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Effect of microstructure on the fragmentation characteristics of malleable cast iron materials
Materials Science and Engineering, 51 (1981) 265 - 269
Short
265
Communication
Effect of microstructure on the fragmentation characteristics of malleable cast iron materials
G. ELKABIR* and A. ROSEN
Department of Materials Engineering, Technion, Israel Institute of Technology, Haifa (Israel) (Received April 23, 1981 ; in revised form June 22, 1981)
1. Introduction Materials selection for internally detonated cylinders is a complex problem, since it is influenced by a large number of factors. The choice of materials is therefore mainly based on experience [1 ]. Mortar shells, for example, were originally made of wrought steel because of its comparative ease of fabrication b u t a substantial amount of cast pearlitic malleable iron explosive shell has also been utilized [2 - 4]. Cast iron offers a substantial improvement in fragmentation effectiveness over low carbon steel because of its ability to break up into a large number of small nearly cubic-shaped fragments [ 1, 3 ] . Furthermore, the structure and properties of cast iron can be varied widely by heat treatment. The graphitization of white cast iron can produce a large spectrum of microstructures and accordingly different mechanical properties. The purpose of this investigation was to study the interdependence between microstructure and fragmentation characteristics of different malleable cast iron materials in comparison with that of normalized SAE 1045 steel, which is a conventional material for mortar shells. Throughout the investigation most of the parameters, such as the specimen size and geometry, the chemical composition of the cast iron, the type of explosive and the weight ratio of the shell to the explosive were kept constant to enable us to study only the effect of structural parameters on fragmentation characteristics. *Present address: Armament Development Authority, Ministry of Defence, Israel. 0025-5416/81/0000-0000/$02.50
2. Materials and specimens The raw material for the study was one heat of white cast iron with the following composition: 2.65 wt.% C; 1.60 wt.% Si; 0.37 wt.% Mn; 0.06 wt.% S; 0.03 wt.% P. Cylinders 110 mm long, 42 mm in inside diameter and 8 mm in wall thickness were sand mould cast. The white cast iron cylinders were divided into four groups and each group underwent the following heat treatment: graphitization at 940 °C for 5 h and then slow cooling (10 °C h - I ) to 870 °C. After this treatment, which was c o m m o n to all four groups, the final microstructures were obtained by employing different cooling rates: group 1 (ferritic), furnace cooling to room temperature; group 2 (ferritic-pearlitic), air cooling to room temperature; group 3 (pearlitic), forced air cooling (with a fan) to room temperature; group 4 (tempered martensitic), oil quenching and subsequent tempering at 600 °C for 90 min. After heat treatment, cylinders 65.2 mm long were machined to 48 mm in inside diameter and 3.3 mm in wall thickness. The explosive bodies were prepared as follows. The cylinders were filled with composition Btype explosive; the weight ratio of the explosive to the cylinder was kept constant at 0.7. The cylinders were painted on the outside with a special heat-resisting paint to enable identification of the original outer surface after detonation. Finally, the two ends were sealed with brass plates. For comparison, identical cylinders were also prepared from normalized 1045 steel. Specimens for optical microscopy were prepared by mounting, polishing and etching in 2% Nital. 3. Experimental procedure The explosive b o d y was hung above a water pool in which approximately 40% of the total fragments were recovered after detonation; the very fine fragments were lost in the pool. The fragments were collected with a magnet and immediately stored in alcohol. They were washed in acetone, dried by hot air and distributed into nine groups of different © Elsevier Sequoia/Printed in The Netherlands
266
masses. The fragments in each group were counted and their masses were determined. The very fine fragments (of mass less than 0.05 g) were not considered. Only a few fragments were heavier than 0.040 g. Metallurgical observations were made on the original material, as well as on the fragments.
