1

Industrial pure iron

annealing

FThe white equiaxed crystal isFGrains, the black network represents the boundaries between grains, namely grain boundaries. The atomic arrangement at the grain boundary is irregular, with high free energy and easy etching, forming grooves, hence it appears black. There are black dots of oxide on it.

2

20steel

refund fire

F+PThe white grains areFThe black block is in the form of a sheetPLow magnification factor,PThe layer structure is not displayed.20Steel has a low carbon content,Foccupy76%，Poccupy24%So it shows the black networkFGrain boundaries.

3

45steel

refund fire

F+PThe white grains areFThe black block is in the form of a sheetP.PThe layered structure is also not clearly displayed.45Carbon content ratio of steel20Steel is abundant,Ffall to42.7%，PAdd to57.3%

4

65steel

annealing

F+PThe white matrix is sheet-likePWhite is distributed in a network like patternF.PThe layer structure is also not clearly displayed.65The carbon content in steel is close to that of eutectoid components, and the matrix structure containsPSignificant increase, already reached84%，FThe quantity correspondingly decreases.FOnly for16%.

5

T8steel

refund fire

FlakyP.PyesFgiveFe₃CMechanical mixtures with the same arrangement.FFor white,Fe₃CIt is black and arranged in a patchy pattern, resembling a fingerprint. It's high temperatureAThe product of the eutectoid reaction. Some samples have a lower limit of carbon content, and there may be a small amount ofFappear. When the discrimination ability of the objective lens is less thanFe₃CLayer thickness,Fe₃CIt is in the form of black strips. When the discrimination ability of the objective lens is greater thanFe₃CThe thickness of the layer is whiteFe₃CThe strip will be clearly displayed.

6

T12steel

refund fire

P+Fe₃C_IIThe black and white layered substrate isPThe white network on the grain boundary isFe₃C_II.T12For hypereutectoid steel, before the eutectoid reaction,Fe₃C_IIFirstly, follow alongAGrain boundaries precipitate in a network like pattern. Subsequently, as the temperature decreases to the eutectoid temperature, an eutectoid reaction occurs, and the remainingAAll transformed into stripsPNet like structureFe₃C_IIIt can be cleared by normalizing treatment.

7

T12steel

annealing

P+Fe₃C_IIEtch with alkaline sodium picrate solution.Fe₃CStained black, F still retains white. Therefore, the black network isFe₃C_II，Yu is P. The etching is shallow, and the layered P does not show a grayish white color.

8

hypoeutectic

pig iron

cast state

P+Fe₃C_II+Ld`The spotted matrix is eutecticLd`The black person's dendrite isPThe newbornATransform the product, resulting in large black blocks.Fe₃C_IIgiveLd`hit the targetFe<sub>3</sub>CConnected together, all white and indistinguishable. As the carbon content in pig iron increases,PThe quantity decreases,Ld`Increase.

9

Eutectic pig iron

cast state

eutectic structureLd`It is fromP+Fe₃C_II+Fe₃Cform.PBy eutecticAIt undergoes eutectoid transformation and has a fine structure, distributed in round and elongated grains on the cementite matrix, appearing black.Fe₃C_IIeutectic structureFe₃CThey are all white, connected together, and cannot be distinguished. itsPgiveFe₃CThe relative content is:Fe₃C 60%，P40%.

10

Hypereutectic

pig iron

cast state

Fe₃C_I+Ld`Due toFe<sub>3</sub>C<sub>IFirst of all, it crystallizes and grows continuously during the crystallization process, so it is in the shape of thick white strips</sub>Ld`Still in the form of black and white spots.

11

T8

normalizing

SFine layered flakesFgiveFe₃CThe mechanical mixture. The magnification of the optical microscope is less than600XThe layers are indistinguishable, like faint black clouds in the sky. Only zoom in to1500XOnly by doing so can we distinguish itPLayered features.

