21CrMoV5-7 (Werkstoff 1.7709 / EN 10269) Cr-Mo-V Bolting Steel

21CrMoV5-7 is a quenched-and-tempered Cr-Mo-V low-alloy steel with carbide-precipitation strengthening from secondary vanadium carbides formed during tempering. The chromium provides solid-solution hardenability through-thickness. The molybdenum suppresses temper embrittlement and contributes to creep resistance. The vanadium drives the secondary hardening peak in the 680 to 740 deg C temper range, locking in the creep-rupture performance that defines the grade. The resulting microstructure is a tempered bainite with fine V4C3 precipitates and a residual ferrite fraction that together deliver yield strength above 550 MPa with Charpy V impact above 63 J at room temperature, holding 0.2 percent proof stress above 450 MPa at 500 deg C.

21CrMoV5-7 has a stable cross-reference chain across the major industrial standards. The European Norm designation 21CrMoV5-7 is the canonical name. The Werkstoff number 1.7709 identifies the grade in the German steel-numbers register. The AFNOR designation 20CDV5.7 is the French naming used in EDF, Areva, and Framatome procurement specifications. The Polish PN designation 21HMF is the equivalent for boiler and turbine bolting in Eastern European power plants. The closest US bolting standard is ASTM A193 Grade B16, a Cr-Mo-V chemistry with similar temper range and service envelope; B16 is not an exact substitute but covers comparable design conditions.

The standard cycle is austenitise 880 to 940 deg C, hold long enough to fully transform to austenite (typically one hour per 25 mm of section thickness), then oil quench. The temper is 680 to 740 deg C, hold at least 2 hours, then air cool. The temper temperature is chosen to land on the secondary hardening peak; tempering too low (below 660 deg C) leaves the V4C3 underdeveloped and the long-time creep performance suffers; tempering too high (above 750 deg C) over-coarsens the carbides and drops the room-temperature yield below the EN 10269 floor. For heavily machined fastener blanks, a stress-relief 50 deg C below the final temper is recommended to control distortion. Inter-pass tempering and PWHT for welded joints are specified separately on the welding page.

21CrMoV5-7 is welded with matched-composition Cr-Mo-V low-hydrogen filler under preheat 200 to 300 deg C with strict diffusible-hydrogen control (typical limit 5 ml/100 g deposited). Post-weld heat treatment at 690 to 720 deg C is required to temper the heat-affected zone and restore creep performance; PWHT hold time is typically 1 hour per 25 mm joint thickness with a minimum of 2 hours. Visual inspection to ISO 5817 quality level B is standard; magnetic-particle and dye-penetrant on cap and root; ultrasonic on butt joints above 25 mm. Hardness traverse across weld plus HAZ plus parent verifies the PWHT achieved the intended tempering; hardness should not exceed 320 HBW at any point.

21CrMoV5-7 is specified into bolting where the design metal temperature exceeds the ASTM A193 B7 envelope but does not require the premium creep performance of 21CrMoV5-7. The 8 primary service areas are linked from the Applications dropdown above and from the body block below.

TorqBolt supplies 21CrMoV5-7 in the full bolting form-factor range, from raw bar through finished fasteners, all to EN 10269 (cold-drawn additionally to EN 10278) with EN 10204 type 3.1 mill test certificate by default and type 3.2 with third-party witness on call-out.

Q. Is 21CrMoV5-7 the same as 1.7783?
No. 1.7783 is X22CrMoV12-1, a 12 percent chromium martensitic stainless steel for steam-turbine blades — an entirely different alloy class. 21CrMoV5-7 is Werkstoff 1.7709, a low-alloy Cr-Mo-V bolting steel.

Q. Is 21CrMoV5-7 an exact substitute for ASTM A193 Grade B16?
Not exact, but close. Both are Cr-Mo-V Q+T bolting steels with overlapping service envelopes. B16 chemistry sits within the 21CrMoV5-7 window for Cr, Mo and V. Procurement specifications that allow either grade typically include both designations on the same order line.

Q. What is the maximum service temperature for 21CrMoV5-7?
550 deg C continuous, to EN 10269. Above 550 deg C the design must step up to Durehete 1055 (Alloy T41 / 1.7729) for the Ti+B-microalloyed creep performance.

Q. Do you supply 21CrMoV5-7 with EN 10204 type 3.2 certification?
Yes. Type 3.1 is supplied by default with heat number, chemistry, Q+T cycle, mechanical results, hardness and dimensional report. Type 3.2 with Lloyd's Register, DNV, BV, SGS or TUV witness is supplied on call-out and is standard practice on turbine and pressure-vessel procurement.

Q. What is the difference between 21CrMoV5-7 and 21CrMoV5-11?
The 5-11 variant (1.8070) has extended hardenability for heavier section thicknesses through a slightly higher Mn and tighter Mo range. For round bar above OD 200 mm in fully-hardened condition, 21CrMoV5-11 is the preferred grade. For OD 16 to 200 mm, 21CrMoV5-7 is the workhorse.