WO2016111274A1 - High-strength plated steel sheet having excellent plating properties, workability, and delayed fracture resistance, and method for producing same - Google Patents
High-strength plated steel sheet having excellent plating properties, workability, and delayed fracture resistance, and method for producing same Download PDFInfo
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- WO2016111274A1 WO2016111274A1 PCT/JP2016/050069 JP2016050069W WO2016111274A1 WO 2016111274 A1 WO2016111274 A1 WO 2016111274A1 JP 2016050069 W JP2016050069 W JP 2016050069W WO 2016111274 A1 WO2016111274 A1 WO 2016111274A1
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Images
Classifications
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
- C23C2/06—Zinc or cadmium or alloys based thereon
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/26—After-treatment
- C23C2/28—Thermal after-treatment, e.g. treatment in oil bath
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/26—After-treatment
- C23C2/28—Thermal after-treatment, e.g. treatment in oil bath
- C23C2/29—Cooling or quenching
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
- C23C2/36—Elongated material
- C23C2/40—Plates; Strips
Definitions
- the present invention relates to a high-strength plated steel sheet having a tensile strength of 980 MPa or more and excellent in plateability, workability including both balance of strength and ductility and bendability, and delayed fracture resistance, and a method for producing the same.
- the plated steel sheet of the present invention includes both hot-dip galvanized steel sheets and alloyed hot-dip galvanized steel sheets.
- Hot-dip galvanized steel sheets and alloyed hot-dip galvanized steel sheets which are widely used in fields such as automobiles and transportation equipment, are not only high-strength, but also a balance between strength and ductility, workability such as bendability, and delayed fracture resistance. It is required to be excellent.
- Patent Document 1 discloses a hot-dip galvanized steel sheet having a tensile strength of 590 MPa or more and excellent bendability and corrosion resistance of a processed part. Specifically, in Patent Document 1, in order to suppress the occurrence of bending cracks and damage to the plating film due to the internal oxide layer formed on the steel plate side from the interface between the steel plate and the plating layer, the growth of the internal oxide layer is suppressed. Therefore, the growth of the decarburized layer is remarkably accelerated. Further, a near-surface structure is disclosed in which the thickness of the internal oxide layer in the ferrite region formed by decarburization is controlled to be thin.
- Patent Document 2 discloses a hot-dip galvanized steel sheet having a fatigue strength, hydrogen embrittlement resistance (synonymous with delayed fracture resistance), and a tensile strength excellent in bendability of 770 MPa or more.
- the steel plate portion is configured to have a soft layer that is in direct contact with the interface with the plating layer, and a soft layer that has ferrite with a maximum area ratio structure.
- the thickness D of the soft layer and the depth d from the plating / base metal interface of the oxide containing one or more of Si and Mn existing in the steel sheet surface layer portion are d / 4 ⁇ D ⁇ 2d.
- a hot-dip galvanized steel sheet that satisfies the requirements is disclosed.
- Patent Document 3 discloses a high-strength cold-rolled steel sheet having excellent bendability and a maximum tensile strength of 700 MPa or more. Specifically, in Patent Document 3, whether or not a steel sheet surface layer can be softened by performing a decarburizing process, and even if it is a high-strength cold-rolled steel sheet having a maximum tensile strength of 700 MPa or more, it is as if it is a low-strength steel sheet. It is described that excellent bendability such as can be obtained.
- Patent Document 4 discloses a high-strength hot-dip galvanized steel sheet that is excellent in delayed fracture resistance without impairing ductility and strength, and that has little anisotropy in delayed fracture resistance even in a thin plate.
- the surface layer portion of the base steel plate in order to prevent delayed fracture starting from the surface layer portion of the base steel plate, is a decarburized layer having a small hard structure, and a hydrogen trap is included in the decarburized layer. It describes that fine oxides acting as sites are dispersed at high density.
- Patent Document 5 discloses a high-strength steel sheet having a maximum tensile strength of 900 MPa or more that provides excellent formability and hydrogen embrittlement resistance. Specifically, Patent Document 5 has a decarburized layer (softening layer) that is softer than the inside of the steel sheet on the surface layer of the steel sheet, so that it has excellent hydrogen embrittlement resistance as if it were a low-strength steel sheet. It is described that (delayed fracture resistance) can be obtained.
- the present invention has been made in view of the above circumstances, and its purpose is to provide a galvanized steel sheet of 980 MPa or more excellent in plating properties; balance between strength and ductility, workability in bendability; and delayed fracture resistance;
- An object of the present invention is to provide an alloyed hot-dip galvanized steel sheet and a method for producing the same.
- the high-strength plated steel sheet having a tensile strength of 980 MPa or more is a plated steel sheet having a hot-dip galvanized layer or an alloyed hot-dip galvanized layer on the surface of the base steel sheet,
- the base steel sheet is in mass%, C: 0.08 to 0.30%, Si: 0.25 to 3%, Mn: 1.5 to 4%, P: more than 0%, 0.1% S: more than 0% and 0.05% or less, Al: 0.005 to 1%, and N: more than 0% and 0.01% or less, with the balance consisting of iron and inevitable impurities,
- the base steel sheet further contains at least one of the following (a) to (c) by mass%.
- Cu more than 0% and 1% or less
- Ni At least one selected from the group consisting of more than 0% and 1% or less
- the average depth d of the internal oxide layer and the average depth D of the soft layer satisfy a relationship of D> 2d.
- the manufacturing method of the present invention that has solved the above-mentioned problems is a method for manufacturing the high-strength plated steel sheet according to any one of the above, and a hot-rolled steel sheet that satisfies the above-described components in the steel at 600 ° C.
- another manufacturing method of the present invention that can solve the above-mentioned problems is a method for manufacturing the high-strength plated steel sheet according to any one of the above, and a hot-rolled steel sheet that satisfies the above-described components in the steel, A hot rolling step of winding at a temperature of 500 ° C. or higher; a step of keeping the temperature at a temperature of 500 ° C.
- the plated steel sheet of the present invention includes an internal oxide layer containing at least one oxide selected from the group consisting of Si and Mn from the interface between the plating layer and the base steel sheet to the base steel sheet side, and a region of the internal oxide layer.