12

T8

austempering

T．TIt's during quenchingADecompose into extremely fine flakesFgiveFe₃CThe mechanical mixture has low magnification under an optical microscope and cannot be distinguishedTThe layered structure is in the shape of a black cluster resembling a chrysanthemum. Only magnified under an electron microscope10000XOnly then can the layered features be displayed.TIt is a structure obtained by quenching, and will always retain some quenchingMDue to shallow erosion,MForm not displayed, andArBoth are white.

13

T8

austempering

Bupper+M+Aincomplete.BThe upper part consists of bundles of roughly parallel arranged strips F and discontinuities distributed between the F stripsFe₃CComposed of a very layered organization. Under an optical metallographic microscope, the bundled F stripes extend into the A crystal and exhibit feather like characteristics. F andFe₃CTwo phases are indistinguishable and turn black, only magnified under an electron microscope8000Only with X or above can two phases be distinguished.

14

T8

austempering

Bbelow+M+Aincomplete.B_belowIt is a flattened supersaturationFDistributed inFShort needle shaped insideFe₃CA mixture of two phases. It's better than quenchingMEasy to corrode, forming black needle like or bamboo leaf like shapes under an optical microscope, only magnified under an electron microscope8000XAbove is the only way to distinguishFinnerFe3CThe white part is quenchedMandAincomplete_.

15

20

quenching

Flat noodlesM. Strip like shapes with roughly the same sizeM,Directional parallel arrangement,Presenting black and white differencesMbind.There is a significant difference in orientation between beams,oneASeveral different phases can be formed within the crystalMbind.Flat noodlesMThe reason for presenting black and white differences,Due to the low carbon steelM_SPoint high First formedMDue to heavy self tempering, it appears black and later formsMSelf tempering light and white in color.

16

T8

quenching

FlakyM+ArHigh carbonMIn the form of flakes, the flakes form a certain angle with each other. In oneAWithin the crystal, the first piece formedMLarger in size, often running through the entire areaAGrains, willAThe grains are divided and subsequently formedMNeedles are gradually reduced in size due to their limitations, resulting in a sheet-like shapeMIn the same field of view, there are differences in length, thickness, and thickness. quenchingMOriginally white needle shaped,ArIt is light gray. Due to tempering during the sample preparation process, martensite appears as light black needle like structures.

18

45steel

Oil quenching

M+TThe black clusters distributed along the grain boundaries areTWhite is quenchedMThe oil quenching speed is slow,45Insufficient hardenability of steel, not all can be obtainedMA small portion will precipitateT.TEasy to corrode, slightly corroded to turn black, quenchedMDifficult to corrode and appears white.

19

45steel

860℃ water quenching

medium carbonM.MMixed distribution in Flat noodles and needle shape. Flat noodlesMMore, needle shapedMThe two ends of the needle are relatively blunt.45#STEELM_SHigher, formed firstMProduced by self tempering, black in color, not self temperingMIt appears white. Thus forming a contrast.

20

45steel

860℃ water quenching and low-temperature tempering

Tempered medium carbonMIn200Tempered within ℃, within MFe₃CPrecipitation, makingMIt is dark black in color. Very fewArCompletely transformed.

21

45steel

860℃ water quenching and medium temperature tempering

temperingTTemperingTIt's fromMDecomposed outFExtremely fine-grained distribution on the matrixFe₃CThe mixture organization. Medium temperature tempering promotesMThe precipitated carbides tend to accumulate towards the edge of the needle. It appears as extremely fine particles that cannot be distinguished under an optical microscope and appears black. ButMThe center appears carbon poor and appears white. So whiteFStrip like instructions still slightly retainedMOrientation. Black carbides can only be distinguished from carbide particles under an electron microscope, and tempering can be observedTStill retains needle like structuresMThe orientation.

22

45steel

860℃ water quenching and high-temperature tempering

temperingSTemperingScorrectFFine grained distribution on the matrixFe₃CThe mixture. As the tempering temperature increases,Fe₃CThe particles grow larger, and their particle size is higher than that of temperingTCoarse, but still cannot be distinguished under an optical microscopeFe₃Cgrain. Obtained by quenchingMBy high-temperature tempering, promoteMThe carbides precipitated in the middle gather towards the edge of the needle, making it easy to corrode and turn blackMThe center is carbon poor and appears grayish white.

