Difference Between Grade 3 、 Grade 5 Titanium

1. Core Distinction: Chemical Composition

The biggest difference lies in their chemical makeup: Grade 3 is nearly pure titanium, while Grade 5 contains intentional alloying elements to enhance strength.

Component	Grade 3 Titanium (ASTM B265)	Grade 5 Titanium (Ti-6Al-4V, ASTM B265)	Key Impact
Titanium (Ti)	≥ 99% (balance)	~88–90% (balance)	Grade 3 relies on pure Ti's inherent properties; Grade 5 uses alloying to modify performance.
Aluminum (Al)	Trace (≤ 0.10 wt%)	5.5–6.75 wt%	Primary alpha-phase stabilizer: boosts strength, improves high-temperature stability.
Vanadium (V)	Trace (≤ 0.10 wt%)	3.5–4.5 wt%	Primary beta-phase stabilizer: enhances toughness, enables heat treatment for further strengthening.
Oxygen (O)	Max 0.35 wt%	Max 0.20 wt%	Grade 3 uses oxygen for minor strengthening; Grade 5 limits oxygen to avoid brittleness (alloying elements already provide strength).
Other Impurities	Low (N ≤ 0.05%, C ≤ 0.08%, H ≤ 0.015%)	Low (N ≤ 0.05%, C ≤ 0.08%, H ≤ 0.015%)	Similar strict limits for both to prevent embrittlement.

In short, Grade 3 is "pure titanium with trace impurities," while Grade 5 is a "purpose-built alloy" with aluminum and vanadium as key performance modifiers.

2. Mechanical Properties: Strength and Toughness

The alloying elements in Grade 5 deliver far higher strength and superior strength-to-weight ratio compared to Grade 3, though Grade 3 retains better ductility.

Mechanical Property (Annealed Condition, unless noted)	Grade 3 Titanium	Grade 5 Titanium (Annealed)	Grade 5 Titanium (Solution-Treated & Aged, STA)	Key Comparison
Tensile Strength (Minimum)	450 MPa (65 ksi)	860 MPa (125 ksi)	1100 MPa (160 ksi)	Grade 5 (STA) is 2.4x stronger than Grade 3.
Yield Strength (Minimum)	380 MPa (55 ksi)	760 MPa (110 ksi)	1030 MPa (150 ksi)	Grade 5 (STA) has 2.7x higher yield strength (resistance to permanent deformation).
Elongation (Minimum, in 50 mm)	15%	10%	8%	Grade 3 is 1.5–1.9x more ductile (stretches further before breaking).
Hardness (Brinell, HB)	~135	~300	~350	Grade 5 is 2.2–2.6x harder than Grade 3.
Density	4.51 g/cm³	4.43 g/cm³	4.43 g/cm³	Grade 5 is slightly less dense, enhancing its strength-to-weight ratio.

Critical Note: Grade 5's strength is fully unlocked via solution treatment and aging (STA)-a heat treatment impossible for Grade 3 (pure titanium cannot be strengthened significantly by heat treatment, only by cold working). This makes Grade 5 the go-to for high-load applications.

3. Corrosion Resistance

Both grades offer excellent corrosion resistance, but their performance varies in aggressive environments:

Grade 3 (CP Titanium): Relies on a dense, self-healing titanium dioxide (TiO₂) passive film. It excels in mild to moderate corrosive environments (freshwater, seawater, neutral/weak acids/alkalis) and is highly resistant to crevice/pitting corrosion in typical conditions. However, it is vulnerable to strong reducing acids (e.g., concentrated sulfuric acid, hydrochloric acid) and high-temperature oxidizing environments (above ~300°C), where the passive film can break down.

Grade 5 (Ti-6Al-4V): The aluminum in its composition reinforces the TiO₂ film, improving resistance to oxidizing environments (e.g., nitric acid, high-temperature air). It also performs well in seawater and most industrial chemicals. However, Grade 5 is slightly less resistant to crevice corrosion in hot, concentrated chloride solutions (e.g., 80°C+ seawater) than Grade 3, due to vanadium's minor impact on film stability.

