The difference between stainless steel materials

Stainless steel water tank is mainly made of stainless steel material, with excellent corrosion resistance and strong load-bearing capacity. The FRP water tank is composed of glass fiber and organic polymer materials, with light weight, corrosion resistance, anti-aging and other characteristics. Second, in terms of performance, stainless steel water tanks have excellent load-bearing capacity and stability, and can withstand greater pressure and impact.

1.Specifications: Commonly used stainless steel plates are divided into two models: 201 and 304. The actual composition is different. 304 is of better quality but more expensive, and 201 is worse. 304 is imported stainless steel plate, and 201 is domestic stainless steel plate.

2.The composition of 201 is 17Cr-4.5Ni-6Mn-N, which is a Ni-saving steel type and a substitute steel for 301 steel. It becomes magnetic after being cold worked and is used for Railway rolling stock.

3.The composition of 304 is 18Cr-9Ni, which is the most widely used stainless steel and heat-resistant steel. Used in food production equipment, Xitong chemical equipment, nuclear energy, etc.

4.201 has a high manganese content, and the surface is very bright with dark brightness. The high manganese content makes it easy to rust. 304 contains more chromium, has a matte surface, and does not rust. Put the two together to compare. The most important thing is the difference in corrosion resistance. The corrosion resistance of 201 is very poor, so the price is much cheaper. And because 201 contains low nickel, the price is lower than 304, so the corrosion resistance is not as good as 304.

5.The difference between 201 and 304 is the nickel content. Moreover, the price of 304 is relatively expensive now, but 304 can at least guarantee that it will not rust during use. (Stainless steel potions can be used for experiments)

6.Stainless steel is not easy to rust because it forms chromium-rich oxides on the surface of the steel body to protect the steel body. 201 material is a high-manganese stainless steel that is harder than 304, with high carbon and low nickel.

7.Different compositions (mainly distinguish 201 and 304 stainless steel in terms of carbon, manganese, nickel, and chromium) steel number carbon (C) silicon (Si) manganese (Mn) phosphorus (P) sulfur (S) chromium ( Cr) Nickel (Ni) Molybdenum (Mo) Copper (Cu)

AISI(304)≤0.08≤1.00≤2.00≤0.045≤0.0318-208-10

AISI(201)≤0.15≤1.005.5-7.5≤0.05≤0.0316-183.5-5.5

What is the difference between 3161 and 304?

1.Different chemical compositions.

2. 304 is cover-type stainless steel, and its material composition is OCr18Ni9.

3. 316L is Ominti stainless steel, and its material composition is 00Cr2Mo2Tl.

4. Different properties, 304 steel can resist corrosion such as phosphoric acid, sulfuric acid, formic acid, urea, etc.

5. 304 steel type is suitable for use in situations where general water, control gas, wine, milk, CIP cleaning fluid, etc. are less corrosive or do not come into contact with materials.

6. 316L steel type adds molybdenum element on the basis of 304, which can significantly improve its resistance to intergranular corrosion.

316L stainless steel is suitable for: seawater equipment, chemical, dye, papermaking, oxalic acid, fertilizer and other production equipment; photography, food industry, coastal area facilities, ropes, CD rods, bolts, nuts. 304 stainless steel is suitable for: Household products (Class 1 and 2 tableware, cabinets, indoor pipelines, water heaters, boilers, bathtubs), auto parts (windshield wipers, mufflers, molded products),Medical equipment, building materials, chemicals, food industry, agriculture, ship parts.

What is the difference between 316 stainless steel and 316L?

General properties of stainless steel. Everyone should know that 316L and 316 stainless steel are austenitic stainless steels. They are based on molybdenum element. Compared with 304 stainless steel, they have better resistance to general corrosion and pitting corrosion, better crevice corrosion, and higher ductility. , stronger stress corrosion resistance, better compressive strength and high temperature resistance. In areas requiring better resistance to general corrosion and pitting corrosion, 317L is better than 316 or 316L because 317L contains 3-4% molybdenum, while 316 and 316L only contain 2-3% molybdenum. 316 stainless steel and 316L and 317L copper-nickel-molybdenum stainless steel also have very good processability and formability.

General corrosion

316 stainless steel, 316L stainless steel and 317L stainless steel have better corrosion resistance than 304 stainless steel in ordinary environments. Media that does not corrode 18-8 stainless steel will also not corrode molybdenum-containing stainless steel. However, stainless steel containing molybdenum is not very corrosion-resistant to highly oxidizing acids such as nitric acid.

In the production and processing of food and pharmaceutical products, molybdenum-containing stainless steel is generally used because this can minimize metal contamination.

Generally speaking, under the same environmental conditions, the performance of 316 and 316L can be regarded as equivalent to that of 317L. However, exceptions are made in environments that can cause intergranular corrosion in welding and heat-affected zones. In such media, 316L and 317L are more commonly used because of their low carbon content, which can improve resistance to intergranular corrosion.

Pitting corrosion/crevice corrosion

Increased chromium, molybdenum, and nitrogen content can improve the pitting/crevice corrosion resistance of austenitic stainless steel in chloride or other halogen ion environments. Pitting corrosion is calculated by PREN (pitting corrosion equivalent), PRE=Cr+3.3Mo+16N. The PREN of 316 and 316L is 24.2, and the PREN of 304 is 19.0. This reflects that 316 (or 316L) has better pitting corrosion resistance than 304. 317L has a molybdenum content of 31% and PREN=29.7, which means it has better pitting corrosion resistance than 316.

