NIST Technical Note 1879

Tensile Properties of Commercially 

Pure, High-Purity and 

Ultra-High-Purity Iron: Results of an 

International Round-Robin

Enrico Lucon

Kenji Abiko

Marlies Lambrecht

Birgit Rehmer 

This publication is available free of charge from:

http://dx.doi.org/10.6028/NIST.TN.1879
NIST Technical Note 1879

Tensile Properties of Commercially 

Pure, High-Purity and 

Ultra-High-Purity Iron: Results of an 

International Round-Robin

Enrico Lucon

Applied Chemicals and Materials Division

Material Measurement Laboratory

Kenji Abiko

Institute for Material Research, Tohoku University

Sendai, Japan

Marlies Lambrecht

Structural Materials Tests, Belgian Nuclear Research Center, SCK•CEN

Mol, Belgium

Birgit Rehmer 

BAM 5.2, Experimental and Model Based Mechanical Behaviour of Materials

Berlin, Germany

This publication is available free of charge from:

http://dx.doi.org/10.6028/NIST.TN.1879

April 2015

U.S. Department of Commerce 

Penny Pritzker, Secretary

National Institute of Standards and Technology 

Willie May, Acting Under Secretary of Commerce for Standards and Technology and Acting Director 
Certain commercial entities, equipment, or materials may be identified in this

document in order to describe an experimental procedure or concept adequately.

Such identification is not intended to imply recommendation or endorsement by the

National Institute of Standards and Technology, nor is it intended to imply that the

entities, materials, or equipment are necessarily the best available for the purpose. 

National Institute of Standards and Technology Technical Note 1879

Natl. Inst. Stand. Technol. Tech. Note 1879, 36 pages (April 2015) 

CODEN: NTNOEF

This publication is available free of charge from: 

http://dx.doi.org/10.6028/NIST.TN.1879
iii

Abstract

The room temperature tensile properties of iron with different purity levels (commercially pure, 

high-purity, and ultra-high-purity) were characterized at different strain rates in the framework of 

an international Round-Robin involving four laboratories (BAM, IMR-TU, NIST, and SCK•CEN). 

The test results were collected and analyzed by NIST, and are presented in this Technical Note.

Data from all the participating laboratories were found in good agreement, thus allowing a clear 

assessment of the influence of strain rate and purity level on tensile properties (mechanical 

resistance and ductility). A clear increase of yield strength and, to a lesser extent, tensile strength 

was observed for all materials as strain rate increases and purity level decreases. The highest strain 

rate sensitivity was associated with the highest purity level (ultra-high-purity Fe). Ductility trends 

were less unequivocal, but typically an increase of elongation at fracture and reduction of area was 

detected as strain rate and purity level increase. Significant differences in tensile properties were 

observed between the two investigated types of high-purity Fe, which can be attributed to an 

influence of the production process in terms of melting environment (atmosphere and crucible), as 

well as differences in chemical compositions.

Keywords

Commercially pure iron; ductility; high-purity iron; purity level; Round-Robin; strain rate; tensile 

strength; ultra-high-purity iron; yield strength. 
iv

Table of Contents

Abstract ........................................................................................................................................................................iii

Keywords......................................................................................................................................................................iii

1. Round-Robin description .......................................................................................................................................1

2. Results of the individual participants ....................................................................................................................4

2.1. BAM results..................................................................................................................................................4

2.2. IMR-TU results..............................................................................................................................................8

2.3. NIST results ................................................................................................................................................12

2.4. SCK•CEN results.........................................................................................................................................17

3. Comparison of participants’ data ........................................................................................................................21

3.1. Yield strength .............................................................................................................................................22

3.2. Tensile strength..........................................................................................................................................23

3.3. Elongation at fracture ................................................................................................................................24

3.4. Reduction of area.......................................................................................................................................25

3.5. General remarks.........................................................................................................................................25

4. Discussion ............................................................................................................................................................26

5. Conclusions..........................................................................................................................................................31

References...................................................................................................................................................................31

References...................................................................................................................................................................32
1

1. Round-Robin description

An interlaboratory comparison (aka Round-Robin) was conducted among four 

international laboratories for the characterization of the room temperature tensile properties of Fe 

with different degrees of purity, ranging from commercial purity (CP) to ultra-high purity (UHP). 

The purpose of this Round-Robin was to investigate the influence of purity level and strain rate on 

the tensile properties of iron.

The laboratories that participated in the Round-Robin are listed in Table 1, along with the 

names of the scientists who were responsible for testing and reporting results. The participants’ 

data were collected and compared by NIST, Boulder CO (USA) in consultation with the 

participating institutes.

Table 1 - Round-Robin participants.

Institute Location Responsible

BAM Berlin

(Germany) B. Rehmer

IMR-TU Sendai

(Japan) K. Abiko

NIST Boulder, CO

(USA) E. Lucon

SCK•CEN Mol

(Belgium) M. Lambrecht

Four types of iron were tensile tested: commercially pure (CP) Fe, two types of high purity 

(HP) Fe, and ultra-high purity (UHP) Fe. The designations of the four types of pure Fe were K05 

(CP), K02 (HP), S11 (HP), and A11 (UHP). Their impurity content, measured by the Institute of 

Material Research at Tohoku University (IMR-TU), is provided in Table 2.

Table 2 – Impurity content (weight ppm) of the investigated materials. (nm = not measured.)

Element CP Fe HP Fe UHP Fe

K05 K02 S11 A11

Fe bal bal bal bal

C 14.0 1.6 0.3 0.5

N 1.8 4 1.5 <0.1

O 8.6 60 72.1 8.3

S 1.1 0.9 12.2 1.2

H nm <0.1 <0.1

Al 75.0 3.0 nm nm

B 10.9 2.6 nm nm

Cr nm 2.3 nm nm

Mn nm 1.3 nm nm

Ni nm 6.3 nm <1

P 49 1 nm nm

Si nm 1 2 <1
2

Adding up the impurity contents in Table 2, the following purity levels are obtained:

 K05 (CP): 99.98396 %;

 K02 (HP): 99.9916 %;

 S11 (HP): 99.99118 %;

 A11 (UHP): 99.9999878 %.

