US20090047168A1 - Continuously Cast Enameled Steel Sheet Remarkably Excellent in Fishscale Resistance and Method of Production of the Same - Google Patents

Continuously Cast Enameled Steel Sheet Remarkably Excellent in Fishscale Resistance and Method of Production of the Same Download PDF

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US20090047168A1
US20090047168A1 US12/084,609 US8460906A US2009047168A1 US 20090047168 A1 US20090047168 A1 US 20090047168A1 US 8460906 A US8460906 A US 8460906A US 2009047168 A1 US2009047168 A1 US 2009047168A1
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oxides
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steel sheet
concentration
mass
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Hidekuni Murakami
Satoshi Nishimura
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Nippon Steel Corp
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    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
    • 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
    • C23D—ENAMELLING OF, OR APPLYING A VITREOUS LAYER TO, METALS
    • C23D5/00—Coating with enamels or vitreous layers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/12—Accessories for subsequent treating or working cast stock in situ
    • B22D11/124—Accessories for subsequent treating or working cast stock in situ for cooling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04—Removing impurities by adding a treating agent
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04—Removing impurities by adding a treating agent
    • C21C7/06—Deoxidising, e.g. killing
    • 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
    • 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
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • 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
    • C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
    • 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
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • 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

Definitions

  • the present invention relates to enameled steel sheet excellent in enameling characteristics (bubble and black spot defect resistance, adhesion, and fishscale resistance) and formability characteristics and a method of production of the same and particularly is characterized by being obtained by continuous casting.
  • the present invention has as its object to further advance the above-mentioned technology of enameled steel sheet and control not only the nitrides, but also the form of the oxides and thereby provide a continuously cast enameled steel sheet with excellent fishscale resistance able to further improve the fishscale resistance and enabling enameling by a single coating process with a small aging characteristic and a method of production of the same.
  • the present invention was obtained after various studies to optimize to the ultimate extent the conventional steel sheet and method of production of steel sheet.
  • the inventors studied the enameling characteristics of enameled steel sheet, in particular the production conditions, especially the steelmaking conditions, for B-containing steel, and as a result newly discovered the items of 1) to 5), as described below.
  • the magnitude of change of the concentration of elements in the oxides can be controlled by the addition of elements at the time of steelmaking, in particular the timing of addition of the oxide-forming elements.
  • the present invention was completed based on the above discovery.
  • the present invention is characterized in that the final product after a process of hot or cold rolling or both has oxides differing in composition or integral oxides having a large change in composition inside and these are present in specific preferable forms.
  • the gist of the present invention is as follows:
  • a continuously cast enameled steel sheet excellent in fishscale resistance characterized by being comprised of, by mass %
  • a continuously cast enameled steel sheet excellent in fishscale resistance as set forth in (1) characterized by having, in complex oxides of 0.10 m or more diameter comprised of Fe, Mn, Si, Al, B, or other oxides combined together in a unit observation field of 100 ⁇ m ⁇ 100 ⁇ m in the sheet cross-section, any two complex oxides with different Mn mass concentrations and not contacting each other and with a ratio of a maximum concentration of an Mn mass concentration (Mnmax %) and a minimum concentration of an Mn mass concentration (Mnmin %) of Mnmax/Mnmin ⁇ 1.2.
  • FIG. 1 is a view explaining the state of oxides when rolling steel containing coarse complex oxides with large differences in concentration of B and Mn.
  • FIG. 2 is a view explaining the state of oxides in the conventional steel containing coarse oxides.
  • FIG. 3 is a view explaining the state of oxides in the rolled steel containing fine oxides.
  • FIG. 4 is a view explaining that the voids around complex oxides become larger in the rolled steel containing coarse complex oxides with large differences in concentration of B and Mn.
  • FIG. 5 is a view explaining that the voids around complex oxides are small in the rolled steel containing coarse complex oxides with no differences in concentration.
  • the diameter of the oxides covered by the control in the present invention is made 0.10 ⁇ m or more.
