1. What’s galvanic corrosion?

When the stainless steel is applied in architecture can be combined with many other metallic and non-metallic compounds to be used in covering of façades, windows frames, stairways railings, handrails, etc. Compositions are possible with glass, ivory and granites, ceramic materials, and concrete.
However the architectonic solutions involving stainless steel and other metals require special care to prevent the formation of the galvanic cell.

The Galvanic cell is formed between two dissimilar metals in contact, in presence of an electrode. The potency difference of both, in a corrosive environment or in a conduction solution, will produce an electron flux between them. The less resistant material will suffer an intense corrosion, becoming anodic. The impulse of the current and consequently, of the corrosion, is the potency difference between then.

The follow galvanic series orientates the stainless steel specification with other materials:
(+ Cathode) GOLD – MONEL – 316 STEEL – 430 STEEL – BRONZE – ALUMINIUM – COPPER – BRASS – CAST IRON – STEEL ALLOYS – LOW CARBON STEEL – ALUMINIUM ALLOYS (+ anodic).

The interaction between the anodic and the cathode parts in a galvanic cell is another effect to be considered. A relation of favorable area consists of a great cathode and small anode. The bigger chain density in the anodic area generates a bigger tax of corrosion in anode, to keep the electric balance between the cathodic (of protection) and anodic (of corrosion) reactions.
Therefore, when the contact of two dissimilar metals is necessary, isolation between both must be foreseen (coating or painting with epoxy primer the noblest material).

Methods for the prevention of the galvanic corrosion:
1. Select the metal materials by the closest proximity in the galvanic series.
2. Avoid unwanted area effects, avoiding low anode and high cathode.
3. Isolate dissimilar metals materials whenever it’s possible, using, for example, Epoxy based coverings.
4. In the welded parts, the cord must have a chemical composition similar to the basis metal. In stainless steel cases, the addiction metals with high levels of Chrome and Nickel are necessary to counterbalance the loss by preferential oxidation.
5. Project anodic parts easily replaceable, or make then dense to have a large durability.
6. Apply a third metal that is anodic to both metals in contact.


2. How to choose a stainless steel sink?

The stainless steel sinks are available in diverse models, sizes and formats. They are available in different types of stainless steel. Look for information on the type of steel used in the manufacture of the sink.

Those manufactured with steel of lesser resistance to the corrosion, will need well-taken care in the maintenance and daily cleanness. The gauge of steel used in the manufacture of the sink is also an important factor in the election. The bigger the thickness, greater resistance it will have to kneading and deformations proceeding from the use. Verify if the sink presents the necessary robustness to day-by-day of your family.

To clean the stainless steel sink: always use the simplest method for the daily cleaning: soap or homemade detergent (neutral), applied with a soft cloth or nylon sponge. Never use in the cleanness, and nor leaves on the steel sink, the common steel sponge: beyond scratch the polishing parts, it leaves very small particles that can provoke spots.


3. What are corrosive foods?

This question is very open wide and the direction is not clearly. Nothing, absolutely nothing, in them seems to be very corrosive. We use to give this example: in certain concentrations, sulfuric acid attacks the stainless steel and not to the steel carbon. The immineralized water, in exchange, attacks the steel carbon and not to the stainless steel. What we can then consider as more corrosive: sulfuric acid or the immineralized water?

To speak that a certain environment is corrosive we must relate them to a determined material, that is, to always consider a certain environment with a material and never separately.

In the feeding we use salt (sodium chloride). It attacks stainless steel. In the period of duration of a baking operation the attack does not happen, but if the contact time was very great, with a good concentration of salt and high temperatures, we would have corrosion. But, nor therefore we will say that any food, for the fact to have salt, is corrosive.

The lemon juice can attack the stainless 304. But it does not attack the 316. We must therefore say that the lemon juice is corrosive. Then, in principle, nothing is corrosive. Or everything is corrosive.

Regarding to the foods that normally we use in our day-by-day, stainless steel pans and places settings material are very adjusted, not only for also having a good resistance to the corrosion but for chemical inertia (metallic migration of cathions for the food does not exist) and for biological inertia (it does not favor the development of bacterial colonies or, if they exist, easily are removed in the stainless steel surfaces). The food industry confirms these advantages of stainless steel. It is used in orange juice industries (and others), in brewery, eatable milk and derivates, cold storage rooms, oils, etc.


