TWI601832B - Hot rolled steel sheet, steel, and container - Google Patents

Description

Hot rolled steel, steel and containers Field of invention

The present invention relates to a hot rolled steel sheet, a steel material, and a container. The present invention relates in particular to a hot-rolled steel sheet having excellent corrosion resistance suitable for use in a corrosive environment containing chloride; a steel obtained by subjecting the hot-rolled steel sheet to shot blasting and coating treatment And a container with the steel.

Background of the invention

Previously, vehicles used in railway vehicles, as well as containers for onshore or offshore transportation, were required to be lightweight and have long life and high corrosion resistance. Therefore, as such materials, materials using aluminum or stainless steel are mainly used. However, since aluminum and stainless steel are expensive and have low strength, steel materials for containers are required to have high strength and corrosion resistance.

Conventionally, the railway vehicle and the container described above are coated with a high corrosion-resistant rolled steel material having a tensile strength of 50 kgf/mm ² (490 MPa) in accordance with JIS G3125 (2010).

However, with the use of marine containers, the actual performance of the containers has increased. The use environment becomes more severe, and even if the coated container made of the high corrosion-resistant rolled steel material as described above is used, there is a problem that the local corrosion progress cannot be withstood and the use is long.

On the other hand, there has been disclosed a steel sheet which improves corrosion resistance in a corrosive environment containing chloride. For example, Patent Document 1 discloses a hot-rolled steel sheet containing Cu, Sn, or the like. Further, Patent Document 2 discloses a hot-rolled steel sheet containing Si, Cu, Cr or the like.

However, in the hot-rolled steel sheet disclosed in Patent Document 1, Cu and Ni which are contained as essential elements coexist with Sn, and the hot-rolled steel sheet is easily embrittled. As a result, the steel sheet has a problem that cracks easily occur. Further, the hot-rolled steel sheet disclosed in Patent Document 2 is required to contain 0.8% or more of Cr. However, when Cr is contained, the corrosion-improving effect can be obtained in a corrosive environment in which chloride is relatively small, but chlorine is contained in a large amount. Under the strict corrosive environment of the compound, there is a problem that the corrosion resistance is deteriorated.

Further, the hot-rolled steel sheet forms a scale layer on the surface during its manufacturing process. Since the scale layer (roll scale) formed at a high temperature generally has excellent corrosion resistance, in the field of civil engineering, there is also a steel material which is used in a state in which rolled scale remains. However, when a scale defect is generated in a state in which rolled scale remains, there is a possibility of local corrosion. Therefore, a container or the like is usually obtained by using an anti-corrosive coating of a hot-rolled steel sheet. Here, when the anti-corrosion coating is applied, since the anti-corrosive paint may be peeled off simultaneously with the scale when it is applied from the rolled scale, it is usually necessary to coat the hot-rolled steel sheet by the bead. After the rolled scale is removed, the coating is carried out. So used to prevent The hot-rolled steel sheet for the purpose of etch coating is expected to have good peeling property of the scale.

Usually, when the rolled scale formed in the hot rolling step is removed, the surface of the hot rolled steel sheet is treated by bead blasting. At this time, when the rolled scale having high adhesion is formed, it is necessary to repeat the treatment by the bead shot several times.

On the other hand, although it is also considered to form a rolled scale having low adhesion by a manufacturing step and an alloying element, it is feared that the rolled scale is peeled off from the surface of the hot-rolled steel sheet in the manufacturing step, or a scale defect portion is generated. On the surface of the hot-rolled steel sheet, rolled scale is formed and rust skin is generated on the surface of the hot-rolled steel sheet.

Prior technical literature Patent literature

Patent Document 1: Japanese Patent Laid-Open No. Hei 7-157841

Patent Document 2: Japanese Patent Laid-Open Publication No. 2002-105596

Summary of invention

In the case of a corrosive environment containing chloride, it is known to enhance the corrosion resistance of the steel sheet by containing Sn. On the other hand, since Cu, Ni, Cr, etc., which are generally considered to contribute to the improvement of corrosion resistance, are contained together with Sn, it is a case where the steel sheet is embrittled or the corrosion resistance is lowered. Therefore, in the hot-rolled steel sheet, in order to improve the corrosion resistance in a corrosive environment, it is preferable to contain the content of Cu, Ni, and Cr after containing Sn.

Further, hot-rolled steel sheets used in railway vehicles, containers for land transportation or sea transportation, etc., are usually provided for use after being subjected to anti-corrosion coating. Therefore, in the case of such applications, in addition to corrosion resistance, Rust peeling is required.

The present invention has been made in view of the above problems. That is, an object of the present invention is to provide a hot-rolled steel sheet which has excellent peeling property and excellent corrosion resistance in a corrosive environment containing chloride. In the present invention, the excellent corrosion resistance is considered to be excellent in both the Bare Corrosion Resistance of the hot-rolled steel sheet and the corrosion resistance after coating when used as a container or the like.

Further, an object of the present invention is to provide a steel material obtained by performing a beading and coating treatment on the hot-rolled steel sheet, and a container having the steel material.

The gist of the present invention is as follows.

(1) A hot-rolled steel sheet according to one aspect of the present invention includes: a steel sheet; and a scale layer formed on the surface of the steel sheet; wherein the chemical composition of the steel sheet is C% or more and more than 0.04% and 0.20% or less, Si: 0.05 to 0.30%, Mn: 0.30 to 2.50%, P: 0.050% or less, S: 0.030% or less, Sn: 0.08 to 0.25%, Al: 0.005 to 0.050%, N: 0.0005 to 0.0100%, Nb: 0.005 ~0.015%, Cu: 0~0.05%, Ni: 0~0.05%, Cr: 0~0.05%, W: 0~0.50%, Mo: 0~0.50%, Ti: 0~0.15%, V: 0~ 0.05%, B: 0~0.0005%, Ca: 0~0.0050%, Mg: 0~0.0050%, REM: 0~0.0050%, the remainder is Fe and impurities; the aforementioned steel plate and the aforementioned corrosion layer in the aforementioned corrosion layer There is an Sn concentration layer at the interface, and the Sn content of the Sn concentration layer is 1.4 times or more of the Sn content of the steel sheet, and the average thickness of the scale layer is 1.0 to 15.0 μm and the scale layer contains galena And one or two or more kinds of iron oxides of hematite and magnetite, wherein the content of the stellite in mass% is set to w in the rust layer, and the hematite is in mass% The content is set to h, the aforementioned magnetite is qualitative Percent, the content of the timepiece is provided as m, the w, the h line and m satisfy the following formula (i), the plate thickness is 2 ~ 16mm.

0.02 ≦ (h + w) / m ≦ 0.20. . . (i)

(2) The hot-rolled steel sheet according to (1) above, wherein the W content in the chemical component is 0.005% or less by mass%.

(3) The hot-rolled steel sheet according to (1) or (2) above, wherein the Mo content in the chemical component is 0.005% or less by mass%.

