How should austenitic stainless steel weldments be surface-treated after welding?

Thread Content

To improve the corrosion resistance of austenitic stainless steel weldments, the surface should be treated after welding, using methods such as polishing and passivation. ⑴Surface polishing: If there are scratches, dents, rough spots, and stains on the surface of stainless steel welded parts, these will accelerate corrosion in a corrosive medium. If the surface of stainless steel is polished, its corrosion resistance can be improved; the finer the surface roughness, the better the corrosion resistance. This is because a weld surface with low roughness can develop a dense, uniform oxide layer that protects the underlying metal from further oxidation and corrosion. ⑵Passivation treatment involves artificially creating an oxide layer on the surface of stainless steel to enhance its corrosion resistance. The passivation process consists of: cleaning and repairing the surface of the welded parts → pickling → washing and neutralization → passivation → washing and drying. Before processing, the welded parts are first cleaned and repaired; any damaged areas on the surface are fixed, polished with a hand-held grinder, and finally, the slag and spatter around the welds are removed. The purpose of pickling is to remove scale. This is because heat-treated stainless steel (such as hot-pressed heads) and the weld heat-affected zones develop an oxide layer that affects their corrosion resistance. Pickling is done in two ways: with acid solution or with acid paste. Pickling acid formula: 20% by mass of nitric acid (density 1.42 g/cm3), 5% hydrofluoric acid, with the remainder being water; the pickling temperature is room temperature. Scrubbing acid formula: 50% hydrochloric acid + 50% water. Acid paste formula: hydrochloric acid (density 1.19 g/cm3) 20 mL, water 100 mL, nitric acid (density 1.42 g/cm3) 30 mL, bentonite 150 g. The dipping method is suitable for smaller devices and parts. During immersion, submerge the equipment and components in the pickling solution for 25–45 minutes, and then rinse them thoroughly with clean water. The scrubbing method is suitable for large equipment; a brush is dipped in the pickling solution and used to scrub until a bright white color is achieved, after which it is rinsed clean with water. Passivation is carried out after pickling. The formula for the passivation solution is: 5 mL of nitric acid, 1 g of potassium dichromate, and 95 mL of water. The treatment temperature is room temperature, and the treatment time is 1 hour. The treatment method involves wiping the passivation solution over the surface of the welded part, leaving it there for 1 hour, then rinsing it with cold water. It is followed by careful cleaning with a cloth, and finally rinsing thoroughly with hot water before drying it. Stainless steel that has been passivated has a completely silver-white appearance and exhibits high corrosion resistance. This post was last edited by shi*qumi on 2008-3-3 22:15]