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Fay Henry Microscopic examination of steel

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Fay Henry Microscopic examination of steel

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Tensile Testing a Stainless Steel Tensile Specimen

Microscopic Examination of Steel Henry Fay Snippet view. The microscopic constituent 4 in quenched steel is known as martensite and is characterized by.

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Full 4 of "Microscopic Examination Of Steel" See other formats WORKS OF PROF. HENRY FAY PUBLISHED BY JOHN WILEY 4 SONS, Inc. Microscopic Examination of Steel.

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An Advanced Course in. 4 Analysis with Explana- tory Notes.

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Investigation of microstructure of low low carbon welded steel

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Microscopic examination of steel.

Fay Henry Microscopic examination of steel

Henry Fay. Abstract "The material contained in this small volume was originally issued by the Ordnance Department 4.

Fay Henry Microscopic examination of steel


Fay Henry Microscopic examination of steel

The branch of materials science dealing with microscopic examination of metals 4 called Metallography. The most common method used to examine the structures of materials is optical technique.

Fay Henry Microscopic examination of steel

A specimen about читать больше on an edge is cut from the metal to be examined.

In some cases where Microscopic Examination of Steel.
An Advanced Course in.
Quantitative Analysis with Explana- tory Notes.
This book is being published by permission of the Chief of Ordnance, United States Army.
The material contained in this small volume was originally issued by the Ordnance Department U.
It was intended for the exclusive use of inspectors of ordnance material.
The demand for the pamphlet however was considerable, and it was thought that it might serve a wider Held of usefulness by being offered to others interested in the inspection of steel.
It is in no sense to be considered 4 text book, and it is meant to present a mere outline of metal- lographic methods illustrating typical examples, and should be used only in conjunction with a study of text books on the metallography of iron and steel and with reference to original papers appearing in the journals bearing on this subject.
It should, furthermore, be used with caution, as it is believed that metallographic diagnosis can be made only after much ex- perience in the handling of a variety of material.
This volume is intended particularly for those who are in need of some help in the interpretation of results.
The author wishes to express his appreciation of the kindly interest which Colonel Wheeler, the Commandant of the Water- town Arsenal, has shown in this as well as in other work of similar nature.
The Wiley Engineering Series will embrace books devoted to single почему Наушники Phiaton MS 100 BA />The object of the series is to place in the hands of the practicing engineer all the essential information regarding the particular subject in which he may be interested.
Extraneous topics are excluded, and the contents of each book are confined to the field indicated by its title.
It has been considered advisable to make these books manuals of practice, rather than theoretical discussions of the subjects treated.
The theory is fully discussed in text books, hence the engineer who has previously mastered it there, is, as a rule, more interested in the practice.
The Wiley Engineering Series there- fore will present the most approved IMT35091 коробка распределительная открытой установки 100X100X50, with only such theoretical discussion as may be necessary to elucidate such practice.
Microscopic Examination of Steel INTRODUCTION.
The supreme test of any metal is a test to destruction, but unfortunately this method is usually too expensive and time consuming to lend itself to useful purposes.
A practical Held test is also satisfactory, but in order to carry on such a test in a systematic manner a certain amount of information must be ob- tained previous to the assembling of the materials for such a test.
In ссылка на подробности to judge whether or not читать далее metal is suitable for the purpose for which it is intended separate parts of the metal are selected 4 test and upon the results of these tests the metal is judged as a whole.
Physical and chemical tests are usually applied and both give satisfactory and necessary information within certain limits but neither is absolutely conclusive in itself and the results of the two methods of testing should al- ways be used in conjunction.
To further supplement the information obtained by physical and chemical tests metallographic tests which give information not obtainable by the other methods have been introduced.
The particular use of metallographic testing is to give information in regard to the homogeneity of the metal, and the heat treat- ment to which it has been subjected.
These observations are extremely useful in conjunction with the results of the other methods, but are not sufficient in themselves at the present time as a basis for conclusion, on account of not узнать больше having been sufficiently standardized.
Interpretation of results is an im- portant factor, and in cases of doubt the results should be re- ferred to someone having had experience.
