Corrosion resistance for fastener used in medical device
Corrosion resistance is closely related to the combination of raw material and finishing chosen.
Although carbon steel fasteners have a variety of surface processes, most of them used for medical parts are black oxide or zinc plated. This is because medical fasteners require more accurate thread tolerances, so plating thickness is very important. The black oxide process is relatively basic and does not have good antirust performance. Even if the antirust oil is applied immediately after the blackening process, it can only reach the salt spray test for about 1-3 hours, but its low cost is also applicable to the market. Zinc plating is a very common finishing chosed by the market. When the coating layer reaches more than 5um, it can basically reach the proformance of salt spray test for 24-48 hours.
If you need fasteners with higher corrosion resistance, stainless steel is your first choice. However, different grades of stainless steel have different corrosion resistance, which is determined by the content and collocation of chemical elements.
| Stainless Steel | Chemical Componet | Corrosion Resistance |
|---|---|---|
| 316/A4 | Cr:16.00-18.00; Ni:10.00-14.00; Mn: ＜2.00 | High |
| 304/18-8/A2 | Cr:16.00-18.00; Ni:8.00-11.00; Mn: ＜2.00 | High, but lower than 316 |
| 430 | Cr:16.00-18.00 | Medium |
| 420 | Cr:12.00-14.00 | Low |
| 410 | Cr:11.50-13.50 | Low, same as 420 |
| 202 | Cr:17.00-19.00; Ni:4.00-6.00; Mn: 7.50-10.00 | High, but lower than 304, higher than 430 |