This document discusses different mounting and preparation techniques for specimens to be examined under a microscope. It describes hot and cold mounting, polishing, grinding, and mesh size. It also discusses the importance of etching, including optimal etching time depending on the system. Microstructures of pure iron, low carbon steel, and 314L stainless steel are described. The principles of a metallurgical microscope and precautions for etching are provided.

1. Submitted to:
Dr. Nida Iqbal
Presented by:
Meezan Hamid 2017-BME-12
Nimra Razzaq 2017-BME-34
Rameen Fatima 2017-BME-45
Iraj Fatima 2017-BME-46

2. Lab
assignment
01

3. Mounting
A processing of bracing or embedding any specimen
on the material for examination with a microscope.
Hot mounting
 Use to mount larger bearings.
 Less expensive
 Short processing time
 Temperature goes up to 200 0C
Cold mounting
 Use to mount smaller bearings.
 More expensive
 Long processing time
 Temperature is up to 60 0C

4.  Polishing:
Polishing is a process by which a smooth, glossy and finished surface is produced
either by fine-scale abrasive removal or by softening and smearing of surface layers
by frictional heating during polishing
 Grinding:
Grinding is an abrasive machining process that uses a grinder as the cutting tool. It’s a
subset of true metal cutting process. Grinding is used to finish work pieces that must
show high surface quality and high accuracy of shape and dimension.
 Mesh size:
The size of spacing between the individual strands of any material. Mesh size refers
to sieve that sifts and lets through particles. Fine mesh will only let through small
particles, leaving ones larger than that in mixture.

5. Importance of etchant
 Immersion time or etching time is highly dependent on the system and in most cases
requires experience. The selection of optimum enchant is also very important in sample
production. Deeper etches are preferred for low magnification examinations, while shallow
etches are preferred for high magnification examinations.
Microstructure of pure iron:
 In pure iron the basic building block are iron atoms (Fe). The grains on the surface of pure
iron are called crystals and they are made up of uniformly arranged atoms of iron in layers.
The lines connecting the centers of the atoms are three-dimensional array of little cubes
stacked together to fill space generated.

6. Principle of metallurgical microscope
 It works on principle of reflected light microscopy. Since metallographic
specimens are opaque to light
 sample must be illuminated by reflected light. It is capable for producing a
magnified image of small objects. Ceramoghraphy and plastography are
collectively called as metallography

7.  Microstructure of low carbon steel:
The structure of low carbon steel is characterized
by smaller grain size, much higher hardness values
and low carbon content.
 Microstructure of 314L steel:
Stainless steel of grade 314 has excellent high
temperature resistance characteristics The silicon
content in microstructure of 314L steel improves
its oxidation and carburization resistance. It’s
microstructure contains following atoms
(Mn, Ni, Si, Cr,C,S,P,Fe).

8. Precautions for etching
 Should wear rubber gloves (latex or nitrile).
 Should have safety goggles: The etching solution might splash, and you don’t
want in your eyes.
 Apron: The etchant would stain your clothes and anything else it touches.
 Good ventilation: Never etch in a small enclosed space. Outdoor is a great place
to etch because its weather permitting.
 Secure screw top plastic container to dispose off used etchant.