Reliability of mechanical properties of induction sintered iron based powder metal parts

Materials and Design 53 (2014) 383–397

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Reliability of mechanical properties of induction sintered iron based powder metal parts Can Çivi ⇑, Necati Tahralı, Enver Atik Celal Bayar University, Engineering Faculty, Department of Mechanical Engineering, 45140 Muradiye-Manisa, Turkey

a r t i c l e

i n f o

Article history: Received 21 March 2013 Accepted 10 July 2013 Available online 23 July 2013 Keywords: Powder metallurgy Sintering Induction sintering Mechanical properties MicroVickers hardness Reliability

a b s t r a c t Reliability and safety are important for machine and construction elements. In this study, iron based powder metal parts (3% Cu, 0.5% Graphite and 1% Kenolube lubricant by weight) were sintered at 1200 °C by medium frequency induction sintering mechanism (30 KW powered and 30 kHz frequency). Mechanical property values of components were determined according to changing sintering time. Three point bending, % maximum strain, MicroVickers hardness (HV) and Rockwell-B hardness tests were applied. Statistical distribution functions were drawn and ultimate strength, ultimate strain, MicroVickers and Rockwell-B hardness values were determined depending on various reliability. As a result of the experiments, it was concluded that, the hardness of powder metal materials should not be based on MicroVickers hardness. Ó 2013 Elsevier Ltd. All rights reserved.

1. Introduction Powder metal parts are widely used as machinery and construction elements. Powder metallurgy is one of the highly preferred production method because of its widely advantages. Powders which have different composition are pressed and then sintered at this method. Sintering is one of the most important issues of powder metallurgy because sintering causes significantly an increase in resistance of pressed powders [1]. The sintering process is generally performed in the sintering furnaces. It is done in batch furnaces and continuous furnaces [1]. In addition, induction sintering method is an important alternative of conventional sintering method. The advantage of this process allows very quick densification to near theoretical density and prohibition of grain growth [2]. Sintering and additional heat treatments of powder mixtures generate the microstructure to meet the performance as required [3]. Sintered materials are generally have a porous structure, with the increase in the amount of porosity, powder metal parts become brittle [1]. Mechanical Strength measurements of brittle materials or of metals under conditions where they behave in a brittle manner show a high variability of results which requires statistical analysis [4]. While classical construction method is based on safety, statistical construction method is based on reliability. Reliability values are range from 0 to 1, so F + R = 1 has a relation from Failure and Reliability [5]. Reliability is characteris⇑ Corresponding author. Tel.: +90 2362012381; fax: +90 2362412143. E-mail addresses: [email protected] (C. Çivi), [email protected] (N. Tahralı), [email protected] (E. Atik). 0261-3069/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.matdes.2013.07.034

tic of an item, expressed by the probability that the item will perform is required function under given conditions for a stated time interval [6]. Normal distribution, also called Gaussian distribution, a probability distribution is very important in many areas. Normal distribution has important applications in engineering and reliability [7]. Normal distribution is used to model of the physical, mechanical or chemical properties of a variety of systems. Gas molecule velocity, clothing, sound, tensile strength of aluminum alloy steels, capacity variation of electrical condensers, electrical power consumption in a field, generator output voltage and electrical resistance are shown as examples application of the normal distribution [8]. In another application, it is using analysis of the materials produced and analysis of their ability to perform of their functions [7]. Also, it is usually considered a normal distribution for Ultimate stress and nominal stress values [9–13]. Stress–Life diagrams can be drawn for for 0.1%. . .99.9% reliability. It is possible to realize the life values for 0.1%. . .99.9% reliability according to the load intensity [14]. It is not proper to realize the life analysis considering 50% reliability, for a machine element which has a vital importance. It is also possible to determine life values by using 90–99.9% reliability. However, these values become more important only in the case of competition of firms [15]. Similarly life values, ultimate stress values of materials can be found in the range of 0.1%. . .99.9% reliability [8]. Normal distribution is defined in the range of (1, +1). However, the reliability theory is dealt with periods of life of object. Therefore, the distribution of objects on the duration of life is assumed to be in the range (0, +1) [16].

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Fig. 4. Sintered samples.

Table 1 Three point bending results of 8.4 min sintered samples. Fig. 1. Induction sintering mechanism.

