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
  • C21D8/0447—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
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
  • B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B45/00—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills
• • 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
  • C21D3/00—Diffusion processes for extraction of non-metals; Furnaces therefor
  • C21D3/02—Extraction of non-metals
  • C21D3/04—Decarburising
• • 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
• • 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
  • C21D8/0473—Final recrystallisation annealing

Definitions

• the present invention is concerned with a process for producing a very low carbon cold-rolled steel strip comprising the first step of hot-rolling a low carbon steel containing 0.03 to 0.12 wt. percent carbon, the second step of allowing to cool the thus hot-rolled steel strip to produce a secondary mill scale layer on the surface of said steel strip and thereafter annealing the resultant steel strip in a heating zone containing a non-oxidizing gas to reduce the carbon in the steel to an amount less than 0.010 wt.
• This invention relates to a process for the production of a very low carbon-containing cold-rolled steel strip having an extremely high enameling property or a onestep enameling property.
• Another object of this invention is to provide an economical process for the production of an extremely low carbon steel strip for high-grade enameling having a high enameling property and an extremely low sagging without using any specific atmospheric gas in the decarburization annealing, or using an inexpensive non-oxidizing atmospheric gas usually used for annealing thin steel strip.
• the steel sheet produced by the conventional process has generally an excellent enameling property but the enameling procedure for the steel cannot be performed by one coat enameling and also the drawability of the steel sheet is not good. Further, there are such drawbacks in the above mentioned known process that skimming must be conducted in the steel-manufacturing step and that the danger of causing hot shortness in the hot-rolling step owing to the presence of sulfur in the steel is very great even though a specific rolling process is adopted.
• a conventional process has also been provided for producing enameling steel sheets by fixing carbon in the steel by titanium but such a process has been used in only a limited case since there are many problems in the process and in the qualities of the products. For example, the addition of titanium becomes very difficult as the carbon content in the steel is reduced, the yield is greatly lowered due to the formation of killed steel, the surface property of the steel sheet is reduced.
• an enameling low carbon steel sheet is produced by applying a process known as a decarburization process for steel, that is, by applying a vacuum degassing process wherein a molten steel from a steel-manufacturing step is subjected to vacuum degassing, or an open coil decarburization annealing process wherein a steel strip coil is in a state of loose coil, subjected to decarburization annealing in a wet hydrogen atmosphere, or a process wherein the carbon in steel is oxidized and removed by treating the surface of a cold-rolled steel strip coated with iron oxide powders.
• a decarburization process for steel that is, by applying a vacuum degassing process wherein a molten steel from a steel-manufacturing step is subjected to vacuum degassing, or an open coil decarburization annealing process wherein a steel strip coil is in a state of loose coil, subjected to decarburization annealing in a wet hydrogen atmosphere,
• an enameling iron sheet obtained by the application of the open coil type decarburization annealing process that is, by decarburizing rimmed cold-rolled steel strip in a state of loose coil in an atmosphere containing wet hydrogen to extremely reduce the carbon content and temper-rolling it in a tight coil state is excellent in sagging as compared with usual coil-rolled steel strip as well as with an enameling pure-iron sheet, and at the same time can be enameled in one step 'and has good formability, but it is very difficult by such process to produce an enameling steel strip of thickness above about 1.6 mm.
• the annealing in a conventional open coil type decarburization annealing equipment, the annealing must be conducted by increasing the diameter of the rolled steel coil as large as possible, in other words, re-. ducing the number of coil-rolling as small as possible, which makes the application of the open coil type decarburization annealing unprofitable in economy.
• a very low carbon-containing cold-rolled steel sheet in particular an enameling thick steelsheet, can be effectively produced without being accompanied by the above-mentioned coil breaking phenomenon and without need of complicated apparatus and procedures. That is, in the process of this invention, the decanburization annealing is conducted not in a wet hydrogen atmosphere as in an open coil annealing method but by covering the surface of a steel strip with surface scales formed by cooling the strip after hot-rolling, therefore, rolling operators, without having an open coil annealing installation, can produce comparatively easily a steel strip having particularly excellent enameling property and formability.
