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During heat treatment of steel, the hardness of various structures in increasing order is
[ME 2003]
  • a)
    martensite, fine pearlite, coarse pearlite, spherodite
  • b)
    fine pearlite, martensite, spherodite, coarse pearlite
  • c)
    martensite, coarse pearlite, fine pearlite, spherodite
  • d)
    spherodite, coarse pearlite, fine pearlite, martensite
Correct answer is option 'D'. Can you explain this answer?
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During heat treatment of steel, the hardness of various structures in ...
Spherodite, Coarse Pearlite, Fine Pearlite, Martensite
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During heat treatment of steel, the hardness of various structures in ...
Heat Treatment of Steel and Hardness of Structures

Heat treatment is a process used to alter the microstructure of a material, particularly steel, in order to improve its mechanical properties. During heat treatment, steel undergoes heating and cooling cycles to achieve desired hardness, strength, and other properties. The hardness of steel structures can vary depending on the cooling rate and the resulting microstructure.

Hardness in Increasing Order

The correct order of hardness of various structures during heat treatment of steel is:

D) Spherodite, Coarse Pearlite, Fine Pearlite, Martensite

Now, let's understand the hardness of each structure in detail.

Spherodite:
Spherodite is a microstructure formed when steel is heated to a temperature just below the eutectoid point and then slowly cooled. It consists of small, spherical cementite particles embedded in a ferrite matrix. Spherodite has the lowest hardness among the mentioned structures due to the presence of soft ferrite and the absence of hard, needle-like cementite.

Coarse Pearlite:
Coarse pearlite is a microstructure formed when steel is heated to a temperature below the eutectoid point and then cooled rapidly. It consists of alternating layers of ferrite and cementite. Coarse pearlite has a higher hardness compared to spherodite due to the presence of hard cementite particles.

Fine Pearlite:
Fine pearlite is a microstructure formed when steel is heated to a temperature just below the eutectoid point and then cooled rapidly. It has a similar composition to coarse pearlite, but the ferrite and cementite layers are much smaller in size. Fine pearlite has a higher hardness compared to coarse pearlite due to the increased number of grain boundaries and smaller cementite particles.

Martensite:
Martensite is a microstructure formed when steel is heated to a temperature above the eutectoid point and then rapidly cooled, usually by quenching in water or oil. It is a supersaturated solid solution of carbon in iron. Martensite has the highest hardness among the mentioned structures due to its unique, needle-like structure and high carbon content.

In conclusion, during the heat treatment of steel, the hardness of various structures in increasing order is spherodite, coarse pearlite, fine pearlite, and martensite.
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During heat treatment of steel, the hardness of various structures in ...
Spherodite, Coarse Pearlite, Fine Pearlite, Martensite
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During heat treatment of steel, the hardness of various structures in increasing order is[ME 2003]a)martensite, fine pearlite, coarse pearlite, spheroditeb)fine pearlite, martensite, spherodite, coarse pearlitec)martensite, coarse pearlite, fine pearlite, spherodited)spherodite, coarse pearlite, fine pearlite, martensiteCorrect answer is option 'D'. Can you explain this answer?
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