Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel

Definitions

• This invention relates to low carbon plus nitrogen free-machining austenitic stainless steel.
• U.S. Patent 3,902,398 discloses that the corrosion resistance of resulfurized free-machining austenitic stainless steels can be significantly improved in acid beverage syrups by restricting their manganese content to a maximum of about 0.50% and by controlling the manganese to sulfur ratio such that chromium or chromium-rich sulfides are formed instead of manganese or manganese-rich sulfides. Chromium sulfides are more corrosion resistant than are manganese or manganese-rich sulfides in acid beverage syprups, and improve machinability bvut not nearly to the same extent as manganese or manganese-rich sulfides. As also disclosed in U.S.
• Patnt 3,902,398 the loss in machinability related to the replacement of manganese or manganese-rich sulfides by chromium sulfides can be partly offset by lowering the carbon content of such steels to below about 0.035%.
• Another object of this invention is to provide machined chromium-nickel austenitic stainless steel fittings and articles with improved machinability and high corrosion resistance, especially in acid soft drink and beverage syrups.
• the steels of this invention have particular advantage in the application of fittings and articles used for handling and dispensing acid soft drink syrups. With these steels, the decrease in machinability normally associated with the replacement of manganese or manganese-rich sulfides by chromium or chromium-rich sulfides is offset by the lower than conventional carbon plus nitrogen contents and by the addition of copper. Further, the copper bearing steels of this invention exhibit much better corrosion resistance in acid soft drink syrups, which is an additional advantage over prior art steels used in these applications.
• the steels and machined fittings and articles of this invention consist essentially of the following elements, by weight percent: carbon plus nirogen - up to 0.06% chromium - 16 to 20% nickel - 6 to 14% manganese - up to 0.60% sulfur - 0.15 to 0.50% phosphorus - 0 to 0.20% silicon - 0 to 1% molybdenum - 0 to 1% copper - 0 to 3.00% boron - 0 to 0.01% iron - balance, except for incidental impurities
• Carbon and nitrogen are normally present in the steels of this invention, but to obtain the desired improvements in machinability, it is essential in the steels of this invention to control the total carbon plus nitrogen levels below 0.06% and preferably below about 0.05 or 0.04%.
• 16 to 20% chormium and preferably 17 to 19% chromium is required in the steels of this invention to obtain the required degree of corrosion resistance in acid soft drink syrups and to adjust for the amount of chromium involved in the formation of chromium or chromium-rich sulfides.
• a maximum of 0.60% manganese is required to minimize the formation of manganese or manganese-rich sulfides which are known to have an adverse effect on corrosion resistance in acid soft drink syrups and still permit the use of low cost scrap revert melting practices.
• the manganese content must be controlled below about 0.50 and the maximum manganese to sulfur ratio is 1 to 1.
• a minimum of 0.15 and a maximum of 0.50% of sulfur are needed in the steels of this invention to obtain the desired degree of machinability.
• Copper in amounts of about 0.75 to 3.00 and preferably in the amounts of 1.00 to 2.50 is very useful for increasing the stability of the austenite, for improving the machinability, and particularly for increasing the corrosion resistance of the steels of this invention in acid soft drink syrups.
• Molybdenum is not necessary in the steels of this invention, but may be used in amounts up to about 1 percent for improving general corrosion resistance.
• Silicon and phosphorus may be present in amounts up to 1% and 0.20%, respectively, in the steels of this invention.
• the remainder of the composition is essentially iron, except for incidental impurities usually associated with the production of stainless steels and except for up to 0.01% boron which may be added to improve hot workability.
• Table I lists the resulting chemical compositions of the laboratory heats. Other than variations in carbon, nitrogen, manganese, molybdenum and copper, all the alloys are essentially 0.40 percent sulfur, 18 percent chromium, 10 percent nickel, free-machining austenitic stainless steels.
• the machinability of the experimental alloys of Table I was evaluated using the aforementioned test specimens and a drill machinability test.
• the drill machinability test the total time taken to drill a specified number of holes to a specified depth in the material to be evaluated is compared to the total time to drill the same number of holes to the same depth in a material having known, established machining characteristics.
• the ratio between the time taken to drill the established material and the time taken to drill the test material multiplied by 100 provides a drill machinability rating (DMR) for the test material.
• DMR drill machinability rating
• Heat number V506 containing 0.079 percent carbon plus nitrogen about the concentrations of these elements in a typical steel of this type, was assigned a DMR of 100.
• steels having DMR values of greater than 100 have better drill machinability than conventional, typical steels of this type; and values less than 100, poorer drill machinability.
• increasing DMR values indicate improved drill machinability.
• Table I presents the results of one drill machinability testing of the laboratory steels. Allowing for some experimental scatter in the data and considering the steels containing about 0.30 percent copper and 0.025 to 0.106 percent carbon plus nitrogen, i.e., heat number V489, V505, V560, V603, V603A, V506, and V541, it is clearly evident that lowering the total combination of carbon plus nitrogen content of the steel results in improved drill machinability. Steels within the scope of the invention, i.e., heat number V489, V505, V560, and V603, all display improved machinability compared to heat number V506.
• H2S hydrogen sulfide

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
• Heat Treatment Of Steel (AREA)
• Rolling Contact Bearings (AREA)
• Treatment Of Steel In Its Molten State (AREA)
• Glass Compositions (AREA)
• Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)
• Hard Magnetic Materials (AREA)

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Citations (6)

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• 1987
  • 1987-08-19 CA CA000544906A patent/CA1330628C/en not_active Expired - Fee Related
  • 1987-09-08 JP JP62223211A patent/JPH0611901B2/ja not_active Expired - Lifetime
  • 1987-09-10 EP EP87307995A patent/EP0265062B1/de not_active Expired - Lifetime
  • 1987-09-10 AT AT87307995T patent/ATE92973T1/de active
  • 1987-09-10 DE DE87307995T patent/DE3786980T2/de not_active Expired - Fee Related

Patent Citations (6)

Non-Patent Citations (3)

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