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Austenitic stainless steels including molybdenum

a technology of stainless steel and molybdenum, which is applied in the direction of manufacturing tools, machines/engines, mechanical apparatuses, etc., can solve the problems of complex corrosion resistance, automotive exhaust system components and other automotive engine components are exposed to contamination, and certain automotive exhaust system applications are exposed to severe corrosion chemical environments. , to achieve the effect of less costly production and increased corrosion resistan

Inactive Publication Date: 2004-08-12
ATI PROPERTIES
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

"The present invention relates to a new corrosion-resistant material for use in high-temperature corrosive environments, such as automotive exhaust system components. The material is an iron-base alloy that is less costly and more readily available than the commonly used superalloys. The technical effect of the invention is to provide a material that can withstand high temperatures and corrosive environments, while also being formable and having resistance to hot salt corrosion and various other corrosion types. This material can be used in flexible connectors and other automotive exhaust system components, providing high corrosion resistance and durability."

Problems solved by technology

Corrosion resistance is complicated by the fact that components used for certain automotive exhaust system applications are exposed to severely corrosive chemical environments at elevated temperatures.
In particular, automotive exhaust system components and other automotive engine components are exposed to contamination from road deicing salts under conditions of elevated temperature due to the hot exhaust gases.
The stainless steel and other metal components subjected to these conditions are susceptible to a complex mode of corrosive attack known as hot salt corrosion.
However, road deicing salt deposits may attack and degrade this protective oxide layer.
As the protective oxide layer is degraded, the underlying metal may be exposed and become susceptible to severe corrosion.
Alloys for use in automotive exhaust system flexible connectors often experience conditions in which elevated temperature exposure occurs after the alloy has been exposed to contaminants such as road deicing salts.
Degradation of the connectors may be quite rapid under such conditions.
Therefore, simple air oxidation testing may be inadequate to reveal true resistance to corrosive degradation in service.
Type 316Ti stainless steel corrodes more rapidly when exposed to elevated temperatures and, therefore, is not generally used in automotive exhaust system flexible connectors when temperatures are greater than approximately 1200.degree. F.
Although alloys of this type are excellent choices for automotive exhaust system flexible connectors, they are quite expensive compared to Type 316Ti alloys.
However, none of those alloys provide high corrosion resistance, especially when exposed to elevated temperatures and corrosive contaminants such as road deicing salts.

Method used

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  • Austenitic stainless steels including molybdenum
  • Austenitic stainless steels including molybdenum
  • Austenitic stainless steels including molybdenum

Examples

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example 1

[0037] Certain embodiments of stainless steels of the present invention were prepared and evaluated for resistance to corrosion in high temperature, corrosive environments. Two heats were melted with a target composition including, by weight, 19 to 23% chromium and 30 to 35% nickel. The first alloy had a target molybdenum concentration of 2%, and the second alloy had a target molybdenum concentration of 4%. The actual compositions of the heats of the invention are shown in Table 1 as Sample 1 and Sample 2. Sample 1 contained 1.81% molybdenum and Sample 2 contained 3.54% molybdenum. The alloy Samples 1 and 2 were prepared by a conventional method, specifically, by vacuum melting the alloy components in concentrations to approximate the target specification. The formed ingots were then ground and hot rolled at approximately 2000.degree. F. (1093.degree. C.) to about 0.1 inches thick by 7 inches wide. The resulting plate was grit blasted and descaled in an acid. The plate was then cold...

example 2

[0057] Austenitic stainless steels can be subject to sensitization when exposed to high temperatures. As is known in the art, sensitization is the intergranular precipitation of chromium carbides in austenitic stainless steel when the steel is exposed to temperatures in the approximate range of 800-1500.degree. F. (427-816.degree. C.). A result of sensitization is that regions of the affected grains are depleted in chromium content, promoting susceptibility to intergranular corrosion in the presence of aqueous chlorides. In order to investigate the susceptibility to sensitization of alloys within the present invention, the present inventor prepared and tested five 50 lb. VIM heats having the chemical compositions shown in Table 3. Table 3 identifies the heats as Heats 6-10 so as to distinguish them from Samples 1-5 in above Example 1. The heats included varying additions of the carbide-forming elements titanium and niobium. Heat 6 was formulated with an aim of zero titanium and zero...

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Abstract

An austenitic stainless steel comprises, by weight, 9 to 23% chromium, 30 to 35% nickel, 1 to 6% molybdenum, 0 to 0.03% titanium, 0.15% to 0.6% aluminum, up to 0.1% carbon, 1 to 1.5% manganese, 0 to less than 0.8% silicon, 0.25 to 0.6% niobium and iron. Embodiments of austenitic stainless steels according to the present invention exhibit enhanced resistance to corrosion. Thus, the stainless steels of the present invention may find broad application as, for example, automotive components and, more particularly, as automotive exhaust system flexible connectors and other components, as well as in other applications in which corrosion resistance is desired.

Description

[0001] The present application claims priority under 35 U.S.C. .sctn. 120 from co-pending U.S. patent application Ser. No. 09 / 641,317, filed Aug. 18, 2000.FEDERALLY SPONSORED RESEARCH[0002] Not ApplicableTECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION[0003] The present invention relates to oxidation and corrosion resistant austenitic stainless steels. More particularly, the present invention relates to austenitic stainless steels adapted for use in high temperature and corrosive environments, such as, for example, use in automotive exhaust system components. The austenitic stainless steels of the invention find particular application in components exposed to temperatures up to 1800.degree. F. (982.degree. C.) and to corrosive environments, such as, for example, chloride-rich waters.DESCRIPTION OF THE INVENTION BACKGROUND[0004] In the manufacture of automotive exhaust system components, concurrent goals are to minimize both cost and weight, while also maintaining the in...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): C22C30/00C22C38/02C22C38/04C22C38/06C22C38/40C22C38/44C22C38/48C22C38/50F01N13/16
CPCC22C38/02C22C38/04C22C38/48C22C38/44C22C38/06C22C38/001C22C38/002C22C38/42C22C38/50C22C38/58B21D26/033B23K31/02F01N13/1816F01N2530/04H05B3/0014H05B3/141H05B3/16H05B3/40
Inventor RAKOWSKI, JAMES M.
Owner ATI PROPERTIES
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