Sample number

Ultimate stress (N/mm2)

Ultimate strain (%)

1 2 3 4 5 6 7 8

425.94 510.26 484.45 510.78 509.75 653.86 575.55 524.99

3.9 3.93 3.62 3.79 3.9 4.63 3.5 3.6

Table 2 Three point bending results of 15 min sintered samples.

Fig. 2. Cupper coil.

Sample number

Ultimate stress (N/mm2)

Ultimate strain (%)

1 2 3 4 5 6 7 8

562.64 426.07 525.41 603.51 613.22 533.06 533.33 464.72

3.37 2.93 4.05 5.35 4.29 4.19 4.2 3.49

Table 3 Three point bending results of 30 min sintered samples.

Fig. 3. Laser pyrometer.

In previous studies, induction sintering was generally carried out with high frequency induction sintering unit at the same time pressing process (HFIFS) [17–23]. In this study, sintering was

Sample number

Ultimate stress (N/mm2)

Ultimate strain (%)

1 2 3 4 5 6 7 8

467.26 539.43 579.15 517.78 577.69 653.92 570.05 534.15

3.24 3.79 4.4 4.28 5.04 5.57 4.66 4.81

carried out after pressing process with medium frequency induction unit (30 kHz). In general, the average values of experimental results were given at powder metallurgy studies. Instead of average values of mechanical properties, most of the time mechanical properties values which have high reliability are more important at usage areas of powder metal parts. In this study, mechanical properties of powder metal parts were determined with mechanical tests. The results of these tests were evaluated statistically and the results which have 10%, 50% and 90% reliability were identified and compared with each other. Reliability analysis of ultimate stress, ultimate strain, Rockwell-B hardness and Vickers hardness were done. The most suitable sintering time according to the

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C. Çivi et al. / Materials and Design 53 (2014) 383–397 Table 4 Comparison of three-point bend test results of the samples sintered in three different times. Time

½ru R10 ðN=mm2 Þ

½ru R50 ðN=mm2 Þ

½ru R90 ðN=mm2 Þ

½eu R10 ð%Þ

½eu R50 ð%Þ

½eu R90 ð%Þ

8.4 min 15 min 30 min

609.985 618.1673 624.8154

524.44 532.74 554.92

438.8949 447.312 485.0245

4.3074 4.9248 5.4046

3.8587 3.9837 4.4737

3.4099 3.0425 3.5427

statistical evaluation was obtained with reliability. Also, as a result of Rockwell-B and MicroVickers hardness measurements, it was determined that Micro-Vickers hardness measurement is not appropriate for sintered components due to the small dimensions of the MicroVickers diamond pyramid hardness tester and porosity and alloying elements of powder metal parts.

2. Experimental studies In this study, Högenas ASC 100.29 iron powder (3% Cu, 0.5% Graphite and 1% kenolube lubricant by weight, size of 45– 106 lm.) was used. Metal powder was pressed under 600 N/mm2 with one axis press and 10  10  55 mm about 37 gr samples

were formed. Samples were sintered in atmosphere with medium frequency induction sintering unit for 8.4, 15 and 30 min at 1120 °C to compare (Fig. 1). Induction sintering was carried out in heat resistant glass in cupper coil (Fig. 2).Sintering temperature was kept constant at 1120° with laser pyrometer (Fig. 3). Sintered samples were given Fig. 4. Ultimate stress and ultimate strain values of sintered samples are determined by three point bending test. Instead of 6.35  12.7  31.7 mm transverse rapture strength sample according to ASTM: B 528-12, 10  10  55 mm samples produced ASTM E23-12c for more homogenous distribution of flow line and heating of the samples. 3 Point bending test was performed on the samples by using Autograph Shimadzu AG-IS 100 kN universal test

0.008

0.006

0.004

0.002

0

200

400

600

800

0

200

400

600

800

1.2

1.0

0.8

0.6

0.4

0.2

Fig. 5. Normal and cumulative distribution curves of ultimate stress values for 8.4 min sintered samples.

