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 Stress-Rupture Tables (Larson-Miller Envelope)
The 21CrMoV5-7 stress-rupture tables give the 10,000, 100,000 and 200,000 hour rupture stress at temperatures from 450 to 575 deg C, derived from the EN 10269 Annex A Larson-Miller envelope. Use as the design input for elevated-temperature bolted-joint stress analysis on steam turbine, gas turbine, pressure-vessel and refinery applications. Larson-Miller parameter LMP = T(K) x (20 + log t(h)) x 10^-3 collapses the time-temperature creep envelope onto a single master curve. For 21CrMoV5-7 the LMP envelope passes through LMP=20.5 at 290 MPa and LMP=21.0 at 250 MPa, giving the design engineer a one-equation route from any design temperature and design life to the allowable stress. The 200,000-hour projection extrapolates the EN 10269 100,000-hour Annex A envelope with a -20 to -30 MPa offset at 540 deg C per the VdTUV Wb 350 extended qualification scope.
Stress-Rupture Envelope
| Temperature | 10,000 h rupture | 100,000 h rupture | 200,000 h rupture |
|---|---|---|---|
| 450 deg C | ~580 MPa | ~470 MPa | ~440 MPa |
| 475 deg C | ~510 MPa | ~400 MPa | ~375 MPa |
| 500 deg C | ~430 MPa | ~340 MPa | ~315 MPa |
| 525 deg C | ~370 MPa | ~290 MPa | ~265 MPa |
| 540 deg C | ~330 MPa | ~260 MPa | ~235 MPa |
| 550 deg C | ~250 MPa | ~180 MPa | ~155 MPa |
| 575 deg C | ~180 MPa | ~120 MPa | extrapolation marginal |
Larson-Miller Master Curve
| Rupture stress (MPa) | LMP (x 10^-3) |
|---|---|
| 400 | 19.5 |
| 350 | 19.8 |
| 300 | 20.3 |
| 250 | 20.9 |
| 200 | 21.4 |
| 150 | 22.0 |
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. How do I use the Larson-Miller parameter?
Look up LMP from the master curve at your design rupture stress. Then back-calculate the time-temperature combination: LMP = T(K) x (20 + log t(h)) x 10^-3. Solve for the allowable design life t at your design temperature T, or solve for the allowable T at your design life t.
Q. What design margin should I apply to the rupture stress?
For bolted-joint design, allowable stress is typically the lesser of: (a) 67 percent of the 100,000-hour rupture stress at design temperature; (b) the 0.2 percent proof stress at design temperature. The design-life margin is conservative for cyclic-load bolted joints.
Q. Where does the 200,000-hour data come from?
Extrapolation of the EN 10269 Annex A 100,000-hour envelope per the VdTUV Wb 350 extended qualification scope. The extrapolation applies a -20 to -30 MPa offset at 540 deg C compared to the 100,000-hour envelope. Above 575 deg C the extrapolation becomes marginal.
Q. What is the relationship between rupture and 1 percent creep strain?
The 1 percent creep strain at 100,000 hours runs approximately 80 percent of the rupture stress at the same temperature. The 0.2 percent creep strain runs approximately 65 percent of the rupture stress.
Q. Does the table include scatter band?
No. Values are mean-line to EN 10269 Annex A. The standard deviation for Cr-Mo-V Q+T bolting steels is typically 8 to 12 percent of the mean rupture stress at the same time-temperature combination. Design codes apply a separate scatter-band factor (typically 1.25 to 1.5) on the mean line.
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