Difference between ASTM F67 and ASTM F136

Sep 16, 2025

Regarding F67 and F136, apart from the difference in grades, what other differences are there between them?

Both of these standards are for medical use in the United States. F67 refers to pure titanium, and the requirement for oxygen in pure titanium is low oxygen, with the oxygen content being below 0.13. F136 refers to Gr5, and in Gr5, it is low oxygen, also known as low interstitial, but actually, low interstitial does not mean low oxygen. There is a difference between oxygen and low interstitial because interstitial elements are not only oxygen; carbon and nitrogen also belong to interstitial elements. It is about lowering the oxygen content. Why is low oxygen necessary?

From a deeper perspective, low oxygen is different from the high oxygen content of 0.13 or above in normal Gr5 rods. What is the difference? It involves a concept called damage melting limit. The more oxides there are, because there is oxygen in it, the possibility of damage between the precise interfaces increases. When pulling this material, the material is under tensile force and other forces. It will break at the interfaces rather than in the middle of the precise parts. The attraction between various atomic and molecular bonds in the precise parts is relatively strong, so it can only break at the interfaces.

If the oxygen content is high, it will affect its fracture toughness. That's why it needs to be low. However, if the low interstitial elements are too few, it will instead cause a decline in the material's performance, that is, a decrease in physical properties. This interstitial element plays a strengthening role in the middle. If the overall content is low, the standard values of low-interstitial Gr5 and ordinary Gr5 are different. The tensile strength of ordinary Gr5 is 930, and the yield strength is 860. The tensile strength of low-oxygen Gr5 may be around 895, and the yield strength may be around 790. These two values are different. This interstitial element has an impact on it. In use, it is not easy to come out. It's just that low-interstitial Gr5 is mentioned. But in fact, the internal control is related to the fracture trace.