SOME STUDIES ON METAL SURFACING
N. MURUGAN
THESIS SUBMITTED
IN FULFILMENT OF THE REQUIREMENTS
FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
+t IMO
Department of Mechanical Engineering
INDIAN INSTITUTE OF TECHNOLOGY, DELHI
NEW DELHI-11001 6, INDIA
OCTOBER, 1993
To my beloved
Wife Santhy
and
Daughter Hephzibah
CERTIFICATE
This is to certify that the Thesis entitled, "SOME STUDIES ON METAL
SURFACING" being submitted by Mr. N.Murugan to the Indian Institute of Technology,
Delhi, for the award of "Doctor of Philosophy" in Mechanical Engineering is a record of
bonafide research work carried out by him. He has worked under our guidance and
supervision and has fulfilled the requirement for the submission of this Thesis which has
reached the requisite standard.
The results contained in this Thesis have not been submitted, in part or in full, to any
other University or Institute for the award of any degree or diploma.
(Shri. S.K.Sud)
Chief Design Engineer,
Instrument Design and Development Centre,
(Dr. R.S.Parmar)1.10- )99
Professor,
Department of Mechanical Engineering,
Indian Institute of Technology, Delhi,
Haus Khas, New Delhi - 110 016,
INDIA.
ACKNOWLEDGEMENT
I wish to record my heartfelt gratitude to God Almighty, the creator and saviour of
this world, for His abundant grace given to me to start and finish this research work
successfully.
I express my deepest sense of gratitude and thanks to Prof.R.S.Parmar, Mech. Engg.
Dept., IIT, Delhi, for his inestimable guidance and supervision in successful completion of
this work. I am extremely indebted to him for his constant encouragement, immense help
and sincere and timely advice.
I wish to express my sincere gratitude to Shri. S.K.Sud, Chief Design Engineer,
IDDC, IITD, for his invaluable help, guidance and supervision.
I am highly indebted to Prof.N.K.Tewari of Mech. Engg. Dept. for his generous
support and help for carrying out this research work.
I am really thankful to Prof. U.R.K.Rao, Head of Mech. Engg. Dept., for the
encouragement, moral support and kind concern about this work. I am very much thankful
to Prof. P.N.Rao of Mech. Engg. Dept. and Prof.Pandey of CMST, IITD for their valuable
helps.
I wish to express my gratitude towards Prof.M.Guruswamy, the Principal of C.I.T.,
Coimbatore and the Director of Technical Education, Madras, for sponsoring me to IIT,
Delhi for Doctoral research programme under QIP scheme of the Ministry of Education,
Govt. of India. I am highly grateful to Dr.R.Natarajan, Head of Mech. Engg., and all my
colleagues in the Dept. of Mech. Engg. of C.I.T. for readily agreeing to share my workload
during my sponsorship period of three years. I thank my friend and colleague, Mr.P.Koshy
Matthews for the encouragement and helps in redirecting all mails.
I am highly indebted to Prof.K.S.Raman, Dept. of Metallurgy, I.I.Sc., Bangalore for
his valuable advice, constructive criticism, encouragement and timely help given during this
work and I sincerely thank him for the keen interest shown.
I am very much indebted to Prof.P.C.Gupta, head of WRL, Uni. of Roorkee, for
providing me all research facilities. My thanks are due to Mr.P.Nagesh Babu, Scientist of
WRL and Mr. A.Asokan, Senior Scientist of USIC for their immense help in conducting
ferrite measurement and EPMA studies.
I am extremely thankful to Dr.Rodriguez, Director of IGCAR, Kalpakam, for his
kind concern about this work and for extending all research facilities. I am very much
thankful to Dr.T.P.S.Gill, Head of Metal Joining Section, Dr.V.S.Ragunathan, Head of
Physical Met. Divn., IGCAR, Kalpakam, for their valuable helps. My thanks are due to
Mr.M.P.Mishra of Matls. development Divsn., and Mr.A.L.E.Terrance of Physical Met.
Divsn., of IGCAR for thier valuable helps.