4. Where is the stainless steel found and produced ? What’s its importance?

The stainless steel is an iron and carbon alloy, containing at least 10,5% of chromium in its chemical composition. The material is produced in ironmaster industries, from scrap iron of the proper stainless steel and for the addition of alloys elements as chromium, nickel, molybdenum, etc.

The importance of the stainless steel inhabits in its attributes and properties, among which if it detaches the resistance to the corrosion, proportionate for the formation of a passive film (formed by a chromium oxide) in the surface of the material and that builds in a barrier to the oxidation of that. Exactly when the steel suffers some type of damage, they are scratches, kneading or cuts, the oxygen of air immediately comminutes with chromium, forming again the protective film.


5. Isn’t the stainless steel against corrosion? Why sometimes is possible to see stainless steel pieces with corrosion dots?

Stainless steel are Iron-Chrome alloys, with at least 10,50% of chrome. Other alloy elements can enter in the chemical composition, like Nickel, Molybdenum and others. As an example, considering the most sold stainless steel in the world, the 430 kind has a chrome level higher than 16% and the 304 kind, chrome level higher than 18% and nickel higher than 8%. These are materials with great corrosion resistance, in a large vary of ambient conditions. Although in some environments they are not resistant. For example, they quickly are attacked in chloridric acid, sulfuric and also in hydrofoil acid (depending, in this last one, of the concentration and the temperature).

Other environments that can attack stainless steel, causing located corrosion spots, are those that contain chloride (depending always on the concentration and the temperature). The resistance to the atmospheric corrosion is usually very good and the most appropriated stainless steel kind must be selected depending on the kind of environment. In agricultural environments, in cities with low contaminated atmospheres, the 430 steel is normally resistant, whereas in great cities the chosen material is normally the 304 steel. But in sea shore cities another type is chosen, the stainless steel 316, which besides chromium and nickel also has molybdenum in the chemical composition.

In certain cases, and probably the question done is in this direction, “rust” points can be observed in cases that shouldn’t be expected a corrosive attack.
For example, the 304 steel when is in contact to the Curitiba city atmosphere: Usually, in cases like this, the problem is related to the stainless and carbon steel contamination that happens in material cut operations, in some manufacture process or in a scouring process. Increasing when equipments that were used in carbon steel previously are used in procedures with stainless steel. Carbon steel particles became encrusted in the stainless steel surface and those particles (of carbon steel) are not resistant to atmospheric corrosion; Appearing "rust" dots and looking like the stainless steel is corroding, when the truth is that those particles are suffering the corrosion.

The lack of cleaning in stainless surfaces can also be the cause of corrosion problems. Frequent cleaning is always recommended to achieve a better corrosion resistance in these materials. To conclude, we can say that stainless steel can suffer corrosion problems under certain circumstances. To avoid problems, is necessary to chose the adequate stainless steel for each situation and also take care procedures for a right use of then. Whenever exists doubts about the choice (specification) and utilization, consult a specialist.


6. Why does a magnet not attract the stainless steel radius to the motorcycle wheels?

Only the Ferritic stainless steels are magnetic. Since the magnet does not attract the motorcycle wheels, we can conclude that the wheels were made with austenitic stainless steel (non-magnetic).


7. Which are the metals compounds in the stainless steel composition?

Stainless steels are alloys (a homogeneous mixture of two or more chemical elements, obtain by chemical compounds fusion), that contains:
- Iron
- Low levels of carbon,
- At least 10,5% of chrome,
- At most 30% of nickel,
- Other elements in lower percents, like carbon, molybdenum, manganese, etc.


8. Is there Lead in the 316 stainless steel chemical composition?

No, the stainless steel 316 steel doesn’t contain Lead in its chemical composition.


9. Which are the diverse types of superficial finishing produced in Brazil, and what is the cost relation between them? Is the application only aesthetic?

