Austenitization of H13 Tool Steels

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Austenitization of H13 Tool Steels
Swati Purohit Prof. Calvin Tszeng
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Objective

• To study the carbide dissolution behavior for
  the H13 tool steels heat treated in a range of
  austenitizing condition.
• Quantify the carbide dissolution behavior bye
  advance electron microscopy and compare against
  the mathematical model developed to study the
  diffusion processes resulting from the change of
  the microstructure.

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Work Plan

• Literature survey on heat-treatment
  microstructure and related properties of Hot Work
  Tool Steels
• Knowing various Equipment
• Design of Experiment
• Model development

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Composition
AISI H13 Tool Steel C 0.35 Si
1.00 Cr 5.00 Mo 1.50 V 1.00

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Carbides Found in the H13 Tool Steel
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As Received Sample
20 µm
20 µm
Magnification 400X Etchant 2-3 Nital
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Heat-Treatment Cycle
Temperature
Holding Time
2000C/S
2000C/S
Temperature
Time
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Magnification 400 X Etchant 4 Picral
1020oC-5
1020oC-1
20 µm
20 µm
1020oC-40
1020oC-20
20 µm
20 µm
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Magnification 400 X Etchant 4 Picral
1050oC-5
1050oC-20
20 µm
20 µm
1050oC-40
20 µm
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Magnification 400 X Etchant 4 Picral
1080oC-5
1080oC-1
20 µm
20 µm
1080oC-20
1080oC-10
20 µm
20 µm
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SEM of the As Received Sample
Etchant 2-3 Nital
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SEM of the Heat- Treated Samples
1020oC-1 Minute
1020oC-5 Minute
1020oC-20 Minute
1020oC-40 Minute
Etchant 4 Picral
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SEM of the Heat- Treated Samples
1050oC-5 Minute
1050oC-20 Minute
1050oC-40 Minute
Etchant 4 Picral
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SEM of the Heat- Treated Samples
1080oC-1 Minute
1080oC-5 Minute
1080oC-10 Minute
1080oC-20 Minute
Etchant 4 Picral
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1020oC-1 Minute
Non uniformity of the carbides
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1020oC-5 Minute
Big carbides are dissolved and form the cluster
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1080oC-5 Minute
Big Carbides are along the grain boundary
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1050oC-20 Minute
Clusters of carbides at the grain boundary
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1050oC-40 Minute
Some carbides are on grain boundary and some are
in the matrix. Mostly round circular particle are
along the grain boundary.
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Volume Fraction Carbide after Austenitization
Volume Fraction Carbide of the as Received Sample
9.17
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Volume Fraction Carbide Vs. Temperature
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Volume Fraction Carbide Vs. Holding Time
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Mathematical Model
Model described by Whelan
Supersaturation
Cp
Concentration
Ci
Cm
Distance
Where,
CiConcentration of solute at particle/matrix
interface
CpConcentration of solute inside the precipitates
CmConcentration of solute in matrix
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Volume Fraction of carbides after Dissolution
time t,
For the case of the dissolution of VC
Dm Diffusivity of the V in the Austenite We
have DoV 0.373 10-4 Q
240 10 3 J/mol T 1293oK
Dm Do exp(-Q/RT)

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? JK/mol


? J/mol
1

80.93
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Dm 4.1010-17 m2/s fo 2.16 ro 1.05 µm
t Holding time (s)
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Future Plan of Work
Calculate a and find the volume fraction of
carbides formed after austenitization and
compare it to the experimental data.
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References
1. Michael L. Schmidt, Effect of Austenitizing
Temperature on the Structure and Mechanical
Property Behavior of Laboratory Treated Specimens
and Large Section Sizes of H13 Tool Steel, SDCE
14 th International Die Casting Congress and
Exposition, May 11-14, 1987, Canada   2. John
Agren Kinetics of Carbide Dissolution,
Scandinavian Journal of Metallurgy, 1990 vol.19
pg.2-8   3. John Agren, Zi-Kui Liu, Lars Hoglund,
Bjorn Jonssons, An Experimental and Theoretical
Study of Cementite Dissolution in an Fe-Cr-C
Alloy, Metallurgical Transaction A, August 1991,
vol. 22A, pg. 1745 4. G. Roberts, G. Krauss, R.
Kennedy, Tool steels, ISBN 3-1272-
00349-0784, Publication ASM International
Materials Park, Ohio, 2000   5. S. F. Dirnfeld,
B. M. Korevaar and F. Vant Spijker,
Transformation to austenite in a fine grain tool
steel, Metallurgical Transactions, June 1974,
vol. 5 pg. 1437-44   6. R. A. Grange, The rapid
heat treatment of steel, Metallurgical
Transactions, Jan 1971, vol. 2 pg. 65-78   7.
Derek L. Cocks, Heat Treatment of H13 Die
Casting Tool Steel, November 1998
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Volume Fraction of V rich Carbide (MC)
Volume Fraction of MC carbide in As Received
Sample 2.16
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Quantitative Analysis of The Matrix
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1020oC
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1050oC
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1080oC
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1050oC-5 Minute
Large difference in the size of the carbides can
be seen
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1050oC-40 Minute
Still some big carbides can be seen in the matrix
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1050oC-40 Minute
Generally small carbides are on the grain
boundary and the bigger Carbides are in the
matrix.