EN 3684:2007

Overview

EN 3684:2007 (CEN) specifies a metallographic method for the determination of the β transus temperature of titanium alloy wrought products intended for aerospace applications. The method supports consistent identification of the temperature at which the primary α phase disappears on heating, enabling reliable heat-treatment control and material certification.

Key Topics

• Principle: Determine β transus by assessing primary α content in test samples heat treated at several temperatures around the assumed β transus. The β transus lies between the treatment temperature where primary α content is 0 % and the next lower temperature where primary α content is > 0 %.

• Sampling: Material should be as homogeneous as possible with fine α/β grain distribution. Additional deformation (for example upsetting at normal forging temperatures in the (α + β) range) may be applied to refine microstructure before testing.

• Test pieces: Preferred geometry is cylindrical (10 mm diameter × 10 mm length) or a 10 mm cube. Sections examined should preferably be transverse. The number of test pieces must match the number of selected test temperatures.

• Heat treatment: Select temperatures around the assumed β transus. For routine work, three temperatures at 10 °C intervals are normally sufficient; smaller intervals improve precision. Each piece is heated to the specified temperature (±5 °C), held for 15–30 minutes, then immediately water-quenched. Annealing after quench is recommended to improve microstructural contrast for α + β alloys.

• Metallographic examination: Cut test pieces, prepare sections and assess primary α content following EN 3683 requirements (point count and line intercept methods as applicable).

• Expression of results: Record the temperature where primary α = 0 % and the next lower temperature with primary α > 0 %. Express the β transus as a range (e.g. (1010/1020) °C). Optionally, a single value may be extrapolated from a primary α content versus temperature plot.

• Test report: Must reference EN 3684 and include product identification, sample location, number and dimensions of test pieces, heat-treatment details, any annealing, test results (per EN 3683), equipment, date, personnel traceability, and any deviations or factors affecting results.

Applications

• Process control for heat treatment and forging of titanium alloy aerospace components.
• Material certification and acceptance testing of wrought titanium products.
• Establishing thermal processing windows for manufacturing and quality assurance.

Related Standards

• EN 3114-001 - Microstructure of (α + β) titanium alloy wrought products (general requirements).
• EN 3683 - Determination of primary α content (point count and line intercept methods).

This standard provides an industry-recognized metallographic route to determine β-transus temperature, helping laboratories and manufacturers maintain reproducible microstructure-based heat-treatment practices for aerospace-grade titanium alloys.