- a soft layer containing and a hard layer other than the soft layer including, as a matrix structure, martensite and bainite: 20 area% or more and less than 60 area%, polygonal ferrite: more than 40 area% and 80 area% or less
- the average depth d of the internal oxide layer is controlled to be 4 ⁇ m or more and used as a hydrogen trap site, hydrogen embrittlement can be effectively suppressed, A high-strength plated steel sheet having a tensile strength of 980 MPa or more excellent in all ductility balance and workability such as bendability and delayed fracture resistance is obtained.
- the relationship between the average depth d of the internal oxide layer and the average depth D of the soft layer including the region of the internal oxide layer is appropriately controlled, particularly
- FIG. 1 is a diagram schematically illustrating a layer configuration from the interface between a plating layer and a base steel plate to the base steel plate side in the plated steel plate of the present invention.
- FIG. 2 is an explanatory diagram for measuring the average depth d of the internal oxide layer in the plated steel sheet of the present invention.
- FIG. 3 is a diagram for explaining the measurement position of the Vickers hardness used for determining the average depth D of the soft layer.
- the inventors of the present invention have a high strength of 980 MPa or more in a base steel plate rich in Si and Mn, and are excellent in all of plating properties, workability, delayed fracture resistance, and shock absorption.
- investigations have been made focusing on the layer structure from the interface between the plating layer and the base steel sheet to the base steel sheet side.
- the internal oxide layer can function as a hydrogen trap site, and hydrogen embrittlement occurs.
- the relationship between the average depth d of the internal oxide layer and the average depth D of the soft layer including the region of the internal oxide layer The appropriate By controlling, we found that is further improved in particular bending resistance and delayed fracture resistance, and have completed the present invention.
- the plated steel sheet includes both a hot dip galvanized steel sheet and an alloyed hot dip galvanized steel sheet.
- a base steel plate means the steel plate before a hot-dip galvanized layer and an alloying hot-dip galvanized layer are formed, and is distinguished from the said plated steel plate.
- high strength means that the tensile strength is 980 MPa or more.
- excellent workability means excellent balance between strength and ductility and bendability. For details, when these characteristics are measured by the method described in the examples described later, those satisfying the acceptance criteria of the examples are referred to as “excellent workability”.
- the plated steel sheet of the present invention has a hot dip galvanized layer or an alloyed hot dip galvanized layer (hereinafter sometimes represented by a plated layer) on the surface of the base steel sheet.
- the characteristic part of the present invention is that it has the following layer configurations (A) to (C) in order from the interface between the base steel plate and the plating layer toward the base steel plate side.
- (A) Internal oxide layer a layer containing at least one oxide selected from the group consisting of Si and Mn.
- the average depth d of the internal oxide layer is 4 ⁇ m or more and less than the average depth D of the soft layer described in (B) described later.
- (B) Soft layer including the internal oxide layer, where the thickness of the base steel sheet is t, the Vickers hardness satisfies 90% or less of the Vickers hardness at t / 4 part of the base steel sheet.
- the average depth D of the soft layer is 20 ⁇ m or more.
- the layer structure of the plated steel sheet according to the present invention on the base steel sheet 2 side is from the interface between the plating layer 1 and the base steel sheet 2 toward the base steel sheet 2 side, A hard layer 5 of (C) is provided inside the base steel plate 2 from the layer 4.
- the soft layer 4 of (B) includes the internal oxide layer 3 of (A). The soft layer 4 and the hard layer 5 are continuously present.
- the portion directly in contact with the interface between the plating layer 1 and the base steel plate 2 has an internal oxide layer 3 having an average depth d of 4 ⁇ m or more.
- the average depth means the average depth from the interface, and a detailed measurement method thereof will be described with reference to FIG.
- the internal oxide layer 3 is composed of an oxide containing at least one of Si and Mn, and a Si and Mn depletion layer in which Si and Mn form an oxide to form a solid solution Si or a small amount of solid solution Mn. .
- the greatest feature is that the average depth d of the internal oxide layer 3 is controlled to be 4 ⁇ m or more.
- the internal oxide layer can be used as a hydrogen trap site, hydrogen embrittlement can be suppressed, and bendability and delayed fracture resistance are improved.
- the surface of the base steel sheet is oxidized with Si oxide and Mn oxide during annealing (oxidation / reduction process in a continuous hot-dip galvanizing line described later)
- Si oxide and Mn oxide during annealing
- an oxide film having a composite oxide of Si and Mn is easily formed, and the plating property is hindered. Therefore, as a countermeasure, a method is known in which the surface of the base steel sheet is oxidized in an oxidizing atmosphere to form a Fe oxide film, and then annealed (reduction annealing) in an atmosphere containing hydrogen.
- the oxidizable elements are fixed as oxides inside the base steel sheet surface layer, and by reducing the oxidizable elements dissolved in the base steel sheet surface layer, A method for preventing the formation of an oxide film on the surface of the base steel plate is also known.
- the use of at least one oxide selected from the group consisting of Si and Mn is effective in improving the deterioration of bendability and hole expansibility due to crystallization.
- the above oxide is useful as a hydrogen trap site that prevents hydrogen from entering the base steel sheet during reduction, and can improve bendability, hole expansibility, and delayed fracture resistance.
- the average depth d of the internal oxide layer containing the oxide is as thick as 4 ⁇ m or more.
- the upper limit of the average depth d of the internal oxide layer is at least less than the average depth D of the soft layer (B) described later.
- the upper limit of d is preferably 30 ⁇ m or less.
- the d is more preferably 18 ⁇ m or less, and still more preferably 16 ⁇ m or less.
- said d is 6 micrometers or more, and it is more preferable that it is 8 micrometers or more.
- the average depth d of the internal oxide layer is preferably controlled so as to satisfy the relational expression of D> 2d in relation to the average depth D of the soft layer (B) described later. This further improves the bendability and delayed fracture resistance, particularly bendability.
- the oxide existing depth d and the soft layer thickness substantially correspond to the average depth d of the internal oxide layer and the average depth D of the soft layer described in the present invention.
- D a hot dip galvanized steel sheet satisfying d / 4 ⁇ D ⁇ 2d is disclosed, and the control directivity is completely different from the relational expression (D> 2d) defined in the present invention.
- Patent Document 2 describes that the range of the oxide depth d is controlled while basically satisfying the relationship of d / 4 ⁇ D ⁇ 2d described above.
