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1、Type 654 SMOUNS S32654Design FeaturesOutstanding resistance to pitting, crevice, and general corrosion Extremely high resistance to chloride stress corrosion cracking Twice the strength of common austenitic stainless steels Excellent ductility and toughness Superior workability, formability, and wel
2、dabilityProduct Forms AvailablePlate Sheet Strip Bar Pipe and Tubing FittingsApplicationsCritical seawater and severe brackish water handling systems Chlorine and chlorine dioxide pulp bleaching systems Chemical processing equipment Desalination systems Hydrometallurgy Municipal waste incineration s
3、ystems Plate heat exchangersASTM Element S32654 TypicalCarbon 0.020 max 0.010 Chromium 24.0-25.0 24.0 Nickel 21.0-23.0 22.0 Molybdenum 7.0-8.0 7.3 Nitrogen 0.45-0.55 0.50 Copper 0.30-0.60 0.50 Sulfur 0.005 max 0.001 Phosphorus 0.030 max 0.020 Silicon 0.50 max 0.40 Manganese 2.00-4.00 3.0 Iron Balanc
4、e BalanceComposition, wt. pct. Table 1SpecificationsSolidification Range 2500-2445 Scaling Temperature in Air 1830 Sigma Phase Formation 1300-1800 Carbide Precipitation 840-1470 Hot Forming 2200-2000 Solution Annealing 2100 min. water quench Stress Relief Annealing 2100 min. water quenchTemperature
5、FCharacteristic Temperatures Table 2 General CharacteristicsWith unusually high levels of chromium, molybdenum, and nitrogen, Outokumpu 654 SMO achieves levels of chloride pitting and crevice corrosion resistance not previously possible with an austenitic stainless steel. Outokumpu was the first sta
6、inless steel producer to introduce a nitrogen- alloyed 6% molybdenum austenitic stainless steel with its innovative 254 SMO steel in the 1970s. Now Outokumpu leads the way to a new level of stainless steel technology with the reintroduction of 654 SMO.StructureAs shown in Table 2, 654 SMO is solutio
7、n annealed at 2100F minimum to achieve a fully austenitic stainless steel structure, although faint traces of intermetallic phases (sigma or chi phase) may be present and tolerated in the center of the heavier sections. These phases may also form on the grain boundaries in the metal during exposures
8、 in the range of 1100-1825F, with detrimental Plate, Sheet, Strip A 240, A 480 SA-240, SA-480 Pipe A 312, A 358 SA-312, SA-358 Tubing A 249, A 269 SA-249, SA-269 Bar A 276, A 479 SA-479 ASME Boiler and Pressure Vessel Code, Section VIII Div. 1, Code Case 2195-1 NACE MR0175UNS S32654 ASTM ASME Type 6
9、54 SMOeffects on corrosion resistance and toughness. The procedures for forming, welding, and heat treatment are designed to prevent this undesirable precipitation of intermetallic phase.Corrosion Resistance Pitting and Crevice CorrosionPitting and crevice corrosion are the most common forms of corr
10、osion for stainless steels. Both types of attack result in a highly localized form of corrosion which can lead to perforation in a short time with relatively little total weight loss. Both pitting and crevice corrosion are accelerated by more acidic conditions and by higher temperatures. With its hi
11、gh levels of chromium, molybdenum, and nitrogen, 654 SMO is the most resistant stainless steel ever produced.One method of estimating the pitting resistance is to use the pitting resistance equivalent (PRE), an index of pitting resistance based on statistical analysis of the effect of composition of
12、 stainless steels on a particular parameter assessing pitting resistance, most usually the critical pitting temperature (CPT) for a selected environment and test procedure. As seen in Table 3, the PRE for 654 SMO is far higher than it is for any of the other stainless steels.The critical pitting tem
13、perature is the highest temperature at which a stainless steel will resist attack in a particular environment. Two test procedures are common, one being ASTM G 48, Practice A, which measures the CPT by exposing coupons to a solution of 10% FeCl3 6H2O at a series of increasing temperatures until pitt
14、ing corrosion is observed. Another newer test is an electrochemical test ASTM G 150 using a test cell specially designed by the research team at Outokumpu. Both of these methods have been effective for all other stainless steels, including the 6Mo austenitic stainless steels, such as Outokumpu 254 S
15、MO. However, these tests are of limited use for 654 SMO because it is completely resistant to attack in these tests at 204F and 217F, the respective boiling points of the chloride media for these tests. So the best evaluation for 654 SMO is obtained by the more aggressive crevice corrosion tests. Ta
16、ble 4 shows critical crevice temperatures for 654 SMO in comparison with those for Alloy 625 and Alloy C-276, and for 254 SMO austenitic stainless steel. The test environments include ASTM G 48, Practice B, and the so-called “Green Death” solution designed to discriminate among the nickel-base alloys and their high levels of corrosion resistance. These test
