Passivation Treatment of Stainless Steel

Introduction

Passivation treatment of stainless steel typically involves high temperature or nitric acid. This guide outlines methods for improving the passivation process.

High-Temperature Passivation

High-temperature passivation is conducted in a heat treatment furnace. The stainless steel is heated to form a passivation film. Before passivation, ensure the surface is clean to facilitate effective film formation.

Nitric Acid Passivation

Nitric acid passivation involves forming a thin passivation film without altering the surface color. Four process plans can be used, depending on the stainless steel type.

Process Plan 1: High Carbon, High Chromium Stainless Steel

Steel Type: High carbon (>0.4%), chromium (≥17%)
Solution: 66% nitric acid, 20-25% (volume), 2.5±0.5% (mass)
Temperature: 49-54°C
Time: 20 minutes

Process Plan 2: Austenitic Chromium Stainless Steel

Steel Type: Cr18, Cr23-25
Solution: 66% nitric acid, 25-45% (volume)
Temperature: 21-32°C
Time: 30 minutes

Process Plan 3: Austenitic and Chromium Stainless Steel

Steel Type: Chromium content (>17%), excluding high carbon, high chromium
Solution: 66% nitric acid, 20-25% (volume)
Temperature: 49-60°C
Time: 30 minutes

Process Plan 4: High Carbon Stainless Steel

Steel Type: High carbon (>0.4%), chromium (≥17%)
Examples: 1Cr12, 0Cr13, 0Cr13Al, 1Cr13, 1Cr17Ni2, 7Cr17, 8Cr17, 9Cr18 (Mo)
Solution: 66% nitric acid, 45-55% (volume)
Temperature: 49-54°C
Time: 30 minutes

Post-Passivation Process

Washing and Sealing

After passivation, wash the stainless steel with water 3-4 times and seal it with chromic acid. For ferritic and martensitic stainless steel, conduct chromic acid treatment within one hour of the final wash.