Compared with stainless steel in industrial structure, medical stainless steel is required to maintain excellent corrosion resistance in the human body, in order to reduce the dissolution of metal ions, to avoid intergranular corrosion, stress corrosion and other local corrosion phenomena, to prevent implant failure and fracture. In order to ensure the safety of implanted devices, the requirements on their chemical composition are relatively strict.
For medical stainless steel, especially for implantation stainless steel, the content of alloying elements such as nickel and chromium is higher than that of ordinary stainless steel (usually up to the upper limit of ordinary stainless steel), and the content of impurity elements such as S and P is lower than that of ordinary stainless steel. The size of non-metallic inclusions in the medium should be less than 115 grade (thin series) and 1 grade (coarse series), the general industrial stainless steel standards have no special requirements for inclusions.
In order to avoid intergranular corrosion of medical stainless steel, it is also required to have a low C content, and the early regulation of C content should not be higher than 0108% and 0103% two grades (mass fraction). With the advancement of metallurgical technology and the improvement of application requirements, in the domestic and foreign standards of medical stainless steel revised in recent years, all require that the C content in steel should not exceed 0.103% (such as ASTMF138-03, ASTMF139-03, ISO5832-1-2007, GB4234-2003).
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