Research Capabilities

Metmech Analytical EngineersA Research Lab

Research Capabilities

Metallography and microstructure: standard specimens taken from genuine materials, heat treated, polished and etched to show how composition and processing shape a metal.

Standard Metallographic Specimens

Each specimen is documented with its photomicrograph, the magnification and etchant used, and a description of the microstructure.

How each specimen is prepared

1. Genuine materialEvery specimen is taken from a genuine material.
2. Heat treatedIt is given the intended heat treatment, such as normalizing, annealing, hardening and tempering or carburizing, in specialized furnaces.
3. Polished and etchedIt is polished through the full polishing sequence and etched with the correct etchant as per ASTM / BS standards.

Two specimen sets

• 24Specimen set of 24Steels, cast irons, non-ferrous alloys, welded joints, an electroplated component, a powder metallurgy sample and bearing metal.
• 12Specimen set of 12Specimens 1 to 12: carbon, high speed, hardened and tempered, stainless and case carburized steels, three cast irons, an aluminium alloy and Muntz metal.

Specimen Catalogue

Photomicrographs from the specimen booklets. The scale bar in each image gives the magnification and length.

1. 01Low Carbon Steel7
2. 02Medium Carbon Steel9
3. 03High Carbon Steel11
4. 04High Speed Steel13
5. 05Hardened and Tempered Steel15
6. 06Grey Cast Iron17
7. 07Malleable Iron19
8. 08Spheroidal Graphitic (S.G.) Cast Iron21
9. 09Austenitic Stainless Steel23
10. 10Case Carburized Steel25
11. 11Aluminium Alloy29
12. 12Muntz Metal31

13. 13Copper Alloy (Brass)33
14. 14White Cast Iron35
15. 15Titanium Alloy37
16. 16Friction Welded Steel39
17. 17Electroplated Component43
18. 18Fusion Welded Mild Steel45
19. 19Copper Alloy (Bronze)49
20. 20AA6061 Aluminium Alloy51
21. 21Magnesium Alloy53
22. 22Powder Metallurgy Sample55
23. 23Bearing Metal57
24. 24Pure Copper59

Specimen

01

Specimen 1: Low Carbon Steel

Plate steel with less than 0.25% carbon, austenitized and cooled in air (normalized). Uniform grains of pearlite (ferrite and cementite) in a ferrite matrix, with flow lines from cold working and rolling. Steel with less than 0.8% carbon is called hypoeutectoid steel.

Photomicrograph

Magnification

200X

Etchant

2% Nital solution

Included in

Sets of 12 and 24

Specimen

02

Specimen 2: Medium Carbon Steel

Steel with about 0.45% carbon, austenitized and cooled slowly inside the furnace (annealed). Coarse pearlite grains in a ferrite matrix; the pearlite is noticeably larger than in a normalized structure because of the slower cooling.

Photomicrograph

Magnification

200X

Etchant

2% Nital solution

Included in

Sets of 12 and 24

Specimen

03

Specimen 3: High Carbon Steel

Steel with 0.90% carbon and 1.2 to 1.3% chromium, austenitized and furnace cooled. Cementite (dark) and chromium carbide grains in a pearlite matrix. Steel with more than 0.8% carbon is called hypereutectoid steel.

Photomicrograph

Magnification

200X

Etchant

2% Nital solution

Included in

Sets of 12 and 24

Specimen

04

Specimen 4: High Speed Steel

Tool steel with 0.8% carbon, 2% molybdenum, 4% chromium, 1% vanadium and 18% tungsten. Austenitized at 1250°C in a salt bath furnace, quenched in a salt bath and tempered at 550°C for 2 hours. White alloy carbide particles in a matrix of tempered martensite.

Photomicrograph

Magnification

500X

Etchant

2% Nital solution

Included in

Sets of 12 and 24

Specimen

05

Specimen 5: Hardened and Tempered Steel

Heated to the austenitizing temperature so the BCC structure transforms to FCC, then quenched in water, oil or polymer to form martensite (body-centred tetragonal) for high hardness and strength. Tempering below the austenitizing temperature avoids cracking and relieves thermal stresses. Tempered martensite, with untempered martensite visible at higher magnification.

Photomicrograph

Magnification

500X

Etchant

2% Nital solution

Included in

Sets of 12 and 24

Specimen

06

Specimen 6: Grey Cast Iron

Cast iron with 3.8% carbon and 2.6% silicon, annealed at 800°C for 1 hour after casting. Carbon in cast iron is present as combined carbon (cementite) and as free graphite. Graphite flakes, in a pearlite and ferrite matrix when etched.