The hot-rolled steel sheet according to any one of the items (1) to (3), wherein the Cu content in the chemical component is 0.02% by mass or less.

(5) The hot-rolled steel sheet according to any one of the items (1) to (4), wherein the Ni content in the chemical component is 0.02% by mass or less.

(6) The hot-rolled steel sheet according to any one of the items (1) to (5), wherein the content of Cr in the chemical component is 0.02% by mass or less.

(7) The hot-rolled steel sheet according to any one of the above (1), wherein the Ti content in the chemical composition may be 0.01% or less by mass%.

(8) A steel material according to another aspect of the present invention, which is subjected to a bead blasting treatment to the hot-rolled steel sheet according to any one of the above items (1) to (7), and further to the aforementioned bead blasting treatment The hot-rolled steel sheet is obtained by coating treatment.

(9) A container according to another aspect of the present invention, comprising the steel material according to (8) above.

Because the above-described aspect of the hot rolled steel sheet of the present invention is excellent Since the scale peeling property is easy, it is easy to peel and use a scale layer, and it is easy to apply and apply. Further, the hot-rolled steel sheet has excellent corrosion resistance regardless of the presence or absence of coating in a chloride-containing corrosive environment. Therefore, it is possible to suitably use a container used for railway vehicles and land transportation or sea transportation.

Further, the steel material according to the above aspect of the present invention is obtained by subjecting a hot-rolled steel sheet having excellent corrosion resistance in a corrosive environment containing chloride to bead shot treatment and coating treatment in a corrosive environment containing chloride. It has excellent corrosion resistance.

Further, since the container of the above aspect of the present invention is provided with the steel material, it has excellent corrosion resistance in a corrosive environment containing chloride.

Form for implementing the invention

Hereinafter, a hot-rolled steel sheet according to an embodiment of the present invention (in the case of a hot-rolled steel sheet according to the present embodiment) and a steel material according to an embodiment of the present invention (in the case of a steel material according to the present embodiment) will be described in detail. And a container according to an embodiment of the present invention (in the case of a container called the present embodiment).

First, the hot-rolled steel sheet according to the embodiment will be described. The hot-rolled steel sheet according to the present embodiment has a steel sheet (base metal sheet) having a predetermined chemical composition, and a scale layer having a composition ratio of a predetermined iron oxide and having a Sn-concentrated layer.

<Target chemical composition (chemical composition)>

In the hot-rolled steel sheet according to the embodiment, each element of the steel sheet (base metal sheet) is limited. The reason for the prime is as follows. In the following description, "%" for the content means "% by mass".

C: greater than 0.04% and less than 0.20%

C is an essential element to ensure the strength of steel. In order to obtain this effect, the C content is set to be more than 0.04%. It is preferably 0.05% or more. The C content may also be set to 0.06% or more, 0.07%, 0.08% or 0.09%. On the other hand, when the C content is more than 0.20%, the weldability is remarkably lowered. Further, while the C content is large, the stellite carbon which is a cathode and promotes corrosion in a pH-lowering environment has a large amount of formation and a low corrosion resistance. Therefore, the content of C is set to 0.20% or less. The C content is preferably 0.18% or less, more preferably 0.16% or less. The C content may be 0.15% or less, 0.14% or less, or 0.13% or less.

Si: 0.05~0.30%

In the Si system, since the surface of the steel sheet becomes fayalite (2FeO.SiO2) and the fine Fe2O3 remains on the outermost surface, the element of the red scale is likely to be formed. Further, when Si is high, the formation of a Si layer at the interface of the scale causes the peeling property of the scale to be low. Therefore, the Si content is set to 0.30% or less. It is preferably 0.25% or less and 0.20% or less. On the other hand, it is an essential element for deoxidation during Si-based steel making. Further, Si has an effect of improving corrosion resistance. In order to obtain such effects, the Si content must be made 0.05% or more. The Si content is preferably 0.08% or more or 0.10% or more.

Mn: 0.30~2.50%

Mn is an essential element for increasing the strength of the steel sheet. When the Mn content is less than 0.30%, it is difficult to obtain a sufficient strength. Therefore, the Mn content is set to 0.30% or more. It is preferably 0.40% or more, 0.50% or more, or 0.60% or more. The other side When the surface Mn content is more than 2.50%, the processability is remarkably lowered. Therefore, the Mn content is made 2.50% or less. It is preferably 2.00% or less, 1.80% or less, 1.70% or less, or 1.60% or less.

P: 0.050% or less

P is an element that is beneficial to the increase in strength and corrosion resistance of steel sheets, and has been used in corrosion resistant steel sheets. However, when P is contained alone in a corrosive environment in which a large amount of chloride is contained and the pH is locally lowered, the corrosion resistance is rather lowered. Further, P is a cause of embrittlement (cracking) of the steel in the production of the steel sheet. In particular, when the P content is more than 0.050%, the embrittlement system becomes remarkable. Therefore, the P content is limited to 0.050% or less. It is preferably 0.025% or less, 0.020% or less, or 0.15% or less. On the other hand, when P is a small amount, it can be simultaneously contained with Sn, and the corrosion resistance can be improved even in a chloride environment. It is presumed that this is because the result of elution of Fe can be suppressed by containing Sn, and P can contribute to the protective property of the rust layer. Therefore, in order to obtain the effect of contributing to the protective property of the rust layer, it is preferable to set the P content to 0.001% or more.

S: 0.030% or less

The S system is bonded to Mn and forms a sulfide of MnS in the steel. Since the sulfide is easily deformed, it is elongated by rolling or the like. The sulfide after stretching deteriorates the flexibility and workability of the steel material. Therefore, the S content is preferably less, and when the S content is more than 0.030%, since the deterioration of the bendability and the workability is remarkable, the S content is made 0.030% or less. In particular, in the case of a high-strength steel material, in order to improve the crack sensitivity, the S content is preferably 0.010% or less, 0.008% or less, or 0.006% or less.

Sn: 0.08~0.25%

Sn is the most important element in this embodiment. Sn has a function of greatly improving the corrosion resistance in a chloride corrosive environment by remarkably suppressing the anodic dissolution reaction of steel in a low pH chloride environment. In order to obtain this effect, it is necessary to set the Sn content to 0.08% or more. It is preferably 0.09% or more, more preferably 0.10% or more or 0.12% or more. On the other hand, when the Sn content is more than 0.25%, the above effect is saturated, and the embrittlement of the steel becomes remarkable. Therefore, the Sn content is made 0.25% or less. It is preferably 0.20% or less, more preferably 0.18% or less or 0.17% or less.

Al: 0.005~0.050%

Al is an element that enhances the corrosion resistance of steel. In order to obtain the effect, the Al content is set to 0.005% or more. On the other hand, when the Al content is more than 0.050%, the above effects are saturated. Therefore, the upper limit of the Al content is set to 0.050%. Further, since the steel sheet is easily embrittled when the Al content is increased, the Al content is preferably 0.030% or less. In the present embodiment, the Al content is T-Al, that is, the total Al amount in the steel.

