The Society of Automotive Engineers (SAE) designates steel with SAE steel grades. These grades are four digit numbers which represent chemical composition standards for steel specifications. In terms of stainless steel, SAE has divided the metal into six principal categories, or series: 100 series, 200 series, 300 series, 400 series, 600 series, and 900 series.
100 series
The types of stainless steel in this series are generally used in furniture or other all purposes uses. This series, though hardenable through cold-working, is generally regarded is the lowest grade stainless steel and is for this reason dispreferred for his stress activities.
200 series
This group of alloys is similar to the more common 300 Series alloys described below as they are non-magnetic and have an austenitic structure. The basic Stainless Steel Grades 200 alloy contains 17% chromium, 4% nickel and 7% manganese. Although these alloys are somewhat more resistant to attack than the more common 300 series stainless steels, their overall performance is similar. Some proprietary grades related to the 200 series, have performance equal or superior to the best 300 series stainless steels.
These alloys are, however, not immune to attack and are very susceptible to concentration cell corrosion and pitting corrosion attack. When corrosion starts they usually corrode rapidly and nonuniformly.
This group of alloys are non-magnetic and have an austenitic structure. The basic Stainless Steel Grades 300 alloy contains 18% chromium and 8% nickel.
These alloys are subject to crevice corrosion and pitting corrosion. They have a range of incubation times in seawater ranging from essentially zero in the case of the free machining grades, such as Type 303, to 6 months to 1 year for the best alloys, such as Type 316. Indeed, type 316L, which is an extra low carbon grade of 316, is generally used in high end stainless steel watches such as Breitling and Tag Heuer and marine applications, as well exclusively in the fabrication of reactor pressure vessels for boiling water reactors, due to its high resistance to corrosion and high strength. They have also been widely used in facilities with mixed results. If used in an application where chloride levels are low or where concentration cell corrosion has been prevented through design, they are likely to perform well. When chloride levels are high and where concentration cells can occur, the performance of these alloys is often poor. They must always be selected with care for a specific application and the effect of potential non-uniform attack on system performance must be addressed.400 series
This group of alloys are magnetic and have a martensitic structure. The basic alloy contains 11% chromium and 1% manganese. These Stainless Steel Grades alloys can be hardened by heat treatment but have poor resistance to corrosion. They are subject to both uniform and non-uniform attack in seawater. The incubation time for non-uniform attack in chloride containing environments is very short, often only hours or a few days. Type 440 is a higher grade of cutlery steel, with more carbon, allowing for much better edge retention when properly heat-treated. It can be hardened to approximately Rockwell 58 hardness, making it one of the hardest stainless steels. Due to its toughness and relatively low cost, most display-only and replica swords or knives are made of 440 stainless.
600 Series
This series of stainless steels grade is commonly referred to as “Precipitation Hardening” stainless steels. These steels can be heat treated to high strength levels. They are subject to crevice corrosion and pitting in chloride containing environments and are also subject to stress corrosion cracking and hydrogen embrittlement. The incubation time for crevice corrosion and pitting in seawater is relatively short, often only a few days. The incubation time for stress corrosion cracking can be very short, sometimes measured in hours. The use of these Stainless Steel Grade in chloride containing environments is not normally recommended unless they are carefully selected, their heat treatment is carefully specified and controlled, and the effect of pitting and crevice corrosion is properly addressed.
900 Series
This is a non-stabilized low carbon high alloy austenitic stainless steel. The addition of copper to this grade gives it greatly improved resistance to strong reducing acids, particularly sulphuric acid. It is also highly resistant to chloride attack - both pitting / crevice corrosion and stress corrosion cracking. This grade is non-magnetic in all conditions and has excellent weldability and formability. The austenitic structure also gives this grade excellent toughness, even down to cryogenic temperatures. The 904L type (such as that used in Rolex watches) does have very substantial contents of the high cost ingredients nickel and molybdenum. Many of the applications in which this grade has previously performed well can now be fulfilled at lower cost by duplex stainless steel 2205 (S31803 or S32205), so it is used less commonly than in the past.
Credit - MATERIAL DETERIORATION PREVENTION AND CONTROL GUIDE OF ARMY MATERIAL, PARTONE, METALS (MlL HDBK-73S (MR)
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