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1.2 1.0 0.8 0.6 0.4 0.2

0

2

4

6

8

0

2

4

6

8

1.2

1.0

0.8

0.6

0.4

0.2

Fig. 6. Normal and cumulative distribution curves of ultimate strain values for 8.4 min sintered samples.

machine. Rockwell-B hardness and MicroVickers hardness test was applied to samples. MicroVickers hardness values were measured with Future-Tech FM-700 microhardness test machine by loading 50 gr of force for 10 s according ASTM: E384-11e1. The results of the experiments were evaluated for each test result, distribution functions were drawn and according to the distribution function; ultimate stress, ultimate strain and hardness values were determined. Rockwell-B test was applied according to ASTM E18-12. Distribution functions were drawn based on the fallowing formulas with computational software program,

FðxÞ ¼

FðxÞ ¼

Z

  1 ðx  xÞ pffiffiffiffiffiffiffi Exp   2 2 sx s 2p

ð1Þ

Z

  1 ðx  xÞ pffiffiffiffiffiffiffi Exp   2 2 sx s 2p

ð2Þ

X: Mechanical property value. Sx: Standard deviation of mechanical property value. Maximum and minimum values of ultimate stress (ru), ultimate strain (eu), MicroVickers (HV), Rockwell-B (HRB) determined with following formulas. Z values were taken from Z table [24].

½xMax  ¼ x þ z sx

ð3Þ

½xmin  ¼ x  z sx

ð4Þ

3. Results and discussion 3.1. Three point bending test results The results of three point bending experiments of the 8 samples for each sintering time can be seen in Tables 1–3, and comparison of three-point bending test results of the samples sintered in three different times according to 10% and 90% reliability values can be seen Table 4. Samples sintered for 8.4 min ru ¼ 524; 44 N=mm2 (The average of ultimate stress values, [ru]R50)

eu ¼ 3:8587 ð%Þ (The average of ultimate strain values, [eu]R50). sr = 66.8321 (The standard deviation of ultimate stress values). z = 1.28 from z table, for 90% (R90) and 10% reliability values (R10).

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387

0.008

0.006

0.004

0.002

0

200

400

0

200

400

600

800

1.2

1.0

0.8

0.6

0.4

0.2

600

800

Fig. 7. Normal and cumulative distribution curves of ultimate stress values for 15 min sintered samples.

½ru R90 ¼ rk  z sr ¼ 532:74  1:28 66:7401

½ru R90 ¼ ru  z sr ¼ 524:44  1:28  66:8321 2

¼ 438:8949 N=mm

ð5Þ

ð9Þ

½ru R10 ¼ rk þ z sr ¼ 532:74 þ 1:28 66:7401

½ru R10 ¼ ru þ z sr ¼ 524:44 þ 1:28  66:8321 ¼ 609:985 N=mm2

¼ 447:312 N=mm2

ð6Þ

se = 0.3506 (the standard deviation of ultimate strain values).

¼ 618:1673 N=mm2

ð10Þ

se ¼ 0:7353

½eu R90 ¼ eu  z se ¼ 3:8587  1:28 0:3506 ¼ 3:4099

ð7Þ

½eu R90 ¼ e  z se ¼ 3:9837  1:28 0:7353 ¼ 3:0425

ð11Þ

½eu R10 ¼ eu þ z se ¼ 3:8587 þ 1:28 0:3506 ¼ 4:3074

ð8Þ

½eu R10 ¼ e þ z se ¼ 3:9837 þ 1:28 0:7353 ¼ 4:9248

ð12Þ

Samples sintered for 15 min

ru ¼ 532:74 N=mm2

Samples sintered for 30 min

ru ¼ 554:9281 N=mm2 eu ¼ 4:4737% sr ¼ 54:6058

eu ¼ 3:9837% sr ¼ 66:7401

½ru R90 ¼ rk  z sr ¼ 554:92  1:28 54:6058 ¼ 485:0245 N=mm2

ð13Þ

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1.2 1.0 0.8 0.6 0.4 0.2

0

2

4

6

8

0

2

4

6

8

1.2

1.0

0.8

0.6

0.4

0.2

Fig. 8. Normal and cumulative distribution curves of ultimate strain values for 15 min sintered samples.

½ru R10 ¼ rk þ z sr ¼ 554:92 þ 1:28 54:6058 2

¼ 624:8154 N=mm

x ¼ e; x ¼ 3; 85 ð14Þ

Sx ¼ Se ; Sx ¼ 0; 3506 Ultimate stress distribution function curves of samples sintered for 15 min were given Fig. 7

se ¼ 0:7273 ½eu R90 ¼ e  z se ¼ 4:4737  1:28 0:7273 ¼ 3:5427

ð15Þ

½eu R10 ¼ e þ z se ¼ 4:4737 þ 1:28 0:7273 ¼ 5:4046

ð16Þ

x ¼ rk ; x ¼ 532; 74 Sx ¼ sr ; Sx ¼ 63:74

It is shown of the tables, by increase of sintering time, the ultimate stress and ultimate strain values with 10%, 50% and 90% reliability percent are increased.

