Mechanical Behavior of CrMo Steel with Tempered Martensite and Ferrite-Bainite-Martensite Microstructure

1. Dr. A. Salemi Golezani
Department of Materials Eng., Islamic Azad University-
Karaj Branch
Mechanical Behavior of CrMo Steel with
Tempered Martensite and Ferrite-Bainite-
Martensite Microstructure

2. From Low Carbon to Advanced High Strength
Conventional Steels
 Low Carbon
 Bake Hardenable
 Solid Solution Strengthened
 High Strength Low Alloy
elAdvanced High Strength Ste
 Dual Phase
Complex Phase
 Transformation Induced Plasticity
 Martensitic

3. Complexe phase steels which contain martensite, bainite,
ferrite and/or retained austenite in quantities sufficient to
produce unique mechanical properties. These steels
exhibit an excellent combination of high strength and high
ductility results.
Definition of Complex Phase

4. Application of Complex Phase
 Automotive
 Pressure Vessels
 Pipelines

5. Materials
C Cr Mo Mn Si P S
0.35 1.10 0.23 0.52 0.36 0.014 0.006

6. Heat Treatment
 Quench Temparing
 Step Quenching

7. Quench Tempering
850o
C, 1hr
650o
C, 1hr
Time
Temperature
Oil-quenched

8. Step Quenching
F+B+M
F+(B+M)
F+(B+M)
F1+(B+M)
F2+(B+M)
F1+(BL+M)
F2+(BL+M)

9. Step Quenching
850o
C, 1hr
650o
C
4, 8, 12 min
430, 400o
C
4min
Water-quenched

10. Microstructure
35µm
T: 850O
C, t: 1 hr o.q
T:650O
C,t:1hr

11. 35µm
650O
C, 4 min 650O
C, 8 min
650O
C, 12 min
T:850 O
C, t: 1 hr

12. Color Tint Etching
F
B
M

13. Strength
400
500
600
700
800
900
1000
FBM
-1
FBM
-2
FBM
-3
FBM
-4
FBM
-5
FBM
-6
M
-T
UTS
YS
Strength(MPa)

14. Ductility
20
30
40
50
60
70
FBM
-1
FBM
-2
FBM
-3
FBM
-4
FBM
-5
FBM
-6
M
-T
Reduction of area
Elongation
Microstructure
Ductility(%)

15. CVN
0
15
30
45
60
75
90
FBM
-1
FBM
-2
FBM
-3
FBM
-4
FBM
-5
FBM
-6
M
-T
Microstructure
ImpactEnergy(J)

16. Yield Drop Effect

17. %25
%31
%39FBM-1
FBM-2
FBM-3 200X
Ferrite Volume Fraction

18. Yield Drop Effect
Pinning of dislocation by:
 Solute atoms
 Formation of short range order region near dislocation
 Electrical charge of solute atoms and depositing on
dislocations
 Dislocation generation

19. Fractography
Tempered Martensite Ferrite-Bainite-Martensite
20µm

20. Fractography
2µm

21. Conclusions
 Mechanical properties of tempered martensite, is
more favorable than F-B-M microstructure.
 Decreasing bainite transformation temperature from
430 to 400o
C, increases yield and tensile strength but
decreases in impact energy.

22. Conclusions
 Fractography of the Charpy impact specimens
indicates ductile and transgranular fracture
mechanisms in quench tempered and step quenched
specimens, respectably.
 Yield drop effect was observed in F-B-M
microstructure with ferritic matrix.

23. Thank You for Your AttentionThank You for Your Attention