KR101065545B1 - Very thin hard steel sheet and method for producing the same - Google Patents

Abstract

In a hard ultra-thin steel sheet having a sheet thickness of 0.400 mm or less, in mass%, C: 0% or more, 0.800% or less, N: 0% or more, and 0.600% or less, Si: 0% or more, and 2.0% or less, Mn : 0% or more, 2.0% or less, P: 0% or more, 0.1: 0% or less, S: 0% or more, Al: 0% or more, 3.0% or less, O: 0% or more The second phase containing 0.200% or less, having an average long diameter of 0.10 µm or more, an average short diameter of 0.05 µm or more, and an average long diameter / average short diameter? 2.0 is contained in a volume fraction of 0.05% or more.

Hard ultrathin steel sheet, ferritic phase, Rockwell hardness, flange formability, grain boundary

Description

Hard ultra-thin steel sheet and its manufacturing method {VERY THIN HARD STEEL SHEET AND METHOD FOR PRODUCING THE SAME}

The present invention relates to a thin steel sheet having a sheet thickness of 0.400 mm or less, including a surface-treated steel sheet used for an electric appliance, an electronic component, a building material or a metal container, and a manufacturing method thereof.

This application assumes Japanese Patent Application No. 2006-102766 as a basic application, and introduces the content.

Thin steel sheets having a sheet thickness of 0.400 mm or less have been used in various applications such as electrical equipment, electronic components, building materials, and metal containers. However, in order to reduce the cost of materials, further thinning of steel sheets has been advanced. When the material becomes thin, the strength of the member using the same also decreases, and therefore, the thickness of the material is also required to be hardened at the same time. One of the problems currently brought about by such ultra-thin hard materials is deterioration of workability. In particular, compared with thick materials used in automobiles and the like, in particular, thin materials are immediately broken when shrinkage occurs, so that uniform deformation becomes very important. This means that in the tensile test generally applied as the evaluation of the steel sheet properties, it is hardened while maintaining uniform elongation. Among these thin materials, in particular, in the steel sheet for containers subjected to strict processing such as drawing, ironing, and stretching, methods such as Patent Documents 1 to 3 are disclosed in order to secure workability.

However, these methods do not pay particular attention to uniform stretching, and although ductility (total stretching) is high, there are many aspects in which ductility is increased by local stretching. Therefore, in practical use, the problem of the present application, such as defects in surface properties due to breakage or constriction, has not been solved.

Patent Document 1: Japanese Patent Laid-Open No. 2-118026

Patent Document 2: Japanese Patent Laid-Open No. 3-257123

Patent Document 3: Japanese Patent Laid-Open No. 10-72640

This invention makes it a subject to suppress generation | occurrence | production of the fracture and shrinkage by lack of uniform deformation which become a problem when using a hard ultra-thin material. That is, in the deterioration of the stretching accompanying the hardening of the material, the uniform stretching is ensured by prioritizing the deterioration of the local stretching, and even if the same total stretching is performed, the occurrence of local deformation (shrinkage) is suppressed to a higher distortion region. We are doing that. And an object of this invention is to clarify the material conditions by this, and to provide the steel plate which applied it, and its manufacturing method.

The present inventors conducted a study to disperse various second phases in the steel sheet in order to harden the steel sheet. This belongs to the category of so-called precipitation strengthening and structure strengthening. Dispersing the second phase hardens the material and deteriorates the ductility as a natural result, but during the experiment, the second phase having a specific shape is steel sheet. When it disperse | distributed in the inside, it discovered that it can harden in the state which suppressed deterioration of uniform extending | stretching. Moreover, the form, quantity, and kind of a 2nd phase, and the range of the steel plate material which can obtain a preferable characteristic were also examined in detail, and the present invention was reached. The summary of this invention is shown below.

(1) Control of the form of the second phase. Anisotropic strong needle-shaped.

(2) Control of the size of the second phase. Increased in comparison with common precipitates.

(3) Control of the water density of the second phase. Distribute relatively sparsely

(4) A mother phase is made into the Fe ferrite phase, and the orientation of a 2nd phase is arrange | positioned in a specific orientation with respect to a mother phase.

MEANS TO SOLVE THE PROBLEM As a result of earnestly examining on the basis of the technical thought mentioned above, this inventor conceived in this invention. The summary is as follows.

(1) It is a hard ultra-thin steel plate whose plate | board thickness is 0.400 mm or less, It is more than 0% and is 0.800% or less, N: More than 0%, and more than 0.600%, Si: More than 0% and Si: 2.0% or less in mass% , Mn: more than 0% and 2.0% or less, P: more than 0% and 0.10% or less, S: more than 0% and 0.100% or less, Al: more than 0% and 3.0% or less, O: more than 0% And 0.200% or less, the balance is Fe and unavoidable impurities, the average long diameter is 0.10 µm or more and 30 µm or less, and the average short diameter is 0.05 µm or more and 30 µm or less, and the average long diameter / average short diameter ≥ The 2nd phase which is 2.0 is contained 0.05% or more and 20% or less by volume fraction.

(2) The hard ultra-thin steel sheet according to the above (1), wherein Ti: 0% or more and 4.00% or less (including 0), Nb: 0% or more and 4.00% or less (including 0), REM: 0% or more and 4.00% or less (including 0), B: 0% or more and 0.0300% or less (including 0), Cu: 0% or more and 8.00% or less (including 0), Ca : 0% or more and 1.00% or less (including 0), Ni: 0% or more and 8.00% or less (including 0), Cr: 0% or more and 20.00% or less (including 0) It contains 1 type, or 2 or more types.

(3) A hard ultra-thin steel sheet according to (1), wherein the average long diameter is 0.5 µm or more and 30 µm or less, and the average short diameter is 0.1 µm or more and 30 µm or less, and the average long diameter / average short diameter? 2.0 The water density of two phases is 0.01 piece / micrometer <^2> or more.

(4) A hard ultra-thin steel sheet according to (1), wherein the average long diameter is 0.5 µm or more and 30 µm or less, and the average short diameter is 0.1 µm or more and 30 µm or less, and the average long diameter / average short diameter? 2.0 The water density of two phases is 0.001 piece / micrometer <^3> or more.

(5) It is a hard ultra-thin steel plate as described in said (1), A columnar phase is a ferrite phase of Fe, and a volume ratio is 80% or more.

(6) A hard ultra-thin steel sheet according to (1), wherein the average long diameter is 0.5 µm or more and 30 µm or less, and the average short diameter is 0.1 µm or more and 30 µm or less, and the average long diameter / average short diameter? 2.0 The direction of the average long diameter of two phases is a <100> orientation or a <110> orientation of the Fe phase which this 2nd phase contact | connects.

(7) A hard ultra-thin steel sheet according to (1), wherein the average long diameter is 0.5 µm or more and 30 µm or less, and the average short diameter is 0.1 µm or more and 30 µm or less, and the average long diameter / average short diameter? 2.0 The two phases are single members or complex compounds of oxides, sulfides, carbides, nitrides, and intermetallic compounds.

(8) A hard ultra-thin steel sheet according to (7), wherein the average long diameter is 0.5 µm or more and 30 µm or less, and the average short diameter is 0.1 µm or more and 30 µm or less, and the average long diameter / average short diameter ≥ 2.0 The two phases are oxides containing one or two of Fe, Mn, Si, Al, Cr, REM, Ti, and Nb.

