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316 steel: is it the best solution for surgical instruments used in a magnetic field?

August 14, 2009

I am an interventional radiologist (surgery under imaging: X ray, CT or MRI). Magnetic resonance imaging is quite new in our field. The major parts of our instruments are in titanium. Which is expensive and have not the elasticity we need? The instruments like needles should be sharp, hard but with some elasticity like our usual needles in medicine. Do you think the 316 steel can be used because some physicians are advocating this material compared to titanium. Is there any advantages compared to titanium? The cost is an important issue in health care.
Any other idea? Carbon needles?
Thank you

A Gangi
Interventional radiologist, M.D., Ph.D. - Strasbourg, France

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I likely wouldn't recommend 316, as I'm thinking that fine drawn needles would probably be cold worked. Cold working will convert some of the atomic structure from non-magnetic FCC to magnetic BCT, and I believe that complete lack of ferromagnetism is important around MRI devices. Annealing the needles would eliminate the ferromagnetism, but why lose the strength you crave?

My first suggestion would be A286, an iron based superalloy designated as 1.4980 in say, EN 12069. It is non-ferromagnetic, has an elastic modulus of 29 million vs. the 16 million that titanium alloys commonly have, costs far less, and is more available than titanium alloys since it's made into high grade fasteners. Cold worked and aged, it can easily give you yield strengths of 180 ksi compared to the 150 ksi of STA 6-4 titanium.

If I thought about it longer I'm sure I could come up with multiple suggestions. Should you send an e-mail to CarTech, ThyssenKruppVDM, or Aubert & Duval, (specialty steel companies) I'm certain they could give even more.

Good luck!

Lee Gearhart
metallurgist - E. Aurora, New York
August 19, 2009