Home/ Questions/Q 938
Next
In Process
metagate.in
Platinum
Asked: 2020-04-23T00:19:32+05:30 In:

BARC-14: What is the effect of grain size on the TTT Curves of Eutectoid Steel?

BARC-14: What is the effect of grain size on the TTT Curves of Eutectoid Steel?
BARC-14: What is the effect of grain size on the TTT Curves of Eutectoid Steel?
BARCgrain sizeheat treatmentsteelttt curve
Share

    You must login to add an answer.

    Need An Account,

    3 Answers

    1. Silver Student
      This answer was edited.

      1. Decrease in Grain size  the curve shifting towards left which means increase in critical cooling rate. Grain size increases,  critical cooling rate is decreases. Reason : Fine grain structure have high grain boundary area. Rate of diffusion is high in grain boundary area. So rate of diffusion isRead more

      1. Decrease in Grain size  the curve shifting towards left which means increase in critical cooling rate. Grain size increases,  critical cooling rate is decreases.

      Reason :

      Fine grain structure have high grain boundary area. Rate of diffusion is high in grain boundary area. So rate of diffusion is high in fine grain structure which causes formation of pearlite (diffusion controlled process). But in coarse grain structure,  grain boundary area is low. So that less nucleation site for pearlite. More Possibility for formation of martensite ( diffusion less process). so that , coarse grain structure, decreases the crtical cooling rate and move the curve towards right.

       

      See less
      • 4
    2. Platinum

      Decrease in grain size shifts TTT curve towards left whereas increase in grain size shifts TTT cure towards right. Brcause decreases in grain size means grain boundary area increases. Grain boundary area acts as a nucleation sites for the formation of ferrite and pearlite from the austenite. So theRead more

      Decrease in grain size shifts TTT curve towards left whereas increase in grain size shifts TTT cure towards right. Brcause decreases in grain size means grain boundary area increases. Grain boundary area acts as a nucleation sites for the formation of ferrite and pearlite from the austenite. So the critical cooling rate increases. And the transformation kinetics also increases and shifts the TTT curve towards left. But when the grain size increases the grain boundary area decreases and the nucleation sites for the formation of ferrite and pearlite also decreases. And it also decreases the critical cooling rate and transformation kinetics also decreases. Hence TTT curve is shifted towards right.

      See less
      • 3

    3. Increase in grain size shifts the TTT curve to the right because the coarser grain size will have less number of nucleating sites for the formation of pearlite due to which hardenability increases  but not significantly as the coarser grain have low toughness

      Increase in grain size shifts the TTT curve to the right because the coarser grain size will have less number of nucleating sites for the formation of pearlite due to which hardenability increases  but not significantly as the coarser grain have low toughness

      See less
      • 1