• the necessary decarburization annealing is applied to a hot-rolled steel strip in a state covered by scales prior to conducting a cold-rolling, that is, after hot-rolling.
• the cold-rolling in this invention is conducted after decarburization, with a reduction ratio of 30-80%.
• the steel strip After cold-rolling, the steel strip is subjected to recrystallization annealing and then to a temper-rolling with a reduction ratio of 0.5-3%.
• the amount of the scales on the surface of the steel strip formed after hot-rolling is not strongly affected by the hot-rolling temperature and rolling conditions, and by cooling the hot-rolled coil after continuous hot-rolling in the air, the scales are uniformly formed.
• the temperature decreasing velocity and humidity until the steel strip is cooled from the hot-rolling temperature to 300 C. must be properly checked to form a necessary amount of scale for subsequent decarburization annealing.
• the process of this invention has an effect that the decarburization ennealing can be carried out without adopting an open coil type decarburization annealing method in a wet hydrogen atmosphere, that is, the decarburization and annealing for steel can be effected at the same time in the state of tight coil and using a conventionally used Hz-Nz non-oxidizing atmosphere. This is caused "by annealing the steel strip coil in a state having secondary mill scales on the surface after hot-rolling. Although there may be a trouble of recoiling, by applying an open coil type decarburization annealing process to a hot-rolled steel strip, uniform and rapid decarburization can of course be effected.
• the steel is first produced in an openhearth furnace or a converter, and the removal of unnecessary components and adjustment of other components are conducted by usual known means according to the uses of thus produced steel. Further, in order to carry out the decarburization effectively in the subsequent annealing procedure, the carbon content in steel must be reduced to 0.12-0.030 percent by weight.
• molten steel is cast into an ingot and although the kind of steel may be rimmed steel or semi-killed steel, rimmed steel is most general when produced for enameling steel sheet.
• the steel ingot is slabbed under uniform heating into steel slabs, which are, after being subjected to a necessary surface treatment, heated and hot-rolled.
• the holt-rolling finishing temperature is 8709l0 C.
• the steel strip is coiled at about 600 C., and allowed to cool in the air to room temperature.
• an iron oxide layer or secondary mill scale is formed on the surface of the hot-rolled steel strip and if a sufficient amount of the iron oxide layer for decarburization is formed, it is unnecessary to cool the plate further, but for preventing the danger of treating the hot steel strip coil, it is generally desirable to cool it to room temperature.
• the surface scale of the hot-rolled steel coil is influenced in the thickness of the formed scale and the scale layer by the oxidation condition until the temperature of the steel strip is reduced to 300 C. and by gradual cooling from a usual hot-rolling finishing temperature, three layers of a wustite layer (FeO), a magnetite layer (Fe O and an a-hematite layer (Fe O' are formed.
• a wustite layer FeO
• Fe O magnetite layer
• Fe O' a-hematite layer
• the scale is usually formed in the thickness of about 10 microns in one side.
• the hot-rolled steel strip having the iron oxide layer or the secondary scales necessary for decarburization annealing is subjected to decarburization annealing in a conventional annealing furnace for thin plates.
• an H N inert gas usually used for annealing thin steel strip coil such as an HNX gas, an NX gas, and an AX gas and N gas as a waste gas from an oxygen production by an air liquefaction process.
• the decarburization can be carried out effectively without using a specific gas atmosphere as in an open coil decarburization annealing process.
• the steel strip coil is annealed using an N gas or an Hg-Nz inert gas (e.g., an HNX gas) and maintained at the annealing temperature until the content of CO in the waste gas becomes less than 1.0%.
• the most suitable annealing temperature is between the A transformation point and 650 C.
• a forcible decarburization may also be carried out by adding wet hydrogen in the above-mentioned annealing atmosphere but the main object of this invention is not concerned with the presence of such wet hydrogen in the annealing atmosphere. However, by applying such a forcible decarburization, the annealing period of time can be reduced.
• the carbon in steel is oxi dized by the oxygen of the scales on the surface of the steel strip and removed therefrom down to 0.01-0.0005 percent by weight, which gives good deep drawing.
• decarburized low carbon steel strip is pickled and cold-rolled into desired dimensions by a known process.
• the strip is cold-rolled with a usual reduction ratio, that is, the reduction ratio of 3080% to the final thickness.
• the conditions, such as atmosphere and temperature, for the aboveamentioned bright recrystallization annealing maybe known ones, for example the annealing may be carried out in an H N inert gas such as an HNX gas and at temperatures between 600 C. and the A transformatlon point.
