Difference Between Grade 1、 Grade 4 Titanium

1. Core Distinction: Interstitial Impurity Content

The primary difference between Grade 1 and Grade 4 is their oxygen content-the most impactful interstitial element for CP titanium. Oxygen acts as a "solid-solution strengthener": higher oxygen content increases atomic packing density in the titanium lattice, raising strength but reducing ductility.

Impurity Element	Grade 1 Titanium (ASTM B265 Standard)	Grade 4 Titanium (ASTM B265 Standard)	Key Impact
Oxygen (O)	Maximum 0.18 wt%	Maximum 0.40 wt%	Grade 4 has 2.2x higher oxygen content than Grade 1-this is the single biggest driver of their performance gap.
Nitrogen (N)	Maximum 0.03 wt%	Maximum 0.05 wt%	Minor difference; both low, with negligible 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 strictly controlled to avoid hydrogen embrittlement.
Iron (Fe)	Maximum 0.20 wt%	Maximum 0.50 wt%	Grade 4 allows slightly more iron, a minor strengthener that complements oxygen's effect.

Other elements (e.g., titanium itself) make up the balance (>99%) for both grades, so oxygen (and to a lesser extent, iron) defines their unique characteristics.

2. Mechanical Properties: Strength vs. Ductility

The higher oxygen (and iron) content in Grade 4 directly translates to far higher strength and hardness, but much lower ductility compared to Grade 1. This is the most practical difference for engineering use.

Mechanical Property (Annealed Condition)	Grade 1 Titanium	Grade 4 Titanium	Key Comparison
Tensile Strength (Minimum)	240 MPa (35 ksi)	620 MPa (90 ksi)	Grade 4 is 2.6x stronger in tensile strength.
Yield Strength (Minimum)	170 MPa (25 ksi)	550 MPa (80 ksi)	Grade 4 has 3.2x higher yield strength (resistance to permanent deformation).
Elongation (Minimum, in 50 mm)	24%	10%	Grade 1 is 2.4x more ductile (stretches much further before breaking).
Hardness (Brinell, HB)	~80	~170	Grade 4 is 2.1x harder than Grade 1.
Density	4.51 g/cm³	4.51 g/cm³	Identical-both are pure titanium, so density does not vary.

Note: "Annealed condition" is standard for CP titanium, as it relieves internal stress and stabilizes properties. While both grades can be cold-worked to further increase strength (at the cost of ductility), the relative gap between them remains consistent (Grade 4 stays significantly stronger/less ductile).

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-creating a stark contrast between Grade 1 and Grade 4:

Grade 1: Its ultra-low strength and high ductility make it the most formable CP titanium grade. It can be cold-worked into extreme shapes (e.g., tight-radius bends, thin foils, small-diameter tubes) with minimal force and near-zero risk of cracking. It even retains good formability at cryogenic temperatures. Machinability is excellent for titanium-its softness reduces tool wear, though titanium's inherent low thermal conductivity still requires coolants to prevent overheating.

Grade 4: Its high strength and low ductility make it the least formable CP titanium grade. Cold forming requires high force and often pre-heating (to ~200–400°C) to avoid fracturing; tight bends or thin sections are rarely feasible. It is typically limited to simple shapes (e.g., thick plates, straight bars). Machinability is poor for CP titanium-its hardness accelerates tool wear, and low ductility causes brittle chip formation, increasing machining time and cost compared to Grade 1.

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4. Corrosion Resistance

Both Grade 1 and Grade 4 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, pharmaceutical manufacturing, wastewater treatment).

Chemical environments like dilute sulfuric acid, nitric acid, and organic solvents.

The minor difference in impurity content (oxygen/iron) does not meaningfully impact corrosion resistance. Both grades are vulnerable to strong reducing acids (e.g., concentrated hydrochloric acid, hydrofluoric acid) and molten salts (where the passive film dissolves), but their performance in these aggressive settings is comparable.

For applications where ultra-high purity is critical (e.g., semiconductor manufacturing, high-purity chemical processing), Grade 1's lower impurity content may offer marginal advantages in preventing trace ion leaching-but this is a niche concern, not a general corrosion performance gap.

5. Typical Applications

Their divergent properties make Grade 1 and Grade 4 suited for entirely different use cases:

Grade 1 Applications (Prioritize Formability, Purity, and Softness)

Chemical processing: Ultra-thin-walled tubes, liners for high-purity tanks, and gaskets (requires formability and minimal ion leaching).

Medical devices: Flexible components (e.g., catheter shafts, surgical staples, orthodontic wires) and cryogenic storage containers (retains formability at low temperatures).

Aerospace: Lightweight, non-structural components (e.g., fuel lines, hydraulic tubes) where formability and corrosion resistance matter more than strength.

Consumer goods: Decorative parts (e.g., jewelry, watch bands) and flexible fasteners (e.g., spring clips) that require shaping into intricate designs.

Grade 4 Applications (Prioritize Strength and Durability)

Medical devices: Load-bearing, non-flexible components (e.g., dental implants, bone plates, surgical instrument handles) where strength and biocompatibility are key.

Industrial equipment: Thick-walled pressure vessels, heat exchanger tubes (for moderate pressures), and structural brackets (requires strength to withstand mechanical loads).

Aerospace: Heavy-duty non-flexible parts (e.g., engine mounts, landing gear components) where CP titanium's corrosion resistance and moderate strength meet requirements (without the cost of alloyed titanium like Grade 5).

Marine engineering: Thick plates for ship hulls, offshore platform components, and fasteners (resists seawater corrosion while withstanding structural loads).

6. Cost

Grade 1 is typically slightly more expensive than Grade 4-though the gap is small (5–15%, depending on form and quantity). The higher cost of Grade 1 stems from:

Purity requirements: Producing Grade 1 requires tighter control over impurity levels (especially oxygen), increasing smelting complexity.

Processing costs: Grade 1 is often processed into high-value, complex forms (e.g., thin foils, small tubes) that require more precise manufacturing.

Grade 4's lower cost reflects its simpler impurity control and limited formability (it is often produced in high-volume, low-complexity shapes like thick plates). Both grades are far cheaper than alloyed titanium (e.g., Grade 5 Ti-6Al-4V).