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The martensitic grades are straight chromium steels containing no nickel. Martensitic grades were developed in order to provide a group of stainless alloys that would be corrosion resistant and hardenable by heat treating. Of Austenitic Grades of stainless steel can be found HERE. More about the physical and chemical properties Physical and Chemical Properties of Austenitic Grades These grades are primarily used in the aircraft industry. Type 321 is made by the addition of titanium and Type 347 is made by the addition of tantalum/columbium. These types have been developed for corrosive resistance for repeated intermittent exposure to temperature above 800 degrees F. Requires molybdenum content of 4.00% min. Restricts maximum carbon content to 0.030% max. It is often used in stacks which contain scrubbers. The molybdenum must be a minimum of 2%.Ĭontains a higher percentage of molybdenum than 316 for highly corrosive environments. Type 316 is used in chemical processing, the pulp and paper industry, for food and beverage processing and dispensing and in the more corrosive environments. The molybdenum is used to control pit type attack. It also has molybdenum added to the nickel and chrome of the 304. It is used for chemical processing equipment, for food, dairy, and beverage industries, for heat exchangers, and for the milder chemicals.Ĭontains 16% to 18% chromium and 11% to 14% nickel. The most common of austenitic grades, containing approximately 18% chromium and 8% nickel. “L” grades are used where annealing after welding is impractical, such as in the field where pipe and fittings are being welded. This means only that the carbides which may have precipitated (or moved) to the grain boundaries are put back into solution (dispersed) into the matrix of the metal by the annealing process. You may hear the phrase “solution annealing”. People ask for “H” grades primarily when the material will be used at extreme temperatures as the higher carbon helps the material retain strength at extreme temperatures. 10% carbon and are designated by the letter “H” after the alloy.
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This results in the material being dual certified 304/304L 316/316L, etc. A case of having your cake and heating it too. There are a couple of reasons:Ĭarbon at high temperatures imparts great physical strengthįrequently the mills are buying their raw material in “L” grades, but specifying the physical properties of the straight grade to retain straight grade strength. You may ask why all stainless steels are not produced as “L” grades. For weldability, the “L” grades are used. By controlling the amount of carbon, this is minimized. This deprives the steel of the chromium in solution and promotes corrosion adjacent to the grain boundaries. Carbon in steel when heated to temperatures in what is called the critical range (800 degrees F to 1600 degrees F) precipitates out, combines with the chromium and gathers on the grain boundaries. 03% or under to avoid carbide precipitation. The letter “L” after a stainless steel type indicates low carbon (as in 304L). The “L” grades are used to provide extra corrosion resistance after welding. As long as the material meets the physical requirements of straight grade, there is no minimum carbon requirement. 03% carbon, but the spec does not require this. There is a misconception that straight grades contain a minimum of. The straight grades of austenitic stainless steel contain a maximum of. They cannot be hardened by heat treatment, but can be hardened significantly by cold-working. The austenitic stainless steels, because of their high chromium and nickel content, are the most corrosion resistant of the stainless group providing unusually fine mechanical properties. The most common austenitic alloys are iron-chromium-nickel steels and are widely known as the 300 series. Austenitic GradesĪustenitic grades are those alloys which are commonly in use for stainless applications. The sub-categories are austenitic, martensitic, ferritic, duplex, precipitation hardening and super alloys. Subsequently several important sub-categories of stainless steels have been developed. This development was the start of a family of alloys which has enabled the advancement and growth of chemical processing and power generating systems upon which our technological society is based. Hence the definition “Stainless Steels”, are those ferrous alloys that contain a minimum of 12% chromium for corrosion resistance. Over 50 years ago, it was discovered that a minimum of 12% chromium would impart corrosion and oxidation resistance to steel. The function that they perform cannot be duplicated by other materials for their cost. Stainless steels are primarily used when corrosion or oxidation is a problem.