Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels
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This document summarizes a study on the effect of surface hardening technique and case depth on the rolling contact fatigue (RCF) behavior of alloy steels. Vacuum carburized AISI 8620 and 9310 steels exhibited the longest RCF lives, over 2 orders of magnitude longer than induction hardened AISI 4140. Higher surface hardness and hardness deeper in the material correlated with longer RCF life. Vacuum carburizing produced greater depth of high hardness (>56 HRC) than other techniques, resulting in smaller plastic deformation zones and longer RCF life. Elasto-plastic modeling predicted stress distributions that matched experimental metallographic observations of plastic deformation zones.
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Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels
- 1. Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels 1 BRP US, Inc. – Marine Propulsion Systems Division, Sturtevant, Wisconsin, USA 2 Center for Surface Engineering and Tribology, Northwestern University, Evanston, Illinois, USA 3 State Key Laboratory of Metal Matrix Composites, Shanghai Jiaotong University, Shanghai, China 4 Midwest Thermal-Vac, Kenosha, Wisconsin, USA 5 State Key Laboratory of Mechanical Transmission, Chongqing University, Chongqing, China David Palmer1, Lechun Xie 2,3, Frederick Otto4, Zhanjiang Wang5, Q. Jane Wang2
- 2. Introduction Two-stroke outboard engine components used in rolling contact fatigue (RCF) 2 Crankshafts Connecting rods Driveshafts Propeller shafts Gears Bearings etc.
- 3. Introduction Typical manufacturing process Forging → Rough machining → Heat treatment Straightening → Grinding 3
- 4. 4 Surface hardening processes Introduction Atmosphere carburizing Induction hardening Vacuum carburizing (with or without high-pressure gas quenching)
- 5. 5 Introduction Carburizing vs. induction hardening Jones et al (2010): Spiral bevel gears Induction hardened AISI 4340 had lower distortion Atmosphere carburized AISI 9310 had higher strength Townshend et al (1995): Straight spur gears Induction hardened AISI 1552 had longer RCF life than atmosphere carburized AISI 9310 Carburized gears were ground after heat treatment; induction hardened gears were not
- 6. 6 Introduction Atmosphere vs. vacuum carburizing Lindell et al (2002): Helical spur gears Atmosphere carburizing (with oil quench) vs. vacuum carburizing (with gas quench) for AISI 8620 Vacuum carburized AISI 8620 had: Higher surface hardness Higher surface compressive residual stress Greater depth of high hardness (>58 HRC) at same case depth
- 7. 7 Introduction Case depth Traditionally measured as depth to 50 HRC (513 HV) May vary due to non-uniform heating, non-uniform carbon pickup, and/or non-uniform stock removal during grinding
- 8. Introduction Problems How do different surface hardening methods affect RCF life? Atmosphere carburizing with oil quenching Vacuum carburizing with oil quenching Vacuum carburizing with gas quenching Induction hardening What is the effect of case depth on RCF life? Can elasto-plastic modeling shed light on this problem? 8
- 12. 12 RCF life Case depth Hardening method Alloy Experimental Design Atmosphere carburize / oil quench Vacuum carburize / oil quench Vacuum carburize / gas quench Induction harden / water quench
- 13. 13 RCF life Case depth Hardening method Alloy Experimental Design Low (0.50 – 0.75 mm) Medium (0.75 – 1.00 mm) High (1.00 – 1.25 mm)
- 14. 14 Procedure Rough machining Heat treatment Centerless grinding RCF testing (ball-on-rod) Microhardness / case depth Metallography Elasto-plastic modelling
