Actually, austenitic SSs have become less used. A certain % of people react badly to the Ni in grades like 316.  Ti alloys, nitinol and Co-based alloys (hip implants) have become more popular. MSSs have too high a modulus of elasticity, likewise the ASSs. The Ti alloys have a lower modulus of elasticity and weigh less, which is a better balance to bone. They have good corrosion resistance in the body.

It depends on the assigned function beside properties, and the most one used is St.St.316.

Regards, Emad

Dear Mr. Emad,

Thank you for your answer. Totally agreed  SS316, 316L, 316LVM is the best but am still not sure about  the biocompatibility or bacterial or platelet activity of Martensitic steels in In-vitro or In-vivo case and what makes it not to be used in human physiological environment.

depending of this propiertes you can usu 316 series

I think the decisive factor is the corrosion resistance of body fluids containing relatively large amounts of chlorides.

Titanium alloys have proven to be the best metal to be used in body prosthesis applications. The metal alloy should have similar mechanical characteristics as human bone. The best metal outside the body (stainless steel) is not the best inside the body. Any new material has to be extensively tested before approval. Medical implants are governed in the EU by the Medical Devices Regulations 2002, which are being revised. In the USA, it is governed by the FDA.

Dear Gopinath,

I am not expert in implant science and related medicine.

However: what I know from the iron and steel alloys, that apart series of austenitic steels which are said non magnetic, most of ferritic and martensitic steels are effectively magnetic and some can be permanently magnetised. These properties can be a break (?) for the use of such hard materials for implant applications. Can you imagine IRM examination if you share magnetic implants in your body.

Please notice that some non-magnetic steels can get some ferro-magnetic susceptibility when submitted to hard-works (e.g. filing)..

Also "cold" workability is a parameter to be considered for, the urgist having to adapt ex-situ the implant shape of the implantation, however he cannot be equipped as a blacksmith.

I remember having been "implanted" once.. I was surprised that the used alloy contained vanadium and cobalt among other elements. This could be reference to the workability of this alloys.

Kind regards

Daniel

Thank you Prof. Fruchart for your answer.

Thank you Prof. Petrus

I think that there are three important things: low biocompatibility, low corrosion resistance and because is a magnetic material.

Gopinath:

Here is the link to a White paper on use of stainless steel in medical devices and systems. It explains some of the reason why certain alloys are preferred.

http://www.worldstainless.org/Files/issf/non-image-files/PDF/Euro_Inox/WhenHealthComesFirst_EN.pdf

Hope this gives you a more in depth understanding of the issues involved.

Niel

Actually, austenitic SSs have become less used. A certain % of people react badly to the Ni in grades like 316.  Ti alloys, nitinol and Co-based alloys (hip implants) have become more popular. MSSs have too high a modulus of elasticity, likewise the ASSs. The Ti alloys have a lower modulus of elasticity and weigh less, which is a better balance to bone. They have good corrosion resistance in the body.

Corrosion (it stainless at normal conditions, but not in the body fluids!) and as the consequence poisoning of the organism by chromium.

Stainless steels but not ferritic or martensitic,are used in short-term applications such as an anastomosis.

Recently, Biodegradable implants are used. SS is not biodegradable. So Ti alloys are preffered

Los aceros inoxidables forman una familia de diferentes tipos. Los martensíticos son los de mejor resistencia mecánica pero los más pobres en cuanto a su inxidabilidad y por tanto, bicompatibilidad. Esto se dbe a su mayor contenido de carbono. Es por ello que no se recomiendan en estos usos.

the corrosion using  matensitic stainless steel in blood can be poisoned by chromiun excess

it's better to use austenitic steels like 316LM medical for implantes because they are totally paramagnetic.

Thank you Prof. Francisco and Mr. Yusdel for your answer

Thank you for your answer Ms. Pavlik Anastasiia. Could you please little bit elaborate why paramagnetic substance are good and why not ferromagnetic?

Also, do you think we need to evaluate the magnetic property of the material when we do some surface modification process ?

Hi!

Because of its carbon content.

Higher carbon content increases the strength of stainless steel but renders the metal more prone to corrosion. 316 is indeed very used in implants because of low carbon content is not corrosive (also it is not ferromagnetic). To make it stronger for implants they use a technique called cold rolling 316LS or 316L.

I agree with D. Fruchart

You really do not need the much greater strength and hardness of martensitic SSs like 420 or 440 (A, B or C) inside a human. Even a lower hardness austenitic stainless steel over-powers bones. The MSSs are not as corrosion resistant as the austenitic grades, which used to be used as implants. But, a percentage of humans had bad reactions to the Ni in these grades (mainly 316 SS). At least that was the belief, which I cannot verify. Ti alloys have a lower modulus of elasticity than ASSs or MSSs, and do not as badly over-power bones. Also, they have good corrosion resistance in the body.

Tha martensitic SS is nor corrosion resistant. You can use Ti aloy or austenitic SS.

Lubos Zilka is correct. 420 ss has a high carbon content which makes it heat treatable to form chrome carbides which are what gives it its high strength. This ties up some of the chromium so there is a loss in corrosion resistance (and it becomes magnetic).

I believe there are three major reasons why may of which have been previously stated by that have already responded. 1. the 400 series generally has lower pitting and crevice corrosion resistance compared to austenitic, nitinol, cobalt-chromium and titanium alloys which is particularily important in when exposed to the in vivo chloride environment 2. the magnetic properties make it much less attractive particularly when patients may be exposed to MRI and 3. the martensitic stainless alloys in hard hardness/high strength conditions tends to make them more susceptible to hydrogen cracking compared to the other alloys generally use for implantable medical devices