Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
  • B21C1/00—Manufacture of metal sheets, metal wire, metal rods, metal tubes by drawing
• • 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
  • C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
• • D—TEXTILES; PAPER
  • D07—ROPES; CABLES OTHER THAN ELECTRIC
  • D07B—ROPES OR CABLES IN GENERAL
  • D07B1/00—Constructional features of ropes or cables
  • D07B1/06—Ropes or cables built-up from metal wires, e.g. of section wires around a hemp core
  • D07B1/0606—Reinforcing cords for rubber or plastic articles
  • D07B1/066—Reinforcing cords for rubber or plastic articles the wires being made from special alloy or special steel composition
• • 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
  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/005—Ferrite
• • 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
  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/008—Martensite

Definitions

• the present invention is directed to a process for making high-strength, high-ductility, low-carbon steel wires, bars and rods by cold drawing dual-phase steels.
• dual-phase steels refers to a class of steels which are processed by continuous annealing, batch annealing, or conventional hot rolling to obtain a ferrite matrix with a dispersed second phase such as martensite, bainite and/or retained austenite.
• the second phase is controlled to be a strong, tough and deformable phase unlike the hard, non-deformable carbide phase found in pearlitic rods and wires. It must be suitably dispersed and in sufficient volume fraction i.e.
• a preferred heat treatment is the intermediate quench method i.e. austenitize and quench to 100% martensite prior to annealing in the two phase ⁇ + ⁇ field and quenching to a ferrite martensite structure.
• the invention is further directed to the high-strength, high ductility steel wires, bars and rods produced by the process of the present invention.
• Steel wire has many known uses, such as for making cables, chains, and springs.
• the diameter requirements range from 0.005 inch to more than 0.25 inch with strength requirements ranging from 250 ksi to as much as 400 ksi in the smaller diameters. In all of these applications, it is important to provide a steel wire having a high tensile strength and good ductility at the required diameter.
• the present invention would replace the conventional method of patenting pearlitic steel to produce wire with a process whereby an alloy of rela ⁇ tively simple composition is cold drawn into wire or rods in a single multipass operation, i.e., without intermediate annealing or patenting heat treatments. Elimination of the patenting heat treatments in the production of high strength steel wire should lower the cost of producing high strength steel wire, especially in light of the present fuel situation.
• the cold drawing process requires a low alloy steel composition with a microstructure and morphology which provides high initial strength, high ductility, rapid work hardening, and good cold formability.
• the steel should be capable of being cold drawn, without inter- mediate anneals or patenting heat treatments, to the desired diameter, tensile strength, and ductility.
• HSLA high-strength, low-alloy
• These steels contain carbon as a strengthening element in an amount reasonably consis ⁇ tent with weldability and ductility.
• Various levels and types of alloy carbide formers are added to achieve the mechanical properties which characterize these steels.
• the high tensile strength and high ductility needed in many applications for steel wire and rods do not seem to be attainable using HSLA steels.
• low carbon steels contain silicon, manganese, or a combination of silicon and manganese.
• carbide forming elements such as, vanadium, chromium, niobium, molybdenum may be added.
• Low carbon, dual-phase microstructured steels charac ⁇ terized by a strong second phase dispersed in a soft ferrite matrix show potential for satisfying the tensile strength, ductility, flexibility and diameter require ⁇ ments of high strength steel wire. Furthermore, they have potential for achieving a level of cold formability which allows cold drawing without patenting or inter-
• ⁇ KNATICS ⁇ mediate heating.
• a low carbon, duplex ferrite-martensite steel disclosed in U.S. Patent No. 4,067,756 issued January 10, 1978, is of interest in the present invention because it has high strength, high ductility characteristics and is composed of inexpensive elements.
• the process of the present invention is directed to producing a high-strength steel wire having a tensile strength of at least about 120 ksi.
• a preferred tensile strength range is 120 ksi to 390 ksi, but strengths above 400 ksi may be achieved.
