Stainless steel is the abbreviation of stainless acid-resistant steel. It is resistant to air, steam, water and other weak corrosive media or stainless steel. It is called stainless steel. It is resistant to chemical corrosion media (chemical, alkali, salt, etc.). Steel grades are called acid-resistant steels.
Stainless steel refers to steel that is resistant to weak corrosive media such as air, steam, water, and chemically etched media such as acid, alkali, salt, etc., also known as stainless acid-resistant steel. In practical applications, steel that is resistant to weak corrosive media is often referred to as stainless steel, while steel that is resistant to chemical media is referred to as acid-resistant steel. Due to the difference in chemical composition between the two, the former is not necessarily resistant to chemical media corrosion, while the latter generally has rust. The corrosion resistance of stainless steel depends on the alloying elements contained in the steel.
Usually divided into metallographic organizations:
Generally, according to the metallographic structure, ordinary stainless steels are classified into three types: austenitic stainless steel, ferritic stainless steel, and martensitic stainless steel. On the basis of these three basic metallographic organizations, for the specific needs and purposes, dual phase steel, precipitation hardening stainless steel and high alloy steel with iron content less than 50% were derived.
1. Austenitic stainless steel.
The base body is mainly composed of austenite structure (CY phase) of face-centered cubic crystal structure, non-magnetic, and mainly strengthened by cold working (and may cause certain magnetic properties) of stainless steel. The American Iron and Steel Association uses numbers in the 200 and 300 series, such as 304.
2. Ferritic stainless steel.
The matrix is a body-centered cubic crystal structure of ferrite (a phase), which is magnetic and generally cannot be hardened by heat treatment, but cold-worked can make it slightly strengthened stainless steel. The American Iron and Steel Association marks 430 and 446.
3. Martensitic stainless steel.
The matrix is a martensite structure (body-centered cubic or cubic), which is magnetic and can be adjusted by heat treatment to adjust its mechanical properties. The American Iron and Steel Association is numbered 410, 420 and 440. Martensite has an austenitic structure at high temperatures, and when cooled to room temperature at an appropriate rate, the austenite structure can be transformed into martensite (ie, hardened).
4. Austenitic-ferritic (duplex) stainless steel.
The matrix has both austenitic and ferritic two-phase structure, wherein the content of less phase matrix is generally greater than 15%, magnetic, can be strengthened by cold working stainless steel, 329 is a typical duplex stainless steel. Compared with austenitic stainless steel, duplex steel has high strength, resistance to intergranular corrosion, chloride stress corrosion resistance and pitting corrosion.
5. Precipitation hardening type stainless steel.
The base is an austenitic or martensitic structure and can be hardened by precipitation hardening. The American Iron and Steel Association uses the 600 series of numbers, such as 630, which is 17-4PH.
In general, in addition to alloys, austenitic stainless steels are superior in corrosion resistance. In environments with low corrosivity, ferritic stainless steels can be used. In mildly corrosive environments, materials are required to be high. For strength or high hardness, martensitic stainless steel and precipitation hardened stainless steel can be used, steel finishing techniques, steel finishes techniques, stainless steel 3d printing, steel finishing, can steel be anodized, how to finish steel, making stainless steel, does stainless steel have iron in it, 3d printed stainless steel, stainless steel printing, 3d printing steel, how to anodize steel at home, aixi stainless steel.
What kind of stainless steel is not easy to rust?
There are three main factors affecting the corrosion of stainless steel:
1. The content of alloying elements.
Generally speaking, the content of chromium in 10.5% steel is not easy to rust. The higher the content of chrome nickel, the better the corrosion resistance. For example, the content of nickel in 304 material is 8-10%, and the content of chromium is 18-20%. Such stainless steel will not rust under normal conditions.
2. The smelting process of the production enterprise will also affect the corrosion resistance of stainless steel.
The large stainless steel plant with good smelting technology, advanced equipment and advanced technology can guarantee the control of alloy elements, the removal of impurities and the control of the cooling temperature of the slab. Therefore, the product quality is stable and reliable, the internal quality is good, and it is not easy to rust. On the contrary, some small steel mills are backward and the process is backward. During the smelting process, impurities cannot be removed, and the products produced will inevitably rust.
3, the external environment, the climate is dry and ventilated environment is not easy to rust.
The environment with high humidity, continuous rainy weather, or high pH in the air is prone to rust. 304 stainless steel, if the surrounding environment is too bad, it will rust.
How to deal with rust spots in stainless steel?
1. Chemical methods
Re-passivation of the rusted portion with a pickling paste or spray to form a chromium oxide film restores corrosion resistance. After pickling, it is important to properly rinse the water with all the contaminants and acid residues. After all treatment, it is re-polished with polishing equipment and sealed with polishing wax. For areas with slight rust, use a 1:1 mixture of gasoline and oil to wipe off the rust with a clean cloth.
