effect of surface hardening technique and case depth on rolling contact fatigue behavior of alloy...

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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 David Palmer 1 , Lechun Xie 2,3 , Frederick Otto 4 , Q. Jane Wang 2

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Surface hardening techniques are widely used to improve the rolling contact fatigue resistance of materials. This study investigated the rolling contact fatigue (RCF) resistance of hardened, ground steel rods made from three different aircraft-quality alloy steels (AISI 8620, 9310 and 4140), and hardened using different techniques (atmosphere carburizing, vacuum carburizing, and induction hardening) at different case depths. The fatigue life of the rods was determined using a three ball-on-rod rolling contact fatigue test machine. After testing, the surfaces of the rods were examined using scanning electron microscopy (SEM), and their microstructures were examined using metallographic techniques. In addition, the surface topography of the rods was measured using white-light interferometry. Relationships between surface hardness, case depth, and fatigue life were investigated. The longest lives were observed for the vacuum carburized AISI 9310 specimens, while the shortest lives were observed for the induction hardened AISI 4140 specimens. It was found the depth to a hardness of 613 HV (56 HRC), as opposed to the traditional definition of case depth as the depth to a hardness of 513 HV (50 HRC), provided a somewhat better correlation to RCF life, and the hardness at a depth of 0.254 mm provided a somewhat better correlation than the surface hardness to RCF life.

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Page 1: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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

David Palmer1, Lechun Xie 2,3, Frederick Otto4, Q. Jane Wang2

Page 2: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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IntroductionTwo-stroke outboard engine components

used in rolling contact fatigue (RCF)

Crankshafts Connecting rods Driveshafts Propeller shafts Gears Bearings etc.

Page 3: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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IntroductionTypical manufacturing process

Forging → Rough machining → Heat treatment

Straightening → Grinding

Page 4: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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Surface hardening processesIntroduction

Atmosphere carburizing Induction hardening

Vacuum carburizing(with or without

high-pressure gas quenching)

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IntroductionCarburizing 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

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IntroductionAtmosphere 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

Page 7: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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IntroductionCase 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

Page 8: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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IntroductionProblems

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? How to account for case non-uniformity?

Page 9: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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Experimental Design and Procedure

Page 10: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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RCF life

Case depth

Hardening method

Alloy

Experimental Design

Page 11: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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RCF life

Case depth

Hardening method

Alloy

Experimental Design

AISI 8620AISI 9310AISI 4140

Page 12: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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RCF life

Case depth

Hardening method

Alloy

Experimental Design

Atmosphere carburize / oil quenchVacuum carburize / oil quenchVacuum carburize / gas quenchInduction harden / water quench

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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)

Page 14: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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ProcedureRough

machiningHeat

treatmentCenterless grinding

RCF testing (ball-on-rod)

Microhardness / case depth Metallography

Scanning electron microscopy

White light interferometry

Page 15: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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AISI 8620, 9310, 4140Vacuum degassed

Certified AQ per SAE AMS 2301

Materials

Material C Mn Si Ni Cr Mo Cu P S Al Fe8620 0.21 0.83 0.24 0.48 0.54 0.21 0.12 0.008 0.010 0.031 Balance9310 0.11 0.62 0.26 3.06 1.16 0.10 0.15 0.007 0.020 0.033 Balance4140 0.41 0.90 0.25 0.06 0.99 0.22 0.07 0.007 0.019 0.030 Balance

Length: 3.00 ± .05” (76.2 ± 1.3 mm)

Diameter: 0.400 ± .005” (10.16 ± 0.13 mm) – before grindDiameter: 0.3750 ± .0001” (9.525 ± 0.002 mm) – after grind

Surface finish: 2 – 4 µin. (0.05 – 0.10 µm)

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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

Page 17: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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RCF testingMaximum contact

stress: 6 GPa

Rotation speed: 3600 rpm

Lubrication:0.3 mL/min TC-W3

Ball diameter:0.500 in. (12.7 mm)

Ball material:AISI 52100

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Case depth measurement

Rough machined diameter Hardened

layer

Ground diameter

Page 19: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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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

Page 20: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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Other measurements

Scanning electron microscopy

Hitachi S-3400

White light interferometry

ADE Phase Shift MicroXAM-100

Page 21: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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Results and Discussion

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Microhardness profilesAISI 8620 – Atmosphere carburized

Hardness at 0.254 mm: 676 HV

Depth to 613 HV: 0.54 mm

Depth to 513 HV: 0.99 mm

Page 23: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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Microhardness profilesAISI 8620 – Vacuum carburized

Hardness at 0.254 mm: 759 HV

Depth to 613 HV: 0.60 mm

Depth to 513 HV: 1.02 mm

Page 24: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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Microhardness profilesAISI 9310 – Vacuum carburized

