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 Stud Bolts (EN 10269 / 1.7709) Cr-Mo-V Q+T Bolting
21CrMoV5-7 stud bolts are double-end threaded fasteners machined from Werkstoff 1.7709 quenched-and-tempered Cr-Mo-V bolting bar to EN 10269. The stud is the workhorse fastener for steam-turbine HP and IP casing flanges, gas-turbine compressor casings, pressure-vessel bolting under VdTUV Wb 350, and refinery heat-exchanger channel-head joints at metal temperatures to 550 deg C continuous. Matched-grade nuts and washers ship with each stud lot.
Stud Bolt Designs
Three thread-end configurations are supplied: double-end equal-thread studs (ASME B16.5 flange standard), double-end unequal-thread tap-end studs for blind tapped holes in turbine casings (see tap studs for the dedicated form-factor), and continuous-thread studs cut from threaded rod for retrofit and field-cut work. Body-bound precision-fit studs with ground shank to H7/n6 are supplied separately as body-bound studs.
Size Range
| Thread system | Diameter range | Length range |
|---|---|---|
| Metric M-thread coarse (ISO 261 / DIN 13) | M12 to M120 | 50 to 800 mm |
| Metric M-thread fine (ISO 261 / DIN 13) | M14 to M120 | 50 to 800 mm |
| Unified inch UN / UNC / UNF (ASME B1.1) | 1/2 inch to 4 inch | 2 inch to 32 inch |
| BSW / BSF | on request | on request |
Mechanical Properties (Q+T, EN 10269)
| Property | Value | Test condition |
|---|---|---|
| Tensile strength (Rm) | 700 to 850 MPa | RT, Q+T |
| 0.2 percent proof stress (Rp0.2) | >=550 MPa | RT, Q+T |
| Elongation A5 | >=16 percent | RT, longitudinal |
| Charpy V impact (KV) | >=63 J | 20 deg C |
| 0.2 percent proof at 500 deg C | >=450 MPa | elevated-temp |
| Hardness | 210 to 250 HBW | Q+T |
Standards Anchor
21CrMoV5-7 stud bolts are manufactured to EN 10269 for chemistry, mechanicals and inspection categories. Stud dimensional standards: ASME B16.5 and ASME B16.47 for flange-mating studs; DIN 938 / DIN 939 / DIN 940 / DIN 949 for tap-end studs to German practice; ISO 4017 / ISO 898-1 for general European studs. Inspection categories to EN 10204 type 3.1 by default with type 3.2 with third-party witness on call-out.
Companion Hardware
Matched-grade Cr-Mo-V companions are supplied from the same heat lot when the procurement specification calls for it: 21CrMoV5-7 nuts in matched grade with proof load to the stud rating, 21CrMoV5-7 washers in matched grade, and 21CrMoV5-7 threaded rod for field-cut continuous-thread studs.
Applications
- Steam Turbine Bolts: LP, IP and lower-HP casing flange studs to 550 deg C metal temperature
- Gas Turbine Bolts: compressor casing studs and combustor liner studs
- Power Plant Bolting: subcritical drum and steam-line flange studs
- Pressure Vessel Bolts: VdTUV Wb 350 unfired pressure-vessel bolting
- Heat Exchanger Bolts: refinery channel-head and shell-side studs
Inspection Documentation
Default delivery is EN 10204 type 3.1 mill test certificate with heat number, melt-shop pour record, chemistry to EN 10269, room-temperature tensile, elevated-temperature 0.2 percent proof at the design temperature, Charpy V impact at 20 deg C, hardness, full Q+T cycle chart and dimensional report tied to the heat lot. Type 3.2 with Lloyd's, DNV, BV, SGS or TUV witness inspection is supplied on call-out and is standard practice on every turbine and pressure-vessel procurement.
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 |
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 |
Frequently Asked Questions
Q. What thread size range do you supply 21CrMoV5-7 stud bolts in?
M12 through M120 in metric coarse and fine, and 1/2 inch through 4 inch in Unified UN, UNC and UNF threads. Lengths from 50 mm to 800 mm cut-to-order. Larger sizes on call-out from forged blank.
Q. Are 21CrMoV5-7 stud bolts an exact replacement for ASTM A193 Grade B16?
Not exact, but close. Both are Cr-Mo-V Q+T bolting steels with overlapping chemistry and service envelope. Procurement specs that allow either grade often print both designations on the same line. The 1.7709 chemistry sits within the B16 window for Cr, Mo and V.
Q. What is the maximum service temperature for a 21CrMoV5-7 stud bolt?
550 deg C continuous to EN 10269. Above 550 deg C the bolt must step up to Durehete 1055 (Alloy T41 / 1.7729) for the Ti+B microalloyed creep performance. Below 450 deg C the cheaper ASTM A193 B7 (carbon-Mo) is the right choice.
Q. Do you supply 21CrMoV5-7 stud bolts with EN 10204 type 3.2 certification?
Yes. Type 3.1 by default with heat number, chemistry, Q+T cycle, mechanicals, hardness and dimensional report. Type 3.2 with Lloyd's Register, DNV, BV, SGS or TUV witness on call-out and standard practice for turbine and pressure-vessel procurement.
Related 21CrMoV5-7 Form Factors
Browse the full 21CrMoV5-7 form-factor range: Hex Bolts · Heavy Hex Bolts · Tap Studs · Body-Bound Studs · Anchor Bolts · U-Bolts · Threaded Rod · Nuts · Washers · Round Bar · Forgings. Back to the 21CrMoV5-7 Alloy Hub.
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