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Asked: 2020-04-21T13:23:15+05:30 In:

BARC-12: Most alloying elements increase the Hardenability of Steel except Cobalt. Why does Cobalt behave differently?

BARC-12: Most alloying elements increase the Hardenability of Steel except Cobalt. Why does Cobalt behave differently?
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    3 Answers

    1. Silver Learner

      Cobalt doesn't dissolve in iron. It is comes out from iron. Then cobalt have crystal structure HCP, Which has some similarity with cubic structure. Ferrite also has cubic structure. So, when we add cobalt element it is act as nucleating site for ferrite. It suppress the formation of martensite. So iRead more

      Cobalt doesn’t dissolve in iron. It is comes out from iron. Then cobalt have crystal structure HCP, Which has some similarity with cubic structure. Ferrite also has cubic structure. So, when we add cobalt element it is act as nucleating site for ferrite. It suppress the formation of martensite. So it does not improve hardenability. And cobalt shift TTT curve towards left.

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    2. Iron Metallurgist, quality assurance (Hot strip mill)
      This answer was edited.

      The presence of Cobalt is helpful for nucleation and growth of Pearlite.therefore,steels containing this element are difficult to harden.

      • The presence of Cobalt is helpful for nucleation and growth of Pearlite.therefore,steels containing this element are difficult to harden.

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    3. Platinum

      Almost all the alloying elements shifts the TTT curve towards right except cobalt. If TTT curve will shift towards right it will increase the hardenability. Because it suppresses the formation of pearlite . But cobalt acts as a nucleation site for pearlite formation. So it shifts the TTT curve towarRead more

      Almost all the alloying elements shifts the TTT curve towards right except cobalt. If TTT curve will shift towards right it will increase the hardenability. Because it suppresses the formation of pearlite . But cobalt acts as a nucleation site for pearlite formation. So it shifts the TTT curve towards left and it suppresses the martensite formation.So hardenability decreases.

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