Stainless steel is the first material that comes to mind when discussing the material with a wide range of applications. Due to its great corrosion resistance and high-temp stability, stainless steel is widely used in tableware, construction, the chemical industry, food processing, energy, automobile manufacturing, medical equipment, aerospace, etc. You can see it commonly in daily life. However, are you all fully familiar with the material, type, and finish of stainless steel?
This article will introduce stainless steel roundly to you, including what stainless steel is, is stainless steel magnetic, types of stainless steel, properties, and others.
Stainless steel is short for stainless acid-resistant steel with resistance to weak corrosive media, such as air, steam, and water. It is an iron alloy containing at least 11% chrome, which is why it does not rust easily. Chrome has high corrosion resistance, and it will form a passive film on the metal surface after oxidation to protect the material. Due to its special property, it can self-repair through slow oxidation even if exposed to air for a long time.
According to the alloy composition and crystal structure, stainless steel is divided into martensite, ferrite, austenitic, duplex, and precipitation hardening.
Martensite stainless steel resembles ferrite stainless steel. The difference between martensite and ferrite is the carbon content. With a high carbon percentage(>1%) and no nickel, Martensite stainless steel has higher strength, hardness, and wear resistance. But the corrosion resistance is slightly poor.
In addition, due to their high carbon content and how they are processed during heat treatment, martensitic stainless steel is magnetic. Its unique property makes it usually used in making springs, pumps, and valves. Standard materials of martensite stainless steel are 410, 414, 416, 431(containing Ni), 440, etc.
Ferrite stainless steels contain 15% ~30% Cr, low C(<0.1%), and little Ni. So, it has strong magnetism, great solderability, and high corrosion resistance. Common ferritic stainless steels are 430 and 434. Due to the near-absence of Ni, ferrite stainless steel is less expensive than austenitic stainless steel.
With poor mechanical and processing properties, ferrite stainless steel is often used for acid-resistance structures with little force and as anti-oxidation steel. You will see it used in automobile exhaust pipes, chimneys, and components operating at temperatures around 700℃.
Austenitic stainless steel makes up about 2/3 of all stainless steel production, which is the most common stainless steel type. It has an extremely high Ni content and Chrome Content combined with Mo, Ti, and N. The characteristics of Austenitic steels include great ductility, toughness, weldability, durability, and weak magnetic/non-magnetic.
With great comprehensive performance, austenitic stainless steel can withstand the corrosion of various media. They can be used for acid-resistant equipment, kitchen utensils, construction, etc. Common ferritic stainless steels are 201, 202, 304, and 316.
Duplex stainless steel, referred to as austenitic-ferrite duplex stainless steel, combines the advantages of austenitic and ferrite and has super ductility. They are less expensive and with high anti-corrosion properties, commonly used in infrastructure, marine chemical tankers, wastewater treatment, and the underwater oil industry.
Is duplex stainless steel magnetic? The answer depends on its composition, microstructure, and processing history. It is the only stainless steel that can vary from magnetic to non-magnetic.
Duplex stainless steels are a type of stainless steel with a mixed microstructure of austenitic and ferritic stainless steel. Its magnetic properties depend on the proportions of the austenitic and ferritic phases in the microstructure. If the ferritic grade dominates, the duplex stainless steel will be magnetic. However, the duplex stainless steel will be non-magnetic if the austenitic phase dominates.
Precipitation hardening stainless steel is strong based on adding elements like Copper, Niobium, and Aluminium. It has corrosion resistance comparable to austenitic stainless steel. Through precipitation hardening, it can obtain higher hardness than martensite stainless steel.
The magnetic properties of precipitation-hardening stainless steels depend on their composition and the specific types of sediments that form during precipitation-hardening. Some precipitation-hardening stainless steels, such as 17-4 PH stainless steel, are magnetic. Others, such as 13-8 PH stainless steel, are non-magnetic.
In summary, the characteristics of each stainless steel are not the same. Before confirming the specification, you must understand the function and scope of use of various stainless steel with your supplier. If you need help estimating whether your stainless steel is magnetic, please browse our blog “Trivia: Is Stainless Steel Magnetic” to learn which stainless steel is magnetic and why magnetism is important.
Does stainless steel rust? The answer is positive. Stainless steel is not easy to rust, but not rust. Stainless steel is an alloy steel containing at least 10.5% Cr. The Cr will react with oxygen to form a Chromium-rich oxide film which is thin and steady on the steel surface. This film can protect the steel from corrosion.