• Another object of the present invention is to provide a process for making high strength, high ductility steel wires or rods comprising the step of cold drawing a dual-phase steel composition to the required strength and ductility without intermediate anneals or patenting heat treatments, thereby providing complete flexibility in choosing the wire diameter.
• a further object of the present invention is to provide a process for making high strength steel wires and rods which is versatile, allowing for a wide range of diame ⁇ ters, strength, and ductility properties in the final steel wire or rod based on the choice of the initial duplex microstructure and manipulation of the micro- structure through appropriate thermal processing.
• a further object of the present invention is to provide high strength, high ductility steel wires or rods which have a tensile strength at least about 120 ksi.
• the present invention is directed to high strength, high ductility, low carbon steel wires or rods and the process for making the same.
• the process involves cold drawing a low carbon dual-phase steel to the desired diameter in a single multipass operation.
• the steel is characterized by a duplex microstructure consisting essentially of a strong second phase dispersed in a soft ferrite matrix and a microstructure and morphology having sufficient cold formability to allow reductions in cross-sectional area of up to about 99.9%.
• One preferred embodiment of the invention is a high strength, high ductility, low carbon steel rod or wire produced from a steel composition characterized by an appropriate duplex ferrite-martensite microstructure, for example as shown in FIG. 1, and the process for making the same.
• the process involves cold drawing the duplex ferrite-martensite steel to the desired diameter
• the strong, deformable second phase consists predominately of martensite but may contain bainite and retained austenite.
• the strong second phase is dispersed in a soft ductile ferrite matrix; the martensite provides the strength in the composite whereas the ferrite provides the ductility.
• FIG. 1 is an optical micrograph showing a typical low carbon dual-phase ferrite-martensite microstructure prior to cold drawing.
• 12FIG. 2 is a transmission electron micrograph of dis ⁇ located lath martensite which comprises the strong second phase in a dual-phase steel according to the present invention.
• FIG. 3 is a graph exemplifying a typical comparison between a cold drawing schedule for duplex icrostruc- ture steel wire according to the present invention and a drawing schedule for pearlitic steel wire according to a patenting method.
• the high strength, high ductility steel wires or rods are produced by a process whereby a low carbon steel composition, charac ⁇ terized by a duplex microstructure consisting essential ⁇ ly of a strong second phase dispersed in a soft ferrite matrix, is cold drawn to the desired diameter in a single multipass operation.
• the starting steel composi ⁇ tion prior to the cold drawing should possess a duplex microstructure and a morphology which are sufficient to provide a level of cold formability allowing reductions
• the process of the invention provides an advantage over known processes in that it eliminates the intermediate heat treatments or patenting steps used in the known process for making pearlitic steel wire, and thereby reduces the complexity, cost, and energy consumption of the process. Furthermore, a wider range of rod and wire diameter sizes can be produced by the process of the invention than in the patenting method. In the patent ⁇ ing method, there is an inherent limitation in the maximum wire diameter that can be produced at a given strength level.
• the solid line illustrates the cold drawing schedule of a low carbon duplex steel wire according to the present invention and the tensile strengths which can be achieved at different diameters.
• the broken lines indicate the drawing schedule of a pearlitic steel wire according to the patenting method, including the intermediate heat treatments.
• the intermediate heat treatments are necessary in order to achieve the greater tensile strength that the process of the present invention can achieve at various diameters.
• These intermediate heat treatments increase the complexity and expense of the process for making high-strength steel wire.
• the process according to the present invention does not involve intermediate heat treatments and thus provides a significant improvement over the known process.
• the process of the present invention can produce steel wires and rods with a wide range of tensile strength, ductility, and diameter.
• the final properties of the steel wire or rod at a given diameter are determined by a combination of the initial microstructure, the prop- erties of the starting steel and the amount of subse ⁇ quent reduction in cross-sectional area during the cold drawing process. Since the microstructure of the steel is easily manipulated through appropriate thermal processing, the properties of the drawn wire can be tailored to match the required specifications of the desired application.
