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
  • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
• • 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
  • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese

Definitions

• the present invention relates to a nonporous, high nitrogen-chromium-manganese, austenitic stainless steel, and to a method for producing it.
• austenitic stainless steels are available in a variety of structures exhibiting a range of mechanical properties which, combined with their excellent corrosion resistance, makes them highly versatile from a design standpoint. Of them, austenitic stainless steels generally possess the best corrosion resistance and the best strength at elevated temperatures. Austenitic stainless steels have generally been comprised of iron, chromium and nickel.
• a high nitrogen-chromium-manganese, austenitic stainless steel characterized by high strength, good corrosion resistance and excellent ductility in the annealed condition.
• an austenitic steel wherein the elements are carefully balanced to insurethe integrity of its austenitic structure and wherein sufficient chromium and manganese are present to provide a nonporous structure.
• the steel contains from 0.85 to 3% nitrogen, from to 30% chromium and from to 45% maganese. At first glance it appears to be somewhat similar to the steels disclosed in U.S. Pat. Nos. 2,778,731 and 2,745,740. However, the steel of US. Pat. No.
• 2,778,731 has a maximum equated chromium and manganese content below the minimum equated sum of chromium and manganese imposed upon the steel of the present invention and US. Pat. No. 2,745,740 does not disclose a composition balanced within the hereinbelow discussed austeniticity and porosity equation limitations imposed upon the present invention, as exemplified by the specific alloys therein. Still other references disclose relatively high nitrogen contents, but yet maximum contents below the minimum taught herein. These references are US. Pat. No. 2,909,425 and an article entitled Study of Austenilic Stainless Steels With High Manganese and Nitrogen Contents, which appeared on pages 399412 of Revue de Metallurgie, No. 5, May, 1970.
• the nonporous, austenitic stainless steel of the present invention has a composition consisting essentially of, in weight percent, from 10 to 30% chromium, from .15 to 45% manganese, from 0.85 to 3% nitrogen, up to 1% carbon, up to 2% silicon, balance essentially iron and residuals.
• its elements are balanced in accordance with the following equations.
• Equation 1 is a measure of the steels austeniticity and Equation 2 is an indicator of its porosity or lack thereof. Steelswhich do not satisfy the equations are outside the scope of the invention. As a general rule, the steel of the invention is melted at an ambient pressure of about one atmosphere, and this method of making it is incorporated as a part of the present invention.
• the particular form in which nitrogen is added is not critical. Illustrative forms includes activated nitrogen, cyanides, and high nitrogen ferro-chrome.
• Nitrogen a strong austenitizer, is present in amounts of from 0.85 to 3 percent. At least 0.85 percent is required as it is the steel s primary strengthening element. An upper limit of 3 percent is imposed as higher nitrogen contents appear to be unrealistic from a melting standpoint. A preferred nitrogen content is from 1.05 to 1.5 percent.
• Chromium is present in amounts of from 10 to 30 percent. At least 10 percent is required in order to give the steel its outstanding corrosion resistance. Chromium also has a secondary effect upon the strength of the steel and is a primary element in increasing the steels solubility for nitrogen. An upper limit of 30 percent is imposed as chromium is a ferrite former and excessive amounts of ferrite might form with higher lev els, and in turn degrade the steels properties. A preferred chromium content is from 15 to 27 percent. Steels with chromium contents below 15 percent and above 27 percent are difficult to process. Those with contents below 15 percent exhibit a greater tendency to hot short while those with contents in excess of 27 percent exhibit a greater tendency to crack during handling and forming.
• Manganese is present in amounts of from 15 to 45 percent. At least 15 percent, and preferably 21 percent is necessary as manganese is an austenitizer and since manganese increases the steels solubility for nitrogen. An upper limit of 45 percent, and a preferred upper limit of 30 percent, is imposed for economic considerations, and since manganese exhibits a tendency to attack furnace refractories.
• Carbon is a powerful austenitizer and strengthener and is present in amounts up to 1 percent. lts content must, however, be controlled as it can disadvantageously remove chromium from solid solution by combining therewith to form chromium carbides, and since it can reduce the steel s solubility for nitrogen by occupying interstitial sites normally filled by nitrogen. A preferred maximum carbon content is 0.15 percent. Higher carbon contents necessitate higher annealing temperatures to put the carbon into solution.
• Silicon levels are maintained below 2 percent and preferably below 1 percent. Higher levels increase the inclusion content of the steel to an undesirable degree, and moreover, tie up excessive amounts of manganese inthe form of manganese silicates.
• the steel may also contain a number of residuals. These residuals include elements such as copper, molybdenum, phosphorus, sulfur, tungsten, cobalt and nickel.
• Equation 1 The carbon, nitrogen, manganese, chromium and silicon values for both the austenitic and duplex heats were inserted into the following equation, discussed hereinabove and referred to as Equation 1 therein:
• Table V compares the 0.2% yield strength, the ultimate tensile strength, the elongation and the hardness for austenitic heat .1 with duplex heat V. These proper- -ties are compared after hot rolling, after annealing at 1,950F for 7 minutes, and after cold reductions of 10, 25.8.05! 5.11%
• austenitic heat J is superior to duplex heat V.
• Heat J had better properties than heat V after hot rolling, after annealing, and after cold rolling.
• Ferrite diminishes the steels yield strength, ultimate tensile strength, elongation and hardness. In addition, it detrimentally affects the steels corrosion resistance and promotes the formation of undesirable sigma phase.
• the steel of this invention has utility in a wide range of applications. Included therein are high strength fasteners, motor/generator retaining rings, marine cable, and castings for pump housings.
• a substantially nonporous, austenitic stainless steel consisting essentially of, in weight percent, from 10 to 30% chromium, from 21 to 45% manganese, from 0.85 to 3% nitrogen, up to 1% carbon, up to 2% silicon, balance essentially iron and residuals; said elements being balanced in accordance with the following equations:
• a substantially nonporous austenitic stainless steel according to claim 1 having up to 1% silicon.
• a substantially nonporous austenitic stainless steel according to claim 1 having from 15 to 27% chromium, from 21 to 30% manganese, from 1.05 to 1.5% nitrogen, up to 0.15% carbon and up to 1% silicon.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Heat Treatment Of Steel (AREA)
• Silicon Compounds (AREA)
• Treatment Of Steel In Its Molten State (AREA)
• Heat Treatment Of Sheet Steel (AREA)
• Structures Of Non-Positive Displacement Pumps (AREA)

