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
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
• • 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
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
  • C21D8/0236—Cold rolling
• • 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
  • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
  • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
  • C23C8/24—Nitriding
  • C23C8/26—Nitriding of ferrous surfaces
• • 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
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
  • C21D8/0257—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment with diffusion of elements, e.g. decarburising, nitriding
• • 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
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
  • C21D8/0268—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment between cold rolling steps

Definitions

• This invention relates to a method of manufacturing thin steel of high strength and good ductility. It is more particularly concerned with a method of making such steel in which the steel is nitrided either before or after it is reduced to gauge.
• Inexpensive thin steel sheet and strip of high strength and good ductility is a desirable article of commerce, particularly as a base for tin plate.
• Thin steel in the form of wire also has many uses.
• steel strip to be tinned is conventionally made of low carbon steel containing no deliberately added alloying elements.
• the strip is hot rolled to intermediate gauge and is brought to the desired gauge by cold rolling.
• Those skilled in the art are aware that the degree of reduction of the steel obtained in cold rolling has a great influence on the physical properties of the product, and adjust the relative reductions eifected by hot and cold rolling accordingly.
• the bulk of the tin plate used in tin cans has thicknesses on the order of .010".
• the cold rolling necessary to reduce the steel to that gauge also reduces its ductility undesirably and it is therefore conventional in the production of steel of that type to anneal the cold reduced material to soften it.
• the annealing reduces the tensile and yield strengths of the material.
• Conventional tin plate displays tensile strengths of about 45,000 to 50,000 p.s.i. and elongations of about 20 to 25% in two-inch gauge length. Those properties are adequate for conventional tin cans.
• Can manufacturers would use even thinner tin plate if its tensile strength were sufficiently higher than conventional material to compensate for the thinner walls of cans made therefrom. Thinner tin plate Weighs less and costs less than conventional tin plate per unit of area. Modern rolling mills can roll strip to the thinner gauges desired but the strip after annealing displays very nearly the same unit tensile strength as conventional material and so does not produce cans of the required strength.
• the desired improvement in tensile strength of the steel is inversely proportional to its thickness. If tin plate .007" thick, for example, is to be manufactured into cans having the same strength as those made from conventional tin plate .010" thick, the tensile strength of the thinner steel must be about 65,000 to 70,000 p.s.i.
• My invention makes it possible to obtain that improvement in tensile strength without decrease in deformability of the material, and is capable of producing thin material having even higher tensile strengths. My invention also makes it possible to provide thin steel of conventional gauge but with improved tensile and yield strength.
• the steel is worked by hot rolling followed by cold rolling to an intermediate gauge.
• the material is then annealed in coil form in a non-oxidizing atmosphere to which is added about 25% by volume of anhydrous ammonia.
• the wraps of the coiled strip must be disposed so that the nitriding atmosphere has access to the entire surface of the coil.
• the coil can be simultaneously annealed and nitrided quite rapidly, the time required depending on the temperature to which the steel is heated. I find the temperature range from about 1000 F. to 1200 F. to be satisfactory, the corresponding times ranging from about one-half hour to two hours.
• the nitrogen content of the steel ranged from about .010% to .030%.
• the annealed and nitrided strip was cooled to room temperature and brought to the desired final gauge by a further cold reduction of about 2 /2 Those skilled in the art will understand that the treatment above described can be given the steel in the form of sheets if the sheets are disposed during annealing and nitriding (so that the furnace atmosphere has access to the entire surface thereof.
• Steel strip rolled to nominal .0061" thickness treated as above described exhibits tensile strength of about 76,000 lbs. p.s.i. and ductility, as measured by elongation over a two-inch gauge length, between 6 and 12%.
• the tensile strength of the material provided by my process is somewhat better than that of conventional material of .0118" nominal thickness made from rephosphorized steel.
