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
  • 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
  • C21D8/0426—Hot 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
  • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
• • 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
  • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
• • 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
  • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
• • 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
  • C21D8/0447—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 heat treatment
  • C21D8/0463—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 heat treatment following hot rolling

Definitions

• ABSTRACT A killed steel having a particular composition is heated, subjected to hot rolling such that the finishing temperature is 750C or less, and subjected to recrystallization treatment. A steel sheet thus obtained has excellent press formability.
• a hot-rolled steel sheet having a low yield point may be manufactured by lowering the finishing temperature down to about 800C.
• the steel sheet becomes soft but the axial density of the plane ⁇ 100 ⁇ parallel to its surface is remarkably increased and thus the deep-drawability of the sheet becomes so low that it can not be used as a steel sheet for deep drawing. Accordingly, as far as deep drawing is concerned, cold-rolled steel sheet which can be manufactured by means of the first-mentioned method is suitable.
• the disadvantage of cold-rolled steel lies, however, in its high production cost due to complicated manufacturing steps as compared with the manufacturing steps used for making hot-rolled steel sheet.
• Rolling at such low temperatures will not only greatly reduce commercial productivity extremely but will also result in increase in rolling load.
• the rolling temperature should be capable of being increased to the highest level possible yet providing a steel sheet having excellent deep-drawability.
• a method for manufacturing a steel sheet having excel.- lent press formability which comprises heating a killed steel composed of not more than 0.10% C, 0.05% to 1.0% Mn, 0.005% to 0.15% A1, at least one member of the group consisting of Ti, Nb and Zr, and the rest Fe and unavoidable impurities, the Ti%/4 Nb%/7.8 Zr%/7.6 being more than the C% in the steel, subjecting the same to hot rolling such that the finishing temperature is 750C or less, and thereafter effecting a treatment for recrystallization.
• said killed steel further contains at least one member selected from the group consisting of not more than 0.15% P, not more than 0.10% W, not more than 0.10% Mo, not more than 0.3% Cr,.not more than 0.3% Cu, and not more than 0.4% Si.
• the chemical composition of the steel material requires such combination of elements as to enhance the recrystallization temperature indicated for that of the cold rolled material. At the same time it is necessary not only to enhance the recrystallization temperature but also to form a deposit or precipitate at hot or warm temperature rolling which is suitable for developing the axial density of the plane ⁇ 1 l 1 ⁇ parallel to a surface of the steel sheet during the recrystallization treatment.
• a composition of the steel according to the instant invention should be that C is not more than 0.10%; Mn is 0.05 to 1.0%; A1 is 0.005 to 0.15%, and that when Ti, Nb or Zr is to be added singly, Ti%/C% 4, Nb%/C% 7.8 or Zr%/C% 7.6. is to be satisfied respectively. If the Ti, Nb or Zr are added in combination, the characteristic properties of the product becomes more stabilized. When they are added in such combination, Ti%/4 l- Nb%/7.8 l'- Zr%/7.6 C% in the steel must be satisfied.
• not more than 0.15% P, not more than 0.10% W, not more than 0.10% Mo, not more than 03% Cr, not more than 0.3% Cu, and not more than 0.4% Si should be added singly or in combination.
• the content of C it should be up to 0.10%. If it is more than 0.10%, it will not only deteriorate the deep-drawability of steel sheet, but will also increase the amount of Ti, Nb or Zr to be added, which gives rise to an increase in the cost. Moreover, the increase of C content will result in elevation of the heating temperature necessary for solubilizing TiC, NbC' or ZrC which extremely lowers the productivity of hot rolling. For these reasons the content of C should preferably be 0.03% or less, if the strength of the product is not stressed very much. Deep drawability is further enhanced by satisfying C 0.02% by means of vacuum degassing treatment and the like.
• Mn is necessary in an amount of at least 0.05%, and preferably at least 0.1% for the purpose of deoxidation and prevention of hot brittleness. However, deep-drawability is lowered when the amount of Mn is more than 1 .0%. If the steel sheet is not stressed, it should preferably be 0.5% or less in view of the deep-drawability.
• Al is necessary in an amount of at least 0.005%, and preferably at least 0.01%, for deoxidation. If it is, however, more than 0.15%, it deteriorates the cleanliness of the steel and degrades the surface condition of the steel.
• P serves to enhance the anti-weather property as well as deep-drawability but it should be added in an amount of 0.15% or less, since an amount more than 0.15% will harden the steel.
• W and Mo will promote deep-drawability.