I am thankful to Shri.V.Jeganath, GM of WRI, Tiruchirapalli, Tamil Nadu, for
providing research facilities.
My thanks are due to Mr.T.V.Deehshitulu, Senior Manager of EIL, Delhi, for his
invaluable help and discussions. I am thankful to Mr.Triani, GM, Advani Orelikon, Delhi,
for supplying necessary materials and M.P.Dhanuka, GM (Technical Services), Advani
Orelikon, Bombay for helping in conducting chemical analysis.
I am very much grateful to Dr.Prasad Rao, Asso. Prof. of Met. Dept. of IIT,
Madras, for providing me corrosion resistance testing facilities and valuble discussions. I
am thankful to Dr.K.S.Raja for his sincere help in conducting corrosion tests.
My thanks are due to Mr.A.Sivakumar and Mr.Mahendra Singh of Welding
Laboratory, and all other staff members of Production Engg. Lab., Machine Shop and
Metrology Lab. of Mechanical Engg. Dept. for their all round help throughout this work.
I am also thankful to all staff members of Workshop and electronics lab. of IDDC for their
help in fabrication of machine and test specimens.
Mr.Brahm Prakash, Mr.P.Thakkar, Dr.Chatter Singh, and the staff of ITMMEC,
IITD are thanked for their help received during microhardness testing and SEM studies.
I take this opportunity to thank my colleagues, Dr.T.Srihari, Dr.Amitava Mandal,
Mr.N.B.Mustafa, V.K.Gupta and Mr.G.K.Purohit for rendering all possible help throughout
this work. I thank my friends Mr.T.R.Kannan, Mr.S.R.K. Jasthy and Mr.A.V.S.R.k.Prasad
for thier voluantary helps.
I am gre,atful to Dr.I.P.Singh, Chief Design Engineer, IDDC, IITD, for his
encouragement and suggestions. My thanks are due to Dr.Sunil Pandey, Asst. Prof. of
Mech. Engg. Dept., for constructive criticism and advice.
I thank all my friends whose names do not figure here, for all types of helps
rendered by them. I sincerely thank those who constantly sustained me through their prayers.
I specially thank my wife, Mrs. A.Santhy, B.com ., B.Ed., for readily sacrificed her
time for the cause of this work and for providing me the necessary moral support and
encouragement during crucial periods.
(N. MURUaAN)
ABSTRACT
Weld surfacing is an indispensable process for producing corrosion resistant surface
by means of depositing stainless steel on low carbon steel components with a view to
achieving maximum economy and enhanced life. It is extensively used in the fabrication of
structures/components for use in chemical, petrochemical, nuclear and other allied
industries. In surfacing, the most important aspect is the dilution of the base metal into the
weld metal which has to be controlled effectively within the optimum range for better
economy and to ensure the desired mechanical and corrosion resistant properties of the
overlay.
A detailed study has been carried out to establish mathematical expressions for MIG
welding and single wire SAW processes relating the controllable welding parameters to weld
bead dimensions using response surface methodology in order to select accurately the
welding procedures and to predict the weld bead shapes and dimensions that will be
deposited. Using the developed mathematical models, surfacing was carried out for
achieving optimum dilution conditions employing the predicted process parameters. The
quality of as-welded claddings and their suitability for service were evaluated by carrying
out metallurgical studies as well as mechanical and corrosion tests.
To carry out surfacing by mechanised means, for achieving high repeatability, an
automatic computer controlled MIG surfacing system consisting of a welding machine, a
manipulator and an operating system was developed and the functions of all control
components were integrated to provide a close loop velocity and position control of slides
and initiating and stopping the arc. This system could not only serve the purpose of the
proposed research work but will be useful for future work with considerable latitude over
ranges of welding processes and techniques and surfacing/welding different configurations.
After the design and development of the MIG surfacing system, trial runs were
conducted to evolve the design matrix based on central composite rotatable design.