  • the fishscale resistance constituting the major feature in the characteristics of the present invention steel that is, the effect of improving the ability to inhibit the hydrogen diffusion, becomes smaller, so there is no particular need to cover this by the control.
  • the features of the oxides explained below are recognized even if covering oxides of 0.50 ⁇ m or more, more preferably 1.0 ⁇ m or more, more preferably 2.0 ⁇ m or more.
  • the upper limit of the diameter does not have to be particularly limited if considering the effect of the present invention.
  • the average diameter of the oxides is kept to 15 ⁇ m or less, preferably 10 ⁇ m or less, more preferably 5 ⁇ m or less.
  • One of the features of oxides defined by the present invention is the B concentration of the oxides.
  • it is necessary to specify ones with high concentration and ones with low ones.
  • 100 of a size of 0.1 ⁇ m or more are measured. That is, there are nonintegral oxides differing in B concentration in terms of the concentration measured for oxides in a 100 ⁇ m ⁇ 100 ⁇ m observation field in the sheet cross-section, and the ratio of the high concentration of the B concentration (Bmax) and the low concentration of the B concentration (Bmin) is Bmax/Bmin ⁇ 1.2.
  • the ratio is preferably 1.5 or more, more preferably 2.0 or more, more preferably 4.0 or more, more preferably 6.0 or more.
  • the sheet is characterized in that there is a similar difference in composition for the amount of Mn as well. That is, it is characterized in that the steel sheet includes nonintegral oxides differing in Mn concentration in a 100 ⁇ m ⁇ 100 ⁇ m observation field in the sheet cross-section and in that the ratio of the high concentration of the Mn concentration (Mnmax) and low concentration of the Mn concentration (Mnmin) is Mnmax/Mnmin ⁇ 1.2. If this Mn concentration ratio becomes 1.2 or more, in the same way as B, the change in form of the oxides during rolling and the accompanying formation of voids become more efficient and as a result the fishscale resistance is remarkably improved.
  • the concentration ratio is 1.5 or more, more preferably 2.0 or more, more preferably 4.0 or more, more preferably 6.0 or more.
  • the method of measuring the concentrations of the elements in the oxides for defining the present invention is not particularly limited, but the concentrations of the oxides have to be specified. Further, as explained later, the change in concentration in single oxides also has to be defined; so for example use of an energy dispersive X-ray detector (EDAX) is convenient.
  • EDAX energy dispersive X-ray detector
  • the measurement method may be an ordinary method, but it is necessary to determine a particularly fine region, so care is required to make the beam diameter of the electron beam sufficiently small. Further, the absolute value of the Nb concentration does not have to be determined. It is sufficient that the relative value be known.
  • the obtained information is therefore from a region broader than the set diameter of the electron beam.
  • the dispersed oxides are believed to have originally been integral oxides. That is, when casting the molten steel finished being adjusted in ingredients, they were large single oxides, but they were extended and fractured and became finely dispersed. This extension and fracture mainly occurred in the rolling process. In particular, in the hot rolling process, the oxides were mainly extended, while in the cold rolling process, they were mainly fractured.
  • the coarse complex oxides 1 are fractured by the hot rolling 2 , extension 3 , and cold rolling 4 , fracture voids 5 are efficiently formed in the steel sheet, and the fishscale resistance is improved.
  • the coarse oxides 6 are hard to extend 3 and fracture by the hot rolling 2 and cold rolling 4 , so even if fracture spaces 7 are formed, preferable fracture voids cannot be obtained like in the present invention steel.
  • FIG. 1 shows that with steel sheet just containing simple complex oxides like in the past, as shown in FIG. 2 , the coarse oxides 6 are hard to extend 3 and fracture by the hot rolling 2 and cold rolling 4 , so even if fracture spaces 7 are formed, preferable fracture voids cannot be obtained like in the present invention steel.
  • FIGS. 1 and 2 show the case where the distance between the crushed complex oxides is relatively short and voids effectively remain between the complex oxides, but the effect of the present invention can be sufficiently obtained even when the voids between the complex oxides formed by the extension and fracture due to the hot rolling and cold rolling are crushed closed by the rolling in the same hot rolling and cold rolling process.
