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428 A COMPARISON OF GRAIN-SIZE MEASTJREMENTS

A Comparison of Grain-size Measurements and Brine11 Hardness of Cartridge Brass

BY TV. H. BASSETT* AND C. H. D A V I S , ~ WATERBURY, COKN.

(New York Meeting, February, 1919)

IN the commercial annealing of cartridge brass there are four points regarding which definite data are essential. They have to do with the correct interpretation of grain count in its relation to annealing tempera&- ture and, incidentally, to Brinell hardness. These points are:

1. The comparison of the grain sizes of two cartridge-brass mixtures: 69 copper, 31 zinc, 0.376-in. (9.5-mm.) gage; and 68 copper, 32 zinc, 0.130-in. (3.3-mm.) gage

2. The comparison of the grain sizes of annealed metal that had previously been reduced by rolling varying amounts; for instance, 20.0, 36.6, 50.9, and 59.1 per cent.

3. The determination of standards for grain sizes on annealed brass of the composition 68 per cent. copper, 32 per cent. zinc and 69 copper, 31 zinc.

4. The comparison of grain size with Brinell hardness on identical samples of annealed metal.

In their comprehensive and thorough investigation of the recrystallization of cold-worked alpha brass on annealing,l Mathewson and Phil- lips have discussed the relations between temperature of anneal, degree of deformation, and structural alteration in alpha brass. They have also shown certain comparisons between the ordinary physical properties and the grain size of annealed brass. The purpose of the present investigation is mainly concerned with the grain size of cartridge brass, its relation to Brinell hardness, and the publication of sufficient data to enable those engaged in the inspection of such material to have a correct foundation upon which to work.

The first alloy was taken from regular mill stock that had been rolled from 0.580 in. to 0.376 in. (14.7 mm. to 9.5 mm.) gage, a reduction of 35.1 per cent. This bar (No. 1) had the following composition: Copper, 69.20 per cent.; zinc, 30.76 per cent.; lead, 0.02 per cent.; iron, 0.02 per cent.

The second alloy was also taken from mill stock of 0.325 in. (8.25 mm.) gage and was rolled as shown in Table 1, in order to get four bars reduced two, four, six, and eight B. & 5. numbers respectively. This second alloy

--- - - * American Brass Co. American Brass Co. 1 Trans. (1916) 64, 608-657.

W. H. BASSETT AND C. H. DAVIS 429

had the composition: Copper, 68.48 per cent.; zinc, 31.47 per cent.; lead, 0.02 per cent.; iron, 0.03 per cent.

TABLE 1.-Results Obtained by Rolling Bars

Annesled Bar Reduction by Bu No. Salected from Rolled to, Inch On* Rolled to, Innh Rollinn

Stock, Inch Per Cent. I i j I

Specimens, 1 by 3 in. (25.4 by 76.2 mm.), from each of these five bars were annealed for % hr. at 50" C. intervals, from 200" C. to 850" C. From 275' C. to 425' C., additional samples were annealed a t 25" C. intervals. The specimens were tightly wrapped together in sheet copper and were quenched with their covering as quickly as possible a t the end of hr. a t the required temperature. A new Bristol indicator'and re- corder with base-metal couple was used, the latter being wrapped with the specimens. The couple was checked and calibrated before and after annealing by the boiling point of sulfur and the melting point of sodium chloride.

The Brinell hardness tests were made with an Aktiebolaget alpha machine. A load of 500 kg. and the standard 10-mrn. diameter ball were used and the pressure maintained for 30 sec. The pressure exerted by this machine was checked by weighing on a standard scale. The surfaces of both hard and annealed specimens were scoured with emery cloth and polished with fine emery before testing. Two impressions were taken, one in the center of the specimen and the other halfway toward the end. Readings of these were made upon an 80 mm. Gaertner comparator, accurate to 0.001 mm. One reading was taken in the direction of the '

original rolling, the other at right angles to that direction for each im- , pression, and the four results averaged. Little or no discrepancy was . found in these results, except in the case of the hard-rolled specimen^ where the impression was oblong, the longer diameter coinciding in direction with the direction of rolling. In the harder samples this difference in diameter was equivalent to as much as 10 Brinell points.

.

The grain size was counted on a section taken parallel to the surface between the two Brinell impressions. On the specimens annealed below 700" C. the magnification used was 150 diameters; at 700" C., 75 diameters; and from 750" C, to 850" C., 50 diameters. The method of counting used is recommended by the American Society for Testing material^.^

- - Tentative Definitions and Rules Governing the Preparation of Micrographs of

Metals and Alloys. Proceedzngs, American Society for Testing Materials (1917) 17, Pt. 1, 838.