Experiments were conducted based on this design matrix and mathematical models were
developed to study the effects of process parameters such as arc voltage, wire feed rate,
welding speed and nozzle-to-plate distance on weld bead dimensions for two different
stainless steel filler wires with two different wire diameters. Using the aforementioned
response surface methodology, linear, quadratic, and two-way interaction effects of process
parameters on bead dimensions were studied. Process conditions were predicted for an
11
optimum dilution of 12-13% and single and multi-layer surfacing was accomplished at
optimum dilution conditions. The observed bead dimensions were well in agreement with
the predicted bead dimensions.
Metallurgical aspects of as-welded overlays such as chemistry, microhardness, ferrite
content, as well as macro- and microstructures including modes of solidification were studied
to evaluate its suitability for service. Five estimation techniques were used to find ferrite
content of overlays. Extensive microhardness survey was carried out across different zones
of overlays to correlate microstructure and microhardness to achieve high degree of
confidence in predicting microstructure of the overlay. Colour etching technique was
employed to assess the primary and secondary microstructures of overlays that resulted from
different modes of solidification. Modes of solidification predicted from Schaeffler and
Hammer & Svensson equivalents were compared with the observed modes. EPMA and SEM
studies were performed to analyze the effects of microsegregation that occurred during the
solidification.
The evaluation of overlay ductility and corrosion resistance was carried out in the
final phase of investigation using shear and side bend tests and corrosion tests respectively.
Shear testing performed as per the ASTM A264 revealed that the single layer overlays
owned good bond integrity. All clad specimens passed 180° side bend test which indicated
that they were sound and ductile. The single- and double-loop Electrochemical
Potentiokinetic Reactivation (EPR) methods employed on as-welded stainless steel overlays,
surfaced at optimum dilution condition, showed that all stainless steel claddings were free
from sensitization and possessed good resistance to intergranular corrosion.
111
CONTENTS
Page
No.
CERTIFICATE
ACKNOWLEDGEMENTS
ABSTRACT
CONTENTS
iii
LIST OF TABLES
ix
LIST OF FIGURES
xii
CHAPTER IINTRODUCTION
1
1.1 WELDING PROCESSES FOR SURFACING
2
1.2 STAINLESS STEEL CLADDING
2
1.3 NEED FOR ESTABLISHING DILUTION CONTROL PROCEDURE4
1.4 PLAN OF RESEARCH
6
1.4.1 DESIGN AND DEVELOPMENT OF COMPUTER CONTROLLED
MIG SURFACING SYSTEM:
1.4.2 PREDICTION OF WELD BEAD GEOMETRY
7
7
1.4.3 SURFACING AT OPTIMUM LEVEL OF DILUTION
CONDITIONS
1.4.4 METALLURGICAL STUDIES
9
9
1.4.4.1Overlay chemistry
10
1.4.4.2Microhardness studies
11
