1. IMPROVED DIE CASTING PROCESS TO PRESERVE THE LIFE OF THE DIE CASTING DIE John F. Wallace David Schwam Nitin Jain Yulong Zhu Case Western Reserve University Cleveland, OH 44106 February 23, 2005

2. This investigation compares the composition, thermal fatigue behavior toughness and the microstructure after austenitizing and tempering ability of four steels of P.G H13, QRO90, Dievar and Hotvar. It is is presented to show some of the recent improvements in die steels. Objectives

3. Chemical Composition of the Four Die Steels SteelsC, %Si, %Mn, %Cr, %V, %Mo, %S, %P % H130.401.00.355.251.01.50.0010.020 QRO900.360.270.822.500.862.210.0010.005 Dievar0.350.160.505.060.542.390.00040.010 Hotvar0.551.00.752.60.852.250.0010.016

4. SteelsAustenitizing Temperature (F) Tempering Temperature (F) High Hardness (HRC) Medium Hardness (HRC) Low Hardness (HRC) H1318701050 – 115047.54542 QRO9019201100 – 123550Not Tested41 Dievar18701050 – 11155046.543 Hotvar19201020 - 115056.546Not Tested Hardness Level of the Thermal Fatigue Specimens

5. Thermal Fatigue Testing Equipment and Specimen

6. Total Crack Area of QRO90/50 HRC, Dievar/51 HRC and H13/ 47 HRC

7. Average Maximum Crack Length of QRO90 /50 HRC, Dievar 51 HRC & H13/47 HRC

8. Total crack area of QRO90/41 HRC, H 13/45 HRC & Dievar/44HRC

9. Average maximum crack length of QRO90 /41 HRC, H13 / 45 HRC and Dievar/44HRC

10. Hardness distribution after 15000 cycles - Different Steels

11. P.G.H13 QRO90DIEVAR 1500  m Thermal fatigue cracks in three die steels after 15,000 thermal cycles Corner

12. Thermal Fatigue Fracture Surface Impact Fracture Surface Sample Corner Surface crack of Dievar (2 joined surface cracks) Corner crack of H13 130X 0.035” (15x) Appearance of typical corner crack and surface crack

13. Corner Corner cracks and surface cracks of H13

14. Appearance of these four steels with the structure as quenched

15. Microstructure of the four steels after tempering at 1200F for 10 hours

16. Effect of tempering cycle on different steels

17. Steel High HardnessMedium HardnessLow Hardness Hardness (HRC) Impact (ft-lbs) Hardness (HRC) Impact (ft-lbs) Hardness (HRC) Impact (ft-lbs) H1347124513.54121 QRO9049.59XX39.521 Dievar48.51146.515.54219 Hotvar551247.59.5XX Impact Results and Hardness of Impact Tests at Room Temperature

18. CONCLUSIONS 1.Results of the work show that thermal fatigue resistance of Dievar is somewhat better than H13. The improved thermal fatigue resistance makes this steel preferable for demanding die casting applications. 2.The QRO90 has good thermal fatigue resistance but is more sensitive to gross cracking. 3.The Hotvar material has low resistance to gross cracking therefore is not suitable for use in demanding aluminum die casting dies exposed to severe thermal gradients or thermal shock. 4.The higher austenitising temperature used for QRO90 produced a smaller number of carbides compared to H13. 5.The tempering curves of these materials show a higher temper resistance of Hotvar, QRO90 and Dievar relative to H13.

19. Acknowledgements This research work is supported by DOE funds provided through by ATI. NADCA and the members of Die Materials Committee approved this work and provided background. The contribution` of this group of people is hereby acknowledged.