Low-magnetization Biocompatible Passivation Process Specification For Medical Low-carbon SUS316L Press-fit Nuts, Based On GB/T10125 Stainless Steel Surface Treatment National Standard

Low-magnetization Biocompatible Passivation Process Specification For Medical Low-carbon SUS316L Press-fit Nuts, Based On GB/T10125 Stainless Steel Surface Treatment National Standard

Martensitic phase transformation easily occurs inside low-carbon SUS316L wire after cold heading forming, leading to rising magnetic permeability of finished goods and interference with NMR imaging. Conventional industrial passivation chemicals aggravate magnetization, and medical imaging equipment must adopt special low-magnetization passivation system. This article distinguishes passivation parameters for two product types: general in-vitro diagnostic and MRI NMR, strictly control micro-etch temperature, chemical pH and soaking time to stably keep saturated magnetic permeability of finished goods ≤1.08.

1. Core Process Comparison Between General Non-magnetic Passivation & MRI Ultra-low Magnetic Passivation

2. Standardized Full Procedures Of Low-magnetization Passivation

1. Dust-free pure water degreasing: Low-temperature weak alkali degreasing, high-temperature strong alkali which induces stainless steel magnetization is forbidden; 2. Multi-stage pure water countercurrent rinsing: Eliminate residual degreasing chemical altering passivation pH value; 3. Low-temperature weak acid micro-etching: Low-concentration citric acid micro-etching to avoid magnetic phase precipitation caused by strong acid washing; 4. Constant temperature low-magnetization passivation: Match temperature and soaking time according to products, monitor tank liquid pH in real time; 5. Biocompatible halogen-free sealing: Special medical sealing agent to block precipitation of metal ions; 6. Low-temperature dust-free drying: Hot air drying at 65℃, high-temperature drying will raise magnetic susceptibility.

3. Root Causes & Rectification Of Three Mass Production Passivation Defects

1. Excessive magnetic permeability of finished goods: Excessively high passivation temperature and strong acidity of micro-etch liquid; Rectify: Lower constant passivation temperature range and replace low-acidity citric acid micro-etch liquid. 2. Metal precipitation appears in 48-hour saline test: Insufficient sealing agent concentration and incomplete rinsing; Rectify: Raise sealing agent ratio and add two more pure water rinsing procedures. 3. Mottled uneven passivation film on nut surface: Incomplete degreasing with local oil stain blocking passivation reaction; Rectify: Extend low-temperature degreasing soaking time and lift pure water resistivity above 12MΩ·cm.