904L stainless steel plate is the gold of a high alloy austenitic stainless steel carbon content is very low. It is specially developed for a highly corrosive environment. At first, its role was to corrode the environment that was resistant to dilute sulfuric acid. As it has been successfully tested, 904L stainless steel is now standardized in many countries and is identified as being able to make pressure vessels.
In terms of performance, 904L stainless steel plate has excellent resistance to pitting and crevice corrosion, stress corrosion cracking and intergranular corrosion resistance as well as other common chromium nickel austenitic steels, and has good machinability and solderability. In hot forging, the maximum heating temperature can reach 1180 degrees C, and the minimum stopping forging temperature is not less than 900. Its thermoforming can be carried out within a temperature range of 1000 – 1150 degrees C. Its heat treatment process is 1100 – 1150 C, and it is cooled fast after heating.
Although it can be welded with a general welding process, the most suitable welding process is manual arc welding and tungsten arc welding. When manual arc welding is used to weld stainless steel plate less than 6 mm, the diameter of the welding rod is less than or equal to 2.5 millimeters. When the plate thickness is higher than 6 mm, the diameter of the welding rod is less than 3.2 mm. When heat treatment is needed after welding, it can be treated quickly after heating at 1075 – 1125 C. The filler metal can be used for the use of tungsten electrode in argon arc welding, and the weld is treated by pickling and passivation.
The metallographic structure of 904L stainless steel plate is completely austenitic. Compared with ordinary austenitic stainless steel with high molybdenum content, 904L is not sensitive to the precipitation of ferrite and alpha phase.
Because the carbon content of 904L stainless steel is very low, the highest is only about 0.020%, so in the ordinary heat treatment and welding, no carbide will be precipitated. This eliminates the risk of intergranular corrosion after ordinary heat treatment and welding. Because of the high content of chromium, nickel and molybdenum and the addition of copper elements, 904L can be passivated in the reductive environment, such as sulfuric acid and formic acid. The high nickel content also has a slower corrosion rate in the active state. In pure sulfuric acid in the concentration range of 0-98%, the use temperature of 904L stainless steel can be as high as 40 degrees C. In the pure phosphoric acid in the 0-85% concentration range, its corrosion resistance is very good. In the industrial phosphoric acid produced by wet process, the effect of impurities on corrosion resistance is great. In all kinds of phosphoric acid, the corrosion resistance of 904L stainless steel is better than that of ordinary stainless steel. In strong oxidizing nitric acid, compared with steel high alloy containing molybdenum, corrosion resistance ability is weak.
In hydrochloric acid, the use of 904L stainless steel is limited to a lower concentration of 1-2%. At this concentration range. The corrosion resistance of 904L is better than that of conventional stainless steel. 904L steel has a high resistance to point corrosion. The anti crevice corrosion ability of the chloride solution is also good. The high nickel content of 904L reduces the corrosion rate at the jute pit and the gap. Ordinary austenitic stainless steel can be sensitive to stress corrosion in a chloride rich environment at temperatures above 60 degrees Celsius, and this sensitization can be reduced by increasing nickel content in stainless steel. Because of high nickel content, 904L has high resistance to stress corrosion cracking in chloride solution, concentrated hydroxide solution and hydrogen sulfide rich environment.
The field of application of 904L stainless steel plate is mainly concentrated in the industrial field. For example, petroleum, petrochemical equipment, reactor in petrochemical equipment and so on. The storage and transportation of sulfuric acid, such as heat exchangers, etc. The main parts of flue gas desulfurization unit in power plant are the tower body, flue, gate plate, inner part, spray system and so on. There are also the scrubber and fans in the organic acid treatment system.
Source: China 904L Stainless Steel Plates Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)