Ultimate strain distribution function curves of samples sintered for 15 min were given Fig. 8

x ¼ e; Sx ¼ S e ;

x ¼ 3:98 Sx ¼ 0:7353

3.2. Normal distribution curves of three point bending test results

Ultimate stress distribution function curves of samples sintered for 30 min were given Fig. 9

Ultimate stress distribution function curves of samples sintered for 8.4 min were given Fig. 5

x ¼ rk ;

x ¼ 534:14

Sx ¼ sr ;

Sx ¼ 54:60

x ¼ rk ;

x ¼ 524:44

Sx ¼ s r ;

Sx ¼ 66:83

Ultimate strain distribution function curves of samples sintered for 8.4 min were given Fig. 6

Ultimate stress distribution function curves of samples sintered for 30 min were given Fig. 10

x ¼ e; x ¼ 4:81 Sx ¼ Se ; Sx ¼ 0:7253

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389

0.008

0.006

0.004

0.002

0

200

400

600

0

200

400

600

800

1.2

1.0

0.8

0.6

0.4

0.2

800

Fig. 9. Normal and cumulative distribution curves of ultimate stress values for 30 min sintered samples.

½HVR90 ¼ HV  z sHV ¼ 258:8104  1:28  24:3241

3.3. MicroVickers hardness measurement results Samples sintered for 8.4 min HV ¼ 245:4854 (the average of Micro-Vickers hardness values, ½HVR50 ). sHV = 28.1622 (the standard deviation of MicroVickers hardness values).

¼ 227:6755 ½HVR10 ¼ HV þ z sHV ¼ 258:8104 þ 1:28  24:3241 ¼ 289:9453

ð19Þ

Samples sintered for 15 min

HV ¼

8 X HV ¼ 258:8104 i¼1

sHV ¼ 28:3241

HV ¼

8 X

HV ¼ 244:3417

i¼1

sHV ¼ 25:5475

½HVR10 ¼ HV þ z sHV ¼ 245:4854 þ 1:28  28:1622 ¼ 281:5330

ð22Þ

Samples sintered for 30 min

½HVR90 ¼ HV  z sHV ¼ 245:4854  1:28  28:1622 ¼ 209:4377

ð21Þ

ð20Þ

½HVR90 ¼ HV  z sHV ¼ 244:3417  1:28  25:5475 ¼ 211:6409

ð23Þ

½HVR10 ¼ HV þ z sHV ¼ 244:3417 þ 1:28  25:5475 ¼ 277:0425

ð24Þ

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1.2 1.0 0.8 0.6 0.4 0.2

0

2

4

6

8

0

2

4

6

8

1.2

1.0

0.8

0.6

0.4

0.2

Fig. 10. Normal and cumulative distribution curves of ultimate strain values for 30 min sintered samples.

3.4. Normal distribution curves of MicroVickers hardness test results

3.5. Rockwell-B hardness measurement results

MicroVickers distribution function curves of samples sintered for 8.4 min were given Fig. 11

Rockwell-B hardness test results of samples are shown Tables 9–12 Samples sintered for 8.4 min

x ¼ HV; Sx ¼ SHV ;

x ¼ 245:48 SHV ¼ 28:1622

MicroVickers distribution function curves of samples sintered for 15 min were given Fig. 12

x ¼ HV; x ¼ 258:81 Sx ¼ SHV ; SHV ¼ 24:3241 MicroVickers distribution function curves of samples sintered for 30 min were given Fig. 13 (see Tables 5–8)

x ¼ HV; Sx ¼ SHV ;

x ¼ 244:34 SHV ¼ 25:5475

HRB ¼ 54:3625 HRB (the average of Rockwell-B Hardness values, [HRB]R50). sHRB = 2.5011 (the standard deviation of Rockwell-B Hardness values).