- the average depth d of the internal oxide layer is controlled to be thicker than 4 ⁇ m.
- this does not describe the effect of the present invention that the action as a hydrogen trap site is effectively exhibited and the bendability and delayed fracture resistance are improved.
- the average depth of the internal oxide layer in the cold rolled steel sheet before passing through the continuous hot dip galvanizing line is 4 ⁇ m or more. It is necessary to control. Details will be described later in the column of the manufacturing method. That is, as shown in the examples described later, the internal oxide layer after pickling and cold rolling is succeeded to the internal oxide layer in the plated steel sheet finally obtained after passing through the plating line.
- the soft layer 4 is a layer including the region of the internal oxide layer 3 of the above (A) and has a Vickers hardness of the base steel plate 2. It satisfies 90% or less of the Vickers hardness at t / 4 part. A detailed method for measuring the Vickers hardness will be described in the column of Examples described later.
- the soft layer is a soft structure having a Vickers hardness lower than that of the hard layer (C) described later, and is excellent in deformability, so that bendability is particularly improved. That is, at the time of bending, the surface steel plate surface layer portion becomes a starting point of cracking, but the bendability is particularly improved by forming a predetermined soft layer on the surface steel plate surface layer as in the present invention. Furthermore, by forming the soft layer, it is possible to prevent the oxide in (A) from becoming a starting point of cracking during bending, and it is possible to enjoy only the above-described merit as a hydrogen trap site. As a result, not only bendability but also delayed fracture resistance is further improved.
- the average depth D of the soft layer is set to 20 ⁇ m or more.
- the D is preferably 22 ⁇ m or more, and more preferably 24 ⁇ m or more.
- the upper limit is preferably set to 100 ⁇ m or less.
- the D is more preferably 60 ⁇ m or less.
- the hard layer is formed on the base steel plate 2 side of the soft layer 4 of the above (B), and martensite and bainite: 20 area% or more and 60 area % And polygonal ferrite: more than 40 area% and 80 area% or less.
- the martensite of the hard layer 5 may be tempered.
- the strength increases as the total area ratio of bainite and martensite increases (that is, the area ratio of ferrite decreases), and the ductility increases as the total area ratio of bainite and martensite decreases (that is, the area ratio of ferrite increases). Tend to improve. Moreover, when the area ratio of ferrite decreases, the balance between strength and ductility deteriorates.
- the preferable area ratio of these tissues is appropriately set in consideration of the relationship with desired characteristics.
- the total area ratio of bainite and martensite is preferably 45 area% or more, and the total area ratio of ferrite is preferably 55 area% or less.
- the total area ratio of bainite and martensite is preferably 40 area% or less, and the total area ratio of ferrite is preferably 60 area% or more.
- the hard layer may contain, in addition to the above structure, a structure that can be inevitably mixed in production, for example, retained austenite ( ⁇ ), pearlite, and the like within a range not impairing the action of the present invention.
- the above structure is 15 area% or less at the maximum, and the smaller the better.
- the organization is described as “Others” in Table 3 to be described later.
- the hard layer in this invention should just contain bainite and a martensite in the range of 20 area% or more and less than 60 area% in a total area as mentioned above, and each ratio of a bainite and a martensite is not limited at all. .
- both the aspect which is comprised only from bainite and does not contain martensite at all; conversely, the aspect comprised only from martensite and does not contain bainite at all are included in the scope of the present invention. From the above viewpoint, in the examples described later, bainite and martensite are not observed separately, only the total area is measured, and the results are shown in Table 3.
- the plated steel sheet of the present invention has C: 0.08 to 0.30%, Si: 0.25 to 3%, Mn: 1.5 to 4%, P: more than 0% and 0.1% or less, S: 0 More than 0.05% or less, Al: 0.005 to 1%, and N: more than 0% and 0.01% or less, with the balance being iron and inevitable impurities.
- C 0.08 to 0.30%
- C is an element important for increasing the strength of steel due to the improvement of hardenability and the effect of hardening of martensite.
- the lower limit of the C amount is set to 0.08% or more.
- the minimum with the preferable amount of C is 0.11% or more, More preferably, it is 0.13% or more.
- the upper limit of the C content is set to 0.30%.
- the upper limit with preferable C amount is 0.25% or less, More preferably, it is 0.20% or less.
- Si 0.25 to 3%
- Si is an element that increases the strength of steel by solid solution strengthening and is effective in improving workability. Moreover, it produces an internal oxide layer and has an action of suppressing hydrogen embrittlement.
- the lower limit of the Si amount is set to 0.25% or more.
- the minimum with the preferable amount of Si is 0.3% or more, More preferably, it is 0.5% or more, More preferably, it is 0.7% or more.
- Si is a ferrite-forming element, and when Si is added excessively, the formation of ferrite cannot be suppressed, the hardness difference between the soft phase and the hard phase increases, and the workability decreases.
- the upper limit of the Si amount is set to 3%.
- the upper limit with the preferable amount of Si is 2.5% or less, More preferably, it is 2.0% or less.
- Mn 1.5-4% Mn is an element that improves hardenability, suppresses ferrite and bainite, generates martensite, and contributes to high strength.
- the lower limit of the amount of Mn is set to 1.5% or more.
- the minimum with the preferable amount of Mn is 1.8% or more, More preferably, it is 2.0% or more.
- the upper limit of the Mn amount is 4%.
- the upper limit with the preferable amount of Mn is 3.5% or less.
- P more than 0% and 0.1% or less P is an element useful for strengthening steel as a solid solution strengthening element.
- the lower limit of the P amount is set to more than 0%.
- the upper limit is made 0.1% or less.
- the amount of P is preferably as small as possible, preferably 0.03% or less, more preferably 0.015% or less.
- S more than 0% and 0.05% or less S is an element that is unavoidably contained, and forms sulfides such as MnS, which may cause cracks and deteriorate workability. Therefore, the upper limit of the S amount is set to 0.05% or less.
- the amount of S should be small, preferably 0.01% or less, more preferably 0.008% or less.
- Al acts as a deoxidizer. Further, Al combines with N to become AlN, and the workability and delayed fracture resistance are improved by making the austenite grain size finer.
- the lower limit of the Al amount is set to 0.005% or more.
- the minimum with the preferable amount of Al is 0.01% or more, More preferably, it is 0.02% or more.
