U. S. NAVAL PROVING GROUND

r DAIILGREN, VIRGINIAm t• L-,=CTE •

Lf) E 18

I)Reproduced From•-• 'REPORT NO. 3-"47 Best Available copy

W.ETALLURGICAL EXAMINATION OF STANDARD U. S. NARMOR-PIERCING PROJECTILES

8E AP PROJECTILE MARK 21-512" AP PROJECTILE MARK !8-1

4I" AP PROJECTILE MARK 16-8

16" AP PROJECTILE MARK 8-6

L;HTI RELEASE. JUNE 1947 n TH

COPY NO. IL

8 7 9I! ! 6 6 --- 7 I

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CommanderNaval Surface Weapons Center 125 At,% 19,81 -Dahigren, Virginia . 22448 ~---

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NPG Report 3-47, Metallurgical Examination of Standard U. S. Navy Armor-piercingprojectiles, 8" AP Projectile Mark 21-5 '12" AP Projectile MARK 18-1,14" AP Projectile MARK 16-8 and 16" AP Projectile MARK 8-6

The following distribution statement SIwOUld be applied: Approved for public release;distribution unlimited.

SII ~A TU R E 0OF Aj ,Ti-.R I ZI G OF F I CIAL. W. L. PARSELL

U. S. NAVAL PROVINu GROUND

DAHLGREN, VIFGINIA

NPG REPORT NO. 3-4?

METALLURGICAL EXAMINATION OF STANDARD U. S. NAVYARMOR-PIERC ING PROJECTILES

88" AP PROJECTILE MARK 21-512" AP PROJECTILE MARK 18-114" AP PROJECTILE MARK 16-816" AP PROJECTILE MARK 8-6

Submitted by: R. _m---_____ Prepared by: Zam± A-IiR. H. LYDDANE G. DeVRIESSenior Physicist AssociateHead of Armor & MetallurgistProjectile Laboratory

Reviewed by- z... Reviewed by:W. . BR V'. G. FRANKLINCapt., USN Comdr., USNExperimental Officer Arpor Officer

Approved by: Reviewed by: BNC. TI/J0Y #- WH. BENSON

Rear mi USNCapt., USNCommanding Officer Ordnance Officer

APPROVED FOR PUDLIC RELEASE,UItiiaL ,,f',R UNLIMITED.

Page i

-\,- - -

NPG REPORT NO. 3-47

METALLURGICAL EXAMINATION OF STANDARD U. S. NAVYARMOR-P IERC ING PROJECTILES

8t1 AP PROJECTILE MARK 21-512" AP PROJECTILE MARK 18-114" AP PROJECTILE MARK 16-816" AP PROJECTILE MARK 8-6

1. The results presented in this report are apart of the general program of development of armor-piercing projectiles being carried out by the Armor andProjectile Laboratory at the Naval Proving Ground.

2. The projectiles were sectioned and the surfacesground at the Naval Gun Factory. The metallurgical exam-ination was performed by the author and other staff membersof the Armor and Projectile Laboratory.

C.(~JOVRe Adm ral,USCommanding Officer

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NPG REPORT NO. 3-47

PREFAC E

AUTHORIZAT ION

Specific directives for this investigation were issuedin BuOrd ltr. NP7/S78 (Re3) of 29 November 1945.

OBJECT

This investigation was conducted to obtain metallurgicalinformation on the present standard 8", 12", 14", and 16"AP projectiles.

SUMMARY

The examination of the projectiles included thedetermination of the hardness distribution, the CharpyV-notch properties, the macro- and mirco-structures, andthe chemical composition. Results are given and discussed.The projectiles are in general quite similar.

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NPG REPORT NO. 3-47

CONT ENTS

Pae

I. INTRODUCTION 1

1. Hardness and Hardness Distribution 12. Impact Test 23. Macroetch 24, Microstructure 2

.Chemical Analysis 2

II. DESIGN FEATURES 3

III. HEAT TREATMENT 4

IV. EXPERIMENTAL 4

1. Chemical Analysis 42. Macroetch and Hardness Pattern 53. Impact Properties of the Base 64. Microstructure 7

V. DISCUSSION 7

1. Cap Hardness 72. Body Hardness r 1 73. Composition N&7

D-IC TAB [E

Q UA D .. . . . . . . . . . ..

