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
  • C22C38/10—Ferrous alloys, e.g. steel alloys containing cobalt
  • C22C38/105—Ferrous alloys, e.g. steel alloys containing cobalt containing Co and Ni
• • 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
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/78—Combined heat-treatments not provided for above
• • 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
• • 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
  • C22C38/10—Ferrous alloys, e.g. steel alloys containing cobalt

Definitions

• This nven o r t to a method of Sofienlllg wherein the steel is heated to the intercritical temperature containing, high-alloy steels, More particularly, the invenrange f f b t 1150 F, to 1400" F. and then ⁇ i011 relates a method of Softening high-alloy Steels cooled to the martensite transformation range, after ing carbon, nickel and other y g elemmtswhich the steel is annealed in the subcn'tical range of An alloy system which has recently received a great from about 1050 Rt 0 about 1175 F. for a time suitideal of attention because of its high yield strength, i.e. cient to further reduce the hardness. After annealing, the
• 180-210 K.s.i. is a group of steels that btain t eir steel is cooled from the annealing temperature to permit strength through a combination of carbide precipitation handling.
• the method is particularly beneficial in softenand age hardening.
• Such steels contain a large amount of ing carbon-containing, high-alloy steels having at least nickel, i.e. at least 4%, and other alloying elements such 0.06% carbon, at least 4% nickel, and other alloying as chromium, molybdenum, cobalt and vanadium, as elements (usually at least two) from the group consisting Well as a significant amount of carbon, i.e. about 0.06% of chromium, molybdenum, vanadium and cobalt.
• the high yield strength alloy steels prevents formation of high temperature transformation with which the invention is concerned are not amenable products and also due to their depressed lower critical to softening by conventional annealing practices.
• Wire be softened by conventional treatments.
• the other steels drawing operations can best be performed when the hardof this type, however, which do contain chromium and mess of the rod stock is in the range of R 10 to 20; howmolybdenum are not softened materially by the convenever, wire can be cold drawn from rods as hard as 29 R tional annealing practices.
• composition P 1 As-Reoeived (hot-rollcd) hardness for composition P, 48.0 R Hardness after normalizing (1,900 F., Furnace Cool) composition P, 42.0 Re.
• the softening practices reported in Table II include three subcritical anneals and two austenitic cyclic anneals and a normalizing treatment.
• the first subcritical anneal involved heating as-received hot-rolled rods to 1150" F. for 24 hours.
• the third subcritic-al anneal involved heating rod quenched from 1700 F. to 1100 F. for 24 hours.
• the first austenitic cyclic anneal involved heating as-received rod to 1400 F. and then, after cooling to 1150 F., subjecting the rod to four heating and cooling cycles wherein the steel is heated to between 1150 F.
• the second austenitic cyclic anneal involved the same conditions as the first austenitic cyclic anneal; however, in addition, the rod was given a final anneal at 1150 F. for 48 hours.
• the typical hardness of as-received steel and after normalizing is given in the footnote (Table II).
• the new softening treatment is believed to make use of the softening effect of large amounts of stable reverted austenite.
• This structure occurs in high nickel steels that are thermally cycled to within the intercritical temperature region producing patches of alloy-enriched austenite that are stable upon cooling to room temperature.
• the series of temperature excursions to within the intercritical region according to my process produces a significant amount of alloy-enriched reverted austenite.
• the final, subcritical anneal over-ages the transformed martensite and. any fresh martensite formed from quenching the unstable reverted austenite.
• optimum results are obtained by cycling between the temperature range of 1150 to 1400 F. and the martensite transformation range and annealing at a temperature in the range of 1050 F.
• Water-Quench Water-Quench 2 Water-Quench Designation cresc e es ps z wrps f s i s ws aows ps s i mww cnrowhmoowoorotoueodimlv 1 2 Times. 2 2 Additional Times.
• Quenching after each temperature excursion to the intercritical range causes fresh martensite to form from unstable reverted austenite and the martensite is then converted to over-aged martensite and reverted austenite in the subsequent intercritical cycle.
• the 1050 to 1175 F. anneal further softens the steels due to over-aging the fresh martensite formed from the final intercritical cycle.
• the time at intercritical temperature during annealing is not critical and satisfactory results can be obtained with only a few seconds exposure. Times greater than one hour per cycle may not be necessary. Virtually all steels of the alloy systems concerned will be softened by employing the annealing conditions described above.
• the initial condition of the steel does not appreciably affect its final hardness. Although some softening in these steels may occur through coallescence of carbides, the major contribution to softening is thought to be the formation of stable reverted austenite. It is believed that the presence of significant amounts, that is at least about 10% of stable reverted austenite, results in a softer steel because it is softer than ferrite and because it absorbs the secondary hardening elements thereby keeping them in solution. I have found that a maximum amount of stable reverted austenite will produce the softest structure and that cycling refines the grain size and increases the grain surface area. It is possible that the smaller grains provide more imperfections and greatly increase the nucleation sites for the austenite.
• the final microstructure consists of ferrite, stable reverted austenite and carbides.
• a method of softening high alloy steels having at least 0.06% carbon, at least 4% nickel, and other alloying elements from the group consisting of chromium, molybdenum, vanadium and cobalt comprising subjecting said steel to at least two heating and cooling cycles wherein the steel is heated to the intercritical temperature range of from about 1150" F. to about 1400 F. and then cooled to the martensite transformation range, annealing said steel in the subcritical temperature range of from about 1050 F. to about 1175 F. and cooling to permit handling.

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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 Sheet Steel (AREA)
• Heat Treatment Of Articles (AREA)
• Heat Treatment Of Steel (AREA)

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Citations (3)

• 1965
  • 1965-11-29 US US510356A patent/US3370994A/en not_active Expired - Lifetime
• 1966
  • 1966-10-28 DE DE19661508454 patent/DE1508454A1/de active Pending
  • 1966-11-24 BE BE690161D patent/BE690161A/xx unknown
  • 1966-11-28 FR FR85175A patent/FR1501652A/fr not_active Expired
  • 1966-11-29 ES ES0333614A patent/ES333614A1/es not_active Expired
  • 1966-11-29 NL NL6616799A patent/NL6616799A/xx unknown

Patent Citations (3)

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