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 Boiler Bolts (Drum-Head + Steam-Pipe + Access)
21CrMoV5-7 boiler bolts are specified into drum-head bolting, steam-pipe flange bolting, reheater header bolting and access-door bolting on conventional fossil-fired, biomass-fired, and waste-heat-recovery boilers. The Cr-Mo-V Q+T chemistry holds preload through the long-duration high-temperature service that defines boiler bolting (typically 95+ percent annual run hours). Drum-head flanges run 320 to 380 deg C; main steam-pipe flanges 480 to 540 deg C; reheater inlet headers 500 to 540 deg C; reheater outlet and final superheater headers 540 to 568 deg C (boundary with Durehete 1055). Form factors: stud bolts for drum-head and steam-pipe flanges, heavy hex bolts for access-door and inspection-port bolting, tap studs for selected drum-head designs, heavy hex nuts to ASME B18.2.2 / DIN 6915 in matched grade.
21CrMoV5-7 Chemistry (Werkstoff 1.7709 Element Ranges)
21CrMoV5-7 (Werkstoff 1.7709) chemistry is fixed within a tight Cr-Mo-V Q+T window to EN 10269. Carbon at 0.17 to 0.25 percent gives the Q+T hardenability backbone without over-hardening for the secondary temper. Chromium at 1.20 to 1.50 percent provides through-thickness hardenability and stabilises the carbide network for creep. Molybdenum at 0.55 to 0.80 percent suppresses temper embrittlement and contributes to the secondary hardening peak. Vanadium at 0.20 to 0.35 percent drives the V4C3 precipitation during the 680 to 740 deg C temper that locks in the creep envelope. The chemistry window is shared with the AFNOR 20CDV5.7 (French) and Polish 21HMF designations.
| Element | Min % | Max % | Role |
|---|---|---|---|
| Carbon (C) | 0.17 | 0.25 | Q+T hardenability |
| Silicon (Si) | — | 0.40 | Deoxidation |
| Manganese (Mn) | 0.40 | 0.80 | Hardenability + solid-solution |
| Phosphorus (P) | — | 0.030 | Tramp limit for toughness |
| Sulphur (S) | — | 0.030 | Tramp limit |
| Chromium (Cr) | 1.20 | 1.50 | Hardenability + creep |
| Molybdenum (Mo) | 0.55 | 0.80 | Secondary hardening |
| Vanadium (V) | 0.20 | 0.35 | V4C3 carbide strengthening |
| Nickel (Ni) | — | 0.60 | Residual |
| Aluminium (Al) | — | 0.030 | Grain refinement |
21CrMoV5-7 Mechanical Properties
21CrMoV5-7 in the quenched-and-tempered condition holds tensile 700 to 850 MPa, 0.2 percent proof stress at least 550 MPa, elongation A5 at least 16 percent, and Charpy V impact at least 63 J at 20 deg C to EN 10269 acceptance. Typical mill datasheet values run 10 to 20 percent above the standard floor. Elevated-temperature 0.2 percent proof stress holds 450 MPa at 500 deg C and 420 MPa at 550 deg C, the dominant design input for steam-turbine casing flange bolting and pressure-vessel bolting at the upper service envelope.
| Property | Value | Condition |
|---|---|---|
| Tensile (Rm) | 700 to 850 MPa | RT, Q+T |
| 0.2 percent proof (Rp0.2) | ≥550 MPa | RT, Q+T |
| Elongation A5 | ≥16 percent | RT, longitudinal |
| Charpy V impact (KV) | ≥63 J | 20 deg C, longitudinal |
| 0.2 percent proof at 500 deg C | ≥450 MPa | EN 10269 elevated-temp |
| 0.2 percent proof at 550 deg C | ≥420 MPa | EN 10269 elevated-temp |
| Hardness (HBW) | 210 to 250 | Q+T condition |
Creep Performance at 500-550 deg C (EN 10269 Annex A)
The defining value-prop of 21CrMoV5-7 is the secondary-hardening creep envelope driven by V4C3 carbide precipitation. The fine V4C3 dispersion formed during the 680 to 740 deg C temper pins dislocation motion during long-time elevated-temperature service. The result is a 100,000-hour stress-rupture envelope to EN 10269 Annex A of approximately 340 MPa at 500 deg C, 290 MPa at 525 deg C, 260 MPa at 540 deg C, and 180 MPa at 550 deg C. Above 550 deg C the V4C3 coarsens faster than the design can tolerate; this is the boundary where the design must step up to Durehete 1055 (Alloy T41 / 1.7729) with Ti+B microalloying for grain-boundary pinning that extends the envelope to 568 deg C continuous service.