  • FIGS. 4 and 5 This situation is shown schematically in FIGS. 4 and 5 .
  • the complex oxides themselves are the same in size and arrangement, in steel of the invention as shown in FIG. 4 where the complex oxides include large differences in concentration of B and Mn and the ability to form voids is large, the voids 11 around the complex oxides become larger and the improvement in the fishscale resistance becomes better.
  • the voids are small.
  • complex oxides with different compositions have specific relative positional relationships in steel sheet. That is, complex oxides exhibiting a high B concentration and complex oxides exhibiting a low B concentration are present at a concentration ratio of 1.2 or more with an angle of the straight line connecting the centers of the complex oxides from the rolling direction of within ⁇ 10° and with a straight line distance between centers of the complex oxides of 0.10 ⁇ m to 20 ⁇ m.
  • the angle is characterized by being preferably within an angle of ⁇ 7°, more preferably within an angle of ⁇ 5°, and more preferably within an angle of ⁇ 3°.
  • the oxides are arranged in lines in the rolling direction.
  • the complex oxides characterizing the present invention are arranged parallel to the steel sheet surface and thereby enable further improvement of the characteristics. Note that if parallel to the steel sheet surface, of course the oxides are not limited to any specific angle from the rolling direction as explained above, but in ordinary methods of production, for example it is difficult to make the complex oxides align in the sheet thickness direction. The rolling is believed to cause the complex oxides to disperse.
  • the present invention defines the arrangement by the angle from the rolling direction.
  • the complex oxides covered are present at a distance between each other, in straight line distance, of 0.10 ⁇ m to 20 ⁇ m. If outside this range, the fishscale resistance deteriorates.
  • the distance is preferably 0.20 ⁇ m or more, more preferably 0.30 ⁇ m or more, more preferably 0.40 ⁇ m or more, more preferably 0.50 ⁇ m or more. The reason why the lower limit of the distance influences the effect of the invention is not clear, but it is believed that complex oxides covered may have fine complex oxides or complex oxides with small differences of concentration present between them and that the ability to inhibit hydrogen diffusion is affected by these complex oxides.
  • the upper limit is preferably 20 ⁇ m or less, more preferably 10 ⁇ m or less, more preferably 5 ⁇ m or less, more preferably 1 ⁇ m or less.
  • the reason for defining the upper limit is that when the complex oxides covered are too far apart, this runs counter to the idea of the present invention of extension and fracture of originally integral coarse complex oxides. According to the ordinary method of production, the oxides are usually arranged within 0.5 ⁇ m of each other.
  • the effect of the present invention is exhibited even without the different composition complex oxides being completely separated. That is, it is sufficient that an individual complex oxide present in a steel sheet have fluctuations in the B concentration and that the ratio of the B concentration of the high concentration part (Bmax) and the B concentration of the low concentration part (Bmin) be Bmax/Bmin ⁇ 1.2.
  • the ratio is preferably 1.5 or more, more preferably 2.0 or more, more preferably 2.5 or more, more preferably 3.0 or more.
  • an individual complex oxide present in a steel sheet have fluctuations in the Mn concentration and that the ratio of the Mn concentration of the high concentration part (Mnmax) and the Mn concentration of the low concentration part (Mnmin) be Mnmax/Mnmin ⁇ 1.2.
  • the ratio is preferably 1.5 or more, more preferably 2.0 or more, more preferably 4.0 or more, more preferably 6.0 or more.
  • the particularly desirable complex oxides are present as B—Mn—Fe complex oxides.
  • Optimum control of the composition and form (arrangement) of these complex oxides is the feature of the present invention. That is, a difference in composition of the complex oxides means a difference in the characteristics of the complex oxides, for example, the hardness or ductility.
  • the preferable form is controlled to by the large effect of hot rolling and cold rolling on the state of extension and fracture of the complex oxides.
  • the content is made 0.010% or less.
  • it is preferably made 0.0025% or less.
  • the more preferable range is 0.0015% or less.
