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
  • C21D5/00—Heat treatments of cast-iron
  • C21D5/04—Heat treatments of cast-iron of white cast-iron
  • C21D5/06—Malleabilising
  • C21D5/14—Graphitising

Definitions

• This invention relates to a method of producing ferritic malleable iron from white cast iron and more particularly relates to an isothermal annealing cycle for the production of ferritic malleable iron.
• the inventive method disclosed herein provides a three-phase heat treatment for producing malleable iron from white cast iron wherein the cast iron is heated to a temperature of approximately 1750 F. and then fast cooled to a temperature of 1300 F., with a holding period at this temperature, and subsequently cooled to 1250 F., with a second hold period at this temperature. The iron is then cooled to ambient.
• ferritic malleable iron has been processed in continuous furnaces using basic two-stage annealing cycle.
• the first stage consisted of heating the work to a temperature between 1700 F. and 1750' F. and holding at that temperature for a given period and the second stage was accomplished by rapidly cooling to approximately 1400" F. and then slowly cooling to 1250 F.
• the reason for the slow cool from 1400 F. to 1200 F. was to insure that all critical temperatures between these two points were held at a sufiiciently long time to catch all phase changes between these two temperature points.
• This slow cooling rate depended 'upon the composition of the work and varied from 5 F. to 30 F. per hour.
• the complete cycle was performed in a single furnace of considerable length, the length usually being in excess of 60 feet.
• the number of temperature zones in a furnace of this nature was in the order of 7 or 8, and resulted in the continuous furnaces being available only for large capacity foundries. It would he obviously advantageous to have a heat treating cycle that would lend itself to a furnace that did not require a plurality of heating zones and with a reduced length that could be placed in foundries having relatively small capacity.
• EXAMPLE In order to isothermally anneal white cast iron to produce malleable iron, a four zone furnace was used having a total length of 37 feet in to in brick. The first zone was set at 1700 F., zone number 2 was also set at 1700" F., zone 3 at 1300 F. and zone 4 at 1250 F. Work, consisting of white cast iron castings, was placed in the first zone for a period of eight hours, which proved sufficiently long to bring the work up to 1700 F., and then placed in the second or soaking zone for 24 hours to assure uniformity at the temperature of 1700 F. and complete the first stage graphitization. After the' heat had completely soaked through the work, it was then placed into the third zone at 1300 F.
• a relatively short furnace may be employed to produce' ferritic malleable iron. More particularly, the number of heat treat zones required is reduced substantially since' there is no more need to gradually change the work temperature. As a result, the cost of producing ferritic malleable iron is reduced and the capabilities of producing this type of iron is no longer limited to those foundries having the capacity to install furnaces of great length.
• an isothermal method of producing malleable iron from white cast iron comprising: placing white cast iron in a first environment at a first temperature between 1700 F. and 1750 F. for a sufficiently long time to reach thermal equilibrium and complete first stage graphitization; placing the iron in a second environment at a second temperature between 1275 F. and 1325 F. for a sufiiciently long time to reach thermal equilibrium and partially complete second stage graphitization; placing the iron in a third environment having a third temperature between 1225 F. through 1275 F. and holding at a sufiiciently long period of time to obtain thermal equilibrium and complete second stage graphitization.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Mechanical Engineering (AREA)
• Physics & Mathematics (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Heat Treatments In General, Especially Conveying And Cooling (AREA)
• Heat Treatment Of Articles (AREA)
• Heat Treatment Of Steel (AREA)
• Heat Treatment Of Sheet Steel (AREA)
• Soft Magnetic Materials (AREA)
• Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=24459582

Family Applications (1)

Country Status (6)

Cited By (1)

Citations (2)

• 1967
  • 1967-02-06 US US614022A patent/US3511721A/en not_active Expired - Lifetime
• 1968
  • 1968-01-29 GB GB4516/68A patent/GB1190321A/en not_active Expired
  • 1968-01-29 BE BE710059D patent/BE710059A/xx unknown
  • 1968-01-30 FR FR1554145D patent/FR1554145A/fr not_active Expired
  • 1968-02-05 ES ES350148A patent/ES350148A1/es not_active Expired
  • 1968-02-06 DE DE19681583998 patent/DE1583998A1/de active Pending

Patent Citations (2)

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