ATI Allegheny Ludlum produces a wide variety of stainless steel alloys known for their excellent corrosion and heat resistance.
Austenitic stainless steels include both the 200 and 300 series alloys, which are hardenable only by cold working. The 300 series alloys contain chromium and nickel as their major alloying additions. Type 304 (also known as 18-8) is the most widely used of all stainless steel alloys. The 200 series alloys possess mechanical properties and corrosion resistance similar to 300 series alloys. They also exhibit high hardness and high yield strength as well as excellent ductility and are non-magnetic in the annealed condition. The 200 series alloys were originally developed to conserve nickel by partially replacing it with manganese. The reduced nickel content results in the 200 series alloys having a lower and more stable cost than their 300 series equivalents.
Designing with Cold Rolled Stainless Steel
Ferritic stainless steels, which are part of the 400 series of stainless alloys, have chromium as their major alloying element and are typically low in carbon content. Ductility is less than that of the austenitic grades. The corrosion resistance is comparable to the austenitic grades in certain applications. Thermal expansion is less than that of austentic stainless steels and comparable to carbon steels. Ferritic stainless steels are magnetic. They generally have good ductility and can be welded or fabricated without difficulty. These grades can be processed to develop an aesthetically-pleasing bright finish. Ferritic grades do not work harden as much as austenitic grades during cold working.
Martensitic stainless steels contain chromium in the range of 11% to 17% and have a carbon content ranging from 0.10% to 0.65%. This radically changes the behavior of the martensitic alloys relative to the ferritic 400 series alloys. Martensitic grades offer a good combination of corrosion resistance and superior mechanical properties. They can be hardened by heating to a high temperature, followed by rapid cooling (quenching). Tempering heat treatments for martensitic grades are tailored to develop the desired combination of hardness, strength, toughness and resistance to abrasion and erosion for the application. The martensitic grades are usually sold in the annealed condition. This allows the customers to cut or form the parts before they are thermally hardened.
Specialty Stainless Steels
Duplex stainless steels have a structure that contains both ferrite and austenite. Duplex alloys have higher strength and better stress-corrosion cracking resistance than austenitic steels and greater toughness than ferritic alloys, especially at low temperatures. The corrosion resistance of duplex alloys depends primarily on their composition, especially the amount of chromium, molybdenum, and nitrogen they contain. Duplex alloys are often divided into three sub-classes: Lean Duplex (ATI 2102® duplex, ATI 2003® duplex, and ATI 2304™ duplex alloys), Standard Duplex (ATI 2205™ duplex alloy), and Superduplex (ATI 255™ duplex and *Zeron® 100 duplex alloys).
*Zeron® 100 is a registered trademark of Rolled Alloys Ltd.
Precipitation-hardening stainless steels contain chromium and nickel as the predominant alloying elements. They are designed to be formable in the solution-annealed condition. The addition of elements such as copper, aluminum, titanium and molybdenum allows these alloys to be hardened by heat treatment to strength levels several times that of Type 304. Precipitation-hardening stainless steels may be martensitic or semi-austenitic. Corrosion resistance is usually better than that of straight chromium ferritics.
Superaustenitic stainless steels are austenitic alloys that contain higher levels of elements such as chromium, nickel, molybdenum, copper, and nitrogen. This results in superior strength and corrosion resistance.
Superferritic stainless steels are ferritic alloys that contain higher levels of chromium and molybdenum. Reduced carbon and nitrogen contents enhance toughness and ductility. Superferritic alloys have improved high-temperature properties and better performance in corrosive environments compared to conventional ferritic stainless steels.
Most of ATI Allegheny Ludlum's stainless steels are offered in sheet, strip and plate product forms.
Nickel, Cobalt and Special Purpose Alloys
ATI Allegheny Ludlum's nickel and cobalt alloys were developed to withstand severe service conditions. The nickel- and cobalt-based alloys known as superalloys are usually used at high temperatures where stainless steels have inadequate strength and/or oxidation resistance. Typical superalloy applications require materials that can withstand high stress and elevated temperatures for extended periods of time. Another group of Ni-based alloys has been designed primarily for use in highly corrosive environments where superior resistance to localized corrosion and stress corrosion cracking is needed. Also included in this category are special purpose alloys, which are used primarily for their controlled thermal expansion; e.g., ATI 36™ and ATI 42™, or their soft magnetic properties; e.g., ATI 4750™ and Moly Permalloy.
Titanium alloys offer an exceptional combination of strength, low density and corrosion resistance. Their high strength to weight ratio makes them ideal for aerospace applications. These alloys provide outstanding resistance to chlorides and many other corrosive environments. They also have excellent biocompatibility, which has led to their use in implanted medical devices. ATI Allegheny Ludlum offers a wide range of titanium and titanium alloy flat-rolled products including sheet, strip, foil, and plate in both alloyed and commercially pure grades.