite Cast Iron
© ISF 2002br-er07-05e.cdr
Figure 6.6
6. Welding of Cast Materials 80
improves castability. Besides the poor mechanical properties (elongation after frac-
ture of approx. 1%), these chemical properties also impede welding with ordinary
means. It is not possible to carry out constructional welding with grey cast iron. Re-
pair welds of grey cast iron are, in contrast, carried out more frequently as damaged
cast parts are not easily replaceable. For those repair welds, the cast parts must be
preheated (entirely or partly) to temperatures of approx. 650°C. Heating and cooling
must be done very slowly as the cast piece may be destroyed already by the thermal
stresses. The highly liquid weld metal also constitutes a problem, and thus the molten
pool must be supported by a carbon pile. Welding may be carried out with similar
filler material (materials of the same composition as the base). If grey cast iron is to
be welded without any preheating, the filler material must, as a rule, be dissimilar (of
different composition to the base metal). During this type of welding, there are always
strong structural changes in the region of the weld which lead to high hardening and
high residual stresses. For the minimisation of these structural changes, a highly duc-
tile filler material is applied. The heat input into the base material should be as low as
possible.
Figure 6.7 depicts
the structural con-
stitution of spher-
oidal graphite cast
iron. The graphite
spheroidization is
achieved by the
addition of magne-
sium and cerium.
As, with this type
of graphite, the
notch actions are
considerably
lesser than this is
the case with grey cast iron, this type of cast iron is characterised by substantially
better mechanical parameters with a considerably higher elongation after fracture
and improved ductility. For this reason, the risk of material failure caused by weld
residual stresses or thermal stresses is considerably reduced for spheroidal graphite
Nodular Graphite Cast Iron
© ISF 2002br-er-07-06e.cdr
Figure 6.7
6. Welding of Cast Materials 81
cast iron. Frequently, nickel-based
alloys are used as filler material. Prob-
lems occur in the HAZ where, besides
the ledeburite eutectic alloy system,
also Ni-Fe-martensite is frequently
formed. Both structures lead to ex-
treme hardening in the HAZ which
can be removed only by time-
consuming heat treatment.
Figures 6.8 and 6.9 show the structures of
Carburized Annealed Malleable Cast Iron
(6.8) and of Decarburized Annealed Malle-
able Cast Iron (6.9). The composition of the
malleable cast iron is thus that during solidifi-
cation, the total of carbon is bound in cemen-
tite and precipitated. During a subsequent
annealing process, the iron carbide disinte-
grates into graphite and iron.
Carburizing Annealed MalleableCast Iron EN-GJMB-350
© ISF 2002br-er07-07e.cdr
Figure 6.8
Decarburizing Annealed MalleableCast Iron EN-GJMW-350
© ISF 2002br-er07-08e.cdr
Figure 6.9
6. Welding of Cast Materials 82
If annealing is carried out in neutral
atmosphere, the structure of Carbur-
ized Annealed Malleable Cast Iron
develops. Annealing in oxidising at-
mosphere leads to the decarburisa-
tion of the workpiece surfaces and
Decarburized Annealed Malleable
Cast Iron is developed, Figure 6.10.
Carburized Annealed Malleable
Cast Iron is not weldable. Decarbur-
ized Annealed Malleable Cast Iron,
in contrast, is weldable.
You can see in Figure 6.11 that, also
with malleable cast iron, hardening in
the region of the HAZ occurs. For car-
rying out constructional welds made of
malleable cast iron parts, a special
material quality has been developed.
Figure 6.11 shows that this material,
EN-GJMW-400-12, is characterised by
considerably less hardening. This ma-
terial is weldable without any problems
up to a wall thickness of 8 mm.
Hardness Process within the
Range of the Heat Influence Zone
GTW-S38
GTW-40
Hard
ness a
fter
Brinell
material thickness: 7 mm
Testspeciem
Distance of center welding seam
0 10 20 mm 30
200
150
100
50
© ISF 2002br-er0-10e.cdr
Figure 6.11
Structure in dependenceof the wall thickness
white-heart malleable cast iron
Structurecore zone : Perlit + (Ferrit) + temper carbontransition zone : Perlit + Ferrit + temper carbonsurface zone : Ferrit
© ISF 2002br-er07-09e.cdr
Figure 6.10