t
Nm = N0 exp --
(1)
where Nm is the cumulative number of fragments with mass greater than m, and No and p are constants. This expression can be rearranged as l o g N m = log N O -- 2.30-----3
(2)
4. Results By plotting log Nm against m 1/2 w e obtain a straight line. The slope o f this line which is a statistical measure of the homogeneity of the distribution of the fragments can be used to represent fragmentation behaviour, and it is called the "fragmentation parameter". The variation in Nm v e r s u s m 1/2 for the four types of malleable iron is shown in Fig. 3 and that for the steel is shown in Fig. 4. All data are based on three experiments for each type of material and therefore each datum point represents the average o f three experiments. The straight lines were obtained by regression analysis. The numerical values of the slopes (tan ~) are listed in Table 1 together with the average fragment masses. Metallographic examinations were performed for the following purposes: (a) to study the general structure of the different types of iron; (b) to observe the shape of frag-
Figure 1 shows the typical size distribution of fragments for the ferritic, pearlitic-ferritic, pearlitic and tempered martensitic malleable irons materials. For comparison the same distribution is shown for the SAE 1045 steel in Fig. 2. The m e t h o d c o m m o n l y used by several investigators [5, 6] of assessing the fragment mass distribution is the empirical analysis proposed by Welch and Mott. The relationship used in the Welch-Mott analysis in its simplest form may conveniently be expressed as
llllilillllr~l ti.|ll~[tl|i
IIIIIdl||lll~$~'|lll|ll|l I ~"t'~illJilltlllJl
{~lli~lllldltllli~l~P~ |tll~ilill~llili~t~
~I0~1~
¢t~I
I[~*'~..d;...
ll.t}l~liil
~ I!
E Z
I000,
n:E z
(a)
(b)
(c)
(d)
I-
\
Fig. 1. Typical size distributions o f fragments o f the various malleable cast iron materials: (a) ferritic; (b) f e r r i t i c - p e a r l i t i c ; (c) pearlitic; (d) martensitic.
\
u. w > tJ
=E (J
IC
\\ 1~)
L
0-1
I
0-2
L 0-3
FRAGMENT ~N~{I!~I~I
{ lillli! il~i ~!i !l~ili !~ ~! E!l/l~ll~l~l~iE
[
Fig. 2. T y p i c a l size d i s t r i b u t i o n f o r S A E 1 0 4 5 s t e e l .
I 0.4
I 0-5
I 0-6
0,7
MASS m 11=(9r II=)
Fig. 3. T h e v a r i a t i o n in N m w i t h m ~ / 2 f o r v a r i o u s malleable cast iron materials: e, ferritic, tan ~ = 7.5;
A ferritic-pearlitic, tan C~= 11.8 ; D, pearlitic, tan a = 12.5; O, martensitic, t a n s = 14.3.
267 TABLE 1 Summary of average results : metallurgical parameters and fragmentation characteristics Mate ria I
Ferritic Ferritic-pearlitic Pearlitic Martensitic SAE 1045
Metallurgical properties
Fragmentation characteristics
Graphite content (wt.%)
Average IGS (#m)
Number o f total Average fragment Fragmentation fragments mass (g) parameter (above 0.05 g) tan c~
2.35 1.85 1.80 1.95
93 147 159 180 --
560 768 770 828 321
0.119 0.083 0.081 0.071 0.246
7.5 11.8 12.5 14.3 3.0
,ooo! E z hl aD
x
Z ~9
~ ioc w (.9
w
>_
"
J
i ÷
"1
o
!
u
1"-'t
I
i
t
!
