US3762964A - Method for producing cold workable hypoeutectoid steel - Google Patents

Method for producing cold workable hypoeutectoid steel Download PDF

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Publication number
US3762964A
US3762964A US00242473A US3762964DA US3762964A US 3762964 A US3762964 A US 3762964A US 00242473 A US00242473 A US 00242473A US 3762964D A US3762964D A US 3762964DA US 3762964 A US3762964 A US 3762964A
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steels
temperature
hypoeutectoid
worked
hardness
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US00242473A
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H Kranenberg
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Bethlehem Steel Corp
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Bethlehem Steel Corp
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    • 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
    • C21D1/26—Methods of annealing
    • C21D1/32—Soft annealing, e.g. spheroidising

Definitions

  • ABSTRACT Hypoeutectoid steels are worked within a temperature range of between the A temperature to 150 F. below [52] :LS. CI. the A] temperature
  • the cross sectional area of the [51] 48/12 steels is reduced by not less than 60 percent during [58] Fred 0 Search l working. After working the steens can be heated to 6 about the A temperature to obtain the optimum hard- [56] I References and ness and ductility for cold-working.
  • This invention is in general directed to a method for working hypoeutectoid steels within a temperature range to effect a desired reduction in cross-sectional area.
  • the hypoeutectoid steels can be heated to a temperature for a time to obtain optimum hardness and ductility suitable for cold-working.
  • the invention is directed to a method for working and heat treating hypoeutectoid steels, for example, steels containing about 0.30 to about 0.80 percent carbon, wherein said steels are worked to reduce the crosssectional area by not less than 60 percent within a temperature range of about the A, temperature to about 150 F. below the A, temperature.
  • the steels are subsequently heated to about the A, temperature to obtain a hardness and ductility suitable for cold-working, such as cold-heating and the like.
  • Steels used for cold working into various products such as bolts, screws and the like, generally are of the hypoeutectoid type containing up to about 0.80 percent carbon.
  • Prior art practice in manufacturing cold-workable hypoeutectoid steels is to refine the steel in a metallurgical furnace, such as an electric furnace and the like, tap and teem the steels into ingot molds to form ingots.
  • the ingots are hot-worked at an austenitizing temperature into the end product, such as bars, billets, rods, wire and the like.
  • the end product is slow cooled to ambient temperature.
  • the steels are spheroidize annealed to obtain a uniform structure which is substantially completely spheroidized; is substantially completely free of a carbide network and pearlite; and is relatively soft and ductile.
  • the spheroidize anneal cycles which are used are lengthy.
  • the steels must be soaked at the proper temperature for from about hours to days to completely and effectively produce the desired microstructure and hardness and ductility re quired for good cold formability.
  • the steels are alternately heated and cooled to a few degrees of temperature above and below the A, temperature several times.
  • the cyclic heating and cooling practice does not effectively reduce the length of the annealing cycle.
  • the microstructure of hypoeutectoid steels treated by the cyclic heating and cooling method can contain evidence of lamellar carbides.
  • the hardness of the steels is reduced to a hardness suitable for cold-working after lengthy time at the spheroidize annealing temperature but maximum reduction in hardness may not be achieved.
  • the as-worked steels contain ferrite and pearlite, therefore the steels must be spheroidize annealed to produce a spheroidized structure.
  • Another improved method is directed to hypereutectoid steels and highly alloyed steels as described in U. S. Pat. No. 3,459,599 issued Aug. 5, 1969 to Raymond E. Grange titled Method of Thermomechanically Annealing Steel.”
  • Hypereutectoid steels are heated to and drastically worked at a temperature not more than 150 F. above the A, temperature and ore finished below the A, temperature but not more than 50 F. below the A, temperature.
  • the method while applicable to hypereutectoid steels, is not applicable to hypoeutectoid steels.
  • the problems of complete spheroidization with elimination of lamellar carbides connected with hypoeutectoid steels is not solved.
  • the invention includes working hypoeutectoid steels within a temperature range of about the A, temperature to about 150 F. below the A, temperature to reduce the cross-sectional area by not less than 60 percent and to heat treat the steels at about the A, temperature for a time to obtain a low hardness and ductility.
  • FIG. 1 is a reproduction of a photomicrograph taken at 2200 diameters of a hypoeutectoid steel as-worked by the method of the invention.
  • FIG. 2 is a reproduction of a photomicrograph taken at 2200 diameters of a hypoeutectoid steel as-worked and heat treated by the method of the invention.