  • the lower limit does not particularly have to be limited, but if making the amount of C on the low side, the steelmaking cost is increased, so 0.0003% or more is preferable.
  • Si can be included in a small amount to control the composition of oxides. To obtain this effect, the content is made 0.001% or more. On the other hand, excessive content not only tends to inhibit the enameling characteristics, but also a large amount of Si oxides poor in ductility in the hot rolling are formed and the fishscale resistance is lowered in some cases, so the content is made 0.100% or less.
  • the content is preferably 0.030% or less, more preferably 0.015% or less. From the viewpoint of improving the bubble resistance and black spot defect resistance etc. and obtain further better enamel surface properties, the preferable range is 0.008% or less.
  • Mn is an important ingredient affecting the changes in composition of oxides relative to the amounts of addition of oxygen and Nb. Simultaneously, it is an element preventing hot embrittlement due to S at the time of hot rolling.
  • the content is made 0.03% or more. It is desirably 0.05% or more.
  • the amount of Mn becomes higher, the enamel adhesion becomes poor and bubbles and black spot defects easily occur.
  • the steel of the present invention which actively uses Mn to the maximum extent a's an oxide there is only little deterioration of these characteristics due to the addition of Mn.
  • addition of Mn facilitates control of the compositions of the oxides, so Mn is positively added. That is, the upper limit of the amount of Mn is specified as 1.30%. The upper limit is desirably 0.80%, more preferably the upper limit of Mn is 0.60%.
  • O is an element which directly affects the fishscale resistance and the formability and simultaneously, linked with the amounts of Mn and Nb, affects the fishscale resistance, so is an essential element in the present invention. To obtain these effects, 0.005% or more is necessary.
  • the content is 0.010% or more, more preferably 0.015% or more, more preferably 0.020% or more.
  • the upper limit is preferably made 0.085%.
  • the content is 0.065% or less, more preferably 0.055% or less.
  • Al is an oxide-forming element. To improve the fishscale resistance of the enameling characteristics, it is preferable to include a suitable amount of the oxygen in the steel as oxides in the steel material. To obtain this effect, 0.0002% or more is included.
  • Al is a strong deoxidizing element. If added in a large amount, it becomes difficult to keep the amount of oxygen required by the present invention in the steel. Not only this, a large amount of Al oxides poor in ductility in the hot rolling are formed and the fishscale resistance is lowered in some cases. Therefore, the Al is made 0.030% or less. The content is preferably 0.015% or less, more preferably 0.010% or less, more preferably 0.005% or less.
  • N is a penetration type solid solution element. If included in a large amount, even if Nb, and further V, B, or other nitride-forming elements are added, the formability tends to deteriorate and production of a nonaging steel sheet becomes difficult.
  • the upper limit of N is made 0.0055%.
  • the content is made 0.0045% or less.
  • the lower limit does not particularly have to be set, but in the current steelmaking technology, production with less than 0.0010% would be costly, so the content is made 0.0010% or more.
  • the content of P increases, it has an effect on the reaction between the glass and steel at the time of firing the enamel.
  • the P precipitating in a high concentration at the grain boundaries of the steel sheet causes deterioration of the enamel appearance due to the bubbles and black spot defects etc. in some cases.
  • the P content is made 0.035% or less, preferably 0.025% or less, more preferably 0.015% or less, more preferably 0.010% or less.
  • S forms Mn sulfides.
  • coprecipitation of these sulfides with oxides has the effect of making the formation of voids at the time of rolling more efficient and improving the fishscale resistance.
  • This element need not be contained at all, that is, 0% is also possible, but to obtain the above effect, 0.002% or more is necessary.
  • the content is preferably 0.005% or more, more preferably 0.010% or more, more preferably 0.015% or more. However, if the content is too high, the effect of the Mn required for control of the composition of the oxides important in the present invention is sometimes lowered, so the upper limit is made 0.080%.
  • the content is preferably 0.060% or less, more preferably 0.040% or less.
  • B is an essential element in the present invention.