1
1
1
1
t
l
t
l
i
(a) ÷
1
0
[
i
0"20
I
i
0.40
J
t
0"60
J
I
0.80
FRAGMENT MASS (ml/2)(gr tlz)
Fig. 4. The variation in N m with m 1/2 for 1045 steel ( t a n s = 3.0).
ments; (c) to analyse the midwall cracks in the fragments; (d) to measure the intergraphite spacing (IGS). Figure 5(a) and Fig. 5(b) show typical fragments from the steel and from the cast iron respectively. Although the steel fragments are large and heavily deformed, the fragments from the cast iron are small and nearly equiaxed. All four types of cast iron gave fragments similar to that shown in Fig. 5(b). Figure 6 is a low magnification photomicrograph of a sectioned fragment which shows that the crack propagates through the graphite particles. The examination of a very large number of fragments clearly indicates that almost all the cracks propagate through and are initiated or terminate at graphite
(b) Fig. 5. Typical fragment shapes: (a) steel; (b) cast iron.
particles. Since the distribution and density of graphite particles must play some role in crack propagation during explosion, it was decided to measure the IGS of the various cast iron materials. The spacing was measured by the linear analysis method. The values of the IGS were determined by carrying out measurements on 20 micrographs from each
268
Fig. 6. Microphotographs of pearlitic malleable cast iron, showing cracks which pass through graphite particles (unetched).
(4
type of cast iron. The results are given in Table 1. 5. Discussion The most dominant feature of this investigation is that the fragmentation characteristics of the steel are quite different from those of the cast iron. The fragmentation parameter of the steel is much smaller and the average mass of fragments is much larger than that of the cast iron, even when compared with ferritic malleable iron. This difference is attributed to the presence of graphite nodules in the various types of cast iron. In Table 1 the graphite contents and the IGSs of the different types of iron are listed. The graphite content is the highest for ferritic iron, since almost all the carbon in this structure is in the form of graphite. The graphite contents for the other three structures are similar and the variation can be well within the accuracy of the chemical analysis. In spite of this, we believe that the higher graphite content for tempered martensitic iron is real and it is a result of graphitization during tempering [7]. The only systematic changes in the different structures can be attributed to the IGSs which depend on the graphite contents and on their distributions. The ferritic structure has the largest percentage of graphite and therefore the shortest IGS. For the ferriticpearlitic and the pearlitic iron structures, the graphite contents and the IGSs are similar: the differences are probably within the scatter of the measurements. Tempered martensitic
(b) Fig. 7. Typical microstructures of (a) ferritic and (b) tempered martensitic malleable iron (etch, 2% Nital).
iron has the largest IGS in spite of the fact that its graphite content is not the smallest. The reason is that, during tempering, the graphite nodules grow at the expense of the carbon in the martensite and also by the elimination of small graphite nodules close to them. To illustrate the marked differences between the IGSs of the various structures, Fig. 7(a) and Fig. 7(b) exhibit typical ferritic and tempered martensitic iron microstructures respectively. Figure 8 shows the variation in the fragmentation parameter and the average mass of fragments with IGS. The linear relationship shown in Fig. 8 is probably incidental; however, the correlation is clear. A similar correlation was reported for ductile cast iron [ 8,9] where the size of the fragments was found to
269 AVERAGE FRAGMENT MASS [gr] 0.05 0.06 0,07 0.08 0.09 0.1 0.11 0.12 i f I I I i i 200 ~' z
2
180
160 140
3
-? 120 G_ ~ nr ir~ 100 w Z 80 607
~ PEARLITI[I o ~ FERRITIC ,
4
$
I
9
I
,0
I
11
I
1'2 13
I
14
I
15
FRAGMENTATION PARAMETER (tg a)
5
Fig. 8. The variation in the fragmentation parameter (e) and the average fragment mass (o) with the IGS for the various malleable cast iron materials.
6
be inversely related to the average size of the graphite nodules. 7
6. Conclusions The results of this research clearly indicate a correlation between the IGS, the average mass of the fragments and the fragmentation parameter. Since the fragmentation parameter is a statistical measure o f the homogeneity of the distribution of fragments, it can be concluded that, the larger the IGS, the smaller is the average fragment mass and the more uniform is the fragment size distribution.