UNANNOUNCEDPage iv

NPG REPORT NO. 3-47

LIST OF FIGURES

InsideBack Cover

Fig. 1 Outlines of Projectiles

Fig. 2 Vickers Hardness Pattern 8" AP

Fig. 3 Brinell Hardness Pattern 8" AP

Fig. 4 Brinell Hardness Pattern 12" AP

Fig. 5 Brinell Hardness Pattern 14" AP

Fig. 6 Brinell Hardness Pattern 16" AP

Fig. 7 Photomicrographs of the 8" AP

Fig. 8 Photomicrographs of tne 12" AP

Fig. 9 Photomicrographs of the 14" AP

Fig. 10 Photomicrographs of the 16" AP

LIST OF TABLES

Table_ Pare

I Design Data on Armor-piercing Projectiles 3

II Chemical Compositions of Armor-piercingProjectiles 5

III Results of Charpy V-notch Impact Tests 6

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NPG REPORT NO. 3-47

I. INTRODUCTIOF

It is usual to subject one representative fromeach group of experimental projectiles to a metallurgicalexamination, which includes the determination of thehardness distribution, the Charpy V-notch properties themacro- and micro-structures, and the chemical analysis. Inthe past, such examinations have been limited to projectilessmaller than 8"1, but the acquisition of new hardness testingequipment has made possible the application to projectilesof any size in use. The present standard 8", 12", 14", and16" AP projectiles have therefore been subjected to exami-nation, in order to provide a comparison for future work withexperimental projectiles.

A brief discussion of the significance of thevarious tests follows.

1. Hardness and Hardness Distribution

The hardness of a projectile cap and also of thenose of the projectile influences its ability to causedamage to the face of Class A armor. The extreme hardnessof the cap is instrumental in starting damage to the surface.After the cap has been shattered the nose of the projectileis able to complete the damage started by the cap. Thehardness alone is not a measure of the quality of theprojectile. The high hardness necessary to cause the plateto fail must be backed up by a more ductile material capableof absorbing shock without failure. The hardness patternor hardness distribution gives a measure of the contour ofthe hardened zone.

Work done at the Naval Proving Ground on APprojectiles equipped with caps of hardness greater than600 Brinell (carbide ball) led to the development by theprojectile manufacturers of 6" and 8" AP projectiles withconsiderably improved penetrative performance against ClassA plate over standard projectiles. As a result of thiswork 6" and 8" AP projectiles are now equipped with caps ofapproximately 680 Brinell (carbide ball) as contrasted withthe old production projectiles which had a cap hardness of550 (carbide ball) Brinell.

Deeper hardness patterns and higher nosehardnesses for the bodies of AP and Common projectiles havebeen advocated by the Proving Ground for several years.It appears that the nose hardness should be as high as

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NPG REPORT NO. 3-47

possible while the body hardness should be that whichgives the maximum bend strength.

2. Imact Test

The Charpy V-notch impact test is a measure ofthe ability of the material to absorb shock withoutfracture. The test is usually applied to a sample fromthe body of the projectile rather than from the cap ornose. The principal property requircd of the cap andnose is hardness while the body of the projectile mustwithstand stresses without failure in order to carry theprojectile through the plate.

3. • acroetch

It is well-known that by macroetching ,importantstructural features of the material are developed. Anydendritic segregation which may have been retained fromthe original ingot will be shown. The fiber of the metalwhich indicates the method of forging will be shown,though this may not be clear in a fine grained well hardenedalloy steel. An added feature of the macroetch is itsability to develop the pattern of the hardened zone.Hardened steels show a darker color than unhardened steelswhen etched with ammonium persulfate.

4. Microstructure

The microstructure shows the general qualityof the steel and also the effect of heat treatment.Physical properties may be predicted with reasonableaccuracy by studying the structure revealed under themicroscope. Un2tched specimens are usually used in orderto determine the number and size of inclusions. Thislatter feature is usually of minor importance in well madealloy steels.

5~. Chemical Analysis

By chemical analysis the type of materialis determined. This information gives a reasonableindication of hardenability and indication of probablephysical properties. Certain features such as suscepti-bility to temper brittleness and possibility of crackingon quenching are also predictable. By determining theamount and kind of alloying elements present it is possibleto predict the results obtainable by tempering at varioustemperatures.