  • B is necessary for fixing the solute N and improving the deep drawability and for nonaging and imparting formability. Further, there is also the effect of improvement of adhesion, but in the present invention, it is included for imparting a special effect completely different from this. That is, the B added bonds with the oxygen in the steel to form oxides and acts effectively to prevent fishscale. To obtain this effect, 0.0003% or more is necessary.
  • the content is more preferably 0.0008% or more, more preferably 0.0012% or more, more preferably 0.0015% or more, more preferably 0.0020% or more. However, if the amount of addition becomes higher, at the time of addition of B, deoxidation occurs and it becomes difficult to keep oxides in the steel. Not only this, the bubble and black spot defect resistance deteriorates. Therefore, the upper limit is made 0.0250%.
  • the content is preferably 0.0150% or less, more preferably 0.0080% or less.
  • Nb has the remarkable effect of improving the r value when added alone, but the deterioration in the elongation becomes great and improvement of the formability is obstructed in some respects.
  • the recrystallization temperature remarkably rises.
  • annealing at an extremely high temperature becomes necessary, so the productivity of the annealing is reduced.
  • the content is preferably kept low. It should not be allowed to exceed 0.0040%.
  • the content is more preferably 0.0025% or less, more preferably 0.0015% or less. If 0, there is no need to consider the detrimental effect of Nb.
  • V is similar to Nb in the effect on the formability, but due to the balance with the amount of oxygen remaining in the steel, the upper limit is higher. Even when co-added to the B-containing steel covered by the present invention, the effect of raising the recrystallization temperature is smaller than Nb. Further, by co-adding it with B to form complex oxides, there is the effect of remarkably improving the fishscale resistance. To obtain the effect relating to V, 0.003% or more is necessary.
  • the content is preferably 0.006% or more, more preferably 0.010% or more, more preferably 0.015% or more. From the viewpoint of the cost of addition and the bubble and black spot defect resistance, the upper limit is made 0.15%. When the amount of B is 0.0015% or more and B alone is enough to obtain the effect of the invention, 0.060% or less, further 0.040% or less, is sufficient.
  • the Cu is included for controlling the reaction of the glass and steel when firing the enamel.
  • the Cu precipitated on the surface at the time of pretreatment has the effect of promoting microscopic changes in the reaction and improving adhesion.
  • double enameling it has little action due to the surface precipitation, but affects the microscopic reaction between the underglaze and steel.
  • 0.01% or more is added in accordance with need. Unintentional excess addition not only inhibits the reaction between the glass and steel, but also causes the formability to deteriorate in some cases, so to avoid this detrimental effect, making the content 0.500% or less is preferable.
  • the preferable range is 0.015 to 0.200%.
  • the content of the one or more of Cr, Ni, As, Ti, Se, Ta, W, Mo, Sn, Sb, La, Ce, Ca, and Mg is made 1.0% or less, preferably 0.5% or less, more preferably 0.1% or less. If included in a large amount, the reaction with the oxide-forming elements can no longer be ignored and the oxides become unpreferable in composition and form. However, even if a greater amount is added, the effect of the present invention is not lost. Merits in production or quality other than those envisioned by the present invention can be expected. It is also possible to deliberately add larger amounts.
  • the timing of addition of each element is preferably after the elapse of 1 minute or more.
  • the timing is more preferably after the elapse of 2 minutes or more, more preferably 3 minutes or more.
  • the steel is cast within 60 minutes. Preferably, it is cast within 40 minutes, more preferably within 20 minutes. Further, in the casting process, the effect of the invention appears more conspicuously with a cooling rate at the time of solidification at the layer of 1 ⁇ 4 the thickness of the slab of ⁇ 10° C./sec.
  • the rate is preferably 5° C./sec or less, more preferably 2° C./sec or less, more preferably 1° C./sec or less, more preferably 0.5° C./sec or less, more preferably 0.1° C./sec or less.
  • the effect of the present invention can be enjoyed to the maximum, it is preferable to add B in the order of Mn, V, Nb, and B as explained above.
