21CrMoV5-7 vs 24CrMoV5-5

21CrMoV5-7 (Werkstoff 1.7709) and 24CrMoV5-5 (Werkstoff 1.7733) are adjacent Cr-Mo-V Q+T bolting grades. 21CrMoV5-7 is in EN 10269 and is the current European specification. 24CrMoV5-5 is the DIN 17240 transitional grade encountered on legacy mid-twentieth-century power plants and on retrofit work where the original procurement specification called out 24CrMoV5-5 by name. The differences are higher carbon and lower chromium in 24CrMoV5-5, which give a slightly lower service-temperature ceiling than 21CrMoV5-7 (~500 deg C against 550 deg C). For new procurement, 21CrMoV5-7 is the default; 24CrMoV5-5 is specified only on retrofit work matching legacy plant.

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Chemistry contrast

Both grades sit in the Cr-Mo-V Q+T low-alloy family. The differentiators:

• 21CrMoV5-7 (1.7709): C 0.17 to 0.25 percent, Cr 1.20 to 1.50 percent, Mo 0.55 to 0.80 percent, V 0.20 to 0.35 percent. EN 10269. See full chemistry.
• 24CrMoV5-5 (1.7733): nominal C 0.20 to 0.28 percent (higher), Cr 0.90 to 1.20 percent (lower), Mo and V also lower. DIN 17240 transitional. The lower V content limits the long-term creep envelope to about 500 deg C continuous metal temperature.

When to specify 21CrMoV5-7

• New-build European procurement under EN 10269.
• Service temperature in the 500-550 deg C range where 24CrMoV5-5 cannot serve.
• Current PED, VdTUV Wb 350 and turbine-OEM specifications that have migrated off DIN 17240.
• Charpy floor at +20 deg C explicitly required.

When to specify 24CrMoV5-5

• Replacement bolting for legacy plant where the original specification calls out 24CrMoV5-5 (1.7733) by Werkstoff number.
• Service at or below 500 deg C where the lower vanadium content is sufficient.
• Mid-twentieth-century steam-turbine and pressure-vessel retrofit work in Germany and Eastern Europe.

Related cross-references

• vs 21CrMoV5-11 — the other DIN 17240 transitional grade
• vs ASTM A193 B16 — current US Cr-Mo-V analogue
• vs ASTM A193 B7 — US Cr-Mo without V
• EN 10269 equivalents master table

FAQs

Q. Is 24CrMoV5-5 still in current specifications?
DIN 17240 has been superseded by EN 10269. 24CrMoV5-5 (1.7733) is now encountered primarily on retrofit and replacement work for legacy mid-twentieth-century plant. New European procurement defaults to 21CrMoV5-7.

Q. Why does 24CrMoV5-5 cap at 500 deg C while 21CrMoV5-7 holds to 550 deg C?
The vanadium content is lower. V4C3 precipitate density during temper is what stabilises strength at long-life elevated temperature. Lower V means earlier carbide coarsening and faster softening above 500 deg C.

Q. Can 21CrMoV5-7 substitute for 24CrMoV5-5 on a retrofit?
In most cases yes, with engineering approval. 21CrMoV5-7 has slightly lower carbon, higher chromium, and higher vanadium, so it generally meets or exceeds the original 24CrMoV5-5 envelope. The substitution decision is usually approved by the OEM engineering office on a project basis.

Q. Can TorqBolt supply 24CrMoV5-5?
Yes, on retrofit call-out for legacy plant. EN 10204 type 3.1 or 3.2 certification against the DIN 17240 cross-reference.