The surface microhardness is improved by 20%~50%. The surface fatigue resistance is improved by more than 200%.
In the field of building application, the surface treatment of stainless steel is important for many reasons. The corrosive environment requires a smooth surface, because it is not easy to accumulate scale. The deposition of dirt will rust stainless steel and even cause corrosion. In the spacious hall, stainless steel is the most commonly used material for elevator decorative plates. Although the fingerprints on the surface can be erased, it affects the appearance, so it is best to choose a suitable surface to prevent fingerprints from leaving. Sanitary conditions are important for many industries, such as food processing, catering, brewing and chemical industry. In these applications, the surface must be easy to clean every day and chemical cleaning agents are often used. Stainless steel is the best material in this field. In public places, stainless steel surfaces are often scribbled. But one of its important features is that it can be washed away, which is a remarkable feature that stainless steel is superior to aluminum. The surface of aluminum is easy to leave traces and often difficult to remove. When cleaning the surface of stainless steel, it should be cleaned along the lines of stainless steel, because some lines of surface processing are unidirectional. Stainless steel is most suitable for hospitals or other areas where sanitary conditions are crucial, such as food processing, catering, brewing, chemical industry, etc., not only because it is easy to clean every day, but also because it is not easy to breed bacteria. Experiments show that the performance of stainless steel in this respect is equivalent to that of glass and ceramics.
1. Natural appearance of stainless steel
Stainless steel gives people a natural feeling of firmness and brightness, and its natural color softly reflects the color of the surrounding environment.
2. The basic types of metal surface processing
There are roughly five kinds of surface treatments that can be used for stainless steel, and they can be combined to transform more final products.
There are five kinds: rolling surface processing, mechanical surface processing, chemical surface processing, mesh surface processing and color surface processing.
There are some special surface treatments, but no matter which surface treatment is specified, the following steps should be followed:
(1) We have reached an agreement with the manufacturer on the required surface treatment, and it is best to prepare a sample as the standard for mass production in the future.
(2) When it is used in a large area (such as composite board), it must be ensured that the base ring or coil used is the same batch.
③ In many building applications, such as inside elevators, although fingerprints can be erased, they are not beautiful. If you choose a textured surface, it will be less obvious.
Mirror stainless steel must not be used in these sensitive places.
④ When selecting surface processing, the manufacturing process should be considered. For example, in order to remove the weld bead, it may be necessary to grind the weld and restore the original surface treatment.
It is difficult or even impossible for diamond table to meet this requirement.
⑤ For some surface processing, grinding or polishing lines, they are directional, which is called unidirectional. If the grain is vertical instead of horizontal when used, dirt will not easily adhere to it and it will be easy to clean.
⑥ No matter which finishing process is adopted, it is necessary to increase the process steps, so it will increase the cost. Therefore, we must be careful when choosing surface treatment.
Therefore, architects, designers, manufacturers and other relevant personnel need to know something about the surface treatment of stainless steel. Through friendly cooperation and mutual communication, we will certainly achieve the expected results.
According to our experience, we don't recommend using alumina as abrasive unless we use it very carefully. It is best to use silicon carbide abrasive.
3. Standard surface treatment
Many surface treatments have always been expressed by numbering or other classification methods, and they have been compiled into relevant standards, such as "British Standard BS 1449" and "Standards of Stainless Steel Producers Committee of American Iron and Steel Association".
4. Rolling surface treatment
There are three basic types of strip rolling surface processing, which are expressed by strip production technology. 1: after hot rolling, annealing, pickling and descaling. The surface of the treated steel plate is dull and a little rough.
2D: It is better than the surface of N0. 1, and it is also a dull surface. After cold rolling, annealing and descaling, it is finally lightly pressed with a rough roller.
2B: This is the most commonly used in architectural applications. Except for the last light cold rolling with polishing roller after annealing and descaling, the other processes are the same as 2D, and the surface is slightly bright and can be polished.
No.2B bright annealing: This is the reflective surface, which is rolled by a polishing roller and finally annealed in a controlled atmosphere. Bright annealing still keeps its reflective surface and does not produce scale. Because there is no oxidation reaction during bright annealing, pickling and passivation are not needed.
5. Polishing surface treatment
Third place: represented by 3A and 3B. "3A: the surface is evenly ground, and the abrasive particle size is 80 ~ 100.
3B: The rough surface is polished, and the surface has a uniform straight line. Generally, it is made by grinding the plate 2A or 2B once with an abrasive belt with a particle size of 180 ~ 200.
Fourth: One-way surface treatment, non-reflective, is probably the most widely used in construction. The process steps are as follows: firstly, polishing with coarse abrasive, and finally grinding with abrasive with particle size of 180.
No.6: It is a further improvement of No.4, and the surface of No.4 is polished with tampico polishing brush in abrasive and oily media. British Standard 1449 does not have this surface treatment, but American Standard does.
No.7: It is called bright polishing, that is, polishing the surface that has been ground very finely but still has wear marks. Usually 2A or 2B plates are used to polish the grinding wheel and the corresponding polishing paste with fibers or cloth.
No.8: Mirror polished surface, with high reflectivity. Because the reflected image is very clear, it is usually called mirror processing. Stainless steel is continuously polished with fine abrasive, and then polished with very fine polishing paste.
In building applications, it should be noted that this surface will leave fingerprints if it is used in places where people have a lot of traffic or frequent contact. Of course, fingerprints can be erased, but sometimes it will affect the appearance.
The surface treatment described in "official" standards and documents is only a general introduction, and samples can most intuitively represent the types of surface treatment. Polishing or metal finishing manufacturers will provide samples of various surface processing, and users should discuss with them.