  • the present invention inherently calls for effectively forming B oxides and optimally combining them with other oxides. If possible to maintain a good balance between the concentration of oxygen in the molten steel and the ratio of concentration of Mn, V, and Nb and B and temperature during refining, the effect of the present invention can be obtained even if adding the Mn, V, Nb, B all at once in the total amounts of addition, adding any two or more elements all at once, or further adding the elements separately.
  • preparing B-based complex oxides having distributions of concentration in advance and adding them to the continuous casting tundish or mold enclosed in wire etc. is one method of producing B-based complex oxides having a characteristic distribution of concentration of the present application.
  • the above-mentioned patent document does not disclose the timing of addition of additive elements, the solidification conditions, or any other matter relating to the production of complex oxides with large changes in composition as defined in the present application. Just adding B alone cannot give the sufficient effects.
  • the oxides have to contain B. Therefore, in the present application, for example, as in the above-mentioned method of production, first Mn is added to form Mn oxides, then B is added or oxides having an effective distribution of concentration themselves are prepared, then added, so as to form the oxides with large changes in composition defined in the present invention having B combined with oxides of Mn etc.
  • the above optimum complex oxides are not formed just by the change or ingredients due to the addition of elements or the elapsed time.
  • the temperature is also highly relevant.
  • the control of the high temperature reaction up until the start of solidification becomes important.
  • the solubility of the various types of elements in the steel also greatly changes. This also has quite an effect on the change in composition. For this reason, the cooling rate at the point of solidification becomes important for sufficiently obtaining the effect of the invention. If too fast, fine oxides and precipitates are formed separate from the original coarse complex oxides and the effect of the invention is inhibited.
  • the cooling rate of a slab during casting differs depending on the position in the thickness direction, so in the present invention, this is defined by the cooling rate at the layer at 1 ⁇ 4 the thickness as a representative value.
  • the 1 ⁇ 4 layer cooling rate is generally recognized and is found by calculations on heat transmission used in operational control etc. as well.
  • the diameter is 4.0 ⁇ m or more, more preferably 10 ⁇ m or more, more preferably 15 ⁇ m or more, more preferably 20 ⁇ m or more.
  • the oxides are preferably coarse at the time of completion of the casting because if fine, the extensibility of the oxides at the time of forming the slab becomes poor and fracture also becomes difficult to occur. What is defined here is the average diameter. Ordinarily, complex oxides of a size able to be observed by an optical microscope or a low power scan electron microscope are covered by the measurement.
  • the complex oxides are extended and fractured by rolling to obtain the targeted characteristics and change them to the more preferable forms. For this reason, a certain extent of work is required.
  • the thickness of the slab after completion of casting is preferably made 50 mm or more.
  • the slab is rolled by hot rolling to 1 to 8 mm or so and further by cold rolling to 2 to 0.2 mm or so, therefore the total strain becomes a logarithmic strain of 3 to 5 or more. Further, to obtain a better fishscale resistance, it is effective in the hot rolling at 600° C. or more to roll under conditions of 1000° C.
  • the voids functioning as hydrogen trap sites are mainly formed by the fracturing of the complex oxides in the cold rolling process after the hot rolling, but in the hot rolling process before that, control of the shape of the complex oxides is important.
  • the complex oxides in the hot rolling process, since the temperature is high, the complex oxides also soften. The difference in hardness from the matrix phase, that is, the iron, becomes small. In the approximately 1000° C. or more temperature range, the rolling causes almost no fracturing of the complex oxides—the complex oxides are just extended. Further, when the temperature is lower than 1000° C. and becomes approximately 900° C. or less, complex oxides become hard to extend, but no remarkable fracturing occurs such as with cold rolling. There is just some cracking of an extent forming fine cracks.
  • the temperature range of the hot working is too high, the recovery is too fast and enough strain for forming cracks can not be imparted to the complex oxides. Further, if too low, the form of the complex oxides becomes not flattened, but close to spherical, so cracks become difficult. Suitable elongation and less thickness are required for formation of cracks. For this, in hot rolling, control is necessary to impart extension of complex oxides by suitable deformation at a higher temperature range and formation of cracks in the lower temperature range. Further, the form of the complex oxides forming these cracks, as explained above, becomes more complicated and enables formation of effective voids efficiently compared with the case where there is a difference in concentration in complex oxides and a difference in deformability.
