Stainless steel is a kind of steel, steel refers to the amount of carbon (C) in the following 2% is called steel, more than 2% is iron. Steel in the smelting process to add chromium (Cr), nickel (Ni), manganese (Mn), silicon (Si), titanium (Ti), molybdenum (Mo) and other alloying elements to improve the performance of steel so that steel has a corrosion resistance (that is, not rust) is we often say that stainless steel.
Stainless steel in the smelting process, due to the addition of alloying elements of different varieties, different varieties of the amount of different. Its characteristics are also different, in order to distinguish the crown on different steel numbers.
Common classification of stainless steel
1. 304 stainless steel
304 stainless steel is the most common kind of steel, as a widely used steel, has good corrosion resistance, heat resistance, low temperature strength and mechanical properties; Stamping, bending and other thermal process ability is good, no heat treatment hardening phenomenon (no magnetic, then use the temperature -196℃ ~ 800℃).
Scope of application: household articles (1, 2 tableware, cabinets, indoor pipelines, water heaters, boilers, bathtubs); Auto parts (windshield wiper, muffler, mold products); Medical Appliances, Building Materials, Chemistry, Food Industry, Agriculture, Ship Parts
2. 304L stainless steel (L is low carbon)
As a low carbon 304 steel, in the general state, its corrosion resistance and 304 just similar, but after welding or stress elimination, its resistance to grain boundary corrosion ability is excellent; In the case of no heat treatment, can also maintain good corrosion resistance, the use of temperature -196℃ ~ 800℃.
Scope of application: used in the chemical, coal and petroleum industries with high requirements of resistance to grain boundary corrosion of outdoor machines, building materials heat resistant parts and parts with difficulties in heat treatment.
3. 316 stainless steel
316 stainless steel because of the addition of molybdenum, so its corrosion resistance, atmospheric corrosion resistance and high temperature strength is particularly good, can be used under harsh conditions; Excellent work hardening (non magnetic).
Scope of application: sea water equipment, chemical, dyestuff, paper making, oxalic acid, fertilizer and other production equipment; Photographs, food industry, coastal facilities, ropes, CD rods, bolts, nuts.
4. 316L stainless (L is low carbon)
As the low carbon series of 316 steel, in addition to the same characteristics with 316 steel, its resistance to grain boundary corrosion is excellent.
Scope of application: special requirements to resist grain boundary corrosion products.
Performance Comparison
1. Chemical composition
Stainless steels 316 and 316L 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 the steel is better than 310 and 304 stainless steels. Under high temperature conditions, when the concentration of sulfuric acid is less than 15% and more than 85%, 316 stainless steels have a wide range of uses. 316 stainless steel also has good and chloride erosion properties, so it is commonly used in Marine environments. 316L stainless steel has a maximum carbon content of 0.03. Suitable for applications where post-weld annealing is not possible and where maximum corrosion resistance is required.
2. Corrosion resistance
The corrosion resistance of 316 stainless steel is better than that of 304 stainless steel. It has good corrosion resistance in the production process of pulp and paper. And 316 stainless steel is also resistant to Marine and aggressive industrial atmosphere erosion. In general, 304 stainless steel and 316 stainless steel in the resistance to chemical corrosion properties of little difference, but in some specific media are different.
304 stainless steel was originally developed, which was sensitive to Pitting Corrosion in certain cases. Adding an extra 2-3% molybdenum reduced this sensitivity, resulting in 316. In addition, these additional molybdenum can reduce the corrosion of some hot organic acids.
316 stainless steel has almost become the standard material in the food and beverage industry. Due to the worldwide shortage of molybdenum and the higher nickel content in 316 stainless steel, 316 stainless steel is more expensive than 304 stainless steel.
Pitting corrosion is a phenomenon mainly caused by corrosion deposited on the surface of stainless steel, which is due to lack of oxygen and cannot form a protective layer of chromium oxide. Especially in small valves, there is little chance of deposition on the disc, so pitting is rare.
In various types of water medium (distilled water, drinking water, river water, boiler water, sea water, etc.), 304 stainless steel and 316 stainless steel corrosion resistance is almost the same, unless the content of chloride ion in the medium is very high, at this time 316 stainless steel is more appropriate. In most cases, the corrosion resistance of 304 stainless steel and 316 stainless steel is not much different, but in some cases may be very different, need to be analyzed on a case-by-case basis.
3. Heat resistance
316 stainless steel has good oxidation resistance in discontinuous use below 1600 degrees and continuous use below 1700 degrees. In the range of 800-1575 degrees, it is best not to continuous effect of 316 stainless steel, but in the temperature range of continuous use of 316 stainless steel, the stainless steel has good heat resistance. 316L stainless steel has better resistance to carbide precipitation than 316 stainless steel, which can be used in the above temperature range.
4. Heat treatment
Annealing is performed in the temperature range 1850 to 2050 degrees, followed by rapid annealing and then rapid cooling. 316 stainless steel cannot be overheated to harden.
5. The welding
316 stainless steel has good weld ability. All standard welding methods can be used for welding. According to the purpose of welding, the 316CB, 316L or 309CB stainless steel packing rod or electrode can be used for welding. In order to obtain the best corrosion resistance, the welding section of 316 stainless steel needs to be annealed after welding. Post weld annealing is not required if 316L stainless steel is used.
Post time: Feb-23-2022