Specifications
Surface Treatments
Certifications
- ISO 9001 - 2015 Certified
- PED 2014/68/EC
- NACE MR0175/ISO 15156-2
- NORSOK M-650
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
21CrMoV5-7 vs ASTM A193 Grade B8
21CrMoV5-7 (Werkstoff 1.7709) and ASTM A193 Grade B8 are not in the same alloy class. 21CrMoV5-7 is a low-alloy Cr-Mo-V quenched-and-tempered ferritic steel for elevated-temperature bolting service to 550 deg C. B8 is austenitic stainless steel (Type 304 base, Class 1 solution treated) chosen for corrosion resistance, cryogenic service, and high-temperature oxidation resistance up to about 540 deg C. Comparing the two is a question of selection criteria, not of mechanical-property substitution. They are not interchangeable.
Alloy class
- 21CrMoV5-7: ferritic low-alloy Cr-Mo-V Q+T, magnetic, ferrite + bainite microstructure after temper
- ASTM A193 B8: austenitic 18Cr-8Ni stainless (304 / 304L base), non-magnetic, face-centred-cubic austenitic microstructure
Chemistry contrast
| Element (wt%) | 21CrMoV5-7 (EN 10269) | ASTM A193 B8 (Type 304) |
|---|---|---|
| Carbon (C) | 0.17 to 0.25 | max 0.08 |
| Chromium (Cr) | 1.20 to 1.50 | 18.0 to 20.0 |
| Nickel (Ni) | max 0.60 | 8.0 to 11.0 |
| Molybdenum (Mo) | 0.55 to 0.80 | not specified |
| Vanadium (V) | 0.20 to 0.35 | not specified |
| Microstructure | ferritic + bainitic (Q+T) | austenitic (solution-treated) |
When to specify 21CrMoV5-7
- High-temperature steam-turbine, gas-turbine and pressure-vessel bolting where strength at 500-550 deg C is the design driver.
- Service environment is non-corrosive; the chemical inertness of stainless is not required.
- Higher strength-to-cost ratio than austenitic stainless for the same temperature envelope.
- Fastener torque-tension predictability and lower thermal expansion are needed.
When to specify ASTM A193 Grade B8
- Aqueous corrosion or chemical-attack environment (chemical processing, marine, food/pharma equipment).
- Cryogenic service down to -250 deg C where ferritic Q+T steels embrittle.
- Hydrogen service where austenitic structure resists hydrogen embrittlement.
- Non-magnetic property requirement (MRI rooms, magnetic separation equipment).
Related cross-references
- vs ASTM A193 B7 — Cr-Mo ferritic, the more direct alloy-class comparison
- vs ASTM A193 B16 — closest US Cr-Mo-V analogue
- ASTM A193 standard overview
FAQs
Q. Can B8 substitute for 21CrMoV5-7 in turbine casing bolting?
No. B8 austenitic stainless has lower strength than 21CrMoV5-7 at 500-550 deg C and a much higher coefficient of thermal expansion, which complicates torque-tension control on hot bolting. For turbine casing flange service the answer is 21CrMoV5-7 or B16.
Q. Can 21CrMoV5-7 substitute for B8 in chemical service?
No. 21CrMoV5-7 has no meaningful aqueous corrosion resistance. In chemical or marine environments it will rust quickly. Where the corrosion resistance of austenitic stainless is the selection driver, only B8 (or higher grades like B8M / Duplex) are appropriate.
Q. What is the magnetic difference?
21CrMoV5-7 is ferromagnetic (ferritic + bainitic structure). B8 in fully solution-treated Class 1 condition is essentially non-magnetic (austenitic). Cold-worked B8 Class 2 develops some magnetic permeability through strain-induced martensite.
Q. Can TorqBolt supply both?
Yes. Both alloy classes are supplied as stud bolts, hex bolts, heavy hex, nuts and washers with EN 10204 type 3.1 or 3.2 certification. The selection should be driven by service environment, not by interchangeability.
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