AK Steel produces a complete family of stainless steels. Our Stainless Steel Comparator offers a brief description of all of our stainless steels. For more detailed information on specific stainless steel alloys, please view the product literature provided below each section.
Ferritic
Ferritic, or nonhardenable stainless steels, are classified in the 400 series, usually with 10% to 20% chromium content, and are normally specified due to superior corrosion resistance and resistance to scaling at elevated temperatures. With inherent strength greater than carbon steels, ferritics provide an advantage in many applications where thinner materials and reduced weight are necessary, such as automotive emission control systems. They are nonhardenable by heat treating and are always magnetic. Commercially available AISI grades are Type 409, Aluminized 409, 410S, AK Steel 11 Cr-Cb, 430, 434, 436, 439, Aluminized 439, AK Steel 18 SR, 444 and AK Steel 18 Cr-Cb. Typical applications for ferritic stainless steels include petrochemical, automotive exhaust systems, heat exchangers, furnaces, appliances and food equipment to name a few.
Martensitic
Martensitic, or hardenable stainless steels, are classified in the 400 series, usually with 11.5% chromium up to 18% chromium, with higher levels of carbon than ferritics, and are capable of being heat treated to a wide range of hardness and strength levels. Commercially produced AISI grades of this class are Type 410, 410H, 420, and 420HC. Martensitic stainless steels are used extensively in cutlery, sport knives and multi-purpose tools.
Austenitic
Austenitic, or nonmagnetic stainless steels, are classified in the 200 and 300 series, with 16% to 30% chromium and 2% to 20% nickel for enhanced surface quality, formability and increased corrosion and wear resistance, and are nonhardenable by heat treating. These steels are the most popular grades of stainless produced due to their excellent formability and corrosion resistance. All austenitic steels are nonmagnetic in the annealed condition. (Depending on the composition, mainly the nickel content, austenitics do become slightly magnetic when cold worked.) Austenitic stainless steel grades include: Type 201, Nitronic 30, 301, 304, 305, 309S, 316, 316L, and 321. Austenitics are used for automotive trim, cookware, food and beverage equipment, processing equipment, and a variety of industrial applications.
Precipitation Hardening
Precipitation Hardening stainless steels, or hardenable chromium-nickel alloys, are classified as martensitic or semi-austenitic. They develop their high strength and hardness through a variety of heat treatments. They are used in aircraft parts and commonly viewed as bar alloys, but are also available in flat roll products with a very high strength-to-weight ratio. The martensitic PH steels are used in aerospace, chemical and petrochemical, and food processing applications. 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. Other grades of PH alloy stainless steels include 17-4 PH and 15-5 PH. The PH grades achieve high tensile properties in heat treated conditions. Applications for PH alloy steels include aerospace components, flat springs and retaining rings, among others.
Duplex Alloy
Duplex alloy stainless steels contain a mixture of austenite and ferrite in their structure, and exhibit characteristics of both phases with higher strength and ductility. Nitrogen is added to the second generation duplex alloys and provides strength and improved weldability. NITRONIC 19D is an example of a duplex stainless steel grade with good cyclic oxidation, high strength and good stress corrosion cracking resistance. 2205 duplex stainless steel is a grade that offers very good pitting and uniform corrosion resistance, high strength and high resistance to corrosion cracking. Typical applications for duplex alloys are heat exchangers, tubes, pipes, pressure vessels and tanks in the oil and gas and chemical processing industries.