The materials K05 and K02 were melted in argon atmosphere at 200 Torr (26.7 MPa) 

pressure, in a ceramics crucible (URC). S11 and A11 were melted in ultra-high vacuum (UHV, 

10-7 Pa), by use of a water-cooled copper crucible.

From the scientific point of view, the most interesting material is A11 (electrolytic UHP 

iron). It was obtained by use of an induction melting furnace, located at IMR-TU in Sendai (Japan). 

The furnace is capable of melting iron ingots up to 10 kg, and its main chamber can be evacuated 

to a base pressure of 6.7 × 10-8 Pa. UHP Fe is used for the fundamental research on the intrinsic 

properties of iron and to determine the inherent effects of each impurity [1-3].

For each material, participants received tensile specimens of the geometry shown in Figure 

1, which corresponds to the ASTM E8/E8M-13a Small-Size Round Specimen (Type 4). The 

specimens were manufactured and distributed by IMR-TU (Prof. Abiko).

Figure 1 - Geometry of the tensile specimens tested for the Round-Robin (dimensions in mm).

For every material, each laboratory was required to test three specimens at three different 

strain rates, i.e., 9 specimens per material, for a total of 36 specimens. Tests were to be conducted 

at room temperature (21 °C ± 3 °C) in accordance with ASTM E8/E8M-13a. As much as possible, 

an extensometer was required to be used to monitor specimen elongation. Due to 

miscommunication among participants, participating labs didn’t all test at the same nominal strain 

rates. A summary of the tests performed is provided in the test matrix shown in Table 3.

The following parameters were reported by participants1:

 Yield strength2, σYS (MPa);

 Tensile strength, σTS (MPa);

 Elongation at fracture, t (%);

 Reduction of area, RA (%).

 

1 Participants also reported uniform elongation u (%). However, three of the four labs estimated u from actuator 

displacement rather than specimen elongation. This parameter was therefore not included in the analyses.

2

In case of discontinuous yielding, the minimum between the strength at an offset of 0.2 % plastic deformation (σp0.2) 

and the lower yield strength (σLYS) was reported as the yield strength for the test.
3

Table 3 - Test matrix for the Round-Robin.

Participant Material No. of tests Strain rate (s-1) Remarks

BAM

K05

3

3

3

10-3

10-4

10-5

Tests were conducted with an

extensometer which was removed at

approximately 1 mm elongation.

K02

3

3

3

10-3

10-4

10-5

S11

3

3

3

10-3

10-4

10-5

A11

3

3

3

10-3

10-4

10-5

IMR-TU

K05

3

3

3

5 × 10-3

5 × 10-4

5 × 10-5

K02

3

3

3

5 × 10-3

5 × 10-4

5 × 10-5

S11

3

3

3

5 × 10-3

5 × 10-4

5 × 10-5

A11

3

3

3

5 × 10-3

5 × 10-4

10-5

NIST

K05

3

3

3

10-3

10-4

10-5

Tests were conducted with an

extensometer which was removed at

approximately 0.7 mm elongation.

K02

3

3

4

10-3

10-4

10-5

S11

3

3

3

10-3

10-4

10-5

A11

3

3

3

10-3

10-4

10-5

SCK•CEN

K05

2

1

2

1

2

1

10-3

5 × 10-3

10-4

5 × 10-4

5 × 10-4

10-5

Tests at 5 × 10-3s

-1

, 5 × 10-4s

-1

, and

5 × 10-5s

-1 were conducted without extensometer.

The remaining tests were conducted with an

extensometer which was removed at

approximately 5-6 mm elongation.

K02

2

1

2

1

2

1

10-3

5 × 10-3

10-4

5 × 10-4

5 × 10-4

10-5

S11

2

1

2

1

2

1

10-3

5 × 10-3

10-4

5 × 10-4

5 × 10-4

10-5

A11

2

1

2

1

2

1

10-3

5 × 10-3

10-4

5 × 10-4

5 × 10-4

10-5
4

2. Results of the individual participants

2.1. BAM results

The test results reported by BAM [4] are presented in Table 4. 

Table 4 - Test results reported by BAM [4].

Average values of all tensile parameters are presented as a function of tested material in 

Table 5 and as a function of strain rate in Table 6. Average values are also illustrated in Figures 2 

to 6.

Specimen Strain sYS sTS  t RA

ID rate (s-1) (MPa) (MPa) (%) (%)

K05-1_19 1E-03 228 288 45 95

K05-1_20 1E-03 233 281 48 95

K05-1_21 1E-03 232 280 47 95

K05-2_21 1E-04 211 264 49 95

K05-2_22 1E-04 200 260 51 96

K05-2_23 1E-04 202 262 53 96

K05-3_19 1E-05 48 95

K05-3_20 1E-05 178 250 50 95

K05-3_21 1E-05 174 250 52 95

K02-1_21 1E-03 198 252 44 86

K02-1_22 1E-03 192 242 45 86

K02-1_23 1E-03 194 241 48 91

K02-2_19 1E-04 189 250 40 88

K02-2_20 1E-04 159 232 49 91

K02-2_21 1E-04 158 229 54 89

K02-3_21 1E-05 184 237 39 91

K02-3_22 1E-05 163 230 44 92

K02-3_23 1E-05 163 230 46 91

S11-1_9 1E-03 111 208 73 97

S11-1_10 1E-03 99 205 73 96

S11-1_11 1E-03 106 205 72 96

S11-2_28 1E-04 89 200 72 94

S11-2_29 1E-04 87 201 74 96

S11-2_30 1E-04 91 203 74 97

S11-1_28 1E-05 66 190 64 95

S11-1_29 1E-05 64 189 65 96

S11-1_30 1E-05 63 188 68 96

A11-1_17 1E-03 68 200 67 95

A11-1_18 1E-03 68 201 74 95

A11-1_19 1E-03 69 201 73 96

A11-2_17 1E-04 43 189 65 95

A11-2_18 1E-04 44 186 65 94

A11-2_19 1E-04 44 188 71 96

A11-3_23 1E-05 27 179 71 95

A11-3_24 1E-05 28 178 66 96

A11-3_25 1E-05 29 177 37 95

Material

CP Fe

HP Fe

UHP Fe

DATA ACQUISITION FAILED
5

Table 5 – Average BAM test results as a function of tested material.