6.
surface finish
The classification of rolling surface processing and polishing surface processing is to illustrate the degree that can be achieved, and another effective expression is to measure surface roughness. The standard measurement method is called CLA (mean value of center line), and the measuring instrument moves laterally on the surface of the steel plate to record the change range of peaks and valleys. The less the amount of CLA, the smoother the surface. From the surface smoothness and CLA value in the table below, we can see the final results of different grades. surface working
CLA, micron 2b0.1-0.52a 0.05-0.12d0.4-1.030.4-1.540.2-1.580.2ep.
EP= electrolytic polishing, which can reduce the range of peak and valley to 1/2 of the original surface.
7. Precautions for mechanical polishing:
We should remember that grinding with sandpaper or abrasive belt is basically a grinding and cutting operation, which will leave fine lines on the surface of steel plate. It is difficult for us to use alumina as abrasive, partly because of pressure.
Any grinding parts of the equipment, such as abrasive belt and grinding wheel, shall not be made of other non-stainless steel materials before use. Because it will pollute the stainless steel surface.
In order to ensure the consistency of surface processing, the new grinding wheel or abrasive belt should be tried on the waste with the same composition first, so as to compare similar products.
8. Electrolytic polishing
This is a metal removal process, in which stainless steel is used as anode in electrolyte, and the metal is removed from the surface after electrification. This process is usually used to process parts because their shapes are difficult to be polished by traditional methods.
This process is often used for the surface of cold-rolled steel plate because its surface is smoother than that of hot-rolled steel plate. However, electrolytic polishing will make the impurities on the surface more obvious, especially for titanium-niobium stabilized materials, which will make the weld zone different due to granular impurities.
Small welding scars and sharp edges can be removed by this process. This process focuses on dealing with the protruding parts of the surface, giving priority to dissolution.
Electrolytic polishing process is to soak stainless steel in heated liquid, and the ratio of liquid involves many proprietary technologies and patented technologies.
The electrolytic polishing effect of austenitic stainless steel is very good.
9. There are many patterns that can be used to process stainless steel on the mesh surface.
The advantages of surface treatment of steel plate with pattern or mesh are as follows: ① Reduce the shrinkage of metal roofing materials (oil
Can-ning), a term used to describe the surface of bright materials, is not uniform from the optical point of view. For example, a large area of decorative board, even after stretching and straightening, the surface is difficult to be completely flat, so the metal roofing material will shrink.
② Mesh pattern can reduce glare in the sun. (3) Whether there are slight scratches and inconspicuous small-area indentations on the diamond plate. ④ Increase the strength of the steel plate. ⑤ It provides a choice for architects.
Patent patterns include cloth patterns (used by Edhouse in London), mosaic patterns, pearl patterns and leather patterns. Corrugated and linear patterns can also be used.
The patterned surface is especially suitable for interior decoration, such as elevator panels, counters, siding and entrances.
For external use, it should be considered that stainless steel can be washed by rain and manual washing, so as to avoid the dead angle where dirt and air impurities are easy to gather, so as not to cause corrosion and affect the appearance.
10. Rough surface treatment
Rough surface treatment is one of the most commonly used surface treatments. The surface of polished or bright annealed steel plate is polished with nylon abrasive belt or brush.
1 1.
Shot peening or shot peening is very popular in internal applications, such as elevator interior and mixed surface treatment.
This mixing process is to spray glass balls to form a matte surface, then cover it with a plastic film through masking treatment to form a polished surface, and finally form a polished and matte mixed surface. Stainless steel pellets can also be used in a similar process.
Glass balls or small balls to be used shall not be used in other materials in advance, especially carbon steel. Because carbon steel particles will be embedded in the surface of stainless steel, it is easy to cause corrosion.
Ceramic balls can also be used as spraying materials.
12. Colored stainless steel
The coloring process of stainless steel was successfully developed by international nickel companies in the 1970s, and many companies have licenses to use this process. As mentioned earlier, stainless steel does not rust because it has an emotional chromium oxide film on its surface.
The color process is to use this film to form the specified color. Because stainless steel uses this ever-present film, it will neither fade nor need to be maintained as often as paint.
Colored stainless steel can also be molded, even in sharp bends, it will not have any adverse effects on color. As for the influence on corrosion resistance, the test shows that the corrosion resistance is improved after this process is adopted.
The process is closely related to the operation time, and the color will change with time. The order of color change is brown, gold, red, purple and green.
One of the characteristics of this process is that its final appearance can reflect the original surface of the material, that is, the mirror or polished surface will produce strong metallic luster, while the processed color of the matte surface is dim. Process flow:
In this method, stainless steel is immersed in a solution tank, and the solution preferably contains 250g of Cr2O3 per liter or 490g of sulfuric acid per liter. The temperature range is 80 ~ 85℃, and the soaking time depends on the required color, and the maximum time is no more than 25 minutes.
After the steel plate was rinsed with clean cold water, it was put into the liquid of 250g/ 1l of hydrochloric acid and 2.5g/ 1l of phosphoric acid, and cathodic treatment was carried out at room temperature for about 10min, and the current density was 0.2 ~ 0.4a/dm2.
To prevent damage, the color treatment is immediately hardened, then rinsed in hot water and dried.
13. Mixed surface processing
Patterns can be added to colored stainless steel, and the proprietary technology developed includes removing the "protruding" part with corundum abrasive belt, so that the final result is to combine the natural beauty of steel plate with the color of colored patterns.
This kind of surface is not easy to leave fingerprints, especially suitable for indoor decoration. Polishing manufacturers can provide samples of surface processing.
14. Etching surface treatment
The pattern is marked on the surface of the steel plate through the film covering process, and then the steel plate is immersed in ferric chloride acid solution (O grade) to etch off the uncovered part, forming beautiful patterns on the stainless steel surface.