The following pages are submitted as a help to inspectors, who should inform themselves more fully in regard to underlying principles involved and to methods employed.
When steel passes from the liquid to the solid state it fo what is called a solid solution.
This solid solution is usu referred to as Austenite.
The temperature at which the cha from liquid to solid Pearl Complex роял комлекс TREATMENT ЧИ волос 177 CHI восстанавливающий ROYAL Гель трэтмент пёрл для takes place is progressively lowc with increase of carbon.
The resulting solid solution is s ject to certain reactions which take place as the solid mas further cooled.
The temperatures at which these reactions t place are known as critical temperatures, or critical points, ; are made evident by evolutions or absorptions of heat.
The reactions which take place at these critical temperate determine the character of the resulting product.
Inasmuch some of these points are dependent upon the percentage ami sition of the metal, particularly carbon, the properties of t steel are then dependent upon the percentage of carbon and completeness with which the reactions have taken place at critical temperatures.
For practical purposes, the Ar 2 and AC-J points need not be c sidered.
In 'steels containing less than 0.
The Ari po for all carbon steels is approximately at the same temperature a represents the final decomposition of the solid solution into MICROSCOPIC EXAMINATION OF STEEL 3 constituents, iron and iron carbide.
The Aci point is approxi- mately 30 higher than the ATI point, and represents the begin- ning of the formation of solid solution.
In steels containing 0.
This is known as an eutectoid steel, and its mi- croscopic constituent is pearlite.
Pearlite always etches dark, and under high magnifications is shown to consist of alternate laminations of iron and iron carbide.
Steels containing less than 0.
Steels containing more than 0.
These facts are illustrated in the diagram.
Hypoeutectoid steels are used for forgings and castings; hy- pereutectoid steels for tools; eutectoid steels for tires, springs, etc.
Examples illustrating 4 constituents are shown in photographs Nos.
With the introduction of carbon there is a decrease in the amount of ferrite and the constituent pearlite begins to appear.
This is shown in photograph No.
Inasmuch as steels containing 0.
In a steel containing 0.
Such a steel is shown in photograph No.
A eutectoid steel containing 0.
Under higher magnifications pearlite shows the laminated struc- ture shown in photograph No.
In hypereutectoid steels the excess carbon beyond that necessary to form pearlite, separates as free cementite and the amount of free cementite can be cal- culated.
Inasmuch as the whole field is made up of pearlite 4 MICROSCOPIC EXAMINATION OF STEEL and cementite and it requires 0.
Thus in a steel containing 1.
It is thus evident that by microscopic examination a rough determination of carbon may be made on slowly cooled steels.
Every chemical reaction has a time factor.
In the slow cooling or heating of steels the reactions taking place at the critical temperatures are almost complete and the products of the re- actions are in a state of stable equilibrium.
If this time factor be disturbed, the state of equilibrium is also disturbed.
If the rate of cooling is rapid enough, the reactions which ordinarily take place on slow cooling are suppressed and the metal is main- tained in the condition in which it existed at the temperatures from which cooling began.
If cooled rapidly from above An, the reactions which ordinarily take place on slow cooling have not time to take place and the solid solution present persists at the ordinary temperatures, but inasmuch as solid solution of iron carbide in iron is in stable equilibrium only at temperatures above Aci, then it must be in a state of unstable equilibrium at the ordinary temperature.
This is the condition, of hardened steel and is produced by quenching in water, brine, or oil at some temperature above Aci.
The tendency toward stable equilibrium is very small at the ordinary temperature, but it increases with rise of temperature and time.
The microscopic constituent pro- duced in quenched steel is known as mar tens!
Com- rcially martensitic steels are unimportant on account of their :reme brittleness and they are found only rarely.
The lower the temperature of re- iting the smaller is the tendency toward stable equilibrium; 5 higher the temperature the more stable is the product pro- :ed.
Practically any degree of hardness may be produced, rying from glass-hard to extreme softness, by properly regu- ing the temperature of the heating.
Intermediate between these extremes are steels in which re адрес less of the unstable solid solution has been partly con- led to more stable forms.
Such forms are represented mi- iscopically by troostite and sorbitc.
They are characterized by having a peculiar lyish color, and the structure is better defined than troostite.
Mmilur effects maybe produced by varying the rate of 4 />Quenching be- 6 MICROSCOPIC EXAMINATION OF STEEL low the critical range should theoretically produce the same effects as slow cooling.
In the heating of steels to a high temperature, and in the slow cooling from a high temperature either without having been forged or after having been forged at a high temperature, there is considerable grain growth of the steel with strong tendency toward granulation.
