Effect of Cooling Line and Hardness on Thermal Fatigue Cracking Behavior

John F. Wallace, David Schwam, Jain Nitin, Xiaohua Hu and Yulong Zhu

Case Western Reserve University, Cleveland, OH

Summary of Presentation at NADCA Meeting on November 2, 2005

This presentation was given by Jack Wallace to outline the number of items that was presented at the meeting on November 2, 2005.

First, a description of the work that we have done with 1.5 inches diameter holes drilled into the centered immersion specimen used for our thermal fatigue measurements. This work involved first picking a desirable hardness range of about 40 to 51 HRC and to make specimen that complied with that requirement. These bars were shipped out to a regular heat treatment shop and the hardness levels were requested.

The second was repeating the request for a hardness of the same range as the first group except this group had a 1.8 inch diameter hole instead of 1.5 inch diameter hole. These specimens were also run as equivalent hardness level of 41 to 50 HRC. The heat treatment shop has some difficulties with the desirable hardness, so it was necessary to run a fifth specimen at 44HRC as requested.

In analysis of the results, it became apparent that the simple factors of heat treatment on the resulting behavior of the thermal fatigue materials differed considerably between the earlier work that was done on thermal fatigue specimens on M.S. Thesis on the subject. It was pointed out that the earlier work showed a much better comparison of the thermal fatigue results on the basis of the size of the hole in the specimen. Since this earlier work was done on the basis of oil quenching the specimens with a tempering temperature done in house was obvious that the tempering was different with was done with a commercial heat treatment.

The final portion of this work consisted of comparing the hardness, the thermal fatigue results for the three groups. This comparison followed an analysis of the tempering temperatures and its effect on the thermal fatigue results. It is apparent that the oil quenching gives a uniform hardness to the parts but that the variation in tempering from thermal fatigue operation is very important in providing consistent thermal fatigue results. Apparently, sufficient difficulty occurred in selecting the tempering temperatures to provide rather wide scatters in thermal fatigue resistance.

The final portion of the work consisted of a presentation of the results of the soldering and washout characteristics resulting from the review that we did to present this results in a NADCA program.

Summary of Presentation at NADCA Meeting on November 2, 2005 (Continued)

0

50

100

150

200

250

300

0 5000 10000 15000

Thermal Cycles

Tot

al C

rack

Are

a (

x 10

6 µm

2 )

H13/ 51 HRC

H13/ 47 HRC

H13/ 44 HRC

H13/ 40 HRC

2"X2"X7"WC7

51HRC

44 HRC

47 HRC

40 HRC

1.5" Cooling Line

0

2

4

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0 5000 10000 15000

Thermal Cycles

Ave

rage

Max

Cra

ck L

engt

h (

x100

µm

)

H13/ 41 - 43 HRC/ 1.8" CL

H13/ 46.5 HRC/ 1.8" CL

H13/ 50 HRC/ 1.8" CL

2"X2"X7" WC7

41 HRC/ 1.8" CL

46.5 HRC/ 18" CL

50 HRC/ 18" CL

1.8" Cooling Line

Effect of Cooling Line and Hardness on Thermal Fatigue Behavior(Vacuum Quenching)

0

50

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150

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250

300

0 5000 10000 15000

Thermal Cycles

Tot

al C

rack

Are

a (

x 10

6 µm

2 )

H13/ 41 HRC/ 1.8"

H13/ 46.5 HRC/ 1.8" CL

H13/ 50 HRC/ 1.8" CL

2"X2"X7"WC7

46.5 HRC

41 HRC

50 HRC

1.8 Cooling Line

0

2

4

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8

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0 5000 10000 15000

Thermal Cycles

Ave

rage

Max

Cra

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engt

h (

x100

µm

)

H13/ 44 HRC

H13/ 47 HRC

H13/ 51 HRC

H13/ 40 HRC44HRC

47HRC

51HRC

2"X2"X7"

40HRC

1.5" Cooling Line

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40

45

50

55

0 0.05 0.1 0.15 0.2 0.25

Distance from the Corner (inch)

Har

dn

ess

(HR

C)

Hardness 40 HRC

Hardness 44 HRC

Hardness 47 HRC

Hardness 51 HRC

1.5" Cooling Line

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25

30

35

40

45

50

55

0 0.05 0.1 0.15 0.2 0.25

Distance from Corner (inch)

Har

dn

ess

(HR

C)

H13/41 HRC/1.8"

H13/46.5 HRC/1.8"

H13/50 HRC/1.8"

1.8" Cooling Line

Effect of Cooling Line and Hardness on Softening Behavior after 15,000 Cycles(Vacuum Quenching)

