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PPT on rail regarding the description of pearlitic and bainitic steel for its application in rail industry. Regarding it's properties with respect to hardness related to 340,370. Also regarding it's microstructure having pearlitic in nature. It's should not have martensitic structure due to it's brittle nature. Fine pearlitic steel will have its lamellar structure. PPT on rail regarding the description of pearlitic and bainitic steel for its application in rail industry. Regarding it's properties with respect to hardness related to 340,370. Also regarding it's microstructure having pearlitic in nature. It's should not have martensitic structure due to it's brittle nature. Fine pearlitic steel will have its lamellar structure. PPT on rail regarding the description of pearlitic and bainitic steel for its application in rail industry. Regarding it's properties with respect to hardness related to 340,370. Also regarding it's microstructure having pearlitic in nature. It's should not have martensitic structure due to it's brittle nature. Fine pearlitic steel will have its lamellar structure. PPT on rail regarding the description of pearlitic and bainitic steel for its application in rail industry. Regarding it's properties with respect to hardness related to 340,370. Also regarding it's microstructure having pearlitic in nature. It's should not have martensitic structure due to it's brittle nature. Fine pearlitic steel will have its lamellar structure. PPT on rail regarding the description of pearlitic and bainitic steel for its application in rail industry. Regarding it's properties with respect to hardness related to 340,370. Also regarding it's microstructure having pearlitic in nature. It's should not have martensitic structure due to it's brittle nature. Fine pearlitic steel will have its lamellar structure. PPT on rail regarding the description of pearlitic and bainitic steel for its application in rail industry. Regarding it's properties with respect to hardness related to 340,370. Also regarding it's microstructure having pearlitic in nature. It's should not have martensitic structure due to it's brittle nature. Fine pearlitic steel will have its lamellar structure. PPT on rail regarding the description of pearlitic and bainitic steel for its application in rail industry. Regarding it's properties with respect to hardness related to 340,370. Also regarding it's microstructure having pearlitic in nature. It's should not have martensitic structure due to it's brittle nature. Fine pearlitic steel will have its lamellar structure. PPT on rail regarding the description of pearlitic and bainitic steel for its application in rail industry. Regarding it's properties with respect to hardness related to 340,370. Also regarding it's microstructure having pearlitic in nature. It's should not have martensitic structure due to it's brittle nature. Fine pearlitic steel will have its lamellar structure. PPT on rail regarding the description of pearlitic and b

1. Multiphase Structures in Case Hardening
Steels following Continuous Cooling
H. Roelofs, S.Hasler, L. Chabbi, U. Urlau, Swiss Steel AG
J. Chen, H.K.D.H. Bhadeshia, University of Cambridge

2. pearlite
ferrite
bainite
Typical steel structure of a MnCr-
case hardening steel Howtomasterstructure
andhardnessbyrolling
conditionsandsteel
composition?

3. •measuring CCT diagrams
•hot rolling trials
•simulating the steel‘s microstructure on a computer
„Complete Calculation of Steel
Microstructure of Strong Alloys“
Excellent agreement for isothermal
treatments
Development of new products

4. Chemical
composition
(C, Mn, Si, Ni,
Mo, Cr, V)
Cooling rate
Austenitic grain
size (AGS)
Steel
Structure
Modified Avrami
model including
simultanuous
nucleation and growth
rates of
•allotriomorphic ferrite,
•pearlite,
•widmanstätten ferrite,
•bainite and
•martensite
The model

5. Dilatometry: experimental conditions
Steel composition (wt.-%):
Cooling rates (K/s): 0.2, 0.3, 0.6, 0.8, 1.0, 1.6, 3.0, 6.0
Austenitic grain size (mm): 13, 23
C Si Mn Ni Cr Mo
0.17 0.19 1.20 0.076 1.05 0.008