430 A COMPARISON OF GRAIN-SIZE: MEASUREMENTS

It is also described by Zay Jeffries and othem3 A circle 79.8 mm. in diameter was used in counting and the diameter of the average grain in millimeters was determined. The following formulas, proposed by Prof. Jeffries, were used :

w = boundary grains; z = completely included grains; x = equivalent number of whole grains in 5000 sq. mm. (circle 79.8

mm. diameter or rectangle having area of 5000 sq. mm.); m: = magnification used; f = multiplier to obtain grains per square millimeter; n = number of grains per square millimeter; d = diameter of average grain in millimeters; a = area of average grain in U2.

Tables 2, 3, and 4 give a resume of the results obtained. T A B L ~ 2.-Brinell Hardness and Grain Size on 69-31 Brass

(See Fig. 2) Bar No. 1. Rolled from 0.580 in. to 0.376 in. (14.7 mm. to 9.5 mm.).

Reduction by rolling 35.1 per cent. (4-B. & S. numbers. Hard)

Anneal. Av. Brine11 Number from

Degrees C. Two Imp. and Four Readinga

- -

850 10.0 50 0 5 5.0 223 0.448 ..... 41.3 800 24.0 59 0 5 12.0 3.4 0.3 ..... 750 62.5 { iu) {:.:,, 26.2 5.1 ) 0.197 46.0

700 73.0 75 60.6

650 55.8

600 127.0 61.7

550 226.0 0.0381 65.9

600 70.4

75.0

425 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75.2 400 376 350 325 300

Uniformly annealed. 1 82.6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Ninety-five per cent. nea grains. ..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Fow new grains. r 276 N o new grains. 250 No new g1,ains. 200 , No new 5i"'

..... . . a . . . . . . . . . . . . . . . ...... ..... Hard.. ..I 1 1 1 1

88.3 102.0 102.0 143.0 153.0 163.0 153.0 146.0

a Trans. (1916) 64, 594-607. Elaborated in Metallurgical and Chemical Engineer- ing (Feb. 15,1918) 8,185.


TABLE 3.-Brinell Hardness and Grain Size on 68-32 Brass (See Figs. 1 and 3)

Bar No. 2 (Mark a). Reduction by rolling 20.2 per cent. (2 -B. & S. numbers)

Av. Brine11 Number from Two Imp. and 1 Four Readings

41.7 43.6 45.7

200

Hard.. . .

fi 1 Anneal. Temp., 1 LT ' 1 %:f 1 f

Degrees C. n

No new grains.

. . . . . ..... I . . . . . . . 1 . . . . . , 1 . . . . , . .

700 650. 600 550 500

148.0

ti::: I142

50 0 .5 2.74 0.365

50 0 . 5 71.0 42.5 62.0 87.0

110.0+

850 800 750'

1 76 I50 150

15.0 32.5 57.5

450 1 118.5 150 ' 4.5 533.25 425 ..... 1 . . 1 . . .

i.125 4 .5 4 .5

150 4 . 5 391.5 150 1 4 . 5 495.0

23.09 1 0.043 . .

78.875 191.25 279.0

65.5 69.1

8.93 10.112 49.0 13.82 0.072 52.0 16.70 0.059+ 56.1

89.7 94.1

101.0 100.0 103.0 104.0 106.0 109.0 110.0

19.7 0 . 0 5 0 7 58.2

400 1 One-fourth area consists of new grains. 375 Few new grains.

22.2 0.045

350 325 300 275 250 200

Hard.. . .

60.5

Bar No. 3 (Mark +). Reduction by rolling 36.6 per cent. (4-B. & S. numbers)

71.5 0 .5 45.9 48.9 51.5

66.4

425 1 . . . . . . Completely recrystallized. 74.6

. . . . . . . . . . . . . . . . . . . . . . . . . . . . 88.8 One-third area, consists of new grains. 100.0

325 Some new griins. 106.0

' No new grains.. No new grains. No new grains. ,

300 1 No new grains. 275 1 No new grains. 250 1 No new grains.

. . . . . .

137.0 140.0 143.0

... . . . . . . . . . . i . . . . . . . . . . . . . . . . . 1 ::::: . . . . . . . . . . . . . . . . . . . . . . . . . . . . I . . . . . . . . . . . . . . . . . . . . . . . . 1 ... , . . . . . .

. . . . . . .

. . . . . . .

432 A COMPARISON OF GRAIN-SIZE MEASUREMENTS

TABLE 4.-Brine11 Hardness and Grain Size on 68-32 Brass (See Figs. 1 and 3)

Bar No. 4 (Mark X). Reduction by rolling 50.9 per cent. (6 f B. & S. numbers)

. . . . . . . . , . . . . . . . . . . . . . . . . One-fourth area consists of new grains.

Few new grains. No new grains.

Anneal. I Temp.