N: 0.0005~0.0100%

The N system is dissolved in an aqueous solution of ammonia, and in an environment where the amount of the fly salt is large, the pH is lowered by suppressing the hydrolysis of Fe3+, and the corrosion resistance of the steel sheet in the salt environment is improved. In order to obtain this effect, the N content is made 0.0005% or more. On the other hand, when the N content is more than 0.0100%, not only the effect is saturated, but also the toughness of the steel sheet is deteriorated. Therefore, the N content is made 0.0100% or less.

Nb: 0.005~0.015%

Nb is an element that increases the strength of the steel sheet. In order to get this effect, The Nb content is set to 0.005% or more. On the other hand, when the Nb content is more than 0.015%, the above effects are saturated, and the toughness is low, which also causes the occurrence of scale cracks on the surface of the steel sheet. Further, in the case of hot rolling, Nb is likely to form Nb oxide at the interface between the scale and the steel sheet to affect the formation of scale. When the corrosion resistance of the steel sheet and the influence on the thickness and composition of the scale layer are considered, the content of Nb is set to be 0.005% or more and 0.015% or less. The lower limit of the Nb content may be set to 0.006% or 0.007% and the upper limit thereof may be set to 0.013% or 0.011%.

Cu: 0~0.05%

The Cu system is generally considered to be an element that enhances the corrosion resistance of steel. However, since the Cu system accelerates the element of the air oxidation of Fe2+ in the solution, the steel containing Cu has a low corrosion resistance in an environment where there are many flying salts. Further, when Cu and Sn coexist, the red hot embrittlement during rolling causes cracks on the surface of the hot-rolled steel sheet. Further, Cu also affects the thickness of the scale, the concentration ratio of Sn, and the composition of the iron oxide. Therefore, the Cu content is set to 0.05% or less. It is preferably 0.04% or less. The lower limit of the Cu content is not particularly limited, and the lower limit thereof is 0%.

Ni: 0~0.05%

Similarly to Cu, Ni is generally considered to improve the corrosion resistance of steel materials. However, the inventors of the present invention found that when Ni is contained in a corrosive environment containing chloride as contemplated in the present embodiment, the corrosion resistance of the steel sheet is lowered. Further, in the hot rolling, the Ni system easily forms an oxide at the interface between the scale and the steel material, and affects the thickness and composition of the scale layer. Therefore, the Ni content is preferably less. However, when it is considered to be mixed as an impurity, the Ni content is made 0.05% or less. It is preferably 0.04% or less. There is no need to specifically limit the Ni content Limit, the lower limit is 0%.

Cr: 0~0.05%

The Cr system is generally considered to improve the corrosion resistance of steel. However, the present inventors have found that when Cr is contained in the corrosive environment containing chloride as contemplated in the present embodiment, the corrosion resistance of the steel sheet is lowered. Further, in the hot rolling, Cr is likely to form a Cr oxide at the interface between the scale and the steel material, and affect the thickness and composition of the scale layer. Therefore, the Cr content is preferably less. However, when it is considered to be mixed as an impurity, the Cr content is made 0.05% or less. It is preferably 0.04% or less. The lower limit of the Cr content is not particularly limited, and the lower limit thereof is 0%.

The hot-rolled steel sheet according to the present embodiment has the above-described components, and the remainder is basically made of Fe and impurities. However, in addition to the above-mentioned components, one or two or more components selected from the following elements may be contained as needed, instead of a part of Fe. However, the following elements are not necessarily required to be contained, and the lower limit thereof is 0%.

W: 0~0.50%

Mo: 0~0.50%

Ti: 0~0.15%

Any of these elements is an element that enhances corrosion resistance. Therefore, it may be contained in one type or in combination of two or more types as necessary. In order to obtain an effect of improving corrosion resistance, it is preferred that the content is 0.01% or more in any of the elements.

However, when the content is excessive, the effect is saturated and the cost becomes high. Therefore, even if it is contained, it is preferable to set the content to 0.50% or less for W and Mo. It is preferable to set Ti to 0.15% or less. When two or more elements are contained, it is preferable to set the total content to 1.0% or less. Since W, Mo, and Ti are expensive and it is not necessary to obtain the corrosion-improving effect by these elements, W and Mo may be made 0.005% or less, and Ti may be 0.01% or less. This range is also the range in which W, Mo, and Ti are contained in the form of impurities.

V: 0~0.05%,

The V system is an element that increases the strength of steel. Further, V is dissolved in a corrosive environment (in an aqueous solution) and exists as an oxyacid ion, and has an effect of suppressing the permeation of chloride ions in the rust layer. In the case where this effect is obtained, it is preferable to contain V0.005% or more. It is preferably 0.01% or more. It is not necessary to obtain this effect, and the lower limit of the V content may not be limited, and the lower limit thereof is 0%. On the other hand, when the V content is more than 0.05%, not only the above effect is saturated but also the cost is remarkably increased. Therefore, even when it is contained, the V content is made 0.05% or less.

B: 0~0.0005%

The B system can increase the strength of the hot rolled steel sheet by a small amount of inclusion. In order to obtain this effect, B may also be contained. It is not necessary to obtain this effect, and the lower limit of the B content may not be limited, and the lower limit thereof is 0%. However, when the B content is more than 0.0005%, it is a cause of cracking during the processing of the hot-rolled steel sheet. Therefore, even when it is contained, the B content is set to 0.0005% or less.

Ca: 0~0.0050%

The Ca system exists in the form of an oxide in the steel, and suppresses the effect of suppressing corrosion by lowering the pH at the interface of the corrosion reaction portion. In the case where the above effects are obtained, it is preferable to contain 0.0002% or more of Ca to contain 0.0005% is preferred. It is not necessary to obtain this effect, and the lower limit of the Ca content may not be limited, and the lower limit is 0%. On the other hand, when the Ca content is more than 0.0050%, the above effects are saturated. Therefore, even when it is contained, the Ca content is made 0.0050% or less.

Mg: 0~0.0050%

The Mg system suppresses the pH of the interface at the corrosion reaction portion and has an effect of suppressing the effect of corrosion. In the case where the above effects are obtained, the Mg content is preferably 0.0002% or more, and more preferably 0.0005% or more. It is not necessary to obtain this effect, and the lower limit of the Mg content is not limited, and the lower limit is 0%. On the other hand, when the Mg content is more than 0.0050%, the above effects are saturated. Therefore, even when it is contained, the Mg content is made 0.0050% or less.

REM: 0~0.0050%

REM (rare earth element) is an element that enhances the weldability of steel. In the case where this effect is obtained, the REM content is preferably 0.0002% or more, and more preferably 0.0005% or more. It is not necessary to obtain this effect, and the lower limit of the REM content is not limited, and the lower limit is 0%. On the other hand, when the REM content is more than 0.0050%, the above effect is saturated. Therefore, even when it is contained, the REM content is made 0.0050% or less. In the present embodiment, the REM is a general term for 17 elements in which the elements of the lanthanoid (Lanthanoid) are added with Y and Sc. The hot-rolled steel sheet according to the present embodiment may contain one or two or more of these 17 elements, and the REM content means the total content of the elements.