23

45steel

780℃ water quenching

Sub temperature quenching microstructureF+MDue to the heating temperature being lower thanAC₃, retaining someFHeating organizationA+FAfter quenching,AConvert toMIt is black in color,FUnchanged, it is white. So the sub temperature quenching structure is blackMOn the substrate, white blocks are distributedF.

24

45steel

1100℃ water quenching

Overheated quenched water structureM_wideDue to the excessively high heating temperature,AThe grains grow rapidly and obtain rows of coarse medium carbon after quenchingMParallel arrangement within different grainsMThe orientation is different.

25

T12

spheroidizing annealing

sphericalPYes, it isFGranular distribution on the substrateFe₃CWhite isFMatrix, white small particlesFe₃CThe part in the picture isFe₃CThe particles are relatively coarse.

26

T12

780℃ water quenching and low-temperature tempering

temperingMAnd granularFe₃CBlack is a hidden needle shaped tempered materialMThe white particles areFe₃C_IIDue to the heating temperature beingA₃existAC₁Between them, the heating tissue isA+Fe₃C_IIAfter quenching, the grain size is fineAacquiredMThe needle is also thin,Fe₃C_IIunchanged. After temperingMTo become black, to become black temperedMWhite particles distributed in the matrixFe₃C_II.Belongs to normal tempering structure. If blackMThe matrix appears light yellow, and even has fine needle like structuresMThis indicates insufficient tempering.

27

T12

1100℃ water quenching and low-temperature tempering

Low temperature tempering microstructure after superheating quenchingM+ArDue to the excessively high heating temperature,Fe₃CAll dissolved in coarse substancesAAfter quenching and tempering, black tempering with coarse needles is obtainedMBody and gray white residueAr.

28

40Cr

Quenching and tempering

temperingSWhiteFFine light black particles are distributed on the substrateFe₃CWhen the quenching temperature is low, alloy carbides are difficult to completely dissolve inAIn the middle. Therefore, during temperingSThere is a very small amount of residual granular alloy carbides.

29

65Mn

Quenching, medium temperature tempering

temperingTWhiteFExtremely fine black distribution on the substrateFe₃CParticles, it still remainsMOrientation. Due to the low magnification, it is difficult to distinguish the morphology of cementite.

30

GCr15

Conventional quenching and low-temperature tempering

temperingMAnd fine particle carbides+Aincomplete.MThe black and white zones are unique structures of bearing steel after quenching with water. The white area isAThe grain boundaries are distributed in a network like pattern. During quenching heating, carbidesAThe grain boundary first dissolves, making it contain more carbon and carbon than inside the crystal,M_SLow, obtained as twinning after quenchingMThe main hidden needleMBody, not easily self tempered, not easily corroded and appears white;ALess dissolution of carbides within the crystal,M_SHigh point, Flat noodles obtained during quenchingMThe main hidden crystalMEasy to temper, easy to corrode and turn black. The white fine particles are alloy carbides that do not dissolve when heated.

31

W18Cr4V

as cast condition

Ld′+T+M+Ar。 eutectic structureLdDistributed in a fishbone shape, the eutectic carbides in it are extremely difficult to dissolve in A and cannot be changed in shape by heat treatment. They can only be crushed by forging and rolling; T is easily corroded and appears black, known as black tissue; M+Ar is not easily corroded and appears white, known as white tissue. Both black and white tissues can be eliminated through annealing and quenching.

32

W18Cr4V

annealing

S+Carbides. The matrix isSLow magnification factor,SThe distance between bars is not displayed and appears dark yellow; The white block is eutectic carbide, and the white fine particles are secondary carbides.