- the upper limit of the Al amount is 1%.
- the upper limit with preferable Al amount is 0.8% or less, More preferably, it is 0.6% or less.
- N more than 0% and 0.01% or less N is an element inevitably contained, but if it is contained excessively, workability deteriorates.
- B boron
- BN precipitates are generated and inhibit the effect of improving the hardenability by B. Therefore, it is better to reduce N as much as possible. Therefore, the upper limit of the N amount is 0.01% or less.
- the upper limit with preferable N amount is 0.008% or less, More preferably, it is 0.005% or less.
- the plated steel sheet of the present invention contains the above components, with the balance being iron and inevitable impurities.
- Cr more than 0% and less than 1%
- Mo more than 0% and less than 1%
- B more than 0% and less than 0.01%.
- the preferable lower limit of the Cr amount is set to 0.01% or more. However, if Cr is added excessively, the plating property is lowered. Moreover, Cr carbide
- the preferable lower limit of the Mo amount is 0.01% or more.
- the preferable upper limit of Mo is 1% or less. More preferably, it is 0.5% or less, More preferably, it is 0.3% or less.
- the preferable lower limit of the B amount is set to 0.0002% or more. More preferably, it is 0.0010% or more. However, when the amount of B becomes excessive, the hot workability deteriorates, so the preferable upper limit of the amount of B is made 0.01% or less. More preferably, it is 0.0070% or less, More preferably, it is 0.0050% or less.
- the preferable lower limit of each of Ti, Nb, and V is set to 0.01% or more.
- the preferable upper limit of each element is set to 0.2% or less. Any element is more preferably 0.15% or less, and still more preferably 0.10% or less.
- At least one selected from the group consisting of Cu: more than 0% and not more than 1% and Ni: more than 0% and not more than 1% is an element effective for increasing the strength. These elements may be added alone or in combination.
- the preferable lower limit of Cu and Ni is set to 0.01% or more.
- the preferable upper limit of each element is 1% or less. Any element is more preferably 0.8% or less, and still more preferably 0.5% or less.
- the production method of the present invention includes a first method in which pickling is performed immediately after hot rolling without holding the heat, and a second method in which pickling is performed after warming after hot rolling.
- the lower limit of the hot rolling coiling temperature is different between the first method (without heat retention) and the second method (with heat retention), but the other steps are the same. Details will be described below.
- the first manufacturing method according to the present invention includes a hot rolling process, a pickling process, a cold rolling process, an oxidation process, a reduction process, and a plating process in a continuous molten Zn plating line [CGL (Continuous Galvanizing Line)]. Broadly divided.
- the characteristic part of this invention is the hot rolling process of obtaining the hot rolled steel plate which formed the internal oxide layer by winding the steel plate which satisfies the said steel component at the temperature of 600 degreeC or more; average depth of an internal oxide layer; Pickling and cold rolling so that the thickness d remains 4 ⁇ m or more; oxidizing in the oxidation zone at an air ratio of 0.9 to 1.4; and in the reduction zone (Ac 1 point + 30 ° C. And a step of soaking in the range of 3 to Ac; and a step of soaking and then cooling the range up to the cooling stop temperature at an average cooling rate of 5 ° C./second or more after soaking in this order. It is in.
- Hot rolling may be performed according to a conventional method.
- the heating temperature is preferably about 1150 to 1300 ° C.
- the finish rolling temperature is preferably controlled to about 850 to 950 ° C.
- the coiling temperature after hot rolling it is important to control the coiling temperature after hot rolling to 600 degreeC or more.
- an internal oxide layer is formed on the surface of the base steel plate, and a soft layer is also formed by decarburization, so that a desired internal oxide layer and soft layer can be obtained on the steel plate after plating.
- the coiling temperature is less than 600 ° C., the internal oxide layer and the soft layer are not sufficiently formed.
- the strength of the hot-rolled steel sheet is increased, and the cold-rollability is reduced.
- a preferable winding temperature is 620 ° C. or higher, and more preferably 640 ° C. or higher.
- the upper limit is preferably made 750 ° C. or lower.
- the hot-rolled steel sheet thus obtained is pickled and cold-rolled so that the average depth d of the internal oxide layer remains at 4 ⁇ m or more.
- the average depth d of the internal oxide layer remains at 4 ⁇ m or more.
- the soft layer remains, so that a desired soft layer can be easily formed after plating.
- mineral acids such as hydrochloric acid, sulfuric acid, and nitric acid can be used.
- the concentration and temperature of the pickling solution are high and the pickling time is long, the internal oxide layer tends to dissolve and become thin. Conversely, if the concentration and temperature of the pickling solution are low and the pickling time is short, removal of the black skin scale layer by pickling becomes insufficient. Therefore, for example, when hydrochloric acid is used, it is recommended to control the concentration to about 3 to 20%, the temperature to 60 to 90 ° C., and the time to about 35 to 200 seconds.
- the number of pickling tanks is not particularly limited, and a plurality of pickling tanks may be used.
- a pickling inhibitor such as an amine, that is, an inhibitor, a pickling accelerator, or the like may be added to the pickling solution.
- cold rolling is performed so that the average depth d of the internal oxide layer remains 4 ⁇ m or more.
- the cold rolling conditions are preferably controlled so that the cold rolling rate is in the range of about 20 to 70%.
- oxidation is performed at an air ratio of 0.9 to 1.4 in an oxidation zone.
- the air ratio means the ratio of the amount of air actually supplied to the amount of air that is theoretically required to completely burn the supplied combustion gas.
- oxygen is in an excess state
- oxygen is in a shortage state.
- CO gas is used as the combustion gas.
- Oxidation in an atmosphere where the air ratio falls within the above range promotes decarburization, so that a desired soft layer is formed and bendability is improved.
- an Fe oxide film can be generated on the surface, and generation of a composite oxide film or the like harmful to plating properties can be suppressed.
- the air ratio needs to be controlled to 0.9 or more, and is preferably controlled to 1.0 or more.
- the air ratio is as high as 1.4 or more, an Fe oxide film is excessively generated and cannot be sufficiently reduced in the next reduction furnace, thereby impairing the plateability.
- the air ratio needs to be controlled to 1.4 or less, and is preferably controlled to 1.2 or less.