• the process of my invention may also be practiced in another preferred embodiment by continuously annealing and nitriding steel strip or Wire in the form of strand.
• the time during which the steel is at annealing and nitriding temperature is much shorter in continuous strand annealing than in coil annealing so that the temperature of the strand must be increased somewhat. Because of the short time for nitriding I accomplish this step in an atmosphere of undiluted anhydrous ammonia. Where the steel is held at maximum temperature for at least 30 seconds, a treating temperature of about 1100 F. to about 1300" F. is satisfactory and raises the nitrogen content of the steel to .07% and upwards.
• the strand was raised to temperature in times ranging from to 36 seconds, held at temperature for seconds, and then cooled.
• Steel in the form of strand can be cooled rapidly, or quenched, which is not possible for steel in coil form. I find that it is desirable to cool the strand to a temperature of about 200 F. or so in about 30 seconds.
• Steel processed as above described exhibits tensile strengths on the order of 68,000 to 70,000 p.s.i. and elongations between 6 and 19% over a two-inch gauge length.
• the same material treated in the same way but not nitrided exhibits tensile strength on the order of 58,000 lbs. p.s.i.
• When the nitrided steel is given a further reduction of 2 /2 to 3% and aged one hour at the temperature of boiling water its tensile strength is increased another 3,000 to 4,000 p.s.i. Without significant impairment of its ductility.
• the final cold Working of my steel includes reductions up to about 15%. I find that value to be critical as far as the deformability of the steel is concerned. I measure deformability by bending a coupon of the material, cut transverse to the rolling direction, 180 around a diameter equal to its original gauge. Table II identifies the effect of various degrees of final reduction of steel of my invention and shows that above about 15% reduction the number of bends which the steel withstands is halved.
• the steel of Table II had a composition within the limits of Table I and contained .0l0%.012% uncombined nitrogen. It was hot and cold reduced to .0195" thickness, and annealed in coils. It is apparent from Table II that thin steel of adequate deformability having tensile strength well over 70,000 p.s.i. is readily attainable by the method of my invention.
• the reduction effected by cold rolling must be more than about 3% if the yield strength of the material is to be raised. This again may be seen from the data of Table II.
• the minimum reduction varies slightly with the composition of the steel and its thickness, but it must be more than a conventional temper reduction to bring about a useful increase in yield strength of the material.
• the method of producing thin carbon steel of high yield and tensile strength and substantial deformability comprising annealing cold reduced steel of intermediate gauge containing up to about .14% carbon and at least .010% uncombined nitrogen and then cold reducing the annealed intermediate gauge steel in amount more than about 3% but not more than about 15% to the desired gauge.
• the method of producing thin carbon steel of high yield and tensile strength and substantial deformability comprising annealing cold reduced steel of intermediate gauge containing up to about .14% carbon and at least about .010% uncombined nitrogen so that the nitrogen is held in solution in the steel and then cold reducing the annealed intermediate gauge steel in amount more than about 3% but not more than about 15% to the desired gauge.
• the method of producing thin carbon steel of high tensile strength and substantial deformability comprising cold reducing carbon steel containing up to about .14% carbon to an intermediate gauge, annealing the cold reduced steel in a nitriding atmosphere so as to nitride the steel to at least about .010% uncombined nitrogen content, and then cold reducing the annealed intermediate gauge steel in amount not more than about 15% to the desired gauge.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Organic Chemistry (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Heat Treatment Of Sheet Steel (AREA)
• Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
• Heat Treatment Of Strip Materials And Filament Materials (AREA)

Priority Applications (6)

Applications Claiming Priority (1)

Publications (1)

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ID=22366351

Family Applications (1)

Country Status (6)

Cited By (11)

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Citations (2)

• 1961
  • 1961-06-12 US US116300A patent/US3139359A/en not_active Expired - Lifetime
• 1962
  • 1962-05-29 GB GB20711/62A patent/GB940359A/en not_active Expired
  • 1962-06-08 NL NL279507A patent/NL279507A/xx unknown
  • 1962-06-12 BE BE618791A patent/BE618791A/fr unknown
  • 1962-06-12 LU LU41867A patent/LU41867A1/xx unknown
  • 1962-06-12 DE DEJ21925A patent/DE1247362B/de active Pending

Patent Citations (2)

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