  • FIG. 3 is a reproduction of a photomicrograph taken at 500 diameters of a hypoeutectoid steel as-worked and heat treated by the method of the invention.
  • FIG. 4 is a reproduction of a photomicrograph taken at 500 diameters of a hypoeutectoid steel as-worked and spheroidize annealed by a conventional method.
  • FIG. 5 is a graph comparing a conventional method of spheroidize annealing and the method of heat treating of the invention.
  • FIG. 6. is a graph showing a comparison of the decrease in hardness of steels worked and spheroidize annealed by a conventional method and by the method of the invention.
  • Hypoeutectoid steels suitable for cold-working can be made by working the steels within a temperature range below about the A, temperature and heat treating the worked steels at about the A, temperature for a time to obtain optimum hardness and ductility.
  • the as-worked hypoeutectoid steels have a microstructure of fine spheroidal carbides well-dispersed in a fine ferritic matrix substantially devoid of lamellar carbides.
  • the heat treated steels have a microstructure of somewhat larger spheroidal carbides well dispersed in a ferritic matrix substantially devoid of lamellar carbides.
  • hypoeutectoid steels are melted and refined in any type of metallurgical furnace, such as basic oxygen furnace, electric furnace, open-hearth and the like.
  • the refined steels are tapped into a ladle and teemed into ingot molds in the conventional manner.
  • the ingots thus formed are heated to an austenitizing temperature and are rolled into billets and cooled to black.
  • the billets can be heated to an austenitizing temperature and worked at the austenitizing temperature to effect a reduction in the cross-sectional area, said reduction is of such a nature that the steels will require additional working at a temperature to effect at least another 60 percent reduction in cross-sectional area to obtain the final size desired, after which the billets are cooled rapidly, for example, in air through the A -A, temperature range to a temperature range between the A, temperature and 150 F. below the A, temperature, in which temperature range the additional reduction in cross-sectional area is achieved, or (2) the billets can be reheated to a temperature range between about the A, temperature and 150 F.
  • hypoeutectoid steels are worked within a temperature range of between about the A, temperature to 150 F. below the A, temperature to obtain not less than 60 percent reduction in crosssectional area to achieve the results of the invention.
  • the hypoeutectoid steels can be heat treated for a time at about the A, temperature.
  • heat treatment includes heating the steels to about the A, temperature for a time to reduce the hardness of the steels and to increase the ductility of the steels with little or no effect on the spheriodization microstructure of the steels other than a slight increase in the size of the carbides and ferritic matrix. It will also be understood that to raise the temperature of the steels to the working temperature range between about the A, temperature and 150 F. below the A, temperature it is possibleto heat the steels above the A, temperature or even above the A, temperature so long as the steels are cooled to within the working temperature range described above before any reduction in cross-sectional area is started.
  • the hypoeutectoid steels are worked within the temperature ranges mentioned above to obtain a reduction in the cross-sectional area of not less than 60 percent.
  • Samples of the steels as-worked by the above described method were examined by electron microscopy at a magnification of 2200 diameters.
  • the microstructure was found to consist of fine spheriodal carbides welldispersed in a fine-grain ferritic matrix.
  • a reproduction of an electron photomicrograph of the structure at the latter magnification is shown in FIG. 1. It can be seen that the carbides are well spheriodized and are less than 1 micron in size when compared with a line 5 microns long drawn on the lower right-hand corner of the elec tron photomicrograph for comparison purposes.
  • the ferritic grains are also small, not more than 1 .5 microns in size, although they appear to be very large when compared to the carbides.
  • the microstructure is substantially free of lamellar carbides.
  • the hypoeutectoid steels were heat treated at about the A, temperature for from about three hours to about six hours.
  • a reproduction of an electron photomicrograph of a sample of the steels after heat treatment taken at a magnification of 2200 diameters is shown in FIG. 2.
  • the spheriodal carbides and ferrite grains have been coarsened by the heat treatment.
  • the carbides are less than 5 microns in size when compared to a line 5 microns in length drawn in the lower right-hand corner of the photomicrograph for comparison purposes.
  • FIG. 3 A microscopic examination at a magnification of 500 diameters of the steels after heat treatment is shown in FIG. 3.
  • the microstructure can be seen to consist of finely divided spheriodal carbides well dispersed in a ferritic matrix.
  • the microstructure is substantially free of carbide network, and lamellar carbides.
  • the carbides are tending to spheriodize but a large portion thereof retain lamellar-like formations and are not welldispersed.