  • the hot rolling heating temperature, the coiling temperature, etc. may be set as usual in the usual range of operation.
  • the hot rolling heating temperature may be 1000° C. or less, but to sufficiently obtain the effect of extension of the complex oxides by the above hot rolling, should be 1050 to 1300° C. for rolling at 1000° C. or more.
  • the coiling temperature is 400 to 800° C.
  • the cold rolling is preferably performed by a cold rolling rate of 60% or more for sufficient fracture of the complex oxides and for obtaining steel sheet with a good deep drawability.
  • a cold rolling rate of 75% or more is preferable.
  • the annealing may be box annealing or continuous annealing.
  • the features of the present invention remain the same.
  • the features of the present invention are exhibited so long as the temperature is the recrystallization temperature or more.
  • continuous annealing is preferable. Box annealing can be performed at 650 to 750° C., while continuous annealing can be performed at 700 to 890° C.
  • steel sheet controlled in change of composition of complex oxides as in the present invention is given extremely excellent fishscale resistance not only by direct single enameling, but also double enameling. Further, no bubbles, black spot defects, etc. occur and an enameled steel sheet with excellent enamel adhesion is obtained.
  • the method of application of the glaze includes enameling of not only a wet glaze, but also a dry powder without problem. Further, the applications etc. are not limited in any way.
  • the invention exhibits its characteristics in bathtubs, eating utensils, kitchen utensils, building materials, household electrical appliance panels, and other products in the technical field of classification of enameled steel sheet.
  • the relative position for the oxides exhibiting a high concentration/low concentration ratio means A: an angle of within ⁇ 5° and a distance within 0.5 ⁇ m, B: the A conditions not satisfied, an angle of within ⁇ 10′, and a distance within 20 ⁇ m, and C: the B conditions not satisfied.
  • oxides means Fe, Si, Mn, Al, Nb, V, B, and other oxides combining together to form complex oxides.
  • Separatate oxides means any two complex oxides not contacting each other.
  • Standard oxide means any one not separate complex oxide”.
  • the enameling was performed by using the powder electrostatic coating method to dry coat an underglaze to 100 ⁇ m and an overglaze to 100 ⁇ m and firing in an atmosphere with a condensation point of 60° C. at 850° C. for 3 minutes.
  • the fishscale resistance was evaluated by placing the fired sheet into a 160° C. constant temperature tank for 10 minutes for a fishscale promotion test and visually judging the state of formation of fishscale by the five stages of A to E of A: extremely excellent, B: excellent: C: slightly excellent, D: ordinary, and E: problematic. Table 3 shows this as the fishscale resistance.
  • the enamel adhesion was evaluated by dropping a 2 kg spherical weight from a 1 meter height, measuring the state of peeling of enamel at the deformed part by 169 contact probes, and determining the area ratio of the unpeeled parts since there was no difference in adhesion by the ordinarily performed P.E.I. adhesion test method (ASTM C313-59).
  • the steel sheet of the present invention is an enameled steel sheet with extremely excellent enameling characteristics, in particular fishscale resistance.
  • steel sheets satisfying the steel ingredients defined by the present invention as shown in Table 3, steel sheets of the steel codes satisfying all of the requirements defined by the present invention, that is, the max/min-ratio of B of separate oxides (defined in claim 1 ), the max/min ratio of Mn of separate oxides (defined in claim 2 ), the separate oxide distribution (defined in claim 8 for B, defined in claim 9 for Mn), and the max/min ratio in the same oxide (defined in claim 6 for B, defined in claim 7 for Mn) had adhesions of 80 to 100% and enameling characteristics of bubbles and black spot defect resistance, adhesion, and fishscale resistance evaluated most highly overall.
