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Stainless Steel Comparator Welcome to AK Steel’s Family of Stainless Steels This product comparator reviews the fundamentals of stainless steels. It compares the types, grades, chemistries, finishes and applica- tions of stainless produced by AK Steel. The basic product information contained in the following pages will help you match the application needs with a specific grade of stainless steel. What is Stainless Steel? In the early nineteen hundreds, metallurgists noticed that chromium had a greater attraction to oxygen than iron did so they added the element chromium to steel. Studies prove that when at least 10% chromium was added, the chrome united with oxygen to form a very tight transparent layer over the steel surface that prevented rusting by precluding further oxidation. This transparent layer is self-healing when damaged by scratches, wear or denting. Stainless steels are materials of enduring beauty. These steels also withstand the corrosive attack of many acids. They possess strength and toughness at both extremes of the temperature scale, yet can be fabricated into intricate shapes for many uses. Because of this outstanding versatility, stainless deserves careful consideration for any product where one or more of the following requirements are involved: Corrosion Resistance Strength at Elevated Temperatures Strength and Ductility at Cryogenic Temperatures Oxidation Resistance at High Temperatures Appearance Abrasion Resistance Let’s Go to Class There are more than 250 different stainless steels. These various grades of stainless are divided into five major families or classes. The general classes have been developed to consolidate the chemistries and mechanical properties required to meet specific cus- tomer application needs. Martensitic Stainless Steels These steels of the 400 series usually contain a minimum of 11.5% up to 18% chromium and have higher levels of carbon than ferritics. They are capable of being heat treated to a wide range of useful hard- ness and strength levels, and are used extensively in cutlery, sports knives and multipurpose tools. Ferritic Stainless Steels This group of steels in the 400 series contains 10.5% to 20% chro- mium for corrosion resistance and resistance to scaling at elevated temperatures. They are nonhardenable by heat treating and are always magnetic. Ferritic stainless is used in applications where resis- tance to corrosion is important, such as automotive emission control exhaust systems. Austenitic Stainless Steels Austenitic stainless steels are the most specified grades produced because of their excellent formability and corrosion resistance. All 200 and 300 series steels are austenitic and con- tain 15% to 30% chromium and 2% to 20% nickel for enhanced surface quality, forma- bility and increased corrosion and wear resistance. They are non-magnetic in the annealed condition and depend- ing on the composition, primarily the nickel content, they become slightly magnetic when cold worked. These steels are used for automotive trim, cookware, pro- cessing equipment and a variety of industrial applications. Precipitation-Hardening Stainless Steels There are two general areas of PH grade stainless steels; martensitic and semi-austenitic. The martensi- tic group includes 17-4 PH® and 15-5 PH® chromium- nickel, with columbium and copper additions. They develop their high strength and hardness through heat treatment, which precipitates the copper. The marten- sitic PH steels are used in aerospace, chemical and petrochemical, and food processing applications. The semi-austenitic grades are 17-7 PH® and PH 15-7 Mo®. They are austenitic in the annealed state, but martensitic in the hardened condition. 17-7 PH stainless has excellent high strength and fatigue properties, and is used in aerospace compo- nents. PH 15-7 Mo stainless is used in applications requiring high strength and hardness, such as retain- ing rings, springs and aircraft bulkheads. Duplex Stainless Steels These alloys have a mixture of austenite and ferrite in their structure. They exhibit characteristics of both phases with higher strength and ductility. Nitrogen is added to second generation duplex alloys and provides strength and increased weldability. AK Steel’s NITRONIC® 19D has good cyclic oxidation, high strength and excellent stress corro- sion resistance, and the 2205 alloy provides very good pitting and uniform corro- sion resistance, high strength and high resistance to stress corrosion cracking. Alloys Make the Grade The manufacture of quality stainless steel, from heat to heat and year to year, demands precise control of raw material ingredients and melting practices. Exact quantities of presorted scrap and alloying elements are delivered to the melting furnaces so that the heats or lots will be within specified composition ranges. Those composition ranges typically include