Introduction to the basic characteristics of the stainless steel

1. History

Stainless steel attached to the name of a British steel industry experts are Harry Brearley. When in 1913, he invented a special type of steel with high wear resistance, by reducing the carbon content down into components for chromium steel (0.24% to 12.8% C and Cr).

Then steel company Krupp in Germany continues to improve this steel by adding nickel to steel elements to improve corrosion resistance to acids and easy processing softer. Based on this discovery that the two types of steel grade 400 and 2 300 was born just before World War First. After the war, 20 years of the 20th century, a British steel industry experts as Mr. W. H Hatfield continued research and development of ideas in stainless steel. By combining the different ratio between nickel and chromium in the steel sectors, he has introduced a new type of stainless steel 18/8, who 8% Ni and 18% Cr, is the familiar steel grade 304 of today. He is also the inventor of the 321 steel by adding titanium to steel composition ratio above 18/8.

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After nearly a century, the advent and development, today stainless steel is widely used in all areas of civil and industrial with more than 100 different steel grades. In the metallurgical industry, the term of stainless steel (stainless steel) is used to indicate a form of iron alloys containing a minimum of 10.5% chromium. The name “Stainless Steel” but in fact it is only iron alloys do not change color or corrode easily as the other ordinary steel. This material may also be called corrosion-resistant steel. Typically, there are many different ways to apply stainless steel for different surfaces to increase the life of widgets. In life, they appear everywhere as the blades cut or strap watches …

Stainless steel is resistant to oxidation and corrosion is very high, but the choice of the right type and their specifications to fit into each specific case is very important. Resistant to oxidation from the surrounding air temperature of stainless steel typically is due to the ratio of chromium present in the alloy (minimum of 13% and up to 26% in the case of work in harsh working environments). Oxidized state of chromium oxide of chromium is commonly (III). When chromium alloy steel in contact with air is a very thin layer of chromium oxide III appeared on the surface of the material; This thin layer that can not be seen with the naked eye, which means that the metal surface is still shiny. However, they absolutely do not react with water and air protection should be below grade steel. This phenomenon is called oxidation engineered stainless material. Can see this phenomenon for some other metals such as aluminum and zinc in.

When these objects made of stainless steel linked together with forces acting as bolts and rivets, the oxide layer may be flying their lost positions at which they are connected together. When disassembled them out, you can see the corrosion that position. Nickel as well as lip-black modules and vanadium also features stainless oxidation similar but not widely used. Besides chromium, nickel and lip-black modules and nitrogen oxidation also features similar rust.

Nickel (Ni) is a common ingredient to enhance ductility, ductile, shaping properties of stainless steel. Lip-black module (Mo) made of stainless steel with high corrosion resistance in acidic environments. Nitrogen (N) create stability for stainless steel at a temperature of minus (Cryogenic). The participation of the various components of chromium, nickel, lip-black module, nitrogen leads to the different crystal structures generate different physical properties of stainless steel.

2. Classification

There are four main types of stainless steel: austenitic, ferritic, austenitic-ferritic (duplex), and martensitic.

Austenitic stainless steel is the most common. Under this line may include the steel grade SUS 301, 304, 304L, 316, 316L, 321, 310S … this type containing a minimum 7% nickel, 16% chromium, carbon (C) 12:08% max. Such components created for this steel has high corrosion resistance in a wide temperature range rather, not magnetized, flexible, pliable, easy to weld. This steel is used to make many household items, tanks, industrial pipes, industrial ships, exterior architecture, construction works …

Ferritic stainless steel is the physical properties similar to mild steel, but potentially higher corrosion resistance of mild steel (low carbon steel). Under this line may include the steel grade SUS 430, 410, 409 … this type containing approximately 12% – 17% chromium. This category, with 12% Cr more often in architectural applications. Type containing approximately 17% chromium is used for household appliances, boilers, washing machines, the architecture of the house …