2, mechanical methods
Sandblasting, blasting with glass or ceramic particles, annihilation, brushing and polishing. It is possible to mechanically remove the contamination caused by previously removed materials, polishing materials or annihilation materials. All kinds of pollution, especially foreign iron particles, can be a source of corrosion, especially in humid environments. Therefore, the mechanical cleaning surface should preferably be cleaned under dry conditions. The mechanical method can only be used to clean the surface and does not change the corrosion resistance of the material itself. It is therefore recommended to re-polish with a polishing device after mechanical cleaning and to seal with polishing wax.
Stainless steel grades and performance
1, 304 stainless steel. It is one of the austenitic stainless steels with a large application volume and the widest range of applications. It is suitable for the manufacture of deep-drawn parts and acid pipelines, containers, structural parts, various instrument bodies, etc. It can also manufacture non-magnetic and cryogenic equipment and component.
2, 304L stainless steel. In order to solve the ultra-low carbon austenitic stainless steel developed by the precipitation of Cr23C6 which causes the 304 stainless steel to have severe intergranular corrosion under some conditions, the sensitized state has better resistance to intergranular corrosion than 304 stainless steel. In addition to the lower strength, other properties are the same as 321 stainless steel, mainly used for corrosion-resistant equipment and components that need to be solution treated after welding, and can be used to manufacture various types of instrument bodies.
3, 304H stainless steel. The internal branch of 304 stainless steel has a carbon mass fraction of 0.04%-0.10%, and the high-temperature performance is better than 304 stainless steel.
4, 316 stainless steel. Adding molybdenum to the 10Cr18Ni12 steel makes the steel have good resistance to reducing medium and pitting resistance. Corrosion resistance is superior to 304 stainless steel in seawater and various other media, mainly used for pitting resistant materials.
5, 316L stainless steel. Ultra-low carbon steel with good resistance to sensitized intergranular corrosion, suitable for the manufacture of welded parts and equipment of thick section size, such as corrosion resistant materials in petrochemical equipment.
6, 316H stainless steel. The internal branch of 316 stainless steel has a carbon mass fraction of 0.04%-0.10%, and the high-temperature performance is better than 316 stainless steel.
7,317 stainless steel. Pitting and creep resistance is superior to 316L stainless steel for the manufacture of petrochemical and organic acid resistant equipment.
8,321 stainless steel. Titanium-stabilized austenitic stainless steel, added titanium to improve intergranular corrosion resistance, and has good high temperature mechanical properties, can be replaced by ultra-low carbon austenitic stainless steel. Except for special occasions such as high temperature or hydrogen corrosion resistance, it is not recommended for general use.
9,347 stainless steel.铌 Stabilized austenitic stainless steel, added yttrium to improve resistance to intergranular corrosion, corrosion resistance in corrosive media such as acid, alkali, salt, etc. Same as 321 stainless steel, good welding performance, can be used as corrosion resistant material and resistant Used in hot steel, mainly used in thermal power and petrochemical fields, such as making containers, pipes, heat exchangers, shafts, furnace tubes in industrial furnaces, and furnace tube thermometers.
10, 904L stainless steel. Super complete austenitic stainless steel, a super austenitic stainless steel invented by OUTOKUMPU, Finland, with a nickel mass fraction of 24% to 26%, a carbon mass fraction of less than 0.02%, and excellent corrosion resistance. It has good corrosion resistance in non-oxidizing acids such as sulfuric acid, acetic acid, formic acid and phosphoric acid, and has good resistance to crevice corrosion and stress corrosion. It is suitable for various concentrations of sulfuric acid below 70 °C. It is resistant to corrosion in acetic acid and mixed acid of formic acid and acetic acid at any concentration and at any temperature under normal pressure. The original standard ASMESB-625 is classified as a nickel-based alloy, and the new standard classifies it as stainless steel. China only has the similar grade 015Cr19Ni26Mo5Cu2 steel. The key materials of a few European instrument manufacturers use 904L stainless steel. For example, the measuring tube of E+H mass flowmeter adopts 904L stainless steel, and the watch case of Rolex watch also adopts 904L stainless steel.
11, 440C stainless steel. Martensitic stainless steel, the hardest in hardenable stainless steel and stainless steel, the hardness is HRC57. Mainly used for making nozzles, bearings, valve spools, valve seats, sleeves, valve stems, etc.
12, 17-4PH stainless steel. Martensitic precipitation hardening stainless steel with hardness HRC44, high strength, hardness and corrosion resistance, can not be used for temperatures above 300 °C. It has good corrosion resistance to the atmosphere and diluted acid or salt. Its corrosion resistance is the same as that of 304 stainless steel and 430 stainless steel. It is used to manufacture offshore platforms, turbine blades, valve spools, seats, sleeves and valve stems.