References 1 R. P. O'Shea, J. C. Dahn and T. Watmough, Development of naturally fragmenting materials,
8
9
AFAL Tech. Rep. 8, January 1970 (Air Force Armament Laboratory, Elgin Air Force Base, FL). M. Famiglietti, A preliminary fragmentation analysis of the wounding effectiveness of some experimental cast ferrous shell as dependent upon casing material, wall thickness and explosive charge, BRL Tech. Note 894, April 1954 (Ballistic Research Laboratory, Aberdeen, MD). S. F. Magis, Materials selection for naturally fragmenting munitions, 1st Partial Rep., January 1965 (Naval Weapons Laboratory, Dahlgren, VA) (AD 356811 (American Scientific and Technical Information Agency)). S. F. Magis, Materials selection for naturally fragmenting munitions, 2nd Partial Rep., September 1965 (Naval Weapons Laboratory, Dahlgren, VA) (AD 365675 (American Scientific and Technical Information Agency)). P. Kranklis and A. J. Bedford, Fragmentation data analysis, Rep. 549, November 1974 (Material Research Laboratory, Department of Defence, Australian Defence Scientific Service, Maribyrnong, Victoria, Australia). A. J. Bedford, The presentation of natural fragmentation data, Tech. Note 262, July 1972 (Defence Standards Laboratories, Department of Supply, Australian Defence Scientific Service, Maribyrnong, Victoria, Australia). ASM Committee on Heat Treating of Cast Iron, Heat treating of cast irons, in Metals Handbook, American Society for Metals, Metals Park, OH, 8th edn., 1961. K. Holmes, E. Wyatt, P. Smoot and E. Deluca, The relationship between trace elements, microstructure, mechanical properties and fragmentation properties of nodular iron, AMMRC Tech. Rep. 71-24, August 1971 (Army Materials and Mechanics Research Center, Watertown, MD) (AD 889828L (American Scientific and Technical Information Agency)). P. C. Rossin, Ad hoc Committee on Shell Steels, Producibility of artillery shells made from HF-1 steel, NMAB Rep. 307, April 1973 (National Materials Advisory Board, National Academy of Sciences, Washington, DC) (AD 763988 (American Scientific and Technical Information Agency)).
Short
265
Communication
Effect of microstructure on the fragmentation characteristics of malleable cast iron materials
G. ELKABIR* and A. ROSEN
Department of Materials Engineering, Technion, Israel Institute of Technology, Haifa (Israel) (Received April 23, 1981 ; in revised form June 22, 1981)
1. Introduction Materials selection for internally detonated cylinders is a complex problem, since it is influenced by a large number of factors. The choice of materials is therefore mainly based on experience [1 ]. Mortar shells, for example, were originally made of wrought steel because of its comparative ease of fabrication b u t a substantial amount of cast pearlitic malleable iron explosive shell has also been utilized [2 - 4]. Cast iron offers a substantial improvement in fragmentation effectiveness over low carbon steel because of its ability to break up into a large number of small nearly cubic-shaped fragments [ 1, 3 ] . Furthermore, the structure and properties of cast iron can be varied widely by heat treatment. The graphitization of white cast iron can produce a large spectrum of microstructures and accordingly different mechanical properties. The purpose of this investigation was to study the interdependence between microstructure and fragmentation characteristics of different malleable cast iron materials in comparison with that of normalized SAE 1045 steel, which is a conventional material for mortar shells. Throughout the investigation most of the parameters, such as the specimen size and geometry, the chemical composition of the cast iron, the type of explosive and the weight ratio of the shell to the explosive were kept constant to enable us to study only the effect of structural parameters on fragmentation characteristics. *Present address: Armament Development Authority, Ministry of Defence, Israel. 0025-5416/81/0000-0000/$02.50
