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ISO 898-1

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Mechanical properties of fasteners made of carbon steel and alloy steel

Contents:

> Scope
> Designation system for property classes
> Table 1 — Ratio of nominal yield strength and nominal tensile strength
> Materials
> Table 2 — Steels
> Mechanical and physical properties
> Table 3 — Mechanical and physical properties of bolts, screws and studs
> Table 4 — Minimum ultimate tensile loads — ISO metric coarse pitch thread
> Table 5 — Proof loads — ISO metric coarse pitch thread
> Table 6 — Minimum ultimate tensile loads — ISO metric fine pitch thread
> Table 7 — Proof loads — ISO metric fine pitch thread
> Table A.1 — Relationship between tensile strength and elongation after fracture
> Influence of elevated temperatures on mechanical properties of fasteners
> Elongation after fracture for full-size fasteners

Scope

This part of ISO 898 specifies mechanical and physical properties of bolts, screws and studs made of carbon steel and alloy steel when tested at an ambient temperature range of 10 °C to 35 °C. Fasteners (the term used when bolts, screws and studs are considered all together) that conform to the requirements of this part of ISO 898 are evaluated at that ambient temperature range. They might not retain the specified mechanical and physical properties at elevated temperatures (see Annex B) and/or lower temperatures.

This part of ISO 898 is applicable to bolts, screws and studs
⎯ made of carbon steel or alloy steel,
⎯ having triangular ISO metric screw thread in accordance with ISO 68-1,
⎯ with coarse pitch thread M1,6 to M39, and fine pitch thread M8×1 to M39×3,
⎯ with diameter/pitch combinations in accordance with ISO 261 and ISO 262, and
⎯ having thread tolerances in accordance with ISO 965-1, ISO 965-2 and ISO 965-4.
It is not applicable to set screws and similar threaded fasteners not under tensile stress (see ISO 898-5).
It does not specify requirements for such properties as
⎯ weldability,
⎯ corrosion resistance,
⎯ resistance to shear stress,
⎯ torque/clamp force performance (for test method, see ISO 16047), or
⎯ fatigue resistance.

Designation system for property classes

The  symbol for property classes of bolts, screws, and studs consists of two numbers, separated by a dot (see Tables 1 to 3):
a) the number to the left of the dot consists of one or two digits and indicates 1/100 of the nominal tensile strength, Rm,nom, in megapascals (see Table 3, No. 1);
b) the number to the right of the dot indicates 10 times the ratio between the nominal yield strength and the nominal tensile strength, Rm,nom, as specified in Table 1 (yield strength ratio). The nominal yield strength, as specified in Table 3 (Nos. 2 to 4), is:
– lower yield strength ReL,nom, or
⎯ nominal stress at 0,2 % non-proportional elongation Rp0,2 nom, or
⎯ nominal stress at 0,0048d non-proportional elongation Rpf,nom.

Table 1 — Ratio of nominal yield strength and nominal tensile strength

Number to the right of dot .6 .8 .9
ReL,nom/Rm,nom  or Rp0,2,nom / Rm,nom  or Rpf,nom / Rm,nom 0,6 0,8 0,9

c) an additional zero to the left of the property class designation indicates that fasteners have reduced loadability.

Materials

Table 2 specifies limits for the chemical composition of steels and minimum tempering temperatures for the different property classes of bolts, screws and studs. The chemical composition shall be assessed in accordance with the relevant International Standards.

For fasteners that are to be hot dip galvanized, the additional material requirements given in ISO 10684 apply.