- the preferable lower limit of the oxidation temperature is 500 ° C. or higher, more preferably 750 ° C. or higher.
- the upper limit of the oxidation temperature is 900 ° C. or lower, more preferably 850 ° C. or lower.
- the oxide film is reduced in a hydrogen atmosphere in the reduction zone.
- soaking is carried out by holding in the range of (Ac 1 point + 30 ° C.) to Ac 3 point. If the soaking temperature is lower than (Ac 1 point + 30 ° C.), the ferrite becomes excessive, while if it exceeds the Ac 3 point, the ferrite is insufficient.
- a preferable soaking temperature is (Ac 1 point + 45 ° C.) or more and (Ac 3 point ⁇ 20 ° C.) or less.
- the Ac 1 point is calculated based on the following equation (i).
- [] represents the content (% by mass) of each element. This equation is described in “Leslie Steel Material Science” (published by Maruzen Co., Ltd., William C. Leslie, p273).
- Ac 1 (° C.) 723-10.7 ⁇ [Mn] ⁇ 16.9 ⁇ [Ni] + 29.1 ⁇ [Si] + 16.9 ⁇ [Cr] + 290 ⁇ [As] + 6.38 ⁇ [W] ⁇ ⁇ (I)
- the Ac 3 point is calculated based on the following equation (ii).
- [] represents the content (% by mass) of each element. This equation is described in “Leslie Steel Material Science” (published by Maruzen Co., Ltd., William C. Leslie, p273).
- the holding time at the soaking temperature is preferably 10 seconds or more. If the holding time is less than 10 seconds, the reduction is insufficient and the plating property is hindered. More preferably, it is 30 seconds or more, More preferably, it is 50 seconds or more.
- the holding time at the time of soaking is not particularly limited from the above viewpoint, but is preferably controlled to about 100 seconds or less, more preferably about 80 seconds or less in consideration of productivity.
- the atmosphere of the reduction zone contains hydrogen and nitrogen, and the hydrogen concentration is preferably controlled in the range of about 5 to 25% by volume.
- the dew point is preferably controlled at -30 to -60 ° C.
- the range up to the cooling stop temperature is cooled at an average cooling rate of 5 ° C./second or more.
- the area ratio of the ferrite can be controlled within a predetermined range.
- it is 8 degreeC / second or more, More preferably, it is 10 degreeC / second or more.
- the upper limit of the average cooling rate is not particularly limited, but it is preferable to control the temperature to about 100 ° C./second or less in consideration of the ease of control of the base steel sheet temperature and the equipment cost.
- a more preferable average cooling rate is 50 ° C./second or less, and further preferably 30 ° C./second or less.
- the cooling stop temperature may be up to a temperature range where ferrite is not generated. For example, it is preferable to cool to 550 ° C. or lower.
- a preferable lower limit of the cooling stop temperature is, for example, 400 ° C. or higher, more preferably 430 ° C. or higher, and further preferably 460 ° C. or higher.
- the subsequent cooling method is not limited to the above.
- the cooling may be performed below the preferable cooling stop temperature described above (see, for example, No. 25 in Table 2 below). Or after cooling to predetermined temperature, you may cool with water.
- hot dip galvanizing is performed according to a conventional method.
- the method of hot dip galvanizing is not particularly limited, and for example, the preferred lower limit of the plating bath temperature is 400 ° C. or higher, more preferably 440 ° C. or higher.
- the upper limit with the said preferable plating bath temperature is 500 degrees C or less, More preferably, it is 470 degrees C or less.
- the composition of the plating bath is not particularly limited, and a known hot dip galvanizing bath may be used.
- the cooling conditions after hot dip galvanizing are not particularly limited, and for example, the average cooling rate to room temperature is preferably controlled to about 1 ° C./second or more, more preferably 5 ° C./second or more.
- the upper limit of the average cooling rate is not particularly defined, but is preferably controlled to about 50 ° C./second or less in consideration of ease of control of the base steel sheet temperature and equipment cost.
- the average cooling rate is preferably 40 ° C./second or less, more preferably 30 ° C./second or less.
- alloying treatment may be performed by a conventional method, whereby an alloyed hot-dip galvanized steel sheet is obtained.
- the conditions for the alloying treatment are not particularly limited. For example, after performing hot dip galvanization under the above conditions, hold at about 500 to 600 ° C., particularly about 530 to 580 ° C. for about 5 to 30 seconds, particularly about 10 to 25 seconds. It is preferable to do so. Below the above range, alloying is insufficient. On the other hand, when the above range is exceeded, alloying proceeds excessively, and there is a possibility that plating peeling may occur during press molding of the plated steel sheet. Furthermore, it becomes easy to produce ferrite.
- the alloying treatment may be performed using, for example, a heating furnace, a direct fire, or an infrared heating furnace.
- the heating means is also not particularly limited, and for example, conventional means such as gas heating, induction heater heating, that is, heating by a high frequency induction heating device can be adopted.
- an alloyed hot-dip galvanized steel sheet is obtained by cooling according to a conventional method.
- the average cooling rate to room temperature is preferably controlled to about 1 ° C./second or more.
- the second production method includes a hot rolling step of winding a hot-rolled steel sheet satisfying the above-mentioned components in the steel at a temperature of 500 ° C. or higher; a step of keeping the temperature at 500 ° C. or higher for 80 minutes or more; Pickling and cold rolling so that the average depth d of the internal oxide layer remains 4 ⁇ m or more; oxidizing in an oxidation zone at an air ratio of 0.9 to 1.4; (Ac 1 point + 30 ° C.) to Ac 3 point holding and soaking; and after soaking, cooling to the cooling stop temperature range at an average cooling rate of 5 ° C./second or more; In this order, there is a feature.
- the lower limit of the coiling temperature after hot rolling is set to 500 ° C. or more, and the heat retaining step is provided after the hot rolling step. Only the first manufacturing method is different. Therefore, only the difference will be described below.
- the first manufacturing method may be referred to.
- the reason for providing the heat-retaining step as described above is that it is possible to maintain for a long time in a temperature range that can be oxidized by heat-retaining, and to expand the lower limit of the coiling temperature range from which a desired internal oxide layer and soft layer can be obtained. .
- the uniformity of the base steel sheet can be improved by reducing the temperature difference between the surface layer and the inside of the base steel sheet.