<For iron oxides in the scale layer>

The rust layer is usually used as iron oxide, containing galena, hematite, and magnetic One or two or more kinds of iron ore.

The composition ratio of the iron oxide in the scale layer of the hot-rolled steel sheet according to the present embodiment satisfies the following formula (i).

0.02 ≦ (h + w) / m ≦ 0.20. . . (i)

However, h in the formula (i) represents the content by mass% of hematite, w is the content by mass% of the ferrocene, and m is the content by mass% of the magnetite. Either one is the ratio of the mass to the scale layer.

By including Sn in the base material steel sheet and adjusting the composition ratio of each of the iron oxide layers in the scale layer to an appropriate range, the peeling property of the scale is improved, which is newly discovered by the inventors. The reason why the peeling property of the scale is improved by controlling the composition ratio of the iron oxide in the scale layer is not clear, but can be estimated as follows.

The scale (rolled scale) formed at high temperature is composed of magnetite and hematite in the surface layer, alloy structure formed by metamorphism of galena or galena in the intermediate layer, and iron in the ferrite The interface of the (ferrite) (base metal plate) has a magnetite joint. When it is considered that the base material contains Sn, since the melting point of Sn is 235 ° C, the concentrated layer of Sn is formed at the interface of the ferrite and iron in the scale layer, and the content of ferrite is lowered, and formation can be suppressed. The joint of magnetite enhances the peelability of the scale layer.

When magnetite is present in a large amount at the interface between the steel sheet and the scale layer, the peeling property of the scale is lowered, and in order to form a scale layer having high peelability, it is preferable to suppress the formation of magnetite at the interface. When the composition ratio (h+w)/m of the iron oxide represented by the formula (i) is 0.02 or more and 0.20 or less, the peeling property of the scale is improved. When the composition ratio is more than 0.20, the peeling property is lowered. On the other hand, (h+w)/m When it is less than 0.02, the scale layer is peeled off during hot rolling, and it is a cause of the occurrence of scale defects in the rolls and the hot-rolled steel sheets. Therefore, the composition ratio (h+w)/m of the iron oxide is 0.02 or more and 0.20 or less. Preferably, the lower limit of the composition ratio (h+w)/m of the iron oxide shown by the formula (i) is 0.04, 0.05 or 0.06. Further, it is preferred that the upper limit of the composition ratio (h+w)/m of the iron oxide shown by the formula (i) is 0.18, 0.16 or 0.15.

The composition ratio of the iron oxide was measured in accordance with the following procedure. In other words, the scale layer on the surface of the hot-rolled steel sheet is first used until the steel surface can be confirmed by using a tweezers and a cutter, and the scale layer is pulverized as a powder sample. The content of magnetite, hematite, and stellite was measured by powder X-ray diffraction (internal standard method) using this powder sample. The scale may be located at the center of the width direction of the steel sheet.

<For Sn Thickened Layer>

In the hot-rolled steel sheet according to the present embodiment, an Sn-concentrated layer having a Sn content of 1.4 times or more of the base material steel sheet is present at the interface with the base material steel sheet in the scale layer.

In the hot-rolled steel sheet according to the present embodiment, in order to impart excellent corrosion resistance to the base material, the Sn content in the steel sheet is set to 0.08% or more. The Sn-concentrated layer is formed in the scale layer formed during hot rolling, and is formed by being dissolved and diffused in the steel sheet to form an interface with the base material steel sheet in the scale layer. When the Sn-concentrated layer is formed at the interface with the base material steel sheet in the scale layer, formation of stellite in the scale layer can be suppressed, and as a result, it is possible to suppress formation of a magnetite joint at the interface with the steel sheet, so that rust is formed. Skin peelability is improved. Therefore, in order to obtain excellent scale peeling property, the Sn content (Sn concentration) contained in the Sn-concentrated layer must be 1.4 times or more (concentration ratio ≧ 1.4) of the Sn content of the base material steel sheet. Sn-concentrated layer When the Sn content is less than 1.4 times that of the base material steel plate, ferrocene is formed in the scale layer, and as a result, since a strong magnetite layer is formed at the interface, the peeling property of the scale layer is low. On the other hand, when the Sn content in the Sn-concentrated layer is 2.0 times larger than that of the base material steel sheet, it is not preferable because the scale layer is likely to be peeled off during hot rolling and becomes the main cause of the roll and the hot-rolled steel sheet. . In order to promote the dissolution of Sn in the steel sheet in the scale and diffusion in the scale to form the Sn-concentrated layer, it is effective to control the scale-removing conditions and the cooling conditions in the process of producing the steel sheet containing Sn.

The content of Sn in the base material steel sheet and the Sn content of the Sn-concentrated layer existing in the interface with the steel sheet in the scale layer are determined as follows. That is, the sample taken from the hot-rolled steel sheet was embedded in a resin and mirror-finished by wet-grinding, and then the scale was applied to the sample at a magnification of 500 times using an electron beam micro analyzer (EPMA). The Sn linear analysis of the steel sheet was used to measure the Sn content on the scale layer side from the interface between the steel sheet and the scale.

<Average thickness for the scale layer>

In the hot-rolled steel sheet according to the embodiment, the average thickness of the scale layer is 1.0 to 15.0 μm . When the thickness of the scale layer is 1.0 μm , when the scale is physically peeled off by a bead shot or the like, the scale may be pressed into the surface of the steel sheet. At this time, it is not preferable because excessive unevenness is imparted to the surface of the steel sheet. Further, when the thickness of the scale layer is more than 15.0 μm , part of the scale peeling occurs during hot rolling, which may be a cause of the cause of the scale of the roll and the hot-rolled steel sheet. The lower limit of the thickness of the scale layer can be set to 2.0 μm , 4.0 μm or 5.0 μm , and the upper limit can be set to 13.0 μm , 11.0 μm or 10.0 μm .

The average thickness of the scale layer was determined by the following method. That is, after the sample taken from the hot-rolled steel sheet is embedded in the resin and mirror-finished by wet grinding, the thickness of the scale layer is measured by an optical microscope and the thickness of the scale layer is measured at 5 or more points, and the average value is set as rust. The average thickness of the cortex.

The strength of the hot-rolled steel sheet according to the embodiment is not particularly limited. However, it is assumed that the application is in the case of a container or the like, and the tensile strength is preferably 400 to 780 MPa. It is also possible to limit the upper limit of the tensile strength to 620 MPa or 550 MPa.

The thickness of the hot-rolled steel sheet according to the present embodiment is not particularly limited, and is preferably 2 to 16 mm. Further, in the case where the hot-rolled steel sheet according to the embodiment is used in a container, it is preferable to set the thickness to 10 mm or less.