33

W18Cr4V

quenching

M+Ar+Carbides. The white matrix is composed of hidden needle shaped quenched M and Ar. After quenching high-speed steel, Ar can reach 20-25%, so a slightly deeper etching can reveal a black network of A grain boundaries; The thickness of grain A reflects the heating temperature during quenching. The white large block is eutectic carbide,

White fine particles are secondary carbides.

34

W18Cr4V

quenching and tempering

M+carbide+Aincomplete The black matrix is temperedM+ArThe large white particles are eutectic carbides, while the small particles are secondary carbides.

35

1Gr18Ni9Ti

solution treatment

AThe white grains areAGrains, some grains are twinned, and the black dots on the matrix are carbides. Some samples have black strip-shaped sulfide inclusions.

36

30CrMnSi

austempering

Bgrain. Made of gray white colorFComposed of small island like organizations surrounded by it. The shapes of islands are diverse, granular or strip-shaped, and very irregular. When the island first formed, it was carbon richAIn the subsequent transformation, there can be three situations: it may beFandFe₃CIt could also happenMTransform or maintain carbon rich statusAr.

37

ZGMn13

as cast condition

A+Carbides. The white matrix isAThe black network represents grain boundaries, along theAGrain boundaries precipitate granular carbides. As cast highMnSteel edgeAThe network carbides distributed at grain boundaries will have adverse effects on the mechanical properties and wear resistance of castings. Must undergo water toughening treatment to dissolve carbonizationAIn the middle.

38

ZGMn13

Water toughening treatment

A. All forAGrains, uneven grain size, twinning deformation. As cast highMnSteel heated to1050-1100At ℃, the carbides dissolve into the matrix, rapidly cool, and obtain a single A. It has good toughness and exhibits high wear resistance when working under large impact loads.

39

20steel

Annealing after carburizing

The equilibrium structure of normal carburizing. The outermost layer is a hypereutectoid layer, and the black matrix isPThe White NetworkFe₃C_IIThe sub surface layer is a eutectoid layer, all of which are black flakesPThe third layer is the hypoeutectoid transition layer, with a gradual decrease in carbon content all the way to the heart. Its tissue features are white in colorFGradually increasing,PReduce accordingly, until20Primitive structure of steel.

40

40Cr

Quenched and tempered soft nitriding

Soft nitriding tissue. The white surface layer is a multiphase compound, and its structure is generally:Fe₄N、Fe₃N、CrNA mixed organization. Relatively dense, the rest is tempered martensite.

41

45steel

Air cooling after boronizing

InfiltrationBOrganization. The surface white is borideFe₂BPhase, presenting a tooth shaped indentation into the matrix; The transition layer of the secondary layer is a diffusion carbonization layer, and the substrate isSAnd a small amount of strip like distribution along grain boundariesFThe heart is45The normalized structure of steel, i.eS+F.

6、 Cast iron structure

Serial Number

material material

form state

group weave speak bright

42

grey cast iron

as cast condition

HTThe graphite form. The black sheet-like tissue is graphite, which has not been etched, so it is basically not displayed and appears white. Metallographic observation shows that graphite is dispersed in individual flakes on the substrate, and they are separate and unrelated to each other.HTThe length of flake graphite varies, and there are differences in performance. Therefore, according to the usage requirements, the morphology and length of graphite are controlled in the process. National standard, divided by graphite morphology6The length of graphite is divided into8Grade.

43

malleable iron

annealing

KTThe graphite form. The black flocculent tissue is graphite, similar to cotton wool, with a relatively regular appearance. Not corroded, the substrate does not appear white.KTIt is made of white cast iron green body. By annealing solid graphitization treatment, primary, secondary, and tertiary carbides are fully graphitized.KTThe shape, distribution, and quantity of graphite have a significant impact on its performance. Grading is included in national standards as a condition for metallographic acceptance.

