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Short answer: Cobalt chromium (also written cobalt chrome, CoCr or CoCrMo) is a family of cobalt-based alloys. For surgical implants, ASTM publishes two specifications for the cobalt-28 chromium-6 molybdenum composition: F75 for cast alloy and F1537 for wrought bar, rod and wire. Which one applies depends on how the material was made.
General product and standards information only. It is not medical advice and not a statement about any specific device.
Definition and scope
Cobalt chromium names a group of alloys in which cobalt is the base metal and chromium is a principal alloying element. In the implant standards the name is usually written as a composition. The ASTM titles read “Cobalt-28 Chromium-6 Molybdenum”, which is why CoCrMo, CoCr, cocrmo and “cobalt chrome” all circulate as shorthand for the same alloy family in laboratory and clinical supply conversations.
What is cobalt chrome?
Cobalt chrome is simply the informal spelling of cobalt chromium. Suppliers, dental laboratories and additive-manufacturing vendors use it interchangeably with CoCr or CoCr alloy. The abbreviation CoCrMo adds the molybdenum that the ASTM titles name explicitly.
Where L605 fits
L605 is a different alloy designation. It is not the cobalt-28 chromium-6 molybdenum composition, so the two ASTM specifications described below do not cover it. A document that says “cobalt chromium” without naming the alloy or specification does not tell you whether it refers to CoCrMo or to something else.
How it is specified in practice
For surgical implants, the practical question is which written specification a material claims to meet. Two ASTM specifications cover the CoCrMo composition, split by the form of the material.
Cast versus wrought: which ASTM specification applies
| Specification | UNS designation | Form covered | Stated limit |
|---|---|---|---|
| ASTM F75 (2023 edition) | R30075 | Unfinished investment product castings, and casting alloy supplied as shot, bar or ingots for making surgical implants | Does not apply to completed surgical implants made from castings |
| ASTM F1537 (2020 edition) | R31537, R31538, R31539 | Three wrought cobalt-28 chromium-6 molybdenum alloys; properties apply to wrought bar, rod and wire | Covers surgical-implant material in these wrought forms |
Both rows come directly from the scope statements of the two standards (see Sources). The useful reading is that the cast specification and the wrought specification are separate documents with separate UNS numbers, and that a casting specification describes the casting or the alloy used to make an implant, not the finished implant.
Where it matters for labs, clinics and supply decisions
This page does not tell anyone what to buy. It offers a short checklist of questions that follow from the scope wording above, useful when reading a material certificate or product documentation:
- Does the document name an alloy composition (for example cobalt-28 chromium-6 molybdenum) or only “cobalt chrome”?
- Does it cite a specification that matches the form of the material, F75 for cast material or F1537 for wrought bar, rod and wire?
- Does the specification cited describe the material or alloy, or is it being used to describe a finished device? F75 states that it does not apply to completed surgical implants made from castings.
- Is the UNS number consistent with the specification cited (R30075 for F75; R31537, R31538 or R31539 for F1537)?
Powder-based routes are covered separately. Our guide to biocompatible 3D printing materials and our guide to metal powder for 3D printing mention cobalt-chromium in that context. For how a finished product is classified and cleared, see what is a medical device and FDA biocompatibility guidance.
Common misunderstandings
- “Cobalt chrome” is one exact material. It is an informal name for a family. The specification, UNS number and form identify what is actually meant.
- An alloy specification is a device clearance. F75 and F1537 are materials standards. F75 says outright that it does not apply to completed surgical implants made from castings.
- Cast and wrought are interchangeable. They are covered by different specifications with different UNS numbers.
- L605 is CoCrMo under another name. L605 is a separate alloy designation and is outside the scope of F75 and F1537.
Frequently asked questions
What is cobalt chrome?
Cobalt chrome is an informal name for cobalt chromium. In the ASTM implant standards the alloy is written as cobalt-28 chromium-6 molybdenum, abbreviated CoCrMo.
What do CoCr and CoCrMo mean?
CoCr is shorthand for cobalt chromium; CoCrMo adds molybdenum, which the ASTM titles name explicitly. Check the document to see which alloy it actually means.
What is the difference between ASTM F75 and F1537?
F75 covers cast material: unfinished investment castings and casting alloy as shot, bar or ingots (UNS R30075). F1537 covers three wrought alloys (UNS R31537, R31538, R31539), with properties that apply to wrought bar, rod and wire.
Does ASTM F75 cover finished implants?
No. Its scope states that it does not apply to completed surgical implants made from castings.
Is L605 the same as CoCrMo?
No. L605 is a separate alloy designation and falls outside the cobalt-28 chromium-6 molybdenum scope of F75 and F1537.
Sources
- ASTM International, F1537-20, Standard Specification for Wrought Cobalt-28Chromium-6Molybdenum Alloys for Surgical Implants (UNS R31537, UNS R31538, and UNS R31539), scope section 1.1: https://store.astm.org/f1537-20.html. Date checked: 2026-10-30.
- ASTM International, F75-23, Standard Specification for Cobalt-28 Chromium-6 Molybdenum Alloy Castings and Casting Alloy for Surgical Implants (UNS R30075), scope section 1.1: https://store.astm.org/f0075-23.html. Date checked: 2026-10-30.