50 1 0 .5 9.25 50 0.5 19.0 50 0.5 33.75 75 1 . 1 2 5 ' 76.50

150 4.5 171.0 150 4.5 378.0 150 4.5 744.75 150 4.5 796.5 150 4.5 2007.0 . . . . . . . . . . . . . . .

200 1 No new grains. 169.0

H a r d . . . . . . . 1 . . . I . . . . . . . . . 153.0

3.04 4.35 5.80 8.75

13.07 19.43 27.28 28.20 44.8 . . . , .

I I I I I

4;

Completely recrystallized. . . . . . . . . , . . . , . . . . . . ,

Few remnants of former crystals.

AT. Brine11 Number from

TWO Imp. and Four Readings

Bar No. 5 (Mark 0). Reduction by rolling 59.1 per cent. (8 - B. & S. numbers)

850 8.0 1 2.83 0.353 41.1 18.25 4.27 0.234 44.1

750 50 0.5 38.5 6.50 0.161 46.4 700 66.0 75 1.125 74.25 1 8.62 0.116 49.2 650 38.5 4.5 173.25 ( 13.17 0.076 52.4 600 78.0

83.8 88.6 91.9 93.3

124.0 154.0 171.0 172.0

168'0 1163 158.0

400 Completely recrystallized 375 350 325 300 275

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Completely recrystallized.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . One-half to six-tenths new grains.

Few new grains 250 No new graias.

. . . . . . . ' . . . . . 1 : : : 1 ....... , . . . . . . . . . . . . . . . . .

434 A COMPARISON O F GRAIN-SIZE MEASUREMENTS

The micrographs taken to illustrate this paper are magnified 75 diameters but the grain counts were made on micrographs taken in the same area but magnified 50, 75, or 150 diameters. Accompanying this report are three plots. The first, Fig. 1, shows the relation of Brinell hardness to annealing temperature and the relation of grain size to annealing temperature for the 68-32 alloy; the second, Fig. 2, shows the same relations for the 69-31 alloy, the third, Pig. 3, shows the relation of Brinell hardness to grain size for a given alloy of copper and zinc.

180

160

5 140 n E

120 V)

c n 2 100 I - - CJ

.s 80 lk

60

40 0 .050 ,100 -200 .300 .400 MM.

Diameter of Average Grain in MM.

FIG. 3.-BRINELL HARDNLSS INDICATEB GRAIN SIZE FOR ANY GIVEN BRASS IN THE ALPHA PHASE. AT &OW TEMPERATURES THE GRAIN srxm IS INFLUENCED BY THE GRAIN SIZE OF THE PREVIOUS ANNEAL, 650' C. IN THIS CASE. PLOTTED FROM THE DATA USED FOB FIG. 1.

The Brinell method is a very accurate way of determining the hardness of sheet brass. The hardness of rolled metal is relatively proportionate to the percentage reduction by r ~ l l i n g . ~ The hardness of annealed metal is relatively proportionate to the temperature of annealing5 (for any fixed period.of time). The Brinell hardness of annealed metal is proportionate to thc annealing temperature, but this proportion varies on account of two factors; namely, the amount of the last rolling the metal received, and the grain size that existed a t the'time of that rolling. Figs. 1 and 4 to 13 illustrate these points in the case of the 0.130-in. (3.3-mm.) gage cartridge brass and show: that in annealing hard-

C. H. Davis: Testing of S h e e t Brass. P~oceedings, American S o c i e t y f o r Testing Materials (1917) 17, Pt. 2, 166.

C. H. Davis: Op cit., Fig. 8 md;Fig. 3.


2 0 . 2 PER CENT. REDUCTION 36.6 PER CENT. REDUCTION

BRIN. 1 1 0 .4s ROLLED B R I N . 142

FIG. 4.-ETCHED WITH A31MONlA AND HYDROGEN PEROXIDE. X 75.

436 A COAIPAKISON OF GRAIN-SIZE MEASUREMENTS

50 9 PER C E N T RLDIJCTION

t x - " . --. , . -

BRIN. 158 As ROLLED BILIN. 163

A ~ N I . : A L Bnrw. 93.3

AND HYDROGEX PRROSIDE. X 75.

W. H. BASSETT AND C . H. DAVIS 437

20.2 PER CEXT. REDUCTION 36.6 PER CENT. REDUCTION

BRIN 9 4 . 1 375" C. A N N E A L BRIN. 88.8

RRIN. 89.7 400" C. ANNEAL BRIN. 74.6

FIG. 6.-ETCI-LED \\'IT11 AhlhlONIh AND HI.DROC:EN PEROXIDE. X 75.

438 A COMPARISON OF GRAIN-SIZE AXEASUREMENTS

BRIN. 79.6 400" C. ANNEAL B ~ I N . 83.8 F I G . 7.-ETCHED WITH AAIMONTA AND HYDROGEN PEROXIDE. X 75.

