Objective This experiment experiment is to study the microstructure microstructure of steel steel by conducting metallurgical metallurgical observation using an optical microscope and observing the crystalline microstructure microstructure of a rail sample that was taken from the low rail on a curved railway track.
Introduction Microscopic examination examination with digital imaging microstructure analysis is conducted by microscopic examination, a process that studies the structure of materials under magnication. The properties of a material determine how it will perform under a given application and these properties are dependent on the material’s structure. structure. Industrial processes or treatments such as casting, welding and heat treating are often applied to metals to prepare prepare them for particular applications and to improve their characteristics characteristics and properties. microscopic examination examination may be conducted to evaluate the e!ects of a process on material using optical microscopy at low or high magnications.
"teel is an alloy of iron and other elements mainly carbon, that is widely used in construction and other applications due to its high tensile strength and low cost. Its base metal is iron, which is able to take on two crystalline forms # body centred cubic $%&&' and face centred cubic $(&&' depending on its temperature. In the steel forming process, the steel structure undergoes several phases, primarily ferrite and cementite that will be observed and discussed throughout this report.
Equipment )ptical microscope, camera, polished and itched steel samples
Procedures The steel crystalline crystalline microstructure microstructure sample is is examined under di!erent di!erent magnications*
Microscope components: •
)cular lens* &ylinder containing two or more lens, function to focus
•
image for the eyes )b+ective* sually in a cylinder housing containing a glass single or
•
multi-element compound lens. (ocus knobs* To move the stage up and down with separate ad+ustment for coarse and ne focusing. nable the microscope to
•
ad+ust to specimens of di!erent thickness. /ight source* "ource of light to direct images of specimen into the
•
eyes. "tage* "upport the specimen being viewed. (ocusing starts at lower magnication in order to centre the specimen. t higher magnication re0uires the stage to be moved higher vertically to refocus.
Results (igure 1 shows the steel microstructure magnied under magnication plan 23 under a microscope.
Discussion (rom (igure 1, it is observed that there are regions of di!ering brightness lining forming multiple dark and light layers. These layers are called lamella structure, which is also labelled as pearlite. The dark region in (igure 1 is cementite and the lighter area is ferrite.
(igure 1* 4icture of steel microstructure
Rail Sample
lement $w.t. 5' &arbon
0.4
"ilicon
0.0!
Manganese
"ulphur
0.0#
4hosphorus &r
0.!" 0.0!
0.0$ % 0.0$
Mo
Table above shows the element composition of the specimen6 consisting 3.275 of carbon and 3.895 of manganese. %y drawing a vertical line from x : 3.27 on the ironcarbon phase diagram, the steel forming phases could be explained in more details $The iron-carbon phase diagram is plotted in appendix'.
s carbon composes 3.275 of the element, from the phase diagram it is said that the steel portion of the metastable (e-& phase diagram exists as hypoeutectoid state $3 ; wt. 5 & ; 3.<9 wt. 5'. lloys formed at this state contain proeutectoid ferrite $formed above the eutectoid temperature' plus the eutectoid perlite that contain eutectoid ferrite and cementite that is seen in (igure 1. s discussed earlier, the dark region is cementite and the bright region is ferrite. &ementite is a hard and brittle substance, which has the ability in in=uencing on the properties of steels. (errite on the other has a body centre cubic structure and can hold very little carbon.
t temperature above 17>9 ° C , the specimen exists as li0uid state. If it is let to cool +ust above 12?> ° C , the specimen is in
δ -ferrite li0uid
solution. t this stage, the specimen is very stable at high temperature typically above 1>?2 ° C . t temperature below 12?> ° C , it contains interstitial solid solution of carbon in
γ
-iron. ustenite has a (&& crystal
structure with carbon solubility as high as @.3<5 at about 1128 ° C . s the
specimen is let to cool further at about 933 ° C ,
α A
γ coexists at this
phase, indicating there are austenite plus ferrite. t temperature below 8@> ° C , ferrite and cementite are both formed at this region.
&onclusion t cooling of steel below 3.95 carbon, the steel solidies and forms austenite. t temperature below ?13 ° C , grains of ferrite start to form. s more grains of ferrite formed, the remaining austenite becomes richer in carbon. t about 8@> ° C the remaining austenite, which now contains below 3.95 carbon changes to pearlite. The resulting structure is a mixture of ferrite and pearlite.