- the coiling temperature after hot rolling is controlled to 500 ° C. or higher.
- the temperature can be set lower than 600 ° C. which is the lower limit of the winding temperature in the first manufacturing method described above.
- a preferable winding temperature is 540 ° C. or higher, more preferably 570 ° C. or higher.
- the preferable upper limit of coiling temperature is the same as the 1st manufacturing method mentioned above, and it is preferable to set it as 750 degrees C or less.
- the hot-rolled steel sheet thus obtained is kept at a temperature of 500 ° C. or more for 80 minutes or more. Thereby, a desired internal oxide layer can be obtained. It is preferable to keep the hot-rolled steel sheet in a heat-insulating device, for example, so that the above-mentioned effect due to heat insulation is effectively exhibited.
- the said apparatus used for this invention will not be specifically limited if comprised with the heat insulating raw material, For example, a ceramic fiber etc. are used preferably as such a raw material.
- a preferred temperature is 540 ° C. or higher, more preferably 560 ° C. or higher.
- a preferable time is 100 minutes or more, More preferably, it is 120 minutes or more.
- it is preferable to control the upper limit of the said temperature and time to about 700 degrees C or less and 500 minutes or less when pickling property, productivity, etc. are considered.
- the plated steel sheet of the present invention obtained by the above-described production method is further subjected to various coatings and coating ground treatments, for example, chemical conversion treatment such as phosphate treatment; organic coating treatment, for example, formation of an organic coating such as a film laminate. May be.
- various coatings and coating ground treatments for example, chemical conversion treatment such as phosphate treatment; organic coating treatment, for example, formation of an organic coating such as a film laminate. May be.
- paint used for various coatings known resins such as epoxy resin, fluorine resin, silicon acrylic resin, polyurethane resin, acrylic resin, polyester resin, phenol resin, alkyd resin, melamine resin, and the like can be used. From the viewpoint of corrosion resistance, an epoxy resin, a fluororesin, and a silicon acrylic resin are preferable.
- a curing agent may be used together with the resin.
- the paint may also contain known additives such as coloring pigments, coupling agents, leveling agents, sensitizers, antioxidants, UV stabilizers, flame retardants and the like.
- the form of paint is not particularly limited, and any form of paint such as solvent-based paint, water-based paint, water-dispersed paint, powder paint, and electrodeposition paint can be used.
- the coating method is not particularly limited, and a dipping method, a roll coater method, a spray method, a curtain flow coater method, an electrodeposition coating method, and the like can be used. What is necessary is just to set suitably the thickness of coating layers, such as a plating layer, an organic membrane
- the high-strength plated steel sheet of the present invention is ultra-high-strength and excellent in workability (balance between strength and ductility and bendability) and delayed fracture resistance. It can be used for collision parts such as side members and crash boxes, pillars such as center pillar reinforcement, body components such as roof rail reinforcement, side sill, floor member, and kick section.
- the balance was iron and inevitable impurity slabs heated to 1250 ° C., hot rolled to 2.4 mm at a finish rolling temperature of 900 ° C., and then wound up at the temperature shown in Table 2.
- the hot-rolled steel sheet thus obtained was pickled under the following conditions and then cold-rolled at a cold rolling rate of 50%.
- the plate thickness after cold rolling is 1.2 mm.
- annealing oxidation, reduction
- cooling were performed under the conditions shown in Table 2 in a continuous molten Zn plating line.
- the temperature of the oxidation furnace installed in the continuous molten Zn plating line was controlled to 800 ° C.
- the hydrogen concentration in the reduction furnace was 20% by volume
- the balance was nitrogen and inevitable impurities, dew point: ⁇ 45 ° C.
- the holding times at the soaking temperature shown in Table 2 were all 50 seconds.
- the average depth of the internal oxide layer was measured not only on the plated steel sheet but also on the base steel sheet after pickling and cold rolling for reference. This is to confirm that the desired average depth of the internal oxide layer has already been obtained in the cold-rolled steel sheet before annealing by controlling the coiling temperature and pickling conditions after hot rolling. It is.
- Pulse sputtering frequency 50Hz
- Anode diameter (analysis area): Diameter 6 mm
- Discharge power 30W
- Ar gas pressure 2.5 hPa
- the position where the Zn content and the Fe content from the surface of the plating layer become equal was defined as the interface between the plating layer and the base steel sheet.
- the average value of the O amount at each measurement position at a depth of 40 to 50 ⁇ m from the surface of the plating layer is the average value of the bulk O amount, which is 0.02% higher than that, that is, the O amount ⁇ (the bulk O amount)
- the average value + 0.02%) was defined as the internal oxide layer, and the maximum depth was defined as the internal oxide layer depth.
- a similar test was performed using three test pieces, and the average was defined as the average depth d of the internal oxide layer.
- the measurement is performed at a pitch of 10 ⁇ m from the interface between the plating layer 1 and the base steel plate 2 at a depth of 10 ⁇ m toward the inside of the thickness, and the measurement is performed every 5 ⁇ m at a pitch up to a depth of 100 ⁇ m.
- Hardness was measured. Interval between measurement points; that is, the distance between x and x in FIG. 3 was at least 15 ⁇ m.
- a region having a Vickers hardness of 90% or less compared with t / 4 part of the base steel plate was defined as a soft layer, and the depth was calculated.
- the same treatment was performed at 10 places on the same test piece, and the average was defined as the average depth D of the soft layer.
- TS ⁇ EL was calculated from the tensile strength and elongation obtained as described above. In this example, TS ⁇ EL of 17000 or more was evaluated as having an excellent balance between strength and ductility (pass).
- the bendability was evaluated for each tensile strength TS based on Rmin / t obtained by dividing Rmin by the plate thickness t of the base steel sheet. Details are as follows. In addition, the evaluation of bendability was not performed for TS not satisfying the acceptable standard of 980 MPa or more (indicated as “ ⁇ ” in Table 3). When TS is 980 MPa or more and less than 1080 MPa, Rmin / t ⁇ 2.0 is satisfied, and when TS is 1080 MPa or more and less than 1180 MPa, Rmin / t ⁇ 3.0 is satisfied, and when TS is 1180 MPa or more, Rmin / t ⁇ 3 .7 passed
- No. Examples 1 to 11, 15, 17, 24 to 26, and 29 to 41 are examples that satisfy the requirements of the present invention, and are strength, workability [balance between strength and ductility (TS ⁇ EL), and bendability], delay resistance Destructive properties and plating properties were all good.