Hardness at 0.254 mm: 776 HV

Depth to 613 HV: 0.78 mm

Depth to 513 HV: 1.06 mm

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Microhardness profilesAISI 4140 – Induction hardened

Hardness at 0.254 mm: 610 HV

Depth to 613 HV: 0.24 mm

Depth to 513 HV: 1.05 mm

Page 26: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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Surface hardnessSurface hardness vs. case depth

Page 27: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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Surface hardnessCycles to failure vs. surface hardness

Page 28: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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Surface hardnessCycles to failure vs. hardness at 0.254 mm

Page 29: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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Case depthCycles to failure vs. case depth

Page 30: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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Case depthCycles to failure vs. depth to 613 HV

Page 31: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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RCF life

Material Surface treatment

Average life (cycles)

Average case depth

(mm)Eccentricity

(mm)Depth to 613 HV (mm)

Hardness at 0.254 mm

(HV)8620 vacuum 2,300,400 0.813 0.066 0.484 7278620 vacuum 29,095,200 1.083 0.075 0.718 7818620 vacuum 37,778,400 1.500 0.066 0.942 849

8620 atmosphere 2,049,300 0.578 0.067 0.287 6308620 atmosphere 8,812,800 1.009 0.093 0.545 6948620 atmosphere 21,772,800 1.332 0.141 0.560 657

9310 vacuum 26,568,000 0.677 0.030 0.470 7069310 vacuum 43,372,800 1.078 0.033 0.793 7769310 vacuum 52,401,600 1.257 0.027 0.931 776

4140 induction 237,600 0.502 0.041 0.080 581

4140 induction 410,400 0.720 0.060 0.342 618

4140 induction 604,800 1.115 0.086 0.465 632

Average cycles to failure

Page 32: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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MetallographyAISI 8620 atmosphere carburized

Case depth: 1.03 mmCycles to failure: 5,248,880

Dark etching area: 0.99 mm wide × 0.15 mm deep

Page 33: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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MetallographyAISI 8620 vacuum carburized

Case depth: 1.14 mmCycles to failure: 29,872,800

Dark etching area: 0.49 mm wide × 0.15 mm deep

Page 34: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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MetallographyAISI 9310 vacuum carburized

Case depth: 1.10 mmCycles to failure: 51,256,800

Dark etching area: 0.44 mm wide × 0.16 mm deep

Page 35: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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MetallographyAISI 4140 induction hardened

Case depth: 1.17 mmCycles to failure: 874,800

Dark etching area: 0.78 mm wide × 0.28 mm deep

Page 36: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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White-light interferometry

AISI 8620 atmosphere carburized

0.58 mm

0.98 mm

1.32 mm

Page 37: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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White-light interferometry

AISI 8620 vacuum carburized

0.80 mm

1.07 mm

1.60 mm

Page 38: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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White-light interferometry

AISI 9310 vacuum carburized

0.67 mm

1.10 mm

1.25 mm

Page 39: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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White-light interferometry

AISI 4140 induction hardened

0.52 mm

0.74 mm

1.17 mm

Page 40: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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Scanning electron microscopy

0.58 mm

0.98 mm

1.32 mm

AISI 8620 atmosphere carburized

Page 41: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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0.80 mm

1.07 mm

1.60 mm

AISI 8620 vacuum carburizedScanning electron microscopy

Page 42: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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0.67 mm

1.10 mm

1.25 mm

AISI 9310 vacuum carburizedScanning electron microscopy

Page 43: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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0.52 mm

0.74 mm

1.17 mm

AISI 4140 induction hardenedScanning electron microscopy

Page 44: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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Conclusions

Page 45: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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Conclusions

• Longest RCF lives: vacuum carburized AISI 8620 and 9310

• Shortest RCF lives: induction hardened AISI 4140

• Vacuum carburizing provided the greatest depth of high hardness (>613 HV) at the same case depth.

• The depth of high hardness provided a better correlation to RCF life than the traditional definition

of effective case depth.

Page 46: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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Conclusions• Lowest case eccentricity: vacuum carburized and

gas quenched AISI 9310• Highest case eccentricity: atmosphere carburized

and oil quenched AISI 8620

• Eccentricity is a means of measuring uniformity of case depth, and an indirect measure of distortion.

• By minimizing distortion, the required grind stock can be reduced, potentially resulting in even greater

improvements to RCF life.

Page 47: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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Conclusions

• Based on SEM observation, with the exception of the vacuum carburized AISI 8620, surface damage

increased with increasing case depth.

• For the vacuum carburized AISI 8620, surface damage decreased with increasing case depth.

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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

Page 49: Effect of Surface Hardening Technique and Case Depth on Rolling Contact Fatigue Behavior of Alloy Steels

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ReferencesJones, 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.