a group of chemical elements for each grade of stainless steel. Alloying Elements Following is a brief look at the alloying elements found in stainless steels and their functions. Chromium forms a surface film of chromium oxide to make the stainless steel corrosion resistant. It also increases the scaling resistance at elevated temperatures. Nickel stabilizes the austenitic structure and increases ductility, making stainless steel easier to form. It increases high temperature strength and corrosion resistance, particularly in industrial and marine atmos- pheres, chemical, food and textile processing industries. Silicon increases scaling resistance by forming a tight initial scale, which will withstand cyclic temperature changes. It resists carburizing at high temperatures and slightly increases tensile strength and hardness. Small amounts of silicon are added to all grades of stainless for deoxidizing. Manganese promotes the stability of austenite, at or near room temperature and improves hot working properties. Addition of up to 2% manganese has no effect on strength, ductility and toughness. Manganese is important as a partial replace- ment of nickel in 200 series stainless grades. Molybdenum increases corrosion resistance, strength at elevated temperatures, and creep resistance. It expands the range of passivity and counter- acts tendency to pit especially in chloride environments. Aluminum is a very strong ferrite former and lowers the hardenability of stainless steel. It improves scaling resistance. Carbon strengthens stainless steel but promotes the formation of precipitates harmful to corrosion resistance. Columbium combines with carbon to reduce suscepti- bility to intergranular corrosion. It acts as a grain refiner and promotes the formation of ferrite. Copper is added to stainless steels to increase their resistance to certain corrosive environments. It also decreases susceptibility to stress corrosion cracking and provides age-hardening effects. Titanium combines with carbon to reduce susceptibility to intergranular corrosion. It acts as a grain refiner and pro- motes the formation of ferrite. 400 12 – .015 Al – .15 Corrosion resistance comparable Applications requiring improved to 409, better surface finish finish over Type 409, caskets 400 Cb 11.5 – .01 Cb – .15, Al – .15 Corrosion resistance comparable Electrical cabinetry to 409, better surface finish 410S 12 – .015 Low-cost, general purpose Mild corrosive service Fractionation towers 11 Cr-Cb 11 – .01 Si – 1.30, Cb – .35 More oxidation and creep resistant High-temperature use, furnaces, than 409 and 439 auto exhaust components 41003 11 .40 .02 Si – .40, Mn – .80 Excellent weldability, toughness and Tubing for bus frames, hopper cars, fabricating characteristics chutes, storage tanks and shipping containers 430 16.5 – .05 General-purpose corrosion Appliance, food equipment, mis- resistance cellaneous automotive, flue liners 434 16.5 – .065 Mo – 1.0 Improved corrosion resistance Automotive trim over 430 436 16.8 – .06 Mo – 1.0, Cb – .40 Controlled roping Automotive trim 439 17 – .012 Ti – .30 Wet corrosion and oxidation Heating units, welded tubing and resistance auto exhaust components Aluminized 439 17 – .012 Ti – .30 Economical corrosion oxidation, Heating units, welded tubing and salt and cosmetic corrosion resistance auto exhaust components 435 Mod. 19.5 – .02 Cb – .70, Cu – .50 Improved formability Automotive trim and weldability 18 SR 17 – .02 Al – 1.70, Ti – .20 High-temperature scaling Industrial ovens, heat resistance exchangers, furnace liners 18 Cr-Cb 17.5 – .02 Ti – .25, Cb – .55 Oxidation resistant, creep resistant Heat exchangers, furnace com- ponents, auto exhaust systems 444 17.5 – .015 Ti – .25, Cb – .15 Oxidation, corrosion and stress Water heaters, solar panels, Mo – 2.0 cracking resistance engine components 410H 11.5 – .18 Increased hardenability Cutlery, rulers 420 12.5 – .38 Increased hardenability Cutlery, multifunctional tools 420 HC 12.5 – .42 Increased hardenability Cutlery, scissors 409 Ni 11 0.85 .02 Ti – .20, Mn – .75 Corrosion resistance superior to Coal handling equipment, exhaust mild and low-carbon steels flanges, transportation equipment Aluminized 409 11 – .01 Ti – .20 Economical corrosion, oxidation, Heat exchangers, furnace liners, Aluminum coating salt and cosmetic corrosion resistance automotive exhaust systems Typical Chemical Composition % Stainless Types Cr Ni C Other Significant Characteristics Typical Applications Elements Ferritic Stainless Steels 409 11 – .01 Ti – .20 Economical corrosion and Heat exchangers, furnace liners, oxidation resistance automotive exhaust systems Martensitic Stainless Steels 410 11.5 – .14 General purpose, hardenable Cutlery, machine parts AK Steel NITRONIC® 30 16 2.5 .02 Mn – 8.5, N – .17 High strength, abrasion resistance, Hose clamps, truck and bus good formability frames, bulk solids handling equipment, coal