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![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]](https://image.slidesharecdn.com/2cbcb08e-b3c2-4fae-8b0f-824fe1c62d59-151011174508-lva1-app6892/85/ResearchSummary-10-320.jpg)
ResearchSummary
- 1. In-Situ Synchrotron PhaseIdentification During Heating and Cooling of DP980, and Its Implication to the Formability Jorge Cisneros Advisor: Xin Wu Wayne State University Detroit, MI 48202
- 2. Outline • Problem statement •Objective • Background • Approach and Experiments • Results • Conclusion • Future work
- 3. Problem Statement • Increasingstrengths 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 testcoupons 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.
- 5. Background The Tensile Test 𝑺= 𝑭 𝑨0 𝒆 = ∆𝒍 𝒍0 𝝈 = 𝑺 ∗ 1 + 𝒆 𝜺 = 𝐥𝐧 𝒍 𝒍0 = 𝒍𝒏 1 + 𝒆
- 6. Background TABLE 1 METALLURGYAND 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 engineeringstress-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
- 9. Experimental Design 0 200 400 600 800 1000 1200 0 5001000 1500 Temperature(C) Time (S) Heating Profile Slow Cooling 800C 850C 900C 950C 1000C 0 200 400 600 800 1000 1200 0 200 400 600 800 Temperature(C) Time (S) Heating Profile Fast Cooling 800C 850c 900c 950C 1000C FIGURE 11:SLOW COOLING RATE FIGURE 12: FAST COOLING RATE 𝑵𝑯𝑽 = 1.854𝑷 𝑳2 Vicker’s hardness equation:
- 10. Tensile Test • Measurew & 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 Thermalcamera Video camera Heat gun Data acquisition computer controlled through wifi
- 13. Analysis of X-raydiffraction • 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 andR 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
- 15. 0 0.02 0.040.06 0.08 0.1 0.12 0.14 0.16 0.18 TrueStress(MPa) Tmax Blue: 800C Green: 850C Cyan: 900C Magenta: 950C Yellow: 1000C No heating True Strain 0 200 400 600 800 1000 1200 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 0 200 400 600 800 1000 1200 True Strain TrueStress(MPa) No heating Tmax Blue: 800C Green: 850C Cyan: 900C Magenta: 950C Yellow: 1000C Slow cooling (20oC/s) Fast cooling (2oC/s) Tensile Curves True Strain vs. Tmax UTS vs. Tmax 800 820 840 860 880 900 920 940 960 980 1000 850 900 950 1000 1050 11100 1150 Peak Temp. StressMax(MPa) Tue stress without heating Slow cooling (2oC/s) Fast cooling (20oC/s) 800 820 840 860 880 900 920 940 960 980 1000 0.1 0.15 0.2 0.25 Peak Temperature e-max Reference without heating
- 16. Microstructure Examination As-received (noheating) 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
- 17. X-Ray Diffraction Results FIGURE26 INTEGRATED 2 THETA VS INTENSITY GRAPH FIGURE 27 INTEGRATED 2 THETA VS INTENSITY GRAPH 101 200 211 202
- 18. Comparison of DifferentHolding Times
- 19. DP980 Different HoldTimes 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 diffractiondata 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 • UseGSAS 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 tomy 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.
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- 25. Other works • Non-Linearstrain path for AHSS • Ultra-sonically welded battery tabs • High temperature tensile test with digital image correlation • Nano-indenter hardness test with actual nano tip
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