  • Ferrite grains are outlined by the carbides. The ferrite grains appear to be larger in the conventionally worked and spheriodize annealed steels than the ferrite grains of the steels worked and heat treated by the method of the invention shown in FIG. 3.
  • the steels of the invention were tested for hardness both in the as-rolled and heat treated conditions.
  • the as-rolled steels with a microstructure shown previously in FIG. 1 were found to have a hardness of 200 DPI-I (Vickers) to about 230 DPI-I (Vickers) which is equiv alent to a hardness within a range of about 190 BHN to about 220 BI-IN.
  • the hardness range is above the hardness desired in steels which are to be cold-worked.
  • the steels After heat treating for a time, about three hours to about six hours, by the method of the invention, the steels had been lowered in hardness by about 80 points in both DPI-I (Vickers) and BI-IN, which is well within the hardness range for cold-working the steels, for example, cold-heading.
  • FIG. 5 A comparison of the short heat treating cycle of the invention and a typical conventional spheriodize annealing cycle is shown in FIG. 5. Note that the heat treating cycle of the invention is considerably shorter than the typical conventional spheriodize annealing cycle.
  • FIG. 6 is a comparison of the effect of the heat treating cycle of the invention on the as-worked hardness of hypoeutectoid steels and a typical conventional spheriodize annealing cycle in the as-worked hardness of the hypereutectoid steels.
  • the asworked hardness of the hypoeutectoid steels of the invention was higher than the as-worked hardness of hypoeutectoid steels prepared by a conventional hot working process.
  • the hardness of the hypoeutectoid steels worked by the method of the invention decreased much more rapidly when heat treated than the hardness of the hypoeutectoid steels worked by conventional hot working process.
  • the hardness of the hypoeutectoid steels of the invention after heat treating at about the A, temperature for about six hours is comparable to the hardness of hypoeutectoid steels hot rolled by conventional hot rolling and spheriodize annealed by conventional annealing cycle for about 17 hours.
  • the hardness of the hypoeutectoid steels of the invention is lowered slightly when heat treated for longer periods of time.
  • the hardness of the hypoeutectoid steels of the invention is lower than the hypoeutectoid steels prepared by a conventional hot rolling ahd spheriodize annealing cycle.
  • hypoeutectoid steels of the invention may be sufficiently high to preclude cold forming, however the tensile stength and reduction in area of these steels are better than conventionally processed steels of the same grade. Therefore. in some applications, the hypoeutectoid steels of the invention can be used in the as-worked condition.
  • a hypoeutectoid steel having a chemical analysis of: carbon 0.39%, manganese 0.75%, phosphorus 0.017%, sulfur 0.022%, silicon 0.18% was prepared in a basic oxygen furnace. The steel was melted, poured and teemed into 34 inch 4; ingot molds. The ingots were bloomed to 4 inches by 4 inches square billets and cooled to ambient temperature. The billets were reheated to austenitizing' temper ature and reduced in size to 246 inches X l-B inches billets, finished at 1900 F. and allowed to drop in temperature to about 1200 F. in air. The billets were reduced in cross-sectional area by 60.4 percent to l-% inches in diameter.
  • the rounds were air cooled to ambient temperature.
  • Microscropic examination at a magnification of 22000 diameters of samples cut from the bars showed a microstructure of fine, well-dispersed spheriodal carbides of about 0.1 to 0.3 microns in size in a fine-grained ferritic matrix of about 0.5 to 1.5 microns in size, devoid of lamellar carbides.
  • the bars were heated in a furnace at a temperature of about 1300 F. for five hours. The bars were slow cooled to room temperature.
  • Microscopic examination at a magnification of 8200 diameters of the steel after heat treatment disclosed a microstructure of well-dispersed spheriods of carbides of about 0.5 to 2.5 microns in size in a ferritic matrix of about 3 to 10 microns in size.
  • the hardness of the as-rolled bars was 229 DPH (Vickers). After heat treating, the hardness was 144 DPH (Vickers).
  • Tensile tests of as-rolled bars showed the steels to have a tensile strength of 101,000 pounds per square inch and a reduction-in-area of 68 percent. The reduction-in-area compares favorably to steels processed by prior art methods which had a tensile strength of 89,000 pounds per square inch and a reductionin-area of 63 percent.
  • the bars were heat treated at 1300 F. for live hours. Tensile tests showed the steels to havea tensile strength of 73,000 pounds per square inch and a reduction-inarea of 79 percent.
  • the ductility of the bars prepared by the method of the invention had improved ductility as compared to the conventionally treated bars.
  • a method for producing hypoeutectoid steel characterized by having good cold formability comprising:
  • step (a) is about 5 F. to about F. below the A, temperature.
  • step (a) is about 75 F. to about F. below the A, temperature.
  • step (c) 9.- The method of claimv8 in which the time of heating [0 in step (c) is between about three hours and about six hours.

