Development of Constitution Diagram for Dissimilar Metal Welds in Nickel Alloys and Carbon and ...

114 Pages·2010·5.26 MB·English

by  Eli Gould

Development of Constitution Diagram for Dissimilar Metal Welds in Nickel Alloys and
Carbon and Low-Alloy Steels

THESIS

Presented in Partial Fulfillment of the Requirements for the Degree Master of
Science in the Graduate School of The Ohio State University

By
Elijah Katunich Gould
Graduate Program in Welding Engineering

The Ohio State University
2010

Master's Examination Committee:
Professor John Lippold, Advisor
Professor Sudarsanam Babu
Copyright by
Elijah Katunich Gould
2010
ABSTRACT
The prevalence of dissimilar metal joints between carbon and low-alloy
steels and solid-solution strengthened nickel-base filler materials has resulted in an
increased desire to understand the metallurgy that controls the properties of welds
between these materials. The increased use of these combinations has been driven
by their successes in applications where austenitic stainless steel weld metals have
failed. Their superior resistance to stress corrosion cracking, elevated temperature
properties, and close match in coefficient of thermal expansion with steels make
them an ideal choice in a variety of situations. However, these materials do have
weldability issues of their own to mitigate. Among the more formidable concerns
regarding dissimilar joints between these materials is the formation of martensite in
the composition transition zone at the fusion boundary, which often accompanies
the formation of Type II boundaries during welding. The presence of substantial
amounts of martensite in this region greatly increases the likelihood of failure
during service. The Schaeffler diagram has been demonstrated to have an ability to
predict the formation of martensite to a certain degree in such situations. Having
been developed based on 300 series stainless steels its overall predictive capability
with regards to these materials can be improved upon.
ii
The goal of this study is to use previously established techniques to develop a
predictive diagram which has greater accuracy when applied to dissimilar welds
between carbon and low-alloy steels and nickel-base alloys. Button melt samples
were created by mixing various proportions of carbon and low-alloy steels and
nickel-base filler metals to produce samples whose microstructure consist of
varying amounts of martensite and austenite. The use of a martensite
characterization technique based on magnetic response (ferrite number) using the
Magne-Gage proved an effective way of determining martensite content of button
melt samples. Additional characterization techniques were used to establish a
relationship between magnetic response and martensite volume fraction. Magnetic
response data generated by the Magne-Gage was analyzed using statistical methods
and fit to a model in order to allow prediction of magnetic response based on alloy
content. The model was then used for construction of a predictive diagram for
dissimilar metal welds between these materials. Finally, predictive capabilities of
the developed diagram were assessed and discussed.
iii
DEDICATION
Dedicated to my mother, without whose constant love, support, and encouragement
I would never have accomplished what I have in life.
iv
ACKNOWLEDGMENTS
I would like to thank my advisors, Professor John Lippold and Professor
Boian Alexandrov whose guidance on this project was pivotal to its success, and
from whom I was able to learn continuously along the way.
Thanks are also extended to Professor Theodore Allen of the Integrated
Systems Engineering Department at the Ohio State University, and Dr. Jerry Gould of
the Edison Welding Institute for their advice and assistance with statistical analysis
preformed as part of this work.
Thanks to Professor Suresh Babu for his advice during parts of this project,
and for taking the time to serve as a member of my master’s examination
committee.
Thanks to the members of the Welding and Joining Metallurgy Group, both
past and present, whose contribution to an enjoyable work atmosphere cannot be
overstated. Thank you to Adam Hope for his work digitizing the Schaeffler diagram.
Thank you to Jeff Rodelas for his assistance with EBSD work.
Finally, I would like to thank the many people in my life whose support,
advice, and encouragement during this project proved essential to its completion.
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VITA
November 22, 1983………………………Born – Valparaiso, IN. United States of America
June, 2008…................................................B.S.W.E. The Ohio State University
Columbus, Ohio
2008 – Present……………………………...Graduate Research Associate
The Ohio State University

FIELD OF STUDY
Major Field: Welding Engineering
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TABLE OF CONTENTS
Abstract ....................................................................................................................................... ii
Dedication .................................................................................................................................. iv
Acknowledgments .................................................................................................................... v
Vita ............................................................................................................................................... vi
Table of Contents .................................................................................................................... vii
List of Tables ............................................................................................................................... x
List of Figures ........................................................................................................................... xi
1. Introduction ...................................................................................................................... 1
2. Background ....................................................................................................................... 3
2.1 Carbon and Low-Alloy Steels ............................................................................................ 3
2.1.1 Composition ..................................................................................................................................... 3
2.1.2 Metallurgy ........................................................................................................................................ 5
2.1.3 Weldability ..................................................................................................................................... 12
2.1.4 Applications ................................................................................................................................... 13
2.2 Solid-solution strengthened nickel-base alloys ..................................................... 13
2.2.1 Composition ................................................................................................................................... 13
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2.2.2 Metallurgy and Mechanical Properties............................................................................... 14
2.2.3 Weldability ..................................................................................................................................... 15
2.2.4 Applications ................................................................................................................................... 18
2.3 Weld Metal Constitution Diagrams ............................................................................. 19
2.3.1 Early Constitution Diagrams ................................................................................................... 20
2.3.2 The Schaeffler Diagram ............................................................................................................. 23
2.3.3 Austenitic-Martensitic Constitution Diagrams................................................................ 27
2.4 Nickel-Steel Dissimilar Metal Welding ...................................................................... 31
2.4.1 Applications ................................................................................................................................... 31
2.4.2 Weldability ..................................................................................................................................... 32
3. Objectives ......................................................................................................................... 39
4. Experimental Procedures ........................................................................................... 41
4.1 Materials ............................................................................................................................... 41
4.2 Sample Production ........................................................................................................... 46
4.3 Characterization ................................................................................................................ 48
4.3.1 Sample Prep ................................................................................................................................... 48
4.3.2 Optical Microscopy ..................................................................................................................... 51
4.3.3 Optical Phase Fraction Analysis ............................................................................................ 51
4.4 Ferrite Number Measurement ...................................................................................... 52
4.5 X-ray Diffraction ................................................................................................................ 54
4.6 Microhardness Testing.................................................................................................... 56
4.7 Chemical Analysis ............................................................................................................. 56
4.8 Data Analysis ...................................................................................................................... 57
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4.9 Diagram Development .................................................................................................... 58
5. Results and Discussions .............................................................................................. 59
5.1 Button Melt Microstructures ......................................................................................... 59
5.2 Microhardness Testing.................................................................................................... 63
5.3 Button Melt Analysis ........................................................................................................ 65
5.4 Magne-Gage Ferrite Number (FN) Measurement .................................................. 66
5.5 X-ray Diffraction ................................................................................................................ 72
5.6 Point Count .......................................................................................................................... 75
5.7 Development of FN to martensite phase fraction relation ................................. 78
5.8 Data Analysis & Diagram Development .................................................................... 79
5.9 Use of the Diagram ............................................................................................................ 83
6. Conclusions ...................................................................................................................... 85
References ................................................................................................................................ 87
A. Additional Micrographs .............................................................................................. 91
B. Button Melt Sample Data ............................................................................................ 97
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