In the making of castings there is good opportunity for grain growth and also for the formation of inter- nal strains.
To remove strains and to refine the grain, steel is annealed.
This cofeesponds to the Acs point, and for steels containing less :" than 0.
In addition to the normal constituents of steel there are some abnormal constituents commonly classified under the name of slag, which may include such substances as silicate of manganese, sulphide of manganese, and oxide of iron.
Mixtures of sili- cates of iron and manganese may occur and also mixtures of silicate of manganese and sulphide of manganese.
Oxide of iron ordinarily occurs near the surface as the result of rolling in some mill scale, but may at times penetrate quite deeply into the in- terior, and in either case is usually accompanied by partial decarbonization.
MICROSCOPIC EXAMINATION OF STEEL 7 It is difficult at times to distinguish readily between silicate and sulphide of manganese without resort to special tests.
They both occur as dove-colored constituents and are best observed on the polished but unetched surface.
The former, especially if occurring in masses, will frequently show crystalline etch figures.
In slowly cooled, unworked steel they will show as rounded dove-colored masses usually in the ferrite; in forged steels they are elongated in the direction of forging.
See photo- graphs Nos.
Inasmuch as all steels contain some slag, it is a matter of opinion as to how much shMftbe allowed.
The form in which it occurs is of greater than actual amount present, although the smaller the of the better the product.
Such slag streaks are frequently of cracks which develop along the slag in the direction By reference to photographs Nos.
Inspectors should observe the following: 1 Macrostructure for a ingot structure, 6 segregat oji, and c blowholes.
Macrostructure is the appearance of the etched surface seen by the naked eye.
Microstructure, on the other hand, is that appearance of the etched surface seen under a microscope.
The macrostructure often yields important evidence concerning the qualities of the metal.
The structure is usually developed on 8 MICROSCOPIC EXAMINATION OF STEEL a roughly polished area of considerable size, or if it is possible to work only with small sections, it is recommended that the test bars be rough-polished нажмите для продолжения Пряжка декоративная CKB10588 ДУ(Ю) sides, at right angles to продолжить чтение other, before being turned into shape.
The development of the structure is основываясь на этих данных by etching the surface with a 6 per cent solution of iodine in alcohol or with an 8 per cent solution of copper ammonium chloride.
The former should always be prepared immediately before use, as it keeps in good condition only a relatively short time.
The copper ammonium chloride should be used only for those specimens which can be dipped into it, and the time of action should be approximately i minute.
This solution will not give results with alloy steels on account of the tenacity with which the deposited copper adheres to the sur- face.
With carbon steels the deposited copper is very easily removed by rubbing with a piece of wet cotton.
In using the iodine the polished surface is swabbed with cotton holding the reagent, and the process is repeated, as fast as the color of the iodine disappears, for a period of five minutes.
The macrostructure thus developed shows ingot structure, seg- regation of carbon or phosphorus, excessive slag, strained metal.
The presence узнать больше здесь ingot structure such as shown in photograph No.
It is not definitely known that the presence of ingot structure is harmful, and it is frequently accompanied by excellent microstructure, but it serves as an indication of the heat treatment to which the metal has been sub- jected after solidification.
It is на этой странице that such a structure would not be found in the best steel, and it is further believed that metal showing ingot structure would be more liable to rupture from shock than metal in which the ingot structure had been wiped out by heat treatment and forging.
Segregation of carbon or phosphorus may be brought out most successfully by etching a complete cross section of the metal under investigation, such as shown in photograph No.
The phenomena ob- served here will be more fully discussed later.
Both iodine and copper ammonium chloride show dark areas where segregated carbon occurs; iodine leaves phosphide areas whiter than the surrounding metal, while copper ammonium chloride leaves the area dark, and the copper adheres more ten- aciously to a phosphide than to a carbide "area.
Excessive slag is shown by a pitted or spongy area where the slag has seg- regated.
Strained metal invariably etches more darkly than metal which has not been strained, and the extent of the strained area may be determined by etching https://prognozadvisor.ru/100/jarrow-formulas-n-a-c-n-atsetil-l-tsistein-500-mg-100-kapsul-jrw-07002.html either reagent.
Slag is undoubtedly harmful if the material, either silicate or sulphide, occurs in large quantities in segregated masses, or if present in masses elongated in the direction of forging.
The position of the slag in the metal is also of importance, and that which occurs in regions of severest strain is most to be feared.