W . H. BASSETT AND C. H. DAVIS 439

20.2 PER CENT. REDUCTION 36.-6 PER CENT. REDUCTION

BRIN. 65 5, d = 0 043 ~ a r . 450" c A N N E h L BRIN. 70.5, d =0.0336 afar.

ANNEAL BRIN. 61.3 d = 0.0395 MM.

AND HYDROGEN PEROXIDE. X 75.

440 A CO&IPARISON OF GRAIN-SIZE MEASUREME~STS

5 0 . 9 PER CENT. REDUCTION 59.1 PER CEKT. REDUCTION

B R I N . 62 0, d = 0 . 0 3 6 6 aral. 5 5 0 " C. ANXEAL BRIX. 6 2 . 0 , d = 0 . 0 3 5 6 n r ~ . F I G . 9.-ETCHED \VITA A>lNONIA AND HYDROGEK PEROXIDE. X 75

W . 1-1. BASSETT AND C. IT. DAVIS 44 1

20.2 PLR CENT. REDUCTION 36.6 PER CEXT. REDUCTION

BRIN. 56.1, d = 0.059 nmr. 600" C. A N N E A L RRIN. 55.4 c l = 0.0518 nrar.

442 A CO;\.IPARISON OF GRAIN-SIZE ~,IEASUREMENTS

W. EI. BASSETT AhrD C. H. DAVIS 443

20.2 PER CENT. REDUCTION 36.6 PER CENT. REDUCTION

BRIN. 43.6, d = 0.247 MM. 800" C. A N N E A L BRIN 43.1, d = 0.213 NM.

BRIN. 4 1 . 7 , d = 0.365 M M 850" C. ANNEAL BRIN. 41.1, d = 0.344 MM.

FIG. 12.-ETCBED WITH AMMONIA AND HYDROGEN PEROXIDE. X 75.

444 A COMPARISON O F GRAIN-SIZE h IEASUREMENTS

BRIN. 42.0, d = 0.329 xr\r. 850" C. ANNEAL BRIN. 41.7, d = 0.353 xru.

FIG. ~~.--ETcRED WITH Ai\lLlOhTA AND HYDROGEN PEROXIDE. X 75.

TV. H. BASSET'P A N D C. 15. DAVIS 44 5

. BRIN. 146-AS ROLLED. Bnrx. 133-250" C.

BRIN. 143-300' C. u~1~._102-325" C.

FIG. 14.-ETCHGD;WITH AMalOhTIA AWD HYDROGEN PEROXIDE. X 75.


F I G . 15.-ETCHED WITH AMMONIA AND HYDROGEN PEROXIDE. X 75.

W . H. BASSETT AND C. H. DAVIS 447

800" C. BRIN. 43.9, d = 0.300 nrar. FIG. 16 . -ETCHED WITH A M M O N I A

550" C. BRIN. 41.3, d = 0.448 MM.

A N D H Y D R O G E N P E R O X I D E . X 75.


rolled metal the drop in Brinell hardness indicates softening of the metal just before the new grains are seen; that the softening of lightly rolled metal progresses considerably before any new crystals can be detected; that the Brinell hardness of all specimens agrees closely fr0.m 600" C . to 850" C. As the previous anneal of the original hard specimens was about 650" C.: the conclusion is drawn, and borne out by experience, that both the Brinell hardness and the grain size of annealed metal are greatly affected by the grain size due to the anneal previous to the anneal under discussion; and, as the grain size of the previous anneal diminishes, the Brinell hardness curves and the grain-size curves will approach those of metal annealed after very hard rolling as a limit; i.e., in Fig. 1, the curve marked 59.1 per cent. rcduction is this limit for the curves that represent more lightly rolled material. Figs. 14 to 16 illustrate the grain- size of 0.376-in. gage cartridge brass containing 69.20 per cent. copper, 30.76 per cent. zinc, 0.02 per cent. lead, and 0.02 per cent. iron. All specimens were reduced 25.1 per cent. before annealing.

For the direct comparison of the Brinell hardness with the diameter of the average grain in millimeters, a third plot (Fig. 3) has been added for the 0.130-in. (3.3-mm.) gage brass. This plot emphasizes two points brought out in the foregoing paragraph: (1) At low temperatures the grain size is influenced by the grain size of the previous anneal (0.060 mm. + in this case); and (2) from this grain size (0.060 mm,) upward, the Brinell hardness plotted against grain size gives a single curve no matter what the previous treatment of the metal has been. Consequently i t may be repeated that in well-annealed brass of any given6 alloy the Brinell hardness indicates grain size.