Table 6 – Average BAM test results as a function of strain rate.

Figure 2 - Average values of yield strength measured by BAM. Error bars indicate standard deviations.

Strain sYS sTS  t RA

rate (s-1) (MPa) (MPa) (%) (%)

1E-03 231 283 47 95

1E-04 204 262 51 95

1E-05 176 250 50 95

1E-03 195 245 46 88

1E-04 169 237 47 89

1E-05 163 232 43 91

1E-03 105 206 73 96

1E-04 88 201 73 96

1E-05 66 189 66 96

1E-03 68 201 71 95

1E-04 44 188 67 95

1E-05 28 178 58 95

Material

K05

K02

S11

A11

Strain sYS sTS  t RA

rate (s-1) (MPa) (MPa) (%) (%)

K05 231 283 47 95

K02 195 245 46 88

S11 105 206 73 96

A11 68 201 71 95

K05 204 262 51 95

K02 169 237 47 89

S11 88 201 73 96

A11 44 188 67 95

K05 176 250 50 95

K02 163 232 43 91

S11 66 189 66 96

A11 28 178 58 95

Material

1E-03

1E-04

1E-05

0

50

100

150

200

250 Yield strength (MPa)

1E-3 1/s

1E-4 1/s

1E-5 1/s

K05

(pure Fe)

K02

(high-purity Fe)

S11

(high-purity Fe)

A11

(UHP Fe)
6

Figure 3 - Average values of tensile strength measured by BAM. Error bars indicate standard deviations.

Figure 4 - Average values of elongation at fracture measured by BAM. Error bars indicate standard 

deviations.

0

50

100

150

200

250

300 Tensile strength (MPa)

1E-3 1/s

1E-4 1/s

1E-5 1/s

K05

(pure Fe)

K02

(high-purity Fe)

S11

(high-purity Fe)

A11

(UHP Fe)

0

10

20

30

40

50

60

70

80 Elongation at fracture (%)

1E-3 1/s

1E-4 1/s

1E-5 1/s

K05

(pure Fe)

K02

(high-purity Fe)

S11

(high-purity Fe)

A11

(UHP Fe)
7

Figure 5 - Average values of reduction of area measured by BAM.

Very clear and consistent trends for yield and tensile strengths can be observed in Figures 

2 and 3. Both parameters decrease as material purity increases and strain rate decreases. Specific 

trends are not detected in Figures 4 and 5 for ductility parameters (t and RA).

75

80

85

90

95

100 Reduction of area (%)

1E-3 1/s 1E-4 1/s 1E-5 1/s

K05

(pure Fe)

K02

(high-purity Fe)

S11

(high-purity Fe)

A11

(UHP Fe)
8

2.2. IMR-TU results

The test results obtained by IMR-TU3are presented in Table 7. Note that reduction of area 

was not measured.

Table 7 - Test results obtained by IMR-TU.

Average values of all tensile parameters are presented as a function of tested material in 

Table 8 and as a function of strain rate in Table 9. Average values are also illustrated in Figures 6

to 8.

 

3

IMR-TU provided raw test data to NIST, who analyzed the tests and calculated the results.

Specimen Strain sYS sTS  t

ID rate (s-1) (MPa) (MPa) (%)

K05-1_29 5E-03 245 282 49

K05-1_30 5E-03 243 280 48

K05-1_31 5E-03 243 279 48

K05-2_31 5E-04 199 257 54

K05-2_32 5E-04 215 259 55

K05-2_33 5E-04 210 259 52

K05-3_29 5E-05 200 248 52

K05-3_30 5E-05 201 248 52

K05-3_31 5E-05 201 255 50

K02-1_31 5E-03 211 247 47

K02-1_32 5E-03 204 243 57

K02-1_33 5E-03 200 239 55

K02-2_29 5E-04 189 241 45

K02-2_30 5E-04 187 240 44

K02-2_31 5E-04 183 237 51

K02-3_31 5E-05 171 235 45

K02-3_32 5E-05 175 235 41

K02-3_33 5E-05 176 239 41

S11-1_12 5E-03 126 211 77

S11-1_13 5E-03 123 210 70

S11-1_14 5E-03 124 212 71

S11-2_25 5E-04 106 207 73

S11-2_26 5E-04 98 205 72

S11-2_27 5E-04 99 206 69

S11-1_25 5E-05 71

S11-1_26 5E-05 67 188 66

S11-1_27 5E-05 70 187 62

A11-1_27 5E-03 92 199 68

A11-1_29 5E-03 91 198 70

A11-1_30 5E-03 94 201 68

A11-2_27 5E-03 56 184 68

A11-2_28 5E-03 59 189 70

A11-2_29 5E-03 59 187 68

A11-3_29 5E-03 41 175 67

A11-3_30 5E-03 44 178 67

A11-3_31 5E-03 42 177 62

HP Fe

FILE INCOMPLETE

CP Fe

UHP Fe

Material
9

Table 8 – Average IMR-TU test results as a function of tested material.

Table 9 – Average IMR-TU test results as a function of strain rate.

Figure 6 - Average values of yield strength measured by IMR-TU. Error bars indicate standard deviations.