(9) A hard ultra-thin steel sheet according to (7), wherein the average long diameter is 0.5 µm or more and 30 µm or less, and the average short diameter is 0.1 µm or more and 30 µm or less, and the average long diameter / average short diameter? 2.0 The two phases are sulfides containing one or two of Ti, Mn, Cu, Ca, and REM.

(10) A hard ultra-thin steel sheet according to (7), wherein the average long diameter is 0.5 µm or more and 30 µm or less, and the average short diameter is 0.1 µm or more and 30 µm or less, and the average long diameter / average short diameter? 2.0 Two phases are carbides containing 1 type or 2 types of Fe, Ti, Nb, Si, Cr.

(11) A hard ultra-thin steel sheet according to (7), wherein the average long diameter is 0.5 µm or more and 30 µm or less, and the average short diameter is 0.1 µm or more and 30 µm or less, and the average long diameter / average short diameter? 2.0 The two phases are nitrides containing one or two of Fe, Ti, Nb, Al, B, and Cr.

(12) A hard ultra-thin steel sheet according to (7), wherein the average long diameter is 0.5 µm or more and 30 µm or less, and the average short diameter is 0.1 µm or more and 30 µm or less, and the average long diameter / average short diameter? 2.0 Two phases are intermetallic compounds containing 1 type or 2 types of Fe, Ti, Nb, Al, Si, Mn.

(13) A hard ultra-thin steel sheet according to (1), wherein the average long diameter is 0.5 µm or more and 30 µm or less, and the average short diameter is 0.1 µm or more and 30 µm or less, and the average long diameter / average short diameter? 2.0 The volume ratio of the two phases is (volume rate in the plate thickness surface layer 1/8) / (volume rate in the plate thickness center layer 1/4)> 10.

(14) A hard ultra-thin steel sheet according to (1), wherein the average long diameter is 0.5 µm or more and 30 µm or less, and the average short diameter is 0.1 µm or more and 30 µm or less, and the average long diameter / average short diameter? 2.0 The water density of two phases is (water density in plate | board thickness surface layer 1/8) / (water density in plate | board thickness center layer 1/4)> 10.

(15) Tensile test which is the hard ultra-thin steel plate as described in said (1), and has a distance between grades of 50 mm and a strain rate of 5 mm / min using the tension test piece which has a parallel part of width 25mm and length 60mm. Highest strength ≥ 350 MPa, and Rockwell hardness HR30T ≥ 54.

(16) A tensile test having a rigid ultra-thin steel sheet according to the above (1) and having a parallel portion having a width of 25 mm and a length of 60 mm, with a distance between ratings of 50 mm and a strain rate of 5 mm / min. For example, uniform stretching / local stretching ≥ 1.0.

(17) The tensile test piece which is a hard ultra-thin steel plate as described in said (1), and has a distance between grades of 50 mm and a strain rate of 5 mm / min using the tension test piece which has a parallel part of width 25mm and length 60mm. Yield stress / maximum strength? 0.9.

(18) A method for producing the hard ultra-thin steel sheet according to the above (8), wherein the steel sheet having a thickness of 50 mm or more and an average diameter of an oxide in the steel sheet of 10 µm to 25 µm is hot rolled at 600 ° C. or higher to 1000 After rolling with a total sum of true strains at conditions equal to or greater than 1 ° C. and a strain rate of 1 / sec or more, the true strain under conditions equal to or lower than 1000 ° C. and strain rate 10 / sec or more. Rolling with a total of 0.7 or more is performed.

(19) A method for producing the hard ultra-thin steel sheet according to the above (9), wherein when rolling a steel strip having a thickness of 50 mm or more and an average diameter of sulfides in the steel slab at 10 to 25 µm at a temperature of 600 ° C. or higher, 1000 After rolling with the sum total of true strain in the conditions more than degreeC and a strain rate of 1 / sec or more being 0.4 or more, rolling with 1000 sum total or less and the total sum of true strain in the conditions of 10 / second or more of strain rate is performed.

(20) A method for producing the hard ultra-thin steel sheet according to the above (10), wherein after cold rolling, at the same time or after the recrystallization annealing, in a temperature range of 600 to 700 ° C, {[carburizing time (seconds)] * (carburizing temperature (° C)]} / {(Carburizing gas concentration (%)] * (Cooling rate in carburizing process (° C / sec)]]} Carburizing treatment is performed under a condition of ≥ 20 to increase the amount of C by 0.0002% or more. .

(21) A method for producing the hard ultra-thin steel sheet according to the above (11), wherein after cold rolling, simultaneously with or after recrystallization annealing, {[nitriding time (seconds)] * [nitriding temperature in a temperature range of 600 to 700 ° C. (° C)]} / {[Nitriding Gas Concentration (%)] * [Cooling Rate in Nitriding Process (° C / sec)]} Nitriding is performed under a condition of ≥ 20 to increase the N amount by 0.0002% or more. .

(22) It is a method of manufacturing the hard ultra-thin steel sheet as described in said (12), In the steel plate manufacturing process, the cooling rate from 900 degreeC to 500 degreeC is 20 degrees C / sec or less in the cooling process from the temperature of 900 degreeC or more. By cooling, the intermetallic compound is increased by 2.0 times or more by volume ratio.

In addition, the symbol "*" in this specification represents a multiplication (x).

Moreover, although this invention relates to the thin steel plate whose plate | board thickness is 0.400 mm or less, and its manufacturing method, there exists a conventional technique which limits hot rolling conditions in order to control the form of an oxide as a manufacturing method of a part of an enamel steel plate.

However, the stretching of the oxide in the present invention is different from the stretching of the oxide as a limitation of the hot rolling conditions in the enamel steel sheet. In other words, as an extension technique for limiting the hot rolling conditions in the enamel steel sheet, it was very difficult to obtain the idea of utilizing the stretched oxide in the thin steel sheet that the steel of the present invention is subjected to. These are demonstrated in detail below.

In general, in the thin steel sheet as in the present invention, the oxide is very undesirable and its content is suppressed. This is because since the base material itself is thin, the concentration of strain around the oxide is very sensitive to the breakage of the base material.

A notable example is the flange formability in canning, whereby steel materials used for this application are strictly controlled and produced at very low levels. The adverse effect of the oxide on the thin material is not limited to the oxide itself, and when the stretched oxide such as an enamel steel sheet is crushed in the cold rolling process to form voids around the voids, the voids exhibit the same effect as cutting and deformability of the base metal. This is further degraded.

For this reason, in the thin material which the steel of this invention makes object, it was not possible to obtain the idea of improving the characteristic by utilizing oxide, the stretched oxide which fractures by cold rolling and forms a space | gap around, conventionally.

Moreover, the following matters are mentioned as a technical difference between the manufacturing method of an enamel steel plate, and this invention.

First of all, in the production of enamel steel sheet, the oxide is temporarily stretched in the hot rolling step, but in order to crush the oxide in the subsequent cold rolling process and to generate a large amount of voids around the crushed oxide, in the final product, each oxide is It becomes a finely crushed isotropic shape.

In the present invention, on the other hand, the oxide needs to be drawn in the final step, and the hot rolling process is used as one solution. That is, the oxide stretched by hot rolling is extended | stretched without crushing after cold rolling and annealing, and it is necessary to maintain the shape with anisotropy to the final product. This difference is basically caused by the difference in the composition of the oxide when the hot rolling conditions are the same. That is, in an enamel steel sheet, it is preferable that a comparatively soft Mn-containing oxide and a hard Nb- and B-containing oxide are in a complex form to promote the fracture. On the other hand, in the steel of the present invention, it is preferable that the oxide is not a composite of an oxide having a different composition, but is homogeneous, so that the deformation during cold rolling is also uniform, thereby avoiding fracture.

