Stainless Steel Alloys

Stainless steel alloys are austenitic, ferritic, martensitic, precipitation hardened, and duplex metals that are available in a wide variety of grades, shapes, and sizes. Austenitic stainless steels have excellent corrosion resistance, unusually good formability, and increased strength due to cold working. They are non-magnetic or only slightly magnetic. Two hundred (200) series austenitic stainless steels contain chromium, nickel, and manganese. Three hundred (300) series austenitic stainless steels contain chromium and nickel. Ferritic stainless steels are straight-chromium, 400 series metals that cannot be hardened by heat treatment, and only moderately hardened by cold working. They are magnetic, have good ductility, and resist corrosion and oxidation. Martensitic stainless steels, another type of straight-chromium 400 series metals, are magnetic, fairly ductile, and resist corrosion in mild environments. Some products can be heated to tensile strengths that exceed 200,000 psi (1379 MPa). Precipitation hardened (PH) stainless steels are chromium-nickel metals, some of which contain alloying elements such as copper or aluminum. They can be hardened by solution treating and aged to high strength. Duplex stainless steel alloys have improved mechanical properties and consist of a combination of ferritic and austenitic phases. 

Many stainless steel alloys meet the compositional standards of the Unified Numbering System (UNS), a specification established by the American Society for Testing and Materials (ASTM), the Society of Automotive Engineers (SAE), and metal trade associations such as the American Iron and Steel Institute (AISI). The UNS assigns metals and alloys a lettered prefix and a five-digit number. Stainless steel alloys belong to the UNS S category and have designations such as UNS S20100. AISI grades are another common specification for stainless steel alloys. Other standards include casting grades, European Norm (EN), American Society of Mechanical Engineers (ASME) standards, and U.S. military specifications (MIL-SPEC). QQ and QQS prefixes are used to designate specific MIL-SPEC metals. Grades with low carbon levels (L or S grades) provide improved weldability and corrosion resistance. Grades that contain superalloys, tool steels, clad or bimetal materials, or that feature a metal matrix composite are also available.

Suppliers provide stainless steel alloys in many stock shapes and forms. Semi-finished stock shapes are suitable for part fabrication by machining, assembly, or other processes. They are also used as feedstock for casting, forging, and spinning. Common stock shapes and forms for stainless steel alloys include bars, rods, tubes, plates, profiles, sheets, strips, shims, spheres, foil, wire, billets, slabs, and blooms. Materials are also supplied as billets, ingots, powders, fillers, and reinforcements. Round, hexagonal, coil, and hollow stock are also available. There are two basic types of anodes. Plating anodes are in used in plating or electroplating processes. Sacrificial anodes are used to protect stainless steel or other metal structures from corrosion.    

Selecting stainless steel alloys requires an analysis of dimensions, production processes, and performance features. Outer diameter (OD), inner diameter (ID) overall length, and overall thickness are important dimensions. Most materials are cast, wrought, extruded, forged, cold-finished, hot-rolled, or formed by compacting powdered metals or alloys. Electric arc furnaces are used to produce very clean metals and alloys with fewer inclusions and lower variability. Performance features for stainless steel alloys include resistance to corrosion, heat, wear, and shock. Cold worked metals have good compressive strength and wear resistance under room temperature conditions. Free-machined metals contain lead, selenium, or sulfur additives.

• Stainless Steel
  One of the features that characterize stainless steels is a minimum 10.5% chromium content as the principal alloying element. Four major categories of wrought stainless steel, based on metallurgical...
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• Let The Chips Fly
  Copper-rich alternatives to conventional AISI austenitic stainless steels sport similar mechanical and corrosion properties but are much easier to machine. Ugine Stainless & Alloys Inc....
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• Stainless Steel
  Anyone who lives by the ocean knows that stainless steel is not stain proof but just what it says, it stains less. In the presence of a strong chloride ion (found in the air by the ocean) the iron in...
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Part Numbers for Stainless Steel Alloys