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
  • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
  • C21D9/48—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals deep-drawing sheets
• • 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
  • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
• • 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
  • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
  • C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
  • C21D8/0436—Cold rolling

Definitions

• This invention relates to low-carbon steels having improved drawability. More particularly, the invention is directedto a method of producing low-carbon sheet steel with improved deep-drawing characteristics and high yield strength.
• Y It is well known that aluminum killed steels have excellent drawability; 'Aluminum killed steels, referred to as,,fSK grade steel, are characterized by flattened or paricake shap'ed ferrite grains which are crystallographically oriented to provide good drawability. Such grains are developed in the final sheet product by a properly controlled box annealing process during which selective growth of'the favorably oriented grains is effected by the. "aluminum 'nitride precipitate. Although the exact mechanism of the process is 'not fully known, the phenomenon that a critically dispersed second phase can markedly affect the recrystallization and grain growth is frequently observed, and in some cases, successfully employed in metallurgical applications.
• the drawability'of'sheet material can be evaluated by simple tension tests. When a strip specimen is pulled to a greater length; its width and thickness are decreased.
• the crystallographic orientation of the grains, and not the grain shape, is primarily responsible for the drawing properties.
• the drawability and the R value can be correlated with the crystallographic texture of the sheet.
• Good drawability and high R values are associated with the socalled cube-on-corner or the (111) texture, i.e. the (111) planes are parallel to the plane of the sheet.
• Poor drawability and low R values are associated with the cube-on-face texture.
• the cube-on-edge or the texture has intermediate drawing properties.
• the amount of the (111) texture should be high, whereas that of the (100) texture should be low.
• the R value varies also with the directions lying in the plane. Therefore, the ideal texture for optimum drawability is 111) fiber texture with the sheet plane normal as the fiber axis.
• the crystallographic texture of a specimen is normally determined by the construction of complete pole figures from X-ray intensity measurements; however, for detection of small variation in the texture, a direct comparison of two pole figures cannot reveal the detailed differences quantitatively. Accordingly, we have found it best to measure the integrated peak intensities of several refiections from the plane of the sheet and express them in units of corresponding peak intensities of a random specimen. The numerical values of these relative intensities so obtained are directly proportional to the pole densities of a specific plane lying parallel to the plane of the sheet. Since the drawability of a sheet depends on the relative population of specific crystallographic planes in the plane of the sheet, this technique is very useful. The intensities of five different reflections, i.e.
• the intensity of the (222) reflection which is the second order reflection of the (111) therefore represents the amount of (111). texture.
• the intensityof the (200) reflection represents the amount of the (100) texture, respectively.
• low-carbon sheet steel of good drawability without sacrificing yield strength which involves a combination of steps applied to low-carbon steels having initially greater than 0.02% carbon.
• Our method produces a crystallographic texture with a high degree of (111) orientation and a lesser quantity of 100) orientation.
• low-carbon steel processed according to the invention has a very favorable average R value indicating good drawability.
• a low carbon, hot rolled plate having more than about 0.02% carbon is cold rolled to from 50% to 85% reduction into sheet gauge.
• the cold-rolled sheet is then annealed at normal annealing temperature in the range from about 1025 F. to'about 1550 F. (below the transformation temperature) for more than 10 hours in an atmosphere containing dry hydrogen.
• dry hydrogen refers tohydrogen having a dew point less than 30 F.
• the sheet steel is annealed at the stated temperature for the stated time until the carbon content is in the range from about 0.004 to about 0.02% and then TABLE I.CHEMICAL COMPOSITION OF STEELS C Mn Si S P A1501 N O It should be noted that compositions A and B had a desired carbon content above 0.02% whereas composi tion C had a lower initial carbon content. Each of these steels was hot rolled in a commercial mill under the following conditions.
• compositions A and B small colonies of fine pearlite were found to exist between the grains and at three grain junctions and carbide plates were present at the grain boundaries.
• composition C pearliteicolonies were rare; however, a few thin carbide plates existed at some of the grain boundaries.
• crystallographic texture is controlled by precipitation of aluminum nitride.
• the crystallographic texture is controlled utilizing the cementite normally present. This may be accomplished by various annealing treatments such as the solution and tempering treatments prior to cold rolling, or decarburization during recrystallization anneal to eliect the development of desired textures.
• Hot-rolled plate samples of compositions A, B and C were cold rolled to 70% reduction in thickness from 0.096 to 0.029 inch for compositions ,A and B, and from 0.086 to 0.026 for composition C. Thesarnples'weredhn annealed at a temperature of 1320 F. in dry hydrogen having a dew point of approximately 90 F. The specimens were held at annealing temperature for 20 hours after which they were allowed to cool in the furnace.
• composition C is equal ,to" those of the SK grade, but the (200) and (310) components are appreciably higher.
• the (112) component of all three low-carbon steels are lower than that of the SK steel.
• the extent of decarburization dependsto some extent on'the flow rate of the hydrogen-containing atmosphere and the surface exposure of the specimen. With'a' flow rate of approximately 6080 ccf/minute, the carbon content may be reduced to as low as 0.004%, if care is exercised in the placement of. the sheets. If the sheets are placed loosely in contact with each other, the carbon content can be maintained at about0.016%, Extensive testing indicates that consistently good texture, high :R values and high yield strength are. always obtained iflthe carbon content in the annealed strip is reduced' jto below 0.02%.
• a method of producing low-carbon sheet steel of improved drawability and high yield strength which comprises cold rolling hot-rolled plate of lowcarbon steel having more than 0.02% carbon to from 50 to 85% reduction into sheet gauge, annealing said cold-rolled sheet at a temperature in the range of from about 1025 F. to about 1550 F. for more than ten hours in an atmosphere containing dry hydrogen having a dew point less than 30 F. to result in a carbon content of from 0.004 to less than 0.02% and cooling the annealed sheet.

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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 Sheet Steel (AREA)

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Publications (1)

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Cited By (4)

Citations (6)

• 1965
  • 1965-12-20 US US515232A patent/US3404047A/en not_active Expired - Lifetime
• 1966
  • 1966-12-06 GB GB54617/66A patent/GB1101110A/en not_active Expired
  • 1966-12-19 FR FR87930A patent/FR1505832A/fr not_active Expired
  • 1966-12-20 NL NL666617890A patent/NL154272B/xx unknown

Patent Citations (7)

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