1. FAILURE ANALYSIS BY
CORROSION AND OBSERVATION
OF MECHANICAL PROPERTIES OF
WELDED JOINTS OF DIFFERENT
METALSSUPERVISED BY-
Dr. Sobahan Mia,
Professor,
Department of Mechanical Engineering
KUET, Khulna.
PREPARED BY-
Farazee Sazzad Hossain Md.
Rakibul Hassan
Roll No. 1105081 Roll No.
1105082
3. INTRODUCTION
• Similar metals were welded together. Selected metals were
mild steel, stainless steel and galvanized iron.
• Annealing of welded joints was done at different temperatures
to observe difference between normal welded joints and heat
treated joints after corrosion.
• Microstructures were observed of welded joints as well as base
metals.
• Brinell hardness test was conducted on the welded joints.
• Tensile test was conducted on the welded joints as well as base
metal sheet without welding.
• Changes of mechanical properties were observed before and
after corrosion.
• Changes of mechanical properties of normal and heat-treated
materials were also observed
4. OBJECTIVES
The objectives of the thesis work are:
• To find the causes of failure of welded joints of similar & dissimilar
different metals.
• To inspect before & after condition on welded joints of corrosion of
different metals.
• To analyses the mechanical properties of welded joints of similar and
dissimilar metal welding.
• To find the effect of mechanical erosion on welded joints of different
welded metals.
5. METHODOLOGY
MATERIAL SELECTION
Mild steel
Carbon 0.16-0.18%
Silicon 0.40% max
Manganese 0.70-0.90%
Sulfur 0.040% Max
Phosphorus 0.040% Max
Stainless steel 304
Carbon 0.08%
Silicon 0.75%
Manganese 2.0%
Phosphorus 0.045%
Sulfur 0.030%
Chromium 18.0-20.0%
Nickel 8.0-10.5%
Galvanized iron coated with a
thin layer of zinc.
7. METHODOLOGY
Mild steel sample after welding.
Stainless steel sample after welding.
Galvanized iron sample after welding.
8. METHODOLOGY
WELDING: Stick welding was used for all welding. For similar metal
welding of mild steel and galvanized iron electrodes of diameter 3.2
mm, length 450 mm with current range 95-125 amps were used. For
similar metal welding of stainless steel electrodes of diameter 2.5 mm
and length 280 mm were used.
Electrode used for mild steel and galvanized iron.
Electrode used for stainless steel.
9. METHODOLOGY
HEAT TREATMENT: Annealing was done to the welded joints. All of
them were held for one hour. Then the furnace was switched off so that the
specimen temperature will decrease with the same rate as that of the furnace.
The objective of keeping the specimen for 1 hour is to homogenize the
specimen.
Heat treated (heated to 700oC)
sample of mild steel.
Heat treated (heated to 1075oC)
sample of stainless steel.
Heat treated (heated to 1000oC)
sample of galvanized iron.
12. METHODOLOGY
Heat treated mild steel sample
after immersion.
Heat treated galvanized iron
sample after immersion.
Mild steel sample after
immersion.
13. METHODOLOGY
BRINELL HARDNESS TEST : Brinell test was done by using a
carbide ball indenter. The indenter was pressed into the sample by an
accurately controlled test force. The force was maintained for a specific
dwell time, normally 10-15 seconds. After the dwell time was complete,
the indenter was removed leaving a round indent in the sample. The size
of the indent was determined optically by measuring two diagonals of
the round indent using either a portable microscope or one that was
integrated with the load application device.
TENSILE TEST: The tensile testing was carried out by applying
longitudinal or axial load at a specific extension rate to a standard tensile
specimen with known dimensions (gauge length and cross sectional area
perpendicular to the load direction) till failure. The applied tensile load
and extension are recorded during the test for the calculation of stress and
strain.
14. RESULT
BHN Before corrosion BHN After corrosion
Mild Steel 144.55 155.61
Heat Treated Mild Steel 187.24 291.5
Stainless Steel 269.11 284.85
Heat Treated Stainless Steel 363.21 387.68
Galvanized Iron 228.76 236.11
Heat Treated Galvanized Iron 241.18 269.11
Experimental data of brinell hardness test.
15. RESULT
0
50
100
150
200
250
300
350
400
0 1 2 3 4 5 6
STRESS(MPa)
STRAIN
MILD STEEL STRESS vs STRAIN CURVE
Before welding
After welding before corrosion
After welding after corrosion
16. RESULT
-50
0
50
100
150
200
250
300
350
400
0 1 2 3 4 5 6
STRESS(MPa)
STRAIN
HEAT TREATED MILD STEEL STRESS vs STRAIN CURVE
BEFORE WELDING
AFTER WELDING BEFORE CORROSION
AFTER WELDING AFTER CORROSION
18. RESULT
0
100
200
300
400
500
600
700
800
900
-0.02 0 0.02 0.04 0.06 0.08 0.1 0.12
STRESS(MPa)
STRAIN
HEAT TREATED STAINLESS STEEL
STRESS vs STRAIN GRAPPH
BEFORE WELDING
AFTER WELDING BEFORE CORROSION
AFTER WELDING AFTER CORROSION
19. RESULT
0
100
200
300
400
500
600
700
800
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45
STRESS(MPa)
STRAIN
GALVANIZED IRON STRESS vs STRAIN CHART
BEFORE WELDING
AFTER WELDING BEFORE CORROSION
AFTER WELDING AFTER CORROSION
20. RESULT
0
100
200
300
400
500
600
700
0 0.1 0.2 0.3 0.4 0.5 0.6
STRESS(MPa)
STRAIN
HEAT TREATED GALVANIZED IRON STRESS vs STRAIN CHART
BEFORE WELDING
AFTER WELDING BEFORE CORROSION
AFTER WELDING AFTER CORROSION
24. CONCLUSION
• The ultimate stress decreases as the annealing is done.
• BHN of heat treated weld joints are greater than normal joints.
• Ultimate stress of heat treated weld joints is smaller than normal
joints.
• After corrosion most reduction of hardness is found in heat treated
mild steel.
• Galvanized iron shows smallest reduction in BHN after corrosion.
• After corrosion ultimate stress of every welded joint is reduced.
• Stainless steel and galvanized iron has almost similar ultimate stress
before corrosion.
• After corrosion ultimate stress of galvanized iron reduces more than
stainless steel.
• Stress vs strain curves are plotted in terms of true stress and true
strain. As a result stress cautiously rises until fracture.