44

nodular cast iron

as cast condition

QTThe form of graphite. The black spherical tissue is graphite, which is approximately circular at low magnification. At high magnification, it is a polygon with concave and convex edges around it. Due to lack of etching, the substrate is not visible and appears white.QTThe smelting of iron is obtained by adding rare earth magnesium spheroidizing agent and ferrosilicon inoculant to cast iron water. Its quality is generally evaluated by the spheroidization rate and can be carried out according to the prescribed standards. It is divided into six levels.

45

vermicular graphite cast iron

as cast condition

The graphite morphology of vermicular cast iron. The graphite structure of vermicular cast iron is between flake graphite and spherical graphite, characterized by a small ratio of length to thickness of graphite, short flake thickness, and rounded and blunt ends. Not corroded, the substrate does not appear white. Creep graphite cast iron is obtained by adding a creep agent, silicon iron alloy or silicon calcium alloy, to molten iron. During the graphite creep process in production, there may be fluctuations, resulting in a small amount of non worm like graphite such as spherical, clustered, and flaky. For creep graphite cast iron, the creep rate of graphite is the main technical indicator, and the creep rate is divided into9Grade.

46

grey cast iron

HT100

annealing

FBase gray iron. matrixFIt is white and displays black network grain boundaries,FBlack flake graphite is distributed on the substrate.FGray iron is usually subjected to high-temperature graphitization annealing, which decomposes the cementite intoFAnd graphite. When the decomposition is insufficient, there will be a very small amount ofP.

47

grey cast iron

HT150

as cast condition

F+PBase gray iron.PIt appears as a black sheet,FDistributed on both sides of flake graphite, it appears white, while flake graphite appears black gray.F+PBasic gray iron can also be obtained by low-temperature graphitization and annealing. The workpiece is about to be heated to720-760℃, keep warm for about 2 hours, cool the furnace to 300 ℃, and then air cool it out of the furnace.

48

grey cast iron

HT200

normalizing

PBase gray iron. The long gray black flakes are graphite, and the matrix is fine gray black pearlite flakes. It is used for normalizing heating and air cooling,AIt precipitates during the eutectic transformation and is relatively fine. Casting status can also be obtainedPBasicHTBut there are often block like precipitates around graphiteFSome are distributed with irregular block shaped black point like phosphorus eutectic.

49

malleable iron

KT350-10

annealing

FBasic malleable cast iron. The matrix isFIt appears white with a distinct black colorFNetwork grain boundary. The black agglomerates are graphite precipitated during annealing, and the gray black fine particles are mostly sulfide inclusions.FForged cast iron undergoes sufficient high-temperature annealing in both the first stage and medium temperature annealing in the second stage, which completely decomposes the cementite in the matrix and precipitates graphite carbon, while the matrix is carbon poor. After cooling, all of it is obtainedFThe matrix structure.

50

malleable iron

KT550-04

First stage graphitization annealing

PBasic malleable cast iron. matrixPIt is a layered black and white pattern. Some have a small amount of whiteFThe black clumps are graphite.PForged cast iron is a microstructure obtained by air cooling white cast iron billets after the first stage of high-temperature graphitization annealing, without undergoing the second stage of graphitization annealing.

51

nodular cast iron

QT400-15

annealing

FBasic ductile iron. The white matrix isFThe Black NetworkFGrain boundary, black spherical graphite. The segregation of manganese and phosphorus elements at the grain boundaries of eutectic clusters, with high carbon content and stability, is not easily graphitized, resulting in a very small residual amountPWhen there are not onlyPAnd when there is free cementite, high-temperature annealing is performed. If the cast iron structure is onlyF+PIf there is no free carbide, low-temperature annealing is required.

52

nodular cast iron

QT500-5

as cast condition

F+PBasic ductile iron. Black spherical graphite, whiteFSurrounding the spherical graphite, it forms a bullseye like tissue. When spherical graphite precipitates in liquid metal, the surrounding area of the sphereAThe carbon content is obviously low and the silicon content is high, so it is easy to precipitate along the graphite balls during the cooling processF.F+PIt can also be obtained through low-temperature normalizing, butFIt is block shaped and called fragmentedF.