buckets and hopper cars 301 17 7 .10 High strength, high work hardening Wheel covers, springs, hose clamps, food processing equipment 304 18 8 .06 Multipurpose Food equipment, tubing, architectural trim 304L 18 9 .02 Low carbon minimizes carbide Welded parts and other 304 precipitation during welding applications 309S 22 12.5 .05 Oxidation resistant Heating elements, furnace parts 316 16.5 10.5 .05 Mo – 2 Pitting corrosion resistance Heat exchangers, chemical equipment, marine applications 316L 16.5 10.8 .02 Mo – 2 Low carbon minimizes carbide Welded Type 316 applications precipitation during welding 321 17 9.5 .02 Ti – 5XC min. Titanium stabilized Heat exchangers to intermediate temperatures, aircraft 15-5 PH® 14.5 4.5 .05 Cu – 3.5, Cb – .25 High strength and hardness, Aerospace, chemical and ferrite free petrochemical, food processing 17-7 PH® 17 7 .085 Al – 1.0 High strength, excellent fatigue Aerospace components, flat properties springs PH 15-7 Mo® 14.5 7.5 .085 Mo – 2.0, Al – 1.0 High strength and hardness Retaining rings, springs, aircraft bulkheads 2205 22 5.5 .02 Mo – 3.0 High strength, low thermal expansion, Heat exchangers, pipe, pressure high resistance to stress corrosion vessels, tanks, fans, shafts and cracking and corrosion fatigue press rolls Typical Chemical Composition % Stainless Types Cr Ni C Other Significant Characteristics Typical Applications Elements Austenitic Stainless Steels 201 16 3.5-5.0 .06 Mn – 6-7.5 Low nickel, high work hardening Hose clamps, cookware Precipitation-Hardening Stainless Steels 17-4 PH® 15.5 4.5 .05 Cu – 3.0, Cb – .25 High strength and hardness Aerospace, chemical and petrochemical, food processing Duplex Stainless Steels NITRONIC 19D 21 1.25 .02 Cu – 0.5, Mn – 5.0 Ferrite/austenite matrix, good cyclic Tubing, water heater tanks oxidation, high strength and good stress corrosion resistance Stainless Steel Aluminized Steel Type 1 Stainless Steels Aluminum coated 409 and 439 stainless steels were developed to provide the automotive industry with longer life exhaust system materials. The Type 1 hot-dipped aluminum coating provides excellent resistance to mu�er condensate corrosion and pitting from road salt which allows the exhaust system to remain virtually rust free, thus retaining its good appearance. Black Coat™ Stainless Steels AK Steel Black Coat stainless steels a re available as Type 409, Aluminized 409, Type 439, and AK Steel 18 Cr-Cb. The Black Coat system is a multi-layer surface coating continuously applied to stainless steel coils. It is especially useful for applications requiring an attractive cosmetic appearance at high temperatures. Black Coat stainless steel products provide enhanced formability compared to bare stainless alloys. These products are particularly useful in applications involving the cold end of exhaust systems such as mu�ers and tail pipes. Color Lock™ AK Steel Color Lock stainless steel consists of a �uoropolymer paint system applied to a clean, pretreated and primed stain- less steel coil. The �uoropolymer top coat is a Duranar® high- performance coating designed for architectural coil coating applications. The coating features excellent color retention and chalk, corrosion, chemical and pollution resistance as well as good �exibility and adhesion. Color Lock is available in a wide range of colors for use in metal roo�ng, mansard roofs, fascias, so�ts and specialty accent applications. AK Steel Coated Stainless Steels Surface �nish is an important element in any speci�cation or pur- chase order for stainless steel regardless of the intended end use. And, for those applications in which appearance is important, �nish is a design element and must be speci�ed. I n architecture or other highly visible applications, the appear- ance of stainless steel is a critical design element and speci�cation of the wrong �nish can alter the desired e�ect. In consumer prod- ucts, the gleam of well-polished stainless steel has strong sales appeal. In institutional kitchen, restaurant, and hospital applica- tions, properly �nished stainless helps to emphasize the feeling of cleanliness. I n addition to visual appeal of polished stainless, there are a number of functions served by properly prepared stainless surfaces. In sanitary applications, polished stainless steel not only looks clean, but also is easy to clean and keep clean. There are also economic considerations in specifying �nish. For example, a cold rolled bright annealed �nish might be speci�ed instead of a more expensive No. 8 polished �nish; or some proprietary rolled �nishes might serve the same purpose as a No. 4 polished �nish. A knowledge of �nishes can sometimes result in signi�cant savings. Reflections on Finish Glossary of Stainless Sheet and Strip Terms Abrasion– resistant Steels — A family of steel products developed for those applications involved in sliding and impact abrasion. Air Hardening Steel — Steels, such as low