- 15. AISI 8620, 9310, 4140 Vacuum degassed Certified AQ per SAE AMS 2301 Materials Material C Mn Si Ni Cr Mo Cu P S Al Fe 8620 0.21 0.83 0.24 0.48 0.54 0.21 0.12 0.008 0.010 0.031 Balance 9310 0.11 0.62 0.26 3.06 1.16 0.10 0.15 0.007 0.020 0.033 Balance 4140 0.41 0.90 0.25 0.06 0.99 0.22 0.07 0.007 0.019 0.030 Balance 15 Length: 3.00 ± .05” (76.2 ± 1.3 mm) Diameter: 0.400 ± .005” (10.16 ± 0.13 mm) – before grind Diameter: 0.3750 ± .0001” (9.525 ± 0.002 mm) – after grind Surface finish: 2 – 4 µin. (0.05 – 0.10 µm)
- 16. 16 Heat treatment Carburizing Temp. (°C) Hold Temp. (°C) Hold Time (min.) Quench Temp (°C) Tempering Temp. (°C) Tempering Time (hours) Atmosphere 954 815 20 80 177 3 Vacuum 940 815 20 80 177 3 Carburizing Temp. (°C) Hold Temp. (°C) Hold Time (min.) Quench Pressure (kPa) Tempering Temp. (°C) Tempering Time (hours) Vacuum 940 815 20 1500 177 3 AISI 8620 AISI 9310
- 17. 17 RCF testing Spring load: 310 N Rotation speed: 3600 rpm Lubrication: 0.3 mL/min TC-W3 Ball diameter: 0.500 in. (12.7 mm) Ball material: AISI 52100
- 18. 18 Case depth measurement Rough machined diameter Hardened layer Ground diameter
- 19. 19 Case depth measurement Microhardness traverse Circumscribed circle Vickers scale (500 g load) Measurements made every .005” (.127 mm) beginning from surface Eccentricity = distance from specimen axis to center of circumscribed circle Average case depth = specimen radius – radius of circumscribed circle
- 21. 21 Elasto-plastic modelling Elasto-plastic modelling for plastically-graded materials (Wang et al, 2013) Assumptions: • Yield strength gradient based on experimentally-determined hardness gradient • Tabor approximation: H = 3σY0 • Isotropic strain hardening: σY = σY0(1+εp)n • Strain hardening exponent: n = 0.140 for AISI 8620 n = 0.035 for AISI 4140 n = 0.113 for AISI 9310 Values from AISI Bar Steel Fatigue database
- 23. 23 Microhardness profiles AISI 8620 – Atmosphere carburized Hardness at 0.005”: 711 HV Depth to 56 HRC: 0.54 mm Depth to 50 HRC: 0.99 mm
- 24. 24 Microhardness profiles AISI 8620 – Vacuum carburized Hardness at 0.005”: 819 HV Depth to 56 HRC: 0.60 mm Depth to 50 HRC: 1.02 mm
- 25. 25 Microhardness profiles AISI 9310 – Vacuum carburized Hardness at 0.005”: 776 HV Depth to 56 HRC: 0.78 mm Depth to 50 HRC: 1.06 mm
- 26. 26 Microhardness profiles AISI 4140 – Induction hardened Hardness at 0.005”: 639 HV Depth to 56 HRC: 0.24 mm Depth to 50 HRC: 1.05 mm
- 27. 27 Surface hardness Surface hardness vs. case depth
- 28. 28 Surface hardness Cycles to failure vs. surface hardness
- 29. 29 Surface hardness Cycles to failure vs. hardness at 0.005 in.
- 30. 30 Case depth Cycles to failure vs. case depth
- 31. 31 Case depth Cycles to failure vs. depth to 56 HRC
- 32. RCF life Material Surface treatment Average life (cycles) Average case depth (mm) Eccentricity (mm) Depth to 56 HRC (mm) Hardness at 0.005” (HV) 8620 vacuum 2,300,400 0.813 0.066 0.484 777 8620 vacuum 29,095,200 1.083 0.075 0.718 812 8620 vacuum 37,778,400 1.500 0.066 0.942 866 8620 atmosphere 2,049,300 0.578 0.067 0.287 693 8620 atmosphere 8,812,800 1.009 0.093 0.545 716 8620 atmosphere 21,772,800 1.332 0.141 0.560 673 9310 vacuum 26,568,000 0.677 0.030 0.470 749 9310 vacuum 43,372,800 1.078 0.033 0.793 782 9310 vacuum 52,401,600 1.257 0.027 0.931 793 4140 induction 237,600 0.502 0.041 0.080 605 4140 induction 410,400 0.720 0.060 0.342 631 4140 induction 604,800 1.115 0.086 0.465 635 32 Average cycles to failure
- 33. 33 Metallography AISI 8620 atmosphere carburized Case depth: 1.03 mm Cycles to failure: 5,248,880 Dark etching area: 0.99 mm wide × 0.15 mm deep