The higher the Cr content, the less likely stainless steel will rust. But, if the oxide film is severely damaged and not repaired in time, the loose iron oxide will form on the stainless steel surface, which will make the stainless steel rust, and this process is irreversible.
Below are some factors that can cause stainless steel to rust.
The composition of stainless steel is the biggest factor affecting its corrosion resistance. The corrosion resistance of stainless steel depends on Chromium. Due to different Cr content, its corrosion resistance strength is not the same for different brands of stainless steel.
Austenitic stainless steels have the highest corrosion resistance. Among them, stainless steel 316 has the highest corrosion resistance, mainly used in the food industry, nuclear fuel recovery equipment, and surgical equipment. In addition to chromium, molybdenum gives it a special anti-corrosion structure. Secondly, stainless steel 321 reduces the risk of weld corrosion because it contains Ti.
Certain specific industries will require high corrosion resistance of stainless steel. At this time, stainless steel surface finishing came into being. Through surface finishing, stainless steel will obtain different grades of surface finish to improve its corrosion resistance. Some common surface treatment techniques for stainless steel include polishing, brushing, and sandblasting.
Some stainless steel finishes with great aesthetics and high corrosion resistance are described as “Beauty and strength coexist.”
Mirror Stainless Steel
Mirror stainless steel is achieved by polishing the surface until the wear marks are barely visible. The most outstanding characteristic of mirror stainless steel is its brightness. Except for visual appeal, the smooth surface can avoid dirt or bacteria, which is the most popular decorative stainless steel. The most commonly used processing materials are stainless steel 304 and stainless steel 316.
Water Ripple Stainless Steel
Water ripple stainless steel can subtly reflect the scenery, bringing a dazzling, vivid, and luxurious atmosphere. It is suitable for ceilings and wall cladding. Combined with PVD coating, the stainless steel surface will be formed with a layer of TI film to improve the overall corrosion resistance. Therefore, colored water ripple stainless steel has stronger corrosion resistance and a higher aesthetic.
PVD Stainless Steel
PVD stainless steel uses physical technology to vaporize solid materials in a vacuum environment and deposit them on the surface of stainless steel, forming a colored coating layer. The protection layer is usually made of Ti, which helps to improve the corrosion resistance of the steel further. PVD stainless steel panels can be achieved by fusing various colors to enhance their beauty. Due to its strong sense of aesthetics, it is highly regarded in architecture.
If you want to learn more about stainless steel finishes or grades of stainless steel surface finish, please browse our last article: 10 types of stainless steel finishes.
The service environment is another major factor affecting stainless steel rust. The corrosion of stainless steel will be accelerated in the environment containing Chlorine or chemical agents, such as swimming pools, oceans, chemical equipment, etc. Therefore, according to the operation of the environment, choose appropriate stainless steel to avoid excessive corrosion caused by pollutant leakage, thus damaging the environment.
Correct maintenance methods can extend the service life of stainless steel. The chromium in the stainless steel reacts with the oxygen in the air to form a protective layer of chromium oxide on the stainless steel surface. It protects the metal from corrosion.
When external pollutants damage the oxide layer, clean the breakage in time to ensure the protective layer is re-formed. When the oxide layer encounters mechanical damage, repair it with stainless steel polish, which helps to repair the damaged surface and restore the protective performance.
Below we will show you various methods of cleaning stainless steel.
Stainless steel requires little repair, but daily touch will leave fingerprints and grease on its surface. TOPSON recommends using Invisible Glass Detergent to clean and Microfiber Cloth to wipe the surface for daily cleaning of mirrored stainless steel.
Dawn® and Sprayway® brand glass cleaners may be used to clean stainless steel routinely. If your stainless steel is carelessly tea-staining, Krud Kutter® stainless steel cleaners can help you.
Brightness and smoothness can affect the aesthetic. You can use a soft cloth dipped in ordinary household white vinegar to maintain it with occasional polishing. Unique polishing product, like Sprayway® or 3M®, is also a good option to regain the brightness of stainless steel.
Due to its high aesthetics and strong properties, stainless steel has become an important material in various industries. By choosing the right stainless steel for your project, you can improve the quality and value of your finished product.
Established in 2009, TOPSON is a top-ranked stainless steel finishing company that designs and manufactures decorative stainless steel materials in public spaces worldwide. By adjusting the processing methodology and materials, we can create various textures and surface finish to meet customer request! Machinable materials include stainless steel, aluminum, bronze, and steel.
Our stainless steel finishes include the hairline, water ripple, mirror, vibration, sandblasting, embossed, and etching. Click here to browse our metal finishes.
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