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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 Steel (AREA)
US00242473A 1972-04-10 1972-04-10 Method for producing cold workable hypoeutectoid steel Expired - Lifetime US3762964A (en)

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JP (1) JPS499421A (sl)
CA (1) CA992440A (sl)
DE (1) DE2317628A1 (sl)
FR (1) FR2179884B1 (sl)
GB (1) GB1435313A (sl)
IT (1) IT980137B (sl)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2558174A1 (fr) * 1984-01-13 1985-07-19 Sumitomo Metal Ind Procede pour la production de barres ou fils d'acier ayant une structure spheroidale de cementite amelioree
US4533390A (en) * 1983-09-30 1985-08-06 Board Of Trustees Of The Leland Stanford Junior University Ultra high carbon steel alloy and processing thereof
EP0523375A2 (en) * 1991-06-14 1993-01-20 Nippon Steel Corporation Process for producing steel bar wire rod for cold working
EP0943693A1 (en) * 1998-03-16 1999-09-22 Ovako Steel AB A method of soft annealing high carbon steel

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4533390A (en) * 1983-09-30 1985-08-06 Board Of Trustees Of The Leland Stanford Junior University Ultra high carbon steel alloy and processing thereof
FR2558174A1 (fr) * 1984-01-13 1985-07-19 Sumitomo Metal Ind Procede pour la production de barres ou fils d'acier ayant une structure spheroidale de cementite amelioree
EP0523375A2 (en) * 1991-06-14 1993-01-20 Nippon Steel Corporation Process for producing steel bar wire rod for cold working
EP0523375A3 (en) * 1991-06-14 1995-05-17 Nippon Steel Corp Process for producing steel bar wire rod for cold working
US6190472B1 (en) * 1993-03-16 2001-02-20 Ovako Steel Ab Method of soft annealing high carbon steel
EP0943693A1 (en) * 1998-03-16 1999-09-22 Ovako Steel AB A method of soft annealing high carbon steel

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CA992440A (en) 1976-07-06
IT980137B (it) 1974-09-30
FR2179884B1 (sl) 1977-08-19
JPS499421A (sl) 1974-01-28
GB1435313A (en) 1976-05-12
DE2317628A1 (de) 1973-10-18
FR2179884A1 (sl) 1973-11-23

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