Even if it is temporarily stretched like an enamel steel sheet, if the shape of the oxide becomes isotropic due to subsequent fracture, the present invention exhibits a characteristic work hardening ability, good uniform stretching as a result, that is, suppression of local deformation. It doesn't work.

As described above, even if the production technique of the enamel steel sheet is recognized, it is not easy for a person skilled in the art to examine the influence of the form by applying a technique containing a large amount of oxide to the steel and the object of the present invention. not.

When the steel of the present invention is kept in an elongated state in a specific form, the work hardening behavior is dramatically changed and the local deformation is strongly suppressed, thereby newly discovering that the steel sheet preferably acts on practical ductility even in a thin steel sheet. .

According to this invention, even if it is the same intensity | strength and the same total stretch, the hard ultra-thin member which has high uniform stretch and suppressed generation | occurrence | production of local deformation (shrinkage) to a higher distortion area | region can be obtained. For this reason, it becomes possible to suppress generation | occurrence | production of the fracture and shrinkage by lack of uniform deformation which become a problem when using a thin member.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure explaining the site | part of the steel plate plate thickness direction of the hard ultra-thin steel plate of this invention.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

First, the component is demonstrated. All components are mass%. The amount of C is made into C: 0.800% or less in order to avoid deterioration of workability. Preferably it is 0.100% or less, More preferably, it is 0.060% or less. In particular, when carbide is used as the second phase characterized by the present invention, the content is preferably 0.0050 to 0.040%, more preferably 0.0080 to 0.030%. In the steel of the present invention in which the material is strengthened by dispersion of various second phases, the C content required from the viewpoint of securing the strength or the like may be low. C: The required strength can be ensured even at 0.0050% or less, and at 0.0030% or less, 0.0015% or less is also possible. It is preferable that the amount of C is lower in the meaning which improves r value and maintains axial moldability high.

N amount is also made into C: 0.800% or less in order to avoid deterioration of workability similarly to C. Preferably it is 0.100% or less, More preferably, it is 0.060% or less. In particular, when nitride is used as the second phase characterized by the present invention, the content is preferably 0.0050 to 0.040%, more preferably 0.0080 to 0.030%. In the steel of the present invention in which the material is strengthened by dispersion of various second phases, the N content required from the viewpoint of securing strength and the like may be low. N: The required strength can be ensured even at 0.0050% or less, even at 0.0030% or less, and 0.0015% or less is also possible. In the sense of improving the r value and maintaining high axial formability, the lower the amount of N is preferable.

If there is too much Si, workability and plating property will deteriorate, so it shall be 2.0% or less. However, in the steel of the present invention, when an oxide is used as the second phase, as described later, it is difficult for oxygen to remain in the steel, but it is difficult to obtain a stretched oxide, which is preferable in the present invention. In addition, when carburizing or nitriding is used to form the second phase, C or N infiltrated into the steel may form coarse Si carbide or Si nitride at grain boundaries and cause brittle cracking. In order to avoid the above-mentioned adverse effects, it may be necessary to make Si 1.5% or less and 1.0% or less. In particular, in the sense of maintaining the formability high, the lower the Si amount is preferable, and the moldability is improved by setting it to 0.5% or less, or 0.1% or less, or 0.07% or less.

If there is too much Mn, workability and plating property will deteriorate, so it shall be 2.0% or less. On the other hand, in the steel of the present invention, when an oxide is used as the second phase, it is easy to obtain a preferred stretched oxide in the present invention as described later. In addition, even when sulfides are used to form the second phase, elongated sulfides are easy to obtain, and thus are useful elements. For this reason, the preferable range of Mn is made into 0.05 to 1.0%. More preferably, it is 0.15 to 0.8%, More preferably, it is 0.25 to 0.7%.

When P is too large, not only the workability deteriorates, but also when carburizing or nitriding is used for formation of the second phase, the carburizing property and nitriding property of the steel sheet are inhibited, so that it is made 0.10% or less. In the meaning of keeping moldability high, the lower one of P amount is preferable, and moldability improves by making it 0.05% or less and 0.01% or less.

S deteriorates hot ductility and becomes an inhibitory factor in casting and hot rolling, so it is 0.100% or less. However, when a large amount of Mn, Cu, Ti, REM and the like are added and these sulfides are used as the second phase required by the present invention, the deterioration of hot ductility is small and is also a useful element. For this reason, the preferable range of S is made into 0.015 to 0.080%. More preferably, it is 0.025 to 0.070%, More preferably, it is 0.035 to 0.060%.

If Al is high, there is a problem that casting is difficult and surface damage is increased, so it is made 3.0% or less. However, since Al is a strong deoxidation element, in the steel of the present invention, when an oxide is used as the second phase, the oxygen remaining in the steel becomes difficult. Therefore, it is 0.010% or less, 0.005% or less, and 0.002% or less, and 0.001%. It may be necessary to make it% or less. On the other hand, it is a forming element of the intermetallic compound such as Ni ₃ Al, and has a desired effect according to the second dispersion on the required by the present invention. Although based also on the kind and quantity of the metal element which forms a compound with Al, in this case, it is preferable to set it as 1.0% or more, or 1.5% or more, or 2.0% or more.

When O is not used as the characteristic second phase in the present invention, O is deoxidized by Al, Si, Ti, or the like, and is preferably 0.010% or less. This is because, when the oxide in the steel has an isotropic (spherical) shape having no effect in the effect of the present invention, it is likely to be a starting point of cracking. Even when an oxide is used as the useful second phase, when the oxide becomes excessive, the starting point of cracking tends to be 0.200% or less. Preferably it is 0.010 to 0.100%, More preferably, it is 0.020 to 0.080%, More preferably, it is 0.030 to 0.050%.

Next, the element which can be added as needed is demonstrated.

Ti raises the recrystallization temperature of a steel plate, and remarkably deteriorates the annealing flow-through property of the ultra-thin steel plate which this invention makes object. For this reason, you may be 4.00% or less. When Ti compound is not used as a 2nd phase characterized by this invention, it is not necessary to add Ti, and may be 0.04% or less, More preferably, it is 0.01% or less. On the other hand, oxides, sulfides, carbides, nitrides, and intermetallic compounds of Ti can be used as the second phase characterized by the present invention, and depending on the type and amount of the elements forming the compound, the effect is more than 0.06%. Is fully exerted. More preferably, it is 0.100% or more.

Mb also has the same effect as Ti, and the recrystallization temperature is raised to significantly deteriorate the annealing flowability of the ultra-thin steel sheet of the present invention. For this reason, you may be 4.00% or less. When Nb compound is not used as a 2nd phase characterized by this invention, it is not necessary to add Nb, More preferably, it is 0.04% or less, More preferably, it is 0.01% or less. On the other hand, oxides, sulfides, carbides, nitrides, and intermetallic compounds of Nb can be used as the second phase characterized by the present invention, and depending on the type and amount of the element forming the compound, the effect is set to 0.06% or more. Is fully exerted. More preferably, it is 0.100% or more.

REM also has the same effects as Ti and Nb, but is an expensive element and is therefore 4.00% or less. When REM compound is not used as a 2nd phase characterized by this invention, it is not necessary to add REM, It is made into 0.04% or less, More preferably, it is 0.01% or less. On the other hand, oxides, sulfides, carbides, nitrides, and intermetallic compounds of REM can be used as the second phase characterized by the present invention, and depending on the type and amount of the element forming the compound, The effect is fully exhibited. More preferably, it is 0.100% or more.

