Ferritic Stainless Steels are, in principle, ferrite at all temperatures. This is achieved by a low content of austenitic forming elements, mainly nickel, and a high content of ferrite forming elements, mainly chromium. Ferritic types, such as 4003 and 4016, are mainly used for household utensils, catering equipment and other purposes where corrosion conditions are not particularly demanding.
Steel with high chromium content, such as 4762 with 24% chromium, are used at high temperature where their resistance to sulphurous flue gages is an advantage. However, the risk of 475 °C embrittlement and precipitation of brittle sigma phase in high-chromium steel must always be taken into consideration. Ferritic stainless steel, such as 4521 with extremely low carbon and nitrogen contents, find greatest use where there is a risk of stress-corrosion cracking.
Ferritic stainless steels have slightly higher yield strength (Rp 0.2) than austenitic stainless steels, but they have less elongation at fracture. Another characteristic that distinguishes ferritic stainless steel from austenitic material is that ferritic stainless steels have much lower strain hardening. Ferritic Stainless Steel grades have been developed to provide a group of stainless steel to resist corrosion and oxidation, while being highly resistant to stress corrosion cracking. These steels are magnetic but cannot be hardened or strengthened by heat treatment. They can be cold worked and softened by annealing. As a group, they are more corrosive resistant than the martensitic grades, but generally inferior to the austenitic grades. Like martensitic grades, these are straight chromium steels with no nickel. They are used for decorative trim, sinks, and automotive applications, particularly exhaust systems.
Type 430
The basic ferritic stainless steel grade, with a little less corrosion resistance than Type 304. This type combines high resistance to such corrosives as nitric acid, sulfur gases, and many organic and food acids.
Type 405
Has lower chromium and added aluminum to prevent hardening when cooled from high temperatures. Typical applications include heat exchangers.
Type 409
Contains the lowest chromium content of all stainless steels and is also the least expensive. Originally designed for muffler stock and also used for exterior parts in non-critical corrosive environments.
Type 434
Has molybdenum added for improved corrosion resistance. Typical applications include automotive trim and fasteners.
Type 436
Type 436 has columbium added for corrosion and heat resistance. Typical applications include deep-drawn parts.
Type 442
Has increased chromium to improve scaling resistance. Typical applications include furnace and heater parts.
Type 446
Contains even more chromium added to further improve corrosion and scaling resistance at high temperatures. Especially good for oxidation resistance in sulfuric atmospheres.
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 and formability are less than that of the austenitic grades. The corrosion resistance is comparable to that of the austenitic grades in certain applications. Thermal conductivity is about half that of carbon steels. Ferritic stainless steel 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 and, hence, are sometimes used for automotive trim and appliance molding. They also find use in functional applications where cost is a major factor, e.g., automotive exhaust systems, catalytic converters, radiator caps, and chimney liners. These grades can be hardened by cold rolling, but cannot be hardened as much as the austenitic alloys. Stainless Steel – FerriticAlloy (UNS Designation) End UseComposition nominal wt%SpecificationsDensity lb/in3 (g/cm3)Tensile Strength ksi. (MPa)0.2% Yield Strength ksi. (MPa)Elong- ation %Hardness
ATI 409 HP S40900, S40910/S40920/S40930 Exhaust systems, mufflers, manifolds, exhaust stainless steel pipes, catalytic converters, tail stainless steel pipes, thermostats fuel filters, culverts, home heating systems, electrical transformer cases, caskets,heat exchanger tubing, farm equipment, blades, vanes in standby power generation turbines and jet engine sound-deadening devices at airportsC 0.03 max, Mn 1.0 max, P 0.04 max, S 0.02 max, Si 1.0 max, Cr 10.5-11.7, Ni 0.5, N 0.03, Ti 0.05 min, (Ti+Cb) [0.08+8x(C+N)] min-0.75 max, Fe BalanceASTM A 176 ASTM A240/A240M ASME SA-240/SA-240M0.280 (7.75)55 min (380 min)25 min (170 min)20 min88RockwellB max
AL 409 Cb S41045 Exhaust componentsC 0.03 max, Mn 1.0 max, P 0.045 max, S 0.03 max, Si 1.0 max, Cr 12.0-13.0, Ni 0.5 max, N 0.03 max, Cb 9x(C+N) min-0.60 max.ASTM A2400.280 (7.75)55 min (380 min)30 min (205 min)22 min80 Rockwell B max
AL 410S S41008 Tower packing, distillation trays, automotive exhaust components, and other high-temperature applicationsC 0.08 max, Mn 1.0 max, P 0.04 max, S 0.03 max, Si 1.0 max, Cr 11.5-13.5, Ni 0.6 max, Fe BalanceASTM A240 ASTM A1760.280 (7.75)60 min (415 min)30 min (205 min)22 min89 Rockwell B max
AL 412 S41003 Rail cars, coal handling equipment, sugar processing equipment, mining equipment, storage bins and hoppers, bus framesC 0.03 max, Mn 1.5 max, Si 1.0 max, P 0.04 max, S 0.03 max, Cr 10.5-12.5, Ni 1.5 max, Fe BalanceASTM A2400.280 (7.75)66 min (455 min)40 min (275 min)18 min20 Rockwell C max
430 S43000 Interior and exterior trim applications such as sinks, sink rims, appliance trim, counter tops, dish washers, range hoods, flatware, roofing, siding and restaurant equipmentC 0.12 max, Mn 1.0 max, Si 1.0 max, Cr 16.0-18.0, Ni 0.75 max, Fe BalanceASTM A2400.278 (7.70)65 min (450 min)30 min (205 min)22 min89 Rockwell B max
AL 430 Ti S43036 Welded stainless steel pipes.C 0.10 max, Mn 1.0 max, P 0.04 max, S 0.03 max, Si 1.0 max, Cr 16-19.5, Ni 0.75 max, Ti (5xC) min-0.75 max, Fe balanceASTM A268 A5540.280 (7.75)60 min (415 min)35 min (240 min)20 min90 Rockwell B max
Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)
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