Strain sYS sTS  t

rate (s-1) (MPa) (MPa) (%)

5E-03 244 280 48

5E-04 208 258 53

5E-05 201 251 51

5E-03 205 243 53

5E-04 187 239 47

5E-05 174 236 42

5E-03 124 211 73

5E-04 101 206 71

5E-05 70 188 64

5E-03 92 199 69

5E-04 58 187 68

5E-05 42 177 65

K05

K02

S11

A11

Material

Strain sYS sTS  t

rate (s-1) (MPa) (MPa) (%)

K05 244 280 48

K02 205 243 53

S11 124 211 73

A11 92 199 69

K05 208 258 53

K02 187 239 47

S11 101 206 71

A11 58 187 68

K05 201 251 51

K02 174 236 42

S11 70 188 64

A11 42 177 65

5E-04

5E-05

Material

5E-03

0

50

100

150

200

250 Yield strength (MPa)

1E-3 1/s

1E-4 1/s

1E-5 1/s

K05

(pure Fe)

K02

(high-purity Fe)

S11

(high-purity Fe)

A11

(UHP Fe)
10

Figure 7 - Average values of tensile strength measured by IMR-TU. Error bars indicate standard 

deviations.

Figure 8 - Average values of elongation at fracture measured by IMR-TU. Error bars indicate standard 

deviations.

0

50

100

150

200

250

300 Tensile strength (MPa)

1E-3 1/s

1E-4 1/s

1E-5 1/s

K05

(pure Fe)

K02

(high-purity Fe)

S11

(high-purity Fe)

A11

(UHP Fe)

0

10

20

30

40

50

60

70

80

90 Elongation at fracture (%)

1E-3 1/s

1E-4 1/s

1E-5 1/s

K05

(pure Fe)

K02

(high-purity Fe)

S11

(high-purity Fe)

A11

(UHP Fe)
11

The observed trends for yield and tensile strengths (Figures 6 and 7) are similar to the BAM 

results shown in Figures 2 and 3: strength decreases with increasing material purity and decreasing 

strain rate. 
12

2.3. NIST results

The test results obtained by NIST are presented in Table 10. Note that a fourth K02 

specimen was tested at 10-5s

-1

because of the anomalous results yielded by specimen K02-3_30.

Table 10 - Test results reported by NIST.

Figure 9 compares force/actuator displacement curves for the K02 (HP iron) specimens 

tested at the lowest strain rate (10-5s

-1

). The outlier behavior of specimen K02-3_30 is evident, 

with higher strength and lower ductility than the other three specimens. No apparent reason for 

this anomaly could be identified. However, we should also note that similar situations were also 

observed at 10-3s

-1

and 10-4s

-1

, in reference to specimens K02-1_30 and K02-2_28 respectively.

Specimen Strain sYS sTS  t RA

ID rate (s-1) (MPa) (MPa) (%) (%)

K05-1_26 1E-03 219 277 58 96

K05-1_27 1E-03 229 282 62 96

K05-1_28 1E-03 243 294 51 96

K05-2_16 1E-04 197 264 53 96

K05-2_28 1E-04 220 271 62 96

K05-2_30 1E-04 213 271 55 96

K05-3_15 1E-05 172 253 50 95

K05-3_27 1E-05 179 259 52 95

K05-3_28 1E-05 205 267 51 95

K02-1_28 1E-03 183 243 61 92

K02-1_29 1E-03 185 246 54 90

K02-1_30 1E-03 202 256 48 91

K02-2_26 1E-04 150 233 59 91

K02-2_27 1E-04 148 231 57 93

K02-2_28 1E-04 186 253 51 91

K02-2_14 1E-05 131 218 42 92

K02-3_28 1E-05 139 224 52 94

K02-3_29 1E-05 137 223 51 93

K02-3_30 1E-05 177 244 42 92

S11-1_15 1E-03 103 219 71 97

S11-1_17 1E-03 109 219 67 96

S11-1_22 1E-03 109 220 67 96

S11-2_22 1E-04 92 212 67 95

S11-2_23 1E-04 94 214 76 96

S11-2_24 1E-04 94 216 63 97

S11-1_16 1E-05 64 194 61 96

S11-1_23 1E-05 71 196 64 95

S11-1_24 1E-05 76 197 61 97

A11-1_24 1E-03 78 214 70 97

A11-1_25 1E-03 74 208 73 96

A11-1_26 1E-03 76 211 65 94

A11-2_24 1E-04 53 197 67 96

A11-2_25 1E-04 52 197 70 96

A11-2_26 1E-04 48 194 65 93

A11-3_20 1E-05 39 183 80 93

A11-3_21 1E-05 37 184 68 93

A11-3_22 1E-05 38 187 59 93

Material

UHP Fe

HP Fe

P Fe
13

Figure 9 - Comparison between K02 specimens tested by NIST at 10-5s

-1

.

Average values for all tensile parameters are presented as a function of tested material in 

Table 11 and as a function of strain rate in Table 12. Average values and standard deviations 

(indicated by error bars) are also illustrated in Figures 10 to 13.

Table 11 – Average NIST test results as a function of tested material.

0

0.5

1

1.5

2

2.5

3

3.5

0 2 4 6 8 10 Force (kN)

Actuator displacement (mm)

K02-3_30

Strain sYS sTS  t RA

rate (s-1) (MPa) (MPa) (%) (%)

1E-03 231 284 57 96

1E-04 210 269 57 96

1E-05 185 260 51 95

1E-03 190 248 54 91

1E-04 161 239 56 92

1E-05 132 228 47 93

1E-03 107 219 68 96

1E-04 93 214 69 96

1E-05 71 196 62 96

1E-03 76 211 69 96

1E-04 51 196 67 95

1E-05 38 185 69 93

Material

K05

K02

S11

A11
14

Table 12 – Average NIST test results as a function of strain rate.

Figure 10 - Average values of yield strength measured by NIST. Error bars indicate standard deviations.

Strain sYS sTS t RA

rate (s-1) (MPa) (MPa) (%) (%)

K05 231 284 57 96

K02 190 248 54 91

S11 107 219 68 96

A11 76 211 69 96

K05 210 269 57 96

K02 161 239 56 92

S11 93 214 69 96

A11 51 196 67 95

K05 185 260 51 95

K02 132 228 47 93

S11 71 196 62 96

A11 38 185 69 93

Material

1E-03

1E-04

1E-05

0

50

100

150

200

250 Yield strength (MPa)

1E-3 1/s

1E-4 1/s

1E-5 1/s

K05

(pure Fe)

K02

(high-purity Fe)

S11

(high-purity Fe)

A11

(UHP Fe)
15

Figure 11 - Average values of tensile strength measured by NIST. Error bars indicate standard deviations.