• the choice of alloying elements such as silicon, aluminum, manganese, and carbide forming elements, such as, molybdenum, niobium, and the like, is determined by the microstructure and properties desired. Thus, a wide range of alloys, including many simple and inexpensive alloys, can be used as long as they can be heat treated to the desired dual-phase microstructure.
• duplex microstructure is the ferrite- martensite microstructure.
• Another preferred micro- structure is the duplex ferrite-bainite microstructure.
• the strong second phase either marten ⁇ site or bainite, is dispersed in a soft, ductile ferrite matrix.
• the starting steel composition con ⁇ sists essentially of iron, from about 0.05 to 0.15 weight % carbon, and from about 1.0 to 3.0 weight % silicon. In another preferred embodiment the starting steel composition consists essentially of iron, from about 0.05 to 0.15 weight percent carbon, from about 1-3 weight percent silicon, and from about 0.05 to 0.15
• the steel composition is thermally treated to form a duplex ferrite-martensite microstructure in a fibrous morphology.
• the preferred process comprises the steps of austenitizing the steel composition, quenching the steel composition to transform the austenite to substantially 100% martensite, heating the resulting steel composition to an annealing temperature for a time sufficient to provide the desired ratio of austenite and ferrite, quick quenching the austenite ferrite composition to transform the austenite to martensite, and cold drawing the resulting dual-phase steel which is characterized by a duplex ferrite- martensite microstructure in a fibrous morphology to the desired diameter in a single multipass operation.
• the starting steel composition is heated to a temperature, T 1 , above the critical temperature at which austenite forms.
• the temperature range for T.. is from about 1050°C to 1170°C.
• the composition is held at that temperature for a period of time sufficient to substantially and completely austeni ⁇ tize the steel.
• the resulting composition is quenched in order to transform the austenite to substantially 100% martensite.
• the composition is then reheated to an annealing temperature, T 2 , in the two phase ( ⁇ + ⁇ ) range.
• the ⁇ + ⁇ temperature range is from about 800°C to 1000°C.
• the composition is held at this temperature for a period of time sufficient to transform the martensitic steel composition to the desired volume ratio of ferrite and austenite.
• the steel composition at this point is characterized by a unique microstructure which is a fine, isotropic, acicular martensite in a ductile ferrite matrix.
• the microstructure results due to the combination of the double heat treatment and the presence of silicon in the above-specified amount.
• the unique microstructure maximizes the potential ductility of the soft phase ferrite and also fully exploits the strong martensite phase as a load carrying constituent in the duplex microstructure. It is the microstructure as well as the morphology of the steel composition that enables the steel to be cold drawn to the desired wire or rod diameter in a single multipass operation.
• Any dual-phase steel may be used in the process of the present invention as long as a duplex microstructure and morphology can be produced having sufficient cold formability to allow reductions in cross-sectional area of up to about 99.9% when the composition is cold drawn.
• dual-phase ferrite-martensite steels have a greater continuous yielding behavior, higher ultimate tensile strength, and better ductility than commercial high strength low alloy steels, including microalloyed, fine-grain steels.
• the high tensile to yield ratio and high strain hardening rate in ferrite- martensite dual-phase steel provides excellent cold formability.
• the exact temperature, T.., to which the steel composi ⁇ tion is heated in the first austenization step is not critical as long as it is above the temperature at which complete austenization occurs.
• the exact temperature, T_, in the second heating step where the composition is transformed to the two phases of ferrite and aus ⁇ tenite depends upon the desired volume ratio of ferrite and austenite, which in turn depends upon the desired volume ratio of ferrite-to-martensite. In general, the desired volume ratio of ferrite and martensite depends upon the ultimate properties desired for the steel wire or rod.
• 10-40 volume percent of martensite in the ferrite-martensite microstructure will allow the steel composition to be cold drawn to diameters repre ⁇ senting up to 99.9% reductions in cross sectional area and will still result in steel wires and rods having a tensile strength at least about 120 ksi.
• tensile strengths in the range of 120 ksi to 390 ksi are obtained, but 400 ksi and above may also be obtained.
• a high strength, high ductility steel wire was made to satisfy the requirements for bead wire used in the manufacture of automobile tires.
