Difference Between Grade 2 、 Grade 3 Titanium

1. Core Distinction: Interstitial Impurity Content

The primary difference between Grade 2 and Grade 3 lies in their oxygen content (the most impactful interstitial element for CP titanium properties). Oxygen acts as a "strengthening agent" in pure titanium: higher oxygen content increases strength but reduces ductility.

Impurity Element	Grade 2 Titanium (ASTM B265 Standard)	Grade 3 Titanium (ASTM B265 Standard)	Key Impact
Oxygen (O)	Maximum 0.25 wt%	Maximum 0.35 wt%	Grade 3 has ~40% higher oxygen content, driving its higher strength.
Nitrogen (N)	Maximum 0.03 wt%	Maximum 0.05 wt%	Minor difference; both low, with minimal effect on overall properties.
Carbon (C)	Maximum 0.08 wt%	Maximum 0.08 wt%	Identical limit; no meaningful difference.
Hydrogen (H)	Maximum 0.015 wt%	Maximum 0.015 wt%	Identical limit; both low to avoid embrittlement.

Other elements (e.g., iron) also have similar maximum limits (~0.20 wt% for both grades), so oxygen content is the defining factor in their performance gap.

2. Mechanical Properties: Strength vs. Ductility

The higher oxygen content in Grade 3 directly translates to higher strength but lower ductility compared to Grade 2. This is the most practical difference for engineering applications.

Mechanical Property (Annealed Condition)	Grade 2 Titanium	Grade 3 Titanium	Key Comparison
Tensile Strength (Minimum)	345 MPa (50 ksi)	450 MPa (65 ksi)	Grade 3 is ~30% stronger in tensile strength.
Yield Strength (Minimum)	275 MPa (40 ksi)	380 MPa (55 ksi)	Grade 3 has ~38% higher yield strength (resistance to permanent deformation).
Elongation (Minimum, in 50 mm)	20%	15%	Grade 2 is ~25% more ductile (can stretch further before breaking).
Hardness (Brinell, HB)	~110	~135	Grade 3 is harder, reflecting its higher strength.

Note: "Annealed condition" is the most common state for CP titanium, as it relieves internal stress and stabilizes properties. Both grades show similar trends (Grade 3 stronger/less ductile) in other tempers, though absolute values may vary.

3. Formability and Machinability

Formability (ability to be bent, rolled, or shaped into complex parts) and machinability (ease of cutting/drilling) are inversely related to strength for CP titanium:

Grade 2: Its lower strength and higher ductility make it highly formable. It can be cold-worked (e.g., bent into tight radii, drawn into thin wires) or hot-worked with minimal risk of cracking. Machinability is moderate-while it is softer than Grade 3, titanium's low thermal conductivity (common to all CP grades) still requires sharp tools and coolants to prevent overheating.

Grade 3: Its higher strength and lower ductility reduce formability. Cold forming may require more force, and tight bends or thin sections are more prone to fracture. Machinability is slightly worse than Grade 2: the harder matrix increases tool wear, and the lower ductility can lead to more brittle chip formation (though the difference is less dramatic than between CP titanium and alloyed titanium like Grade 5).

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4. Corrosion Resistance

Both Grade 2 and Grade 3 exhibit excellent corrosion resistance-a hallmark of CP titanium-thanks to their dense, self-healing titanium dioxide (TiO₂) passive film. Their corrosion performance is nearly identical in most environments, including:

Freshwater, seawater, and marine atmospheres (no pitting or crevice corrosion under typical conditions).

Neutral/weakly acidic/alkaline solutions (e.g., food processing, chemical storage).

Biomedical environments (biocompatible, no harmful ion leaching).

The minor difference in impurity content does not meaningfully impact corrosion resistance. Both grades are inferior to alloyed titanium (e.g., Grade 7 Ti-Pd) in highly aggressive environments (e.g., concentrated chloride solutions, strong reducing acids), but they perform equally well in standard applications.

5. Typical Applications

The choice between Grade 2 and Grade 3 depends on whether formability (Grade 2) or strength (Grade 3) is prioritized, as their corrosion resistance and cost are similar.

Grade 2 Applications (Prioritize Formability + Moderate Strength)

Chemical processing: Thin-walled tubes, tanks, and fittings (easily formed into complex shapes for fluid handling).

Architecture/design: Decorative panels, lightweight structural components (formable into curved or custom profiles).

Medical devices: Non-load-bearing parts (e.g., surgical instruments, catheter tubes) where ductility and biocompatibility are key.

Consumer goods: Watch cases, eyewear frames (easily machined and shaped into intricate designs).

Grade 3 Applications (Prioritize Higher Strength + Moderate Formability)

Aerospace: Low-load structural parts (e.g., brackets, ducting) where strength is more critical than extreme formability.

Marine engineering: Small components (e.g., fasteners, valve stems) exposed to seawater, requiring higher strength than Grade 2 can provide.

Industrial equipment: Pressure vessels or pumps for low-to-moderate pressure applications (needs strength to withstand internal forces).

Medical devices: Lightly loaded implants (e.g., some dental abutments) where biocompatibility and extra strength are needed.

6. Cost

Grade 2 and Grade 3 are among the most affordable titanium grades (second only to Grade 1). Their cost is nearly identical, as the minor difference in impurity control (slightly stricter for Grade 2's lower oxygen limit) does not create a significant price gap. Both are far cheaper than alloyed titanium (e.g., Grade 5 Ti-6Al-4V), which requires expensive alloying elements.