Austenitic ferritic-(Duplex) This is the nature of steel “in the middle” ferritic and austenitic type collectively called DUPLEX. Under this line may include LDX 2101, SAF 2304, 2205, 253MA. Duplex steel contains less than Ni austenitic type. DUPLEX with typical characteristics are high strength and durability flexibility widely used in petrochemical industry, paper, pulp, manufactured marine vessels … Given the escalating price of stainless steel due to the scarcity of nickel DUPLEX lines are increasingly more applications to substitute for some grades of austenitic steels such as SUS line 304, 304L, 316, 316L, 310S …

Martensitic type contains about 11% to 13% Cr, bearing strength and hardness, corrosion resistance relative degree. Widely used to manufacture turbine blades, blades …

3. Basic features:

Inox430: magnetic, vulnerable to environmental impacts of tarnish
Inox202: magnetic, vulnerable to environmental impacts of tarnish
Inox201: nonmagnetic (99%), stable with time, but avoid direct contact with acids or salts
Inox304: nonmagnetic, can be used in any environment, always shiny, ensure food safety

4. Inox magnetic and non-magnetic (stainless steel magnetic attraction phenomenon and why)

4.1. According to the traditional view, the stainless steel is considered stainless steel, nonmagnetic, this concept has been largely influenced by the history of the development of stainless steel industry. Nowadays, with the rapid growth of the industry SS (inspection), the notion of such stainless steel is considered to be not quite right, and not science, can even cause misunderstandings about the nature of stainless steel . Due to the requirements of different conditions, stainless steel is developed into hundreds of different kinds. Of these, only a few types are nonmagnetic, while the majority are magnetic.

4.2. The magnetism of stainless steel related to its metal structure. Currently, according to the stainless steel metal structure is divided into 4 types: martensitic, austenitic, ferritic and austenitic and ferritic type combination (also called Duplex). Only the type of austenite is nonmagnetic, and the rest are kind of magnetized. In the 4 categories above, their magnetism is ranked in order from highest to lowest as follows: ferritic – martensitic – Duplex – austenitic. In addition, no differences in the magnetic properties of ferritic and martensitic stainless steel with common steel. Everything has used before (at the start) is 2Cr15Mn15Ni2N and 1Cr18Ni9Ti, both of which are non-magnetic stainless steel austanitic. However, the environmental conditions increasingly polluted by the development of modern industry, corrosion resistant stainless steel on the two types can not meet the requirements as before. In particular, we have a high carbon content, substances that affect the largest corrosion resistance. So two types of stainless steel and 1Cr18Ni9Ti 2Cr15Mn15Ni2N not widely used, especially industrial interior decoration.

4.3. The magnetism of stainless steel is also heavily influenced by the production and processing. Some types of austenitic stainless steel components with unstable austenite and low temperature variations turned into martensitic and ferritic stainless steel by pressure and body temperature during practice and polish.

4.4. The relationship between magnetic and corrosion resistant stainless steel of (stainless): Magnetism and corrosion resistance of stainless steel is completely two concepts relate to each other in the process of forming them. We can say, resistance to corrosion of stainless nonmagnetic is always very good and corrosion resistance of stainless steel is not magnetic low.

Criteria for assessing good or not good stainless steel is resistant to corrosion and not the possibility of infection from. Get the 316 stainless steel is a typical example, Adding substance Mo (Mo-Phil-black) austenitic stainless steel giving unstable and easily transforms into martensite, then magnetism decreases. However, due to the addition of molybdenum, the chloride ion freedom is enhanced corrosion resistance.

4.5. Although Inox 316 (0Cr17Ni12Mo2) used today belong austenictic stainless steel, however, the reduction of carbon content (versus 1Cr18Ni9Ti) and chemical composition of Ti (titanium) – free (versus 1Cr8Ni9Ti) lead to the unstable and temperature variation in austenite stainless steel. So the pressure and temperature are reduced during preparation and polishing body made of stainless steel converter, which is the surface of austenitic stainless steel is completely transformed into martensite stainless steel, so its magnetic well high up. However, resistance to corrosion is affected by its chemical composition, so it is not changed.

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