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NPG REPORT NO0 . 3-47

By examining a projectile with all of the abovemethods it is usually possible to determine the effectivenessof heat treatment and also to discover if the proper heattreatment has been applied.

II. DESIGN FEATURES

Outline drawings of the projectiles are shownin Figure 1 and a tabulation of some of their major designfeatures is given in Table I.

TABLE I

Design Data on Armor-piercing Projectiles

8" AP 12" AP 14" AP 16" AP

Mk2 21-5 Mk, 18-1 Mk. 16-8 Mk. 8-6

Diameter (in.) 8 12 14 16

Overall length 36 54 56 72(in)

Body length (in) 23.2 37.7 36.5 49.8

Cap length (in) 5.1 5.5 6.0 6.8

Loaded wt. (lbs.) 335 1146 1500 2700

Body wt. (lbs.) 245 925 1203 2191

Cap wt. (lbs.) 58 124 153 312

% Cap by wt. 17.3 10.9 10.2 11.6

% Bursting charge 1.5 1,5 1,5 1.5by wt.

Maximum cap hard- 683 578 578 555ness (BHN)

% Windshield by 1.3 1.2 2.3 1.2wt.

Length of wind- 9.9 15.1 23.7 19.65shield

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NPG REPORT NO. 3-47

The 8" AP projectile has a greater percentageof cap and a harder cap than the other projectiles. The14" AP projectile is only 4 calibers long, while the otherprojectiles are 4-1/2 calibers long. The 14" projectilehas the windshield threads cut in the soft part of theskirt of the cap rather than in the hard upper part of thecap, which causes it to have a longer and heavier windshieldthan the other projectiles. Variations in the contours ofthe cap, the nose, and the cavity are apparent in Figure 1.

III. HEAT TREATMENT

According to the manufacturer's data the bodyof the 8" AP Mark 21-5 was hardened decrementally, afterthe conditioning treatment by dipping nose downwards intolead at 1650OF and then waier quenching; followed by anoverall temper at 475 0 F. The triple alloy cap was hardenedin the same way except that the overall temper was at 325 0 F.The 16" AP Mark 8-6 was given the same hardening treatmentexcept that the cap was tempered at 4500F. The dataavailable at the Proving Ground indicate that the 12" and14" AP projectiles were heat treated similarly to the 16"AP projectile.

IV. EXPERIMENTAL

1. Chemical Analyses

The results of chemical analysis of specimensfrom the caps and bodies of the projectiles are given inTable II. The values reported were obtained spectrochemicallywith the exception of those of carbon, phosphorus and sulfurwhich wce determined by standard chemical procedures.

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NPG REPORT NO. 3-47

TABLE II

Chemical Compositions of Armor-piercing Projectiles

Bodies

C Mn P S Si Ni C Mo Cu

8" Mk. 21-5 .64 .38 .018 .x18 .43 3.38 2.22 .08 .09

12" Mk. 18-1 .59 .38 .023 .015 .37 3.20 2.16 .o8 .10

14" Mk. 16-8 .58 .41 .022 .015 .43 3.00 2.22 .06 .11

16" Mk. 8-6 .60 .34 .025 .O17 .26 3.33 2.30 .09 .10

C Mn P s Si Ni Cr Mo Cu

8" Mk. 21-5 .81 .80 .021 .022 .27 1.65 .96 .33 .15

12" Mk. 18-1 .60 .39 .023 .014 .31 3.15 2.23 .08 .09

14" Mk. 16-8 .60 .46 .023 .020 .43 3.05 2,21 .06 .14

16" Mk. 8-6 .60 .35 .031 oO18 .39 3.60 2.49 o06 .1o

The caps and bodies of all the projectiles weremade of the same type of nickel chromium steel except the8" AP projectile which had a high carbon triple alloy steelcap.

2. Macroetch and Hardness Patterns

One projectile of each type was sent to theNaval Gun Factory for sectioning and surface grinding. Theresults of the macroetch and hardness survey of the groundhalves are shown in Figures 2, 3, 4, 5 and 6.

The macroetch patterns of all projectiles weregenerally similar. The 12" AP body had the dark etchingarea extending all the way to the end of the base insteadof ending above the bandscore, as for the other projectiles.The dark etching area at the base was about 7 points Rcgreater in hardness than the light etching area. The 14"AP cap had a greater amount of light etching area than the

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NPG REPORT NO. 3-47

caps of the other projectiles. The cracks visible in thehardened part of some of the projectiles are believed tohave been caused by the splitting process.

