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
Durehete Heat Treatment — Quench-and-Temper Cycle (EN 10269)
The Durehete family is supplied in the quenched-and-tempered condition. The cycle is identical across 1055, 950 and 900 with grade-specific tempering temperature targeting the room-temperature 0.2 percent proof stress required by EN 10269.
Austenitise
970 to 1010 degrees Celsius, hold 30 minutes per 25 mm of section. Furnace atmosphere is controlled to prevent decarburisation of the bar surface. The dwell time delivers a uniform austenite microstructure across the section.
Quench
Oil or water quench. Quenchant selection depends on bar diameter: water quench for sections above 50 mm; oil quench for thinner sections to prevent quench cracking. The quench delivers a martensitic or bainitic microstructure depending on cooling rate.
Temper
660 to 730 degrees Celsius, minimum 2 hours per 25 mm of section, air cool. The tempering temperature is the production lever that targets the EN 10269 room-temperature mechanical floor (660 MPa minimum 0.2 percent proof stress for Durehete 1055). Higher tempering temperature delivers lower strength but better toughness; lower tempering temperature delivers higher strength but reduced ductility.
Resulting Microstructure
Tempered martensite or tempered bainite, depending on cooling rate during quench. The Cr-Mo-V matrix carries M23C6 + V4C3 + (in 1055) TiC + AlN + boron-segregated grain-boundary precipitates. Prior austenite grain size is fine (ASTM grain size 7 or finer) due to the low austenitising temperature.
Heat-Treatment Inspection
EN 10204 type 3.1 inspection certificate documents the heat-treatment cycle: actual austenitising temperature, actual quenchant, actual tempering temperature, actual dwell times. Mechanical testing on the heat-treated bar verifies the EN 10269 acceptance values (room-temperature 0.2 percent proof stress, tensile strength, elongation, hardness).
Frequently Asked Questions
Why is the tempering window 660-730 degrees Celsius?
It's the production lever to target the room-temperature mechanical floor. Lower temper = higher strength + lower ductility. Higher temper = lower strength + better toughness. The mill chooses the temperature inside the window to land in the middle of the EN 10269 acceptance band.
What happens if the temper is below 660 degrees Celsius?
Risk of temper embrittlement in the 350-600 degree window for Cr-Mo-V steels. The 660-degree minimum keeps the temperature above the embrittlement zone.
Is stress-relief required after machining?
Not normally. The Q+T condition is dimensionally stable through standard machining. Heavy welding repair would warrant post-weld stress-relief at 600-650 degrees Celsius.
Can Durehete be re-heat-treated after machining?
Yes if the dimensional stability after re-heat-treatment is acceptable for the application. Re-Q+T may be needed after major repair welding. The re-treatment cycle is identical to the original.
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