1.5 Inch 1.8 Inch

Effect of Hardness and Testing Temperature on Charpy V-Notched Impact Properties

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70

0 100 200 300 400 500 600

Testing Temperature(F)

Imp

act

Pro

per

ty(f

t-lb

)

40HRC-1.5"

43HRC-1.5"

47HRC-1.5"

49HRC-1.5"

0

10

20

30

40

50

60

70

-50 50 150 250 350 450 550

Testing Temperature(F)

Imp

act

Pro

per

ty(f

t-lb

)

41HRC-1.8"

46.5HRC-1.8"

50HRC-1.8"

Heat treated with 1.5” Dunker Specimens Heat treated with 1.8” Dunker Specimens

1.5 Inch 1.8 Inch

Testing Temperature (F) -5 68 212 300 500

41HRC Impact (ft-lb) 16 23 34 52 64

Fibrous Fracture (%) 0 10 20 40 60

46.5HRC Impact (ft-lb) 14 15 26 26 45

Fibrous Fracture (%) 5 10 20 40 100

50HRC Impact (ft-lb) 6 6 15 8

Fibrous Fracture (%) 0 0 10 25

Effect of Hardness and Testing Temperature on Charpy V-Notched Impact Properties and Fibrous Fracture Percentage(Specimens Heat Treated with 1.8” Dunker Samples )

Effect of Cooling Line Size on Average Max Crack Length(Previous Data & Dunk Specimens Were Quenched in Oil)

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Thermal Cycles

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h (

x 10

0 µm

)

H13-1.5"

H13-1.6"

H13-1.7"

H13-1.8"

2" X 2" X 7", WC7-- 46 HRC

From Our Previous Study

Effect of Cooling Line Size on Total Crack Area(Previous Data & Dunk Specimens Were Quenched in Oil)

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150

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0 5000 10000 15000

Thermal Cycles

Tot

al C

rack

Are

a(x

106

µm

2 )

H13-1.5"

H13-1.6"

H13-1.7"

H13-1.8"

2" X 2" X 7", WC7--46HRC

From Our Previous Study

20

25

30

35

40

45

50

55

0 0.05 0.1 0.15 0.2 0.25

Distance from Corner(inch)

Har

dn

ess(

HR

C)

1.5"

1.8"1.7"

1.6"

Effect of Cooling Line Size on Softening Behavior(Previous Data & Dunk Specimens Were Quenched in Oil)

From Our Previous Study: 46HRC after 15,000 cycles

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Thermal Cycles

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Max

Cra

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engt

h (

x 10

0 µm

)

H13-1.5" Oil Quenched

H13-1.8" Oil Quenched

H13-1.5" Vacuum Quenched

2" X 2" X 7", WC7-46.5 HRC

Comparison of Current and Previous Thermal Fatigue Behavior(Average Max Crack Length)

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0 5000 10000 15000

Thermal Cycles

Tot

al C

rack

Are

a(x

106

µm

2 )

H13-1.5-Oil Quenched

H13-1.8 Oil Quenched

H13-1.5 Vacuum Quenched

2" X 2" X 7", WC7--46.5 HRC

Comparison of Current and Previous Thermal Fatigue Behavior(Total Crack Area)

1092 oF

1004 oF

Temperature Simulation of 1.5” and 1.8” Hole (Showing Max Temperature of 1092F for 1.5” and 1004F for1.8”)

1.5” 1.8”

37.2 MPa (5.31 KSi)

58.2 MPa (8.3 KSi)

1.5” 1.8”

Stress Simulation of 1.5” and 1.8” Hole (Showing Max Tensile Stress of 5.31ksi for 1.5” and 8.3ksi for 1.8”)

Maximum Cracking/wearing

observed at this spot in dunker

test results.

Compressive Stress of 717.2 MPa (102.45 KSi)

Maximum Cracking/wearing

observed at this spot in dunker

test results.

Compressive Stress of 798.4 MPa (112.7 KSi)

1.5” 1.8”

Stress Simulation of 1.5” and 1.8” Hole (Showing Max Compressive Stress of 102.45ksi for 1.5” and 112.7ksi for 1.8”)

Conclusion

The stress at the corner of the 1.8” specimens is higher than that of 1.5” specimens.

The softening is significantly improved by using 1.8” hole instead of 1.5” hole because the max temperature at the corner of 1.8” specimens is lower than that of 1.5” specimens.

The calculated max tensile stress on the corners of the 1.5” specimen is 5.31ksi and 8.3ksi for the 1.8” specimen.

The calculated max compressive stress on the corners of the 1.5” specimen is 102.45ksi and 112.7ksi for the 1.8” specimen.

The calculated max temperature on the corners of the 1.5” specimen is 1092F and 1004F for the 1.8” specimen.