1、what is stainless steel?
Stainless steel is a kind of steel. Steel refers to the steel containing less than 2% carbon (c), and more than 2% iron. Alloy elements such as chromium (CR), nickel (Ni), manganese (MN), silicon (SI), titanium (TI) and molybdenum (MO) are added to the steel in the smelting process to improve the performance of the steel and make the steel have corrosion resistance (i.e. no rust), which is what we often call stainless steel.
What are “steel” and “iron”, what are their characteristics, and what are their relations? How do 304, 304L, 316 and 316L come from? What are the differences between them?
Steel: materials with iron as the main element, carbon content generally below 2%, and other elements—— Steel classification (GB / T 13304-91)
Iron: a metallic element, atomic number 26. Iron materials have strong ferromagnetism and good plasticity and thermal conductivity.
Stainless steel: it is resistant to air, steam, water and other weak corrosive media or stainless steel. The commonly used steels are 304, 304L, 316 and 316L, which are 300 series steels of austenitic stainless steel.
-304 stainless steel-
Performance introduction
304 stainless steel is the most common type of steel. As a kind of steel with a wide range of applications, it has good corrosion resistance, heat resistance, low temperature strength and mechanical properties; Good hot workability such as stamping and bending, no heat treatment hardening phenomenon (no magnetism, convenient temperature – 196 ℃ ~ 800 ℃).
Scope of application
Household appliances (Class 1 and 2 tableware, cabinets, indoor pipelines, water heaters, boilers, bathtubs)
Auto parts (windshield wiper, muffler, molded products)
Medical appliances, building materials, chemicals, food industry, agriculture, ship parts
-304L stainless steel-
(L is low carbon)
Performance introduction
As a low-carbon 304 steel, in general, its corrosion resistance is similar to that of 304 steel, but after welding or stress elimination, its resistance to grain boundary corrosion is excellent; It can also maintain good corrosion resistance without heat treatment, and the service temperature is – 196 ℃ ~ 800 ℃.
Scope of application
It is applied to outdoor machines in chemical, coal and petroleum industries with high requirements for grain boundary corrosion resistance, heat-resistant parts of building materials and parts with difficulties in heat treatme
-316 stainless steel-
Performance introduction
Due to the addition of molybdenum, 316 stainless steel has excellent corrosion resistance, atmospheric corrosion resistance and high temperature strength, and can be used under harsh conditions; Excellent work hardening (non-magnetic).
Scope of application
Equipment used in seawater, chemical, dye, papermaking, oxalic acid, fertilizer and other production equipment; Photography, food industry, coastal facilities, ropes, CD rods, bolts, nuts.
-316L stainless steel-
(L is low carbon)
Performance introduction
As a low-carbon series of 316 steel, it has the same characteristics as 316 steel and excellent grain boundary corrosion resistance.
Scope of application
Products with special requirements for grain boundary corrosion resistance.
Chemical composition:
316 and 316L stainless steels are molybdenum containing stainless steels. The molybdenum content of 316L stainless steel is slightly higher than that of 316 stainless steel Due to the molybdenum in the steel, the overall performance of this steel is better than 310 and 304 stainless steel. Under high temperature conditions, when the concentration of sulfuric acid is lower than 15% and higher than 85%, 316 stainless steel has a wide range of applications. 316 stainless steel also has good chloride corrosion resistance, so it is usually used in marine environment. 316L stainless steel has a maximum carbon content of 0.03, which can be used in applications where annealing cannot be performed after welding and maximum corrosion resistance is required.
Corrosion resistance:
The corrosion resistance of 316 stainless steel is better than 304 stainless steel, and it has good corrosion resistance in the production process of pulp and paper. Moreover, 316 stainless steel is also resistant to marine and aggressive industrial atmospheres.
Generally speaking, 304 stainless steel and 316 stainless steel have little difference in chemical corrosion resistance, but they are different in some specific media.
The originally developed stainless steel is 304, which is sensitive to pitting corrosion under certain circumstances. An additional 2-3% of molybdenum can reduce this sensitivity, and thus 316 was born. In addition, these additional molybdenum can also reduce the corrosion of some thermal organic acids.