Table 2 — Steels

Property class Material and heat treatment Chemical composition limits
(cast analysis, %) a		 Tempering temperature
·C
min.
C P
max.		 S
max.		 Bb
max.
min. max.
4.6cd Carbon steel or carbon steel with additives – 055 0.050 0,060 Not specified —
4.8d
5.6c 013 055 0.050 0,060
5.8d – 055 0.050 0,060
6.8d 015 055 0.050 0,060
8.8f Carbon steel with additives (e.g. Boron or Mn or Cr) quenched and tempered 015e 040 0.025 0,025 0,003 425
or
Carbon steel quenched and tempered		 025 055 0.025 0,025
or
Alloy steel quenched and temperedg		 020 055 0.025 0,025
9.8f Carbon steel with additives (e.g. Boron or Mn or Cr) quenched and tempered 015e 040 0,025 0,025 0,003 425
or
Carbon steel quenched and tempered		 025 055 0.025 0,025
or
Alloy steel quenched and temperedg		 020 055 0.025 0,025
10.9f Carbon steel with additives (e.g. Boron or Mn or Cr) quenched and tempered 0,20e 055 0,025 0,025 0,003 425
or
Carbon steel quenched and tempered		 025 055 0.025 0,025
or
Alloy steel quenched and temperedg		 020 055 0,025 0,025
12..9fhi Alloy steel quenched and temperedg 030 050 0.025 0,025 0,003 425
12..9fhi Carbon steel with additives (e.g. Boron or Mn or Cr or Molybdenum)quenched and tempered 028 050 0.025 0,025 0,003 380
a In case of dispute, the product analysis applies.
b Boron content can reach 0,005 %, provided non-effective boron is controlled by the addition of titanium and/or aluminium.
c For cold forged fasteners of property classes 4.6 and 5.6, heat treatment of the wire used for cold forging or of the cold forged fastener itself may be necessary to achieve required ductility.
d Free cutting steel is allowed for these property classes with the following maximum sulfur, phosphorus and lead contents:
S: 0,34 %; P: 0,11 %; Pb: 0,35 %.
e In case of plain carbon boron steel with a carbon content below 0,25 % (cast analysis), the minimum manganese content shall be 0,6 % for property class 8.8 and 0,7 % for property classes 9.8 and 10.9.
f For the materials of these property classes, there shall be a sufficient hardenability to ensure a structure consisting of approximately 90 % martensite in the core of the threaded sections for the fasteners in the “as-hardened” condition beforetempering. This alloy steel shall contain at least one of the following elements in the minimum quantity given: chromium 0,30 %, nickel 0,30 %, molybdenum 0,20 %, vanadium 0,10 %. Where elements are specified in combinations of two, three or four and have alloy contents less than those given above, the limit value to be applied for steel class determination is 70 % of the sum of the individual limit values specified above for the two, three or four elements concerned.
h Fasteners manufactured from phosphated raw material shall be dephosphated before heat treatment; the absence of white phosphorus enriched layer shall be detected by a suitable test method.
i Caution is advised when the use of property class 12.9/12.9 is considered. The capability of the fastener manufacturer, the service conditions and the wrenching methods should be considered. Environments can cause stress corrosion cracking of fasteners as processed as well as those coated. 

Mechanical and physical properties

The bolts, screws and studs of the specified property classes shall, at ambient temperature (Impact strength is tested at a temperature of −20 °C), meet all the applicable mechanical and physical properties in accordance with Tables 3 to 7, regardless of which tests are performed during manufacturing or final inspection.

Clause 8 sets forth the applicability of test methods for verifying that fasteners of different types and dimensions fulfil the properties in accordance with Table 3 and Tables 4 to 7.

NOTE 1 Even if the steel properties of the fasteners meet all relevant requirements specified in Tables 2 and 3, some types of fasteners have reduced loadability due to dimensional reasons.

NOTE 2 Although a great number of property classes are specified in this part of ISO 898, this does not mean that all classes are appropriate for all fasteners. Further guidance for application of the specific property classes is given in the relevant product standards. For non-standard fasteners, it is advisable to follow as closely as possible the choice already made for similar standard fasteners.

