1. Metallurgical defects of cast steel
Foundry-Institute
Seminar
Metallurgical defects of cast steel
Claudia Dommaschk
TU Bergakademie Freiberg
Foundry Institute, Germany 1

2. Structure Gas cavities Oxide and slag inclusions, Nonmetallic
Shrinkage cavities
Hot tear
Primary grain boundary fracture
Defects caused by heat treatment 2

3. Description and reasons:
Gas cavities
Description and reasons:
Cavities in castings, especially in the upper parts of the castings
Formation during solidification because of degrease of gas solubility
often in combination with oxide and slag inclusions
formation of gas cavities depends on the concentration of oxygen,
nitrogen and hydrogen
the inner surface of the cavities is smooth 3

4. Gas cavities 4

5. use of dry materials and ladles use of clean charge
Gas cavities
Prevention:
use of dry materials and ladles
use of clean charge
degasification of the melt
look at the mould sands (permeability of gas, vent…) 5

6. Oxide and slag inclusions, nonmetallic inclusions
Description and reasons:
Classification: endogenous and exogenous inclusions
endogenous inclusions are caused by the reaction products during the
melting process (especially during deoxidation)
exogenous inclusion are caused by other materials in the melt
(e.g. refractory lining)
thin fluid slag can precipitate at the grain boundaries  danger of
formation of hot tears is higher
Classification of size:
Macro inclusions > 20 μm
Micro inclusions < 20 μm 6

7. Oxide and slag inclusions, nonmetallic inclusions
GX3CrNiMoN GX2CrNiMo 7

8. Oxide and slag inclusions, nonmetallic inclusions
Prevention:
use of clean charge
optimization of gating and feeding system (lamellar flow)
decrease of the dissolved oxygen
decrease of the overheating temperature 8

9. Oxide and slag inclusions, nonmetallic inclusions
Example: G42CrMo4
nonmetallic inclusions arise by
reason of the reactions during the
melting process 9

10. Description and reasons: specific volume of melt is higher than
Shrinkage cavities
Description and reasons:
specific volume of melt is higher than
the specific volume of solid 
contraction during solidification and
cooling
feeding is necessary – if the feeding
is not optimal  formation of
shrinkage cavities
the shrinkage volume of cast steel is
about 4-7 %
the inner surface is rough
Liquid
shrinkage
Solidification
shrinkage
Specific volume
shrinkage
RT TS TL TP 10

11. Shrinkage cavities
GE 300 (GS 60) 11

12. use of optimal feeding system (calculation and simulation)
Shrinkage cavities
Prevention:
use of optimal feeding system (calculation and simulation)
warranty of directional solidification
use of exothermic feeder sleeve
decrease of the pouring temperature 12

13. Description and reasons: hot tears are intercrystalline discontinuity
cracks run along the grain boundaries
the risk of cracks at alloys with a high freezing range is higher than with
a small freezing range
the reason are stresses during solidification because of hindered
contraction (residual stress)
the main reason for formation of hot tears are the geometry of casting
if melt can flow into the crack - partial or completely annealed hot tears
are possible 13

14. Influence of Carbon content on the inclination of hot tears
Influence of Manganese and Sulphur content on the inclination of hot tears
Influence of Carbon content on the inclination of hot tears
Sulphur is very dangerous
- Manganese compensate
Maximum of the hot tearing tendency
by ~0.4 % C
- Low tendency below 0.2 % 14

15. Hot tear 15

16. Partial annealed hot tear16

17. design appropriate to casting, prevention of residual stresses, wide
Hot tear
Prevention:
design appropriate to casting, prevention of residual stresses, wide
difference in the wall thickness and hot spots)
prevention of hot sand effects 17

18. Primary grain boundary fracture (“Rock candy or shell fracture”)
Al-N-precipitations
G24Mn5
Caused by Al-N-precipitations
high content of Al and N and thick-walled castings 18

19. Defects caused by heat treatment
GS33NiCrMo
left: quenching and tempering not correct – ferrite, pearlite and bainite 
lower ductility 19

20. Defects caused by heat treatment
G24Mn5 (thick-walled casting)
quenching and tempering not complete – ferrite, pearlite and bainite
different structure and lesser properties 20

21. Defects caused by heat treatment
G30Mn GS25
Decarburization of the surface area caused by heat treatment without
protective atmosphere  Chance of properties in the surface area 21

22. Defects caused by heat treatment
GX3CrNiMo
temperature of solution heat
treatment to low and/or cooling
rate not correct 
precipitation of delta-ferrite 
these components are brittle 
lower ductility 22

23. Defects caused by heat treatment
GX 120Mn13
temperature of austenitizing to high 
coarse grain  bad mechanical properties 23

24. Defects caused by heat treatment
G105Cr4 = hypereutectoid cast steel
hardening crack
structure: coarse martensite and
residual austenite
reason: temperature of austenitizing
and cooling rate to high 24

25. Defects caused by heat treatment
GX 5CrNiMo
intercrystalline corrosion
heat treatment not correct  precipitation of Cr-carbides on the grain
boundary  corrosion was possible 25

26. Defects caused by heat treatment
G71Si7 = spring steel
“Black shortness”
Softening anneal not correct 
precipitation of graphite 26

27. 27