Ttt diagram of eutectoid steel and martensitic transformation
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Ttt diagram of eutectoid steel and martensitic transformation





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Ttt diagram of eutectoid steel and martensitic transformation Ttt diagram of eutectoid steel and martensitic transformation Presentation Transcript

  • Muhammad Umair Bukhari 03136050151
  •  T-T-T diagram is plotted for different length of times and temperature These curves gives us the information of transformation for different phases With the help of T-T-T diagram we can control the phase transformation by changing the conditions
  •  The left side of C- shape curve is Austenitic region The right side of C- shape curve contain three regions • Pearlite • Pearlite+Bainite • Bainite
  •  The left line of C-shape curve shows the start of phase transformation The right line shows the end of transformation The dotted line is theoretically determined line shows 50% transformation
  • The region below Ms is martensitic regionMs shows start and Mf shows end of Martensite transformation
  •  Martensitic crystal structure is Body centered tetragonal (BCT) It is the intermediate structure of Fcc and Bcc It forms due to the realignment of atoms from austenitic structure to martensitic structure
  •  Atoms arrange themselves to move towards stability from higher temperature to lower temperature Only realignment is occur but there is no diffusion There is no concentration change in parent and product phase
  •  Due to the realignment of atoms the lattice smmetry is different from the parent phase
  •  At 300oc the bainite and martensite are formed along curve 3 As temperature decreases the bainite formation rate is lowers At 160oC for 20min the 50% martensite and austenite are formed
  •  Mf line which shows the end of martensite transformation But 100% martensite can’t be formed even theoretically at absolute zero At room temperature there is 3% retaine austenite
  •  The reason is the retained autenite As the little amount of austanite is remain it is difficult to transform That’s why Mf lline is showed dotted
  • •Regular arrangements of atoms in acrystal is called order.•Order of atoms in crystals are mostlyat room temperature
  •  Irregular arrangements of atoms in a crystal is called disorder . Disorder mostly occurs at elevated temperature.
  •  In most substitutional solid solutions two kinds of atoms A and B are arranged more or less random on the atomic sites of the lattice. In solution of this type of a change in temperature is to Increase or decrease of a thermal vibrations. If the ordered solution is heated above Tc the atomic arrangement becomes more or less random again and the solution is said to be disordered.
  •  The gold and copper atoms of AuCu3 above a critical temperature of about 390’C are arranged more or less random on the atomistic sites of FCC lattice as shown in following figure. Below the critical temperature the gold atoms in a perfectly ordered alloy occupy only the corner position of the unit cube and the copper atoms on the face centered cubic as shown in following figure.
  •  When the periodic arrangement of A and B atoms persists over longer range distance in a crystal than it is called a long range order.