Stainless Steel Introduction
Writer： admin Source： 未知 Date：2017-02-14
Stainless steel refers to the steel resistance of air, steam, water and other corrosive medium, weak acid, alkali, salt and other chemical etching medium corrosion. In practical applications, we call the corrosion resistance steel stainless steel, and the chemical resistance medium corrosion steel is called acid resistant steel. Due to the difference in chemical composition of the two, the former is not necessarily resistant to chemical medium corrosion, while the latter is generally non rust. The corrosion resistance of stainless steel depends on the alloy elements contained in the steel.
A, Stainless steel profile
All metals react with oxygen in the atmosphere to form an oxide film on the surface. Unfortunately, the iron oxide formed on the ordinary carbon steel continues to oxidize, so that the corrosion is enlarged, and finally holes are formed. But we can use a paint or oxidation resistant metal plate(e.g., zinc, nickel, and chromium) to protect the surface. However, as is known, this protection is only a thin film, so if the protective layer is damaged, the following steel begins to rust.
Chrome is the basic element for stainless steel to get corrosion resistance. When the chrome content in steel reaches about 12%, it reacts with the oxygen to form a thin film on the surface of steel (self passivation film). It can prevent further corrosion of steel. In addition to chrome, the commonly used alloy elements are nickel, molybdenum, titanium, niobium, copper, nitrogen, etc., to meet the needs of various applications of stainless steel structure and performance.
Stainless steel is usually divided into:
1, Ferritic stainless steel, 12% ~ 30% chromium. The corrosion resistance, toughness and weldability increased with chromium increases. The resistance to chloride stress corrosion is better than other types of stainless steel.
2, Austenitic stainless steel, more than 18% chromium and 8% nickle and small amounts of molybdenum, titanium, nitrogen and other elements, good comprehensive performance, and corrosion resistant to varieties of medias.
3, Austenite ferrite duplex stainless steel. It has the advantages of austenitic and ferritic stainless steel, and has the superplasticity.
4, Martensitic stainless steel, high strength but poor ductility and weldability.
B, Stainless steel history
During 1820 and 1900, there were very few records of the progress of stainless steel.
In 1932, the successful of hot strip mill.
In 1934, the successful development of stainless steel sheet.
C, Stainless steel grades
According to the compositions, stainless steel can be divided into Cr series (SUS400), Cr-Ni series(SUS300), Cr-Mn-Ni series(SUS200) and the precipitation hardening series (SUS600).
200 series----Cr Ni Mn austenitic stainless steel
300 series----Cr Ni austenitic stainless steel
301----Good ductility for molding products. Also can pass through the machine speed hardening. Good welding. Wear resistance and fatigue strength are better than 304 stainless steel.
302----Same corrosion resistance with 304 but better intensity due to higher carbon content.
303----By adding a small amount of sulfur and phosphorus to make it more cutting.
304----18/8 stainless steel. GB brand is 0Cr18Ni9.
309----Better temperature resistance than 304.
316----Following the 304, second of the most widely used steel, mainly used in the food industry and surgical equipment, adding Mo to obtain a special corrosion resistant structure. It is also used as "marine steel" because of its better corrosion resistance than 304. SS316 is usually used in nuclear fuel recovery unit. Grade 18/10 stainless steel is also generally consistent with this application level.
321----Other than the addition of titanium to reduce the risk of corrosion of the weld material, other properties are similar to 304.
400 series----Ferritic and martensitic stainless steel.
408----Good heat resistance, weak corrosion resistance, 11% Cr, 8% Ni.
409----The cheapest model (Europe and US), usually used as automobile exhaust pipe, is a ferritic stainless steel (chrome steel).
410----Martensite (high strength steel), good wear resistance but poor corrosion resistance.
416----The addition of sulfur improves the process ability of the material.
420----"Cutting class" martensitic steel, similar to Brandt's first high chromium stainless steel this. Also used in surgical knives, can be very bright.
430----Ferritic stainless steel, decorative, such as for car accessories. Good formability, but poor temperature resistance and corrosion resistance.
440----High strength cutting tool steel, carbon content is slightly higher. After appropriate heat treatment to obtain a higher yield strength and hardness can reach 58HRC, which belongs to the most hard stainless steel. The most common example is the "razor blade"". There are three commonly used models: 440A, 440B, 440C, in addition to 440F (easy processing).
500 series----Heat resistant chromium alloy steel.
600 series----Martensitic precipitation hardening stainless steel.
