B381 F1
B381 F1 is a pure titanium forging material (unalloyed titanium), which comes from ASTM B381 “Standard Specification for Titanium and Titanium Alloy Forgings” (current version ASTM B381-21). With the core advantage of “corrosion resistance× biocompatibility× low density”, B381f1 has replaced stainless steel and nickel-based alloys in medical, marine and chemical fields. The following is systematically analyzed from five dimensions:
I. Standards and brand codes
1. Core standards
- American standard: ASTM B381 (which regulates the chemical composition, mechanical properties and flaw detection requirements of titanium and titanium alloy forgings, covering more than 20 brands, and F1 is pure titanium);
- Substitution relationship: the old version of ASTM B381-13 has been replaced by ASTM B381-21 (updating impurity control and detection methods).
2. Brand correspondence
- UNS number: UNS R50250 (American Uniform Numbering System logo);
- Domestic approximation: there is no completely equivalent brand, and the composition and properties of TA2 pure titanium in GB/T 16598 are highly close to those of F1 (but for forgings in F1, TA2 covers more fully processed forms).
II. Chemical composition (mass fraction%, ASTM B381 standard)
B381 F1 is pure titanium with high purity, and interstitial elements (O, N, C, H) are strictly controlled to ensure plasticity and corrosion resistance;
| element | Content range | Core role |
|---|---|---|
| Ti+O | ≥99.5 | Matrix element, providing corrosion resistance and low density (4.5 g/cm³) |
| O | ≤0.18 | Gap strengthening, balancing strength and plasticity (O content =→ strength =, plasticity ↓) |
| N | ≤0.03 | Strictly control the precipitation of titanium nitride to avoid embrittlement |
| C | ≤0.08 | Restrain titanium carbide and ensure weldability and formability. |
| H | ≤0.015 | Prevent hydrogen embrittlement (avoid hydrogen absorption during forging processing/service) |
| Fe | ≤0.20 | Impurity elements are easy to reduce corrosion resistance when exceeding the limit. |
III. Mechanical properties (annealed state, forgings)
B381 F1 has excellent plasticity and corrosion resistance far exceeding that of stainless steel due to high purity and annealing treatment;
| Performance index | Typical value (ASTM requirements) | Contrast 304 stainless steel |
|---|---|---|
| tensile strength | ≥400 MPa | 25% lower（304≥515 MPa） |
| yield strength | ≥275 MPa | 35% lower（304≥205 MPa） |
| extensibility（δ₅） | ≥20% | 50% higher (F1 elongation ≥20%, 304≥40%, so the plasticity of pure titanium is slightly lower, but its corrosion resistance is better. ) |
| hardness | 80~120 HB | 50% lower (304 ≤ 217 HB) |
| heat resistance | The corrosion rate in 3.5% NaCl is less than 0.01 mm/year. | Excellent 3 times (304 about 0.03 mm/year) |
IV. Requirements for heat treatment (core: annealing to relieve stress)
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Annealing treatment (must be done to optimize plasticity):
- Temperature: 700~800℃ (heat preservation for 1~2 hours, adjusted according to the thickness of forgings);
- Cooling: air cooling (avoiding oxidation and hydrogen absorption, keeping the surface smooth);
- Function: eliminate forging stress and restore plasticity (convenient for subsequent machining and welding).
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Machining and welding:
- Machining: the cutting performance is better than that of alloy titanium (such as Ti-6Al-4V), so cemented carbide tool and sufficient cooling are recommended;
- Welding: TIG welding (ERTi-1 welding wire) is used, and the whole process is protected by high-purity argon gas (preventing O, N and H pollution, and pure titanium is easy to absorb impurities and become brittle at high temperature).
V. Main Application Fields (Corrosion Resistance+Biocompatibility Scenes)
B381 F1 relies on “corrosion resistance of pure titanium × low density × biocompatibility”, and monopolizes the following fields (ultra-stainless steel performance, with the cost only 1/5 of tantalum):
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Medical health:
- Implants: orthopedic prosthesis (hip joint, dental implant), heart stent (biocompatible, no rejection, life span over 20 years);
- Medical instruments: surgical instruments, disinfection containers (body fluid corrosion resistance, hygiene compliance).
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Ocean engineering:
- Seawater system: tube plate of ship condenser, deep-sea cage frame (resistant to seawater erosion+biological fouling, with a service life exceeding 3 times that of brass);
- Marine energy: tidal energy generator blades, seawater pump impellers (low density reduces weight by 40%, replacing stainless steel).
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Chemical industry and food:
- Corrosion medium: dilute sulfuric acid, hydrochloric acid (non-oxidizing acid) pipeline, reaction kettle (corrosion resistance is better than 316L, cost is reduced by 30%);
- Food processing: brewing equipment, dairy pipeline (sanitary grade, resistant to organic acid corrosion).
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High-end equipment:
- Aerospace: satellite structural parts, UAV frame (low density+space radiation resistance, weight reduction of 30%);
- Precision instruments: watch movement, optical equipment parts (excellent plasticity, easy to process complex shapes).
Key summary
- Core advantages:
- Corrosion resistance: the corrosion rate in seawater and dilute acid is less than 0.01 mm/year, far exceeding that of stainless steel;
- Biocompatibility: the only metal material approved for long-term implantation in human body;
- Low density: 4.5 g/cm³ (only 57% of stainless steel, with remarkable light weight).
- Limitations:
- Low strength (only 60% of titanium alloy, alloy titanium needs to be replaced in high stress scene);
- Cold working and hardening are fast (multiple annealing is needed, and the processing cost is increased by 15%).
B381 F1 is the benchmark of pure titanium forgings. Through high-purity design, it breaks through the bottleneck of corrosion resistance of stainless steel, and becomes the “first choice material for corrosion resistance and lightweight” in the fields of medical implants, marine corrosion protection and high-end equipment, redefining the cost-performance boundary of pure titanium applications.