The document discusses welding processes and their importance, types of welds and weld defects, including causes and methods of detection. It examines the microstructure of welds and defines features like the fusion zone, heat affected zone, and unaffected base metal zone. Various weld defects are described such as cracks, cavities, inclusions, lack of fusion/penetration, imperfect shape, and miscellaneous faults.

1. METALURGI LAS

2. Tujuan:
• Lebih mengenal proses pengelasan dan efeknya
pada material
• Untuk melihat strukturmikro dan hardness pada
Heat Affected Zone (HAZ)
• Mengetahu cacat-cacat las, penyebab dan
usaha penanggulanganya.
• Industrial radiography techniques

3. Definitions:
• Welding is the joining of multiple pieces of metal
by the use of heat and or pressure. A union of
the parts is created by fusion or recrystallization
across the metal interface. Welding can involve
the use of filler material, or it can involve no
filler.

4. What commercial and technological
importance does welding have?
• Provides a permanent joint
• Weld joint can be stronger than parent material
– If the filler material has superior strength characteristics and proper
techniques are used
• Usually the most economical way to join components
• Can be done in the field away from a factory

5. Limitations?
• Expensive in terms of labour cost
• Most welding processes involve the use high energy, are
inherently dangerous
• Welds are permanent bonds, not allowing for convenient
disassembly
• The welded joint can suffer from certain quality defects
that are difficult to detect, these defects can reduce the
quality of the joint

6. Types:
• Arc Welding
– A fusion welding process in which the coalescence of the metals is
achieved by the heat from an electric arc between an electrode
and the work

7. • Shielded Metal Arc Welding (SMAW)
– An arc welding process that uses a consumable electrode
consisting of a filler metal rod coated with chemicals that
provide flux and shielding

8. • Gas Metal Arc Welding (GMAW)
– Arc welding process in which the electrode is a consumable bare
metal wire and shielding is accomplished by flooding the area
with gas

9. • Submerged Arc Welding
– Arc welding process that uses a continuous, consumable bare
wire electrode, arc shielding is provided by a cover of granular
flux

10. • Resistance Welding
– A fusion welding process that utilizes a combination of heat and
pressure to accomplish coalescence, the heat being generated
by electrical resistance to current flow at the junction to be
welded

11. • Oxyacetylene Welding
– A fusion welding process performed by a high-temperature flame
from a combustion of acetylene and oxygen
C2 H 2 + O2 → 2CO + H 2 + HEAT
2CO + H 2 + 1.5O2 → 2CO2 + H 2O + HEAT

12. Fusion Weld Joint
• Fusion Zone
– A mixture of filler metal and base metal that has completely
melted
– High degree of homogeneity among the component metals that
have been melted during welding
– The mixing of these components is motivated largely by
convection in the molten weld pool

13. • Weld Interface
– The narrow boundary that separates the fusion zone and the
heat affected zone
– This interface consists of a thin band of base metal that was
melted or partially melted (localized melting within the grains)
during the welding process, but immediately solidified before any
mixing could take place
• Heat Affected Zone (HAZ)
– The metal in this region has experienced temperature below its
melting point, but high enough to change the microstructure
– This metal consists of the base metal which has undergone a
heat treatment due to the welding temperatures, so that its
properties have been altered.
– The amount of metallurgical damage in the HAZ depends on the
amount of heat input, peak temp reached, distance from fusion
zone, time at elevated temp, cooling rate, and the metal’s
thermal properties

14. • Heat Affected Zone (HAZ) cont’d
– The effect on the mechanical properties is usually negative, and
it is most often the region of the weld joint where failure occurs
• Unaffected Base Metal Zone
– Where no metallurgical change has occurred
– The base metal surrounding the HAZ is likely to be in a state of
high residual stress, due to the shrinkage in the fusion zone

15. Weld Defects:
1. Cracks
Detection
Surface: Visual examination, magnetic particle, dye or
fluorescent penetrant inspection
Internal: Ultrasonic flaw detection, radiography

16. Solidification Cracking
• Causes:
– Large depth/width ratio of weld
bead
– High arc energy and/or preheat
– Sulphur, phosphorus or niobium
pick-up from parent metal

17. Hydrogen Induced HAZ Cracking
• Causes:
– Hardened HAZ coupled with the
presence of hydrogen diffused from
weld metal
– Susceptibility increases with the
increasing thickness of section
especially in steels with high carbon
equivalent composition
– Can also occur in weld metal
– Increase welding heat beneficial
– Preheating sometimes necessary
– Control of moisture in consumables
and cleanliness of weld prep
desirable

18. Lamellar Tearing
• Causes:
– Poor ductility in through-thickness
direction in rolled plate due to non-
metallic inclusions
– Occurs mainly in joints having weld
metal deposited on plate surfaces
– Prior buttering of surface beneficial
for susceptible plate

19. Reheat Cracking
• Occurs in creep resisting and some
thick section structural low alloy steels
during post weld heat treatment
• Causes:
– Poor creep ductility in HAZ
coupled with thermal stress
– Accentuated by severe notches X 35
such as preexisting cracks, or
tears at weld toes, or unfused root
of partial penetration weld
– Heat treatment may need to
include low temperature soaking
– Grinding or peening weld toes
after welding can be beneficial
X 200

20. 2. Cavities
Detection
Surface: Visual inspection
Internal: Ultrasonic flaw detection, radiography