Next, the steel material of this embodiment will be described.

The steel material of the present embodiment can be obtained by performing a beading treatment on the hot-rolled steel sheet of the present embodiment and performing a coating treatment. That is, the steel material of the present embodiment has an anti-corrosive coating film layer on the hot-rolled steel sheet of the embodiment in which the rolled scale is removed. Therefore, the chemical composition is the hot-rolled steel sheet of this embodiment. The beading conditions, the coating conditions, the coating method, and the like are not limited, and may be carried out according to the required characteristics and using a known method.

Next, the container of this embodiment will be described.

Since the container of the present embodiment is used by using the steel material of the present embodiment, the steel material of the present embodiment is provided. The formation method is not particularly limited.

Next, preferred manufacturing conditions of the hot-rolled steel sheet according to the embodiment will be described.

The hot-rolled steel sheet according to the present embodiment can obtain the effects of the above-described configuration regardless of the production method. But because of the use of the package It is preferable that the production method of each step disclosed below can be stably produced. Hereinafter, preferred conditions at each step will be described in detail.

<melting step>

<casting step>

The molten steel is produced by melting a steel having the above chemical composition by a converter, an electric furnace or the like. Then, a treatment such as vacuum degassing may be performed as necessary.

Subsequently, a steel sheet (steel blank) is formed by a conventional method, for example, a continuous casting method, or a method of forming a steel block and then rolling the block. Further, it is also possible to use a method such as thin strip casting which directly produces a steel sheet from molten steel. At this time, since the component segregation of the steel block increases the variation in the carbide particle diameter, it is preferable to reduce the solidification segregation by rolling in the unsolidified region, electromagnetic stirring or the like.

<heating step>

Next, the steel blank produced by the above method is heated. It is preferable to set it to 1200 ° C or more in order to uniformly heat the heating temperature to the Worthite iron zone. On the other hand, in order to avoid deterioration of surface properties due to scale formation, the heating temperature is 1250 ° C or lower.

<Rolling step>

It is preferable to use a rolling mill having at least a rough rolling mill and a finishing rolling mill to perform hot rolling so that the rolled steel preform has a rolling start temperature of 1000 ° C or higher and a rolling end temperature of 800 to 950 ° C. When the rolling end temperature is less than 800 ° C, the Worthfield iron particles are flattened, and mechanical properties are deviated in the rolling direction and the width direction, and the workability is deteriorated. Again, in order to make When the precipitate is made fine, it is preferable to set the rolling end temperature to 800 ° C or higher. On the other hand, when the rolling is completed at a temperature of more than 950 ° C, there is a problem that crystal grains are coarsened and rust is likely to occur.

In the hot rolling, it is preferable to set the cumulative rolling reduction ratio in the temperature range from the rolling start temperature to the rolling end temperature to 60% or more. When the cumulative rolling reduction ratio is less than 60%, there is a possibility that the Worthfield iron particles are not sufficiently fined to deteriorate the toughness. Therefore, the cumulative rolling reduction ratio from the rolling start temperature to the roll end temperature is preferably 60%. Preferably, the cumulative reduction ratio between 1050 and 800 ° C is set to 60% or more.

Further, at the time of rolling, at least 10 MPa or more is used after the end of the rough rolling and before the first rolling pass of the finishing rolling (hereinafter, referred to as after the rough rolling is completed) and at the initial stage of the finishing rolling. It is preferred to carry out descaling at a water pressure of 20 to 300 L/min. The hot-rolled steel sheet according to the present embodiment contains 0.05% or more of Si for deoxidation and corrosion resistance. When Si is contained, a composite oxide of Fe and Si, that is, Fe ₂ SiO ₄ , is formed at the interface with the steel sheet in the scale layer formed on the surface of the steel sheet. Since the adhesion of the Fe ₂ SiO ₄ to the steel sheet is very good and it is difficult to remove, the Fe ₂ SiO ₄ can be removed by descaling under the above conditions.

Hereinafter, the conditions of descaling will be described in detail.

The initial stage of the so-called finishing rolling is performed simultaneously with at least one pass from the first pass to the third pass of the finishing rolling. In addition, "at least after the completion of the rough rolling and in the initial stage of the finishing rolling", the descaling is not performed in the period other than "after the rough rolling is completed and the initial stage of the finishing rolling".

When the water pressure (discharge pressure) from the nozzle is less than 10 MPa when the scale is removed, it is difficult to remove the above-mentioned Fe ₂ SiO ₄ , so that the scale cannot be sufficiently removed.

On the other hand, when the water pressure is more than 20 MPa, there is a case where it is necessary to strictly control the heating conditions of the steel sheet. In addition, there is a situation in which equipment is increased in size and costs are increased. Therefore, the water pressure system is preferably 20 MPa or less. Preferably, the water pressure is 15 MPa or less.

The jet flow rate for colliding the average unit area of the steel sheet is preferably 1.2 to 6.0 L/mm ² . When the flow rate is less than 1.2 L/mm ² , the scale is not sufficiently removed because the thermal shock force is small. On the other hand, in the case of high-pressure water having a flow rate of more than 6.0 L/mm ² , the surface temperature of the steel sheet is lowered, and uneven temperature is generated to cause uniform rolling to become difficult. In order to achieve stable peeling and rolling, the jet flow rate is preferably in the range of 1.5 to 5.5 L/mm ² .

<Cooling step>

After the completion of the rolling, the water cooling zone is cooled to 500 to 650 ° C at an average cooling rate of 25 ° C / s or more. When the average cooling rate is less than 25 ° C / s, the growth of the scale is promoted, and the thickness of the scale is greater than 15.0 μm , or the scale with low peeling property is formed. On the other hand, when the cooling rate after rolling is more than 100 ° C / s, the steel sheet tends to become a granulated iron structure, which makes it difficult to wind up the steel sheet. Therefore, the average cooling rate is preferably 100 ° C / s or less.

The time from the end of the rolling to the start of cooling is preferably set to be within 5 seconds. When the time from the end of the rolling to the start of the cooling is more than 5 seconds, the difference in the introduction of the difference in the rolling step is restored, so that the core of the ferrite-grain metamorphosis is insufficient, and the crystal grains are coarsened and the toughness is lowered. Again, hot rolling The surface of the steel sheet is grown with scale, and there is a possibility of forming a scale with low peelability.

After cooling, the coiling is carried out at a temperature ranging from 500 to 630 ° C. When the coiling is performed at a temperature of more than 630 ° C, the scale is grown in the coiled steel coil and the thickness of the scale layer is 15.0 μm or more. Further, it is feared that the formation of magnetite in the scale is concerned that the composition ratio (h+w)/m of the iron oxide represented by the formula (i) is less than 0.02. On the other hand, when the coiling temperature is less than 500 ° C, it causes a shape defect.