Table 3 — Mechanical and physical properties of bolts, screws and studs

No. Mechanical or physical property Property class
4.6 4.8 5.6 5.8 6.8 8.8 9.8 10.9 12.9
d ≤ d > d ≤
16 mma 16 mmb 16 mm
1 Tensile strength, Rm, MPa nom.c 400 500 600 800 900 1000 1200
min. 400 420 500 520 600 800 830 900 1040 1220
2 Lower yield strength, ReLd, MPa nom.c 240 — 300 — — — — — — —
min. 240 — 300 — — — — — — —
3 Stress at 0,2 % non-proportional elongation, Rp0,2, MPa nom.c — — — — — 640 640 720 900 1080
min. — — — — — 640 660 720 940 1100
4 Stress at 0,0048d non-proportional elongation for full-size fasteners, Rpf, MPa nom.c — 320 — 400 480 — — — — —
min. — 340e — 420e 480e — — — — —
5 Stress under proof load, Spf, Mpa nom. 225 310 280 380 440 580 600 650 830 970
Proof strength ratio
Sp,nom/ReL,min or
Sp,nom/Rp0,2 min or
Sp,nom/Rpf,min		 0,94 0,91 0,93 0,90 0,92 0,91 0,91 0,90 0,88 0,88
6 Percentage elongation after fracture for machined test pieces, A, % min. 22 — 20 — — 12 12 10 9 8
7 Percentage reduction of area after fracture for machined test pieces, Z, % min. — 52 48 48 44
8 Elongation after fracture for full-size fasteners, Af (see also Annex C) min. — 0,24 — 0,22 0,20 — — — — —
9 Head soundness No fracture
10 Vickers hardness, HV
F ≥ 98 N		 min. 120 130 155 160 190 250 255 290 320 385
max. 220g 250 320 335 360 380 435
11 Brinell hardness, HBW
F = 30 D2		 min. 114 124 147 152 181 245 250 286 316 380
max. 209g 238 316 331 355 375 429
12 Rockwell hardness, HRB min. 67 71 79 82 89 —
max. 95,0g 99,5 —
Rockwell hardness, HRC min. — 22 23 28 32 39
max. — 32 34 37 39 44
13 Surface hardness, HV 0,3 max. — — 390 435
14 Non-carburization, HV 0,3 max. — h h h
15 Height of non-decarburized thread zone,
E, mm		 min. — ½ H1 2/3 H1 ¾ H1
Depth of complete decarburization in the thread, G, mm max. — 0,015
16 Reduction of hardness after retempering, HV max. — 20
17 Breaking torque, MB, Nm min. — in accordance with ISO 898-7
18 Impact strength, KVij J min. — 27 — 27 27 27 27 k
19 Surface integrity in accordance with ISO 6157-1l ISO 6157-3
a Values do not apply to structural bolting.
b For structural bolting d ≥ M12.
c Nominal values are specified only for the purpose of the designation system for property classes. See Clause 5.
d In cases where the lower yield strength, ReL, cannot be determined, it is permissible to measure the stress at 0,2 % nonproportional elongation Rp0,2.
e For the property classes 4.8, 5.8 and 6.8, the values for Rpf,min are under investigation. The values at the time of publication of this part of ISO 898 are given for calculation of the proof stress ratio only. They are not test values.
f Proof loads are specified in Tables 5 and 7.
g Hardness determined at the end of a fastener shall be 250 HV, 238 HB or 99,5 HRB maximum.
h Surface hardness shall not be more than 30 Vickers points above the measured base metal hardness of the fastener when determination of both surface hardness and base metal hardness are carried out with HV 0,3 (see 9.11).
i Values are determined at a test temperature of −20 °C (see 9.14).
j Applies to d ≥ 16 mm.
k Value for KV is under investigation.
l Instead of ISO 6157-1, ISO 6157-3 may apply by agreement between the manufacturer and the purchaser.