630----The most common type of precipitation hardening stainless steel, usually also called 17-4; 17%Cr, 4%Ni.
D, Why is stainless steel corrosion resistance?
All metals react with oxygen in the atmosphere to form an oxide film on the surface. Unfortunately, the iron oxide formed on the ordinary carbon steel continues to oxidize, so that the corrosion is enlarged, and finally the hole is formed. We can use a paint or oxidation resistant metal (e.g., zinc, nickel, and chromium) to ensure the surface of the carbon steel, but, as is known, this protection is only a thin film. If the protective layer is damaged, the following steel begins to rust.
The corrosion resistance of stainless steel depends on chromium, but chromium is one of the components of steel, so the protection methods are not the same.
The corrosion resistance of the steel increased significantly when the content of Cr gets 10.5%, but if the chromium content is higher, although it could improve the corrosion resistance, but not obvious. The reason is that when the steel is treated with chromium, the type of surface is changed into a surface oxide similar to that of pure chromium metal. This close adhesion chromium oxide protection surface, prevent further oxidation. This very thin oxide plate, through which you can see the natural luster of steel surface, to make the stainless steel a unique surface. Moreover, if the surface plate is damaged, the exposed steel surface will be self - repaired with the atmospheric reaction to form the oxide "passivation film" and continue to play a protective role.
Therefore, all stainless steel elements have a common characteristic, that is, chromium content of more than 10.5%.
Stainless steel 204Cu compared with 304, has stronger tensile strength and yield strength, lower strain hardening rate and better cold forming performance; corrosion resistance is superior at least equivalent to 304. Plus 200 series’ own advantages of wear-resistant, low cost, 204Cu absolutely ca replace 304 stainless steel. In recent years, the United States vigorously promote the 204Cu in the field of electronics, communications, security, food processing, energy and tobacco processing industry, with remarkable results.
The use of 304 stainless steel in dry indoor environment is quite good. However, in the countryside and the city, in order to maintain their appearance outdoors, you need to clean regularly. In heavily polluted industrial areas and coastal areas, the surface will be very dirty, and even rust. So in order to obtain the aesthetic effect in the outdoor environment, we need to use nickel stainless steel. Therefore, 304 stainless steel is widely used in curtain walls, side walls, roofs and other construction purposes, but in the severely corrosive industrial or marine atmosphere, the best choice is stainless steel 316.
Now, people have fully realized the superiority of using stainless steel in structural application. Several design criteria include 304 and 316 stainless steel. Because "duplex" stainless steel 2205 has a good atmosphere corrosion resistance and high tensile strength and elastic limit strength integration, the European standards also include it.
Difference between 201 and 304 stainless steel
1, Specifications: commonly used stainless steel plate is divided into 201 and 304 two models. The composition is different. 304 has better quality, but the price is expensive. 304 is imported stainless steel plate, while, 201 is China made.
2, The 201 is made up of 17Cr-4.5Ni-6Mn-N, instead of steel 301. After cold processing, it is used for railway vehicles.
3, 304 is composed of 18Cr-9Ni, the most widely used stainless steel and heat-resistant steel. It is good for food production equipment, chemical equipment, nuclear power, etc..
4, 201 has high manganese content, the surface is shinning with dark bright. High manganese content is easy to rust. 304 has more chromium and the surface is matte, not rust. We can see the surface difference when they are put together. The most important thing is the corrosion resistance difference. 201 corrosion resistance is very poor, so the price will be much cheaper. And because of the low content of nickel containing of 201, the corrosion resistance is not as good as 304.
5, The difference between 201 and 304 is the nickel content. And 304 price is more expensive, generally close to 50,000RMB/ton, but 304 can guarantee the use of the process will not rust. (can be tested with salty water)
6, Stainless steel does not rust because the formation of chromium oxide on the surface can protect the steel body. 201 belongs to the high manganese stainless steel, and compared with 304 with higher hardness, higher carbon but lower nickel.
7, Different components (mainly from carbon, manganese, nickel, chromium and several aspects to distinguish between the 201 and 304 stainless steel) carbon (C) silicon (Si) Mn (Mn) and phosphorus (P) and sulfur (S) chromium (Cr) nickel (Ni) copper (molybdenum rod (Mo) Cu AISI) (304) = 0.08 = 1 = 2 = 0.045 = 0.03 18-20 8-10 AISI (201) = 0.15 = 1 = 0.05 = 0.03 16-18 3.5-5.5 5.5-7.5
(86)-533-2070506 