B also has the same effect as Ti and Nb. However, depending on the addition amount, the ability to form carbonitrides is smaller than Ti and Nb, and when added simultaneously with these elements for the purpose of forming carbides or nitrides as the second phase, the recrystallization temperature of the steel sheet is raised and the present invention The annealing through-flow property of this ultra-thin steel plate is made to deteriorate remarkably. For this reason, it becomes useful when there is little content of Ti and Nb. However, since excessive cracking of the cast piece at the time of casting becomes remarkable, the upper limit is made 0.0300%. When B compound is not used as a 2nd phase characterized by this invention, it is not necessary to add B and it may be 0.0020% or less, More preferably, you may be 0.0010% or less. On the other hand, the oxides, carbides, nitrides, and intermetallic compounds of B can be used as the second phase characterized by the present invention, and depending on the type and amount of the elements forming the compound, the effect is sufficient when the content is 0.0040% or more. Exerted. More preferably, it is 0.0100% or more.

If the Cu content is too large, not only the recrystallization temperature will increase significantly, but also the surface properties will deteriorate, resulting in deterioration of workability and plating property, so it is 8.00% or less. In the steel of the present invention, a metal Cu phase, an intermetallic compound phase, or the like can also be used as the second phase. Moreover, even when sulfide is used for formation of a 2nd phase, since it is easy to obtain a stretched sulfide, it is a useful element. For this reason, a preferable range is made into 0.10 to 4.00%. More preferably, it is 0.20 to 3.00%, More preferably, it is 0.30 to 2.50%.

Ca is a useful element in the steel of the present invention in the case where sulfide is used as the second phase, elongated sulfides are easily obtained. However, since it is rich in reactivity and generally contains a large amount in steel, it is made into 1.00% or less. The preferred range is 0.01 to 0.50%. More preferably, it is 0.05 to 0.30%.

Since Ni is an expensive element, it is made 8.00% or less. In the present invention, as the compound-forming elements between the metal such as Ni ₃ Al, and has a desired effect according to the second dispersion on the required by the present invention. Although based on the kind and quantity of the metal element which forms a compound with Ni, it is preferable to set it as 1.0% or more, or 1.5% or more, or 2.0% or more.

Since Cr is an expensive element, it is made into 20.00% or less. When not using a Cr compound as a 2nd phase characterized by this invention, it is not necessary to add Cr, It is made into 0.06% or less, More preferably, you may be 0.02% or less. On the other hand, oxides, sulfides, carbides, nitrides, and intermetallic compounds of Cr can be used as the second phase characterized by the present invention, and depending on the type and amount of the element forming the compound, the effect is set to 0.10% or more. Is fully exerted. More preferably, it is 0.50% or more, More preferably, it is 1.50% or more, More preferably, it is 2.50% or more.

Although content with respect to elements other than the above is not specifically limited, In order to provide the characteristic which is not prescribed | regulated by this invention, Sn, Sb, Mo, Ta, V, W is 0.10% or less with respect to each element, and 0.50% or less in total. Inclusion does not impair the effects of the present invention at all. However, since these elements may form the compound which has coarse isotropic form and impair workability, care should be taken. It is preferable to set it as 0.010% or less with respect to each element, and 0.050% or less in total unless there is no objective in particular. More preferably, it is 0.0020% or less with respect to each element, 0.0050% or less in total, More preferably, it is 0.0010% or less and 0.0030% or less with respect to each element.

Next, the second phase most important in the present invention will be described. First, observation of the second phase and the like will be described. The observation method of the 2nd phase limited by this invention is not specifically limited. The form can be directly observed by a physical measuring instrument which can observe a micro area | region, such as an electron microscope. If it is relatively large, observation is possible even in a high magnification optical microscope. If it is an optical microscope or a scanning electron microscope (SEM), what grind | polished the steel plate cross section, and what etched it can be applied. If it is a transmission electron microscope (TEM), a thin film may be sufficient and the extraction replica obtained by the SPEED method etc. It is also possible to observe. Moreover, you may observe the residue which melt | dissolved the mother phase by electrolytic extraction. In addition, although the observation of the observed 2nd phase can be performed by EDX, an electron beam diffraction pattern, etc., it is not limited to these methods, You may use what kind of analysis apparatus which performance improvement is remarkable now. That is, what is necessary is just to be able to determine the shape, size, and number density of a 2nd phase, and the kind as needed by the method recognized as appropriate. Depending on the type, it is considered that it is a complex of various phases, and it may be difficult to make a complete discrimination. However, the effect of the present invention is obtained by dispersing the second phase in a specific form regardless of the type, so that the type can be determined. None is included in the present invention. Volume fractions and water densities are increased by taking into account even finer nitrides using more sophisticated analytical instruments. It is possible to determine.

The second phase observed as described above contains 0.05% or more of the second phase having an average long diameter of 0.10 µm or more, an average short diameter of 0.05 µm or more, and an average long diameter / average short diameter ≥ 2.0 by volume. It is a feature of the present invention. The size is preferably at least 0.20 μm, more preferably at least 0.50 μm, even more preferably at least 1.00 μm, even more preferably at least 2.00 μm, even more preferably at least 5.00 μm with respect to the average long diameter. However, if too large a second phase is present, it may be a starting point of breakage at the initial stage of processing, and the ductility may be significantly degraded. More preferably, it is 20 micrometers or less. However, even when the number is coarse, the degree of adverse effect is small when the number is very small. Therefore, the presence of a coarse exceeding this does not immediately depart from the present invention. The average long diameter / average short diameter becomes like this. Preferably it is 3.0 or more, More preferably, it is 5.0 or more, More preferably, it is 8.0 or more. Further, the volume fraction is preferably 0.1% or more, more preferably 0.3% or more, still more preferably 1.0% or more, and still more preferably 2.0% or more. However, when there is too much quantity of a 2nd phase, since it will become a starting point of a break at the beginning of a process, and ductility may deteriorate remarkably, it is preferable to set it as 20% or less. More preferably, it is 10% or less.

The water density of the second phase is measured to be 0.011 / μm ³ or more when observed in the cross section of the steel sheet, when the spatial dispersion is measured, such as observation of a thin film using 0.01 or more μm ² or thin film observation in an extraction replica or transmission electron microscope. , The effect of the present invention becomes remarkable. In the case of cross-sectional observation, Preferably it is 0.03 piece / micrometer <^2> or more, More preferably, it is 0.1 piece / micrometer <^2> or more, More preferably, it is 0.3 piece / micrometer <^2> or more. Moreover, in the case of spatial measurement, Preferably it is 0.003 piece / micrometer <^3> or more, More preferably, it is 0.01 piece / micrometer <^3> or more, More preferably, it is 0.03 piece / micrometer <^3> or more. These water densities are related to the size and volume fraction described above, and care must be taken not to make them extremely large or small in a range that does not deteriorate workability similarly to the size and volume fraction.

The mechanism by which the occurrence of local deformation is suppressed by controlling the form of the second phase in this way is not clear, but the following description is attempted.

