THE EFFECTS OF NON-CONTACT ACOUSTIC VIBRATIONS ON THE SOLIDIFICATION AND ...

166 Pages·2008·5.91 MB·English

The Pennsylvania State University
The Graduate School
Department of Industrial and Manufacturing Engineering
THE EFFECTS OF NON-CONTACT ACOUSTIC VIBRATIONS ON THE
SOLIDIFICATION AND MICROSTRUCTURE OF
DUCTILE AND GRAY CAST IRON

A Thesis in
Industrial Engineering
by
Timothy M. Grenko

© 2008 Timothy M. Grenko

Submitted in Partial Fulfillment
of the Requirements
for the Degree of

Master of Science
December 2008
ii

The thesis of Timothy M. Grenko was reviewed and approved* by the following:

Robert C. Voigt
Professor of Industrial and Manufacturing Engineering
Thesis Advisor

Richard A. Wysk
Professor and Leonhard Chair in Engineering

Richard J. Koubek
Professor of Industrial and Manufacturing Engineering
Head of the Department of Industrial and Manufacturing Engineering

*Signatures are on file in the Graduate School
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ABSTRACT
Numerous research studies have examined the use of vibration to treat solidifying
metals. The topic was first investigated by the Russians in the early 1900’s. Early efforts
were unsophisticated and poorly documented. The method of rocking molds by hand to
create low frequency vibrations was first employed. Since these first experiments were
performed, significant advances have been made in equipment and technique.
Researchers have pursued the treatment of solidifying metals with vibration for increased
fluidity, improved casting yield, and overall casting quality improvements. Energy
transmitted through vibration has been found to degas melts, modify final
microstructures, and improve mechanical and corrosion properties. Until recently,
studies of the application of ultrasonic energy to solidifying metals have been performed
almost entirely using methods of contact energy transmission. Contact resonator
practices were plagued with problems of melt contamination and chill. Limited study has
been aimed at the use of non-contact methods of ultrasonic stimulation of solidifying
metals.
This thesis investigates the use of non-contact ultrasonic vibration treatment
during the solidification of ductile and gray cast iron alloys, which. The solidification
behavior of ductile cast iron and gray cast iron was evaluated in the inoculated and
uninoculated conditions when subjected to non-contact ultrasonic vibration of various
frequencies. Solidification cooling curves and final microstructure of each iron alloy as
was examined.
Ultrasonically treated ductile iron produced increased graphite nodularity, with a
corresponding decrease in graphite nodule size. Inoculated and uninoculated gray cast
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iron treated with ultrasonic energy realized an increase in flake graphite size. Minor
increase in overall solidification time was realized through non-contact ultrasonic
vibration.
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TABLE OF CONTENTS

LIST OF FIGURES vii
LIST OF TABLES x
ACKNOWLEDGEMENTS xii
Chapter 1 Introduction 1
Chapter 2 Literature Review 5
2.1 Gray and Ductile Cast Irons 5
2.1.1 Solidification of Gray and Ductile Cast Irons 6
2.1.2 Cast Iron Inoculation 9
2.1.3 Microstructure and Property Relationships 11
2.1.4 Cast Iron Feeding and Fluidity Properties 24
2.1.5 Thermal Analysis of Gray and Ductile Irons 25
2.2 Acoustic Vibrations is Liquids and Solidifying Metals 27
2.2.1 Cavitation 28
2.2.2 Acoustic Streaming 29
2.2.3 Radiation Pressure and Sonocapillary Effect 32
2.2.4 Attenuation of Acoustic Vibrations in Varied Materials 33
2.3 Acoustic Vibrations in Solidifying Cast Iron 36
2.3.1 Microstructure 36
2.3.2 Mechanical Properties 40
2.4 Summary 41

Chapter 3 Experimental Procedure 43

3.1 Materials and Equipment used in Acoustic Experiments 44
3.2 Procedure for Acoustic Experiments 46
3.3 Solidification Date Collection 48
3.4 Procedure for Microstructure Analysis of Samples 51
3.5 Quantitative Metallography 52

Chapter 4 Results 53

4.1 Results for Preliminary Experimental Phase of Non-contact 56
Ultrasonic Experiments
4.2 Phase One Experiments 59
4.3 Phase Two Experiments 64
4.4 Phase Three Experiments 66
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Chapter 5 Discussion of Results 72

5.1 Effect of Acoustic Vibration on Undercooling and Grain Refinement 72
5.2 Effect of Acoustic Vibration on Graphite Nucleation and Growth 73
5.3 Effect of Acoustic Vibration on Solidification Time 79
5.4 Expected Effect of Acoustic Vibration on Mechanical Properties 80
5.5 Non-Contact Treatment Distance and Attenuation 81

Chapter 6 Conclusions 84

Bibliography 88

Appendix A: Acoustic Trial Details 90

Appendix B: Microstructure Characterization Details 98

Appendix C: Statistical Analysis 118

C.1 Ductile Iron Microstructure 118
C.1.1 Nodule Size 118
C.1.2 Nodule Count 121
C.1.3 Nodularity 124
C.2 75% FeSi Inoculated Gray Iron 127
C.2.1 Flake Size 127
C.2.2 Flake Count 130
C.3 Uninoculated Gray Iron 133
C.3.1 Flake Size 133
C.3.2 Flake Count 136

Appendix D: Statistical Analysis – Designed Experiments 140

D.1 Phase Two Designed Experiment 140
D.1.1 Undercooling 140
D.1.2 Solidification Time 143
D.2 Phase Three Designed Experiment 145
D.2.1 Undercooling 145
D.2.2 Solidification Time 147
D.2.3 Average Flake Size 149
D.2.3 Average Flake Count 152
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LIST OF FIGURES

Figure 2.1: Cooling curves of hypoeutectic and hypereutectic cast iron 6
alloys [7].