• the temper-rolling may be conducted with a reduction ratio of below 3% preferably 0.5-1.5
• One of the important properties for excellent enameling low carbon steel sheets is that the strain of the steel sheet itself at high-temperature baking, that is, sagging is small and among various steel plate products produced by various processes in same conditions, sagging of the product by the process of this invention and the enameling low carbon steel sheet decarburized by an open coil annealing process is smallest. Moreover, while one-step enameling cannot be adopted in a cold-rolled rimmed steel sheet and pure-iron sheet due to the formation of defects, it is possible in the low carbon steel sheet obtained by the present invention and adhesive property in this case is better.
• the mechanical properties of the steel sheet by this invention such as the yield point, the total elongation 6 and the Erichsen value are almost the same as those of Thus obtained low carbon steel sheet was investigated a cold-rolled rimmed steel sheet and the former has a with respect to sagging, appearance by one-step enamelfor'mability the same as that of the latter. ing, adhesive property of enameling, and mechanical
• the carbon content in the product according to this properties, which showed they were almost same as those invention is about 0.002 percent by weight, or about the of the low carbon steel sheet obtained by an open coil same as that of an enameling low crabon steel sheet 5 type decarburization annealing of acold-rolled strip.
• the tempered rolled steel strip was, according to Therefore by the Process of thls lhvehtloh ehamehhg the standard of the Porcelain Enamel Institute in U.S.A., low carbon steel sheet having the thickness of about 1.6 ground coated in a test piece of X and heated for to 2.5 mm.
• the low strip was as follows, which shows the carbon content becarbon steel sheet made by this invention was almost the ing remarkably reduced. same as the open coil annealed enameling steel sheet in P r n sagging, adhesive property, enameling property and the C 0-002 like.
• the open coil annealed enameling steel sheet for gin comparative test had 1.6 mm. in thickness.
• Example 1 the tempered steel strip of 2.0 mm. in thickness was obtained.
• a process for producing a very low carbon coldrolled steel strip comprising the first step of hot-rolling a low carbon steel containing 0.03 to 0.12 wt. percent carbon, the second step of allowing to cool the thus hotrolled steel strip to produce a secondary mill scale layer on the surface of said steel strip and thereafter annealing the resultant steel strip in a heating zone containing a non-oxidizing gas to reduce the carbon in the steel to an amount less than 0.010 wt.
• a process for producing a very low carbon steel strip comprising the first step of hot-rolling a low carbon rimmed steel containing 0.03 to 0.12 wt. percent carbon, the second step of allowing to cool the thus hot-rolled low carbon rimmed steel strip to room temperature in the air to produce a fine secondary mill scale layer on the surface of said steel strip and then annealing the resultant steel strip, as it is in the state of a tight coil, in a heating zone containing a non-oxidizing gas to reduce the carbon in the steel to an amount less than 0.010 wt.
• a process for producing a very low carbon coldrolled steel strip comprising the first step of hot-rolling a low carbon rimmed steel containing 0.03 to 0.12 wt. percent carbon, the second step of allowing to cool the thus hot-rolled low carbon rimmed steel strip to room temperature in the air to produce a fine secondary mill scale layer on the surface of said steel strip, and then annealing the resultant steel strip, as it is in the state of a tight coil, in a heating zone containing a non-oxidizing gas at a temperature of from the A transformation point to 650 C., until the CO content in the waste gas becomes less than 1.0%, to reduce the carbon in the steel to an amount less than 0.010 wt.
• a process for producing a. very low carbon coldrolled steel strip comprising the first step of hot-rolling a low carbon rimmed steel containing 0.03 to 0.12 wt. percent carbon, the second step of allowing to cool the thus hot-rolled low carbon rimmed steel strip to room temperature in the air to produce a fine secondary mill scale layer on the surface of said steel strip and then annealing the resultant steel strip, as it is in the state of a tight coil, in a heating zone containing a non-oxidizing gas, that is, HNX gas, NX gas, or N gas as a waste gas from an oxygen production by an air liquefaction process, or mixed gas of above-mentioned waste N gas and AX gas, at a temperature of from the A transformation point to 650 C., until the CO content in the waste gas becomes less than 1.0% to reduce the carbon in the steel to an amount less than 0.010 wt.
• a non-oxidizing gas that is, HNX gas, NX gas, or N gas as a waste

Landscapes

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

Applications Claiming Priority (2)

Publications (1)

Family

ID=26387886

Family Applications (1)

Country Status (3)

Cited By (4)

Citations (3)

• 1965
  • 1965-08-20 GB GB35793/65A patent/GB1122584A/en not_active Expired
  • 1965-08-20 US US481399A patent/US3420718A/en not_active Expired - Lifetime
  • 1965-08-23 DE DE19651483519 patent/DE1483519A1/de active Pending

Patent Citations (3)

Also Published As

Similar Documents