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 B7
21CrMoV5-7 (Werkstoff 1.7709) and ASTM A193 Grade B7 are both Cr-Mo alloy bolting steels for elevated temperature, but B7 is Cr-Mo only with no vanadium. The absence of vanadium caps B7's service envelope at about 450 deg C continuous metal temperature. 21CrMoV5-7 with vanadium holds to 550 deg C through V4C3 precipitation hardening that stabilises strength against long-term creep. B7 is the workhorse US bolting grade for flanges, pressure vessels, and refinery piping below 450 deg C. 21CrMoV5-7 is the European specification for the higher-temperature 450-550 deg C band where B7 cannot serve.
Chemistry side by side
| Element (wt%) | 21CrMoV5-7 (EN 10269) | ASTM A193 B7 |
|---|---|---|
| Carbon (C) | 0.17 to 0.25 | 0.38 to 0.48 |
| Silicon (Si) | max 0.40 | 0.15 to 0.35 |
| Manganese (Mn) | 0.40 to 0.80 | 0.75 to 1.00 |
| Phosphorus (P) | max 0.025 | max 0.035 |
| Sulfur (S) | max 0.030 | max 0.040 |
| Chromium (Cr) | 1.20 to 1.50 | 0.80 to 1.10 |
| Molybdenum (Mo) | 0.55 to 0.80 | 0.15 to 0.25 |
| Vanadium (V) | 0.20 to 0.35 | not specified |
The defining difference is vanadium. Without it, B7 has no V4C3 precipitation strengthening at temperature, so the upper service limit drops from 550 deg C (21CrMoV5-7) to about 450 deg C. Molybdenum content is also markedly higher in 21CrMoV5-7 (0.55-0.80) than in B7 (0.15-0.25), supporting both temper resistance and through-thickness hardenability.
Mechanical property floor
| Property | 21CrMoV5-7 (+QT, d ≤ 160 mm) | ASTM A193 B7 (M64 / 2.5 in. and under) |
|---|---|---|
| 0.2 percent proof stress, min | 550 MPa | 720 MPa |
| Tensile strength | 700 to 850 MPa | min 860 MPa |
| Elongation A5, min | 16 percent | 16 percent |
| Reduction of area, min | 60 percent | 50 percent |
| Charpy V impact at +20 deg C, min | 63 J | not specified |
| Hardness ceiling | via tensile cap | 321 HBW or 35 HRC |
When to specify 21CrMoV5-7
- Service temperature is in the 450-550 deg C band where B7 cannot serve.
- Procurement is European (EN 10269, PED, VdTUV Wb 350) or the OEM uses metric designations.
- Long-life creep performance with verified Charpy floor at room temperature is contractual.
- Heavy-section bolting where tighter chromium and higher molybdenum improve through-thickness hardenability.
When to specify ASTM A193 Grade B7
- Service temperature is at or below 450 deg C — by far the most common bolting service range.
- Procurement is US (ASME BPVC, B31.3, API) or the project specification calls out B7 by name.
- Cost-efficient general-purpose bolting where the V-bearing 21CrMoV5-7 premium is not justified.
- Refinery flange, pressure-vessel and pipe-support service below 450 deg C.
Related cross-references
- vs ASTM A193 B16 — the actual Cr-Mo-V US analogue
- vs ASTM A193 B8 — austenitic stainless, different alloy class
- vs 42CrMo4 / AISI 4140 — another Cr-Mo without V
- ASTM A193 standard overview
FAQs
Q. Why does B7 cap at 450 deg C while 21CrMoV5-7 holds to 550 deg C?
B7 has no vanadium. Vanadium forms V4C3 carbide precipitates during temper which resist softening at elevated temperature. Without V, B7 loses strength rapidly above 450 deg C through carbide coarsening and tempering progress.
Q. Can B7 be substituted for 21CrMoV5-7 in turbine bolting?
Not at the upper service temperature. For LP turbine casing and lower-temp pressure vessel bolting under 450 deg C, B7 is the standard choice. For IP and HP turbine casing flange bolting at 500-550 deg C, only 21CrMoV5-7 or B16 are appropriate.
Q. Which is cheaper?
B7 is cheaper. Vanadium is an expensive alloying element, and 21CrMoV5-7's tighter chromium window and higher molybdenum also add cost. For below 450 deg C service B7 delivers required strength at significantly lower per-tonne cost.
Q. Can TorqBolt supply both?
Yes. Stud bolts M12 to M120, hex bolts to M64, heavy hex to ASME B18.2.6, and matching nuts and washers in B7 or 21CrMoV5-7 with EN 10204 type 3.1 or 3.2 certification.
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