  • the max/min-ratio of B of separate oxides defined in claim 1
  • the max/min ratio of Mn of separate oxides defined in claim 2
  • the separate oxide distribution defined in claim 8 for B, defined in claim 9 for Mn
  • the max/min ratio in the same oxide defined in claim 6 for B, defined in claim 7 for Mn
  • the steel sheets of the steel codes (a2, a5, c4, d5, e2, h1, k1) satisfying the requirement of the max/min ratio of B of the separate oxides (defined in claim 1 ) but not satisfying one of the other above requirements had adhesions of 75 to 85% and had enameling characteristics of a bubble and black spot defect resistance, adhesion, and a fishscale resistance evaluated as excellent (B) or slightly excellent (C), but were evaluated as overall excellent and gave the effects aimed at by the present invention.
  • the comparative examples (l1 to n2) do not satisfy the requirement of the max/min ratio of B of the other oxides (defined in claim 1 ) and even if satisfying the other requirements, are inferior in enameling characteristics (bubble and black spot defect resistance, adhesion, and fishscale resistance), so the effects targeted by the present invention cannot be obtained.
  • A means the total of the true strain imparted at 1000° C. or more and a strain rate of 1/sec or more
  • B means the total of the true strain impared at 1000° C. or less and a strain rate of 10/sec or more.
  • the relative position for the oxides exhibiting a high concentration/low concentration ratio means A: an angle of within ⁇ 5° and a distance within 0.5 ⁇ m, B: the A conditions not satisfied, an angle of within ⁇ 10°, and a distance within 20 ⁇ m, and C: the B conditions not satisfied.
  • the “oxides” means Fe, Si, Mn, Al, Nb, V, B, and other oxides combined together to form complex oxides.
  • “Separate oxides” means any two non-contacting composite oxides.
  • “Same oxide” means any single complex oxide not separated.
  • the fishscale resistance was judged in five stages of A to E including A: extremely excellent, B: excellent: C: slightly excellent, D: ordinary, and E: problematic.
  • the surface characteristics of the bubble/black spot defects were visually judged in five stages of A to E including A: extremely excellent, B: excellent, C: slightly excellent, D: ordinary, and E: problematic.
  • Max/min ratio Separate Max/min Enamel characteristics (separate oxide ratio Bubble/black Steel oxides) distribution (in same oxide) spot defect
  • Adhesion Fishscale code B Mn B Mn B Mn resistance % resistance Remarks a1 4.5 2.7 A A 3.3 2.2 A 100 A Inv. ex. a2 1.5 1.9 B A 1.1 1.7 A 85 B Inv. ex. a3 2.4 2.4 A A 3.4 2.2 A 95 A Inv. ex. a4 1.8 2.3 A A 2.0 1.4 A 85 B Inv. ex. a5 1.3 1.4 C B 1.1 1.5 A 85 C Inv. ex. b1 1.5 1.9 C B 1.2 1.7 A 80 B Inv. ex.
  • the enameled steel sheet of the present invention satisfies all of the fishscale resistance, bubble and black spot defect resistance, enamel adhesion, and surface characteristics required for an enameled steel sheet.
  • the fishscale resistance is remarkably improved, the defect rate in the process of production of an enamel product greatly falls, and therefore the industrial significance is large.

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  • Organic Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • Physics & Mathematics (AREA)
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US12/084,609 2005-11-09 2006-11-09 Continuously Cast Enameled Steel Sheet Remarkably Excellent in Fishscale Resistance and Method of Production of the Same Abandoned US20090047168A1 (en)

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US9382597B2 (en) 2010-12-27 2016-07-05 Posco Steel sheet for enamel having no surface defects and method of manufacturing the same
US11236427B2 (en) 2017-12-06 2022-02-01 Polyvision Corporation Systems and methods for in-line thermal flattening and enameling of steel sheets

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CN104250705A (zh) * 2014-09-19 2014-12-31 宝山钢铁股份有限公司 一种具有高温烘烤硬化性的搪瓷用钢及其制造方法
US11236427B2 (en) 2017-12-06 2022-02-01 Polyvision Corporation Systems and methods for in-line thermal flattening and enameling of steel sheets

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