Metallography

These are some micrographs that were taken of samples made by the Spring 2003 semester of Physical Metallurgy Lab. All samples below are at 500x.

These samples were sectioned with a high speed saw, mounted in Bakelite and then polished using a series of grinding papers, and then diamond paste. After grinding and polishing, they were etched with various etching agents.

Brass

Cartridge Brass: The approximate composition is 70.0% copper and 30.0% zinc for this sample. This brass comes “as received.” Brass is a single phase compound, so there is no distinction between the copper and zinc.

Free Machining Brass: This sample is composed of approximately 61.5% copper, 35.5% zinc, and 3.0% lead. This brass is ‘as received.’ Brass is a single phase compound, so there is no distinction between the copper and zinc. However, the lead that is added to make the brass more ductile is visible as dark spots.

Free Machining Brass: This sample is composed of approximately 61.5% copper, 35.5% zinc, and 3.0% lead. This brass is ‘as received.’ Brass is a single phase compound, so there is no distinction between the copper and zinc. However, the lead that is added to make the brass more ductile is visible as dark spots.

Steel

1045 Steel: This sample’s composition was unknown. Due to the large amounts of Fe3C, it was determined that this steel was also a 1045 Steel. The dark areas represents Fe3C (cementite) and the light represents Ferrite. The striped sections of ferrite and cementite (called lamella) make up a constituent known as pearlite, which is a desirable part of steel. (The lamella are much clearer in this picture than the other 1045 Steel).

1045 Steel: This sample was composed of between 0.42% and 0.50% carbon, between 0.60% and 0.90% manganese and the remainder was iron. This sample was fully annealed. The dark areas represents Fe3C (cementite) and the light represents Ferrite. Note that there is far more Fe3C in this steel than in 1018 Steel. The striped sections of ferrite and cementite (called lamella) make up a constituent known as pearlite, which is a desirable part of steel.

1018 Steel: This sample was composed of between 0.14% and 0.20% carbon, 0.60% – 0.90% manganese, and the remainder was iron. The sample was fully annealed. The dark areas represents Fe3C (cementite) and the light represents Ferrite. Note that there is far less Fe3C in this steel than in 1045 Steel. The striped sections of ferrite and cementite (called lamella) make up a constituent known as pearlite, which is a desirable part of steel.

Cast Iron

Gray Iron: The actual composition of the ductile iron is unknown. However, cast irons have greater than 2% carbon, 1 to 3% silicon and the remainder as iron. The dark areas represents Fe3C (cementite) and the light represents Ferrite. Note the ball structures- this differentiates gray iron from ductile iron. Also notice the dark balls with the light spots in the middle. This is where balls of cementite used to be- they were ripped from the sample during grinding or polishing, and this is actually all ferrite, but the lighting is poor in the concave area, producing a dark color.

Gray Iron: The actual composition of the ductile iron is unknown. However, cast irons have greater than 2% carbon, 1 to 3% silicon and the remainder as iron. The dark areas represents Fe3C (cementite) and the light represents Ferrite. Note the ball structures- this differentiates gray iron from ductile iron. Also notice the dark balls with the light spots in the middle. This is where balls of cementite used to be- they were ripped from the sample during grinding or polishing, and this is actually all ferrite, but the lighting is poor in the concave area, producing a dark color.

Gray Iron: The cast iron is composed of between 3.00% and 3.70% carbon, between 0.50% and 1.00% manganese, between 2.10% and 2.30% silicon, between 0.07% and 0.15% phosphorus, 0.15% Sulphur and the remainder is iron. The dark areas represents Fe3C (cementite) and the light represents Ferrite. Note the worm-like structures- this differentiates gray iron from ductile iron.