Stainless Steel for medical devices

Stainless steel is the base material of medical technology, but "stainless steel" is not a specification. What matters is the material number. Instruments that cut and transmit force use hardenable martensitic steels — 1.4021, 1.4034, 1.4197 — because they can be heat treated to cutting hardness. Instruments that mainly need corrosion resistance, and implants, use austenitic steels, above all 1.4441 to ISO 5832-1.

The property that really matters is the passive layer. It forms from chromium at the surface and protects against corrosion — but only if the surface is clean. Grinding dust, foreign iron from machining, residues from cleaning: every contamination is a flaw where pitting begins. That is why passivation or electropolishing belongs to stainless steel manufacturing, and why separating stainless from unalloyed materials is a matter of course in good workshops.

For buyers this means: ask for the material number and the inspection certificate, for purity grade and melting route, and for how the surface is treated afterwards. Two parts made from the same steel can differ markedly in corrosion behaviour — not because of the steel, but because of what happened to it afterwards.