- the average depth d of the internal oxide layer and the average depth D of the soft layer satisfy the relationship of D> 2d (ie, the value of “D / 2d” in Table 2 exceeds 1).
- No. No. 12 is an example using the steel type L in Table 1 with a large amount of C, and the bendability and delayed fracture resistance were deteriorated.
- No. 13 is an example using the steel type M in Table 1 with a small amount of Si. Since the average depth of the internal oxide layer after pickling and cold rolling is shallow, the internal oxide layer is not sufficiently formed, and the bendability and strength are reduced. The balance between ductility and delayed fracture resistance decreased.
- No. No. 14 is an example in which the steel type A in Table 1 whose components in the steel satisfy the requirements of the present invention is used, but the coiling temperature at the time of hot rolling is low, and the average depth of the internal oxide layer after pickling and cold rolling Therefore, the average depth d of the internal oxide layer after plating and the average depth D of the soft layer were also reduced. As a result, bendability, delayed fracture resistance, and plating properties were reduced.
- No. No. 16 used steel type A in Table 1 whose components in the steel satisfy the requirements of the present invention, but the air ratio in the oxidation furnace is low, the iron oxide film was not sufficiently generated, and the plating property was lowered. . In addition, since the soft layer was not sufficiently generated, the bendability and delayed fracture resistance were deteriorated.
- No. No. 18 is an example in which the steel type A in Table 1 whose components in the steel satisfy the requirements of the present invention is used, but the coiling temperature at the time of hot rolling is low and the air ratio in the oxidation furnace is low. Since the average depth of the internal oxide layer after cold rolling was shallow, the average depth d of the internal oxide layer after plating and the average depth D of the soft layer were also shallow. As a result, bendability, delayed fracture resistance, and plating properties were reduced.
- No. No. 19 is an example in which the steel type A in Table 1 whose components in the steel satisfy the requirements of the present invention is used, but the coiling temperature during hot rolling is low, and the average depth of the internal oxide layer after pickling and cold rolling Is shallow, the average depth d of the internal oxide layer after plating was also shallow. As a result, delayed fracture resistance and plating properties were reduced.
- No. 20 and no. No. 21 uses steel type A in Table 1 whose components in the steel satisfy the requirements of the present invention, but is an example of a high soaking temperature, and ferrite is not sufficiently generated (B + M), and the total area ratio is large. As a result, the balance between strength and ductility decreased.
- No. No. 22 uses the steel type A in Table 1 whose components in the steel satisfy the requirements of the present invention, but is an example where the soaking temperature is low, ferrite is excessively generated and the total amount of (B + M) is also reduced. The desired hard layer was not obtained. Therefore, TS became low.
- No. No. 23 was an example in which the steel type A in Table 1 whose components in the steel satisfied the requirements of the present invention was used, but the average cooling rate after soaking was slow, and ferrite was excessively generated during cooling (B + M) As a result, the desired hard layer could not be obtained. As a result, TS decreased.
- No. No. 27 is an example in which the steel type A in Table 1 whose components in the steel satisfy the requirements of the present invention is used, but the coiling temperature at the time of hot rolling is low, and the average depth of the internal oxide layer after pickling and cold rolling Therefore, the average depth d of the internal oxide layer after plating and the average depth D of the soft layer were also reduced. As a result, bendability, delayed fracture resistance, and plating properties were reduced.
- No. No. 28 used steel type A in Table 1 whose components in the steel satisfy the requirements of the present invention, but is an example of insufficient heat retention time, and the average depth of the internal oxide layer after pickling and cold rolling is shallow Therefore, the average depth d of the internal oxide layer after plating and the average depth D of the soft layer are also shallow. As a result, bendability, delayed fracture resistance, and plating properties were reduced.
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Abstract
Description
(a)Cr:0%超1%以下、Mo:0%超1%以下、およびB:0%超0.01%以下よりなる群から選択される少なくとも一種
(b)Ti:0%超0.2%以下、Nb:0%超0.2%以下、およびV:0%超0.2%以下よりなる群から選択される少なくとも一種
(c)Cu:0%超1%以下、およびNi:0%超1%以下よりなる群から選択される少なくとも一種 In a preferred embodiment of the present invention, the base steel sheet further contains at least one of the following (a) to (c) by mass%.
(A) At least one selected from the group consisting of Cr: more than 0% and 1% or less, Mo: more than 0% and 1% and B: more than 0% and 0.01% or less (b) Ti: more than 0% and 0 .2% or less, Nb: more than 0% and 0.2% or less, and V: at least one selected from the group consisting of more than 0% and 0.2% or less (c) Cu: more than 0% and 1% or less, and Ni : At least one selected from the group consisting of more than 0% and 1% or less
(A)内部酸化層:SiおよびMnよりなる群から選択される少なくとも一種の酸化物を含む層である。内部酸化層の平均深さdは、4μm以上、後記する(B)に記載の軟質層の平均深さD未満である。
(B)軟質層:上記内部酸化層を含み、上記素地鋼板の板厚をtとしたとき、ビッカース硬さが、上記素地鋼板のt/4部におけるビッカース硬さの90%以下を満足する。軟質層の平均深さDは、20μm以上である。
(C)硬質層:マルテンサイトおよびベイナイト:20面積%以上60面積%未満と、ポリゴナルフェライト:40面積%超80面積%以下と、を含む組織で構成される。 As described above, the plated steel sheet of the present invention has a hot dip galvanized layer or an alloyed hot dip galvanized layer (hereinafter sometimes represented by a plated layer) on the surface of the base steel sheet. The characteristic part of the present invention is that it has the following layer configurations (A) to (C) in order from the interface between the base steel plate and the plating layer toward the base steel plate side.
(A) Internal oxide layer: a layer containing at least one oxide selected from the group consisting of Si and Mn. The average depth d of the internal oxide layer is 4 μm or more and less than the average depth D of the soft layer described in (B) described later.
(B) Soft layer: including the internal oxide layer, where the thickness of the base steel sheet is t, the Vickers hardness satisfies 90% or less of the Vickers hardness at t / 4 part of the base steel sheet. The average depth D of the soft layer is 20 μm or more.