53

nodular cast iron

QT700-2

normalizing

PBasic ductile iron. The black and white layered structure isPThe gray black spherical shape is graphite.PThe acquisition of the body is generally carried out through high-temperature normalizing. But often around the spherical graphite, there is a small amount ofFGenerally not allowedFexceed15%.

54

High phosphorus cast iron

as cast condition

P+Flake Graphite+Phosphorus eutectic. The layered matrix isPDue to deep etching, it turns black; The gray black flakes are graphite, and the white angular shapes are phosphorus eutectic. Phosphorus eutectic is distributed along grain boundaries, resembling a mesh, and interconnected to form a hard skeleton. During friction, graphite and substrate are worn and dented, which can store lubricating oil and play a role in reducing friction; The mesh like phosphorus eutectic protrusions bear friction, thereby improving the wear resistance of the parts.

55

ZL102

as cast condition

Cast state. Undeteriorated aluminum silicon alloy. Light gray coarse needle shaped silicon crystals and whiteα solid solution composition eutectic structure+A small amount of primary silicon grains with light gray polygons.

56

ZL102

as cast condition

Degraded aluminum silicon alloy. White dendritic tissue is primaryAlpha solid solution, the rest is a eutectic structure composed of gray black fine-grained silicon and white alpha solid solution.

57

LY12

as cast condition

The casting structure of hard aluminum. White isα(AL)Matrix and dark black [alpha](AL)+θ phase（CuAL₂）+SXiang（AL₂CuMg）Ternary eutectic and ［α(AL)+θ phase（CuAL₂）Binary eutectic. Both ternary and binary eutectics are distributed in a network and difficult to distinguish.

58

LY12

Time effective board

The aging structure of hard aluminum. whiteα(AL)Black θ phase distributed on the substrate（CuAL₂）AndSXiang（AL₂CuMg）Strengthen phase particles. Due to sampling along the longitudinal phase of the board, the strengthening phase particles are distributed along the longitudinal phase. Some samples were not made as longitudinal phase samples, and the strengthening phase particles were dispersed in the cross-section.

59

H70

Deformation annealing

Single phase brass structure. For zincDissolved in copperAlpha solid solution equiaxed grains. Some grains contain twinning.

60

H62

annealing

Dual phase brass structure. The white part isAlpha solid solution matrix, with black bar like structures composed of electronic compoundsCuZuBased on β solid solution. The etched shallow α phase grain boundaries are not displayed.

61

QSn10

as cast condition

Tin bronze as cast microstructure. Bright white tree like structure with tin dissolved in copperAlpha solid solution. The alpha tree trunk is rich in copper, while the darker areas around it are rich in tin; The small white dots distributed in the gaps between tree branches are (α)+δ) Eutectics. δ is an electronic compoundCu₃₁Sn₈A solid solution based on. Some samples have black spots indicating loose casting.

62

QSn10

Squeezing rod

Alpha solid solution single-phase structure with slip bands within the grains.

63

tin-based bearing alloy

as cast condition

α+β’+The organization. The matrix is an alpha solid solution of antimony in tin, which is easily corroded and appears black in color. The white square represents β’Xiang, it is based onSnSbOrdered solid solution based on, difficult to corrode. Particles that are small and difficult to etch into white star like or radial needle like shapes are called the η phaseCu₆Sn₅It is also difficult to corrode.

64

Aluminum based bearing alloy

as cast condition

β+（αPb）+β）common+Cu2SbOrganize white squares as beta phase（SnSb）Hard dots, some needle shaped copper antimony compounds（cu2Sb）The rest are (α)+（Pb）+β) Eutectic soft matrix.

65

QPb30

as cast condition

The cast microstructure of lead bronze. Lead cannot dissolve in copper. Bright whiteα（Cu）There are dark lead grains distributed on top.

66

TC4

annealing

（α+β) Dual phase titanium alloy. The white strip like structure represents alpha solid solution, while the black strip like structure represents beta solid solution. The alpha strips are arranged in a staggered manner, resembling a woven basket like structure, known as the basket like structure.