Figure 12 - Average values of elongation at fracture measured by NIST. Error bars indicate standard 

deviations.

0

50

100

150

200

250

300 Tensile strength (MPa)

1E-3 1/s

1E-4 1/s

1E-5 1/s

K05

(pure Fe)

K02

(high-purity Fe)

S11

(high-purity Fe)

A11

(UHP Fe)

0

10

20

30

40

50

60

70

80 Elongation at fracture (%)

1E-3 1/s

1E-4 1/s

1E-5 1/s

K05

(pure Fe)

K02

(high-purity Fe)

S11

(high-purity Fe)

A11

(UHP Fe)
16

Figure 13 - Average values of reduction of area measured by NIST. Error bars indicate standard deviations.

As already observed for BAM and IMR-TU results, yield and tensile strength 

systematically decrease as the material purity increases and strain rate increases (Figures 10 and 

11). Ductility parameters do not exhibit equally clear patterns.

50

55

60

65

70

75

80

85

90

95

100 Reduction of area (%)

1E-3 1/s

1E-4 1/s

1E-5 1/s

K05

(pure Fe)

K02

(high-purity Fe)

S11

(high-purity Fe)

A11

(UHP Fe)
17

2.4. SCK•CEN results

The test results obtained by SCK•CEN are presented in Table 13. For every test condition, 

specimens were tested at two strain rates (e.g., 10-3 s

-1

and 5 × 10-3 s

-1

). The tests performed at 5 × 

10-3 s

-1

, 5 × 10-4 s

-1

, and 5 × 10-5 s

-1 were conducted without extensometer. For these tests, the 

parameter sp02 was estimated from force and actuator displacement data, after linearization of the 

initial portion of the test record. For 9 of these 12 tests, sYS corresponds to sLYS, which is not

affected by the use of actuator displacement or specimen elongation.

Table 13 - Test results obtained by SCK•CEN.

Specimen Strain sYS sTS  t RA

ID rate (s-1) (MPa) (MPa) (%) (%)

K05-1_16 5E-03 250 292 51 94

K05-1_17 1E-03 246 284 50 95

K05-1_18 1E-03 244 293 47 96

K05-2_18 5E-04 228 275 57 96

K05-2_19 1E-04 215 265 53 96

K05-2_20 1E-04 227 271 49 96

K05-3_16 5E-05 195 257 57 94

K05-3_17 1E-05 189 254 50 95

K05-3_18 1E-05 193 256 50 94

K02-1_18 5E-03 224 262 50 91

K02-1_19 1E-03 194 246 50 92

K02-1_20 1E-03 208 257 46 90

K02-2_16 5E-04 201 253 49 88

K02-2_17 1E-04 185 244 47 91

K02-2_18 1E-04 202 261 38 88

K02-3_18 5E-05 177 242 52 92

K02-3_19 1E-05 167 234 48 91

K02-3_20 1E-05 187 250 40 92

S11-1_6 5E-03 145 229 71 97

S11-1_7 1E-03 111 218 68 97

S11-1_8 1E-03 111 218 71 97

S11-2_31 5E-04 117 221 76 96

S11-2_32 1E-04 93 208 70 97

S11-2_33 1E-04 96 209 70 95

S11-1_31 5E-05 75 203 68 96

S11-1_32 1E-05 67 195 62 97

S11-1_33 1E-05 71 197 65 97

S11-3_23 1E-05 114 210 61 93

A11-1_14 5E-03 107 215 80 96

A11-1_15 1E-03 72 204 72 97

A11-1_16 1E-03 72 204 71 94

A11-2_14 5E-04 71 206 75 97

A11-2_15 1E-04 52 195 68 96

A11-2_16 1E-04 49 194 68 96

A11-3_26 5E-05 44 188 68 94

A11-3_27 1E-05 38 180 65 94

A11-3_28 1E-05 39 181 65 95

Material

CP Fe

HP Fe

UHP Fe
18

Average values of all tensile parameters (considering only tests conducted at 10-3 s

-1

, 

10-4s

-1

, and 10-5 s

-1

) are presented as a function of tested material in Table 14 and as a function of 

strain rate in Table 15. Average values are also illustrated in Figures 14 to 17.

Table 14 – Average SCK•CEN test results as a function of tested material.

Table 15 – Average SCK•CEN test results as a function of strain rate.

Strain sYS sTS  t RA

rate (s-1) (MPa) (MPa) (%) (%)

1E-03 245 289 49 96

1E-04 221 268 51 96

1E-05 191 255 50 95

1E-03 201 252 48 91

1E-04 194 253 43 90

1E-05 177 242 44 92

1E-03 111 218 70 97

1E-04 95 209 70 96

1E-05 84 201 63 96

1E-03 72 204 72 96

1E-04 51 195 68 96

1E-05 39 181 65 95

Material

K05

K02

S11

A11

Strain sYS sTS t RA

rate (s-1) (MPa) (MPa) (%) (%)

K05 245 289 49 96

K02 201 252 48 91

S11 111 218 70 97

A11 72 204 72 96

K05 221 268 51 96

K02 194 253 43 90

S11 95 209 70 96

A11 51 195 68 96

K05 191 255 50 95

K02 177 242 44 92

S11 84 201 63 96

A11 39 181 65 95

Material

1E-03

1E-04

1E-05
19

Figure 14 - Average values of yield strength measured by SCK•CEN.

Figure 15 - Average values of tensile strength measured by SCK•CEN.

0

50

100

150

200

250 Yield strength (MPa)

1E-3 1/s

1E-4 1/s

1E-5 1/s

K05

(pure Fe)

K02

(high-purity Fe)

S11

(high-purity Fe)

A11

(UHP Fe)

0

50

100

150

200

250

300 Tensile strength (MPa)

1E-3 1/s

1E-4 1/s

1E-5 1/s

K05

(pure Fe)

K02

(high-purity Fe)

S11

(high-purity Fe)

A11

(UHP Fe)
20

Figure 16 - Average values of elongation at fracture measured by SCK•CEN.