chromium and martensitic stainless steels, that do not require quenching to produce hardening by the martensitic reaction. Alloying — Alloying, in the com- mon metallurgical sense, refers to the dissolving of one or more elements in a metal to produce a metallic mix or alloy. Balanced Analysis — A term used to indicate the relative quantities of alloying elements necessary to produce the speci�ed properties or metallurgical structures in a speci�c type of steel. Bright Annealed — Bright anneal- ing prevents the formation of undesirable scale that occurs on the surface of steel during the annealing process. During typ- ical annealing, t he heated steel combines with oxygen in the air to form a layer of oxide on the steel’s surface. In bright annealing, the steel is heated in a furnace �lled with hydrogen or nitrogen gases, which prevents oxide scale formation. Stainless Steel Sheet Finishes No. 1 — A rough, dull surface that results from hot rolling to the speci�ed thick- ness followed by annealing and descaling. No. 2D — A dull �nish produced by cold rolling to gauge, then annealing and pick- ling in acid to remove scale and oxide from an open air anneal. No. 2B — A re�ective cold- rolled �nish produced in the same manner as a 2D Sheet Finish, except that a light temper pass on polished rolls is performed on the annealed and pickled product. This is the general-purpose cold-rolled �nish that can be used as is, or as a preliminary step to polishing. Bu�ng — A polishing operation utilizing a very �ne abrasive compound on a prepared rotating wheel, which con- tacts the work surface. Duplex — Steels exhibiting both austenitic and ferritic structures. Intergranular Corrosion — Cor- rosion that occurs at the grain boundaries in austenitic stainless steels that have been heat treated between 850˚ and 1450˚F. Usually caused by precipitation of the chrome carbides. Orange Peel — Roughening of the surface sometimes encountered in form- ing or drawing stainless steels that have a coarse grain structure. Oxide Film Theory — An explana- tion of passivity based upon the supposi- tion that a relatively impermeable layer of oxide forms on the surface of stainless steel that retards attack by corrosives. Passivity — The ability of certain metals and alloys, especially the stainless steels, to resist normal corrosion to the point where the metal remains unat- tacked. ©2007 AK Steel Corporation AK Steel, the AK Steel logo, 17-4 PH, 15-5 PH, 17-7 PH, PH 15-7 Mo, NITRONIC and Unibrite are registered trademarks of AK Steel Corporation. G reystone, Black Coat and Color Lock a re trademarks of AK Steel Corporation. Duranar is a registered trademark of PPG Industries. Precipitation Hardening — Har- dening that is caused by the precipitation of a metallic compound from a supersatu- rated solid solution. Retained Austenite — A tendency in martensitic alloys that increases with the alloy and carbon content and with rate of cooling, to retain at room temper- ature a fraction of the austenite phase that is stable at the high temperature and which fails to transform to martensite on cooling. Roping — A fibrous surface pat- tern that can occur in 400 series sheet and strip when stretched or drawn. This pattern is always in the rolling direction and may require metal removal by polish- ing if a smooth surface is desired. Semi-hardening — A hardening treatment for martensitic steels in which the metal is quenched from such a low austenitizing temperature that only a portion of the metal transforms, yielding a semimartensitic alloy particularly adaptable to machining operations. Sensitization — A term used to describe the condition of the austenitic stainless steels resulting from heating them in the temperature range of approx- imately 800˚ to 1500˚F and cooling to room temperature. When the metal is held in the sensitization range, the carbon in the steel combines with some of the chromium and precipitates as chromium carbide at the grain boundaries. This depletes chromium in the area of the grain boundaries and makes the metal susceptible in those areas to attack in some corrosive media. Sigma Phase — A brittle and hard intermetallic compound of the general formula FeCr, but having a composition range of broad extension, tending to form particularly in the ferrite of high chro- mium stainless steels when heated for a period of time in the general range of 925˚ to 1750˚F. Subzero Treatment — Part of a hardening treatment in which the marten- sitic steel is quenched from the austeniz- ing temperature and brought immediately to a very low temperature to promote the development of martensite — particularly useful for steels tending to have “retained austenite”. Bright Annealed — A highly reflective cold-rolled finish produced by cold rolling to gauge, then bright annealing in a protective inert atmosphere. This process results in no scaling of the product, leaving a bright reflective