Figure 2.2: Dendrite arm showing primary, secondary, and tertiary arms 7
[9].

Figure 2.3: Intermediate stages of the development from cell to dendrite 7
[9].

Figure 2.4: Crystalline structure of graphite [10]. 8

Figure 2.5: The influence of cerium content and the ratio of free energy 9
to growth velocity on the graphite structural transitions of cast
iron [11].

Figure 2.6: Typical graphite shapes found in cast iron alloys [2]. 12

Figure 2.7: Flake graphite in as cast gray iron [12]. 13

Figure 2.8: Types of graphite flakes in gray iron (AFS-ASTM) [2]. 14

Figure 2.9: Effect of section thickness on hardness and structure [2]. 15

Figure 2.10: Illustrating the effects of thickness of section, and hence 15
rate of cooling on the structure of a gray iron [13].

Figure 2.11: Spherical-graphite in as cast ductile iron [12]. 17

Figure 2.12: Spheroidal-graphite in as cast ductile iron [12]. 19

Figure 2.13: As-cast ductile iron microstructure etched in 4% nital with 21
bulls-eye structure (100x) [12].

Figure 2.14: Lamellar structure of pearlite in as-cast gray iron under 22
high magnification [12].

Figure 2.15: Correlation between type of matrix in non-alloyed cast 24
irons, silicon and phosphorus content as well as thickness [2].

Figure 2.16: Fluidity versus degree of superheat for four gray irons of 25
different carbon contents [2].

Figure 2.17: Cast iron solidification cooling curve with key points of 26
solidification labeled [7].
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Figure 2.18: Acoustic streaming in an undercooled melt at various times 30
[21].

Figure 2.19: Influence of ultrasonic pressure amplitude and frequency 31
on acoustic streaming velocity [21].

Figure 2.20: Sonocapillary effect observed in water at room temperature 32
[21].

Figure 2.21: Effect of ultrasonic vibration on microstructures of flake- 37
graphite cast iron ingots [24].

Figure 2.22: Effect of ultrasonic vibration on microstructures of 38
spheroidal-graphite cast iron ingots [24]

Figure 2.23: Effect of ultrasonic vibration during solidification on the 39
number and the diameter of equivalent circle graphite nodule
[24].

Figure 3.1: Ultrasonic instrumentation used for non-contact ultrasonic 45
experimentation.

Figure 3.2: Equipment and instrumentation used for cooling curve 47
analysis.

Figure 4.1: Sample micrographs of ductile and gray irons in polished 54
condition and 2% nital etch.

Figure 4.2: Solidification cooling curve for a hypoeutectic cast iron 55
showing points of interest during solidification [7].

Figure 4.3: Microstructures of ductile and gray cast irons from the 57-59
preliminary phase of experiments.

Figure 4.4: Microstructures of ductile and gray cast irons from phase 61-62
one, trial 1 experiments.

Figure 4.5: Microstructures of ductile and gray cast irons from phase 63-64
one, trial 2 experiments.

Figure 4.6: Eutectic undercooling portion of phase two sample 66
solidification cooling curves.

Figure 4.7: Eutectic undercooling portion of phase three sample 68
solidification cooling curves.
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Figure 4.8: Microstructures of inoculated gray cast irons from the 69-70
control group of phase three experiments.

Figure 4.9: Microstructures of inoculated gray cast irons from the non- 70-71
contact ultrasonic treatment group of phase three experiments.

Figure 5.1: Average experimental graphite particle size and count from 75
Trials 1 and 2 of phase one experiments.

Figure 5.2: Typical graphite microstructure of uninoculated gray iron 77
samples collected in trial 1 of phase one experiments.

Figure 5.3: Chart of modified solidification time from phase two and 80
three experiments. Differences in solidification time of phase
two and three are a result of inoculation technique.

Figure 5.4: 3D-surface plots of the factors of frequency (Hz) vs. distance 82
(in.) for eutectic undercooling and solidification time.
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LIST OF TABLES

Table 2.1: Compositional limits of gray and ductile irons [2]. 6
Table 2.2: Comparison of the cost of mechanical properties for common 11
ferrous and nonferrous casting materials [5].
Table 2.3: ASTM A48 requirements for Tensile Strength of Gray Cast 16
Irons in Separately Cast Test Bars (Inch-Pound) [14].
Table 2.4: ASTM A536 tensile strength requirements for ductile irons 20
[16].
Table 2.5: Mechanical properties of common iron matrix structures [2]. 20
Table 2.6: Key thermal analysis values from the cooling curve of a 26
hypoeutectic cast iron [7].
Table 2.7: The speed of sound in various media [22]. 34

Table 2.8: Effect of vibration on the hardness and microstructure of sand 40
molded, magnesium treated cast iron [26].

Table 3.1: Charge materials used for each experimental trial. 44

Table 3.2: Inoculation ladle additions (wt%) for ductile and gray cast 44
irons.

Table 3.3: Target composition for ductile and gray irons poured in non- 44
contact ultrasonic experiments.

Table 3.4: Sample output from DATACAST 2000 data acquisition unit. 49

Table 4.1: Summary of quantitative microstructure data examined in 54
experimental phases

Table 4.2: Summary of the experimental phases conducted. 56

Table 4.3: Microstructure results for the preliminary experiments phase 57
of experiments.

Table 4.4: Microstructure results for phase one experiments. 60

Table 4.5: Undercooling and modified solidification time measurement 65
for uninoculated gray iron during phase two experimentation.