304 stainless steel is resistant to pitting corrosion and crevice corrosion in water environments containing 100ppm chloride. 316 and 317L containing molybdenum are resistant to pitting corrosion and crevice corrosion in water environments containing 2000ppm and 5000ppm chloride respectively. Although these two stainless steels have achieved certain results when used in seawater environments (chloride content 19000ppm), such use is not recommended. 2507 stainless steel, with a molybdenum content of 4%, a chromium content of 25%, and a nickel content of 7%, is specially designed for salt water environments. 316,317L is only suitable for applications in certain marine environments, such as ship guide rails, exterior walls of buildings near the ocean, etc. 316 and 317L stainless steel showed no corrosion in the 100-hour 5% salt spray test.

intergranular corrosion

316,317L stainless steel exposed to temperatures of 800°F to 1500°F (427°C to 816°C) may cause chromium carbide to precipitate at grain boundaries. This type of stainless steel is prone to intergranular corrosion when exposed to harsh environments. However, when exposed briefly, such as during welding, 317L is more resistant to intergranular corrosion than 316 due to its higher chromium and molybdenum content. When the welding thickness exceeds 11.1mm, even 317L stainless steel needs to be annealed.

Compared with corresponding high carbon content stainless steels, 316L and 317L have the same corrosion resistance and mechanical properties. In applications prone to intergranular corrosion, these two stainless steels have additional advantages. Although the brief heat encountered during welding and stress relief is not sufficient to cause intergranular corrosion, it is worth noting that continuous or long-term exposure in the temperature range of 800 to 1500F (427 to 826°C) will affect both stainless steels. All are harmful. Stress relieving in the temperature range of 1100 to 1500°F (593 to 816°C) may cause mild embrittlement in this type of stainless steel.

Intergranular corrosion of stainless steel

stress corrosion cracking

In halogenated environments, austenitic stainless steels are susceptible to stress corrosion cracking. Although 316,317L has better resistance to stress corrosion cracking than 18Cr-8Ni stainless steel to a certain extent due to its molybdenum content, they are still relatively susceptible. Conditions that cause stress corrosion cracking include: (1) the presence of halides (generally chlorides); (2) residual tensile stress; (3) temperatures exceeding 120F (49°C).

During the welding process, cold deformation or thermal cycling can produce stress. Annealing, a stress-relieving heat treatment, can effectively reduce stress and, therefore, reduce the material’s susceptibility to halide stress corrosion cracking. The low-carbon L grade has no special advantages in resistance to stress corrosion cracking, but when operating in a stress-relieved state, the L grade is still the first choice because intergranular corrosion may occur in such an environment.

Stainless steel halide corrosion

Antioxidant

316,317L has considerable oxidation resistance. In atmospheric environment, even if the temperature reaches 1600 to 1650°F (871 to 899°C), the scale production rate is relatively low. Generally speaking, the performance of 316 is slightly inferior to that of 304 stainless steel because the chromium content of 304 is slightly higher (18% and 316 chromium content is 16%). The oxidation rate is usually affected by the atmosphere and operating environment, so the exact oxidation rate cannot be provided for reference.

Stainless steel physical properties

Structure

When properly annealed, 317,316 stainless steel is primarily austenitic. Small amounts of ferrite may be present. When slowly cooling from 800 to 1500°F (427 to 816°C), carbide precipitation will occur, and the structure will consist of austenite and carbides.

Melting range: 2450 to 2630°F (1390 to 1440℃)

Density: 0.29 Ib/in3 (8.027 g/cm3)

Tensile modulus of elasticity: 29×106 psi (200 Gpa)

Shear modulus: 11.9×106 psi (82 Gpa)

Linear thermal expansion coefficient:

Austenitic stainless steels, including 316 and 317L, are commonly machined into a wide variety of components. Processing methods include perforation, forming, etc., and the equipment used is basically the same as that used to process carbon steel. The considerable ductility of austenitic stainless steel makes it easy to form by bending, stretching, deep drawing and other methods. However, austenitic stainless steel itself has greater strength and hardening properties, so the power requirements for processing austenitic stainless steel are much greater than those of carbon steel.

Welding

Austenitic stainless steels are considered the easiest to weld and can be welded with all fusions as well as resistance welded. There are two important factors to consider in welding joints: 1) avoid hardening cracks; 2) maintain the corrosion resistance of the weld joint and heat-affected zone.

Welding metals with a completely austenitic structure are more likely to form cracks during the welding operation. Therefore, a small amount of ferrite is added to 316, 316L, and 317L stainless steel to reduce the crack sensitivity of the material.

For welding parts used in corrosive environments, it is recommended to use low-carbon 316L and 317L welding base metals and solders. The higher the carbon content of the weld metal, the more likely it is to produce carbide precipitation (sensitization), which may lead to intergranular corrosion. The low-carbon L grade can effectively reduce and avoid sensitization.

Weld deposits with high molybdenum content may have reduced corrosion resistance due to micro-segregation of molybdenum in harsh environments. To overcome this side effect, the molybdenum content of the solder should be increased. 317L In some harsh applications, the molybdenum content of the weld deposit must reach 4% or higher. 904L stainless steel (AWS ER 385, 4.5%Mo) or 625 stainless steel (AWS ERNiCrMo-3, 9%Mo) are often used as this solder.

Contamination of copper and zinc should be avoided in the welding area, as these two components can form low melting point compounds that can lead to welding cracks.

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