|Stainless Steel Chemical Values (%)|
|Heat Resistence Austenitic||304H||0.05||18,3||8,70||—||—|
304 Quality Good oxidation resistance is available at 870 ºC with short rotational intervals and continuous working at 925 ºC. 304 is not recommended within the temperature range of 425 – 860 ºC, if the operation is in an aqueous environment at the following application room temperature. However, this temperature can sometimes show good performance in the changing environment above the temperature range. It is more resistant to 304L quality carbide deposits and can be used at the stated temperature range. High carbon values are needed where material resistance is critical at high temperatures. As an example, the AS1210 pressure vessel code limits the operating temperature of 304L to 425 ºC, and the use of 304 qualities is restricted to values of 0.04% or higher for carbon values above 550 ºC. The 304 quality liquefied gas has excellent stability at low temperatures and can be applied at these temperatures.
Metallurgical stainless steel is described as an iron-carbon alloy containing a minimum of 10.5% chromium element. The chrome element is the basic component that protects the steel against rusting, as seen below. The fact that these steels are not stained like other steels is due to corrosion and non-corroding. This material is also referred to as corrosion-resistant steel, especially in the aviation industry, not elaborated by alloy type and qualities. Nowadays, it is very easy to reach stainless steels with many different and easily achievable qualities and surface properties that work without any problem in difficult environment conditions during product life. Even in normal everyday life, we can see that these products are used extensively for hours at forks.
Stainless steel is highly resistant to corrosion and oxidation in many natural and man-made environments. However, it is very important to select the correct quality and type of stainless steel for each particular application. The first step in quality selection begins with a detailed analysis and identification of all possible working conditions that will be exposed to the stainless steel during the design phase.
High oxidative resistance at normal room temperature and weather conditions is achieved with a minimum of 13% (by weight), up to 30% chromium in very hard and difficult environmental conditions. When the chromium element in stainless steel is exposed to oxygen (which means oxygen in the normal atmosphere), it immediately forms a chromium oxide (Cr2O3) passivation layer. This layer is so inconspicuous that water or any gas that forms the product (stainless steel) protects the metal it contains, completely blocking oxygen penetration. In addition, the clearance that will occur if this layer is torn, opened or scratched for any reason consists of a very rapid re-formation of the layer itself. This is called pasivation and is also seen in some other metals such as titanium. The nickel element also contributes to the passivation properties such as molybdenum and vanadium, which are used in other low ratios.
The resistance to corrosion and smudging of the stainless steel makes it an ideal and indispensable material because of its wide commercial application, low maintenance cost, cheaper in comparison with others and having an eye-catching appearance. Though there are over 150 stainless steel qualities in total, 15 of these are stainless steels that are very popular and very popular on the market.
Stainless steels can be used in many ways as cold rolled and hot rolled methods and casting parts, such as flats, as flat products, as plates, as rods, as wires, as pipes, as shaped long products, in the food industry, It is widely used in many areas such as equipment, automotive, white goods, structures and building elements, buildings. One of the areas where stainless steel is used is the products we use in our everyday life such as jewelery and watches. The most common quality used in jewelry is 316L. Stainless steel does not oxidize and darken over time like silver. In addition, the density of stainless steel is slightly lighter than silver, so it is easier for designers.
Stainless steel can be recycled 100%. 60% of the stainless steel used is produced by evaluating recycled materials such as stainless steels and production processes from recycled materials from finished products.
Antiquity has achieved several corrosion-resistant iron arriving daily. The most famous and greatest example of this is Delhi ‘s Steeped Demyra, built by Kumara Gupta I in Delhi, India in the 400’ s. However, unlike stainless steel, this iron monument is not made of chrome, but has high corrosion resistance. Phosphorus, together with suitable local weather conditions, forms a protective surface layer consisting of iron-oxide and phosphonite on the surface of the monument and provides resistance against corrosion of the iron.
The resistance to corrosion of iron-chromium alloys was first recognized by French metallurgist Pierre Berthier in 1821. At that time the technology could not be used practically because chromium and iron were not enough to keep the process like today.
In the 1890s, the German Hans Goldschmidt discovered the alimunothermic method of producing carbon-free chromium. Since then, many studies have been made on stainless steel.
The beginnings of modern stainless steel were first discovered in 1913 by British metallurgist Harry Brearly when he was accidentally researching to improve rifle barrels. This was the starting point of the stainless steel. In later work, austenitic stainless steel (304), which is described as 18-8, went on the market in about 1920s and achieved great success in its application. From the 1930’s onwards, stainless steel industry has taken an indispensable place in our everyday life. With these alloying elements, researchers have improved their stainless steel qualities that we know today.
Duplex stainless steels were developed about 70 years ago for use in the sulphite paper industry. Duplex alloys were used in the first place to cope with corrosion problems caused by chlorite bed cooling water and other sharp chemical process fluids. By the development of gas and oil stations in the North Sea in the 1970s, a second generation duplex stainless steel was developed. According to this, in a certain way nitrogen addition, toughness, weldability, chlorite increased corrosion resistance. The most widely used mixed composition, called UNS S31803, was standardized in 1996 by the duplex steel UNS S32205.
II. During World War II, stainless steels have been discovered which have been hardened by sedimentation. The first example of these non-standard qualities was stainless steel, which was called 17-7PH in 1948.