| Temperature | 100,000 h rupture stress | 1 percent creep strain at 100,000 h |
|---|---|---|
| 450 deg C | ~470 MPa | ~380 MPa |
| 500 deg C | ~340 MPa | ~280 MPa |
| 525 deg C | ~290 MPa | ~235 MPa |
| 540 deg C | ~260 MPa | ~210 MPa |
| 550 deg C | ~180 MPa | ~150 MPa |
Heat Treatment (Q+T Cycle)
The standard cycle for 21CrMoV5-7 is austenitisation at 880 to 940 deg C with hold time of 1 hour per 25 mm section, followed by oil quench. The temper is at 680 to 740 deg C for minimum 2 hours then air cool. The temper temperature is chosen to land on the secondary-hardening peak; below 660 deg C the V4C3 carbide precipitation is under-developed and long-term creep performance suffers; above 750 deg C the carbides over-coarsen and the room-temperature yield drops below the EN 10269 floor of 550 MPa. For heavily machined fastener blanks where dimensional stability matters, a stress relief at 50 deg C below the final temper is recommended after machining.
Welding Procedure (Matched Cr-Mo-V Filler + PWHT)
21CrMoV5-7 is welded with matched-composition Cr-Mo-V low-hydrogen filler (AWS A5.5 E9018-B3L for SMAW, AWS A5.28 ER90S-B3L for GTAW, AWS A5.23 EB3 for SAW) under preheat 200 to 300 deg C and diffusible-hydrogen cap of 5 ml per 100 g deposited. Post-weld heat treatment at 690 to 720 deg C for 1 hour per 25 mm joint thickness, minimum 2 hours, slow furnace cool to 300 deg C then air cool. The PWHT re-tempers the heat-affected zone and restores creep performance. Hardness traverse across weld plus HAZ plus parent metal verifies the PWHT achieved the intended tempering; HAZ hardness must not exceed 320 HBW.
Material Selection: 21CrMoV5-7 vs ASTM A193 B16 vs B7 vs Durehete 1055
21CrMoV5-7 sits between ASTM A193 Grade B7 (carbon-Mo only, no vanadium, capped at 450 deg C) and Durehete 1055 (Alloy T41 with Ti+B microalloying, 568 deg C envelope). Its direct US cousin is ASTM A193 Grade B16, with overlapping Cr-Mo-V chemistry and similar 540 deg C service envelope. Dual-certification to EN 10269 21CrMoV5-7 plus ASTM A193 B16 from the same heat lot is standard practice on cross-procurement projects.
| Grade | Chemistry | Max temp | When to specify |
|---|---|---|---|
| ASTM A193 B7 | Cr-Mo (no V) | 450 deg C | Lower-temp bolting where cost matters |
| 21CrMoV5-7 | Cr-Mo-V Q+T | 550 deg C | Workhorse mid-tier turbine + power + refinery |
| ASTM A193 B16 | Cr-Mo-V Q+T | 540 deg C | US dual-cert cousin |
| 21CrMoV5-11 (1.8070) | Cr-Mo-V Q+T higher Mo | 550 deg C | Heavier section (OD above 200 mm) |
| Durehete 1055 (Alloy T41 / 1.7729) | Cr-Mo-V-Ti-B | 568 deg C | HP turbine + supercritical + USC |
21CrMoV5-7 Applications by Industry
21CrMoV5-7 covers the bolting envelope from 450 to 550 deg C continuous metal temperature across power generation, refinery and petrochem sectors.