Figure 17 - Average values of reduction of area measured by SCK•CEN.

Similar to the other participants, the results obtained by SCK•CEN confirm that yield and 

tensile strengths decrease with increasing material purity and decreasing strain rate, whereas 

ductility parameters do not exhibit specific trends.

0

10

20

30

40

50

60

70

80 Elongation at fracture (%)

1E-3 1/s

1E-4 1/s

1E-5 1/s

K05

(pure Fe)

K02

(high-purity Fe)

S11

(high-purity Fe)

A11

(UHP Fe)

50

55

60

65

70

75

80

85

90

95

100 Reduction of area (%)

1E-3 1/s

1E-4 1/s

1E-5 1/s

K05

(pure Fe)

K02

(high-purity Fe)

S11

(high-purity Fe)

A11

(UHP Fe)
21

3. Comparison of participants’ data

Table 16 is the master table which presents all the test results provided by the Round-Robin 

participants. When multiple tests on the same material and at the same strain rate are available for 

a single participant, the corresponding average values are given in Table 16.

Table 16 – Master table of the tensile Round-Robin results.

Strain sYS sTS  t RA

rate (s-1) (MPa) (MPa) (%) (%)

BAM 1E-03 231 283 47 95

NIST 1E-03 231 284 57 96

SCK-CEN 1E-03 245 289 49 96

IMR-TU 5E-03 244 280 48

SCK-CEN 5E-03 250 292 51 94

BAM 1E-04 204 262 51 95

NIST 1E-04 210 269 57 96

SCK-CEN 1E-04 221 268 51 96

IMR-TU 5E-04 208 258 53

SCK-CEN 5E-04 228 275 57 96

BAM 1E-05 176 250 50 95

NIST 1E-05 185 260 51 95

SCK-CEN 1E-05 191 255 50 95

IMR-TU 5E-05 201 251 51

SCK-CEN 5E-05 195 257 57 94

BAM 1E-03 195 245 46 88

NIST 1E-03 190 248 54 91

SCK-CEN 1E-03 201 252 48 91

IMR-TU 5E-03 205 243 53

SCK-CEN 5E-03 224 262 50 91

BAM 1E-04 169 237 47 89

NIST 1E-04 161 239 56 92

SCK-CEN 1E-04 194 253 43 90

IMR-TU 5E-04 187 239 47

SCK-CEN 5E-04 201 253 49 88

BAM 1E-05 163 232 43 91

NIST 1E-05 132 228 47 93

SCK-CEN 1E-05 177 242 44 92

IMR-TU 5E-05 174 236 42

SCK-CEN 5E-05 177 242 52 92

BAM 1E-03 105 206 73 96

NIST 1E-03 107 219 68 96

SCK-CEN 1E-03 111 218 70 97

IMR-TU 5E-03 124 211 73

SCK-CEN 5E-03 145 229 71 97

BAM 1E-04 88 201 73 96

NIST 1E-04 93 214 69 96

SCK-CEN 1E-04 95 209 70 96

IMR-TU 5E-04 101 206 71

SCK-CEN 5E-04 117 221 76 96

BAM 1E-05 66 189 66 96

NIST 1E-05 71 196 62 96

SCK-CEN 1E-05 84 201 63 96

IMR-TU 5E-05 70 188 64

SCK-CEN 5E-05 75 203 68 96

BAM 1E-03 68 201 71 95

NIST 1E-03 76 211 69 96

SCK-CEN 1E-03 72 204 72 96

IMR-TU 5E-03 92 199 69

SCK-CEN 5E-03 107 215 80 96

BAM 1E-04 44 188 67 95

NIST 1E-04 51 196 67 95

SCK-CEN 1E-04 51 195 68 96

IMR-TU 5E-04 58 187 68

SCK-CEN 5E-04 71 206 75 97

BAM 1E-05 28 178 58 95

NIST 1E-05 38 185 69 93

SCK-CEN 1E-05 39 181 65 95

IMR-TU 5E-05 42 177 65

SCK-CEN 5E-05 44 188 68 94

A11

Material Institute

K05

K02

S11
22

3.1. Yield strength

The values of yield strength obtained by BAM, NIST and SCK•CEN at 10-3s

-1

, 10-4s

-1

, 

and 10-5s

-1

are illustrated in Figure 18. Yield strengths measured by IMR-TU and SCK•CEN at 5 

× 10-3s

-1

, 5 × 10-4s

-1

, and 5 × 10-5s

-1

are shown in Figure 19.

Figure 18 – Yield strength values measured at 10-3s

-1

, 10-4s

-1

, and 10-5s

-1

.

Figure 19 – Yield strength values measured at 5 × 10-3s

-1

, 5 × 10-4s

-1

, and 5 × 10-5s

-1

.

0

50

100

150

200

250 Yield strength (MPa)

BAM NIST SCK-CEN

K05 K02 S11 A11

10-3 s

-1

10-4 s

-1

10-5 s

-1

10-3 s

-1

10-4 s

-1

10-5 s

-1

10-3 s

-1

10-4 s

-1

10-5 s

-1

10-3 s

-1

10-4 s

-1

10-5 s

-1

0

50

100

150

200

250 Yield strength (MPa)

IMR-TU SCK-CEN

K05 K02 S11 A11

5×10-3 s

-1

5×10-4 s

-1

5×10-5 s

-1

5×10-3 s

-1

5×10-4 s

-1

5×10-5 s

-1

5×10-3 s

-1

5×10-4 s

-1

5×10-5 s

-1

5×10-3 s

-1

5×10-4 s

-1

5×10-5 s

-1
23

3.2. Tensile strength

The values of tensile strength obtained by BAM, NIST and SCK•CEN at 10-3s

-1

, 10-4s

-1

, 

and 10-5s

-1

are illustrated in Figure 20. Tensile strengths measured by IMR-TU and SCK•CEN at 

5 × 10-3s

-1

, 5 × 10-4s

-1

, and 5 × 10-5s

-1

are shown in Figure 21.