For most standard applications (e.g., marine, medical, general industry), both grades are corrosion-resistant enough. Grade 3 is preferred for extreme mild environments where purity matters; Grade 5 is chosen when strength is critical and corrosion resistance is still required.

4. Formability and Machinability

Formability (shaping into complex parts) and machinability (cutting/drilling) are vastly different due to Grade 5's higher strength:

Grade 3: Its lower strength and higher ductility make it highly formable. It can be cold-worked (bent, rolled, drawn into thin sheets/wires) with minimal force and low risk of cracking. Machinability is moderate-titanium's low thermal conductivity (common to all grades) causes heat buildup, but Grade 3's softness reduces tool wear compared to alloys.

Grade 5: Its high strength (especially in STA condition) makes it poorly formable. Cold forming requires extreme force and often pre-heating (to ~300–500°C) to avoid fracturing; complex shapes are typically produced via casting or forging (not bending/rolling). Machinability is difficult: Its high hardness and low thermal conductivity lead to rapid tool wear, requiring specialized tools (e.g., carbide inserts), coolants, and slow cutting speeds. Machining Grade 5 is often 2–3x more time-consuming and costly than Grade 3.

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5. Heat Treatment Response

This is a defining difference between pure and alloyed titanium:

Grade 3: As a CP titanium grade, it cannot be strengthened by heat treatment. Annealing (heating to ~650–700°C, slow cooling) is the only common heat treatment-it relieves internal stress from cold working and restores ductility, but does not change strength. Cold working (e.g., rolling, drawing) is the only way to increase Grade 3's strength (at the cost of ductility).

Grade 5: As an alpha-beta alloy, it responds strongly to heat treatment. The most common process-solution treatment and aging (STA)-involves:

Heating to 920–960°C (alpha-beta phase region) to dissolve vanadium into the alpha matrix.

Rapid quenching (water cooling) to trap vanadium in a metastable state (martensitic α'-phase).

Aging at 480–650°C to precipitate fine, uniform beta-phase particles, which block dislocation movement and drastically increase strength.

This heat treatment capability is why Grade 5 dominates high-strength applications.

6. Typical Applications

Their divergent properties lead to entirely different use cases:

Grade 3 Applications (Prioritize Formability + Mild Strength + Corrosion Resistance)

Marine engineering: Small seawater-exposed parts (e.g., valve stems, pump impellers) where moderate strength and corrosion resistance suffice.

Chemical processing: Low-pressure tanks, pipes, and fittings for non-aggressive fluids (e.g., food-grade acids).

Medical devices: Non-load-bearing components (e.g., surgical instrument shafts, dental trays) where formability and biocompatibility are key.

Consumer goods: Lightweight hardware (e.g., fasteners for outdoor gear) where cost and ease of fabrication matter more than high strength.

Grade 5 Applications (Prioritize High Strength + Strength-to-Weight Ratio)

Aerospace: Primary structural components (e.g., aircraft frames, engine blades, landing gear) where weight savings and strength are critical.

Biomedical: Load-bearing implants (e.g., hip/knee replacements, spinal fusion rods) where high strength, biocompatibility, and fatigue resistance are essential.

Automotive: High-performance parts (e.g., racing engine valves, exhaust components) to reduce weight and improve durability.

Industrial machinery: High-load parts (e.g., pressure vessel internals, heavy-duty fasteners) that require strength beyond CP titanium's capabilities.

7. Cost

Grade 5 is significantly more expensive than Grade 3-typically 2–3x the cost. The price gap stems from:

Alloying elements: Aluminum and vanadium add raw material costs.

Manufacturing complexity: Grade 5 requires more precise smelting (to control alloy ratios) and often heat treatment/forging (vs. simple rolling for Grade 3).

Machining costs: Grade 5's poor machinability increases fabrication time and tool expenses.