Bolt grades and property classes

There are bolt designation system and property classes

Steel for the various property classes is as shown in the table blow.

For size M20 and larger a temperature of 425 ºC may be used.

The minimum tempering temperatures listed in above table are mandatory for property classes 8.8 to 12.9 in all cases.

Property Class Material and Treatment Tempering Temperature ÂºC Minimum
4.6 Low or medium carbon steel _
4.8
5.6
5.8
6.8
8.8 Low carbon steel with additives (e.g. boron or Mn or Cr), quenched and tempered 425
Medium carbon steel, quenched and tempered 450*
9.8 Low carbon steel with additives (e.g. boron or Mn or Cr), quenched and tempered or 410
Medium carbon steel, quenched and tempered
10.9 Low carbon steel with additives (e.g. boron or Mn or Cr), quenched and tempered or 340
Medium carbon steel, quenched and tempered or 425
Medium carbon steel with additives (e.g. boron or Mn or Cr), quenched and tempered or
Alloy steel
12.9 Alloy steel 380

Mechanical properties

Some of the important properties like tensile strength,Brinell hardness and elongation after fracture as % for various property classes are as under .

Clause No. Mechanical Property 4.6 4.8 5.6 5.8 6.8 8.8≤ M16 8.8>M16 9.8 10.9 12.9
4.1 & 4.2 Tensile strength,Rm, N/mm2,
Nominal
400 400 500 500 600 800 800 900 1000 1200
Tensile strength, Rm, N/mm2,
Minimum
400 420 500 520 600 800 830 900 1040 1220
4.4 Brinell hardness HB Minimum 114 124 147 152 181 219 242 266 295 353
Brinell hardness HB Maximum 209 238 285 319 342 362 412
4.7 Yield stress, ReL, N/mm2,
Nominal
240 320 300 400 480 - - - - -
Yield stress, ReL, N/mm2,
Minimum
240 340 300 420 480 - - - - -
4.8 Stress at permanent set limit, Rp0.2,
N/mm2Nominal
- 640 640 720 900 1080
Stress at permanent set limit, Rp0.2,
N/mm2Minimum
- 640 660 720 940 1100
4.9 Stress under proof load, S, Sp/ReL
Ratio of proof load stress and yield stress
0.94 0.91 0.94 0.91 0.91 0.91 0.91 0.91 0.88 0.88
Stress under proof load, S, N/mm2 225 310 280 380 440 580 600 650 830 970
4.10 Elongation after fracture A5 % 22 14 20 10 8 12 12 10 9 8

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