Stainless steel knowledge and stainless steel brand stainless steel is only corrosion-resistant and rust-resistant, not rust-free. Under certain conditions, all metals that are rusted react with oxygen in the atmosphere to form an oxide film on the surface. Unfortunately, the iron oxide formed on ordinary carbon steel continues to oxidize, causing the rust to continuously expand, eventually forming holes. The carbon steel surface can be secured by electroplating with paint or oxidation-resistant metals (for example, zinc, nickel and chromium), but, as is known, this protection is only a thin film. If the protective layer is destroyed, the steel below will begin to corrode the steel that is corroded by weak corrosive media such as air, steam, and water, and chemically etched media such as acids, alkalis, and salts. Also known as stainless steel. In practical applications, steels that are resistant to weak corrosive media are often referred to as stainless steels, and steels that are resistant to chemical corrosion are known as acid-resistant steels. Because of the difference in chemical composition between the two, the former is not necessarily resistant to chemical media corrosion, while the latter is generally non-rust. The corrosion resistance of stainless steel depends on the alloying elements contained in the steel. Chromium is the basic element for obtaining corrosion resistance of stainless steel. When the chromium content in the steel reaches about 1.2%, chromium reacts with oxygen in the corrosive medium to form a very thin oxide film on the surface of the steel (self-passivation film). , can prevent further corrosion of the steel substrate. In addition to chromium, the commonly used alloying elements are nickel, molybdenum, titanium, niobium, copper, nitrogen, etc., to meet the various requirements of stainless steel organization and performance requirements.
Stainless steel is usually divided into matrix structures:
1, ferritic stainless steel. Chrome contains 12% to 30%. Its corrosion resistance, toughness and weldability increase with the increase of chromium content, and resistance to chloride stress corrosion is superior to other types of stainless steel.
2, austenitic stainless steel. Chromium is more than 18%, also contains about 8% nickel and a small amount of molybdenum, titanium, nitrogen and other elements. Good overall performance, resistant to many media corrosion.
3, austenitic - ferritic duplex stainless steel. It combines the advantages of austenitic and ferritic stainless steels and has superplasticity.
4, martensitic stainless steel. High strength but poor plasticity and weldability.
Stainless steel grade precipitation hardened stainless steel. With good forming properties and good weldability, it can be used as an ultra-high strength material in the nuclear industry, aerospace and aerospace industries.
The components can be classified into Cr series (SUS400), Cr-Ni series (SUS300), Cr-Mn-Ni (SUS200), and precipitation hardening series (SUS600).
200 Series—Chromium-Nickel-Manganese Austenitic Stainless Steel Series 300—Chromium-Nickel Austenitic Stainless Steel 301—Good ductility for molding products. It can also be hardened by speed. Good weldability. The wear resistance and fatigue strength are better than 304 stainless steel.
302—Corrosion resistance is the same as 304. The strength is better due to the relatively high carbon content.
303 - It is relatively processed by adding a small amount of sulfur and phosphorus.
304 - that is 18/8 stainless steel. The GB grade is 0Cr18Ni9.
309 - better temperature resistance than 304.
316—Since 304, the second most widely used steel grade, mainly used in the food industry and surgical equipment, is the addition of molybdenum to obtain a special structure that resists corrosion. Because it has better resistance to chloride corrosion than 304, it is also used as "marine steel". SS316 is usually used in nuclear fuel recovery devices. 18/10 grade stainless steel also generally meets this application level. [1]
Model 321 - Other properties are similar to 304 except that the addition of titanium reduces the risk of corrosion of the weld material.
Series 400 - ferrite and martensitic stainless steel 408 - good heat resistance, weak corrosion resistance, 11% Cr, 8% Ni.
409 - The cheapest model (British and American), commonly used as automotive exhaust pipe, is a ferritic stainless steel (chrome steel).
410—Martensite (high strength chrome steel), good wear resistance, poor corrosion resistance.
416 - Added sulfur improves the material's processability.
420—"Blade-grade" martensitic steel, similar to Brinell's high chromium steel, the earliest stainless steel. Also used for surgical tools, can do very bright.
430—ferritic stainless steel, decorative, for example for automotive accessories. Good formability, but poor temperature resistance and corrosion resistance.
440—High-strength cutting tool steel with slightly higher carbon content. After appropriate heat treatment, it can obtain higher yield strength, and the hardness can reach 58HRC, which is among the hardest stainless steels. The most common application example is the "razor blade." There are three commonly used models: 440A, 440B, 440C, in addition to 440F (easy processing type).
Series 500 - Heat-resistant chromium alloy steel.
Series 600 - martensitic precipitation hardened stainless steel.
630—The most commonly used precipitation-hardening stainless steel model, also commonly called 17-4; 17% Cr, 4% Ni.