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
• • 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
  • C21D1/34—Methods of heating
  • C21D1/40—Direct resistance heating

Definitions

• the annealing temperature is no more than and preferably 50-75% of the melting temperature of the steel in Kelvin degrees. The material is then quenched below the austenitic transformation temperature to prevent austenitic transformation and carbide precipitation.
• the furnace annealing is carried out with the steel being in large coils and in an operation requiring high furnace capacity, large working area, intensive material handling and is highly labour-consuming.
• the hardening and tempering, or the patenting consists of several steps and is an even more intricate process than the furnace annealing, the first step being the relatively long annealing at a high temperature causing often scaling and decarbonization difficulties.
• the subsequent quicker or slower cooling results eventually in cracks and nearly always in coolant problems.
• the tempering or soaking following the quick cooling is as lengthy an operation as the furnace annealingThe expense of this intricate heat treatment consisting of several steps is increased by the intricacy and the high investment costs of the required equipment.
• the process according to the present invention is suitable for the replacement of both the furnace annealing and the hardening and tempering or patenting by one single short soaking operation at a moderate temperature, in accordance with the structural changes occurring in the steel during the annealing.
• the new process is based on the better utilization of the structural changes occurring in the steel during the plastic deformation and the subsequent annealing and its essence is as follows: During the processing to finished or semi-finished product, the steel is cold-worked. For the plastic deformation the material must be previously in a suitably soft state. This is ensured by the structure developing therein during the hot plastic deformation preceding the cold deformation and the subsequent slow cooling, respectively, or as a result of a separate furnace-annealing heat treatment.
• the ferrite suitable for plastic deformation is in a soft, readily cold-workable state.
• the cementites, and other carbides present in the structure are relatively coarse and show an irregular distribution.
• the cold plastic deformation influences the structure of the steel in three different ways:
• the hardening of the ferrite, the breaking of the more or less coarse carbide particles and lamellae and their uniform distribution in the structure result in that the tensile strength, the yield point and especially the plasticity of the material are very low so that it cannot be plastically deformed economically any more in this state. Due to the low plasticity, it cannot be sold as a finished product.
• the cold-worked, hardened material was annealed in a furnace, which operation consisted ofa relatively slow heating, of a suitably long soaking at suitably high temperature, dissolving often the eventually present cementite or other carbides and of a slow cooling together with the furnace and during this operation the prevention of the scaling and the elimination of decarbonization in steels of higher carbon content was ensured by a suitable protective atmosphere.
• the process according to the present invention is based just on the recognition that for the achievement of the required result such intricate and expensive operations causing great difficulties and containing much risks of failure are not necessary.
• the new process solves the above mentioned technical and economical problems of the hardening and tempering or of the patenting in the following manner.
• the steel Following the plastic deformation, the steel generally has physical properties approximately meeting the demands of the consumers. Moreover, its strength indices are better, only the plasticity indices are worse. Now, it may seem obvious that, in order to provide for the meeting of solves for the finished products, a heat treatment must be applied not destroying the strength indices but improving to the required extent the plasticity indices.
• the process according to the invention solves the problem by the heat treatment consisting of a single quick heatingup and a short soaking at a moderate temperature, in the course of which the ferrite rendering possible the metalworking and hardening during the metalworking anneals to the required extent but the brittle cementite or other carbides that are present and broken during the metalworking dissolve to a small extent or do not dissolve at all.
• the short soaking shall not be followed by all means by quick or slow cooling.
• the plasticity indices, the elongation, the reduction in area of the alloy considerably improve, whereas the strength indices, the tensile strength and the yield point reduce nevertheless, the material can meet the demands of the consumer.
• These properties can be suitably controlled by the velocity of heating-up, by the temperature and duration of the soaking.
• the velocity of heating-up by the temperature and duration of the soaking.
• EXAMPLE 1 1 mm. thick and mm. wide band made of manganese-alloyed steel containing 0.2% carbon, having a C52 quality according to the Hungarian Standard is annealed before rolling since as a consequence of previ ous cold rolling it is too hard and unsuitable for further deformation.
• the annealing is carried out with the process according to the invention as follows: The coldrolled, smooth, bright band runs from a coil in between two contact rollers of mm width and 200 mm diameter each.
• the contactrollers are made of tin bronze.
• the contact surfaces of the rollers are covered with soldered tungsten-silver plates and segments, respectively, containing of silver in order to provide for perfect power transmission and to prevent the risk of burning due to sparking.
• the rollers press the band surface with a force of about 10 kp.
• the band running out from between the contact rollers arrives after an about 2000 mm long section in a melted lead bath of about 350C, providing for the electric contact.
• One pole of a direct-current power source of 40 V is connected to the contact rollers, whereas the other pole is connected to the lead bath.
• a current of about 600 A flows and the Joule heat of the current heats up the band to 700C.
• the band runs between the two contacts at a speed which makes it possible to cover the 2000 mm distance in 20 secs. Thereof about 2 secs are required until 700C is reached and 18 secs remain for the soaking.
• the band is moving between two graphite plates in order to avoid oxidation and decarbonization.
• the band running out of the contact is guided between lead stripping plates made similarly of graphite and then into a cooling oil bath.
• the elongation of the band treated in this way is at least 25% rendering possible further plastic deformation.
• EXAMPLE 2 The steel band described in Example 1 would be used as finished product with 0.8 X 10 mm. dimensions.
• the cold-deformed band is led through the equipment described in Example 1 but in such a manner that the distance between the two contacts is only 200 mm.
• the voltage is 6 V, the current is 800 A.
• the running speed of thhe band is the same as in Example 1 so that each point thereof covers the distance between the contacts in 2 seconds.
• the Joule heat of the current heats'up the band to 760C in about 1 second and the band remains at this temperature for another 1 second.
• the material has a tensile strength of to kp per sq.mm. and an elongation of 14 to 18%.
• a process for the rapid heat treatment of cold worked steel comprising heating the steel at the rate of at least 50C. per second to a temperature above the austenitic transformation temperature, holding the steel at said temperature for a time at most 300 seconds to recrystallize the ferrite without substantial dissolution of the carbides present in the steel, and quenching the steel from said temperature to a temperature below the austenitic transformation temperature to prevent the occurence of austenitic transformation and carbide precipitation.