All projectiles had similar hardness patternsexcept the 8" AP projectile which had 1, much harder cap thanthe others. Both Vickers and Brinell hardness tests weremade on the same 8" AF projectile so that the values couldbe compared. As would be expected the Vickers values weresomewhat higher than the Brinell numbers in the higherranges but otherwise the hardness patterns obtained byeither method were similar.

3. ImPact Properties of the Base

Specimens for impact tests were taken from thebase of the unground half of each projectile. The resultsof these tests are shown in Table III.

TABLE III

Results of Charpy V-notch Impact Tests

2 AP 12" AF 14" AP 16" A?

Temp. C Ft. Ft. lbs Ft. lbs, Ft. lbs.

+100 55 F 45 F 69 F 65 F

+ 50 57 F 48 F 57 F 58 F

0 45 F 48 F 47 G10% 56 F

- 50 26 G50% 24 G80% 21 G1O0% 39 G40%

- 78 17 G100% 20 G100% 17 G1OO% 20 GlOO%

F = All fibrous fracture.G = Grain) fracture, percent.

All the projectiles have about the same impactproperties. The hardness of the impact specimens variedbetween 23 and 27 Rc. Impact specimens were taken from thelight etching part of the base of the 12" AP projectile.

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NPG REPORT NO, 3-47

4. Microstructure

Photomicrographs were made of samples takenfrom the nose and skirt of the caps and from the base andnose of the bodies of all the projectiles. These are shownin Figures 7, 8, 9 and 10. The microstructure in the noseof the caps and in the nose of the bodies consisted ofslightly tempered martensite while the microstructure ofthe skirt of the caps and base of the bodies consisted ofspheroidized carbides in a ferritic matrix.

V. DISCUSSION

1. Cap Hardness

The present standard 12", 14" and 16" APprojectiles have caps of relatively low hardness 550Brinell (carbide ball). As was pointed out in the intro-duction the penetrative ability of the 8" AP was increasedby increasing the cap hardness so that increasing the caphardness of the 12", 14" and 11" AP projectiles might increasetheir penetrative ability.

2. Body Hardness

Higher nose and body hardness for the subjectprojectiles might be desirable. VNith many steels thebreaking strength on impact is greater when the steel istempered at 350OF than when the steel is tempered at 450 0 Feven though the steel is harder when tempered at 3500 F.Therefore, if the bodies of the subject projectiles weregiven a final tempering at 350OF instead of 450-475OF as atpresent, the ballistic performance might be improved.Tempering at 350OF would give hacder steel that is likelyto have greater impact strength.

3. C omposition

Most Navy projectiles regardless of size aremade of steel of the same analysis (.60C, 2.2 Cr and 3.2 Ni).Considering hardenability only, it may be that a more highlyalloyed steel would produce better properties in the largerprojectiles (12", 14" and 16").

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FIGURE 3

MPS 34004 No,. 35, 1946

HARDNESS DISTRIBUTION AND MACROSECTIONOF CRUCIBLE 12" A.P PROJECTILE MK. 18-1 LOT 21

Briniell HarIes Values! 10 mrm. Carbide Sol) - (3000 kg)- 10 SecondsEtch: Ammoniumn Persulfate

CONFIDJENTIAL

"5 35" 5;5 "55 516

" S? 5;1 55 555 535 5 B5 578

ire 5B5 355 5B5 555 555 576

5P5 35 5ý 85 S55 532 555 555 5B5 578

555 :8 3555 5 12 55 5:8

75 576 a"6 w9 M9 5 598 57 5 1

595 81 A8)512- 5 ep si;I

2T 55: .444 44 444 4"4 56 555 27?