Photomicrograph

Magnification

100X

Etchant

3% Nital solution

Included in

Sets of 12 and 24

Specimen

07

Specimen 7: Malleable Iron

Made from white cast iron by a malleabilising heat treatment, which gathers the free carbon into near-spherical temper carbon nodules and improves elongation and bending. Temper carbon nodules in a fully pearlitic matrix: pearlitic malleable cast iron.

Photomicrograph

Magnification

100X

Etchant

3% Nital solution

Included in

Sets of 12 and 24

Specimen

08

Specimen 8: Spheroidal Graphitic (S.G.) Cast Iron

Molten grey cast iron is nodularized with an inoculant just before it is poured from the ladle, so graphite forms as spheres. Also called nodular or ductile iron. Graphite nodules ringed by ferrite (the “bull’s-eye” structure) in a mainly ferritic matrix with some pearlite. Its elongation is far higher than that of grey cast iron, which is almost negligible.

Photomicrograph

Magnification

100X

Etchant

3% Nital solution

Included in

Sets of 12 and 24

Specimen

09

Specimen 9: Austenitic Stainless Steel

18% chromium, 8% nickel stainless steel. Single-phase, solution-annealed austenite in equiaxed, uniform grains with clear boundaries and no carbide precipitation at them. The black dots are non-metallic inclusions, with some alloy carbide particles inside the grains.

Photomicrograph

Magnification

100X

Etchant

Electrolytic oxalic acid etching

Included in

Sets of 12 and 24

Specimen

10

Specimen 10: Case Carburized Steel

Magnification

100X

Etchant

2% Nital solution

Included in

Sets of 12 and 24

PhotomicrographCase

Specimen

10

Specimen 10: Case Carburized Steel

Low carbon steel (0.15% carbon) gas carburized at 925°C for five hours, raising the surface carbon to a depth of 0.35 mm. The case, at 0.85% carbon, shows cementite and pearlite; the core shows a little fine, spheroidized pearlite in a ferrite matrix, the spheroidization coming from the long soak at temperature.

PhotomicrographCore

Specimen

11

Specimen 11: Aluminium Alloy

Aluminium alloy with 3% copper and 6% silicon. Fine Al-Si eutectic in a matrix of aluminium solid solution, with dendritic, acicular Al-Si particles in the primary aluminium. The eutectic particles are rounded rather than sharp or script-like. Dark grains are Al-Si eutectic; light grains are CuAl₂.

Photomicrograph

Magnification

100X

Etchant

Hydrofluoric acid solution

Included in

Sets of 12 and 24

Specimen

12

Specimen 12: Muntz Metal

Cast copper alloy of 60% copper and 40% zinc. Fine, needle-like alpha phase in a beta matrix, formed by eutectic solidification during casting. This two-phase alpha-beta structure gives the alloy its strength and hardness.

Photomicrograph

Magnification

100X

Etchant

Potassium dichromate solution

Included in

Sets of 12 and 24

Specimen

13

Specimen 13: Copper Alloy (Brass)

Wrought leaded tin brass of about 70% copper, 15 to 20% zinc, 2 to 3% tin and 1% lead. Fine, dark lead particles dispersed in beta solid solution, with recrystallized alpha grains from prior cold working. A structure with good strength and machinability.

Photomicrograph

Magnification

100X

Etchant

Ammonia and hydrogen peroxide solution

Included in

Set of 24

Specimen

14

Specimen 14: White Cast Iron

Produced by suddenly chilling molten grey cast iron, so no graphite forms. About 3.5% carbon, present as massive cementite carbides in a dendritic pattern. Very hard and wear resistant (also called abrasion-resistant iron), it is used in steel rolling mills, pump impellers, vane pumps and flour mills.

Photomicrograph

Magnification

100X

Etchant

2% Nital solution

Included in

Set of 24

Specimen

15

Specimen 15: Titanium Alloy

Alpha-beta alloy to ASTM Grade 5 (Ti6Al4V): under 6% aluminium and under 4% vanadium, balance titanium. Solution annealed above the beta transus at 980°C for 30 minutes and air cooled, then held at 704°C for 1 hour and air cooled. Coarse, plate-like alpha grains (light) with beta phase (dark) at their boundaries.

Photomicrograph

Magnification

100X

Etchant

Kroll’s reagent

Included in

Set of 24

Specimen

16

Specimen 16: Friction Welded Steel

Magnification

100X

Etchant

2% Nital solution

Included in

Set of 24

PhotomicrographParent metal

Specimen

16

Specimen 16: Friction Welded Steel

Friction welding is a solid-state process: heat comes from friction between a moving and a stationary part, and an upset force fuses them without melting, so it is closer to forging than to conventional welding. Low carbon steel welded from both sides. The parent metal shows pearlite in ferrite; the weld zone shows much finer, uniform pearlite with no filler metal and some voids from lack of fusion, refined by severe plastic deformation and frictional heat.

