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Durehete Elevated-Temperature Mechanical Properties — Alloy T41 / T31 / T22
EN 10269 Annex A tabulates the design-stress envelope for each Durehete grade between 425 and 565 degrees Celsius. The tables below summarise the 0.2 percent proof stress, the modulus of elasticity decline, and the mean coefficient of thermal expansion that drive bolt-preload calculations.
0.2 Percent Proof Stress at Elevated Temperature
| Temperature | 1055 (T41) | 950 (T31) | 900 (T22) |
|---|---|---|---|
| 20°C (room temp) | 660 MPa min | 620 MPa | 580 MPa |
| 425°C | 540 MPa | 510 MPa | 460 MPa |
| 475°C | 500 MPa | 460 MPa | 410 MPa |
| 500°C | 475 MPa | 430 MPa | 370 MPa |
| 525°C | 440 MPa | 390 MPa | — |
| 540°C | 420 MPa | 360 MPa | — |
| 565°C | 380 MPa | — | — |
Approximate envelope figures from EN 10269 Annex A; design specifications must reference the standard.
Modulus of Elasticity
| Temperature | Modulus E (GPa) — typical for all 3 grades |
|---|---|
| 20°C | 211 |
| 200°C | 199 |
| 400°C | 180 |
| 500°C | 170 |
| 565°C | 162 |
Modulus drives bolt elastic strain at preload. The 23 percent drop between room temperature and 565°C is significant for thermal-cycle stress calculations.
Mean Coefficient of Thermal Expansion
Mean linear expansion (20°C to T) for all three grades sits in the 12.0 to 13.5 x 10^-6 per kelvin band, with the Cr-Mo-V matrix dominating the response. Differential expansion against the flange or casing material is the principal driver of bolt-preload thermal cycling and is calculated against this coefficient set.
Hardness at Operating Temperature
Brinell hardness in the Q+T condition is 250-320 HB at room temperature for 1055 / 950, 230-280 HB for 900. Hardness drops approximately 10-15 percent at 540°C operating temperature; recovery on cool-down is essentially complete.
Frequently Asked Questions
Where do I find the design-stress envelope for Durehete bolted joints?
EN 10269 Annex A tabulates 0.2 percent proof stress and 100,000-hour stress-rupture for each grade between 200 and 600 degrees Celsius.
Does modulus of elasticity drop matter for bolt preload?
Yes. Modulus drops 23 percent from 20 to 565 degrees Celsius. This is incorporated into the thermal-cycle preload calculation alongside the expansion mismatch between bolt and flange material.
What is the thermal expansion coefficient for Durehete grades?
Mean linear expansion 20 to 540 degrees Celsius is approximately 12.5 x 10^-6 per kelvin for all three grades; the Cr-Mo-V matrix dominates.
How is hardness measured in Q+T condition?
Brinell 10-mm-3000-kgf indentation is the standard test; Vickers HV30 and Rockwell C correlations follow the standard conversion tables.
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