ATI - Model 409 Cb - Ferritic Stainless Steels
From Advanced Alloys and Solutions - Standard Stainless Sheet Products
ATI 409HP (UNS S40900) ferritic stainless steel was introduced by ATI in 1961 to provide improved oxidation and corrosion resistance for automotive exhaust systems in comparison to carbon steel. The alloy was designated 'MF-I', indicating its end use: automotive mufflers. The good fabricability of this alloy, combined with its basic corrosion resistance and economy have significantly broadened the utility of ATI 409HP™ stainless.
Product Details
Since its introduction, the ATI 409HP™ alloy has been widely used in automotive exhaust systems for manifolds, exhaust pipes, catalytic converters, mufflers, tail pipes and other components. ATI 409HP™ stainless steel sheet has also found many other applications such as in culverts, home heating systems, automotive thermostats and fuel filters, electrical transformer cases, caskets, heat exchanger tubing, and various farm equipment components. Plate has been used as blades and vanes in standby power generation turbines and as jet engine sound-deadening devices at airports.
The performance of ATI 409HP™ (UNS S40900) ferritic stainless steel in most applications is excellent. However, some industry applications have resulted in intergranular corrosion of weld heat-affected zones. The result of research into this problem led to ASTM's re-definition of ATI 409HP™ stainless steel. The old UNS S40900 with 0.08% carbon maximum and Ti>5xC was found to be inadequate, but there was no consensus among users how to define the new grade. Therefore, three new grades of ATI 409HP™ stainless steel were created,
UNS S40910, S40920, and S40930, all with reduced (0.03% maximum) carbon but with somewhat different stabilization formulae. Under ASTM A240, orders for S40900 material may be fulfilled by supplying any one of the new 409 grades unless the purchaser states additional requirements. Composition requirements for the three varieties of ATI 409HP™ alloy are shown in the composition table below.
The ATI 409HP™ stainless steel alloys contain nominally 11 percent chromium for greatly enhanced corrosion resistance in comparison to carbon steel. It is an excellent choice for all automotive exhaust system applications where 11 percent chromium provides sufficient resistance to oxidation and corrosion. Hot end exhaust applications may require an 18 percent chromium alloy such as ATI 439 (18 Cr-Ti, UNS S43035), ATI 468™ (18 Cr-Ti + Cb, UNS S46800), ATI 436S™ (18 Cr-1.2 Mo-Ti), or ATI 441HP™ (18 Cr-0.5 Cb-Ti) alloys. Other nonautomotive applications also will benefit from the excellent fabricability which the ATI 409HP™ allnv nrovirifis
The UNS S40930 alloy contains balanced amounts of titanium and columbium to provide resistance to sensitization and intergranular corrosion which might occur in the heat affected zones of welds or in base metal following other thermal exposures. A low incidence of titanium nitride surface imperfections is also a characteristic of this alloy. The balance of stabilizing elements is designed to optimize weldability without post-weld annealing to restore ductility.
ATI 409Cb™ alloy (UNS S40945) was developed to eliminate the problems encountered when brazing S40900 stainless steel that was stabilized only with Ti. The dual-stabilized S40930 version of ATI 409HP™ alloy usually provides the same benefit and now is used for brazing applications.
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