Microstructural and Torsional Fatigue Characteristics of Singleshot and Scan Induction Hardened 1045 and 10V45 Steels

1

Microstructural and Torsional

Fatigue Characteristics of Single-

shot and Scan Induction Hardened

1045 and 10V45 Steels

Lee Rothleutner1, Jody Burke2, Dr. Chester J. Van Tyne1, and Robert Cryderman1

1Advanced Steel Processing and Products Research Center

Colorado School of Mines, Golden, CO 80401 USA

2Gerdau Special Steel North America, Jackson, MI 49201 USA

Additional support from Rob Goldstein of Fluxtrol Inc.

as well as Rob Madeira and Jeff Elinski of Inductoheat Inc.

2

Study Design

Induction hardened shaft ...

Performance

↑ Strength

↑ Fatigue life1. High case depth

2. Favorable case

microstructure

3. Favorable residual

stress profile

Processing

• Power

• Frequency

• Quenchant(conc. & flow rate)

• Coil design

• Scan speed

3

Study Design

Scope...

• Scan vs. Single-shot induction hardened

– Effective case depth of 44% (~70% of area)

– 1045 and 10V45 (F/P starting microstructure)

Outline...

1. Case microstructure

2. Residual stresses (near surface)

3. Torsional fatigue performance (550, 600, 650 MPa stress amplitude, R=0.1)

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Materials – Chemistry

wt pct C Mn Si Ni+Cr+Mo V Al N P S Cu DIb (mm)

1045 0.44a 0.74 0.23 0.25 0.002 0.016 0.0068 0.010 0.006 0.26 35.6

10V45 0.47a 0.82 0.28 0.24 0.080 0.007 0.0100 0.007 0.009 0.22 45.5

Minc 0.43 0.60 --- --- --- --- --- --- --- --- ---

Maxc 0.50 0.90 --- --- --- --- --- 0.040 0.050 --- ---

a Standard Deviation of 0.01 wt pct (n = 5)b ASTM A255-10: Standard Test Methods for Determining Hardenability of Steelc ASTM A29-12: Standard Specification for General Requirements for Steel Bars, Carbon and Alloy, Hot-Wrought

Hot Rolled to 39.7 mm (1.563 in) Diameter Bar (18.8 to 1)

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Materials – Microstructure

1045 10V45

Transverse Characteristics 1045 10V45

Pearlite (%) 83.1 ± 2.0 86.5 ± 1.5

Pearlite ILS (nm) 225 ± 6.4 207 ± 7.1

Ferrite Grain Size (µm) 6.4 ± 0.2 3.3 ± 0.1

Ferrite Grain Circularity 0.76 ± 0.01 0.82 ± 0.01

Hardness (HV1kg) 217 ± 5 281 ± 9

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Materials – V(C,N) Precipitation

V(C,N) diameter

4.5 ± 0.3 nm

10V45 – Proeutectoid Ferrite

BF DF

𝑏 = 011 𝛼𝐹𝑒 𝑔 = 0 20 𝑉(𝐶,𝑁)

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Materials – V(C,N) Precipitation

10V45 – Pearlitic Ferrite

V(C,N) diameter

3.3 ± 0.3 nm

DFBF

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Torsional Fatigue Specimen

(mm)

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Induction Hardening

Scan Single-shot

Scan Single-Shot

Power (kW) 72 128

Freq. (kHz) 196 31

Scan Rate (mm/s) 17.3 ---

UCON A Concentration 6% 2%

Flow Rate (L/min) 75 144

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Induction HardeningMeasured at Minimum Specimen Diameter

Scan

Single-shot

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Equivalent Hardness

𝐻𝑉𝑒𝑞 =3

𝑅3 0

𝑅

𝐻𝑉(𝑟)𝑟2𝑑𝑟

𝑑𝑟𝑟

𝑅

Tempered at 176 °C for 90 min

after induction hardening.

HVeq ∝ Torsional Strength

∝ Fatigue Life

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Microstructure – Scan


10V45-Scan

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Microstructure – Single-shot

10V45-Single


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Case Microstructure

Depth from

Surface

Scan Single-shot

1045 10V45 1045 10V45

0.0 mm --- --- --- R

0.5 mm --- R + T R R + T

0.0 mm

0.5 mm

10V45...

Higher tendency for non-martensitic

transformation products both retained (R)

and transformed (T) ferrite.