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

Applications Claiming Priority (1)

Publications (1)

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ID=11000569

Family Applications (1)

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Cited By (7)

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Citations (4)

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• 1973
  • 1973-03-01 SE SE7302933A patent/SE396769B/xx unknown
  • 1973-03-05 US US00337910A patent/US3855013A/en not_active Expired - Lifetime
  • 1973-03-06 CS CS731617A patent/CS190402B2/cs unknown
  • 1973-03-06 DD DD169238A patent/DD103461A5/xx unknown
  • 1973-03-06 IT IT48614/73A patent/IT982872B/it active
  • 1973-03-06 FR FR7307996A patent/FR2220585B1/fr not_active Expired
  • 1973-03-07 ES ES412418A patent/ES412418A1/es not_active Expired
  • 1973-03-07 LU LU67168A patent/LU67168A1/xx unknown
  • 1973-03-07 BE BE128497A patent/BE796418A/xx unknown
  • 1973-03-07 AT AT200973A patent/AT343159B/de not_active IP Right Cessation
  • 1973-03-07 JP JP48026240A patent/JPS49119A/ja active Pending
  • 1973-03-07 ZA ZA731588A patent/ZA731588B/xx unknown
  • 1973-03-07 NL NL7303220A patent/NL7303220A/xx not_active Application Discontinuation
  • 1973-03-07 AU AU52997/73A patent/AU5299773A/en not_active Expired
  • 1973-03-07 DE DE19732311283 patent/DE2311283A1/de active Pending

Patent Citations (4)

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