It must always be remembered that in observing slag the par- ticular spot in view is magnified 50 to 100 diameters, and it may be only an isolated spot.
If found, an exploration 4 the neigh- boring region should be made to see if it is generally distributed.
It should also be remembered that low-carbon steels may carry with safety more slag than high-carbon steels.
An example of this is shown in photograph No.
On the left of the crack is the normal structure and on the right is a decarbonized area containing slag.
Such an area would probably be large enough to show to the naked eye and would be considered unsafe.
Other examples of oxide inclosures are cited on pages 14 and 15, in the discussion of the failure of 10- inch gun and i4-inch gun lever.
On machining a metal there may often be seen lines or areas on the surface which have a different luster from the main mass of metal, and which 4 machine quite differently from the metal surrounding it; or on polishing and etching, lines of перейти luster may stand BOOMZEE BWL-01 Декоративные лепестки роз 5 x 5 см 100 шт №02 ярко-розовый prominently and invariably elon- gated in the direction of forging.
Such lines or areas are known as streaks or ghost lines, and may occur as either dark or light in comparison to the surrounding metal.
Streaks are usually accompanied by slag.
If the slag is oxidizing in character, the streak will be decarbonized, and at the same time the ferrite areas will be embrittled by being rich in phosphorus.
Such streaks may be the source of fracture, and should be looked upon with suspicion.
Dark-colored streaks usually contain silicate of manganese and are less harmful, the metal showing considerable ductility как сообщается здесь the streaked region.
Radial test pieces from gun forgings will frequently show streaks, and as the tension is normal to the direction of exten- sion the specimen will show low ductility.
It is important that the heat treatment should represent the best practice.
This will vary with the purposes for which the material 4 to be used.
In annealed steels the structure should not only show the finest grain which it is possible to give the material but it should be uniform throughout the metal, con- sidering, however, that the mass of metal influences the structure.
Thus the surface indications are not always the same as would be found in the center of a large- section.
Variations between the exterior and interior should therefore be expected on account of slower cooling of the interior and the inability to always have the forging affect the whole mass of metal alike.
Coarse struc- ture on the surface will usually indicate coarser material in the center of the mass.
Coarse-structured material may pass physi- cal specifications, but nevertheless it does not represent the best practice.
Failure to obtain uniformity of structure is shown in photo- graph No.
Discussion of photographs Nos.
Dangerous overheat- ing is shown in photograph No.
In this case the material is burnt, as is shown by the oxide between the granules of pearlite.
In material which has been quenched and subsequently tem- pered there is greater difficulty in defining the structure, but in general it should be fine and usually sorbitic, unless in unusual cases especially high strength and lower ductility is desired, in which cases troostite may be found.
In steels in which it is desired to have high strength and high ductility and obtained by either oil or water quenching, followed by a tempering proc- ess, and in which the structure is usually sorbitic, it should be 12 MICROSCOPIC EXAMINATION OF STEEL observed that the original martensitic structure is completely removed by the tempering process.
This point is illustrated by photograph No.
Such a steel properly heat treated ought to show a structure similar to photographs Nos.
On slowly cooled or annealed steels the percentage of carbon may be roughly estimated.
On quenched steels this estimation is much more difficult and usually impossible.
However, with some experience the observer can tell approximately whether or not the percentage of carbon is what the specifications call for.
The chemical analysis, however, gives more accurate data and should always be relied upon for final decision.
In certain cases, however, a rough microscopic analysis may be made with advantage.
For example, in photograph No.
Such material is evidently unsuitecl перейти на источник spring steel on account of the presence of the weak and very brittle constituent, cementite.
The main body of this spring showed troostite, not in itself unsuitable, most of the carbon being in solid solu- tion, but the center portion was not cooled rapidly enough to prevent the separation of free cementite.
The conclusion is evident that a steel containing less carbon would have been more suitable.
по этой ссылке cooled slowly and undisturbed from a high temperature will show a coarsely granular or crystalline structure, and the size of the grain is a function of the temperature and the time during which the material was held at the maximum tempera- ture, and the rate at which the material was cooled.
In large masses of material the structure will be coarser in the center than at the surface, due to the difference in rate of cooling.
In order to overcome this difference and at the same time to produce MICROSCOPIC EXAMINATION OF STEEL a homogeneous, uniform material, the steel is wort AC-B фик.

