effect of surface hardening technique and case depth on rolling contact fatigue behavior of alloy...
DESCRIPTION
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.TRANSCRIPT
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
2
IntroductionTwo-stroke outboard engine components
used in rolling contact fatigue (RCF)
Crankshafts Connecting rods Driveshafts Propeller shafts Gears Bearings etc.
3
IntroductionTypical manufacturing process
Forging → Rough machining → Heat treatment
Straightening → Grinding
4
Surface hardening processesIntroduction
Atmosphere carburizing Induction hardening
Vacuum carburizing(with or without
high-pressure gas quenching)
5
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
6
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
7
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
8
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?
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Experimental Design and Procedure
10
RCF life
Case depth
Hardening method
Alloy
Experimental Design
11
RCF life
Case depth
Hardening method
Alloy
Experimental Design
AISI 8620AISI 9310AISI 4140
12
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)
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ProcedureRough
machiningHeat
treatmentCenterless grinding
RCF testing (ball-on-rod)
Microhardness / case depth Metallography
Scanning electron microscopy
White light interferometry
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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)
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
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
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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
20
Other measurements
Scanning electron microscopy
Hitachi S-3400
White light interferometry
ADE Phase Shift MicroXAM-100
21
Results and Discussion
22
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
23
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
24
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
25
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
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Surface hardnessSurface hardness vs. case depth
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Surface hardnessCycles to failure vs. surface hardness
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Surface hardnessCycles to failure vs. hardness at 0.254 mm
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Case depthCycles to failure vs. case depth
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Case depthCycles to failure vs. depth to 613 HV
31
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
32
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
33
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
34
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
35
MetallographyAISI 4140 induction hardened
Case depth: 1.17 mmCycles to failure: 874,800
Dark etching area: 0.78 mm wide × 0.28 mm deep
36
White-light interferometry
AISI 8620 atmosphere carburized
0.58 mm
0.98 mm
1.32 mm
37
White-light interferometry
AISI 8620 vacuum carburized
0.80 mm
1.07 mm
1.60 mm
38
White-light interferometry
AISI 9310 vacuum carburized
0.67 mm
1.10 mm
1.25 mm
39
White-light interferometry
AISI 4140 induction hardened
0.52 mm
0.74 mm
1.17 mm
40
Scanning electron microscopy
0.58 mm
0.98 mm
1.32 mm
AISI 8620 atmosphere carburized
41
0.80 mm
1.07 mm
1.60 mm
AISI 8620 vacuum carburizedScanning electron microscopy
42
0.67 mm
1.10 mm
1.25 mm
AISI 9310 vacuum carburizedScanning electron microscopy
43
0.52 mm
0.74 mm
1.17 mm
AISI 4140 induction hardenedScanning electron microscopy
44
Conclusions
45
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.
46
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.
47
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.
48
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
49
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.