Since the 2nd phase in this invention is harder than Fe phase which is a mother phase, when a steel plate deform | transforms, a deformation | transformation of a mother phase takes precedence. Moreover, since deformation of a mother phase is restrained by a 2nd phase, work hardening of a mother phase becomes remarkable. For this reason, it is thought that the propagation | transformation of distortion becomes favorable, deformation continues while carrying out deformation | transformation in a wider area | region, and uniform extending | stretching becomes high. In the case where the second phase having anisotropy is dispersed, the degree of confinement of the phase phase is considered to be larger than that of the general isotropic second phase. Alternatively, apart from this, the second phase with strong anisotropy has a weak bonding state with the mother phase, and the interface is slid and deformed with deformation, and furthermore, it is considered that the second phase is responsible for deformation by generating a large number of voids. For this reason, the deformation | transformation of the base material itself is suppressed to a higher distortion area | region, and it is also considered that uniform deformation continues. Although the steel of the present invention has a large work hardening amount and the local deformation ability is often lowered, the mechanisms that can fully explain the phenomenon including these are not clear.

It is clear that the uniform deformation in the steel of the present invention is not caused by the second phase but by the deformation of the mother phase, that is, the largest columnar volume. Naturally, the main phase is Fe, but in the present invention, it is assumed that the main phase is a ferrite phase of Fe, and the volume ratio thereof is preferably 80% or more. Generally, a phase mainly composed of Fe is known to be a pearlite, bainite, martensite phase or the like. However, in the present invention, since the high strength is achieved by dispersion of the second phase, the main phase is soft and uniform in terms of processability. This is because it is preferable. In addition, the volume ratio is preferably 85% or more, and more preferably 90% or more, in order to avoid ductile deterioration due to excessive generation of the second phase.

In addition, the orientation relationship between the second phase and the main phase is also an important requirement. Although also mentioned in the above mechanism, the effect of the present invention is related to what is considered to be due to the combined state of the Fe phase and the second phase, and the direction of the average long diameter of the second phase is in the <100> orientation of the Fe phase that the second phase is in contact with. Or <110> orientation. This orientation relationship can be detected by ordinary electron beam diffraction or the like.

Next, the type of the second phase itself will be described. In the present invention, a remarkable effect can be obtained when the second phase is a single member or a complex compound of oxides, sulfides, carbides, nitrides, and intermetallic compounds. In the case of oxide, it is an oxide containing one or two of Fe, Mn, Si, Al, Cr, REM, Ti, and Nb, and in the case of sulfide, one or two of Ti, Mn, Cu, Ca, and REM. Sulfides containing species, carbides containing one or two species of Fe, Ti, Nb, Si, Cr in the case of carbides; Fe, Ti, Nb, Al, B, Cr in the case of nitrides It is a nitride containing 1 type or 2 types, and when it is an intermetallic compound, it is an intermetallic compound containing 1 type or 2 types of Fe, Ti, Nb, Al, Si, Mn. Regarding carbides, the pearlite structure observed in the general steel, that is, the layered structure of the ferrite phase and cementite produced by transformation from the austenite phase at high temperature is not obtained at all because the effect of the present invention cannot be obtained. As the intermetallic compound, NiAl, Ni ₃ Al, Ni ₃ (Al, Ti), Ni ₂ TiAl, Ni ₃ Ti, Ni ₃ Mo, Ni ₄ Mo, Ni ₃ Nb, Co ₃ W, Fe ₂ Mo, Fe ₂ Ti, Fe ₂ (Ni, Co) and the like. The above-described oxides, sulfides, carbides, nitrides, and intermetallic compounds are generally compounds observed in steel materials, and need not be special, but it is also possible to form special compounds in the form of the invention. The kind is not limited to what was mentioned above, It is only what contained the typical element to the last. In addition, the 2nd phase which exists in steel is not limited to 1 type, It is contained in this invention also when 2 or more types exist. These may exist independently and may form the composite compound. In addition, the phase which is not included in this invention in the form may exist simultaneously.

In short, the morphological features of the second phase are important. Even so, it is true that there is a considerable difference in the magnitude of the effect due to the formed second phase. This difference is due to the type and amount of the second phase which can be produced in the steel sheet, the difference in the form which can be controlled by the manufacturing conditions as described later, or the type of the second phase itself related to the bonding state with the mother phase. The impact of

These influences cannot be completely separated, but in terms of development, the kind of the second phase and the elements forming the second phase can be classified as follows. As a kind, it is an intermetallic compound> carbide-nitride> oxide> sulfide. However, this is an estimation of the effect of assuming that the shape and quantity are the same, and depending on the manufacturing method and the type of the second phase, it may be difficult to secure the quantity and control the form. It is not too much. As an effect of each element, the following can be said. In the case of an oxide, it is preferable that Fe, Mn, and REM are included, and Si, Al, Cr, Ti, and Nb have little effect. In the case of a sulfide, Mn, Ca, and REM are preferable, and the effect of Ti and Cu is small. In the case of carbides, Cr, Ti, and Si are preferred, and the effects of Fe and Nb are small. In the case of nitride, Fe, Ti, B, Cr are preferred, and the effects of Nb and Al are small. In the case of an intermetallic compound, Fe, Al, Si, and Mn are preferable, and Ti and Nb have a small effect.

Here, the site | part of the steel plate plate thickness direction used in this specification is described using FIG. "Plate thickness surface layer 1/8" and "plate thickness center layer 1/4" represent the corresponding area | regions in FIG. In addition, although the area | region corresponding to "plate thickness surface layer 1/8" exists with respect to both surfaces of a steel plate, this invention makes it an object corresponding to the limited range of this invention also in any one surface thereof. Although it is relatively easy to study the manufacturing method and change the nitride distribution on the front and back sides, the present invention also covers the steel sheet of such a front and back surface layer. This is because only one side can obtain the improvement effect of the uniform deformation which this invention aims at. In addition, the volume ratio and the water density mentioned above collect data such that the measured value is not an abnormal value, and satisfy the conditions of the present invention at each specific location within the surface layer 1/8 and the central layer 1/4. Is enough. Moreover, "plate thickness 1/8 position" is also contained in "plate thickness surface layer 1/8".

When considering the distribution in the plate thickness direction of a steel plate, the characteristic 2nd phase in this invention does not need to be disperse | distributed uniformly to the whole, and may be unevenly distributed in the plate thickness direction. On the contrary, if the multilayer structure can be formed by alternating a layer having many second phases and a few layers in a layer shape in the plate thickness direction, it is better for the effect of the present invention to do so. Although this mechanism is not clear, it is thought that the work hardening amount is increased and local deformation is suppressed because the layers with a large number of second phases and the layers with little restrain each other's deformations. This is also considered to be the effect similar to the restraint relationship between the second phase and the mother phase described above occurring in the macroscopic space. In particular, by intensively distributing the second phase to the steel plate surface layer portion, it is possible to obtain a portion having a large effect of the present invention. That is, for the volume ratio of the second phase, (volume ratio at the plate thickness surface layer 1/8) / (volume ratio at the plate thickness center layer 1/4) ≥ 10, or for the water density of the second phase, (plate thickness It is preferable to set the water density in surface layer 1/8) / (water density in plate | board thickness center layer 1/4) ≥10. These ratios become like this. Preferably it is 20 or more, More preferably, it is 50 or more, More preferably, it is 100 or more, More preferably, it is 200 or more. However, when too many 2nd phases are formed in a surface layer part, it may become a surface defect and it may become easy to break, and it requires attention.