On account of the thickness of this particular brass as commercially used, the specimens were taken from a single bar as rolled in mill practice with a 35.1 per cent. reduction. In Fig. 2, the Brinell hardness and the grain size are plotted against annealing temperature so that they may be directly compared. The curves follow closely those of the 68 copper, 32 zinc alloy for the same percentage reduction and previous heat treatment.

1. The grain sizes of the annealed alloys 68 copper, 32 zinc and 69 copper, 31 zinc agree closely when the previous heat treatment and reduction by rolling are made to correspond. The differcnce in thickness -0.374-in. (9.4-mm.) gage and0.130-in. (3.3-mm.) gage-does not appreci- ably affect the grain size or the Brinell hardness.

L - - - --- -

a The grain size and the Brinell hardness change progressively with the percentage of copper in brasses. The relation between the two, however, remains a constant for each brass mixture in the alpha phase.

DISCUSSION 449

2. The grain sizes of brasses annealed a t low temperatures are greatly affected by the grain size and the reduction by rolling, previous to such annealing.

3. The grain size and Brinell data for the several conditions described, when plotted against temperature, give curves that approach the curve of metal annealed after hard rolling as a limit. I t is desirable to select for standard of grain size (as determined by the temperature of annealing) those specimens that have been previously reduced by rolling a t least 50 per cent.

4. In the case of cartridge brass of the composition 68 copper, 32 zinc, Brinell hardness indicates grain size. At low annealing temperatures the grain size is influenced by the grain size of the previous anneal. The finer the grain size of the previous anneal, the more closely will the curve, Brinell Hardness- Grain Size, approach the standard curve.

5. Since grain size is influenced by the grain size in the previous anneal and also by the amount of reduction by rolling previous to annealing, the hardness of cartridge brass may be determined with greater accuracy by the Brinell-hardness measurement than by attempting to judge it from the grain size.

DISCUSSION

ARTHUR PHILLIPS, * Bridgeport, Conn. (written discussiont) .-- It is to be regretted that the very valuable paper by Messrs. Bassett and Davis did not appera in the early war period. The data presented would have been of inestimable service to inspectors of cartridge brass who, admittedly, had little or no knowledge regarding the relation of grain size to temperature of anneal, and no real appreciation of the significance of the Brinell hardness test. The paper is of considerable interest to metallurgists also.

WALTER R. HIBBARD,$ Bridgeport, Conn. (written discussion§) - The writer has carefully studied Messrs. Bassett and Davis's paper with considerable interest, inasmuch as our laboratory has tested cartridge brass by means of a Brinell machine. I n March, ?91?, st the suggestion of the Technical Department of the American Brass Co., we started a comparison of grain-size measurements and Brinell hardness of cartridge brass with a gage of 0.1 in. or greater. This was continued until March, 1918, when we adopted the Brinell hardness test as standard for brass 0.1 in. gage or greater, and discontinued grain-size measurements up on this metal. The data collected during the test showed that the Brinell hardness indicated more accurately how the metal acted in actual working operations. I t was also more reliable because two manipulators check themselves closer by the Brinell test than by the grain-size measure- -- -

*Metallurgical Department, Bridgeport Brass Co. ?Received Jan. 18, 1919. 4 The Remington A r m Union Metallic Cartridge Go. Received Jan. SO, 1919.

VOL. u.-29.

ments. I t also consumed less time in making the tests. Alfred V. de Forest, formerly assistant research engineer of our laboratories, has described the apparatus and some of the checking results in a paper read June, 1918, before the American Society for Testing Materials.' The writer hopes that a more satisfactory method for testing cartridge brass and gilding in gages thinner than 0.1 in. may be devised than the present method of grain-size measurements.

T. C. MERRIMAN, New Haven, Conn. (written discussion").-This most interesting paper gives much carefully obtained and valuable data. However, there are two points in connection with the commercial application of such dataLthat might possibly be a source of trouble and mis- understanding. I n the first place, the examination of thin sections of annealed brass, subjected to standard Brinell test (500 kg. on a 10-mm. diameter ball) a t thicknesses from 0.075 to 0.150 in. (1.9 to 3.8 mm.) indicates that cold work has been performed on the specimen during the application of the load sufficient to extend way through the sectdon and have the hardness of the metal affected by the backing. If the usual steel support is used, this effect is very evident. If a piece of soft brass is used as a support, there is an indentation in the surface of the support accompanied by a bulge on the under side of the tested specimen opposite the impression made by the 10-mm. ball. The result is that Brinell specifications (governmental or otherwise) on stock for a certain purpose may not be fair in all cases, since manufacturers, owing to differences in equipment, etc., may not all use precisely the thickness and conditions of stock on which the Brinell specifications were based. This would mean that the government Brinell specification might not give them the temper of stock best suited for their manufacturing methods.