2. Materials and specimens The raw material for the study was one heat of white cast iron with the following composition: 2.65 wt.% C; 1.60 wt.% Si; 0.37 wt.% Mn; 0.06 wt.% S; 0.03 wt.% P. Cylinders 110 mm long, 42 mm in inside diameter and 8 mm in wall thickness were sand mould cast. The white cast iron cylinders were divided into four groups and each group underwent the following heat treatment: graphitization at 940 °C for 5 h and then slow cooling (10 °C h - I ) to 870 °C. After this treatment, which was c o m m o n to all four groups, the final microstructures were obtained by employing different cooling rates: group 1 (ferritic), furnace cooling to room temperature; group 2 (ferritic-pearlitic), air cooling to room temperature; group 3 (pearlitic), forced air cooling (with a fan) to room temperature; group 4 (tempered martensitic), oil quenching and subsequent tempering at 600 °C for 90 min. After heat treatment, cylinders 65.2 mm long were machined to 48 mm in inside diameter and 3.3 mm in wall thickness. The explosive bodies were prepared as follows. The cylinders were filled with composition Btype explosive; the weight ratio of the explosive to the cylinder was kept constant at 0.7. The cylinders were painted on the outside with a special heat-resisting paint to enable identification of the original outer surface after detonation. Finally, the two ends were sealed with brass plates. For comparison, identical cylinders were also prepared from normalized 1045 steel. Specimens for optical microscopy were prepared by mounting, polishing and etching in 2% Nital. 3. Experimental procedure The explosive b o d y was hung above a water pool in which approximately 40% of the total fragments were recovered after detonation; the very fine fragments were lost in the pool. The fragments were collected with a magnet and immediately stored in alcohol. They were washed in acetone, dried by hot air and distributed into nine groups of different © Elsevier Sequoia/Printed in The Netherlands
266
masses. The fragments in each group were counted and their masses were determined. The very fine fragments (of mass less than 0.05 g) were not considered. Only a few fragments were heavier than 0.040 g. Metallurgical observations were made on the original material, as well as on the fragments.
t
Nm = N0 exp --
(1)
where Nm is the cumulative number of fragments with mass greater than m, and No and p are constants. This expression can be rearranged as l o g N m = log N O -- 2.30-----3
(2)
4. Results By plotting log Nm against m 1/2 w e obtain a straight line. The slope o f this line which is a statistical measure of the homogeneity of the distribution of the fragments can be used to represent fragmentation behaviour, and it is called the "fragmentation parameter". The variation in Nm v e r s u s m 1/2 for the four types of malleable iron is shown in Fig. 3 and that for the steel is shown in Fig. 4. All data are based on three experiments for each type of material and therefore each datum point represents the average o f three experiments. The straight lines were obtained by regression analysis. The numerical values of the slopes (tan ~) are listed in Table 1 together with the average fragment masses. Metallographic examinations were performed for the following purposes: (a) to study the general structure of the different types of iron; (b) to observe the shape of frag-
Figure 1 shows the typical size distribution of fragments for the ferritic, pearlitic-ferritic, pearlitic and tempered martensitic malleable irons materials. For comparison the same distribution is shown for the SAE 1045 steel in Fig. 2. The m e t h o d c o m m o n l y used by several investigators [5, 6] of assessing the fragment mass distribution is the empirical analysis proposed by Welch and Mott. The relationship used in the Welch-Mott analysis in its simplest form may conveniently be expressed as
llllilillllr~l ti.|ll~[tl|i
IIIIIdl||lll~$~'|lll|ll|l I ~"t'~illJilltlllJl
{~lli~lllldltllli~l~P~ |tll~ilill~llili~t~
~I0~1~
¢t~I
I[~*'~..d;...
ll.t}l~liil
~ I!
E Z
I000,
n:E z
(a)
(b)
(c)
(d)
I-
\
Fig. 1. Typical size distributions o f fragments o f the various malleable cast iron materials: (a) ferritic; (b) f e r r i t i c - p e a r l i t i c ; (c) pearlitic; (d) martensitic.
\
u. w > tJ
=E (J
IC
\\ 1~)
L
0-1
I
0-2
L 0-3
FRAGMENT ~N~{I!~I~I
{ lillli! il~i ~!i !l~ili !~ ~! E!l/l~ll~l~l~iE
[
Fig. 2. T y p i c a l size d i s t r i b u t i o n f o r S A E 1 0 4 5 s t e e l .