Table 4 — Minimum ultimate tensile loads — ISO metric coarse pitch thread

 

Threada

d
Nominal
stress areaAs,nomb
mm2		 Property class
4.6 4.8 5.6 5.8 6.8 8.8 9.8 10.9 12.9/12.9
Minimum ultimate tensile load, Fm,min (As,nom × Rm,min), N
M3 5,03 2 010 2 110 2 510 2 620 3 020 4 020 4 530 5 230 6 140
M3,5 6,78 2 710 2 850 3 390 3 530 4 070 5 420 6 100 7 050 8 270
M4 8,78 3 510 3 690 4 390 4 570 5 270 7 020 7 900 9 130 10 700
M5 14,2 5 680 5 960 7 100 7 380 8 520 11 350 12 800 14 800 17 300
M6 20,1 8 040 8 440 10 000 10 400 12 100 16 100 18 100 20 900 24 500
M7 28,9 11 600 12 100 14 400 15 000 17 300 23 100 26 000 30 100 35 300
M8 36,6 14 600c 15 400 18 300c 19 000 22 000 29 200c 32 900 38 100c 44 600
M10 58 23 200c 24 400 29 000c 30 200 34 800 46 400c 52 200 60 300c 70 800
M12 84,3 33 700 35 400 42 200 43 800 50 600 67 400d 75 900 87 700 103 000
M14 115 46 000 48 300 57 500 59 800 69 000 92 000d 104 000 120 000 140 000
M16 157 62 800 65 900 78 500 81 600 94 000 125 000d 141 000 163 000 192 000
M18 192 76 800 80 600 96 000 99 800 115 000 159 000 — 200 000 234 000
M20 245 98 000 103 000 122 000 127 000 147 000 203 000 — 255 000 299 000
M22 303 121 000 127 000 152 000 158 000 182 000 252 000 — 315 000 370 000
M24 353 141 000 148 000 176 000 184 000 212 000 293 000 — 367 000 431 000
M27 459 184 000 193 000 230 000 239 000 275 000 381 000 — 477 000 560 000
M30 561 224 000 236 000 280 000 292 000 337 000 466 000 — 583 000 684 000
M33 694 278 000 292 000 347 000 361 000 416 000 576 000 — 722 000 847 000
M36 817 327 000 343 000 408 000 425 000 490 000 678 000 — 850 000 997 000
M39 976 390 000 410 000 488 000 508 000 586 000 810 000 — 1 020 000 1 200 000
a Where no thread pitch is indicated in a thread designation, coarse pitch is specified.
b  To calculate As,nom, see 9.1.6.1.
c  For fasteners with thread tolerance 6az in accordance with ISO 965-4 subject to hot dip galvanizing, reduced values in accordance with ISO 10684:2004, Annex A, apply.
d  For structural bolting 70 000 N (for M12), 95 500 N (for M14) and 130 000 N (for M16).

Table 5 — Proof loads — ISO metric coarse pitch thread

 