½HRBR90 ¼ HRB  z sHV ¼ 54:3625  1:28 2:5011 ¼ 51:161

ð25Þ

½HRBR10 ¼ HRB þ z sHV ¼ 54:3625 þ 1:28 2:5011 ¼ 57:5639 Samples sintered for 15 min

HRB ¼ 55:5937HRB sHRB ¼ 2:8609

ð26Þ

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391

0.20

0.15

0.10

0.05

0

20

40

60

80

100

0

20

40

60

80

100

1.2

1.0

0.8

0.6

0.4

0.2

Fig. 11. Normal and cumulative distribution curves of MicroVickers values for 8,4 min sintered samples.

½HRBR90 ¼ HRB  z sHV ¼ 55:5937  1:28 2:8609 ¼ 51:9317

3.6. Normal distribution curves of Rockwell-B hardness test results

ð27Þ 

½HRBR10 ¼ HRB þ z sHV ¼ 55:5937 þ 1:28 2:8609 ¼ 59:2556

ð28Þ

Samples sintered for 30 min

Rockwell-B distribution function curves of samples sintered for 8.4 min were given Fig. 14

x ¼ H;

sHRB ¼ 5:3954

x ¼ H;

¼ 52:7063

H ¼ 55:59

Sx ¼ SHRB ;



½HRBR90 ¼ HRB  z sHV ¼ 59:6125  1:28 5:3954 ð29Þ

½HRBR10 ¼ HRB þ z sHV ¼ 59:6125 þ 1:28 5:3954 ¼ 66:5186

SH ¼ 2:5011

Rockwell-B distribution function curves of samples sintered for 15 min were given Fig. 15

HRB ¼ 59:6125HRB



H ¼ 54:36

Sx ¼ S H ;

Rockwell-B distribution function curves of samples sintered for 30 min were given Fig. 16

x ¼ H; ð30Þ

SHRB ¼ 2:8609

Sx ¼ SH ;

¼59:13 SH ¼ 6:0197

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0.20

0.15

0.10

0.05

0

20

40

60

80

100

0

20

40

60

80

100

1.2

1.0

0.8

0.6

0.4

0.2

Fig. 12. Normal and cumulative distribution curves of MicroVickers values for 15 min sintered samples.

Khalil and Almajid [25] reported that the compressive strength was significantly improved with increasing sintering time up to 3 min and then decreased after 4 min of sintering with high frequency induction sintering of nanostructured magnesium/ hydroxyapatite nanocomposites. In this study, the increasing of strength of materials was continued up to 30 min unlike Khalil and Almajid [25]. Çavdar and Atik [26] reported that strength and Microhardness values of iron based powder metal materials in the medium frequency induction sintering process (30– 50 kHz) were increased with sintering time. Mechanical tests results were decreased via decreasing temperature 900–1200° and sintering time up to 700 s (11.66 min). In this study, induction sintering time was increased up to 30 min (the same time as conventional sintering time in furnace) and it was seen that mechanical property values were increased with sintering time. Çivi and Atik [27] reported that Maximum stress of the 8.4 min medium frequency induction sintered Fe based samples were caught and passed samples sintered 30 min by classic sintering furnace and

by increase of sintering time, maximum stress and maximum strain values of samples were increased. Zhang and Sandström [28] investigated the effects of sintering temperature, time and atmosphere on the properties of classically sintered steels with these Fe–Mn–Si master alloy powders. Eventually, they found the density of the compacts increased with sintering temperature and time. The ultimate tensile strength and hardness increased with sintering temperature and time mainly due to increasing amounts of bainite and martensite after cooling. Elongation was initially raised with sintering temperature and time probably due to improved bonding between powder particles. And also they saw liquid phase sintering accelerates the sintering process, which leads to improved mechanical properties. In this study, medium frequency induction sintering was done. As a result of this study, mechanical property values of induction sintered powder metal samples except Vickers hardness results were generally increased with sintering time up to 30 min classically sintering time in furnace likely Khalil and Almajid [25], Çavdar and Atik [26] and Çivi

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0.20

0.15

0.10

0.05

0

20

40

60

0

20

40

60

80

100

1.2

1.0

0.8

0.6

0.4

0.2

80

100

Fig. 13. Normal and cumulative distribution curves of MicroVickers values for 30 min sintered samples. Table 5 Vickers microhardness test results of 8.4 min sintered samples. Sample number

1

2

3

4

5

6

7

8

Average (HV)

242.97

196.13

236.13

268.83

282.93

228.18

271.93

236.77

Table 6 Vickers microhardness test results of 15 min sintered samples. Sample number

1

2

3

4

5

6

7

8

Average (HV)

