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 ºC 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/mm2, Nominal |
– | 640 | 640 | 720 | 900 | 1080 | ||||
| Stress at permanent set limit, Rp0.2, N/mm2, Minimum |
– | 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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