After the coiling, in the state of the coil, the temperature is gradually cooled at a coiling temperature (temperature range of 500 to 630 ° C) to 350 ° C at an average cooling rate of 0.05 to 0.12 ° C / s. By slow cooling, Sn diffuses and forms a Sn-concentrated layer. However, when the high temperature state continues for a certain period of time or longer, there is a fear that Sn diffuses in the scale layer or the like and the Sn concentration of the Sn-concentrated layer is lowered. When the average cooling rate in the temperature region is less than 0.05 ° C / s, the Sn concentration of the Sn-concentrated layer becomes less than 1.4 times the Sn concentration of the base material steel sheet, and the peeling property of the scale is low, which is not preferable. Further, when the average cooling rate is more than 0.12 ° C / s, the Sn concentration of the concentrated layer becomes less than 1.4 times that of the base material steel plate, and the peeling property of the scale is low, which is not preferable. The average cooling rate of the coil is the cooling rate in the middle of the coil. The slow cooling system is not limited as long as the cooling rate described above can be ensured, and for example, the cover can be slowly cooled and slowly cooled in the heat storage chamber.

In the production of the hot-rolled steel sheet according to the present embodiment, the rod heater can be used in a row, and the hot-rolling in which the rod-joined material after the rough rolling is rolled can be used continuously without any problem.

Next, a method of producing the steel material according to the embodiment will be described.

The steel material of the present embodiment can be produced by performing a beading treatment on a hot-rolled steel sheet obtained by the above-described steps and performing a coating treatment. For the beading and coating treatment, it can be a conventional method.

Next, a method of manufacturing the container of the present embodiment will be described.

The container of the present embodiment can be formed by a conventional method such as welding using the steel material (coated steel material) of the present embodiment obtained in the above-described step.

Hereinafter, the present invention will be described more specifically by way of examples, but the present invention is not limited by the examples.

Example

Steel slabs having the chemical compositions of steel types a to s shown in Table 1 were produced under the conditions shown in Table 2 to obtain hot-rolled steel sheets having a thickness of 3.2 mm and a sheet width of 1000 mm.

From the obtained hot-rolled steel sheet, a test piece having a thickness of 3.2 mm, a plate width of 60 mm, and a plate length of 100 mm was cut out and subjected to various tests. Specifically, it is performed as follows.

<Drop impact test>

A test piece of the above-described size was taken from the obtained hot-rolled steel sheet, and a weight of 500 g was dropped from each of the test pieces from a height of 200 mm, and the strength of the scale layer was evaluated by visually determining the damage state of the scale layer. When cracks and peeling occurred in the scale layer, it was evaluated as "OK" (that is, the peeling property of the scale was good), and when it was not cracked and peeled off, it was evaluated as "NG" (that is, the peeling property of the scale was poor). The results are shown in Table 3.

Next, the obtained hot-rolled steel sheets were subjected to bead blasting treatment (steel shot treatment of SB20). Further, a test piece was taken from a part of each of the steel sheets subjected to bead blasting treatment and supplied to a container corrosion test. In addition, one part of the remaining portion of each of the steel sheets subjected to the bead blasting treatment is applied as a coating by spray-coating a modified epoxy-based paint (Neo Gosei (registered trademark)) manufactured by Shinto Paint Co., Ltd. A steel plate was attached, and a test piece was taken from the coated steel plate to be supplied to the SAE J2334 test.

<Container Corrosion Test>

First, the following cycle test was carried out for 18 cycles: after the test piece was kept at 30 ° C and 90% RH in a humid environment for 0.5 hour, 30 ° C, 5% NaCl brine was sprayed for 0.5 hour, again at 30 ° C, 95% RH. The wet environment was maintained for 1.0 hour, and it was allowed to dry for 6.0 hours in a 40 ° C, 50% RH environment. Subsequently, the following cycle test 144 cycles were carried out: after 40 hours at 40 ° C, 90% RH in a humid environment, at 40 ° C, 40% RH ring The cycle was allowed to dry for 4.0 hours. The weight of the test piece before and after the test was measured and the corrosion loss was calculated. Here, the amount of corrosion reduction is converted into a thickness by reduction. The results are shown in Table 3.

For the evaluation of corrosion resistance, a corrosion reduction of 30 μm or less was set as a good result.

<SAE J2334 test>

As a test for simulating the corrosive environment in which a large amount of chloride is flying, the SAE J2334 test was carried out. The SAE J2334 test is an accelerated deterioration test in which the dry-wet repeat conditions described below are set to one cycle (total 24 hours), and is a test for simulating a strict corrosion environment in which the fly salt component is more than 1 mdd.

. Wet: 50 ° C, 100% RH, 6 hours,

. Salt adhesion: 0.5% by mass NaCl, 0.1% by mass CaCl ₂ , 0.075% by mass NaHCO ₃ aqueous solution impregnation, 0.25 hours,

. Drying: 60 ° C, 50% RH, 17.75 hours

It is believed that the above corrosion morphology is similar to the corrosion morphology of the atmospheric exposure test.

The evaluation was carried out as follows.

A crucible is formed on the coated surface of each of the coated steel sheets to expose a part of the steel material as the base. Further, at the position where the weir portion was formed, the maximum corrosion depth of the steel material as the base (the maximum value of the corrosion depth from the steel material surface) was measured. Further, in order to evaluate the area of the portion which was formed from the crotch portion and peeled off, the coating peeling area ratio (%) was determined. Specifically, the portion after peeling (the portion which is formed from the crotch portion and peeled off) is removed by using a cutter or the like, and the removed portion is set as the coating peeling portion. Then, the image processing software was subjected to binarization processing to obtain a value of (coating peeling area) / (test piece area) × 100 and as a coating peeling area ratio (%). The area of the test piece means the area of the face on which the crotch portion is formed among the six faces of the test piece.

The criterion for the eligibility of the SAE J2334 test is that the maximum corrosion depth is rated as 400 μm or less. Further, for the coating peeling area ratio, 60% or less was rated as acceptable. Moreover, it was also observed whether or not peeling and rusting of the scale were observed for all the hard parts other than the coating film part.

<Measurement of the Sn-concentrated layer>

The Sn concentration of the Sn-concentrated layer in the scale layer at the interface with the steel sheet was measured by linear analysis of EPMA three times at intervals of 0.5 μm from the scale to the steel sheet. Among the measurement results of the Sn concentration of 20 points in the scale layer of the interface between the steel sheet and the scale obtained from the measurement (60 points), the data from the maximum 10 points and the minimum 10 points are set as abnormalities. The value was removed, and the average value of the remaining 40 points was set as the Sn concentration of the Sn-concentrated layer in the scale layer at the interface with the steel sheet. The ratio of the Sn concentration to the Sn analysis value by the ladle of the steel sheet was set as the Sn concentration ratio.

It is clear that the hot-rolled steel sheets of the test numbers 1 to 10 satisfying the requirements of the present invention have sufficient scale peeling properties, and the hot-rolled steel sheets after peeling off the scale layer, and the coated steel materials after the subsequent coating are applied. It has sufficient corrosion resistance.

