Failure Analysis of H13 Tool Steel in Aluminum Extrusion Dies

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Failure Analysis of H13 Tool Steel in Aluminum
Extrusion Dies

• Mesut Varlioglu, Taehyung Kim
• Joseph Benedyk, Philip Nash, Sheldon Mostovoy
• Thermal Processing Technology Center
• 01/16/04

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Fracture Surface Analysis for the die exposed to
aluminum.
The previous crack surface investigation was done
with the dies exposed to caustic. A slice with 10
mm thick from the center of the die was cut.
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1
Die parts after cutting operation.
The Die piece. Red circles show the area observed
in SEM.
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SEM Pictures
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2
3
7 6 5 4 3 1 2 8 9
Area 1 Area 2
The chemical distributions of Zn and Al in the
interface of fracture and interaction area.
With poor precision.
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Surface Analysis of the extrusion material
2
1
Inside of the extrusion material.
Material surface.
Chemical compositions of two points. With poor
precision.
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Step Loading Test Procedure

• The tensile test specimen that has a cylinder
  gap inside is filled with 7XXX series Al alloy
  and heated in 550 C.
• Then, the inside part is closed with a screw.
• In the high temperature tensile test machine,
  the specimen is heated at around 550 C and
  started to load at P/8 in each cycles in 8 hour
  period.
• Then the data from the specimen filled with
  other substances including air is compared. Also,
  the fracture surface is compared with the real
  fracture surface of the bridge of the die.

Source ASTM F 1624-95.
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Specimen Shape
Specimen cross section was calculated for 200 ksi
tensile strength and 12 kips max. load for the
Instron Machine.
19/64 in.
Specimen after machined.
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Heat Treatment and Test Conditions

• Heat Treatment
• Atmosphere Nitrogen.
• Austenitization Temperature 1850 F, 1 hour.
• Hardness 52 HRC.
• Tempering Temperature 1100 F, 6 hrs.
• Hardness 49 HRC.
• Rising Load Test
• Loading Rate 5 lbs/s.
• Test Temperature 521 C.
• Load in each step 1.5 kips (8 steps).

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First Test Result
Stress 142 ksi No fracture.
Load vs. Time
Load vs. Displacement
Test material H13 filled with 7116 Al alloy.
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Second Test
Stress 180 ksi Fracture
after 9.8 hours.
Load vs. Time
Mechanical properties of H13 at 550 C
Source ASM Specialty Handbook, Tool Materials,
1995, p.140-141.
Same Sample.
Load vs. Displacement
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3 Sample Conditions
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Test Results
Stress 237.5 ksi
Load vs. Time
Stress 88 ksi
Load vs. Displacement.
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Samples after the test
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IV DETERMINING THE RETAINED AUSTENITE IN DIE
STEEL
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Metallograhic Method for Retained Austenite
Calculations

• The method can be summarized with 4 stages
• 1- Mechanical Polishing
• 2- Electrolytic Polishing
• Direct power source (0-10 V, 0-5 A)
• Electrolyte 10 gr CrO3, 100 ml distilled water
  in a 250 ml beaker.
• Conditions 4 V, 1.6 A/in2, 15 to 30 s.
• 3- Copper Deposition Solution of 955 ml H2O,
  14.2 gr CuSO4 and 7.4 ml H2SO4is swabbed in 5 to
  10 seconds.
• The copper deposition can be seen by green light
  filter.
• 4- Copper Coloring Solution of 1 gr Na2S, 100 ml
  distilled water, 1 ml HNO3 in ph of 5 is applied
  to the sample surface by cotton in 5 to 20
  seconds.
• Source E.J. Klimek, A Metallograhic Method for
  Measuring of Retained Austenite, 1995.

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Results
1750 ºF 1850 ºF
1950 ºF
20 ?m
0 h
0 h
0 h
(a) (b)
8 h
8 h
8 h
H13 samples that austenitized at different
temperatures and tempered at 1100 ºF at different
times. 1000x.
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Pearlite Study
Grain size was tried to calculated in this
reseach. Austenitization Temp. 1750 F, 1850 F,
1950 F 1 hour 1400 F in 13-15 min to hit pearlite
nose. Then air cool.
Source Ray Reynoldson, The Heat Treatment of
Extrusion Tools Using Fluidized Bed Technology,
ET 1996 Seminar.
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Micrographs
1750 F, 1000 x. 1850 F, 1000x.
1950 F, 1000x.
ASTM Grain Size 10.52 ASTM Grain Size 9.74
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Alternative for U-Bend Device
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FUTURE WORK

• To continue the SEM analysis on the die not
  exposed to caustic.
• To continue the metallographic method for
  revealing the retained austenite and compare the
  results with other dies as well as Rising Load
  Test specimens.
• Duplicate the rising load test results by using
  different filling material, testing temperature,
  loading rate.
• Continue investigating fracture surfaces in
  different dies.