6. as measured as calculated
Comparison for AGS = 13 mm

7. as measured as calculated
Comparison for AGS = 23 mm

8. Furnace
Precision
Sizing Mill
Cooling Bed
(16 –64 mm)
Descaler
Shears
Coilers
Garrrett
(16 –38 mm)
Finishing Mill
Stelmor
(5.5 –16 mm)
Water
Boxes
Industrial trials: layout of hot rolling mill

9. •sampling for AGS determination is sometimes difficult
•AGS and phase contributions vary over the cross-
section of the wire/bar
•the cooling curve is not linear
Challenges under real industrial conditions

10. Stelmor line
Positions of sampling: 6.5 mm wire
sampling
phase
transformation
Furnace
Precision
Sizing Mill
Finishing Mill
Stelmor
Water
Boxes

11. Distance from surface Austenitic grain size (mm)
X Min Max Stddev
surface: 0 20.3 15.2 26.3 2.8
mid-radius 1/2 25.4 22.7 29.4 2.7
centre: 1 36.2 26.3 55.7 8.0

Average over
radius 27.3 21.4 37.1
C Si Mn Ni Cr Mo
0.16 0.21 1.21 0.130.980.015
Steel composition (wt.-%):
Cooling rate (K/s): 0.34 K/s (800-500°C)
mean AGS as calculated
by hot rolling simulation
model: 33.8 mm
Input data for modeling

12. Comparison calculation versus experiment
6.5 mm wire

13. Garrett line
Position of sampling: 23.5 mm wire
sampling
Furnace
Precision
Sizing Mill
Coilers
Garrrett
Water
Boxes

14. Distance from surface Austenitic grain size (mm)
X Min Max Stddev
surface: 0 26.0 22.7 31.3 4.0
mid-radius 1/2 31.8 26.3 35.7 3.7
centre: 1 49.5 31.3 167.1 20.9

Average over
radius 35.8 26.8 78.0
C Si Mn Ni Cr Mo
0.20 0.19 1.23 0.111.000.017
Steel composition (wt.-%):
Cooling rate (K/s): 0.16 K/s (800-500°C)
Input data for modeling
large scattering AGS
due to the hot rolling
deformation

15. Comparison calculation versus experiment
23.5 mm wire

16. Bar production line
Position of sampling: 36 mm
Furnace
Precision
Sizing Mill
Cooling Bed
Water
Boxes
C Si Mn Ni Cr Mo
0.17 0.19 1.22 0.091.030.018
Steel composition (wt.-%):
Cooling rate (K/s): 0.80 K/s (800-500°C)
sampling

17. Distance from surface Austenitic grain size (mm)
X Min Max Stddev
surface: 0 19.3 14.1 28.3 4.2
mid-radius 1/2 47.8 27.8 71.4 13.2
centre: 1 66.9 29.4 250.7 31.8

Average over
radius 44.7 23.8 116.8
excellent
good
modest
Comparison calculation versus experiment
36 mm bar

18. Conclusions
•the predictions of the model agree qualitatively well
with the measured data from industrial hot rolling
distinguishing ferrite, pearlite and „remaining phases“
•there is a first indication that the model underestimates
bainite and overestimates Widmannstätten ferrite (this
is still under investigation)

19. Outlook
The quantitative analysis of phase contributions in modern
high-strength bainitic-martensitic steels is a very
challenging task.
Together with advanced EBSD techniques this model will in
future be applied to bring more light into the microstructure
of such steels.

20. High strength bainitic steel
Stelmor line, 13 mm wire rod
cooling rate ~ 3.0 K/s
very fine steel structureC Si Mn Cr Mo
0.15 % 1.19 % 1.50 % 1.19 % 0.31 %

21. 0
50
100
150
200
23°C -20°C -40°C
Charpy impact energy ISO-V in J Rp
0.2=1001MPa
Rm =1135MPa
A5 =15%
Z = 68 %
High strength bainitic steel
Stelmor line, 13 mm wire rod
Estimated cooling rate ~ 3.0 K/s

22. Thank you !
Muchas gracias !