Heat Treating: The How and Why of Quenching Metal Parts
ResearchSummary
1. In-Situ Synchrotron Phase Identification
During Heating and Cooling of DP980,
and Its Implication to the Formability
Jorge Cisneros
Advisor: Xin Wu
Wayne State University
Detroit, MI 48202
3. Problem Statement
• Increasing strengths of advanced high strength steels
(AHSS), cause stamping presses to quickly approach
tonnage limitation, becoming a limiting factor for
application of DP980 or higher grades. (1)
• For many AHSS, forming limit decreases with increasing
strength
• Fracture in specific locations from concentrated
strains
• Transformation between Martensite, Austenite, and
Ferrite is of great technological importance for UHSS
• Understanding of phase transition allows better design
of microstructure and process to compromise strength
and ductility
• Traditional ex-situ method can’t provide actual phase
transformation during heating and cooling
4. Objective
• Prepare test coupons with various induction heating
profiles
• Develop new tensile test coupon to investigate local
properties
• Investigate the induction heating process window that
could be applied for other laboratory scale formability
tests.
• Verify effect of heating via tensile and harness test.
• To achieve hopeful goals of total elongation improve
20% by induction softening and less than 5% unevenness
inside heat treated zone.
• Determine phase transmission vs. temperature curve for
different holding times, using synchrotron X-ray
diffraction from Argonne National lab.
6. Background
TABLE 1 METALLURGY AND GENERAL CHARACTERISTICS OF VARIOUS ADVANCED HIGH STRENGTH STEEL
Figure 2 typical microstructure of dp steel Figure 3 Total elongation vs. ultimate tensile
strength
7. Background
Figure 4 engineering stress-strain curve
of five advanced high strength steels
Figure 5 Cooling schedule in the
production of DP strips
8. Experimental Design
• Equipment:
– Induction Power Supply
– Controller
– Heating Coil
– Furnace tube
• Configuration:
900°C
30s
400°C
Programmable
Temp. Controller
T/C Coil
Feedback
Induction
Power
Supply
DP980
PC
8-Channel T/C
BN coating to reduce oxidation
10. Tensile Test
• Measure w & t with two extensometers, or w & R
where R from interrupt test;
R = ew/et = ln(w/wo)/ln(t/to)
• True strain el :
el = (ew + et) = ew (1+ 1/R) = (1+ 1/R) ln(w/w0)
• True stress,
from t/t0=(w/w0)1/R
sl = F/(wt)=F/[wt0(w/wo)1/R]
11. In-Situ Approach and
Experiments
• All the test coupons were made of ASP 1.2 mm GA
DP980 and Boron Steel
• In-Situ X-ray diffraction of Steel using
synchrotron source Beam line 11 at Arrgone APS
– Beam size 0.10804 Å
– Beam Power 115 kev
– Detector distance 1600 mm
– Heating rate 50 oC/min
– Hold time 50 , 100, 600 seconds
– Cooling rate 60 oC/min
• Microstructure Examination to verify final phases
of material
12. In-Situ Set Up
Thermal camera
Video camera
Heat gun
Data acquisition
computer controlled
through wifi
13. Analysis of X-ray diffraction
• Diffraction analysis software FIT2D
– Calibrated using known sample CeO2
– Used to process raw Tiff diffraction
files
• Time lapse video of diffraction rings
and intensity value used to identify
key events
• Phase of experimental data identified
with known diffraction patterns using:
– Crystallography open Database (COD)
– International Center for Diffraction
Data (ICDD)
14. Hardness Test and R Value
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
0 0.1 0.2 0.3 0.4 0.5
RValue
Strain Length (εl)
Elogation vs. R value
No heat
700C Slow
800C Slow
800C Fast
900C Slow
900C Fast
• Approaches asymptote of 0.3
• No clear trend for low values
of strain
• Fast cooling shows high hardness
• Reduction in hardness from heating
0
50
100
150
200
250
300
350
400
450
500
Hardness(HV)
WC 1 WC 2 AC1 AC 50 AC100
Hardness Results
16. Microstructure Examination
As-received (no heating) COOLING FROM 900 °C
• Martensite clusters have been dissolved via heating
• Fast cooling produced finer grain structure
• Samples heated to 800°C have finer grain than 1,000°C
COOLING FROM 800 °C COOLING FROM 1000 °C
2 °C/S
2 °C/S
2 °C/S
20 °C/S
20 °C/S20 °C/S
20 µm
Argonne 100
20 µm
Argonne 25
19. DP980 Different Hold Times
30 oC
847 oC
950 oC
675 oC
201 oC
Holding time = 50s Holding time = 100s
101
200
211
202
101
200
211
202
111
200
202
311
222
222
311
202
200
111
20. Final product results
• Air cooling left approximately 10%
retained austenite
• Hold time did not show much effect on
final composition
• Hold time needs to be long enough to
ensure complete conversion
• 100 second non complete conversion
Hold time Alpha iron % Austenite %
600 89.3 10.7
100 87.2 12.8
50 92.7 7.3
Volume % of final product
21. Conclusion
• X-ray diffraction data allow a highly detailed
view of the re-crystalization of Steel.
• Peak heating temperature and cooling rate are the
two most important parameters.
• New tensile test sample showed consistent results
• Induction local heating resulted in strength
reduced, and formability is significantly
increased for DP980 steel sheet.
• Boron steel has complete transformation to
ferrite.
• Fast cooled shows fine grain structure.
• Water cooled is significantly harder than air
cooled
22. Future work
• Use GSAS to separate martensite from
ferrite Volume fraction
• In-situ compression to create martensite
• Analysis of higher miller index to better
identify martensite from ferrite
• EBSD to obtain high resolution
microstructure image
• Repeat trials In-situ with quenching
furnace.
23. Acknowledgement:
Many thanks to my parents for their encouragement of continuing my
education and helping to fund both classes and my research.
Thank you to Dr. Xin Wu for his guidance, inspiration, equipment, and
materials. The trip to Argonne National lab changed everything.
This study is supported by US Department of Energy-US Advanced Materials
Partnership (DOE-USAMP) under Award Number DE-FC26-02OR22910 and
subcontracted from Auto Steel Partnership (A/SP) under contract No. 440850,
and by matching fund from member companies.
The assistance by Dr. Yang Ren of Argonne National Laboratory on
Synchrotron analysis is greatly appreciated.
25. Other works
• Non-Linear strain path for
AHSS
• Ultra-sonically welded
battery tabs
• High temperature tensile
test with digital image
correlation
• Nano-indenter hardness test
with actual nano tip