Figure 20 – Tensile strength values measured at 10-3s

-1

, 10-4s

-1

, and 10-5s

-1

.

Figure 21 – Tensile strength values measured at 5 × 10-3s

-1

, 5 × 10-4s

-1

, and 5 × 10-5s

-1

.

150

170

190

210

230

250

270

290 Tensile strength (MPa)

BAM NIST SCK-CEN

K05 K02 S11 A11

10-3 s

-1

10-4 s

-1

10-5 s

-1

10-3 s

-1 10-4 s

-1

10-5 s

-1

10-3 s

-1

10-4 s

-1

10-5 s

-1

10-3 s

-1

10-4 s

-1

10-5 s

-1

150

170

190

210

230

250

270

290 Tensile strength (MPa)

IMR-TU SCK-CEN

K05 K02 S11 A11

5×10-3 s

-1

5×10-4 s

-1

5×10-5 s

-1

5×10-3 s

-1

5×10-4 s

-1

5×10-5 s

-1

5×10-3 s

-1

5×10-4 s

-1

5×10-5 s

-1

5×10-3 s

-1

5×10-4 s

-1

5×10-5 s

-1
24

3.3. Elongation at fracture

The values of elongation at fracture obtained by BAM, NIST and SCK•CEN at 10-3s

-1

, 

10-4s

-1

, and 10-5s

-1

are illustrated in Figure 22. Values measured by IMR-TU and SCK•CEN at 

5 × 10-3s

-1

, 5 × 10-4s

-1

, and 5 × 10-5s

-1

are shown in Figure 23.

Figure 22 – Elongation at fracture values measured at 10-3s

-1

, 10-4s

-1

, and 10-5s

-1

.

Figure 23 – Elongation at fracture values measured at 5 × 10-3s

-1

, 5 × 10-4s

-1

, and 5 × 10-5s

-1

.

0

10

20

30

40

50

60

70

80 Elongation at fracture (%)

BAM NIST SCK-CEN

K05 K02 S11 A11

10-3 s

-1 10-4 s

-1

10-5 s

-1

10-3 s

-1 10-4 s

-1

10-5 s

-1

10-3 s

-1 10-4 s

-1

10-5 s

-1

10-3 s

-1

10-4 s

-1 10-5 s

-1

0

10

20

30

40

50

60

70

80

90 Elongation at fracture (%)

IMR-TU SCK-CEN

K05 K02 S11 A11

5×10-3 s

-1

5×10-4 s

-1 5×10-5 s

-1

5×10-3 s

-1

5×10-4 s

-1

5×10-5 s

-1

5×10-3 s

-1

5×10-4 s

-1

5×10-5 s

-1

5×10-3 s

-1

5×10-4 s

-1

5×10-5 s

-1
25

3.4. Reduction of area

The values of reduction of area obtained by BAM, NIST and SCK•CEN at 10-3s

-1

, 10-4s

-1

, 

and 10-5s

-1

are illustrated in Figure 24. 

Figure 24 – Reduction of area values measured at 10-3s

-1

, 10-4s

-1

, and 10-5s

-1

.

3.5. General remarks

The comparisons presented in the previous sections show a tendency for SCK•CEN to 

measure higher yield strengths than the other participants (Figures 18 and 19). The same is 

observed in Figure 21 for tensile strengths with respect to IMR-TU.

No other trends can be detected from the examination of Figures 18 to 24.

80

82

84

86

88

90

92

94

96

98

100 Reduction of area (%)

BAM NIST SCK-CEN

K05 K02 S11 A11

10-3 s

-1 10-4 s

-1

10-5 s

-1

10-3 s

-1

10-4 s

-1

10-5 s

-1

10-3 s

-1

10-4 s

-1 10-5 s

-1

10-3 s

-1

10-4 s

-1

10-5 s

-1
26

4. Discussion

The tensile properties of the investigated materials, obtained by averaging the results 

provided by the Round-Robin participants, are presented in Table 17.

Table 17 - Average tensile properties of the investigated materials.

Standard deviations for yield and tensile strengths are provided in Table 18.

Strain sYS sTS  t RA

rate (s-1) (MPa) (MPa) (%) (%)

1E-03 236 285 51 95

5E-03 247 286 50 94

1E-04 212 266 53 96

5E-04 218 267 55 96

1E-05 184 255 50 95

5E-05 198 254 54 94

1E-03 195 248 49 90

5E-03 214 253 51 91

1E-04 174 243 48 90

5E-04 194 246 48 88

1E-05 157 234 45 92

5E-05 175 239 47 92

1E-03 108 214 70 96

5E-03 135 220 72 97

1E-04 92 208 71 96

5E-04 109 213 74 96

1E-05 74 195 63 96

5E-05 72 195 66 96

1E-03 72 205 71 95

5E-03 100 207 74 96

1E-04 48 193 67 95

5E-04 65 196 72 97

1E-05 35 181 64 94

5E-05 43 182 67 94

Material

K05

K02

S11

A11
27

Table 18 – Standard deviations for yield and tensile strengths.

Tensile parameters, with the exception of uniform elongation, are represented in Figures 

25 to 28 as a function of strain rate. The power law relationships obtained by least-square 

regression of the mean sYS and sTS values given in Table 17 have the following form:





s  













dt

d

, (1)

where s is yield or tensile strength in MPa, and 













dt

d

is strain rate in s-1. The regression 

coefficients  and  are listed in Table 19 for the four materials, along with the coefficient of 

determination (R2) of the regression. A power law is generally considered to provide the best 

description of the relationship between yield strength and strain rate at a given temperature [5].

The exponent  represents the material’s strain rate sensitivity at the test temperature.

In Figures 27 and 28, elongation at fracture and reduction of area are also fitted by the use 

of power functions, just as a guide for the eye. However, trends are not clear and scatter is 

significant, so fitting coefficients for ductility parameters are not reported.