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Cited By (6)

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• 1972
  • 1972-05-08 US US00251637A patent/US3820980A/en not_active Expired - Lifetime
• 1973
  • 1973-04-17 CA CA169,470A patent/CA974797A/en not_active Expired
  • 1973-04-18 AU AU54641/73A patent/AU469922B2/en not_active Expired
  • 1973-05-03 NL NL7306155A patent/NL7306155A/xx not_active Application Discontinuation
  • 1973-05-04 DE DE2322528A patent/DE2322528C3/de not_active Expired
  • 1973-05-07 PL PL1973162392A patent/PL83802B1/pl unknown
  • 1973-05-07 BR BR3264/73A patent/BR7303264D0/pt unknown
  • 1973-05-07 GB GB2155573A patent/GB1373197A/en not_active Expired
  • 1973-05-08 IT IT49850/73A patent/IT984959B/it active
  • 1973-05-08 ES ES414527A patent/ES414527A1/es not_active Expired
  • 1973-05-08 JP JP5039873A patent/JPS5613787B2/ja not_active Expired
  • 1973-05-08 BE BE130877A patent/BE799250A/xx not_active IP Right Cessation
  • 1973-05-08 AT AT402673A patent/AT337235B/de not_active IP Right Cessation
  • 1973-05-08 SE SE7306469A patent/SE384534B/xx unknown
  • 1973-05-08 AR AR247893A patent/AR196246A1/es active
  • 1973-05-08 FR FR7316519A patent/FR2183933B1/fr not_active Expired

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