67

45steel

Forging and Rolling

Banded organization. The white grains areFThe black block isPThe two are arranged alternately in black and white layers along the deformation direction, forming a distinct band like pattern. Some samples are20Steel.

68

ZG30

as cast condition

Low carbon Weibull body. White needle shaped and block shapedFBlack isPWhiteFNeedle insertion in blackPInside the crystal, there is a severe Weishi structure.

69

T13

Overheating and normalizing

High carbon Weibull body. The black block isPThe White NetworkFe₃C，Fe₃CInserting in a needle like shape, even penetratingPGrains.

70

Industrial pure iron

cold rolling

Fibrous tissue. The compression amount reaches70%above.FThe grains elongate along the deformation direction and are divided into small pieces by many slip bands within the grains,FThe grain boundaries and slip bands are indistinguishable and present a fibrous structure.

71

A3steel

arc welding

Welding organization. The left weld seam area isF+P, forming columnar crystals along the direction of heat dissipation; The overheated zone adjacent to the weld seam area,AThe grain size is coarse and presents a Weibull structure; Subsequently, the heated temperature drops to the normalizing zone, where it becomes fineF+PGradually transitioning to the original microstructure of annealed base materialF+P.

72

Iron based powder metallurgy

Pressing sintering

ferrite+pearlitic+Pores. The white matrix is ferrite, the black coarse flakes are pearlite, a small amount of strip-shaped carbide, and the black particles are pores.

73

T12steel

normalizing

P+Fe₃C_IIThe substrate is blackPThe white small block isFe₃C_IIIn the raw materialsFe₃C_IIThe network has been eliminated.

74

T8steel

annealing

Microscopic organization of decarburization layer. It can be divided into two types according to its decarbonization severity program. One type is severe decarburization on the surface, resulting in a fully decarburized layer, with the outermost layer being whiteFDeep etching still showsFGrain boundary; The subsurface layer isFAnd sheet-likePWith centripetal forcePIn depth,FReduce,PIncrease until there is no complete decarbonizationPuntil. Another type of surface only has a partially decarburized layer, with a structure ofF+PThe second layer isPThe surface of this map is a fully decarburized layer.

75

20CrMnTi

Carburizing, cooling quenching, low-temperature tempering

The surface layer is the quenched and tempered structure of the carburized layer of over precipitated steel.Mcircle+Aincomplete+Carbides. The matrix is needle shapedMtempering+ArAfter prolonged high-temperature carburizing, the grain size becomes coarse, although it cools down to860℃ oil cold, blackMcircleThe needles are still relatively thick, and there are many clustered white block like carbides on the surface of the infiltration layer.

76

QT900-2

900Heating and isothermal quenching at ℃

Bbelow+M+Aincomplete+Graphite. Dark gray spherical graphite, black needle shaped graphiteBbelow.BbelowThere are many and fine carbide particles inside, which preferentially form at the edge of the nodular graphite and are highly susceptible to tempering and corrosion into black. quenchingM+AincompleteThe substrate appears white due to shallow etching. For workpieces with complex cross-sectional dimensions that require high comprehensive mechanical performance, isothermal quenching can be used to obtain themBbelowOrganization.

77

Aluminum bronze

as cast condition

a+（a+y2）Eutectics.aThe appearance is based onCuThe solid solution based on is white;y2Phase is an electronic compoundCu32AL19Based solid solution（a+y2）The eutectoid is very fine and black in color, and cannot be distinguished at low magnification. There are also a small number of black spotsFeAL3.

78

T10steel

780℃ quenching+low-temperature tempering

M+AincompleteThe gray black matrix isMtempering+a small amountADisabled,The white particles are secondary carbides. The quenching temperature of carbon tool steel is generally selected at780-800Between ℃. At this point, the A grains are finely quenched to obtain needle shaped M, and a portion of the carbonized particles from the original spheroidization annealing still remain on the M matrix, increasing wear resistance.

