Stainless steel welding point how to deal with

The methods of surface treatment of stainless steel after welding are polishing and passivation.

First, surface polishing

The surface of stainless steel welders, such as nicks, dents, rough spots and stains, will accelerate corrosion in the medium. If the stainless steel surface is polished, it can improve its corrosion resistance, the finer the surface roughness, the better the corrosion resistance. Because the surface of the weldment with fine roughness can produce a layer of dense and uniform oxide film, which can protect the inner metal from oxidation and corrosion.

Two, passivation treatment

Passivation is the process of manually forming an oxide film on the surface of stainless steel to increase its corrosion resistance. The passivation process is as follows:

Weldment surface cleaning and repair → pickling → washing and neutralization → passivation → washing and drying.

Before treatment, clean and repair the surface of the weldment, repair the surface damage, polish it with hand-held grinding wheel, and finally clean up the standard shell on the weld and the spatter near it.

The purpose of pickling is to remove the oxide skin. Because the hot working stainless steel (such as hot pressed head) and welding heat affected zone will produce a layer of oxide skin, affecting its corrosion resistance. There are two methods of acid pickling: acid liquid pickling and acid paste pickling.

Pickling acid formula: the mass fraction of nitric acid (density 1.42g/cm3) is 20%, hydrofluoric acid 5%, the rest is water, pickling temperature is room temperature.

Formulation of scrub acid: hydrochloric acid 50%+ water 50%.

Acid paste formula: hydrochloric acid (density 1.19g/cm3) 20mL, water 100mL, nitric acid (density 1.42g/cm3) 30Ml, 150g bentonite.

The dip method is suitable for smaller equipment and parts. For dipping, immerse the equipment and components in the acid washing solution for 25-45min, remove and rinse with clean water. Scrubbing method is suitable for large equipment. Brush dipped in acid lotion and scrubbing until the color is white and bright, then rinse with water.

Passivation is carried out after pickling. Passivation solution formula: 5mL nitric acid, 1g potassium dichromate, 95mL water. The treatment temperature was room temperature and the treatment time was 1h. The treatment method is to wipe the passivation solution on the surface of the weldment once, keep it for 1 hour, then rinse it with cold water, scrub it carefully with cloth, and finally rinse it with hot water, and blow dry it.

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