Question

Define and discuss both ASTM grain size and Vickers hardness in details.
I need a full and detailed answer with references.

Answer 1

1) ASTM :

Firstly we have to define grain size that it is Dimeter of individual grain of particles in given material. American society of texting and material gives the measuring parameter for grain size called as ASTM grain size number.

ASTM grain size number is denoted as G and given as

G = (NAE + 1) / 2

Here NAE is number of grains per inch in 100x magnification that when you see the material through Scanning Electron microscope. If N is magnification then ASTM grain size given as

N = 2^(g-1)

This implies that ASTM grain size number and grain size are inversely proportional.

ASTM grain size have values 1 to 8 . that is 1 is for fine and 8 is for coarse.

2) Vickers hardness :

To measure hardness of material in small portion , Vickers hardness test is used. It is quite easy compare to other tests.

Principle of Vickers hardness test is given as to observe material's ability to resist plastic deformation from given standard parameters. Thus can be measured by using two parameters as

1) Vickers Pyramid number and

2) Diamond Pyramid hardness

Instrument used for testing hardness have indenter with Diamond head which is in square size with pointy end. The indenter is impress on the surface of material under study. So there is a impression of Diamond head on surface . the surface area of this impression is given as,

A = (d²)/ 1.85

d is length of diagonal of impressed Diamond head .

Hence Vickers Pyramid number is given as,

HV = (1.85 × F ) / d²

Unit is N/cm²

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