Ручка Fuaro (медь) защелка 892 period at which grain growth would ordinarily 1 Steel.
Steel which has been wor Ari cold-worked will show considerable distortio: as shown in photograph No.
The tube of this gun was found to be cracked after p The crack was situated about 2 feet in from the breec extended in the form of a crescent through a visit of about 10 inches.
At the central portion of the crac were considerably more separated than at either end siderable metal had been removed at this point.
T appearance is shown in photograph No.
It wil that the crack is not continuous.
The segregation of phosphorus is indicated b; lines in pieces Nos.
The dark streaks were found to be elong, lei to the direction of forging, and it is reasonable that the elongation will always be parallel to the surj forged.
By inspection of the two larger pieces of met; the region of the crack photograph No.
This would seem to indicate that by some means a fold in the metal had taken place at this point and that in forging it out the phosphide areas had been Видеокамера Canon LEGRIA HF M306 to the same extent as the surface of the fold.
In photographs of test piece No.
In all specimens cut in a similar direction there is always the same evidence of ingot structure or primary crystallization, which is indicated by the appearance of the white interpenetrating lines as shown.
This crystallization was produced at the time of the passage of the metal from the liquid to the solid state and during the cooling from the tempera- ture of solidification to about 4 C.
This is characteristic of ingot crystallization.
Subsequent heat treatment and forging should have com- pletely eliminated all traces of this, and its presence is an in- dication of faulty manipulation.
Further evidence of faulty heat treatment is found продолжить чтение the microstructure https://prognozadvisor.ru/100/tualetnaya-voda-annick-goutal-eau-d-hadrien-eau-sans-alcool-dlya-zhenshin-100-ml-parfyum-o-hadrien.html the steel.
Examination of sections in 4 vicinity of the crack showed many fine cracks, slag inclusions, and carbonless areas.
The cracks led to slag, and where the slag was found there were also found decarbonized areas.
The course of the slag was quite irregular, as shown in photographs Nos.
That the slag originated and was folded into the metal dur- ing the process of forging rather than during the manufacture of the steel is indicated by the fact that it is strongly oxidizing in character.
If it had originated at the time of making the steel, and had then burned out some of the carbon, there would still have been plenty of time for more carbon to have diffused back into these areas.
It is found here, however, 4 by free ferrite along the slag lines, as shown in photograph No.
Examination was made of the surfaces normal to the lands and grooves of the rifling, and there was no evidence of hardening MICROSCOPIC EXAMINATION OF STEEL 15 of the surface.
It is thus highly improbable that a crack could have originated from the presence of hardened metal It is believed that the crack in this gun was caused by folding in of some of the metal during forging.
Incidentally some other defects are pointed out.
This lever was made of cast steel and was broken during the test of the carriage.
A microscopic examination revealed the structures shown in photographs Nos.
These ferrite areas are of such a size that they are easily visible to the eye.
In the fractured ends of the test pieces the metal shows de- cidedly bright spots, and these are due, it is believed, to the presence of the segregated ferrite.
Further, it has been notkred that along the stem of the test pieces incipient cracks are developed, as shown in photograph No.
It is highly probable that these incipient fractures are developed in such areas as shown in photograph No.
It is possible that if the forces are trans- mitted equally throughout the test piece that such a portion, would yield more readily where the carbon was lowest.
The strength of such a spot would be approximately that of pure iron, or about 40,000 pounds per square inch, while the darker areas which contain more carbon would show considerably higher values.
The presence of much slag in the ferrite areas would also increase the brittleness at this point, and would account for the low ductility in some specimens.
Further examples of this form of segregation are shown in photographs Nos.
The crystalline structure 4 shown in photo- graphs Nos.
Proper annealing should have completely wiped out all appearance of this kind.
Evidence of this crystal- line nature was found in all specimens examined, and it is highly 1 6 MICROSCOPIC EXAMINATION OF STEEL probable that wherever such structure appears casting strains exist.
Proper annealing would also have removed all initial strains and would have refined the structure.
The strength and ductility have undoubtedly been affected by the aforementioned factors, viz.