I 0.4
I 0-5
I 0-6
0,7
MASS m 11=(9r II=)
Fig. 3. T h e v a r i a t i o n in N m w i t h m ~ / 2 f o r v a r i o u s malleable cast iron materials: e, ferritic, tan ~ = 7.5;
A ferritic-pearlitic, tan C~= 11.8 ; D, pearlitic, tan a = 12.5; O, martensitic, t a n s = 14.3.
267 TABLE 1 Summary of average results : metallurgical parameters and fragmentation characteristics Mate ria I
Ferritic Ferritic-pearlitic Pearlitic Martensitic SAE 1045
Metallurgical properties
Fragmentation characteristics
Graphite content (wt.%)
Average IGS (#m)
Number o f total Average fragment Fragmentation fragments mass (g) parameter (above 0.05 g) tan c~
2.35 1.85 1.80 1.95
93 147 159 180 --
560 768 770 828 321
0.119 0.083 0.081 0.071 0.246
7.5 11.8 12.5 14.3 3.0
,ooo! E z hl aD
x
Z ~9
~ ioc w (.9
w
>_
"
J
i ÷
"1
o
!
u
1"-'t
I
i
t
!
1
1
1
1
t
l
t
l
i
(a) ÷
1
0
[
i
0"20
I
i
0.40
J
t
0"60
J
I
0.80
FRAGMENT MASS (ml/2)(gr tlz)
Fig. 4. The variation in N m with m 1/2 for 1045 steel ( t a n s = 3.0).
ments; (c) to analyse the midwall cracks in the fragments; (d) to measure the intergraphite spacing (IGS). Figure 5(a) and Fig. 5(b) show typical fragments from the steel and from the cast iron respectively. Although the steel fragments are large and heavily deformed, the fragments from the cast iron are small and nearly equiaxed. All four types of cast iron gave fragments similar to that shown in Fig. 5(b). Figure 6 is a low magnification photomicrograph of a sectioned fragment which shows that the crack propagates through the graphite particles. The examination of a very large number of fragments clearly indicates that almost all the cracks propagate through and are initiated or terminate at graphite
(b) Fig. 5. Typical fragment shapes: (a) steel; (b) cast iron.
particles. Since the distribution and density of graphite particles must play some role in crack propagation during explosion, it was decided to measure the IGS of the various cast iron materials. The spacing was measured by the linear analysis method. The values of the IGS were determined by carrying out measurements on 20 micrographs from each
268
Fig. 6. Microphotographs of pearlitic malleable cast iron, showing cracks which pass through graphite particles (unetched).
(4
type of cast iron. The results are given in Table 1. 5. Discussion The most dominant feature of this investigation is that the fragmentation characteristics of the steel are quite different from those of the cast iron. The fragmentation parameter of the steel is much smaller and the average mass of fragments is much larger than that of the cast iron, even when compared with ferritic malleable iron. This difference is attributed to the presence of graphite nodules in the various types of cast iron. In Table 1 the graphite contents and the IGSs of the different types of iron are listed. The graphite content is the highest for ferritic iron, since almost all the carbon in this structure is in the form of graphite. The graphite contents for the other three structures are similar and the variation can be well within the accuracy of the chemical analysis. In spite of this, we believe that the higher graphite content for tempered martensitic iron is real and it is a result of graphitization during tempering [7]. The only systematic changes in the different structures can be attributed to the IGSs which depend on the graphite contents and on their distributions. The ferritic structure has the largest percentage of graphite and therefore the shortest IGS. For the ferriticpearlitic and the pearlitic iron structures, the graphite contents and the IGSs are similar: the differences are probably within the scatter of the measurements. Tempered martensitic
(b) Fig. 7. Typical microstructures of (a) ferritic and (b) tempered martensitic malleable iron (etch, 2% Nital).
