By Ronald A. Fante, The Body Wire Co., LLC
It’s apparent that there needs to be clarification regarding the differences between 316L and 316LVM Stainless Steel. I'm may not be able to clear up all the issues, but I'll tell you what I know, hopefully it will help resolve a few misconceptions. The first thing that needs clarification is the term 316LVM. There is no such grade of material called 316LVM. The material is 316L, the VM only stands for the type of re-melt (Vacuum Melt) required to achieve the micro-cleanliness (inclusion limitations) of many industry specifications. The term “316LVM” has evolved to become synonymous with 316L Vacuum Melt. The Vacuum Melt process is typically a second melt, sometimes referred to as a premium melt. The most common premium melts or re-melts are, Electro Slag Re-melt (ESR), Vacuum Arc Re-Melt (VAR) and Vacuum Induction Melt (VIM).
It's important to understand the relationship between 316LVM per ASTM-F138 and the standard version of 316LVM with respect to micro-cleanliness. The standard version of 316LVM and 316L generally meet the requirements of ASTM-A-580, ASTM-A-276, ASTM-A-479, QQS763 and the Intergranular Corrosion Resistance requirements of ASTM-A-262 Practice E, they do not meet the requirements of ASTM-F-138. This specification is unique in that it has a modified chemistry with inclusion limitations suitable for implants. Even though the standard version of 316LVM may meet the inclusion limitations, the chemistry is not suitable for most implants.
Micro-cleanliness plays a very important role in qualifying a material as Implant Quality, the additional Nickel plays a very important role also. The ASTM-F138 requires a Nickel content of 13.00/15.50% to insure the material does not become magnetic during cold working, which is often part of the manufacturing process. It also offers additional corrosion resistance. Standard 316L or 316LVM has a lower nickel content (10.00/14.00) and is usually at the low end of this range, consequently the material can become magnetic after severe cold working.
I often hear comments about the Chromium oxide layer on the surface of 316LVM F-138. This is true, but I feel clarification is needed. These materials all have a Chromium oxide layer on the surface. This is one of the primary reasons stainless steel resists corrosion. The varying combinations of Chromium, Nickel and Molybdenum allows for different degrees of corrosion resistance. In the case of 316L or 316LVM more Chromium and Nickel is added for this reason. Molybdenum is also added to help the Chromium and Nickel do their job.
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