Threada

d
Nominal
stress areaAs,nomb
mm2		 Property class
4.6 4.8 5.6 5.8 6.8 8.8 9.8 10.9 12.9/12.9
Proof load, Fp (As,nom × Sp,nom), N
M3 5,03 1 130 1 560 1 410 1 910 2 210 2 920 3 270 4 180 4 880
M3,5 6,78 1 530 2 100 1 900 2 580 2 980 3 940 4 410 5 630 6 580
M4 8,78 1 980 2 720 2 460 3 340 3 860 5 100 5 710 7 290 8 520
M5 14,2 3 200 4 400 3 980 5 400 6 250 8 230 9 230 11 800 13 800
M6 20,1 4 520 6 230 5 630 7 640 8 840 11 600 13 100 16 700 19 500
M7 28,9 6 500 8 960 8 090 11 000 12 700 16 800 18 800 24 000 28 000
M8 36,6 8 240c 11 400 10 200c 13 900 16 100 21 200c 23 800 30 400c 35 500
M10 58 13 000c 18 000 16 200c 22 000 25 500 33 700c 37 700 48 100c 56 300
M12 84,3 19 000 26 100 23 600 32 000 37 100 48 900d 54 800 70 000 81 800
M14 115 25 900 35 600 32 200 43 700 50 600 66 700d 74 800 95 500 112 000
M16 157 35 300 48 700 44 000 59 700 69 100 91 000d 102 000 130 000 152 000
M18 192 43 200 59 500 53 800 73 000 84 500 115 000 — 159 000 186 000
M20 245 55 100 76 000 68 600 93 100 108 000 147 000 — 203 000 238 000
M22 303 68 200 93 900 84 800 115 000 133 000 182 000 — 252 000 294 000
M24 353 79 400 109 000 98 800 134 000 155 000 212 000 — 293 000 342 000
M27 459 103 000 142 000 128 000 174 000 202 000 275 000 — 381 000 445 000
M30 561 126 000 174 000 157 000 213 000 247 000 337 000 — 466 000 544 000
M33 694 156 000 215 000 194 000 264 000 305 000 416 000 — 576 000 673 000
M36 817 184 000 253 000 229 000 310 000 359 000 490 000 — 678 000 792 000
M39 976 220 000 303 000 273 000 371 000 429 000 586 000 — 810 000 947 000
a Where no thread pitch is indicated in a thread designation, coarse pitch is specified.
b  To calculate As,nom.
c  For fasteners with thread tolerance 6az in accordance with ISO 965-4 subject to hot dip galvanizing, reduced values in accordance with ISO 10684:2004.
d  For structural bolting 50 700 N (for M12), 68 800 N (for M14) and 94 500 N (for M16).

Table 6 — Minimum ultimate tensile loads — ISO metric fine pitch thread

 

Thread

d x P
Nominal
stress areaAs,noma
mm2		 Property class
4.6 4.8 5.6 5.8 6.8 8.8 9.8 10.9 12.9/12.9
Minimum ultimate tensile load, Fm,min (As,nom × Rm,min), N
M8×1 39,2 15 700 16 500 19 600 20 400 23 500 31 360 35 300 40 800 47 800
M10×1,25 61,2 24 500 25 700 30 600 31 800 36 700 49 000 55 100 63 600 74 700
M10×1 64,5 25 800 27 100 32 300 33 500 38 700 51 600 58 100 67 100 78 700
M12×1,5 88,1 35 200 37 000 44 100 45 800 52 900 70 500 79 300 91 600 107 000
M12×1,25 92,1 36 800 38 700 46 100 47 900 55 300 73 700 82 900 95 800 112 000
M14×1,5 125 50 000 52 500 62 500 65 000 75 000 100 000 112 000 130 000 152 000
M16×1,5 167 66 800 70 100 83 500 86 800 100 000 134 000 150 000 174 000 204 000
M18×1,5 216 86 400 90 700 108 000 112 000 130 000 179 000 — 225 000 264 000
M20×1,5 272 109 000 114 000 136 000 141 000 163 000 226 000 — 283 000 332 000
M22×1,5 333 133 000 140 000 166 000 173 000 200 000 276 000 — 346 000 406 000
M24×2 384 154 000 161 000 192 000 200 000 230 000 319 000 — 399 000 469 000
M27×2 496 198 000 208 000 248 000 258 000 298 000 412 000 — 516 000 605 000
M30×2 621 248 000 261 000 310 000 323 000 373 000 515 000 — 646 000 758 000
M33×2 761 304 000 320 000 380 000 396 000 457 000 632 000 — 791 000 928 000
M36×3 865 346 000 363 000 432 000 450 000 519 000 718 000 — 900 000 1 055 000
M39×3 1 030 412 000 433 000 515 000 536 000 618 000 855 000 — 070 000 1 260 000

Table 7 — Proof loads — ISO metric fine pitch thread

 