Strain

rate (s-1) sYS sTS

1E-03 8.2 2.9

5E-03 4.5 8.4

1E-04 8.5 3.7

5E-04 14.1 11.7

1E-05 7.6 4.8

5E-05 4.1 4.5

1E-03 5.7 3.3

5E-03 13.6 13.4

1E-04 16.9 8.5

5E-04 10.2 9.7

1E-05 22.8 7.3

5E-05 2.2 4.0

1E-03 3.0 7.4

5E-03 14.6 12.6

1E-04 3.5 6.3

5E-04 11.5 10.6

1E-05 9.4 5.9

5E-05 3.8 10.8

1E-03 3.8 5.1

5E-03 10.4 11.1

1E-04 4.1 4.5

5E-04 9.2 13.5

1E-05 5.9 3.3

5E-05 1.3 7.8

St. dev. (MPa) Material

K05

K02

S11

A11
28

Table 19 - Regression results for yield and tensile strengths (average values).

Material Designation Parameter   R2

CP Fe K05 sYS

sTS

320.25

321.14

0.0476

0.0213

0.9698

0.8356

HP Fe

K02 sYS

sTS

275.62

269.88

0.0479

0.0121

0.9795

0.9869

S11 sYS

sTS

229.81

248.23

0.1041

0.0213

0.9163

0.8925

UHP Fe A11 sYS

sTS

237.57

237.89

0.1702

0.0243

0.9945

0.9170

Figure 25 - Average yield strength values as a function of strain rate. Error bars correspond to one 

standard deviation.

y = 320.25x0.0476

y = 275.62x0.0479

y = 229.81x0.1041

y = 237.57x0.1702

0

50

100

150

200

250

300

1E-05 1E-04 1E-03 Yield strength (MPa)

Strain rate (s-1)

K05 (pure Fe)

K02 (HP Fe)

S11 (HP Fe)

A11 (UHP Fe)
29

Figure 26 - Average tensile strength values as a function of strain rate. Error bars correspond to one 

standard deviation.

Figure 27 - Average elongation at fracture values as a function of strain rate.

y = 321.14x0.0213

y = 269.88x0.0121

y = 248.23x0.0213

y = 237.89x0.0243

150

170

190

210

230

250

270

290

310

1E-05 1E-04 1E-03 Tensile strength (MPa)

Strain rate (s-1)

K05 (pure Fe)

K02 (HP Fe)

S11 (HP Fe)

A11 (UHP Fe)

40

45

50

55

60

65

70

75

80

1.E-05 1.E-04 1.E-03 Elongation at fracture (%)

Strain rate (s-1)

K05 (pure Fe)

K02 (HP Fe)

S11 (HP Fe)

A11 (UHP Fe)
30

Figure 28 - Average reduction of area values as a function of strain rate.

Examination of Figures 25 and 26 confirms the well-documented increase of yield and 

tensile strength with increasing strain rates [6-9]. The strain rate sensitivity, expressed by the 

coefficient  in Table 19, increases with material purity, and is maximum for A11 (UHP iron). 

Note also that the strain rate sensitivity of CP Fe (K05) and HP Fe (K02) is almost identical.

The influence of strain rate on tensile strengths (Figure 26) is smaller than for yield 

strengths, more so for the higher purity materials (Table 19). Once again, the coefficient  is 

highest for A11 (UHP iron). In this case, K05 (CP Fe) and S11 (HP Fe) yielded identical values 

of .

As already mentioned, trends for ductility parameters (elongation at fracture in Figure 27

and reduction of area in Figure 28) are less clear. Generally, ductility appears to increase with 

strain rate, with a few exceptions. 

Strengthening mechanisms in iron typically include precipitation, as well as interstitial and 

solid-solution strengthening. As the purity of iron increases, the mechanical resistance (yield and 

tensile strength) decreases because of a cleaner microstructure which offers less resistance to the 

movement of dislocations. Trends for elongation at fracture and reduction of area are somewhat 

less well-defined. The effect of iron purity level on tensile properties can be appreciated in Figures 

25 to 28, but also in Figures 18 to 24 and Table 17.

It is interesting to note that the Round-Robin results indicate a clear difference between the 

two materials classified as high-purity iron, K02 and S11. The former has mechanical properties 

which are relatively close to the commercially pure iron (K05), whereas the latter behaves very

87

88

89

90

91

92

93

94

95

96

97

98

1.E-05 1.E-04 1.E-03 Reduction of area (%)

Strain rate (s-1)

K05 (pure Fe)

K02 (HP Fe)

S11 (HP Fe)

A11 (UHP Fe)
31

similar to the ultra-high purity iron (A11). Differences in chemical composition, such as the 

significantly different contents of C, N, and S in Table 2, are certainly among the main causes of 

these observations. The effect of the melting environment (200 Torr argon in a ceramics crucible 

for K05 and K02; ultra-high vacuum in a water-cooled Cu crucible for S11 and A11) can also be 

considered a contributing factor.

5. Conclusions

An international Round-Robin was conducted among four laboratories (BAM, IMR-TU, 

NIST and SCK•CEN) in order to characterize the tensile properties of iron with different purity 

levels, ranging from commercially pure (99.984 %) to ultra-high purity (> 99.999 %). Tensile tests 

were performed at room temperature and at different strain rates in the range 10-5s

-1

to 5 × 10-3s

-1

.

The data collected from the participating labs provide a consistent picture of the investigated 

materials’ tensile properties, as well as of the influence of strain rate and material purity.

The following conclusions can be drawn from the analysis of the Round-Robin results.

(1) As expected, an increase of strain rate causes an increase of yield strength and, to a lesser 

extent, tensile strength for all the materials. Average test results were fitted by power law 

relationships, showing that the strain rate sensitivity (quantified by the regression exponent) 

increases with material purity. The effect of strain rate is most pronounced for ultra-highpurity iron (A11).

(2) Yield and tensile strength clearly decrease with increasing material purity. Ductility is 

similarly affected, although once again trends are less well-defined.

(3) A clear difference in tensile properties was observed between the two high-purity materials 

(K02 and S11), caused by differences in chemical composition and in the production process.

Acknowledgments

The collaboration of Jeff Sowards and David McColskey at NIST Boulder is gratefully 

acknowledged, as well as the many fruitful discussions and the technical review of this report.
32

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