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Durehete Creep-Rupture & Stress-Rupture Properties — Alloy T41 / T31 / T22 (EN 10269)
Durehete 1055, 950 and 900 are specified into elevated-temperature bolted joints because of their creep-rupture envelope. EN 10269 publishes 0.2 percent proof stress and 100,000-hour stress-rupture design curves in Annex A; the family pulls ahead of plain Cr-Mo-V steels because of the Ti and B microalloying additions in 1055 (T41) which pin grain boundaries against M23C6 carbide coarsening.
100,000-Hour Stress-Rupture Envelope
| Grade | Alloy | Service ceiling | 100,000-h rupture stress at 540°C | 100,000-h rupture stress at 565°C |
|---|---|---|---|---|
| Durehete 1055 | T41 / 1.7729 / 20CrMoVTiB4-10 | 565°C | ~280 MPa | ~200 MPa |
| Durehete 950 | T31 / 1.7711 / 40CrMoV4-6 | 540°C | ~230 MPa | — |
| Durehete 900 | T22 / 42CrMoV5-6 | 500°C | ~180 MPa | — |
Values are approximate envelope figures from EN 10269 Annex A. Procurement specifications must reference the standard for design-stress lookup.
Larson-Miller Parameter
Long-term creep performance is interpolated through the Larson-Miller parameter P = T(C + log t), with C = 20 the conventional constant for Cr-Mo-V steels. Plotting stress against P linearises the rupture data so a 100,000-hour value at 540°C maps to the same P value as a 1,000-hour value at higher temperature. EN 10269 Annex A tabulates the LM curve for each grade.
Why Ti+B Microalloying Lifts the Envelope
Plain Cr-Mo-V steels (such as 21CrMoV5-7 and 24CrMoV5-5) lose creep resistance once M23C6 carbides coarsen at grain boundaries. Durehete 1055 adds 0.07-0.15 percent titanium plus 0.02 percent maximum boron. Titanium ties up free nitrogen and forms fine TiC plus TiN dispersoids that pin grain boundaries; boron segregates to the boundaries and slows carbide coarsening. The combined effect is an extra 25-50°C of usable service temperature versus plain Cr-Mo-V grades at the same 100,000-hour design stress.
Stress Relaxation in Bolted Joints
Bolt preload decays over time at elevated temperature through stress relaxation. EN 10269 Annex B publishes residual-stress curves out to 30,000 hours. For 1055 at 540°C, 1,000-hour residual stress is approximately 70 percent of initial preload; at 30,000 hours residual stress holds near 50 percent. Periodic re-tightening intervals and gasket selection follow from these curves.
Frequently Asked Questions
What service temperature does Durehete 1055 reach in continuous bolted service?
565°C continuous, governed by the EN 10269 Annex A stress-rupture envelope and matching the 1055°F maximum design temperature encoded in the trade name.
How does Durehete 1055 creep performance compare to plain Cr-Mo-V bolting steels?
The Ti+B microalloying delivers 25-50°C of additional usable service temperature at the same 100,000-hour design stress versus plain Cr-Mo-V grades like 21CrMoV5-7 and 24CrMoV5-5.
What design code governs Durehete creep-rupture lookup?
EN 10269 Annex A for stress-rupture and 0.2 percent proof stress at elevated temperature. ASME Section II Part D carries equivalent data for the ASTM A193 B16 cousin specified for Durehete 950 imports into the US market.
Are stress-relaxation curves available for bolt re-tightening intervals?
Yes. EN 10269 Annex B publishes 1,000-hour, 10,000-hour and 30,000-hour residual-stress data per grade. Use the curve to set the re-tightening cycle for HP and IP turbine flanges.
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