Stainless Steel Surface Treatment Common Problems and Methods

common cause of rust and corrosion of stainless steel parts 

The stainless steel equipment production process will appear to show damage, defects, and some of the substances affecting the surface, such as dust, floating iron powder or embedded iron, hot tempering color and other oxide layer, rust spots, grinding burrs, welding arc marks, Welding spatter, welding flux, welding defects, oil and grease, residual adhesives and paint, chalk and marker pen marks. Most of them are not taken seriously or done well because their harmful effects are ignored. However, they are potentially harmful to the oxide protective film. Once the protective film has been damaged, thinned, or otherwise altered, the stainless steel below will begin to rust. Corrosion is generally not across the entire surface but at or around the defect. This bureau’s total corrosion will usually be pitting or crevice corrosion, which will develop to depth and breadth while most of the surface is not eroded. The following talks about the various causes of these problems. 

1.1 Dust Production is often carried out in dusty sites, and the air often carries a lot of dust, constantly falling on the equipment’s surface. They can be removed with water or alkaline solutions. However, dust and dirt with adhesion need to be cleaned with high-pressure water or steam. 

1.2 Floating iron powder or embedded iron On any surface, free iron will rust and cause stainless steel corrosion. Therefore, it must be removed. The floating powder can generally be removed with dust. Some of the adhesion is very strong and must be handled by the embedded iron. In addition to dust, the surface iron from many sources, including ordinary carbon steel wire brush cleaning and blasting with sand, glass beads, or other abrasives previously used on plain carbon steel, low-alloy steel or cast iron parts, or in stainless steel parts and equipment near the previously mentioned non-stainless steel products for regrinding. In the down or hanging over the process, if not, take protective measures for stainless steel, wire rope, spreader, and iron on the table surface is easy to embed or stain the surface. 

1.3 Scratch To prevent process lubricants or generation and dirt accumulation, scratches and other rough surfaces must be mechanically cleaned. 

1.4 Hot temper color and other oxide layer If the stainless steel is heated to a certain high temperature in the air during the welding or regrinding process, both sides of the weld, the lower surface of the weld, and the bottom will appear chromium oxide hot temper color. The hot temper color is thinner than the protective oxide film and is visible. The thickness determines the color and can be iridescent, blue, purple, pale yellow, or brown. Thicker oxides are generally black. It is caused by high temperatures or prolonged exposure to higher altitudes. When any of these oxides are present, the chromium content of the metal surface is reduced, causing a decrease in the corrosion resistance of these areas. In this case, the hot temper color and other oxide layers should be eliminated, and the chromium-poor metal layer beneath them should be cleaned. 

1.5 Rust spots Before making or during the production process, we sometimes see rust on stainless steel products or equipment, which indicates that the surface is heavily contaminated. Equipment must be put into use before the rust is removed, thoroughly cleaned surface should be tested by iron test and water test. 

1.6 Rough grinding and machining Grinding and machining can cause the surface to be rough, leaving defects such as grooves, overlaps, and burrs. Each defect may also damage the metal surface to such a depth that the damaged metal surface cannot be cleaned off by pickling, electropolishing, or shot peening. Rough surfaces can become a source of corrosion and deposition of generators; cleaning weld defects before rewelding or removing excess weld reinforcement high can not be ground with coarse grinding. For the latter case, it should then be ground with fine abrasives. 

1.7 welding arc pilot marks when the welder pilot arc on the metal surface can cause surface roughness. The protective film is damaged, leaving a potential source of corrosion. The welder should lead the arc on the already welded channel or the side of the weld joint. The arc lead trace is then fused into the weld. 

1.8 Welding spatter has much to do with the welding process. For example, there is no spatter with GTAM (gas-shielded tungsten arc welding) or TIG (inert gas-shielded tungsten electrode welding). However, GMAW (gas-shielded metal arc welding) and FCAW (arc welding with flux core), two welding processes, can cause a lot of spatter if the welding parameters are not used properly. When this happens, the parameters must be adjusted. If the problem of Welding spatters is to be solved, an anti-spatter agent should be applied to each side of the joint before Welding, which will eliminate the adhesion of the spatter. After Welding, this anti-spatter and various spatter can be easily cleaned off without damaging the surface or bringing about minor damage. 

