What heat treatment changes

Heating, holding and cooling control phase transformation, grain condition, precipitation and residual stress. These features influence strength, ductility, toughness, hardness and elevated-temperature behaviour.

Different grades use different routes, such as normalizing and tempering or quench-and-temper processes. The manufacturer must follow the applicable grade requirements rather than applying one shop cycle to every chrome-moly flange.

Why forging section size matters

A large flange hub and rim do not heat and cool at the same rate as a small test coupon. Furnace loading, soak time, transfer time and cooling medium affect uniformity. Test specimens must represent the product in the manner required by the specification and purchase order.

For critical orders, buyers may request furnace charts, calibrated-instrument records and defined test locations.

Special attention for F91

F91 properties depend on its normalized-and-tempered condition. An unapproved subcritical or excessive heat cycle can change hardness and long-term performance. Welding and PWHT therefore need coordination with the base-material condition.

PMI cannot verify microstructure. Hardness, mechanical testing, thermal records and any specified metallurgical examination provide different pieces of evidence.

Heat-treatment documents to review

• Material grade and heat number
• Furnace identification and calibration status
• Cycle temperatures, hold time and cooling method
• Batch or item traceability
• Tensile, impact and hardness results as applicable
• Records of re-heat treatment or repair

Certificate review should resolve inconsistent dates, heat numbers or treatment descriptions before release.