- Steam Turbine Bolts: LP, IP, and lower-HP casing flange studs to 550 deg C metal temperature
- Gas Turbine Bolts: compressor casing flanges and combustor liner flanges in industrial gas turbines
- Power Plant Bolting: subcritical and transition supercritical drum and steam-line flanges
- Pressure Vessel Bolts: unfired pressure-vessel bolting per VdTUV Wb 350
- Boiler Bolts: drum-head and steam-pipe flanges on conventional fossil and biomass boilers
- Heat Exchanger Bolts: channel-head studs and shell-side flanges in refinery and petrochem
- Fired Heater Bolts: convection-section flanges below the Durehete envelope
- Petrochem Reactor Bolts: hydrocracker and reformer manway and main-flange studs
Related 21CrMoV5-7 Forms and Fasteners
21CrMoV5-7 is supplied across the full bolting form-factor range, all to EN 10269 with EN 10204 type 3.1 mill test certificate by default and type 3.2 with third-party witness on call-out.
- Round Bar: raw stock OD 16 to 300 mm (cold-drawn bright to EN 10278 h9/h10 tolerance)
- Stud Bolts: M12 to M120 + 1/2 inch to 4 inch, lengths 50 to 800 mm
- Hex Bolts + Heavy Hex Bolts: DIN 931 / DIN 933 / ASME B18.2.1
- Tap Studs + Body-Bound Studs: turbine half-joint bolting (DIN 938 / 939 / 940 / 949 + H7/n6 ground shank)
- Anchor Bolts: L-bolts, J-bolts and headed anchors for foundation anchorage
- U-Bolts + Threaded Rod
- Nuts + Washers: matched-grade companion hardware
- Forgings: closed-die and open-die blanks up to 800 kg piece weight
Request a Quote
TorqBolt supplies 21CrMoV5-7 (Werkstoff 1.7709) bolting stock and finished fasteners worldwide from Mumbai head office and Rajkot production plant. Type 3.1 EN 10204 mill test certificate by default; type 3.2 with Lloyd's Register, DNV, BV, SGS or TUV witness inspection on call-out. Send your enquiry →
Frequently Asked Questions
Q. What is the metal-temperature envelope for 21CrMoV5-7 in boiler bolting?
Up to 550 deg C continuous to EN 10269. Covers drum-head flanges (320-380 deg C), main steam-pipe flanges (480-540 deg C), and reheater inlet header flanges (500-540 deg C). Reheater outlet and final superheater flanges (540-568 deg C) step up to Durehete 1055.
Q. Which OEMs specify 21CrMoV5-7 for this service?
Boiler builders Rafako, Foster Wheeler Energy Polska, Babcock-Hitachi, Mitsubishi Power, Doosan Skoda. Polish utility PGE, Czech CEZ, German VEAG/RWE/EnBW for European-PED-certified boilers. US procurement via ASTM A193 B16 dual-cert.
Q. Where does Durehete 1055 take over from 21CrMoV5-7?
On reheater outlet and final superheater header flanges (540-568 deg C). For drum-head, main steam-pipe and reheater inlet header flanges (up to 540 deg C), 21CrMoV5-7 is the workhorse choice.
Q. What inspection documentation is standard?
EN 10204 type 3.1 by default with heat number, melt-shop pour record, chemistry, Q+T cycle, mechanicals at RT and elevated temperature, hardness, dimensional report. Type 3.2 with Lloyd's Register, DNV, BV, SGS or TUV witness on call-out and standard practice on turbine and pressure-vessel procurement.
Q. Do you supply matched-grade nuts and washers from the same heat lot?
Yes. Matched-grade nuts and washers in 21CrMoV5-7 from the same heat lot ship on call-out and are standard practice on every turbine, pressure-vessel, refinery and petrochem procurement. Heat-lot traceability documented on EN 10204 type 3.1 or type 3.2.
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