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
  • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten

Definitions

• This invention relates to a high strength martensitic precipitation-hardenable stainless steel with resistance to stress-corrosion cracking.
• the steel of this invention is a relatively low carbon, nominally percent chromium and 6 percent nickel, martensitic stainless steel, in which resistance to stress-corrosion cracking is imparted by the addition of titanium and molybdenum, and the restriction of aluminum and nitrogen contents.
• the steel contains sufficient chromium (about 15%) for good resistance to atmospheric corrosion and elevatedtemperature oxidation.
• the steel contains the austenitizing elements, carbon and nickel, in such proportions that these elements balance the ferritizing elements, chromium molybdenum, and titanium, and enable the austenite to martensite transformation to occur upon cooling.
• the titanium and carbon are controlled so that an aging as high as 1100 F., a critical dispersion of titanium carbide and other titanium containing intermetallic compounds are precipitated to develop the relatively high yield and tensile strengths needed for many engineering applications.
• the titanium in addition to its function as a precipitation-hardening element, combines with the nitrogen in the steel and thereby reduces the amount of nitrogen in solid solution.
• a low-nitrogen martensitic structure is generally less susceptible to stress-corrosion cracking in a chloride-type environment than is a high-nitrogen martensitic structure.
• the steel also contains molybdenum for strength at high temperatures and improved resistance to stress-corrosion cracking. Molybdenum probably gives improved resistance to stress-corrosion cracking because it increases the resistance of the steel to pitting corrosion thus retarding the formation of pits which act as stress raisers.
• Cobalt may also be added to the steel, preferably in the range of about 2 to 6%, Without any deleterious ice effect on the stress-corrosion resistance of the steel in a chloride-type environment.
• Cobalt like molybdenum, improves elevated-temperature strength, and because cobalt is an austenitizing element, it helps balance the ferritizing elements and also reduces the amount of delta ferrite in the new steel, thereby improving transverse ductility and hot workability.
• the aforementioned balance of austenitizing and ferritizing elements must be maintained. That is, if the ferritizing elements are on the high side of the composition range, the austenitizing elements must also be on the high side of the range.
• the preferred heat treatment for the new steel is as follows: (1) anneal for 5 to 30 minutes at 1750" to 2050 F., air cool to room temperature, (2) if necessary to effect the austenite to martensite transformation, cool to about F. for a minimum of 2 hours, and (3) age at 850 to 1100 F. for a minimum of 30 minutes.
• Steels A, B, C, and D are commercially available steels, while Steel E represents a low nitrogen laboratory melt of a steel otherwise analogous to Steel D.
• a comparison of the test results of Tables I-A and II-A indicates the relative stress-corrosion resisting advantages of the steel of the invention.
• a martensitic precipitation-hardenable stainless steel with resistance to stress-corrosion cracking comprising Percent Carbon 0.06-0.12 Manganese 0.50-0.80 Silicon 0.40-0.60 Nickel 5.5-6.5 Chromium 14.5-16.0 Molybdenum 2.25-2.75 Titanium 0.85-1.15 Aluminum (maximum) 0.05 Nitrogen (maximum) 0.015
• a martensitic precipitation-hardenable stainless steel with resistance to stress-corrosion cracking comprising with the balance iron and residual amounts of other elements which do not adversely alfect the properties.
• a martensitic, precipitation hardenable stainless steel consisting essentially of .03% to .05 carbon, traces to .3% manganese, traces to .2% silicon, 14.5% to 15.5% chromium, 5.25% to 6.5% nickel, .6% to 1% titanium, 1% to 2% molybdenum and the balance essentially iron.
• a martensitic precipitation hardenable stainless steel consisting essentially of 0.03 to 0.12% carbon, traces to 0.6% manganese, traces to 0.35% silicon, 14.0 to 16.5% chromium, 5.0 to 7.0% nickel, 0.6 to 1.25% titanium and 1.0 to 3.0% molybdenum.

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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)
• Heat Treatment Of Strip Materials And Filament Materials (AREA)
• Heat Treatment Of Articles (AREA)

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Cited By (6)

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Citations (4)

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• 0
  • BE BE643029D patent/BE643029A/xx unknown
• 1963
  • 1963-01-28 US US254493A patent/US3512960A/en not_active Expired - Lifetime
• 1964
  • 1964-01-21 GB GB2659/64A patent/GB1018674A/en not_active Expired
  • 1964-01-23 DE DEU10441A patent/DE1264074B/de active Pending
  • 1964-01-27 ES ES295752A patent/ES295752A1/es not_active Expired

Patent Citations (4)

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