No ghost pearlite was observed within

0.5 mm of surface in any condition.

10V45-Single

10V45-Single

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Case Microstructure – PAGS

1045-Scan

10V45-Single

10V45 is not significantly different from

1045 for a given processing routine.

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Residual Stress



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Residual Stress

Octahedral Shear Stress

𝜎𝐻 = ±1

2𝜎12 + 𝜎2

2 + 𝜎1 − 𝜎22

−𝜏𝑥𝑦𝑟𝑒𝑠

-𝜎𝑦𝑟𝑒𝑠

-𝜎𝑥𝑟𝑒𝑠 -𝜃

𝜎1

-𝜎2

•=



35%

25%

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Torsional Fatigue Specimen

95% of Max Shear Stress

Longitudinal Cross-section

15.5 mm

(mm)

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Torsional Fatigue

Crack System

𝜎

𝜏

=

−𝜏𝑥𝑦𝑎𝑝𝑝

-45°

𝜎1𝑎𝑝𝑝

−𝜎2𝑎𝑝𝑝

𝜏𝜏𝑚𝑎𝑥

𝜏𝑚𝑖𝑛

𝜏𝑚

𝜏𝑎

𝑡𝑖𝑚𝑒

I

III

II

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Torsional Fatigue – Scan

1045 10V45

650 MPa

43,100 cycles

650 MPa

46,400 cycles

1045 exhibits more ductility in case

during crack propagation then 10V45.

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Torsional Fatigue – Scan

1045 10V45

550 MPa

122,500 cycles

550 MPa

510,000 cycles



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Torsional Fatigue – Single-shot

1045 10V45

650 MPa

128,600 cycles

650 MPa

127,100 cycles



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Torsional Fatigue – Single-shot

1045 10V45

550 MPa

240,000 cycles

550 MPa

448,000 cycles



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Torsional Fatigue

(MPa)

Scan Single-shot

1045 10V45 1045 10V45

650 --- --- --- 1/5

600 --- --- --- 4/5

550 3/5 3/5 2/5 4/5

𝜏𝑎

Sub-surface Initiations

Initiation location:

Case hardness in 10V45 is higher

then 1045 (~2 HRC).

~70%

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Scan vs. Single-shot

Hardness Profiles:

Scan ≈ Single-shot

Case Non-martensitic Trans. Products:

Scan < Single-shot

Prior Austenite Grain Size:

Scan > Single-shot (~25%)

Near-Surface Residual Stress:

Scan < Single-shot

Fatigue Life:

Scan ≈ Single-shot (at 550 MPa)

Scan < Single-shot (~70% higher )𝜏𝑎

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Thank you for your attention!

Lee M. Rothleutner

[email protected]

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Residual Stress• Incremental Hole Drilling Method

– ASTM E837

– Type A strain gage rosette.

– Inverted cone diamond mill.

– Strain measured every 0.05

mm to 1 mm.

– H-DRILL (v3.11) software

• Prof. Gary Schajer (UBC)

Hoop

Axial

Diamond

Mill

Micrometer

Head

Air Turbine

Assembly

Light

•Vishay M-M•RS-200

X & Y

Adjustment

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Net Stress

-𝜎𝑦𝑠

-𝜎𝑥𝑠

𝜏𝑥𝑦𝑠

Residual

Stress State

Applied

Stress State

Net

Stress StateResultant

Principal

Stresses

𝜎

𝜏

+−𝜏𝑥𝑦

𝑟𝑒𝑠

-𝜎𝑦𝑟𝑒𝑠

-𝜎𝑥𝑟𝑒𝑠 -𝜃

𝜎1

-𝜎2

=𝜏𝑥𝑦𝑎𝑝𝑝

𝜎

𝜏

+ =𝜎

𝜏

𝜎

𝜏

=

=

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Net Stress

Maximum Reduction in Applied Stress

-𝜃𝜎1

-𝜎2

Positive throughout test.

Negative throughout test.

Between -30° (at min)

and -45° (at max).

-𝜎2

𝜎1

-𝜃



(MPa) Scan Single-shot

650 -400 -560

550 -400 -560

𝝈1

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Torsional Fatigue

Engineering

Microstructural and Torsional Fatigue Characteristics of Singleshot and Scan Induction Hardened 1045 and 10V45 Steels