On the other hand, in the hot-rolled steel sheets of test numbers 11 to 26, the chemical composition, the composition ratio in the scale layer, the thickness of the scale layer, the Sn-concentrated layer at the surface of the scale, and the Sn concentration ratio to the base material are one or more. It is deviated from the scope of the present invention, and the peel peeling property and/or the corrosion resistance are inferior.

In the hot-rolled steel sheet of Test No. 11, the water pressure and the spray amount of the scale-removed skin were large, and the rolling was uneven, so that a thin scale having a thickness of 0.8 μm was formed on the surface of the hot-rolled steel sheet. Further, the formula (i) is 0.02 or less. This is considered to be because the scale layer is easily peeled off during hot rolling and the surface layer of galena and hematite is peeled off. Further, the Sn concentration ratio of the interface is less than 1.4. In the hot-rolled steel sheet of Test No. 11, since the scale was pressed into the hot-rolled steel sheet during hot rolling, the container corrosion test and the SAE J2334 test were not performed.

In the hot-rolled steel sheet of Test No. 12, the water pressure and the amount of the rust-removed steel were small, and the thickness of the scale formed on the surface of the hot-rolled steel sheet was increased, and the scale defect portion was generated during hot rolling and coiling. Further, the peeling property of the scale is insufficient. Further, since the scale is insufficient, the hematite formed at a high temperature remains and the formula (i) is more than 0.20. Further, the thickness of the scale layer is thick, and since Sn diffuses from the interface between the scale and the base material into the scale, the Sn concentration ratio at the interface is less than 1.4. In the hot-rolled steel sheet of test No. 12, since the scale was pressed into the hot-rolled steel sheet during hot rolling and rolling, the container corrosion test and the SAE J2334 test were not performed.

The hot-rolled steel sheet of test No. 13 was subjected to descaling only after the rough rolling was completed. Therefore, the thickness of the scale formed on the surface of the hot-rolled steel sheet becomes large, and a scale defect portion is generated during hot rolling and winding. Further, the peeling property of the scale is insufficient. Further, since the scale is insufficient, the hematite formed at a high temperature remains and the formula (i) is larger than 0.20. Further, the thickness of the scale layer is thick, and Sn diffuses from the interface between the scale and the base material into the scale and the Sn concentration ratio at the interface is less than 1.4. In the hot-rolled steel sheet of Test No. 13, since the defective portion of the scale was formed, the scale was pressed into the hot-rolled steel sheet, and the container corrosion test and the SAE J2334 test were not performed.

The hot-rolled steel sheet of Test No. 14 was cooled slowly after finishing rolling, and formed a strong and thick scale layer, resulting in insufficient peelability of the scale. Therefore, the rust layer remains slightly on the surface of the steel sheet after the bead blasting treatment and the corrosion resistance is low. When the time until the start of cooling is long, since the high temperature state continues and the scale is formed due to the temperature of the steel sheet, hematite is easily formed in the scale so that the formula (i) is more than 0.20. Further, since the high temperature state continues for a long period of time, Sn diffuses from the interface between the scale and the base material into the scale and the Sn concentration ratio at the interface is less than 1.4. Further, in the hot-rolled steel sheet of the test No. 14, even if it was applied, the peeling and rust due to the residual scale were observed in all the hard parts other than the coating film portion in the SAE J2334 test, and as a result, the corrosion resistance was lowered.

In the hot-rolled steel sheet of test No. 15, since the coiling temperature was high, the magnetite was added and the galena was reduced. Therefore, the composition ratio of iron oxide (tallowite + hematite) / magnetite is less than 0.02 and the peeling property of the scale is deteriorated. Moreover, since the coiling temperature is high, the formation of scale is promoted and the thickness of the scale is increased. also, Since the high temperature state continues for a long time, Sn diffuses from the interface between the scale and the base material into the scale and the Sn concentration ratio of the interface is less than 1.4. Further, since the peeling property of the scale is deteriorated, the scale layer of the scale is slightly left on the surface of the steel sheet after the beading treatment, and the corrosion resistance is lowered. Further, even if the coating was applied, peeling and rust due to the residual scale were observed in all the hard parts other than the coating film portion in the SAE J2334 test, and as a result, the corrosion resistance was lowered.

In the hot-rolled steel sheet of test No. 16, since the cooling rate after the coiling was too small, the composition ratio of the iron oxide was increased and the amount of the ore was reduced. Therefore, the composition ratio of iron oxide (tallowite + hematite) / magnetite is less than 0.02 and the peeling property of the scale is deteriorated. Further, since the cooling rate after the coiling is too small, since the high temperature state continues for a long time, Sn diffuses from the interface between the scale and the base material into the scale, so that the Sn concentration ratio of the interface is less than 1.4. Further, since the peeling property of the scale is deteriorated, the scale layer remains slightly on the surface of the steel sheet after the beading treatment, so that the corrosion resistance is lowered. Further, even if the coating was applied, peeling and rust due to the residual scale were observed in all the hard parts other than the coating film portion in the SAE J2334 test, and as a result, the corrosion resistance was lowered.

In the hot-rolled steel sheet of test No. 17, since the cooling rate after winding is too large, the diffusion of Sn from the base material is suppressed, so that the Sn concentration ratio of the scale interface to the base material is less than 1.4, and a strong magnet is formed. Thinner scale of the ore layer. As a result, magnetite is added and the side iron ore is reduced. Therefore, the composition ratio of iron oxide (twillite + hematite) / magnetite is less than 0.02, resulting in deterioration of scale peelability. Moreover, scale cracks are generated in the steel coil. Therefore, the rust layer remains slightly on the surface of the steel sheet after the bead blasting treatment, resulting in low corrosion resistance. Moreover, even if the coating is applied, the coating film in the SAE J2334 test is All of the outer parts were observed for peeling and rust caused by the residual scale, and as a result, the corrosion resistance was low.

In the hot-rolled steel sheet of test No. 18, Sn was less than 0.08%, and a concentrated layer of predetermined Sn was not formed. Further, the formula (i) is also larger than 0.20 and the peeling property is insufficient. Therefore, the rust layer remains slightly on the surface of the steel sheet after the bead blasting treatment, and the corrosion resistance is low. Further, even if the coating was applied, as a result of the SAE J2334 test, significant peeling of the coating due to the coating film crotch portion was observed.

In the hot-rolled steel sheet of test No. 19, since the amount of Sn in the steel material was more than 0.25%, the formation of galena was suppressed and the formula (i) was less than 0.02. Further, it promotes the peeling of the scale in the hot working and generates a thick scale. Since a thicker scale was formed, the scale of the base material was pressed by the scale after peeling at the time of hot rolling, so that the subsequent test was not performed.

