Titanium Grades
The titanium grade system takes into consideration mechanical characteristics, heat resistance, conductivity, microstructure, creep, ductility and corrosion resistance of titanium plates, bars, wire and other forms. The allotropic behavior of titanium allows diverse changes in microstructure which result from the thermo-mechanical processing used in titanium extraction and the creation of alloys. Additionally, oxygen, nitrogen and carbon found in the atmosphere alter the hardness and ductility of even pure titanium. These natural and production related occurrences add to the already numerous variations of titanium and titanium alloys, each with deviating qualities and characteristics. The grade system was established to more easily make distinctions and allow manufacturers to use the most applicable materials for their processes. Although there are several regulatory bodies which make grade designations, the 38 grades system established by the American Society for Testing Materials (ASTM) is most used. The American Society of Mechanical Engineers (ASME), the European Norm (EN) and the European Committee for Standardization (CEN) are a just a few of the many known titanium grading organizations.
In the ASTM grading system, grade numbers are given based on chemical composition, mechanical, physical and fatigue properties. While grade designation may simply be a number, most have a corresponding alpha numeric title that is more descriptive. The most common alloy, for example, is referred to as grade 5 titanium or Titanium 6AL-4V. The first portion ‘6AL' indicates the alloy composition as being six percent aluminum while ‘4V' signifies four percent vanadium. The other 90% is titanium. In addition to aluminum and vanadium, common elemental additives include nickel, ruthenium, molybdenum, chromium, zirconium, palladium and manganese. Grades one through five are considered pure, though oxidation and other natural effects alter their composition slightly. Grade two, for example, is the most common ‘pure' titanium but is only 98.99% titanium. Further designations can be made by grouping grades together. One system for doing so is based on the applications of a material. Categories include corrosion resistance, high strength and high temperature grades. Another three class designation is based on structural properties. Alpha or near Alpha encompasses those substances with low to medium strength that are non heat treatable, Alpha Beta is medium to high stress and heat treatable titanium, and Beta or near Beta includes the strongest, most dense and fully heat treatable grades.