Next, the characteristic etc. of the steel plate which this invention makes object are described. First, this invention is limited to what is applied to the steel plate whose plate | board thickness is 0.400 mm or less. This is because, in the steel sheet with a large plate thickness, in processing, the molding proceeds by local ductility to a certain extent even after shrinkage occurs, and therefore, a technique limited to uniform stretching like the technique of the present invention has no meaning. The present technology is more preferably exhibited in an ultrathin steel sheet which is more preferably 0.250 mm or less, still more preferably 0.200 mm or less, and still more preferably 0.150 mm or less.

In addition, even if it is a thin member, in a flexible material, since it is possible to give uniform stretch of its own, the range of application of this technology shall be a hard material. This is also a result of being hardened not only by the 2nd phase which is a characteristic of this invention. A preferred application material is a tensile test by a JIS 5 test piece (i.e., a tensile test having a width of 25 mm and a parallel part having a length of 60 mm, a tensile test having a distance between ratings of 50 mm and a strain rate of 5 mm / min). Steel sheet having a maximum strength of ≥ 350 MPa and a Rockwell hardness of HR30T ≥ 54. More preferably the highest strength ≥ 400 MPa, also Rockwell hardness HR30T ≥ 57, more preferably the highest strength ≥ 450 MPa, and also the Rockwell hardness HR30T ≥ 61. In addition, the steel of the present invention is characterized in that uniform stretching / local stretching ≥ 1.0 in the tensile test by the JIS 5 test piece. This ratio becomes like this. Preferably it is 1.5 or more, More preferably, it is 2.0 or more, More preferably, it is 3.5 or more, More preferably, it is 5.0 or more. As described above, the steel of the present invention is also characterized by a large amount of work hardening. In the tensile test by the said JIS5 test piece, yield stress / highest strength <= 0.9, More preferably, it is 0.8 or less, More preferably, it is 0.7 or less, More preferably, it is 0.6 or less.

Below, an example of a manufacturing method preferable for each kind of 2nd phase of the steel of this invention is shown.

First, the case where an oxide is used as a characteristic 2nd phase is shown.

One of the preferred forms is that the oxide is stretched by rolling in the hot rolling process to change to the desired form. For this purpose, a certain amount of processing is required, and it is preferable to make thickness of the steel piece which completed casting into 50 mm or more. More preferably, it is 150 mm or more. Moreover, in order to make an oxide have a suitable size after extending | stretching, it is preferable that the size of the oxide before extending | stretching shall be 10 micrometers-25 micrometers. Excessively fine ones are difficult to stretch, and coarse ones become linear in the spatially dispersed state after rolling, which is not preferable in the effect of the present invention. And in the hot rolling, the total deformation of the true strain is at least 1000 ° C. and the strain rate is 1 / sec or more, and the total strain is 0.4 or more, and then the total deformation of the true strain is 1000 ° C. or less and the strain rate is 10 / sec or more. It is effective to perform this rolling of 0.7 or more. This mechanism is not clear, but is considered as follows. In the high temperature region of 1000 ° C or higher, the oxide is also softened, so that the hardness difference with the work hardened base iron becomes small, so that the oxide is stretched by rolling, and thus, a needle-shaped oxide which is preferable in the present invention can be obtained. When the temperature is lower than about 1000 ° C. and about 900 ° C. or less, the oxide is less likely to be stretched and partially crushed, so that the oxide having an appropriate needle shape is dispersed in the steel sheet at appropriate intervals. In order to appropriately stretch and disperse as described above, control of the strain rate is also important for controlling the temperature control during hot rolling, the amount of distortion in each temperature region, and the softening of the work hardened base iron.

By applying this temperature, the amount of distortion and the strain rate condition to the sulfide, it is possible to obtain the same preferable effect as the oxide.

Next, the case where carbide is used as a characteristic 2nd phase is shown.

In this case, it is possible to produce a carbide having a desirable form from C and the additional element previously contained in the steel by heat treatment of the manufacturing process, but the present invention shows a method utilizing carburization as a more preferred form. According to the carburization, as described above, it is possible to disperse the characteristic second phase only on the surface of the steel sheet, and since the C concentration gradually increases, it is easy to form a carbide having an anisotropic form grown in a preferential orientation. As the conditions, after cold rolling, simultaneously with or after recrystallization annealing, or in a temperature range of 600 ° C to 700 ° C thereafter, {[carburizing time (seconds)] * [carburizing temperature (° C)]} / {[carburizing gas concentration (%)] * [Cooling rate in carburizing treatment (° C / sec)]} Carburizing treatment is performed under the condition of? 20, and the amount of C is increased by 0.0002% or more. If the temperature is out of this range, the carburizing efficiency is lowered at the low temperature side. On the contrary, if the temperature is too high, the form of the carbide tends to be isotropic. {{Carburization time (seconds)] * [carburizing temperature (° C)]} / {[carburizing gas concentration (%)] * [cooling rate in carburizing process (° C / sec)] is 20 or more Preferred forms are achieved. Basically, the development of the second phase having anisotropy becomes remarkable by sufficiently growing the carbide by treatment of high temperature, long time and slow cooling while suppressing the generation of precipitation nuclei of carbide at low C concentration. However, when carburizing at high temperature for a long time, C invading into steel from the surface of the plate reaches the center of the plate thickness by diffusion, and the effect of increasing the invention effect by the multilayer structure described above is lost. For this reason, it is preferable to control the value of said Formula so that only surface layer part may be carburized according to carburizing process conditions. Although this value is based also on plate | board thickness etc., it is preferable to set it as 500 or less or 200 or less. As the conditions of the atmosphere including the type of carburizing gas, generally known conditions may be used. In addition, the carburization method is not limited to the gas carburization shown here, but it is possible to apply the carburization method generally known. In addition, although the amount of increase of C and 0.0002% or more seems to be very small as the amount of increase, considering the amount of increase in the surface layer of the steel sheet in the ultrathin material, it is an amount sufficient for the expression of the effect of the invention.

In addition, by making these carburization conditions into the conditions at the time of applying nitride by nitriding as a 2nd phase, it is possible to obtain the preferable effect similar to carbide. That is, after cold rolling, simultaneously with or after recrystallization annealing, or in a temperature range of 600 to 700 ° C., {[nitriding time (seconds)] * [nitriding temperature (° C.)]} / {[Nitriding gas concentration (%)] * [Cooling rate in nitriding treatment (° C / sec)]} Nitriding treatment is performed under the condition of? 20, so that the amount of N is increased by 0.0002% or more. What is necessary is just to use the conditions generally known as conditions of the atmosphere containing the kind of nitriding gas. In addition, the nitriding method is not limited to the gas nitriding shown here, and it is possible to apply generally known nitriding methods as in the case of carburization.

In the case of using the intermetallic compound as the second phase, the second phase is preferable in the present invention by advancing the formation mainly by growth of the intermetallic compound by completely cooling from the state in which all or most of the intermetallic compound is dissolved. It is suitable to obtain. For this purpose, in the steel plate manufacturing process, in the cooling process from the temperature of 900 degreeC or more, the cooling rate from 900 degreeC to 500 degreeC is cooled to 20 degrees C / sec or less, and an intermetallic compound is increased by 2.0 times or more by volume ratio. To do that. When the temperature before the start of cooling is too low, dissolution of the intermetallic compound is insufficient, and subsequent growth does not occur. In addition, if the cooling rate is too fast, the frequency of nucleation of the intermetallic compound is high, and anisotropic growth does not occur, and the isotropic intermetallic compound is formed at a high density.

