Stainless steel or corrosion-resistant steel is a generic name for many different steels that are primarily used due to their corrosion resistance for a specific application or a specific environment. It is an alloy of iron and at least 12% chromium.
In addition to alloying with 12% chromium to make steel was corrosion-resistant (passive), another condition must be met, and that is the existence of homogeneous monophasic ferritic, austenitic, or martensitic microstructures, to avoid hazards from the formation of areas with different electrical potential from the base mass potential.
Other alloying elements that are added serve to improve the structure and mechanical properties such as shape and toughness, and can be e.g. nickel, molybdenum, titanium, and copper.
In general, a group of corrosion-resistant steels must contain:
- ferrites: chromium (Cr), silicon (Si), aluminum (Al), molybdenum (Mo), niobium (Nb),
- titanium (Ti), vanadium (V);
- austenitic: nickel (Ni), manganese (Mn), copper (Cu), cobalt (Co), nitrogen (N)
Long before the turn of the century, it was discovered that the addition of nickel and chromium could improve the anti-corrosion properties of steel. However, some of the steels enriched with these elements did not meet all the needs they needed. The decisive breakthrough came in 1912 in Germany. By combining nickel and chromium in combination with precisely dosed heat treatment, for the first time they achieved optimal corrosion resistance with good mechanical properties at the same time.
Stainless steel has wide application in many industries. Today’s world of construction, the automotive industry, mechanical engineering, and many other branches is almost unimaginable without stainless steel. It is also used to make jewelry, and it is no less used in catering to make high-quality dishes. You can find more information about decorative stainless steel by visiting www.steelcolor.com.
What are the benefits of using stainless steel?
Endurance
Stainless steel is a very durable metal, allowing it to withstand wear and tear by daily activities. This material is non-porous, the alloy is extremely durable, it protects against bacteria and microbes much better than plastic or wooden surfaces. Odo material devices are suitable for homes with children and families with pets.
It is enough to use a disinfectant and you can very easily clean the devices and have a safe place to prepare food. Water and rust resistance are two important reasons for its use in the kitchen. It is also durable and the devices will be without signs of wear even after many years.
Forget about the possibility of oxidation
The hard metal resists scratches and corrosion thanks to an invisible layer of chromium that prevents oxidation, making it a wonderful metal of choice for body jewelry.
It is easy to maintain
Maintaining stainless steel jewelry is also much easier because you don’t want to have a special cleaning solution to take care of wholesale jewelry. Just use warm water, liquid soap, and a little elbow grease, and your stainless steel ring will be like new. Since it is not a precious metal such as gold, silver, or bronze, very affordable, making stainless steel pieces quite budget-friendly.
As a rule, a detergent solution is sufficient to remove fingerprints. Some detergent manufacturers offer special products where the cleaning effect is complemented by a care component. For stubborn dirt, we usually offer household cleaning milk that also removes traces of limescale and slight discoloration. The surface is rinsed with clean water after cleaning.
Extremely greasy contaminants can be removed with alcoholic cleaners or solvents, e.g. pure alcohol or acetone. Care should be taken not to distribute the dissolved dirt over most of the surface. There are special alkaline cleaners and solvent-based cleaners for paint marks. Under no circumstances should chloride-containing products be used, especially those containing hydrochloric acid, bleach, and silver cleaners.
Stainless?
Stainless steel owes its corrosion resistance to a simple chemical reaction: it is caused by the chromium in the steel in combination with oxygen from the air or water, which creates a very thin passive layer on the surface. He repels all aggressive substances. And if external influences damage it at some point, it is re-created from the steel matrix in hundreds of seconds.
Corrosion resistance is primarily due to the proportion of chromium. Reinforcement can be achieved with nickel or molybdenum, but also with other alloys. So today there are several types of stainless steel that are adapted to special applications with certain alloy variants.
Corrosion resistance also depends on the surface, ie. the smoother and more homogeneous it is, the better the corrosion resistance will be. Local corrosion that spreads rapidly can be caused primarily by inclusions or deposits, e.g. imprinted rust particles or dust from processing.
The following types of corrosion occur on stainless steel:
-
Intergranular corrosion
Intergranular corrosion occurs when chromium carbides in the critical form are excreted at the grain boundaries. This leads to chromium depletion in the environment, due to which the passivating effect is lost.
-
Pitting corrosion
In pit corrosion, the passive layer is penetrated only in special places. As a result, pits or holes form on the surface. Pitting corrosion is mainly caused by ions of halogen elements, primarily chlorine. Pitting corrosion can occur primarily in the area of water or wastewater because there are often chlorine or chloride ions.
-
Contact corrosion
Contact corrosion is a very common form that occurs when metallic materials of different potential come into contact with the presence of electrolytes. Here the electrolytes act aggressively on the less precious metal and it turns into a solution.
The strength of the corrosion depends on the magnitude of the current flowing through this galvanic cell. Contact corrosion is very common. As a well-known example, the connection with steel and stainless steel flanges should be highlighted. Contact corrosion is also known when screwing cast flanges with stainless steel screws.
-
Crack corrosion
Crack corrosion occurs when a passive layer of stainless steel is destroyed, e.g. due to the presence of aggressive media with the simultaneous absence of oxygen. Crack corrosion is, therefore, more common nowadays in narrow cracks and smaller cavities, e.g. under the seals or under the screw heads. One example to be mentioned here is the cover in the digesters, where we have an aggressive medium in the form of sludge gas on the one hand and no oxygen at all on the other. Particular attention should be paid here to crack corrosion.
