Passivation of Stainless Steel

Advanced material engineers in aerospace, engineering, electronics, medical and similar high-tech industries use chemical passivation and have done for years. Electromold Australia performs this proven process of Stainless Steel Passivation and it is performed in accordance with a variety of standards and specifications. People believe it is effective because it is a cleaning process. Others credit the enhanced corrosion resistance properties to the thin, transparent oxide film resulting from chemical passivation. If your applications demand the maximum performance from your corrosion-resistant steels, passivation is one of the most effective methods of achieving these results.

Passivation is the removal of iron, iron compounds, lead, carbon and most other elements from the surface of stainless steel, enhancing the spontaneous formation of a protective passive film and without significantly affecting the stainless steel itself. Thus leaving the components in a passive state.

Basically, the passivation process removes "free iron, lead, etc" contamination left behind on the surface of the stainless steel from machining and fabricating. These contaminants are potential corrosion sites that result in premature corrosion and ultimately result in deterioration of the component if not removed. In addition, the passivation process facilitates the formation of a thin, transparent oxide film that protects the stainless steel from selective oxidation (corrosion).

Although recently cancelled, the most commonly referenced industry specifications regarding passivation are Federal Specification QQ-P-35C, which is now superseded by ASTM A-967 and ASTM A-380. Here at Electromold we can conform to all of these specifications, if you are not sure what you need don't hesitate in contacting our Technical service team.

Machining and heat treating techniques to improve passivation.

Perhaps the most overlooked variable in the entire passivation equation is the negative impact of poor machining and heat treating practices. All too often, cross contamination introduced during manufacturing and/or thermal processes leads to unacceptable test results. The following practices will reduce cross contamination during manufacturing and increase the chances of successful passivation and tests results.

  • Never use grinding wheels, sanding materials or wire brushes made of iron, iron oxide, steel, zinc or other undesirable materials that may cause contamination of the stainless-steel surface.
  • The use of carbide or other non-metallic tooling is recommended.
  • Grinding wheels, sanding wheels and wire brushes that have been previously used on other metals should not be used on stainless steel.
  • Use only clean, unused abrasives such as glass beads or iron-free silica or alumina sand for abrasive blasting. Never use steel shot, grit or abrasives that have been used to blast other materials.
  • Thorough cleaning prior to any thermal processing is critical. Stress relieving, annealing, drawing or other hot-forming processes can actually draw surface contaminants deeper into the substrate, making them almost impossible to remove during passivation.
  • Care should be taken during all thermal processes to avoid the formation of oxides. Passivation is not designed to remove discoloration and will not penetrate heavy oxide layers. In extreme situations, additional pickling and descaling operations are required prior to passivation to remove the discoloration. Controlled atmosphere ovens are highly recommended for all thermal processes to reduce airborne contamination and prevent oxides from developing.

Passivation will enhance the corrosion resistance of stainless steels, but please remember to gain the maximum performance from your corrosion-resistant steels, all parties involved with manufacturing must understand their responsibility in maintaining the integrity of the material throughout the process.

If you require any further information regarding this process or any of Electromold Australia's plating processes, please contact us on +61 3 9464 0922 and one of our technical staff will be able to assist you.