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


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


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


Figure 6.5

Microstructure ofLamellar Graphite Cast Iron


Figure 6.6


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


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


Figure 6.8

Decarburizing Annealed MalleableCast Iron EN-GJMW-350


Figure 6.9


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


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


Figure 6.10

6. welding of cast materials

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