In Brazil, the following types of superficial finishing can be found more often:

BB - Buffing Bright, burnishing with cotton brushes and abrasive folders of #400, #600, #800

MIRROR - Known as Mirror Finish, reflective finishing gotten by burnishing with felt and abrasive folders of different particle size analyses until #3000

RF - Known as Rugged Finish. Made in a dry direction, with abrasive sandpapers of #60 to #100
SF - Known as Super Finish. Dry finishing made with abrasive sandpapers of #220 to #320

ST - Known as Satin Finish, Made with abrasive coils of Scotch Bright of #100 to #180 with no use of abrasive folders.

BF-1 - Known as Butterfly Finish. Made with small grinder of #80 to #120, giving to the surface the decorative aspect of circles overlapped in standardized distribution.

BF-2 - Known as Exclusive Design. Made with small grinder of #80 to #120, giving to the surface decorative aspect of symmetrical waves.

Besides the decorative aspect, the finishing can improve the performance of the material, making it resistant to corrosion. Less rugged finishing makes it difficult for dust and particles of corrosive elements to tack, favoring the resistance to the corrosion of the material. In the same way, smoother finishing facilitates the operations of wash of the surface of the stainless steel, helping to keep its appearance and improving the performance and durability.


10. How is made the brushed stainless steel?

The brushed finishing of the stainless steel is gotten by the scouring of the surface of the steel with sandpapers or grinder of different particle size analyses.


11. To say “inox” or “stainless steel” is the same thing? Does the stainless steel conduct electricity? We possess listening equipment, for detention of emptying in easels of water. If the material conducts electricity, the people who use the equipment may be in danger. That’s the reason for the question. Where I live, in Pirassununga-SP, there is some company in the state that sells stainless steel bars of 1/4 ". I’m in need of bars about 1,20 cm to develop a listening model.

To say inox and stainless steel is really the same, therefore both the terms mention the stainless steel to it. The steel inox, as all the metals, conducts electricity and in such a way if the instrument of emptying detention will be of inox, the area of contact of the same with the operator would have to be isolated to prevent possible risks. With regard to the supply of bar of 1/4 " Mr. will be able easily finds it next to one of the steel deliverers inox established in the state of São Paulo.


12. Can the stainless steel can become rusty? Why?

The stainless steel does not oxidize in the same way that carbon occurs with the steel, which presents a colored oxide layer in the surface that it peels. If you to observe spots in the surface probably the iron particles must that had contaminated the steel inox and are these particles that are rusting. It verifies if it is possible to remove the spots of the surface of inox.

If the iron will be impregnated in the surface, tries a nitric acid solution of 10% and acid hydro fluoridric 2% the ambient temperature or lightly warm. It washes the area affected with abundant water. Folders available removers in the market, can also be used.


13. Is the stainless steel magnetic?

It has some types of stainless steel. The stainless steel of series 300 (austenitic) that it contains Chromium and Nickel in its chemical composition NÂO is magnetic.

The stainless steel of series 400 (ferritic) that it contains only Chromium in its chemical composition, YES are magnetic.


14. Why does the stainless steel have thermal treatment?

The used stainless steel for operations of cut, where it is important to have a superior superficial hardness, are submitted the operations of thermal treatment. It is what it occurs with used maraging stainless steel for the manufacture of knives, shears, penknives, etc.


15. What does it mean the letter L after the type of the stainless steel?

The use of letter L after the type of stainless steel (former: 304L), means that the carbon content in the league is restricted to the 0,03% MAXIMUM (the normal carbon levels is of 0.08% max. e in some leagues can reach 0,15% max.). This lesser carbon level is used when the material will have to be welded. The lesser carbon text helps to prevent the chromium precipitation (forming carbonates of chromium in the region of the weld) and therefore being assured a minimum of 10,5% of chromium and the possibility of formation of the passive film that provides to the stainless steel the resistance to the corrosion.


16. What is passsivity? Is it a cleanness procedure?

The main objective of the passivity is to renew the passive layer protecting the stainless steel against the corrosion.

Although the passivity process is spontaneous for protective the chromium oxide formation, through the passivity the formation of the passive layer is sped up.

The passivity banns also contribute to dissolve small iron oxide spots and therefore they are used in some cases as cleanness procedures.


17. Which are the meanings of the devices registrations 18/8, 18/10 in stainless steel? Is this codification associated to different applications?

Registrations 18/8 and 18/10, mention texts to it of Chromium and Nickel and correspond to the types of stainless steel types 304 and 316, respectively.