• the bead wire requires a tensile strength of 270 ksi with 5% elongation, and a proportional limit of 216 ksi.
• the bead wire should be about .037 inch in diameter with sufficient ductility to pass a torsion test requiring 58 axial twists in an 8 inch length.
• a 0.220 inch diameter steel rod having a composition consisting essentially of iron, 0.1 weight percent carbon, 2 weight percent silicon, and 0.1 weight percent vanadium was austenitized and rapidly quenched to yield a substantially 100% martensitic composition.
• the rod was then reheated to a temperature of 950° C in the two phase ⁇ + ⁇ range and rapidly quenched to produce a duplex ferrite-martensite microstructure of approxi ⁇ mately 30 volume percent martensite and 70 volume percent ferrite.
• the needle-like, acicular character of the ferrite-martensite microstructure is shown in the optical micrograph in FIG. 1.
• the heat treated rod was then cold drawn through lubricated conical dies down to a diameter of 0.037 inch in 8 passes of approximately 36% reduction in area per pass. After a short stress relief anneal at 425°C similar to the current practice, an ultimate tensile strength of 276 ksi was achieved, thus satisfying the tensile strength requirement of bead wire.
• the ductility of the steel wire was sufficient to satisfy the twist test requirement.
• Example 2 A steel rod consisting essentially of iron, 0.1 weight percent carbon, and 2.0 weight percent silicon was hot rolled to a diameter of 0.25 inch. The rod was then heated to a temperature of about 1150°C for about 30 minutes to austenitize the composition. The steel was then quenched in iced brine to transform the austenite to substantially 100% martensite. The rod was then rapidly reheated to a temperature of 950°C in order to convert the structure to qpproximately 70% ferrite and 30% austenite. The steel rod was then quenched in iced brine to convert the austenite to martensite.
• the rod was cold drawn to a diameter of 0.030 inch where its tensile strength was 357 ksi, and also drawn to a diameter of 0.024 inch where its tensile strength was 360 ksi. Continued cold drawing may achieve tensile strengths to 400 ksi or higher.

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• Engineering & Computer Science (AREA)
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• Crystallography & Structural Chemistry (AREA)
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• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Heat Treatment Of Steel (AREA)
• Heat Treatment Of Strip Materials And Filament Materials (AREA)
• Metal Extraction Processes (AREA)
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• 1982
  • 1982-12-09 BR BR8208108A patent/BR8208108A/pt unknown
  • 1982-12-09 AU AU11087/83A patent/AU561976B2/en not_active Ceased
  • 1982-12-09 WO PCT/US1982/001722 patent/WO1984002354A1/fr not_active Application Discontinuation
  • 1982-12-09 EP EP19830900309 patent/EP0128139A4/fr not_active Withdrawn
  • 1982-12-09 JP JP83500427A patent/JPS60500177A/ja active Pending
• 1983
  • 1983-02-01 IN IN117/CAL/83A patent/IN157840B/en unknown
  • 1983-02-04 ZA ZA83757A patent/ZA83757B/xx unknown
  • 1983-12-02 NZ NZ206472A patent/NZ206472A/en unknown
  • 1983-12-08 CA CA000442845A patent/CA1217997A/fr not_active Expired
  • 1983-12-09 IT IT24103/83A patent/IT1194512B/it active
  • 1983-12-09 PT PT77796A patent/PT77796B/pt not_active IP Right Cessation
  • 1983-12-09 KR KR1019830005825A patent/KR890003401B1/ko not_active IP Right Cessation
  • 1983-12-09 ES ES528241A patent/ES8504946A1/es not_active Expired
• 1984
  • 1984-07-20 DK DK359084A patent/DK359084A/da not_active Application Discontinuation
  • 1984-07-20 FI FI842931A patent/FI78929C/fi not_active IP Right Cessation
  • 1984-08-08 NO NO843184A patent/NO843184L/no unknown
• 1989
  • 1989-06-28 KR KR1019890009331A patent/KR890003402B1/ko not_active IP Right Cessation

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