79

9CrSi

Quenching+Low temperature tempering

Mtempering+Carbide, extremely fine black needle shaped, low-temperature temperedMThe white particles are undissolved alloy carbides.9CrSiSteel,SiCan strengthenFObstructing quenchingMThe decomposition and aggregation of carbides hinder the reduction of hardness during tempering250-300Tempered at ℃, its hardness still has HRC60, so it is widely used to manufacture tools and molds.

80

CrWMn

Quenching+Low temperature tempering

Mtempering+Carbides. Black for hidden needle temperingMThe white particles are alloy carbides, exhibiting a black and white color phenomenon. In steelMnMakeMsWhen the point drops strongly during quenching, it will causeAincompleteIncreased, can offsetMVolume expansion occurs during formation, reducing the total deformation after quenching, which is beneficial for manufacturing molds and cutting tools with strict deformation requirements. However, the unevenness of carbides is severe and often the main cause of mold and tool peeling and brittle fracture.

81

Cr12

Raw materials undergo quenching+Low temperature tempering, take longitudinal phase samples

The substrate is black temperedM+Aincomplete, and white block shaped carbides.Cr12The amount of eutectic carbides in the matrix is high, and the unevenness is severe. The longitudinal structure of the steel billet is often distributed in a network or strip shape, and in severe cases, it needs to be forged.

82

Cr12

quenching+Low temperature tempering

Mtempering+ Aincomplete+Carbides. The black matrix is tempered+a small amountAincompleteThe white large blocks are eutectic carbides, and the white particles are secondary carbides.Cr12Steel containsCrHigh quantity, high hardenability, formed with carbonCr7C3Alloy carbides have high hardness, greatly increasing the wear resistance of steel. When quenchedCrsendAincompleteIncreased, can offset some of the reasonsMThe volume expansion generated by transformation and quenching deformation are minimal, belonging to micro deformed steel. thereforeCr12Steel is widely used in molds. However, the carbon content in steel is as high as2.3%There are many carbides, and if the distribution is uneven or the tempering is not sufficient, the mold is prone to early peeling or brittle aging.

83

Cr12MoV

quenching+Low temperature tempering

Mtempering+ Aincomplete+Carbides. The black matrix is temperedM + AincompleteThe large white blocks are eutectic carbides, and the small particles are secondary carbides.Cr12MoVSteel andCr12Compared to the decrease in carbon content, the addition ofMo、VElements, in addition to improving hardenability and tempering stability, can also refine grains, improve uneven carbides, and thus enhance their strength, toughness, and wear resistance.

84

5CrMnMo

quenching+460℃ tempering

Ttempering. That is, whiteFMixed structure with black extremely fine carbonization.5CrMnMoQuenching to obtain needle shaped productsMThen, through medium temperature tempering, promoteMThe carbides precipitated in the middle gather towards the edge of the needle, which are easily eroded and turn black; And needle needlesMThe carbon poor center transforms into a grayish white colorF.5CrMnMoCommonly used as small and medium-sized hot work molds.

85

3Cr2W8V

1120℃quenching+580Tempering twice at ℃

Mtempering+ Aincomplete+Carbides. The matrix is black and fine temperedM+ AincompleteA small amount of undissolved white fine carbides.3Cr2W8VContaining high alloy elements, good hardenability, and high strength and hardness at high temperatures, it is suitable for manufacturing hot work molds that require high stress and wear resistance at high temperatures without being subjected to impact loads. But the toughness and plasticity of steel are poor, and its resistance to cold and hot fatigue is poor.

86

T8steel

InfiltrationCrRear air cooling

The matrix is finePAnd a small amount of carbides. The surface white isCrThe carbide has a structure of（Cr.Fe）7C3.T8Steel infiltrationCrMicrohardness reaches1404-1482Compared to the carburizing, nitriding, and boronizing layers, it has high wear resistance, good oxidation resistance, and wear resistance. When applied in cold and hot work molds, it has the effect of improving the service life.