CPC F28F 21/083 (2013.01) [B22D 11/002 (2013.01); C21D 6/002 (2013.01); C21D 8/0226 (2013.01); C22C 38/04 (2013.01); C22C 38/20 (2013.01); C22C 38/22 (2013.01); C22C 38/38 (2013.01)] | 3 Claims |
1. A ferritic stainless steel for an exhaust system heat exchanger, the ferritic stainless steel comprising, by weight percent, 0.001 to 0.01% of carbon (C), 0.001 to 0.01% of nitrogen (N), 0.2 to 1% of silicon (Si), 0.1 to 2% of manganese (Mn), 10 to 30% of chromium (Cr), 0.001 to 0.1% of titanium (Ti), 0.001 to 0.015% of aluminum (Al), 0.51 to 0.60% of niobium (Nb), 0.01 to 2.5% of molybdenum (Mo), and the balance of iron (Fe) and other unavoidable impurities, further comprising any one or more 0.01 to 0.15% of copper (Cu), 0.0002 to 0.001% of magnesium (Mg), and 0.0004 to 0.002% of calcium (Ca),
wherein the number of inclusions existing in a ferrite matrix in which a length of a longer side is greater than 2 μm and satisfying Formula 1 is 5 ea/mm2 or more, and the inclusions comprise two or more of Al2O3, MgO, SiO2 and CaO:
L/T≥3 Formula 1
wherein L is the length of the longer side of each inclusion and T is a length of a shorter side of the inclusion;
wherein a composition of the inclusions satisfies Formulae 3 and 4:
% (Al2O3)+% (MgO)+% (SiO2)+% (CaO)>90% Formula 3%
(Al2O3)+% (MgO)<50% Formula 4
wherein % (Al2O3), % (MgO), % (SiO2) and % (CaO) mean the content (% by weight) of each inclusion;
wherein a sound absorption index of the ferritic stainless steel is 7.0*10−4 or more.
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