• the amount of W and Mo to be added should be not more than 0.10% since an amount more than 0.10% will add substantially nothingto the effect thereof.
• Cr and Cu will promote the anti-weather property.
• the amount of Cr and Cu to be added should be not more than 0.3% since an amount more than 0.3% will add substantially nothing to the effect thereof.
• Si to be added should be not more than 0.4%. If it is more than 0.4%. it will impart an adverse effect upon the ductile property of the material.
• another condition to consider in carrying out the method of the instant the invention is the control of the rolling conditions.
• the rolling conditions In order to effectively generate finely-divided deposits or precipitates which are considered to be necessary for enhancing the recrystallization temperature and for forming an aggregative structure desirable for deepadrawability in the recrystallization treatment after hot rolling, that is, in order to allow the TiC in case of Ti-added steel, or the NbC in case of Nb-added steel, etc. to effectively deposit or precipitate, or in order to allow the cold strain to remain in the rolled material, it is necessary to keep the finishing temperature at 750C or less.
• the deep-drawability of the material subjected to hot rolling, followed by recrystallization treatment. is inferior to that of the hot rolled material subjected to finish rolling at a temperature more than A;, point which has been a common practice.
• the finishing temperature will promote the deep-drawability as it decreases as shown in Table 2. It is thus preferable to keep the finishing temperature as low as possible.
• a finishing temperature below 400C is not practicable since it will increase the deformation resistance of the mill to such an extent that the rolling power must be made greater, and in addition it will fail to provide a better deep drawing.
• the finishing temperature when the total reduction rate below 800C is made greater, preferably made 40% or more of the thickness of the material at 800C, the deep-drawability is further promoted.
• the limitation of the finishing temperature to 750C or less will give a steel sheet having better deep-drawability than the conventional case in which the rolling is finished at more than A point.
• the recrystallization treatment is effected so as to release the strain accumulated in the rolled material as well as develop the axial density of the planes ⁇ 1 1 l ⁇ which are parallel to the surface of the steel and which are desirable for the deep-drawability.
• This recrystallization treatment is conducted by heating at temperatures ranging from the recrystallization temperature up to A point, or by such suitable methods as box annealing, open coil annealing, continuous annealing, etc.
• box annealing open coil annealing
• continuous annealing etc.
• EXAMPLE A steel material having a chemical composition shown in Table .3 was melted in a converter, from which a slab was manufactured by the conventional steps.
• the slab was heated at about 1,200C, then subjected to hot rolling in a continuous hot rolling mill at three levels of finishing temperatures, 550C, 650C and 740C, followed by water cooling and then, coiling. Thereafter the steel was subjected to a box annealing at 700C for 4 hours or to a continuous annealing at 850C for 5 minutes.
• the conical cup value and the axial density of-the planes ⁇ 1 11 ⁇ and ⁇ 100 ⁇ parallel to the surface with respect to'the above-treated steel sheet and the same steel sheet differing only by having subjected'to hot rolling at the conventional finishing temperature, 900C, are shown in Table 4 and Table 5, respectively.
• the thickness of the sheet was 2.7 mm in both cases.
• the steel sheet of the invention has the high axial density of the planes ⁇ 1 l l ⁇ and excellent deep-drawability as compared with that of the prior art, said deep-drawability being comparable to that of cold rolled steel sheet.
• Thickness 2.7 mm (onicnl cup blank diz1.; 108 mm Table 5 Strength of X-ray reflection in Example Strength of X-ray reflection ⁇ l l 1 ⁇ axial density 100 ⁇ axial density] Finishing Control tempera- Heat treatment steel Steel of this Invention ture after rolling C D. 1 E, J F, K G, L
• a method for manufacturing a steel sheet having an excellent press formability which comprises heating 21 killed steel composed of not more than 0.10% C, 0.05% to 1.0% Mn, 0.005% to 0.15% A1, at least one member of the group consisting of Ti, Nb and Zr, and the rest Fe and unavoidable impurities, the Ti%/4 -l- Nb%/7.8 Zr%/7.6 being more than the C in the steel, subjecting the same to hot rolling such that the finishing temperature is 750C or less, and thereafter effecting a treatment for recrystallization.
• said killed steel further contains at least one member selected from the group consisting of not more than 0.15% P, not more than 0.10% W, not more than 0.10% Mo, not more than 0.3% Cr, not more than 0.3% Cu and not more than 0.4% Si.

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

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Citations (4)

• 1973
  • 1973-12-11 US US423821A patent/US3897280A/en not_active Expired - Lifetime
  • 1973-12-13 GB GB5805673A patent/GB1450131A/en not_active Expired
  • 1973-12-17 DE DE2362658A patent/DE2362658C3/de not_active Expired
  • 1973-12-20 BR BR10000/73A patent/BR7310000D0/pt unknown
  • 1973-12-21 IT IT54538/73A patent/IT1000382B/it active

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