Naturally, the manufacturing method with respect to the various 2nd phase shown here differs according to the element which forms the target 2nd phase, and its quantity, Of course, it is not limited to the said range. Knowing the kind of elements that form the second phase, the kind, amount, and orientation of the form of the second phase to be formed, finding suitable conditions is a general metallurgical category, and those skilled in the art will recognize them after several trials. It is not too difficult to confirm.

In manufacture of a thin steel plate, re-rolling may be performed after recrystallization annealing for hardness adjustment and sheet thickness adjustment. The reduction ratio is in practical use from about a few percent close to the skin pass performed for shape adjustment to 50% or more similar to cold rolling. When the re-rolling method is applied to the present invention, the effect of the present invention is not impaired at all. However, if the reduction ratio is excessively high, of course, the absolute value of uniform stretching becomes small. The amount of work hardening in the uniformly stretched region is also small, and considering the application of the present invention effect, this is not a preferred method. Preferably it is 30% or less, More preferably, it is 20% or less, Preferably it is 10% or less, Preferably you may be 3% or less.

The effect of the present invention is not dependent on the heat history before the annealing and the manufacturing history after the component adjustment. In the case of hot rolling, the slab is not limited to manufacturing methods such as the ingot method and the continuous casting method, and also depends on the thermal history up to the hot rolling. Therefore, the slab reheating method and the directly hot rolled slab without reheating the cast slab are CC-DR. The effect of the present invention can also be obtained by thin slab casting in which the method and the defect rolling are omitted. Moreover, the effect of this invention can be acquired also by two-phase region rolling which makes finishing temperature into the abnormal region of (alpha) + (gamma), or continuous hot rolling which joins and rolls a crude bar, regardless of hot rolling conditions.

Moreover, when using the steel of this invention as a raw material which has a welded part, since uniform deformation in a heat affected zone can be improved and generation | occurrence | production of shrinkage can be suppressed, it is especially preferable.

The steel plate of this invention also includes the case where it is used by performing any surface treatment. If it is in the scope of the present invention, it is not damaged by surface treatment by application. As surface treatment, tin, chromium (tin free), Ni, zinc, aluminum, etc. which are normally applied about metal plating are performed. Moreover, also about the original board for laminated steel sheets which coat | covered the organic film currently used, the effect of this invention becomes possible.

As a use, it can be used for an electrical device, an electronic component, a building material, or the metal container as a whole, and of course, it is applicable when there exists the same subject as what was mentioned above in any use in other fields.

(Example)

The steel of each component shown in Table 1 was subjected to hot rolling, cold rolling, recrystallization annealing and re-cold rolling to produce various steel sheets, and various evaluation tests were performed. The second phase was observed by cross section of the steel sheet, thin film thin film, extraction replica and electrolytic extraction residue using SEM and TEM. In addition, the elements contained in the second phase were qualitatively analyzed using EDX. Material properties were measured by a tensile test and a Rockwell surface hardness by JIS 5 tensile test piece in the rolling direction.

Measurement results and evaluations are shown in Tables 2 to 5. The meaning of the term in each table | surface is shown below.

"Average long diameter", "Average short diameter": It is sufficient not to be biased about the 2nd phase which satisfy | fills an average long diameter of 0.10 micrometer or more, an average short diameter of 0.05 micrometer or more, and an average long diameter / average short diameter ≥ 2.0. Each average value when measured against number.

"Average long diameter / average short diameter": Ratio of "average long diameter" and "average short diameter". It is an index indicating the degree of anisotropy of the oxide which is the source of the invention effect.

"Containing element": The element detected from the 2nd phase which shows the characteristic of this invention.

"Azimuth | direction": The relationship between the orientation of the average long diameter of a 2nd phase, and the crystal orientation of the columnar image which the 2nd phase is in contact with. When related to orientation, it represents the crystal orientation of columnar shape.

"Flange formability": The body part of the three-piece can which rounded and welded the flat plate to a cylindrical shape is prepared for 10000 cans. And when these are flange-molded using a metal mold | die, as a result, when the whole can can be flange-molded without fracture | rupture, it passes and fails even when one can is broken.

"Evaluation": Normal level: C, Excellent: B, Remarkably excellent: A. A and B are made into this invention.

(First embodiment)

Table 2 shows the experimental results when the second phase was used as an oxide. The form of the oxide was mainly controlled by the oxide size under casting conditions and the amount of stretching under hot rolling conditions. The "water density" of the oxide was determined by cross-sectional observation in SEM. By controlling the state of an oxide within the range of this invention, it can confirm that favorable uniform elongation is obtained.

(2nd Example)

Table 3 shows the results of the experiment when the second phase was sulfide. The form of the sulfide was mainly controlled by the sulfide size under casting conditions and the amount of stretching under hot rolling conditions. The "water density" of the sulfide was determined by TEM observation. By controlling the state of a sulfide within the range of this invention, it can confirm that favorable uniform extending | stretching is obtained.

(Third Embodiment)

Table 4 shows the results of experiments where the second phase was carbide or nitride. The form of carbide or nitride was controlled primarily by carburizing or nitriding conditions. In this embodiment, the "platelets" are all steel sheets recrystallized annealed at 700 degreeC. As a comparative material, the characteristics are shown also about having made hardness similar to a carburizing or nitriding board by re-rolling, without carburizing and nitriding. Carbide or nitride was observed at the plate thickness 1/8 position and the plate thickness center. The "water density" of the carbide or nitride was obtained by SEM observation of the residue when the sheet thickness surface layer 1/8 or the plate thickness center layer 1/4 was electrolyzed. In Table 4, the values relating to the "volume fraction", "water density", and columnar phases relating to the second phase are for sheet thickness surface layers 1/8. By controlling the state of carbide or nitride within the scope of the present invention, it can be confirmed that good uniform stretching is obtained.

(Example 4)

Table 5 shows the experimental results when the second phase was used as the intermetallic compound. The intermetallic compound was referred to as Ni ₃ Al, and its form was mainly controlled by the recrystallization annealing conditions, in particular, the degree of solubilization by the annealing temperature and the nucleation and growth by the subsequent cooling process. In this embodiment, the "platelets" are all steel sheets in a cold rolled state. The "water density" of Ni ₃ Al was determined by TEM observation. As compared with the steel sheets other than the present invention shown in the first to fourth examples, it can be confirmed that favorable characteristics can be obtained by controlling the state of the intermetallic compound within the scope of the present invention.

According to this invention, even if it is the same intensity | strength and the same total stretch, the hard ultra-thin member which has high uniform stretch and suppressed generation | occurrence | production of local deformation (shrinkage) to a higher distortion area | region can be obtained.