21. Worm Holes
• Resulting from the entrapment of gas
between the solidifying dendrites of
weld metal, often showing ‘herringbone’
array ( B )
• Causes:
– The gas may arise from
contamination of surfaces to be
welded, or be prevented from
escaping from beneath the weld by
joint crevices

22. Uniformly Distributed Porosity
• Resulting from the entrapment of gas
in solidified weld metal
• Causes:
– Gas may originate from dampness
or grease on consumables or
workpiece, or by nitrogen
contamination from the
atmosphere
– If the weld wire used contains
insufficient deoxidant it is also
possible for carbon monoxide to
cause porosity

23. Restart Porosity
• Causes:
– Unstable arc conditions at weld
start, where weld pool protection
may be incomplete and temperature
gradients have not had time to
equilibrate, coupled with inadequate
manipulative technique to allow for
this instability

24. Surface Porosity
• Causes:
– Excessive contamination from
grease, dampness, or atmosphere
entrainment
– Occasionally caused by excessive
sulphur in consumables or parent
metal

25. Crater Pipes
• Resulting from shrinkage at the end
crater of a weld run
• Causes:
– Incorrect manipulative technique or
current decay to allow for crater
shrinkage

26. 3. Solid Inclusions
Detection
- normally revealed by radiography
Linear Slag Inclusions
• Cause:
– Incomplete removal of slag
in multi-pass welds often
associated with the
presence of undercut or
irregular surfaces in
underlying passes

27. Isolated Slag Inclusions
• Causes:
– Normally by the presence of mill
scale and/or rust on prepared
surfaces, or electrodes with
cracked or damaged coverings
– Can also arise from isolated
undercut in underlying passes of
multi-pass welds

28. 4. Lack of Fusion and Penetration
Detection
– This type of defect tends to be sub surface and is therefore
detectable only by ultrasonics or X-ray methods
– Lack of side wall fusion which penetrates the surface may be
detected using magnetic particle, dye or fluorescent
penetrant inspection
Cause
– Incorrect weld conditions (eg. low current) and/or incorrect
weld preparation (eg. root face too large)
– Both cause the weld pool to freeze too rapidly

29. Lack of side-wall fusion Lack of root fusion Lack of inter-run fusion
Lack of penetration

30. 5. Imperfect Shape
Detection
- all shape defects can be determined by visual inspections
Linear Misalignment
• Cause:
– Incorrect assembly or
distortion during fabrication

31. Excessive Reinforcement
• Causes:
– Deposition of too much weld metal,
often associated with in adequate
weld preparation
– Incorrect welding parameters
– Too large of an electrode for the
joint in question

32. Overlap
• Causes:
– Poor manipulative technique
– Too cold a welding conditions
(current and voltage too low)

33. Undercut
• Results from the washing away of edge
preparation when molten
• Causes:
– Poor welding technique
– Imbalance in welding conditions

34. Excessive Penetration
• Causes:
– Incorrect edge preparation
providing insufficient support
at the weld root
– Incorrect welding conditions
(too high of current)
– The provision of a backing bar
can alleviate this problem in
difficult circumstances

35. Root Concavity
• Causes:
– Shrinkage of molten pool at
weld root, due to incorrect root
preparation or too cold of
conditions
– May also be caused by
incorrect welding technique

36. 5. Miscellaneous Faults
Arc Strikes
• Cause:
– Accidental contact of an
electrode or welding torch
with a plate surface remote
from the weld
– Usually result in small hard
spots just beneath the
surface which may contain
cracks, and are thus to be
avoided

37. Spatter
• Causes:
– Incorrect welding conditions
and/or contaminated
consumables or preparations,
giving rise to explosions within
the arc and weld pool
– Globules of molten metal are
thrown out, and adhere to the
parent metal remote from the
weld

38. Copper Pick-Up
• Causes:
– Melting of copper contact tube in
MIG welding due to incorrect
welding conditions
X 275

39. PROCEDURE
1. Students are provided with weldments of approximately 0.4% C
steel. The first weldment was prepared without preheat treatment.
The electrode used produces a large amount of hydrogen which
diffuses into the weld metal. The second was preheated to 150˚C.
An electrode with relatively low hydrogen content was used. For
each of these samples:
a) Examine the microstructure of the weldments in a traverse from weld
metal to parent metal, sketching about five different areas. Using the
Fe-C diagram and your knowledge of the phase transformations in
steel, comment on the microstructures describing the time-temperature
history and how this history resulted in the observed structure.
b) Conduct a microhardness traverse across the HAZ and correlate the
hardness with the microstructure observed in (a).
2. Some radiographs of weld defects are provided. Examine these
radiographs and describe the defects responsible, citing ways of
avoiding the problem.

40. Radiographs
ID # Position Comments Results Page
1
Q13 1gf Shallow undercut by cap pass Acceptable
Q18 4gf Incompletefusion at the root Fail
Q10 1gf Incompletefusion at the root Fail
2
H2 4gf Incompletefusion at the root & slag throughout Fail
H1 1gf Porosity throughout Fail
J3 4gf Slag inclusions Acceptable
3
F10 1gf Slag inclusions Fail
F2 2g Incompletefusion at the root Fail
F7 3gf Minor slag Acceptable
4
983 2g Slag inclusions Acceptable
983 3gf Slag inclusions at the root & inner passes Fail
982 3gf Slag inclusions Fail
5
852 2g No defects Acceptable
852 3gf Slag inclusion at the root & porosity Fail
850 4gf Minor slag & film scratch Acceptable