The hot-rolled steel sheet of test No. 20 had a high Si content of 0.50%. Therefore, the growth of the scale layer is suppressed. Further, Si is concentrated at the interface, and the deformation of the scale is suppressed. When the formula (i) is less than 0.02, the peeling property of the scale is lowered. Further, although the reason is not clear, the Sn concentration at the interface is suppressed and the Sn concentration ratio is 1.4.

In the hot-rolled steel sheet of Test No. 20, since the peeling property of the scale was lowered due to the concentration of Si at the interface, the scale layer of the scale after the beading treatment was slightly left on the surface of the steel sheet, and the corrosion resistance was lowered. Further, even if the coating was applied, peeling and rust due to the residual scale were observed in all the hard parts other than the coating film portion in the SAE J2334 test, and as a result, the corrosion resistance was lowered.

The hot-rolled steel sheet of test No. 21 had a low Si content of 0.02%. Si affects the growth of scale during hot rolling. At test number 21 because of steel Since the Si content is small, the scale growth during hot rolling is promoted and a thicker scale having a lower adhesion is formed. Since a thicker scale layer containing magnetite is formed in a large amount, the formula (i) is less than 0.02. Further, since Si can be used as a deoxidizing agent, affinity with oxygen is high. Therefore, in the hot-rolled steel sheet of test No. 21 having a low Si concentration, the steel material is easily oxidized, and the thickness of the scale layer is changed, and the formation of the Sn-concentrated layer is hindered and the concentration ratio of Sn is less than 1.4.

In the hot-rolled steel sheet of the test No. 21, since the peeling of the scale was promoted and the scale after the peeling was caused to be pressed into the base material, the subsequent test was not performed.

In the hot-rolled steel sheet of test No. 22, the amount of Cu was 0.08%, the thickness of the scale layer was thick, the Sn concentration of the scale interface and the base material was relatively low, and it was 1.2, and the composition ratio of iron oxide (square iron ore) + Hematite) / Magnetite becomes high and is 0.25. Further, since fine cracks were generated on the surface and the end portion of the hot-rolled steel sheet during hot rolling, subsequent tests were not performed.

In the hot-rolled steel sheet of test No. 23, the amount of Ni was as high as 0.10%. Although the reason was not clear, the scale of the scale was 1.2 in comparison with the Sn concentration of the base material, and the magnetite was added and the galena was reduced. Therefore, the composition ratio of iron oxide (tallowite + hematite) / magnetite is less than 0.02 and the peeling property of the scale is deteriorated. Moreover, since the Ni content is high, the corrosion resistance is lowered.

In the hot-rolled steel sheet of test No. 24, the amount of Cr is 0.10%, the thickness of the scale layer is small, the Sn concentration of the scale interface and the base material is relatively low, and is 1.2, and because of the composition ratio of iron oxide (square iron) The ore/hematite/magnetite becomes high and becomes 0.25, so the peeling property of the scale is deteriorated. Moreover, since Cr is contained, corrosion resistance is low.

The hot-rolled steel sheet of test No. 25 has a higher amount of Nb. 0.020%, in addition, although the thickness of the scale is small, the Sn concentration of the scale interface and the base material is relatively low, being 1.2, because the composition ratio of iron oxide (ferrangite + hematite) / magnetite becomes high. On the other hand, since it is 0.25, a scale crack occurs on the surface of the hot-rolled steel sheet from the time of finishing rolling to winding. Thus, no subsequent tests were conducted.

The hot-rolled steel sheet of test No. 26 has a thickness of 0.001% because the amount of Nb is low, so the thickness of the scale layer is large and the Sn concentration of the scale interface and the base material is relatively low, and is 1.0, and the composition ratio of iron oxide (square) Iron ore + hematite) / magnetite is higher than 0.25, resulting in poor peeling of the scale. Therefore, the rust layer remains slightly on the surface of the steel sheet after the bead blasting treatment, and the corrosion resistance is low. Further, even if the coating was applied, peeling and rust due to the residual scale were observed in all the hard parts other than the coating film portion in the SAE J2334 test, and as a result, the corrosion resistance was lowered.

Industrial use possibility

According to the present invention, since the hot-rolled steel sheet has the peeling property of the scale, the scale layer can be peeled off and used, and can also be applied by painting. Moreover, such a hot-rolled steel sheet has excellent corrosion resistance in a corrosive environment containing chloride. Therefore, the hot-rolled steel sheet of the present invention can be suitably used for a railway vehicle, a container for land transportation or sea transportation.

Claims (9)

A hot-rolled steel sheet characterized by comprising: a steel sheet; and a scale layer formed on the surface of the steel sheet; wherein the chemical composition of the steel sheet comprises, by mass%, C: more than 0.04% and less than 0.20%, and Si: 0.05 to 0.30% Mn: 0.30 to 2.50%, P: 0.050% or less, S: 0.030% or less, Sn: 0.08 to 0.25%, Al: 0.005 to 0.050%, N: 0.0005 to 0.0100%, Nb: 0.005 to 0.015%, Cu: 0~0.05%, Ni: 0~0.05%, Cr: 0~0.05%, W: 0~0.50%, Mo: 0~0.50%, Ti: 0~0.15%, V: 0~0.05%, B:0 ~0.0005%, Ca: 0~0.0050%, Mg: 0~0.0050%, REM: 0~0.0050%, the remainder is Fe and impurities; in the corrugated layer, the Sn thickening layer exists at the interface between the steel plate and the rust layer, and the Sn content of the Sn concentrated layer It is 1.4 times or more of the Sn content of the steel sheet, and the average thickness of the scale layer is 1.0 to 15.0 μm, and the scale layer contains one or more kinds of iron oxides of galena, hematite, and magnetite. In the above-mentioned scale layer, the content of the above-mentioned stellite in terms of mass% is set to w, the content of the aforementioned hematite in mass% is set to h, and the content of the aforementioned magnetite in mass% is set as In the case of m, the above w, the h, and the m-form satisfy the following formula (i), and the steel sheet has a thickness of 2 to 16 mm and 0.02 ≦ (h+w)/m ≦ 0.20. . . (i). The hot-rolled steel sheet according to claim 1, wherein the W content in the chemical component is 0.005% or less by mass%. The hot-rolled steel sheet according to claim 1 or 2, wherein the Mo content in the chemical component is 0.005% or less by mass%. The hot-rolled steel sheet according to claim 1 or 2, wherein the Cu content in the aforementioned chemical component is 0.02% by mass or less. The hot-rolled steel sheet according to claim 1 or 2, wherein the Ni content in the aforementioned chemical component is 0.02% by mass or less. A hot rolled steel sheet according to claim 1 or 2, wherein Cr in the aforementioned chemical composition The content is 0.02% by mass or less. The hot-rolled steel sheet according to claim 1 or 2, wherein the Ti content in the aforementioned chemical component is 0.01% by mass or less. A steel material obtained by subjecting a hot-rolled steel sheet according to any one of claims 1 to 7 to a bead blasting treatment, and further subjecting the hot-rolled steel sheet subjected to the bead blasting treatment to a coating treatment. A container provided with the steel material of claim 8.