The concluding paragraph of this paper, stating that "the hardness of cartridge brass may be determined with greater accuracy by the Brinell hardness measurement than by attempting to judge it from the grain size" appears to be in line with the movement of the last year or so among brass manufa'cturers toward substitution of the Brinell test for microscopic examination as an acceptance test on cartridge brass. The statement may be strictly true that the Brinell test is the best test for hardness, but i t is not, as the statement might readily be construed, a sufficient test of suitable condition. For instance, some cartridge brass might accidentally have been overheated to a point where 'it would be distinctly unsafe to use for the manufacture of small arms cases and then be so rolled (reduction 3 to 5 per cent.) as to pass perfectly proper Brinell specifications. Under such conditions the microscope would reveal its unsuitability where the Brinell test had failed so to do.

l Proceedzngs, American Society for Tcsting Materials (1918) 18, Pt. 2, 449. *Received Feb. 24, 1919.

DISCUSSION 45 1

It is not intended to object to the Brinell test as a general test for the temper of cartridge brass, for I am in full agreement with the authors as to the ueefulness and suitability of the Brinell test under many conditions, and I am sanguine that the development of the "Baby Brinell" will elimi- nate the likelihood of difficulty frorn the first point I have mentioned. However, Brinell specifications for cartridge brass are as yet given for 500-kg. load-10-mm. ball, and I firmly believe that even after the baby Brinell comes into fairlygeneral use the Brinell test must be supplemented by frequent microscopic examinations and that microscopic inspection requirements should be retained as a vital part of cartridge-brass specifications.

C. H. MATHEWSON, New Haven, Conn. (written discussion*).-Recent papers from Mr. Bassett's laboratory constitute a very a~elcome addition to the rather meager amount of scientific literature dealing with structure and properties, or in other words, the rnetallography of brass. They seem to have been developed mainly from the standpoint of supplying reliable and useful data that may be expected to further the intelligent handling of brass products. The collected data shown in the tables, when exhib- ited in graphic form, present several features of general interest and significance. There is a striking difference in the early parts of the several annealing curves shown in Fig. 1. While the heavily worked samples harden quite materially before they begin to soften, the lightly worked samples soften without any prior hardening.

The fact that hardening sometimes occurs after treatment a t low temperatures before a true annealing effect begins has been known for some time, but, so far as I am aware, the supplementary information brought out by these curves is quite new. This early hardening has been attributed to a redistribution or relief of internal strain, but Howe considers this explanation hardly competent to account for similar effects of much greater intensity which occur in steel. Jeffries, however, in his discussion of the amorphous theory anticipates a condition of internal stress incident to the formation of amorphous metal12 which may be gradually relieved at ordinary temperature or more rapidly relieved a t somewhat elevated temperatures. This explanation is quite in harmony with the observation that the more severe the initial deformation, the more pro- nounced the hardening in question.

We might even find a relation between season-cracking, an effect of internal strain, and this unique hardening. Thus, it is conceivable that metal which has not been worked severely enough to show an appre- ciable hardening when healed to about 200' C. will be stable under all conditions, while metal that hardens under this treatment will be subject to season cracking. This point appears to be, worth some investigation.

- -- -- - *Received Feb. 17, 1919. This volume, p. 474.

452 A COMPARISON OF GRA~N-SIZE MEASUREMENTS

I t is noticeable that each curve of Fig. 1 intersects the curve lying below it in two localities before they merge into one common curve. The first intersection is due to a progressive lowering of the recrystallization temperature as the degree of deformation decreases and a reasonable explanation of these conditions has been given in the first paper cited by the authors. The second intersection indicates that when the more severely worked metal has nearly.completed its recrystallization, and the less severely worked metal has recrystallized to a considerably lesser extent, both possess the same hardness. This would naturally occur at some characteristic temperature and the measured grain sizes would not be the same because there would be a greater number of grain areas com- posed of invisible fragments in the case of the less severely deformed material. These mea&rcmcnts would be greatly influenced by the grain size that existed prior to deformation and the authors have alluded to the hearing of this factor on the results.

I t is quite probable that the less severely deformed material may develop abnormal grains, at favorable temperatures, by selective growth and this may account for the widening of the loops made by the last intersections of the curves of Fig. 1 as the degree of deformation decreases.

In the discussion of Dr. Jeffries' paper, I have referred to the relationship between Brinell hardness and grain size indicated by Fig. 3. of the paper by Messrs. Bassett and Davis. Using thc equation:

1 Brinell hardness = K 4̂=-==-----

d d i a m . of average grain in mm. and placing the constant equal to 30 the following set of figures is obtained. These plot rathcr close to the curve shown in Fig. 3.

It is interesting to observe that. beyond a hardness value of approxi- mately 75, at which point grain-size measurements became impracticable, the authors carry dotted extensions of the curves up to the limiting hardness value of the cold-rolled metal, 160. In other words, they represent a continued decrease in grain size down to a minimum of zero size at the maximum hardness value.

