The microstructure of HT200 steel is of great importance for its mechanical properties. Microscopic examination of HT200 steel reveals that it is composed of ferrite and pearlite. The presence of pearlite and ferrite is indicative of a hypereutectoid pearlite-ferrite microstructure, also known as a duplex microstructure. The relative amounts of ferrite and pearlite are determined by the heating and cooling rate of HT200 steel.
In order to understand the microstructure of HT200 steel, there is need to study the microstructure of HT200 steel through the use of a microscope or other optical tools. For the study, the microstructure of HT200 steel was analyzed under the microscope after etching with a reagent such as alcohol, or hydrochloric acid. The etched sample revealed a typical hypereutectoid pearlitic-ferritic microstructure consisting of ferrite, pearlite, and some secondary phases.
Pearlite appears as light-colored bands of alternating ferrite and cementite, while ferrite appears as light-colored grains of calcium, silicon and aluminum. The secondary phases present in the microstructure of HT200 steel are untempered martensite, spheroidite, and faicelite. Acicular ferrite, also known as white layer, was observed to be largely absent in the microstructure of HT200 steel.
To examine the size of the ferrite and pearlite grains, the specimens were viewed under a scanning electron microscope (SEM). The photographed images revealed that HT200 steel has a very fine microstructure of the pearlite and ferrite grains. The pearlite colonies were found to have an average size of 5-10 micrometers, while the ferrite grains had an average size of 1-5 micrometers.
The observation of the microstructure of HT200 steel with higher magnification revealed that some of the ferrite and pearlite bands were not homogeneously dispersed, i.e.had a large number of discontinuous fine pearlitic and ferritic grains. This discontinuity was due to the existence of other fine phases such as carbide particles or cementite particles.
To further examine the microstructure and composition of HT200 steel, energy-dispersive spectroscopy (EDS) was employed, providing the elements present in the material. The EDS analysis revealed that HT200 steel is composed of, Iron (Fe): 83.48%, Carbon (C): 1.94%, Manganese (Mn): 0.54%, Silicon (Si): 1.09%, Chromium (Cr): 0.54%and Aluminum (Al): 0.34%.
The aforementioned results demonstrate that HT200 steel generally features finer grain sizes, a duplex microstructure of ferrite and pearlite, with some secondary phases present. Such a microstructure is generally beneficial for improved toughness and wear resistance. The chemical composition of HT200 steel is also beneficial for improved mechanical properties, as it has high levels of Fe, and relatively high levels of alloying elements such as Mn, Cr, and Al.
In conclusion, HT200 steel has a hypereutectoid pearlitic-ferritic microstructure with some secondary phases present. Its microstructure is characterized by fine grains, with some discontinuities apparent due to the presence of carbide and cementite particles. Its chemical composition is beneficial for improved mechanical properties, such as increased strength, wear resistance, and toughness.