260.22

236.10

265.60

221.07

247.93

283.77

296.38

259.42

Table 7 Vickers microhardness test results of 30 min sintered samples. Sample number

1

2

3

4

5

6

7

8

Average (HV)

210.25

273.05

230.27

214.92

261.28

231.23

262.13

271.60

Table 8 Comparison of Vickers microhardness test results of the samples sintered in three different durations. Time

[HV]R10

[HV]R50

[HV]R90

8.4 min 15 min 30 min

281.5331 289.9453 277.0426

245.4854 258.8104 244.3417

209.4378 227.6755 211.6408

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Table 9 Rockwell-B hardness test results of 8.4 min sintered samples. Sample Number

1

2

3

4

5

6

7

8

Average (HRB)

51.9

55.875

52.75

55.325

54.125

51.55

59.25

54.125

Table 10 Rockwell-B hardness test results of 15 min sintered samples. Sample number

1

2

3

4

5

6

7

8

Average (HRB)

59

54.65

53.875

56.15

59.25

51.025

57.3

53.5

Table 11 Rockwell-B hardness test results of 30 min sintered samples. Sample number

1

2

3

4

5

6

7

8

Average (HRB)

65.25

57.675

60.575

55.375

55

67.875

50.425

62.65

Table 12 Comparison of Rockwell-B test results of the samples sintered in three different durations.

8.4 min 15 min 30 min

[HRB]R10

[HRB]R50

[HRB]R90

57.5639 59.2556 66.5186

54.3625 55.59375 59.6125

51.161 51.9317 52.7063

0.014 0.012 0.010 0.008 0.006 0.004 0.002

0

100

200

300

400

100

200

300

400

500

1.0

0.5

500

0.5

Fig. 14. Normal and cumulative distribution curves of Rockwell-B values for 8.4 min sintered samples.

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0.015

0.010

0.005

0

100

200

300

400

500

100

200

300

400

500

1.0

0.5

0.5

Fig. 15. Normal and cumulative distribution curves of Rockwell-B values for 15 min sintered samples.

and Atik [27]. The increasing of mechanical property values were continued up to 30 min maximum sintering time contrarily Khalil and Almajid [25]. Many powder metal and induction sintering studies, MicroVickers hardness test have been using. In this study, it is suggested from results of the statistical investigation of tests that MicroVickers hardness is not appropriate for the powder metal parts which have porosity and alloying element. Also, in this study, statistical investigation of experimental results was performed unlike other studies and values which have different reliability were obtained. Thus, the mechanical property values that investigated in this study, which have different reliability depending on usage areas of powder metal parts could be used in industry.

4. Conclusions Generally, average mechanical property values of powder metal parts are used in the studies and catalogs. In this study,

statistical investigations of mechanical properties of induction sintered powder metal parts were done. The mechanical properties were investigated in normal distribution. Mechanical property values can be determined in the range of 0.1%. . .99.9% reliability by severity of usage area of powder metal component. As a result of,  Mechanical properties of the samples in any reliability are possible to read from graphics of normal distribution and cumulative distribution functions. In this way, a reliability value which is determined the area of usage of parts can be seen from the graphics.  The mechanical properties with 90% reliability have great importance in the use of powder metal parts because of safety. These values can be read of the graphics. Also the graphics provide to determine corresponding to 0–99.9% reliability and failure values.  The percentage of damaged parts at a certain value of stress, strain and hardness can be determinable with graphics of cumulative statistical distribution functions.

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0.015

0.010

0.005

0

100

200

300

400

500

100

200

300

400

500

1.0

0.5

0.5

Fig. 16. Normal and cumulative distribution curves of Rockwell-B values for 30 min sintered samples.

 By increase of sintering time, the ultimate stress, ultimate strain, Rockwell-B hardness values with 10%, 50% and 90% reliability percent were increased at this study.  It was also found that Vickers hardness values were not increased in generally with induction sintering time. It could be obtained because of porosities, alloying elements and small dimensions of the MicroVickers diamond pyramid hardness tester. It is suggested that MicroVickers hardness test is not appropriate for the powder metal parts which have porosity and alloying element. Due to results of the Rockwell-B hardness tests, it is also suggested that macrohardness tests such as Rockwell-B and Brinell are more appropriate for powder metal parts which have porosities and alloying elements because of bigger dimensions of these hardness testers.

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