- 34. 34 Metallography AISI 8620 vacuum carburized Case depth: 1.14 mm Cycles to failure: 29,872,800 Dark etching area: 0.49 mm wide × 0.15 mm deep
- 35. 35 Metallography AISI 9310 vacuum carburized Case depth: 1.10 mm Cycles to failure: 51,256,800 Dark etching area: 0.44 mm wide × 0.16 mm deep
- 36. 36 Metallography AISI 4140 induction hardened Case depth: 1.17 mm Cycles to failure: 874,800 Light etching area: 0.78 mm wide × 0.28 mm deep
- 37. 37 Stress and plastic deformation Maximum von Mises stress: 3638 MPa at 0.148 mm depth (0.006”)
- 38. 38 Stress and plastic deformation Material Surface treatment Case depth Maximum von Mises stress (MPa) Depth of maximum stress (mm) Volume of plastic deformation zone (mm³) Average life (cycles) 8620 vacuum low 3566 0.138 0.065 2,300,400 8620 vacuum medium 3603 0.148 0.056 29,095,200 8620 vacuum high 3653 0.148 0.042 37,778,400 8620 atmosphere low 3279 0.128 0.113 2,049,300 8620 atmosphere medium 3356 0.138 0.085 8,812,800 8620 atmosphere high 3229 0.128 0.093 21,772,800 9310 vacuum low 3556 0.138 0.078 26,568,000 9310 vacuum medium 3638 0.148 0.057 43,372,800 9310 vacuum high 3647 0.148 0.057 52,401,600 4140 induction low 3531 0.128 0.189 237,600 4140 induction medium 3665 0.148 0.148 410,400 4140 induction high 3636 0.189 0.120 604,800 Maximum stress and plastic zone size
- 39. 39 Conclusions
- 40. Conclusions (1.) Longest RCF lives: vacuum carburized 8620 and 9310 Shortest RCF lives: induction hardened 4140 More than 2 orders of magnitude! (2.) Higher surface hardness → longer RCF life (except for atmosphere carburized 8620) (3.) More important than surface hardness: hardness at depth of maximum von Mises stress (in this case, approximately 0.13 mm) 40
- 41. 41 Conclusions (4.) RCF life correlates more closely with depth of high hardness (>56 HRC) than with case depth as traditionally defined (>50 HRC) (5.) Vacuum carburizing → greater depth of high hardness → smaller plastic deformation zone → longer RCF life (6.) Metallographically light- and dark-etching areas correspond with plastic deformation zones as predicted by elasto-plastic simulation
- 42. 42 Dissemination activities STLE Annual Meeting & Exhibition Lake Buena Vista, Florida May 22, 2014 Design News “Understanding Case Hardening of Steel” September 4, 2014 Tribology Transactions Volume 58, Issue 1 2015 (forthcoming)
- 43. Acknowledgements • BRP US, Inc. – Marine Propulsion Systems Division, Sturtevant, Wisconsin, USA • Center for Surface Engineering and Tribology, Northwestern University, Evanston, Illinois, USA • Midwest Thermal Vac., Kenosha, Wisconsin, USA • China Scholarship Council (No. 2011623074), Beijing, China • Shanghai Jiao Tong University, Shanghai, China • Chongqing University, Chongqing, China 43
- 44. References Jones, K.T., et al. (2010), "Gas Carburizing vs. Contour Induction Hardening in Bevel Gears," Gear Solutions 8 (82), pp. 38-44, 51, 54. Lindell, G.D, et al. (2002), "Selecting the Best Carburizing Method for the Heat Treatment of Gears (AGMA Technical Paper 02FTM7)," American Gear Manufacturers Association, Alexandria, VA, ISBN 1 55589 807 6. Townsend, D.P., et al. (1995), "The Surface Fatigue Life of Induction Hardened AISI 1552 Gears (AGMA Technical Paper 95FTM5)," American Gear Manufacturers Association, Arlington, VA, ISBN 1 55589 654 5. 44
- 45. 45 References Wang, Z.J., et al. (2013), “An Efficient Numerical Method With a Parallel Computation Strategy for Solving Arbitrarily Shaped Inclusions in Elasto-Plastic Contact Problems," ASME Journal of Tribology 135 (3), pp. 031401.