The ASTM titanium grade system is the largest in the global titanium market and it is the foundation of international purchasing, production and engineering application, which is also the most recognized in aerospace, chemical, pharmaceutical, mechanical and other major industries. Among them, ASTM Grade 2 (industrial pure titanium) and Grade 5 (Ti-6Al-4V) and Grade 23(Ti-6Al-4V ELI) are the best-seller and most widely used grades. The difference in composition and impurities influences its mechanical properties, corrosion resistance and processing performance. Hence, the correct choice is essential for the engineering safety, cost and lifetime of the vessel.
ASTM Grade 2 Pure Titanium is a non-ferrous pure metal that is the most widely used grade of commercial Titanium. Major impurities are iron (≤ 0.30%), oxygen(≤0.20%),nitrogen(≤0.03%),carbon(≤0.08%). The lower level of impurity provides it with good corrosion resistance and formability. As with other grades of titanium, it has moderate strength, but it is more stable and weldable - you can make high class welds without any elaborate pre-treatment, and the strength of the welding joint can be more than 90% of base metal. This material is simple to make into plates, tubes, rods and all different forms of shapes for many applications.
Grade 2 is the most popular grade of titanium for the chemical, marine and oil and gas industries due to its corrosion resistance. It is widely used in heat exchangers, reactors, pipelines, valves and can resist corrosion by such media as low/medium concentration of hydrochloric and sulfuric acids, and is less likely to suffer from pitting or crevice corrosion. In marine engineering, it is mature in seawater desalination and ocean pipelines with the life-span over 20 years, much better than stainless steel. At the same time, the material meets food and medical hygiene standards and can be applied in pressure vessels, and foods processing machinery. Its tensile strength is 345-450MPa, yield strength is about 275MPa, and elongation is ≥ 20%, and it can move stable in pressure and room temperature. It is the most economical grade of titanium.
Grade 5 is the most popular & widely known titanium alloy ([Ti-6Al-4V] the "king of titanium alloys"). Its constituent elements are Al (aluminum): 5.5% -6.75%, V (vanadium): 3.5% -4.5%, Ti (titanium): the rest. It is α+β type alloy, which has both strength and plasticity. It possesses both better mechanical properties than pure titanium and is less difficult to process than other high strength titanium alloys, therefore, it is applicable for components that carry structural loads.
The tensile strength of the material is ≥ 930 MPa, the yield strength is ≥ 860 MPa, the elongation is ≥ 10%, and the fatigue strength is about 420 MPa (about twice that of Grade 2). It can withstand high and alternating loads while maintaining good corrosion resistance. In the aviation industry, its usage accounts for over 70% of aircraft titanium materials, used for landing gear, wing connectors, and engine components of Boeing 787 and China C919. In the field of chemical engineering, it can be used for high-pressure reactors and heavy-duty pipelines; In mechanical manufacturing, it is suitable for precision molds. Although priced higher than pure titanium, its comprehensive cost-effectiveness is outstanding.
ASTM Grade 23 (Ti-6Al-4V ELI) is the low gap element version of Grade 5 ("ELI" means extremely low gap element). However, it has a more stringent control of impurities: oxygen ≤ 0.13%, iron ≤ 0.25%, hydrogen ≤ 0.012%. It also offers significant improvements in toughness, impact strength and biocompatibility while retaining the strength and corrosion resistance of Grade 5.
Grade 23 has minimum tensile strength of 860 MPa, minimum yield strength of 795 MPa, minimum elongation of 14%, minimum impact toughness of 60 J (approximately 50% higher than Grade 5) and better resistance to brittle fracture. The very low impurity content makes it non-toxic, hypoallergenic and has good compatibility with biological tissues, so it can be used in medical implanting fields such as artificial joints, dental implants, and stents. At the same time, it is also used in high-precision equipment such as semiconductor components and aviation sensors. But its production process requires strict standards and the cost is higher than Grade 5.
When selecting procurement materials, Grade 2 is recommended for conventional corrosive and low load conditions; Grade 5 is recommended for aerospace and high load chemical structures; Medical implants and high-precision devices should use Grade 23. Proper selection can ensure quality, control costs, and avoid losses, which is a key link in titanium procurement. With the growth of industrial demand, the application of these three types of grades will become more widespread, and performance improvement and process improvement will still be the focus of future development.
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