Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous alloys
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/02—Hardening by precipitation
• • 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
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel

Definitions

• the invention relates to the use of a corrosion-resistant austenitic iron-chromium-nickel-nitrogen alloy as a material for components which are exposed to high mechanical loads.
• Austenitic stainless steels or alloys generally have more favorable corrosion properties and are easier to process than ferritic ones. Since the austenitic structure is mainly stabilized by nickel, such steels are alloyed with more than 7% Ni according to DIN 17 440, December 1972 edition, and steel-iron material sheet 400-73, 4th edition, December 1973. They also contain at least 16.0% Cr to guarantee sufficient passivity. Addition of Mo and Si increases pitting resistance and mainly of Cu the corrosion resistance in non-oxidizing acids (see E. Houdremont, handbook of special steel engineering, Springer-Verlag, Berlin, Göttingen, Heidelberg, 1956, pp. 969, 1176 and 1261 ff.). Increased nickel content of approx. 50% improve the resistance to stress corrosion cracking (see Berg- und Wegtenmännchen Monthly Bulletin 108, pp. 1/8 and 4 ff.).
• the austenitic chrome-nickel steels have the disadvantage of the low 0.2 limits. These strength values can be increased by contents of up to about 3% tungsten (see quotation from E. Houdremont, p. 899 ff.). However, mixed crystal hardening with nitrogen is of greater importance.
• the chromium depletion of austenite caused by chromium nitrides should be mentioned.
• the passivity of the mixed crystal in the vicinity of the separated particles can thereby be eliminated.
• a measure of this corrosion is the susceptibility of the steels to grain decay. It was shown that steels with approx. 18% Cr and 10% Ni only then susceptible to annealing above 800 ° C, e.g. B. Ausscheidungs 7 or recrystallization annealing, if the nitrogen contents are above 0.27% (see Stahl and Eisen 93 (1973), pp. 9/18 and 15 ff.).
• the invention is based on the object of contributing to the greatest possible elimination of the disadvantages of these nitrogen-alloyed, austenitic steels such as too low 0.2 limits, too high consumption of alloying elements and too difficult to process.
• This object is achieved in that a corrosion-resistant austenitic iron-chromium-nickel-nitrogen alloy with the known chemical composition specified in claim 1 is used as a material for corrosive and highly mechanically stressed components in such a way that After passing through a high temperature area to dissolve as large a quantity of nitrogen as possible, the alloy is cooled and cold-formed and then annealed so that precipitates form and an ultra-fine-grain recrystallized structure with an average grain diameter of less than 8.5 ⁇ m (greater than about No.
• the main advantages of the invention can be traced back to the type of processing, the chemical composition and the technological properties of the alloys to be used according to the invention. For this reason, the 7 exemplary embodiments given in the table and the advantageous effects of the invention are to be discussed together.
• the table shows the yield strengths, elongations and tensile strengths determined in compliance with DIN 50215, April 1951 edition and DIN 50145, May 1975 edition. or yield strength ratios on samples of rolled sheets up to 10 mm thick. Furthermore, information is given about the 4 processing steps carried out in the production of the sheets, in the order hot rolling of 50 kg cast ingots, solution annealing, cold forming and recrystallization (see columns 2 to 5 of the table). Solution annealing can also be dispensed with at sufficiently high hot forming temperatures, as is shown by way of example for steel No. 3.
• the total growth for the steels is 340, 390 and 485 N / mm 2 depending on the nitrogen content.
• the figures are extremely high.
• niobium-free alloys the strengthening of precipitation based on precipitation hardening is set particularly high at 90 N / mm 2 .
• a comparison shows that these niobium-free steel alloys to be used according to the invention even by about 10% and the niobium-containing alloys unexpectedly by approx. Have 20% higher yield strengths than the calculated maximum values.
• Steels No. 7, 6 and 4 each have the chemical composition that corresponds to the steels dealt with in the presentation of the prior art (see p. 2, line 29 and p. 4, line 17).
• a comparison makes again the advantages of the alloys to be used according to the invention are clear. Yield strengths from 813 to 870 compared to 725 and from 658 to 490 N / mm 2 are measured.
• the ratio even increased to 783 to 490 N / mm2 by adding niobium according to steel No. 5.
• the steels of serial numbers 1 and 2 show that even with relatively low-alloy steels of the type 18 Cr-12 Ni-2 Mo, which can be hot-worked better, yield strengths as high as previously are achieved by alloying with 0.2% N. only of steels with significantly larger amounts of nitrogen and consequently also of chromium, manganese and nickel was known.
• Pipes are made by means of cold vocationalage of usually hot-pressed blanks. In the case of very difficult hot formability, blanks would also have to be produced using the centrifugal casting process. Flat products are cold rolled using the Sendzimir or Quarto process.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Heat Treatment Of Steel (AREA)
• Heat Treatment Of Sheet Steel (AREA)

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• 1984
  • 1984-02-24 DE DE19843407307 patent/DE3407307A1/de active Granted
• 1985
  • 1985-01-21 EP EP85730007A patent/EP0154600A3/fr not_active Withdrawn
  • 1985-02-20 JP JP60032547A patent/JPS60194016A/ja active Pending
  • 1985-02-22 CA CA000474923A patent/CA1232515A/fr not_active Expired
  • 1985-02-22 US US06/704,206 patent/US4559090A/en not_active Expired - Fee Related

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