1.9 flux welding process using flux is manual Welding; with flux core arc welding and submerged arc welding, these welding processes will leave small particles of flux on the surface, and ordinary cleaning methods can not be removed from them. This article will be the source of crevice corrosion; mechanical cleaning methods must be used to remove this residual flux. 

1.10 welding defects such as: galling, not welding through, dense porosity, and cracking reduce not only the solidity of the joint but also become a source of crevice corrosion corrosion corrosion. Improve this result when cleaning operations; they will also entrain solid particles. These defects can be repaired by re-welding or re-welding after regrinding. 

1.11 oil and grease organic substances such as oil, grease, and even fingerprints can become local corrosion of corrosion sources. Since these substances can act as a barrier, they can affect the chemical and electrochemical cleaning effect and must be completely cleaned out.  1.12 Residual adhesive When removing the tape and protective paper, a part of the adhesive always remains on the stainless steel surface. If the adhesive is not yet hard, you can use organic fusion to remove it. However, when exposed to light and air, the adhesive hardens and forms a source of corrosion for crevice corrosion. Mechanical cleaning with fine abrasives is then required.  1.13 Paint, Chalk, and Marker Stamps The effects of these contaminants are similar to those of oil and grease. It is recommended to wash with a clean brush and clean water or alkaline detergent, or you can use high-pressure water or steam rinse.    

Stainless steel products using surface treatment processes 

2.1 Polishing Manual mechanical polishing is used, mainly dealing with undercutting defects, weld defects, riveting points during riveting, and various scratches produced during processing.  

2.2 Weld pickling passivation mainly deals with the black oxide skin at the weld seam.  

2.3 Overall passivation Overall, pickling passivation mainly deals with the requirements of consistent products, but the current treatment method is difficult to achieve the desired consistent effect.  

2.4 polishing passivation manual grinding and polishing after pickling passivation treatment, mainly to deal with the surface of the product with decorative requirements, but the current treatment method is difficult to achieve a better treatment effect, and the material cost and labor costs are relatively high. 

stainless steel products in the processing of common problems

3.1 Weld defects are more serious, using manual mechanical grinding processing methods to compensate for the resulting grinding traces, resulting in an uneven surface affecting the beauty.  

3.2 Surface inconsistency Only the weld seam pickling passivation also results in surface unevenness, affecting the aesthetics.  

3.3 Scratches are difficult to remove Overall pickling passivation, but also can not remove the various scratches generated during processing, and also can not remove impurities such as carbon steel, spatter, and other impurities adhering to the surface of stainless steel due to scratches, Welding spatter, resulting in chemical or electrochemical corrosion and rusting in the presence of corrosive media conditions.  

3.4 grinding polishing passivation is not uniform manual grinding and polishing after pickling passivation treatment, the area of a larger workpiece, it is not easy to achieve a uniform and consistent treatment effect, can not get the ideal uniform surface. And the cost of person-hours and auxiliary materials is also higher.  

3.5 Limited pickling ability Pickling passivation paste is not a panacea, and it is difficult to remove the black oxide skin produced by plasma cutting and flame cutting. 

3.6 Scratches caused by human factors are more serious. In the process of lifting, transportation, and structural processing, scratches caused by human factors such as bumping, dragging, and hammering are more serious, making surface treatment more difficult, and are also the main cause of rust and corrosion after treatment.  

3.7 Equipment factors The scratches and creases caused in the process of profile and plate roll bending and bending are also the main reasons for rust and corrosion after treatment.  

3.8 Other factors The bump and scratch caused by the lifting and transportation process during the procurement and storage of stainless steel raw materials is also more serious and is also one of the reasons for rust and corrosion. 

 

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