Claims (22)

It is a hard ultra-thin steel sheet whose plate thickness is 0.400 mm or less, In mass%, C: more than 0% and 0.800% or less, N: more than 0% and 0.600% or less, Si: more than 0% and not more than 2.0%, Mn: more than 0% and 2.0% or less, P: more than 0% and 0.10% or less, S: more than 0% and 0.100% or less, Al: more than 0% and not more than 3.0%, O: more than 0% and containing 0.200% or less, The balance is Fe and inevitable impurities, The second phase having an average long diameter of 0.10 µm or more and 30 µm or less and an average short diameter of 0.05 µm or more and 30 µm or less, and an average long diameter / average short diameter ≥ 2.0, contains 0.05% or more and 20% or less by volume fraction. Hard ultra-thin steel plate, characterized in that there is. The method according to claim 1, wherein Ti is 0% or more and 4.00% or less, Nb: 0% or more and 4.00% or less, REM: 0% or more and 4.00% or less, B: 0% or more and 0.0300% or less, Cu: 0% or more and 8.00% or less, Ca: 0% or more and 1.0O% or less, Ni: 0% or more and 8.00% or less, Cr: Hard ultra-thin steel sheet which contains 0% or more and further contains 2 or more types of 10.00% or less. The number density of the second phase according to claim 1, wherein the average long diameter is 0.5 µm or more and 30 µm or less, and the average short diameter is 0.1 µm or more and 30 µm or less, and the number density of the second phase is 0.01 pieces / µm Hard ultra-thin steel sheet of ² or more. The water density of the second phase according to claim 1, wherein the average long diameter is 0.5 µm or more and 30 µm or less, the average short diameter is 0.1 µm or more and 30 µm or less, and the number density of the second phase is 0.001 pieces / µm Hard ultra-thin steel plate which is ^three or more. The hard ultra-thin steel sheet according to claim 1, wherein the main phase is a ferrite phase of Fe and has a volume ratio of 80% or more. The direction of the average long diameter of the second phase according to claim 1, wherein the average long diameter is 0.5 µm or more and 30 µm or less, and the average short diameter is 0.1 µm or more and 30 µm or less, and the average long diameter / average short diameter? The hard ultra-thin steel plate which is the <100> orientation or <110> orientation of the Fe phase which this 2nd phase contact | connects. The second phase according to claim 1, wherein the second phase having an average long diameter of 0.5 µm or more and 30 µm or less and an average short diameter of 0.1 µm or more and 30 µm or less and an average long diameter / average short diameter ≧ 2.0 Ultra-thin steel sheet which is a single member or a composite compound of a nitride, a nitride, and an intermetallic compound. The second phase according to claim 7, wherein the second phase having an average long diameter of 0.5 µm or more and 30 µm or less and an average short diameter of 0.1 µm or more and 30 µm or less and an average long diameter / average short diameter ≥ 2.0 of Fe, Mn, and Si An ultra-thin steel sheet, which is an oxide containing one or two of Al, Cr, REM, Ti, and Nb. The second phase according to claim 7, wherein the second phase having an average long diameter of 0.5 µm or more and 30 µm or less and an average short diameter of 0.1 µm or more and 30 µm or less and an average long diameter / average short diameter ≥ 2.0 of Ti, Mn, Cu Ultra-thin steel sheet which is a sulfide containing 1 type, or 2 types of, Ca, REM. The second phase according to claim 7, wherein the second phase having an average long diameter of 0.5 µm or more and 30 µm or less and an average short diameter of 0.1 µm or more and 30 µm or less and an average long diameter / average short diameter ≥ 2.0 is Fe, Ti, Nb. Ultra-thin steel sheet which is a carbide containing one or two of Si, Si and Cr. The second phase according to claim 7, wherein the second phase having an average long diameter of 0.5 µm or more and 30 µm or less and an average short diameter of 0.1 µm or more and 30 µm or less and an average long diameter / average short diameter ≥ 2.0 is Fe, Ti, Nb. A hard ultra-thin steel sheet which is a nitride containing one or two of Al, B and Cr. The second phase according to claim 7, wherein the second phase having an average long diameter of 0.5 µm or more and 30 µm or less and an average short diameter of 0.1 µm or more and 30 µm or less and an average long diameter / average short diameter ≥ 2.0 is Fe, Ti, Nb. Ultra-thin steel sheet which is an intermetallic compound containing 1 type, or 2 or more types of Al, Si, Mn. The volume ratio of the second phase according to claim 1, wherein the average long diameter is 0.5 µm or more and 30 µm or less, and the average short diameter is 0.1 µm or more and 30 µm or less, and the volume ratio of the second phase having an average long diameter / average short diameter? A hard ultra-thin steel sheet having a volume fraction in a thickness surface layer 1/8) / (volume ratio in a sheet thickness center layer 1/4) ≥ 10. The water density of the second phase according to claim 1, wherein the average long diameter is 0.5 µm or more and 30 µm or less, and the average short diameter is 0.1 µm or more and 30 µm or less, and the water density of the second phase having an average long diameter / average short diameter? Hard ultra-thin steel sheet with water density at surface layer 1/8) / (water density at plate thickness center layer 1/4) ≥10. The tensile strength of 350 mm MPa in a tensile test according to claim 1, wherein a tensile test piece having a parallel portion having a width of 25 mm and a length of 60 mm is used to have a distance between ratings of 50 mm and a strain rate of 5 mm / minute. And ultra-thin steel sheet having Rockwell hardness HR30T ≧ 54. The tensile test according to claim 1, wherein a tensile test piece having a parallel part having a width of 25 mm and a length of 60 mm has a distance between ratings of 50 mm and a strain rate of 5 mm / minute, wherein uniform stretching / local stretching is performed. Hard ultra-thin steel plate which is 1.0. The tensile test according to claim 1, wherein a tensile test piece having a parallel portion having a width of 25 mm and a length of 60 mm has a distance between ratings of 50 mm and a strain rate of 5 mm / min. Hard ultra-thin steel plate that is 0.9. It is a method of manufacturing the hard ultra-thin steel plate of Claim 8, When rolling a steel piece having a thickness of 50 mm or more and an average diameter of the oxide in the steel piece of 10 µm to 25 µm by hot working at 600 ° C or more, After rolling with a total sum of true strains of 0.4 or more at a condition of 1000 ° C. or more and a strain rate of 1 / sec or more, A method for producing a hard ultra-thin steel sheet, characterized by rolling with a total of true strains of 0.7 or more under conditions of 1000 ° C or less and a strain rate of 10 / second or more. It is a method of manufacturing the hard ultra-thin steel plate of Claim 9, When rolling a steel slab having a thickness of 50 mm or more and an average diameter of sulfides in the steel slab of 10 µm to 25 µm by hot rolling at 600 ° C or more, After rolling with the sum total of true strain on the conditions which are 1000 degreeC or more and strain rate 1 / sec or more 0.4 or more, A method for producing a hard ultra-thin steel sheet, characterized by rolling with a total of true strains of 0.7 or more under conditions of 1000 ° C or less and a strain rate of 10 / second or more. It is a method of manufacturing the hard ultra-thin steel plate of Claim 10, After cold rolling, simultaneously with or after recrystallization annealing, in a temperature range of 600 to 700 ° C., {[carburizing time (seconds)] * [carburizing temperature (° C.)]} / {[Carburizing gas concentration (%)] * [ Cooling rate in carburizing treatment (° C./sec)]} The carburizing treatment is performed under a condition of? 20, and the amount of C is increased by 0.0002% or more. It is a method of manufacturing the hard ultra-thin steel plate of Claim 11, After cold rolling, simultaneously with or after recrystallization annealing, in a temperature range of 600 to 700 ° C., {[nitridation time (seconds)] * [nitriding temperature (° C.)]} / {[Nitrifying gas concentration (%)] * [ Cooling rate in nitriding treatment (° C / sec)]} The nitriding treatment is carried out under a condition of? 20, and the N content is increased by 0.0002% or more. It is a method of manufacturing the hard ultra-thin steel plate of Claim 12, In the steel sheet manufacturing process, the cooling rate from 900 ° C to 500 ° C is cooled to 20 ° C / sec or less in the cooling process from a temperature of 900 ° C or more, and the intermetallic compound is increased by 2.0 times or more by volume ratio. The manufacturing method of the hard ultra-thin steel plate.

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