B381 F5

I. Standards and brand system

1. Core standards

• International specification: ASTM B381 (covering pure titanium and titanium alloy forgings, F5 belongs to pure titanium series, and the strength gradient is defined by the classification of interstitial element content: F1 < F4 < F5, the interstitial element (O) content increases in turn, the strength increases and the plasticity decreases);
• Domestic adaptation: there is no completely equivalent brand, and the composition of pure titanium of TA4 in GB/T 25137 (titanium and titanium alloy forgings) is close (oxygen content of TA4 is 0.20~0.30%, and oxygen content of F5 is 0.25~0.35%, with slightly higher strength).

2. Brand characteristics

• Commercial name: no exclusive alias, collectively referred to as “ASTM B381 F5 pure titanium forgings”;
• Positioning: “Medium-high strength grade” in pure titanium (the most significant grade of pure titanium strengthened by interstitial elements, its strength is close to that of low-end titanium alloy, and its cost is only 60% of that of alloy titanium).

II. Chemical composition (mass fraction%, ASTM B381 standard)

III. Mechanical properties (annealed state, forgings)

IV. Requirements for Heat Treatment and Processing

1. Annealing treatment (necessary, balance performance):
   • Temperature: 700~800℃ (heat preservation for 1~2 hours, α phase region, eliminating forging stress and stabilizing the distribution of interstitial elements);
   • Cooling: air cooling (keep α single-phase structure to avoid plastic collapse caused by β phase precipitation);
   • Function: Restore cutting and welding performance (cold working hardening of high-gap pure titanium is more obvious, and annealing process should be strictly controlled).
2. Machining and welding:
   • Machining: the cutting difficulty is higher than F4 (the hardness is improved by interstitial elements), and cemented carbide tools and high pressure cooling are recommended (reducing cutting heat and preventing hydrogen embrittlement);
   • Welding: TIG welding (ERTi-1 welding wire) is used, and the whole process is protected by high-purity argon (99.999%) (pure titanium is easy to absorb impurities at high temperature, and high-gap pure titanium is more sensitive to pollution).

V. Main application fields (medium and high stress+corrosion resistance scene)

1. Ocean engineering:
   • High-pressure system: components of deep-sea Christmas tree and high-pressure seawater pipeline (resistant to 3000m water depth and corrosion, with strength superior to F4 and cost lower than alloy titanium);
   • Wear-resistant parts: propeller edge, seawater pump impeller (high clearance strengthening improves wear resistance, and the service life is 4 times longer than that of brass).
2. Chemical industry and energy:
   • Medium-voltage equipment: fasteners of chlor-alkali electrolyzers and lining of medium-voltage reaction kettle (resistant to wet chlorine/dilute acid corrosion and strong enough to support medium-voltage working conditions);
   • Geothermal application: 200~250℃ geothermal well pipeline (corrosion resistance+medium strength, 30% cost reduction instead of stainless steel).
3. Medical health:
   • High-stress implants: bone nails, interbody fusion cage (biocompatible+medium-high strength, the fixation effect is better than F4 pure titanium);
   • Surgical instruments: orthopedic drill, high-stress fixture (body fluid corrosion resistance+wear resistance, life is twice that of stainless steel instruments).
4. Military industry and high-end equipment:
   • Corrosion-resistant pump valves: medium and high pressure corrosion-resistant pump bodies and valves (instead of stainless steel, the corrosion resistance is improved by 3 times);
   • Precision structural parts: suspension joint of racing car, high-stress bracket of UAV (specific strength is better than steel, lightweight and durable).

Key summary

• Core advantages:

  • Performance ladder: the strength is 10-15% higher than F4, which is suitable for medium and high stress corrosion-resistant scenes, and the cost is only 60% of alloy titanium;

  • Corrosion resistance is unchanged: it inherits the excellent corrosion resistance of pure titanium, and the corrosion rate in 3.5% NaCl is less than 0.01 mm/year;

  • Processing compatibility: hot workability is better than alloy titanium, and the manufacturing cost is 15-20% lower (only annealing is needed, and complex alloying heat treatment is not needed).

• Limited challenges:

  • Plastic sensitivity: the elongation is 15% lower than F4, so the cold working needs to be more cautious (multi-pass annealing increases the cost);

  • Risk of gap out of control: excessive O/N content will easily lead to embrittlement, and the production needs to strictly control the composition (the quality inspection cost will increase by 10%).