iron has the largest IGS in spite of the fact that its graphite content is not the smallest. The reason is that, during tempering, the graphite nodules grow at the expense of the carbon in the martensite and also by the elimination of small graphite nodules close to them. To illustrate the marked differences between the IGSs of the various structures, Fig. 7(a) and Fig. 7(b) exhibit typical ferritic and tempered martensitic iron microstructures respectively. Figure 8 shows the variation in the fragmentation parameter and the average mass of fragments with IGS. The linear relationship shown in Fig. 8 is probably incidental; however, the correlation is clear. A similar correlation was reported for ductile cast iron [ 8,9] where the size of the fragments was found to
269 AVERAGE FRAGMENT MASS [gr] 0.05 0.06 0,07 0.08 0.09 0.1 0.11 0.12 i f I I I i i 200 ~' z
2
180
160 140
3
-? 120 G_ ~ nr ir~ 100 w Z 80 607
~ PEARLITI[I o ~ FERRITIC ,
4
$
I
9
I
,0
I
11
I
1'2 13
I
14
I
15
FRAGMENTATION PARAMETER (tg a)
5
Fig. 8. The variation in the fragmentation parameter (e) and the average fragment mass (o) with the IGS for the various malleable cast iron materials.
6
be inversely related to the average size of the graphite nodules. 7
6. Conclusions The results of this research clearly indicate a correlation between the IGS, the average mass of the fragments and the fragmentation parameter. Since the fragmentation parameter is a statistical measure o f the homogeneity of the distribution of fragments, it can be concluded that, the larger the IGS, the smaller is the average fragment mass and the more uniform is the fragment size distribution.
References 1 R. P. O'Shea, J. C. Dahn and T. Watmough, Development of naturally fragmenting materials,
8
9
AFAL Tech. Rep. 8, January 1970 (Air Force Armament Laboratory, Elgin Air Force Base, FL). M. Famiglietti, A preliminary fragmentation analysis of the wounding effectiveness of some experimental cast ferrous shell as dependent upon casing material, wall thickness and explosive charge, BRL Tech. Note 894, April 1954 (Ballistic Research Laboratory, Aberdeen, MD). S. F. Magis, Materials selection for naturally fragmenting munitions, 1st Partial Rep., January 1965 (Naval Weapons Laboratory, Dahlgren, VA) (AD 356811 (American Scientific and Technical Information Agency)). S. F. Magis, Materials selection for naturally fragmenting munitions, 2nd Partial Rep., September 1965 (Naval Weapons Laboratory, Dahlgren, VA) (AD 365675 (American Scientific and Technical Information Agency)). P. Kranklis and A. J. Bedford, Fragmentation data analysis, Rep. 549, November 1974 (Material Research Laboratory, Department of Defence, Australian Defence Scientific Service, Maribyrnong, Victoria, Australia). A. J. Bedford, The presentation of natural fragmentation data, Tech. Note 262, July 1972 (Defence Standards Laboratories, Department of Supply, Australian Defence Scientific Service, Maribyrnong, Victoria, Australia). ASM Committee on Heat Treating of Cast Iron, Heat treating of cast irons, in Metals Handbook, American Society for Metals, Metals Park, OH, 8th edn., 1961. K. Holmes, E. Wyatt, P. Smoot and E. Deluca, The relationship between trace elements, microstructure, mechanical properties and fragmentation properties of nodular iron, AMMRC Tech. Rep. 71-24, August 1971 (Army Materials and Mechanics Research Center, Watertown, MD) (AD 889828L (American Scientific and Technical Information Agency)). P. C. Rossin, Ad hoc Committee on Shell Steels, Producibility of artillery shells made from HF-1 steel, NMAB Rep. 307, April 1973 (National Materials Advisory Board, National Academy of Sciences, Washington, DC) (AD 763988 (American Scientific and Technical Information Agency)).