A section of the metal i inch square was cut from the region of the fracture, and the macrostructure was developed by etching with iodine solution.
Small fissures were visible and both faces indicated the presence of slag.
The cause of rupture is believed to have been due to the pres- ence of a zone of streaked metal, and further, that this resulted from the presence of slag in the original ingot.
To prepare a specimen for microscopic examination it is neces- sary to polish the surface until a perfectly smooth finish free from scratches is obtained.
Frequent examination under the microscope will enable the operator to determine when the pol- ishing should end.
Small specimens are easiest to handle, and the threaded ends of broken test specimens are commonly used.
The broken ends are cut off with a saw and smoothed with a dead smooth file, then rubbed on a piece of No.
The piece is then rubbed on a block of -wood covered MICROSCOPIC EXAMINATION OF STEEL I?
This is usually applied with a fine 2-inch brush.
The specimen is then rubbed successively on similar blocks moistened with tripoli and jeweler's rouge.
The piece should be carefully cleaned before changing from one abrasive to an- other.
If power is available it will be found much easier to polish the specimens on rapidly revolving wheels covered with fine duck or broadcloth, to which the abrasive is applied with a brush or in the form of a spray.
After polishing, the specimen is washed carefully in running water 4 immediately wiped dry with a towel or piece of absorbent cotton.
An alcoholic solution of nitric acid is the most common re- agent used for etching, and is prepared by adding 4 cubic centi- meters of nitric acid Sp.
It is then removed and washed thoroughly in running water or in alcohol and quickly dried, either by a soft cloth or by a blast of air.
Examination under the microscope will determine whether the etching has been carried far enough.
The time of etching will vary, depend- ing on the hardness of the steel, and therefore the period must be learned by experience.
A 5 per cent alcoholic solution of picric acid is sometimes used for a reagent, and on low-carbon soft steels it gives practically the same indications as the alcoholic nitric acid.
Its use on hardened or tempered steels is not recommended.
Sodium picrate is used to distinguish between ferrite and ce~ mentite.
This solution is made by dissolving 2 grams of picric acid in 98 cubic -centimeters of a solution of 250 grams of caustic 18 MICROSCOPIC KXAMiXATIOX OK STEEL soda NaOH dissolved in 750 cubic centimeters of water.
Ferrite remains bright when boiled in sodium pie- rate solution.
If a permanent record is desired, photomicrographs are made the magnification being always marked on the negative and print It will be found that polished surfaces will oxidise if exposed to the air or to moisture.
Specimens should be washed in alcohol and stored in air-tight boxes.
For the examination of large pieces of metal, such as guns, etc.
This can be done with any of the portable outfits now on the market, or may be done by hand.
The study of the following books is recommended, to sup- plement the information contained herein: Howe, Metallography of Cast Iron and Steel Rosenhain, Physical Metallurgy.
Edwards, Physico-Chemicul Properties of Steel Desch, Metallography.
Osmond and Stead, Microscopic Analysis of Metals.
In conclusion it may be stated that there is a tendency to over-rate the application of metallography.
Used in conncc- tion with the physical tests and chemical analyses it furnishes valuable supplementary data.
The inspector is warned to be conservative in his conclusions, at least until he has acquired sufficient experience in the examination of steels to make his conclusions agree with the facts.
Ferrite white and pearlite dark.
Ferrite white and pear-lite dark.
Ferrite white and pearlite dark.
Sulphide of manganese in gun steel.
InK'ol' strurture in steel.
Microstructure showing: Incomplete heat treatment.
Microstructure of overheated steel.
Mlcrostructure of forging which had been originally martensitic.
Mic restructure in center of broken recoil spring showing excess cementite, Indicating high carbon.
Left, white lines are cementite etched with nitric acid solution; right, dark lines are cementite etched with sodium plcrate solution.
Microstructure of steel subjected to cold work, and showing: distortion of grain.
Slag; In lO-lneh rifle, unetched.
Island of slag: in decarbonized area in 10-inch rifle.
Segregated ferrite white with slag inclosures.
по ссылке ferrite on edge of test piece.
Segregated ferrlte white with slag: inclusions.
Segregated ferrlte and crystalline structure.
Crystal II no structure.
Macrostructur of rnetal removed from 12-inch grun.
больше на странице showing: slag and fissures.
Slag' In unetched specimen.

Fay Henry Microscopic examination of steel

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