1.4.4.3Ferrite measurement
11
1.4.4.4Microstructural studies
11
1.4.4.5EPMA and SEM studies
12
1.4.5 SHEAR AND BEND TESTING
12
1.4.6 CORROSION TESTING
12
1.5 SEQUENCE OF INVESTIGATION
13
CHAPTER IILITERATURE SURVEY
20
2.1 INTRODUCTION
20
2.2 WELD BEAD GEOMETRY
20
iv
2.2.1 PENETRATION
20
2.2.2 BEAD WIDTH AND REINFORCEMENT
22
2.2.3 DILUTION
24
2.2.3.1Primary parameters
24
2.2.3.2Secondary parameters
25
2.2.3.3Welding techniques
26
2.3 EXPERIMENTAL TECHNIQUE
27
2.4 DESIGN OF EXPERIMENTS
29
2.5 METALLURGICAL TRANSFORMATIONS
29
2.5.1 HAZ OF BASE METAL
30
2.5.2 FUSION ZONE
30
2.5.3 MICROSTRUCTURE IN AUSTENITIC STAINLESS STEEL
WELDS
31
2.5.4 FERRITE CONTENT AND MORPHOLOGY
32
2.5.5 CARBON MIGRATION
34
2.6 MECHANICAL SHEAR AND BEND TESTS
35
2.7 CORROSION TESTING
36
2.7,1 CORROSION RESISTANCE
37
2.7.2 CORROSION TESTS
39
CHAPTER IIIDESIGN AND DEVELOPMENT OF
COMPUTER CONTROLLED AUTOMATIC
MIG SURFACING SYSTEM
3.1 INTRODUCTION
46
46
3.2 DESIGN AND DEVELOPMENT OF A COMPUTER CONTROLLED
AUTOMATIC MIG SURFACING SYSTEM
47
3.2.1 WELDING MACHINE
47
3.2.2 WELDING MANIPULATOR
48
3.2.2.1Mechanical system
48
3.2.2.2Electrical drive and its control unit
49
3.2.3 PROCESS CONTROL SYSTEM
50
3.2.3.1Personal computer (PC)
50
3.2.3.2Arc control
51
V
Speed and position control
3.2.3.3
Operating programme
3.2.3.4
3.3 SYSTEM PERFORMANCE AND ITS CAPABILITIES
CHAPTER IVDESIGN OF EXPERIMENTS
51
52
52
62
4.1 INTRODUCTION
62
4.2 BASE MATERIAL USED
62
4.3 CONSUMABLE USED
63
4.3.1 WIRES
63
4.3.2 FLUX
63
4.4 EXPERIMENTAL SETUP USED
63
4.5 TERMINOLOGY IN DESIGN OF EXPERIMENTS
64
4.6 FACTORIAL DESIGN
64
4.7 RESPONSE SURFACE DESIGNS
65
4.8 SELECTION OF DESIGN
66
4.9 DESIGN OF EXPERIMENTS
67
4.9.1 IDENTIFICATION OF THE PROCESS VARIABLES
67
4.9.2 FINDING THE LIMITS OF THE PROCESS VARIABLES 67
4.9.3 DEVELOPMENT OF DESIGN MATRIX
68
CHAPTER V
DEVELOPMENT OF MATHEMATICAL
MODELS AND SURFACING AT
OPTIMUM DILUTION LEVEL
75
5.1 INTRODUCTION
75
5.2 EXPERIMENTAL PROCEDURE
75
5.3 SELECTION OF MATHEMATICAL MODELS
77
5.4 ESTIMATION OF COEFFICIENTS OF MODELS
77
5.5 CHECKING THE ADEQUACY OF THE DEVELOPED MODELS78
5.6 TESTING COEFFICIENTS FOR SIGNIFICANCE
79
5.7 DEVELOPMENT OF FINAL MODELS
80
5.8 RESPONSE SURFACE ANALYSIS
80
5.8.1 EFFECT OF WELDING VARIABLES ON DEPTH OF
PENETRATION (P)
81
5.8.1.1Effect of wire feed rate
81
vi
5.8.1.2Effect of welding speed
82
5.8.1.3Effect of arc voltage
82
5.8.1.4Effect of nozzle-to-plate-distance
82
5.8.2 INTERACTION EFFECT OF WELDING VARIABLES ON
PENETRATION (P)
83
5.8.2.1Interaction of arc voltage and wire feed rate 83
5.8.2.2Interaction of arc voltage and welding speed 84
5.8.2.3Interaction of wire feed rate and welding
speed
84
5.8.2.4Interaction of welding speed and nozzle-to-plate
distance
85
5.8.3 EFFECT WELDING VARIABLES ON WELD WIDTH (W)85
5.8.3.1Effect of wire feed rate
86
5.8.3.2Effect of welding speed
86
5.8.3.3Effect of arc voltage
86
