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October 21, 2022
Titanium is a polycrystalline metal. It is a crystal form below 882 ℃. Its atomic structure is a close packed hexagonal lattice. From 882 ℃ to the melting point, it is a B crystal form, which is a body centered cubic lattice. Industrial pure titanium presents a phase in the metallographic structure. if the annealing is complete, it is an equiaxed single crystal lattice with the same size. Due to impurities, a small amount of B phase also exists in commercially pure titanium. It is basically distributed along the grain boundary.
According to the new standard GB/T3620.1-2007, industrial pure titanium has nine brands, three TA1 types and two TA2-TA4 types. The difference between them is the purity.
From the table, we can see that each brand of TA1-TA4 has a brand with the suffix ELI, which is the abbreviation of English low clearance element, which means high purity.
Because Fe, C, N, H, O exist as interstitial elements in a-Ti, their content has a great impact on the corrosion resistance and mechanical properties of industrial pure titanium. The solid solution of C, N, O in titanium can cause great distortion of titanium lattice, and make titanium strongly strengthened and brittle. These impurities are brought in by raw materials during production, mainly the quality of titanium sponge. If you want to produce high-purity industrial pure titanium ingots, you must use high-purity sponge titanium.
In the standard, the highest content of the six elements of the brand with ELI is lower than that of the brand without ELI. The revision of these standards is based on the international or western standards (our national standards are trying to move closer to the western countries, because many of our basic industries are still lagging behind them, and many old standards follow the former Soviet Union), especially in terms of impurity content and room temperature mechanical properties, the indicators of each brand are basically consistent with those of the international and western countries. This new standard mainly refers to ISO (international standard) surgical implants and American ASTM material standards (B265, B338, B348, B381, B861, B862 and B863). It also corresponds to ISO and American ASTM standards, for example, TA1 corresponds to Gr1, TA2 corresponds to Gr2, TA3 corresponds to Gr3, and TA4 corresponds to Gr4. This is conducive to clear reference of national standards in material selection and application of various industries, and also conducive to international exchanges in technology and commerce.
Alloy grade, nominal chemical composition, impurities no more than
Fe C N H O Other elements
TA1ELI industrial pure titanium 0.1 0.03 0.012 0.008 0.1 0.05 0.2
TA1 industrial pure titanium 0.2 0.08 0.03 0.015 0.18 0.1 0.4
TA1-1 industrial pure titanium 0.15 0.05 0.03 0.003 0.12 ---- 0.1
TA2ELI industrial pure titanium 0.2 0.05 0.03 0.008 0.1 0.05 0.2
TA2 industrial pure titanium 0.3 0.08 0.03 0.015 0.25 0.1 0.4
TA3ELI industrial pure titanium 0.25 0.05 0.04 0.008 0.18 0.05 0.2
TA3 industrial pure titanium 0.3 0.08 0.05 0.015 0.35 0.1 0.4
TA4ELI industrial pure titanium 0.3 0.05 0.05 0.008 0.25 0.05 0.2
TA4 industrial pure titanium 0.5 0.08 0.05 0.015 0.4 0.1 0.4
(Table I: Designation and chemical composition of titanium and titanium alloys)
Two problems should be noted in the pure titanium table of this new standard. One is that in comparison with GB/T3620.1-1994 and GB/T3620.1-2007, the original TA0 changes to TA1, the original TA1 changes to TA2, the original TA2 changes to TA3, the original TA3 changes to TA4, and the original TA4 changes to TA28. The other is that with the increase of brand number, the content of these five impurity elements also increases, which means that the strength increases and the plasticity decreases gradually. One thing to note here is that Fe, the element, exists as an impurity, not as an alloy element. From the GB/T3620.1-2007 standard, we can see that the content of TA1~TA4 impurity elements increases gradually, but mainly Fe and O increase obviously, while C, N and H increase slightly.
Industrial pure titanium is different from chemical pure titanium. Chemical pure titanium is used by scientific research institutions to conduct scientific research on some characteristics of pure metals, while industrial pure titanium is a material directly used in various industries, and contains more of the above five impurities than chemical pure titanium. Industrial pure titanium is characterized by its low strength, good plasticity, easy processing and forming, and can be stamped, Welding and machining properties are also good, and it has good corrosion resistance in various oxidation and corrosion environments. Therefore, more than 70% of the plates are industrial pure titanium, which is mainly used for the processing and molding of chemical reaction kettles and pressure vessels. Among these pure titanium grades, TA1 is the most widely used, followed by TA2. When it comes to industrial pure titanium, we must make it clear that the strength of industrial pure titanium cannot be improved by heat treatment. If the mechanical properties of a batch of pure titanium are low, don't imagine how to treat it to make it qualified. It's a waste of effort.
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