Any attempt to count in this range would show a reversal of griin size with hardness and the grain ~ i z e corresponding to maximum hardness

Brinell Hardness Diameter of Average Grain, in Mm.

FIG. 1. FIG. 2. FIG. 1.-SHEET BRASS ROLLED 4 NUXBERS AND ANNEALED HR. 3 5 0 ° C. F I G . SHEET BRASS ROLLED 7 KUAIBERS AND ANNEALED HR. 3 5 0 " C.

F I G . 3 . FIG. 4. FIG. 3.-HIGH SIDE OF ECCENTRIC SHELL WHICH FAILED IN hIERCURY TEST. 1 MIX.

SOOo I?. (427" C.) FIG. 4.-Lo.rr SIDE OF ECCENTRIC SHELL WHICH FAILED IN MERCURY TEST. 1 MIN.

SOOO F. (427" C.)

FIG. 5. FIG. 6. FIG. 5.-HIGH SIDE OF SCRATCHED ECCENTRIC SHELL. 1 MIN. SOOo F. (427' C.) FIG, 6 . - L o w SIDE OF SCRATCHED ECCENTRIC SHELL. 1 MIN. 8 0 0 " F. (427OC.)

NH4OH + H202 X 7 5 .


FIG. 7. FIG. 8. FIG. 7.-HIGH SIDE O F SCRATCHED ECCENTRIC SHELL. 1 MIN. 850" F. (454O C.) FIG. 8.-LOW SIDE OF SCRATCHED ECCENTRIC SHELL. 1 MIN. 850' F. (454O C.)

FIG. 9. FIG. 10. FIG. 9.-HIGH SIDE O F SCRATCHED ECCENTRIC SHELL. 1 MIN. 900' F. ( 4 8 2 O C.) FIG. 10.-Low SIDE OF SCRATCHED ECCENTRIC SHELL. 1 MIN. 900' F. ( 4 8 2 ' C.)

FIG. 11. F I ~ . 12. FIG. 11.-HALF SHELL 1 MIN. 800' F. (427' C.) FIG. 18.-HALF SHELL 1 XIN. 900' F. (482O C.)

NH4OH + HnOz X 75.

DISCUSSION 455

would be the cold-worked equivalent of the original grain. The theo- retical curve passes through decreasing values of grain size in this region down to a minimum of about 0.001 mm. a t the maximum hardness value of about 160. This represents what I conceive to be the order of size of the indistinguishable crystalline grain fragments present in severely worked brass and I look upon the process of hardening by cold working as essentidly a process of fragmentation with a building up of amorphous or suhcrystalline boundaries.

W. B. PRICE,* Waterbury, Conn. (written discussiont).-The practical application of Brinell hardness measurements in controlling the annealing of cartridge brass is of very great importance. While it is realized that the paper under discussion is supposed to deal only with the relation between grain size and Brinell hardness, it would have been interesting if other physical properties could have been added. In connection with the anneal shown at 350" C. with diflerent reductions, analogous annealing experiments were carried out in this laboratory in 1914, with common high brass (copper, 64.13 per cent.; lead, 0.21 per cent.; iron, 0.04 per cent.; zinc, 35.62 per cent.) reduced four and seven numbers hard (Brown & Sharpe gage). Thcsc results are illustrated by Figs. 1 and 2.

It may be of interest to state in connection with the author's conclusions, "the grain size of brasses annealed at low temperatures are greatly affected by the grain size and the reduction by rolling previous to such annealing," an expericnce with low-temperature anneals on the mouth annealing of brass artillery cases. Occasionally a littlc trouble was experienced with a shell cracking on the mouth in the mercuric chloride test, and upon investigation it was found that failure usually took place upon the thin side of an ecccntric shell. The photomicrographs of a shell that failed are shown in Figs. 3 and 4. The mouth anncal of 1 min. a t 800" I?. (427" C.) has caused a partial recrystallization on the thick, or more heavily worked, section, while there is very little evidence of recrystallization on the thin, or little worked, section. By raising the temperature of the anneal high enough, recrystallization was effected regardless of variation in amount of reductior, on the mouth.

Another practical illustration of the important relationship between degree of cold worlung and temperature of recrystallization was noticed in a case that had been rather deeply scratched by an imperfect die previous to the mouth anneal. Examination under the microscope, after the annealing treatment, showed that recrystallization had taken place on the scratch but had not appcared on other parts of the case. Some cases were then purposely scratched and annealed for 1 min. a t 800°, 850" and 900" F. (427", 454" and 482" C.) (see Figs. 5 to 10). Recrystal- lization of the specimen was hardly effected a t 850" F. (454" C.) ; incipient - -- - - - - - ----

* Scovill Mfg. Co. 1 Rereived Feb. 17, 1919.

recrystallization has taken place both on the scratch and on some of the boundaries of the large deformed crystals. At 900" F. (482" C.), recrystallization has replaced the large originally deformed crystals with a much finer structure. The crystals on the scratch are much smaller than those on the unaltered section.