5.8.3.4Effect of nozzle-to-plate distance
86
5.8.4 INTERACTION EFFECT OF WELDING VARIABLES ON WELD
WIDTH (W)
87
5.8.4.1Interaction of arc voltage and welding speed 87
5.8.5 EFFECT OF WELDING VARIABLES ON HEIGHT OF
REINFORCEMENT (R)
87
5.8.5.1Effect of wire feed rate
87
5.8.5.2Effect of welding speed
87
5.8.5.3Effect of arc voltage
88
5.8.5.4Effect of nozzle-to-plate distance
88
5.8.6 INTERACTION EFFECT OF WELDING VARIABLES ON
REINFORCEMENT
88
5.8.6.1Interaction of arc voltage and wire feed rate 88
5.8.6.2Interaction of arc voltage and welding speed 89
5.8.6.3Interaction of open circuit voltage and welding
speed
89
5.8.7 EFFECT OF WELDING VARIABLES ON DILUTION (D)89
5.8.7.1Effect of wire feed rate
90
vii
5.8.7.2Effect of welding speed
90
5.8.7.3Effect of arc voltage
90
5.8.7.4Effect of nozzle-to-plate distance
91
5.8.8 INTERACTION EFFECT OF WELDING VARIABLES ON
DILUTION (D)
91
5.8.8.1Interaction of open circuit voltage and welding
speed
91
5.8.8.2Interaction of arc voltage and nozzle-to-plate
distance
91
5.9 SURFACING AT OPTIMUM DILUTION LEVEL
92
5.9.1 PREDICTION OF WELDING VARIABLES
93
5.9.2 SURFACING AT DESIRED DILUTION LEVEL
94
5.9.3 MULTI-LAYER SURFACING
94
CHAPTER VIMETALLURGICAL STUDIES
151
6.1 INTRODUCTION
151
6.2 METALLURGICAL ASPECTS OF A WELDMENT
153
6.2.1 WELD METAL
154
6.2.2 HEAT-AFFECTED ZONE
155
6.3 PLAN OF INVESTIGATION
157
6.4 EXPERIMENTAL INVESTIGATIONS
157
6.4.1 ANALYSIS OF CHEMISTRY OF OVERLAYS
157
6.4.2 MICROHARDNESS SURVEY
158
6.4.3 FERRITE MEASUREMENT
158
6.4.4 MICROSTRUCTURAL STUDIES
159
6.4.5 EPMA AND SEM STUDIES
160
6.5 RESULTS AND DISCUSSIONS
160
6.5.1 ANALYSIS OF CHEMISTRY OF OVERLAYS
161
6.5.2 ANALYSIS OF MICROHARDNESS SURVEY
161
6.5.3 ANALYSIS OF FERRITE CONTENT
163
6.5.4 MICROSTRUCTURAL ANALYSIS
164
6.5.5 EPMA AND SEM STUDIES
169
viii
CHAPTER VII EVALUATION OF OVERLAY DUCTILITY
AND CORROSION RESISTANCE
210
7.1 INTRODUCTION
210
7.2 SHEAR AND BEND TEST
211
7.3 CORROSION TEST
211
7.4 PLAN OF INVESTIGATION
213
7.5 EXPERIMENTAL PROCEDURE
214
7.5.1 SHEAR TEST
214
7.5.2 SIDE BEND TEST
214
7.5.3 CORROSION TEST
215
7.6 RESULTS AND DISCUSSIONS
216
7.6.1 SHEAR TEST
216
7.6.2 SIDE BEND TEST
216
7.6.3 CORROSION TEST
217
CHAPTER VIII CONCLUSIONS
231
8.1 DESIGN OF EXPERIMENTS (CHAPTER IV)
231
8.2 DEVELOPMENT OF MATHEMATICAL MODELS AND SURFACING
AT OPTIMUM DILUTION LEVEL (CHAPTER V)
8.3 METALLURGICAL STUDIES (CHAPTER VI)
232
235
8.4 EVALUATION OF OVERLAY DUCTILITY AND CORROSION
RESISTANCE (CHAPTER VII)
236
8.5 SCOPE FOR FURTHER WORK
237
REFERENCES
238
APPENDIX ICALIBRATION OF X AND Y MOTOR
256
APPENDIX IIDETAILS OF ENCODER AND ITS BIASING CIRCUIT258
APPENDIX III12 BIT 16 CHANNEL ANALOG TO DIGITAL AND
DIGITAL TO ANALOG CONVERTER CARD
259
APPENDIX IVBRIEF DETAIL OF I/O TIMER/COUNTER CARD262
APPENDIX VAMPLIFICATION AND PULSE SHAPING CIRCUIT265
APPENDIX VIDETAILS OF ARC SENSOR
LIST OF TECHNICAL PAPERS BASED ON THIS WORK
CURRICULUM VITAE
267