PhotomicrographWeld zone

Specimen

17

Specimen 17: Electroplated Component

Electroplating coats one metal over another for mechanical or corrosion properties. This component, of the kind used for car and two-wheeler shock absorber rods, is coated with hard chromium and nickel. The coating, 30 microns thick in total, reaches up to 1200 HV against 250 HV for the base metal, giving a hard surface that resists wear and corrosion. Hard chromium differs from decorative chromium, which only adds lustre.

Photomicrograph

Magnification

100X

Etchant

2% Nital solution

Included in

Set of 24

Specimen

18

Specimen 18: Fusion Welded Mild Steel

Magnification

100X

Etchant

2% Nital solution

Included in

Set of 24

PhotomicrographParent metal

Specimen

18

Specimen 18: Fusion Welded Mild Steel

Two low carbon steel plates welded with a low carbon electrode. Fusion welding melts the joint, creating a heat-affected zone. The parent metal shows uniform pearlite grains in ferrite; the weld zone shows fine dendritic grains from rapid solidification, with pearlite dendrites within primary ferrite dendrites.

PhotomicrographWeld zone

Specimen

19

Specimen 19: Copper Alloy (Bronze)

Commercial bronze recorded as 45% zinc, 0.8% lead and 0.5% tin, with traces of bismuth and iron and copper as the remainder. Uniform dendritic alpha grains (white) in a matrix of transformed beta (dark).

Photomicrograph

Magnification

100X

Etchant

Potassium dichromate solution

Included in

Set of 24

Specimen

20

Specimen 20: AA6061 Aluminium Alloy

A medium to high strength, heat-treatable alloy with very good corrosion resistance and weldability (with reduced strength in the weld zone) and medium fatigue strength. Mg₂Si and Al-Si precipitates dispersed uniformly in primary alpha aluminium. Used in automobile components.

Photomicrograph

Magnification

100X

Etchant

Keller’s reagent

Included in

Set of 24

Specimen

21

Specimen 21: Magnesium Alloy

ASTM grade AZ91: magnesium with about 9% aluminium and 1% zinc. A dendritic structure, with eutectic beta phase (Mg₁₇Al₁₂) along the grain boundaries of primary alpha magnesium. Used for gearbox housings, laptop frames, camera bodies and non-load-bearing aerospace parts for its strength-to-weight ratio and castability.

Photomicrograph

Magnification

100X

Etchant

Picric acid solution

Included in

Set of 24

Specimen

22

Specimen 22: Powder Metallurgy Sample

Steel powder compacted under high pressure and sintered at high temperature in argon to prevent oxidation. Medium carbon steel grains of pearlite in ferrite. The black areas are pores from compaction, reduced by finer powder and higher compaction pressure.

Photomicrograph

Magnification

100X

Etchant

2% Nital solution

Included in

Set of 24

Specimen

23

Specimen 23: Bearing Metal

Bearing metal lined over a steel bush, as used in automobile connecting rod bearings running against the crankshaft. The lining is sintered copper powder with dark lead and tin particles (right) on a medium carbon steel base (left); the proportions are chosen for sliding wear resistance.

Photomicrograph

Magnification

100X

Etchant

Potassium dichromate and Nital solutions

Included in

Set of 24

Specimen

24

Specimen 24: Pure Copper

Wrought copper of about 98% purity. Equiaxed, polygonal grains of different sizes, with some twinned grains from cold working and fine copper oxide particles at the grain boundaries. Its face-centred cubic structure gives copper its ductility and electrical conductivity.

Photomicrograph

Magnification

200X

Etchant

Ferric chloride solution

Included in

Set of 24

Specimen Reference Table

All 24 specimens with the magnification and etchant used for each micrograph.

Handling and Storage

From the instructions supplied with each specimen set.

• Handle specimens with care. Avoid finger marks and scratches on the polished and etched surface.
• Do not wipe the etched surface.
• Store the specimens in desiccated boxes when they are not in use.
• If a specimen rusts, repolish it on a polishing machine with ½ or ¼ micron diamond paste and etch it again with the correct etchant.
• Keep each specimen in its own slot after use; do not interchange their positions.

Enquire About Metallographic Specimens

Tell us which specimen set or specimens you are interested in, or send us a sample for micro examination.

Related testing services

• Material Characterization
• Sample Preparation & Processing

Metmech Analytical Engineers