The relation of crystal size to tensilestrength and per cent. of elongation is illustrated by the following experiment: A concentric shell was cut in two longitudinally; one half was annealed for 1 min. a t 800" F. (427' C.) and the other half was annealed for 1 min. a t 900" F. (482" C.). These are illustrated in Figs. 11 and 12. The 800" F. (427" C.) case when tested had a tensile strength of 57,385 lb. per sq. in. (4034 kg. per sq. cm.) and an elongation in 2 in. of 35.3 per cent., whereas the 900" F. (482" C.) case had a tensile strength of 51,567 Ib. (3620 kg.) and an elongation of 52.2 per cent.

On pages 434 and 448, the authors state that in annealing hard rolled metal the drop in Brinell hardness indicates softening of the metal just before the new grains are seen. Upon examination of Fig. 1, page 433, however, showing graphically the relation between the Brinell hardness values and the annealing temperatures, it will be noted that the hardness curve rises perceptibly from the hard material to the 200" C. anneal for metal reduced 36.6 per cent. and upward. This indicates that for temperatures below visible recrystallization, possibly amorphous, material resulting from severe working undergoes some readjustment, which causes a distinct hardening instead of softening as would generally be expected. This phenomenon was observed by Mathewson and Phillips," and came under my observation4 when I annealed artillery cases a t low temperatures.

J. BURNS READ," Washington, D. C.-There is nothing I can say other than in support of the data that Messrs. Bassett and Davis have furnished. I n fairness to them, after what Mr. Phillips has said, I wish to state that these data were in the hands of officers of the Ordnance Department early last year and were very helpful in the manufacturing of cartridge cases for both small arms and artillery. Many contractors who undertook the manufacture of cartridge cases knew nothing of the control of brass quality through its working and anneal, consequently this information was most helpful and such troubles as too soft and too hard cases and season or corrosion cracking of cases were readily over- come through the application of the principles brought out in this article. A large number of micrographs and records of Brinell tests collected by the Ordnance Department certify as to the correctness of the data.

*Captain, Technical Staff, Ordnance Dept., U. S. A. Trans. (1916) 64, 608-657.

4 KT. B. Price: American Society for Testing Materials (1918) 18.

DISCUSSION 457

The question of Brinell tests has been given much attention by the Ordnance Department. As stated, the Brinell test has not been reliable when applied to thin material, and if it makes an impression through to the other side of the metal i t is no longer a Brinell test.

The Ordnance Department in its laboratory a t Pittsburgh has been working on the development of what it calls a baby Brinell machine, and has obtained some very satisfactory results in the brinelling of thin sheet metals. Since the signing of the armistice, this machine has been used in the direct brinelling of 0.30 caliber cartridge cases and very consistent results have been obtained. Because of these results, we feel that the brinelling of thin sheet metal is soon to be a reliable method of determining its hardness.

W. H. BASSETT.-T~~ discussion of this paper has been gratifying and I am glad to hear the various conclusions that have been drawn from the data supplied. I t was our intention to arrive a t a practical method which would allow the rapid testing of cartridge brass in inspection. Of course, this work has a commercial bearing now that we are no longer manufacturing munition supplies. The Brinell standard test using the 10-mm. ball is not serviceable for thin metal, and I am glad to hear of the development of the baby Brinell; this should certainly offer a means for the more rapid testing of the hardness of thin brass.

Notwithstanding what Mr. Merriman said about the possibility of brass passing a Brinell hardness specification, in the case of over-annealing followed by light rolling, I do not believe that this fact detracts from the practicability of the Brinell test. It is, of course, possible by combinations of working to obtain false impressions from the grain count, as we attempted to bring out in the paper. If, for instance, work done on the brass is not sufficient to make apparent a deformation of the grain, the grain size will not be an accurate measure of the hardness of the material. In other words, the material may be much harder than the grain diameter indicates. Likewise, certain combinations may be arranged that will make the Brinell hardness figures misleading.

The purpose of proposing the Brinell hardness test t o replace the grain count is to make possible more rapid inspection, but the two methbds should be used in connection with each other. If the Brinell ' hardness test is used in inspection, an occasional microscopic examination should be made in order to obtain a proper understanding of the material being considered. So far as material above 0.100 in. thick is concerned, the Brinell hardness test can be trusted, provided an occasional microscopic examination is made.

a comparison of grain-size measurements and brine11 ...library.aimehq.org/search/docs/volume...

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