78 BOB/I 440 44 4M6 3" 444 SA\ 501 5Sm

5B6 5P5 440 4W 424 97 492 4P " 4 64\ a"

505,/152 4)4 317 307 B01 393 WIF 408 8)6\.4rG

vi p ~ ~ ~ ~ ~ ~ 3 410 27 , 2 I " " 4 4

:kz 571 r - . 2 . 72 t98 7 \ 2 It"4882 S

T? te," 02 n655 23, ega M4

4B0 5/ 27 29 8825 235 t9o k7?" 440

587 ý40 8286 a" 8 no92 248 23 2116 57

367 ý?I 2a" w 298 295 299 296 2et bý 344

391 /511 a98 to 2on 282 2" 1"8 2to 2114\344

35! 1138 249 286 296 252 209 216 It" 277

340 2182" Z09 to 92 252 20 98 896 M 96 34(0" 350 BRINELL

No0 2M tog58 24422 242 P48 2M 27T 342

340 277 269 24 202 A"8 277 332

3B2 20 62 282 mot 332Bi

52~21 7 53 242 q 298 81,

521 277 258 321

591 2TF 2"9 3?1

52. 268 249 341

521 "41 249 Ski

321 242 "t2 502

1 11 242 2210

502 to2 292 293

263 2og 262 553

293 285 242 214

2*3 1102 242 2ol6

277 249 248 277

350?

FIGURE 4

NP9 340hI Nov,. 1, 1946

HARDNESS DISTRIBUTION AND MAGROSECTIONOF CRUCIBLE 14" AP PROJECTILE MK. 16-8

Brinell Hardness Values: IOmm. Carbide Ball -(3000kg.)- 10 seconds

Etch: Ammonium Persulfote

Standord Projectile

CONFIDENTIAL

Go$ all 554 ,s9 55" 545 N osp 5,0 21 5

/-157 40O 440 4"4 519. 576 -

515 5ee/ 414 w5 .,p 43.D 441-

are it -is 3 5' 44, 5 40 4 54 475

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5G51 s 2/ "I4 25 292 to2 2I5S*

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5 totl 2 02 44 2 01 22 I 12 4 4\1 S ,RC)

44 177 2qg 255" 295 to2 I5\ 4

470 294 244 Eat lpý 4+4

4I! 4o 4 219 2095 4 10 * .

375' too21 1

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FIGURE N5 L

HARDNESS DISTRIBUTION AND MACROSECTIONOF BETHLEHEM 16" AP PROJECTILE MK. 8-6 LOT 5 NO 6E9B

Brinell Hardness Values lrnvn Corbide Ball 13000 kq)-1O seconds

Etch. Ammonium Persuffate

Standard Projectile

CONFIDENTIAL

11 p I!' s

555 1 5, 111 515 55 2

S•2 * 75 552 57•2 5775 S'4 332 4 5 1752,•0BNL

35lJ5 355 5' 4"2749270.2 3"1 c2

350 ' 52! 37 75 6P 5Bo 4ý "54 P5 5P5 5 .2

W4 4 57. 55 555 5 55 472 4*S 2 542

514 'A5 . ;,5 5 124 55; 555 5"5 51

25 5 5.- 55 5 T, .(' 5 ;2 ,'4" 2

l7-2 55 4 4 474 457 57 2 542

554.-557 4..) 444 4446 • 474 444 444 4277 52 51

555 552 4•4 416 416 4!q 44 4!9 ". 552 S4

5 B2 492 3755 114 377 450 1[? 542 550 BRINELL

52z 4,1 " ' 4 1?' 1? "4 377 512 N2

4R5 457 4,I3k V, 227 244 272 37 34 I4 460 4.,5

477 444 734 25. 35. 25*. 254 2 3 35 14 444 4"4

447 4', 74. 727! III -5 7 , 732 7 41

-I 4UR 26 255 45 1 135 I5 2 11 1147 47

""I6 7'3 20" 755 22I5I52 40 5 4B.

202 262 204 202 274 427 57ý 444

444 5.4 777 274 2546 77 2.4 257 35' 444

43 31, 277 444 249 W7 340 4W

415 332 277 257 3- 4-w

347 521 MR 271 2' 117'

-7 24 244 -7~ 31* 377

564 2'1 244 257 244 4755

35 I7 27"' 277 277 351

2 :7 234 277 277 255 284 350 BRINELL

2. > 244 2,7 277 254 256

25 24 Zn07 245 21

15 7 ! '7 252 244f

FIGURE 6

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Hardness

A. NP9 34435' - Nose of body, tempered martensite 555 BHNB. NP9 34214 - Base of body, spheroidized structure 269 BHN'C. NP9 34200 - Nose of cap, tempered martensite 555' BHND. NP9 34215' - Skirt of' cap, spheroidiZed structure 286 BHN

Figure 9

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