Observations & Study:
Steels, as one of the main
components of construction requires great strength. Steel can be modified its
strength by adjusting the percentage of the amount of its constituent substance
composition. Some substances that can be used as a composition in steel include:
Iron (Fe), Carbon (C), Phosphorus (P), Manganese (Mn), Sulfur (S), Chrome (Cr),
and so on. In addition, according to its use, steel can also be mixed with
other substances to form alloy steel. However, most steels are only dominated
by a mixture of iron (Fe) and carbon (C) called carbon steel. In its initial
condition, in carbon steel, a mixture of Fe and C will form ferrite as the main
component of steel. The ferrite contained in the steel will make the steel more
ductile, but its hardness value is minimal. In some cases, sometimes steel with
a higher hardness value will be needed, with the same percentage of content.
For this reason, an effort is needed to increase the hardness value of steel.
Efforts to increase the value of this steel hardness can be done by treating
the steel with heat treatment. One method of this heat treatment is by quenching.
This is done by heating the steel to a temperature of 850oC, and then rapidly
reducing the temperature. With an increase in temperature, the crystal structure
of the steel will deform to a ferlite structure. The ferlite structure will
deform again slowly into ferrite as the temperature decreases. However, if the
temperature is lowered rapidly, the steel structure will deform to martensite
instead of unformed ferrite. The martensite phase is harder than ferrite.
The quenching process is a
process of heating the metal so that it reaches a homogeneous austenite limit. To obtain
this homogeneity, the austenite needs sufficient heating time. Furthermore, the
steel is rapidly immersed in the cooling medium, depending on the cooling speed
we want to achieve the hardness of the steel. At the time of rapid cooling the
austenite phase did not have time to change to ferrite or pearlite because there
was no opportunity for the carbon atoms that had dissolved in the austenite to
carry out diffusion movements and cementite was formed, therefore the mertensite
phase occurred, this is a very hard phase and depending on the carbon state.
Martensite is a metastable phase formed by rapid cooling, all alloying elements
are still soluble in the solid state. Heating must be done gradually and slowly
to minimize deformation or the risk of cracking. After the austenitizing temperature
is reached, the temperature is held for a certain time and then cooled rapidly.
In the quenching process,
the cooling medium greatly affects the metal structure and the mechanical ability
that can be achieved by the metal. Here are some cooling media that are often
used:
·
Salt Water
·
Water
·
Lubricating Oil
·
Circulating Air
Results
The following conclusions
can be drawn:
1. Quenching using
lubricating oil, salt water, and liquid smoke can increase the hardness to a
higher level, while quenching using circulating air media causes a decrease in
the hardness value the following conclusions can be drawn:
2. Quenching using liquid
smoke media gave the highest hardness value.
