High temperature, scale resistant, for heat exchangers Higher alloy content for corrosion/heat resistance, for welding rod/wire Low carbon, economical grade, not seawater resistant but weldableĮxtra-low carbon improves resistance to post-weld corrosion Higher work hardening, for trailer bodies, fastenersįree machining version of 302, for screw machining Low nickel equivalent of 302, used for kitchenware Low nickel equivalent of 301, used in flatware Some of the steels with suffixes (L, S, etc.) have not been included, nor have many of the specialty PHSSs.ĭescription of strengths, characteristics, and applications Table 1 below describes many of the AISI stainless steels, their strengths, and typical applications. With good corrosion resistance and weldability akin to that of austenitic stainless steel, they are used in a variety of special applications-on offshore platforms and in pressure vessels, for instance, where strength is imperative. Duplex Stainless Steelĭuplex steels have structures that combine both ferritic and austenitic phases, giving them almost twice the strength of austenitic varieties. A-286 alloy was one of the first of the so-called superalloys. Some of these PHSSs are austenitic, some are martensitic, and some fall somewhere in between. This special heat-treating process increases the metal’s resistance to stress corrosion cracking. Temperature resistance is increased by adding titanium, as in Type 321, a popular material in aerospace applications.Ī relatively new grade of stainless steels, sometimes called PHSSs and carrying identifiers such as 15-5, 17-4, and 17-7 PH, are precipitation hardened. An “L” after the grade indicates improved weldability under the harshest of welding conditions.
The improved corrosion-resistant 316 is used for industrial applications and is considered the most corrosion-resistant of the austenitic stainless steels. The economical 304, sometimes called food-grade, is used for general-purpose corrosion-resistant applications where welding-related corrosion is of concern. This group is the most commonly used of all the stainless steels, notably Type 302. These steels have relatively low carbon content, which makes them weldable. Austenitic Stainless SteelĪdding nickel (8-20%) to the chromium-iron alloy produces a steel that is austenitic at room temperature, with a face-centered cubic structure that resists corrosion, and whose magnetic field is one of a soft magnet (ie, it can be magnetized in an electric field, but not permanently). Martensitic stainless steel is magnetic and, with a high carbon content, difficult to weld. Type 416 is considered free-machining and has the best machining characteristics of all the stainless steels it is used for many turned SS parts. AISI Type 410, for example, is used for making food-machine parts, pump shafts, etc., while Type 403 is used in high-heat applications such as turbines. Martensitic stainless steels tend to be used in specialty applications. Although unable to be hardened to the level of iron-carbon martensite, martensitic stainless steel can be sufficiently hardened to produce rust-resistant cutlery, surgical instruments, ball valves and seats, for example. Martensitic Stainless SteelĪdding carbon (up to 2%) to the chromium-iron alloy increases the alloy’s hardenability. where corrosion resistance, ductility, formability, and cost are important, and strength is not a concern. It is an inexpensive grade and is often used for kitchen equipment, architectural/ornamental applications, etc. It cannot be hardened through heat treatment but can be cold-worked to increase hardness. The addition of chromium (>17%) to a steel alloy stabilizes the ferritic phase of the alloy, making a material that is highly corrosion-resistant, if not exceptionally strong. The principal types of stainless steels include: This article briefly discusses some of the popular grades of stainless steel as well as the settings in which these grades excel. AISI Type 316 SS, containing the alloying element molybdenum, is even more resistant to chemical attack than Type 304, making it useful for exposure to seawater, brine, sulfuric acids, and other corrosives found in the industrial environment. For example, AISI Type 304 SS, having a chromium-nickel constituent and low carbon, is popular for its good corrosion resistance, cleanability, and formability, making it popular for many everyday items such as kitchen sinks. Although there are many grades of stainless steel only a dozen or so are used with any regularity. Stainless steel is an iron-chromium alloy that contains anywhere from 10 to 30% chromium which gives the metal high resistance to corrosion.
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