Stainless steel valves are usually used in the working medium has a certain corrosive occasions, the use of steel is usually 304,304 L, 316, 316L, this article will introduce you to the difference between these four stainless steel, hope for the future Work helpful!
304 stainless steel:
304 stainless steel is the most popular steel, as a wide range of steel, with good corrosion resistance, heat resistance, low temperature strength and mechanical properties; stamping, bending and other hot workability, no heat treatment hardening (non-magnetic , Then use the temperature -196 ℃ ~ 800 ℃).
Scope of application:
Household goods (1,2 class tableware, cabinets, indoor pipelines, water heaters, boilers, bathtubs)
Auto parts (windshield wipers, muffler, molded products)
Medical equipment, building materials, chemical, food industry, agriculture, ship parts
304L stainless steel (L is low carbon):
As a low-carbon 304 steel, in its normal state, its corrosion resistance is similar to 304, but after welding or after the elimination of stress, its resistance to grain boundary corrosion is excellent; in the case of no heat treatment, can also maintain good Of the corrosion resistance, the use of temperature -196 ℃ ~ 800 ℃.
Scope of application:
Used in anti-grain boundary corrosive requirements of high chemical, coal, oil industry, outdoor open-air machines, building materials, heat-resistant parts and heat treatment difficult parts.
316 stainless steel:
316 stainless steel due to the addition of molybdenum, so its corrosion resistance, atmospheric corrosion resistance and high temperature strength is particularly good, can be used in harsh conditions; processing hardening excellent (non-magnetic).
Scope of application:
Water, equipment, chemicals, dyes, paper, oxalic acid, fertilizer and other production equipment; photography, food industry, coastal areas facilities, ropes, CD rods, bolts, nuts.
316L stainless steel (L is low carbon):
As a low-carbon series of 316 steel, in addition to the same characteristics with the 316 steel, the anti-grain boundary corrosion excellent.
Scope of application:
Against the grain boundary corrosive special requirements of the product.
316 and 316L stainless steel are molybdenum-free stainless steel. 316L stainless steel in the molybdenum content is slightly higher than 316 stainless steel due to the molybdenum steel, the overall performance of the steel is better than 310 and 304 stainless steel, high temperature conditions, when the sulfuric acid concentration of less than 15% and higher than 85% Stainless steel has a wide range of uses. 316 stainless steel also has good properties of chloride erosion, so it is usually used in marine environments. 316L stainless steel maximum carbon content of 0.03, can be used after welding can not be annealed and the need for maximum corrosion resistance in the use.
316 stainless steel corrosion resistance is better than 304 stainless steel, in the pulp and paper production process has a good corrosion resistance. And 316 stainless steel is also resistant to erosion of marine and erosive industrial atmospheres. In general, 304 stainless steel and 316 stainless steel in the chemical corrosion resistance is not very different, but in some specific media are different. The initial development of stainless steel is 304, in some cases, this material is more sensitive to point corrosion (Pitting Corrosion). An additional 2-3% increase in molybdenum can reduce this sensitivity, so that the birth of the 316. In addition, these additional molybdenum can also reduce the corrosion of certain hot organic acids. 316 stainless steel almost become the food and beverage industry standard materials. Due to the shortage of molybdenum elements in the world and 316 stainless steel in the nickel content more, 316 stainless steel prices more expensive than 304 stainless steel Point corrosion is a phenomenon mainly caused by the deposition of stainless steel surface corrosion, which is due to lack of oxygen and can not form a protective layer of chromium oxide. Especially in small valves, the possibility of deposition on the valve plate is very small, so the point of corrosion is also rare. In all 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 medium chloride content is very high, then 316 stainless steel more suitable. In most cases, 304 stainless steel and 316 stainless steel corrosion resistance is not much difference, but in some cases may also be very different, specific circumstances need specific analysis. In general, the valve users should be aware of, because they will be based on the media to choose the container and pipe material, we do not recommend to recommend materials to the user.
In the continuous use of 1600 degrees below the continuous use and below 1700 degrees, 316 stainless steel has good resistance to oxidation. In the range of 800-1575 degrees, it is best not to continuously use 316 stainless steel, but in the temperature range outside the continuous use of 316 stainless steel, the stainless steel has good heat resistance. 316L stainless steel resistance to carbide precipitation better than 316 stainless steel, available above the temperature range.
Annealing at a temperature in the range of 1850 to 2050 degrees, then rapidly annealing, and then rapidly cooling. 316 stainless steel can not be superheated to harden.
316 stainless steel has good welding performance. All standard welding methods can be used for welding. Welding can be used according to the use of 316Cb, 316L or 309Cb stainless steel filler rod or welding electrodes. For optimum corrosion resistance, 316 stainless steel welded sections require post-weld annealing. If 316L stainless steel is used, no post-weld annealing is required.
Among all steels, the yield point of austenitic stainless steel is the lowest. Therefore, from the mechanical properties, austenitic stainless steel is not used in the best material stem, because to ensure a certain strength, the stem diameter will increase. The yield point can not be increased by heat treatment, but can be improved by cold forming.
Due to the extensive application of austenitic stainless steel, it is the impression that all stainless steel does not have magnetic properties. For the austenitic stainless steel, the basic can be understood as non-magnetic, hardened forged steel is indeed the case. But through the cold forming treatment of 304 will be a little bit of magnetic. For cast steel, if it is 100% austenitic stainless steel is no magnetic.
Low-carbon type of stainless steel:
Austenitic stainless steel corrosion resistance from the metal surface of the formation of chromium oxide protective layer. If the material is heated to a high temperature of 450 ° C to 900 ° C, the structure of the material will change and chromium carbide will form along the edge of the crystal. So that the oxide edge can not form a protective layer of chromium oxide, resulting in reduced corrosion resistance. This corrosion is called "intergranular corrosion".
Which developed a 304L stainless steel and 316L stainless steel to combat this corrosion. 304L stainless steel and 316L stainless steel are low carbon content, because the carbon content is reduced, so it will not produce chromium carbide, it will not produce intergranular corrosion.
It should be noted that the higher intergranular corrosion sensitivity does not mean that non-low carbon materials are more susceptible to corrosion. In the high chlorine environment, this sensitivity is also higher.
Please note that this phenomenon due to high temperature (450 ℃ -900 ℃). Usually the welding is the direct cause of this temperature. For soft valve seat conventional butterfly valve, because we are not on the valve plate for welding operation, so the use of low-carbon stainless steel and not much significance, but most specifications will require 304L stainless steel or 316L stainless steel.