Thread

d x P
Nominal
stress areaAs,noma
mm2		 Property class
4.6 4.8 5.6 5.8 6.8 8.8 9.8 10.9 12.9/12.9
Proof load, Fp (As,nom × Sp,nom), N
M8x1 39,2 8 820 12 200 11 000 14 900 17 200 22 700 25 500 32 500 38 000
M10x1,25 61,2 13 800 19 000 17 100 23 300 26 900 35 500 39 800 50 800 59 400
M10x1 64,5 14 500 20 000 18 100 24 500 28 400 37 400 41 900 53 500 62 700
M12x1,5 88,1 19 800 27 300 24 700 33 500 38 800 51 100 57 300 73 100 85 500
M12x1,25 92,1 20 700 28 600 25 800 35 000 40 500 53 400 59 900 76 400 89 300
M14x1,5 125 28 100 38 800 35 000 47 500 55 000 72 500 81 200 104 000 121 000
M16x1,5 167 37 600 51 800 46 800 63 500 73 500 96 900 109 000 139 000 162 000
M18x1,5 216 48 600 67 000 60 500 82 100 95 000 130 000 — 179 000 210 000
M20x1,5 272 61 200 84 300 76 200 103 000 120 000 163 000 — 226 000 264 000
M22x1,5 333 74 900 103 000 93 200 126 000 146 000 200 000 — 276 000 323 000
M24x2 384 86 400 119 000 108 000 146 000 169 000 230 000 — 319 000 372 000
M27x2 496 112 000 154 000 139 000 188 000 218 000 298 000 — 412 000 481 000
M30x2 621 140 000 192 000 174 000 236 000 273 000 373 000 — 515 000 602 000
M33x2 761 171 000 236 000 213 000 289 000 335 000 457 000 — 632 000 738 000
M36x3 865 195 000 268 000 242 000 329 000 381 000 519 000 — 718 000 839 000
M39x3 1 030 232 000 319 000 288 000 391 000 453 000 618 000 — 855 000 999 000

Relationshipbetween tensile strength and elongation after fracture

Table A.1 — Relationship between tensile strength and elongation after fracture

ISO 898-1, Table A.1, tensile strength and elongation

Influence of elevated temperatures on mechanical properties of fasteners

Elevated temperatures can cause changes in the mechanical properties and in the functional performance of a fastener.

Up to typical service temperatures of 150 °C, no detrimental effects due to a change of mechanical properties of fasteners are known. At temperatures over 150 °C and up to a maximum temperature of 300 °C, the functional performance of fasteners should be ensured by careful examination.

With increasing temperature, a progressive
⎯ reduction of lower yield strength or stress at 0,2 % non-proportional elongation or stress at 0,0048d nonproportional
elongation for finished fasteners, and
⎯ reduction of tensile strength
can be experienced. The continuous operating of fasteners at elevated service temperatures can result in stress relaxation, which increases with higher temperatures. Stress relaxation accompanies a loss of clamp force.

Work-hardened fasteners (property classes 4.8, 5.8, 6.8) are more sensitive with regard to stress relaxation compared with quenched andtempered

or stress-relieved fasteners.

Care should be taken when lead-containing steels are used for fasteners at elevated temperatures. For such fasteners, a risk of liquid metal embrittlement (LME) should be taken into consideration when the service temperature is in the range of the melting point of lead.

Information for the selection and application of steels for use at elevated temperatures is given, for example, in EN 10269 and in ASTM F2281.

Elongation after fracture for full-size fasteners, Af

In Table 3, minimum values for elongation after fracture for full-size bolts, screws and studs (Af,min) are specified for the property classes 4.8, 5.8 and 6.8 only. Values for the other property classes are given in Table C.1 for information. These values are still under investigation.

Property class 4.6 5.6 8.8 9.8 10.9 12.9
Af,min 0,37 0,33 0,20 — 0,13 —
ISO ISO 898-1 Mechanical Properties Tables ISO 898-1
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