(C) Hard layer: composed of martensite and bainite: 20 area% or more and less than 60 area% and polygonal ferrite: more than 40 area% and 80 area% or less.
まず、めっき層1と素地鋼板2の界面に直接接する部分は、平均深さdが4μm以上の内部酸化層3を有する。ここで、平均深さとは、上記界面からの平均深さを意味し、その詳細な測定方法は、後記する実施例の欄において図2を用いて説明する。 (A) Internal oxide layer First, the portion directly in contact with the interface between the
本発明において軟質層4は、図1に示すように、上記(A)の内部酸化層3の領域を含む層であって、且つ、ビッカース硬さが、素地鋼板2のt/4部におけるビッカース硬さの90%以下を満足するものである。上記ビッカース硬さの詳細な測定方法は、後記する実施例の欄で説明する。 (B) Soft layer In the present invention, as shown in FIG. 1, the
本発明において硬質層は、図1に示すように、上記(B)の軟質層4の素地鋼板2側に形成され、且つ、マルテンサイトおよびベイナイト:20面積%以上60面積%未満と、ポリゴナルフェライト:40面積%超80面積%以下と、を含む組織で構成される。上記硬質層5のマルテンサイトは焼き戻しされていても良い。ベイナイトとマルテンサイトの合計面積率が多い程(すなわち、フェライトの面積率が少ない程)強度が向上し、ベイナイトとマルテンサイトの合計面積率が少ない程(すなわち、フェライトの面積率が多い程)延性が向上する傾向にある。また、フェライトの面積率が少なくなると強度と延性のバランスが悪くなる。よって、これら組織の好ましい面積比率は、所望とする特性との関係を考慮して適宜設定することが推奨される。例えば強度向上の観点から、ベイナイトとマルテンサイトの合計面積率は45面積%以上、フェライトの合計面積率は55面積%以下であることが好ましい。また、強度と延性のバランス向上を考慮すれば、ベイナイトとマルテンサイトの合計面積率は40面積%以下、フェライトの合計面積率は60面積%以上であることが好ましい。 (C) Hard layer In the present invention, as shown in FIG. 1, the hard layer is formed on the
Cは、焼入れ性を向上させ、またマルテンサイトの硬質化効果により、鋼の高強度化に重要な元素である。このような効果を有効に発揮させるため、C量の下限を0.08%以上とする。C量の好ましい下限は0.11%以上であり、より好ましくは0.13%以上である。しかし、Cを過剰に添加すると、軟質相と硬質相の硬度差が大きくなり、加工性および耐遅れ破壊特性が低下するため、C量の上限を0.30%とする。C量の好ましい上限は0.25%以下であり、より好ましくは0.20%以下である。 C: 0.08 to 0.30%
C is an element important for increasing the strength of steel due to the improvement of hardenability and the effect of hardening of martensite. In order to effectively exhibit such an effect, the lower limit of the C amount is set to 0.08% or more. The minimum with the preferable amount of C is 0.11% or more, More preferably, it is 0.13% or more. However, when C is added excessively, the hardness difference between the soft phase and the hard phase increases, and the workability and delayed fracture resistance deteriorate, so the upper limit of the C content is set to 0.30%. The upper limit with preferable C amount is 0.25% or less, More preferably, it is 0.20% or less.
Siは固溶強化により鋼の強度を高め、加工性向上にも有効な元素である。また、内部酸化層を生成し、水素脆化の抑制作用も有する。このような効果を有効に発揮させるため、Si量の下限を0.25%以上とする。Si量の好ましい下限は0.3%以上であり、より好ましくは0.5%以上、更に好ましくは0.7%以上である。しかし、Siはフェライト生成元素であり、Siを過剰に添加すると、フェライトの生成を抑制できず、軟質相と硬質相の硬度差が大きくなり、加工性が低下する。更には、めっき性も悪くなるため、Si量の上限を3%とする。Si量の好ましい上限は2.5%以下であり、より好ましくは2.0%以下である。 Si: 0.25 to 3%
Si is an element that increases the strength of steel by solid solution strengthening and is effective in improving workability. Moreover, it produces an internal oxide layer and has an action of suppressing hydrogen embrittlement. In order to effectively exhibit such an effect, the lower limit of the Si amount is set to 0.25% or more. The minimum with the preferable amount of Si is 0.3% or more, More preferably, it is 0.5% or more, More preferably, it is 0.7% or more. However, Si is a ferrite-forming element, and when Si is added excessively, the formation of ferrite cannot be suppressed, the hardness difference between the soft phase and the hard phase increases, and the workability decreases. Furthermore, since the plating property also deteriorates, the upper limit of the Si amount is set to 3%. The upper limit with the preferable amount of Si is 2.5% or less, More preferably, it is 2.0% or less.
Mnは、焼入れ性向上元素であり、フェライトおよびベイナイトを抑制し、マルテンサイトを生成させて高強度化に寄与する。このような効果を有効に発揮させるため、Mn量の下限を1.5%以上とする。Mn量の好ましい下限は1.8%以上であり、より好ましくは2.0%以上である。しかし、Mnを過剰に添加すると、めっき性が低下し、また偏析も著しくなる。更に、Pの粒界偏析を助長する虞がある。そのため、Mn量の上限を4%とする。Mn量の好ましい上限は3.5%以下である。 Mn: 1.5-4%
Mn is an element that improves hardenability, suppresses ferrite and bainite, generates martensite, and contributes to high strength. In order to effectively exhibit such an effect, the lower limit of the amount of Mn is set to 1.5% or more. The minimum with the preferable amount of Mn is 1.8% or more, More preferably, it is 2.0% or more. However, when Mn is added excessively, the plating property is lowered and segregation is also remarkable. Furthermore, there is a possibility of promoting grain boundary segregation of P. Therefore, the upper limit of the Mn amount is 4%. The upper limit with the preferable amount of Mn is 3.5% or less.
Pは、固溶強化元素として鋼の強化に有用な元素である。このような効果を有効に発揮させるため、P量の下限を0%超とする。しかし、過剰に添加すると、加工性のほか、溶接性、靱性を劣化させる虞があるため、その上限を0.1%以下とする。P量は少ない方が良く、好ましくは0.03%以下、より好ましくは0.015%以下である。 P: more than 0% and 0.1% or less P is an element useful for strengthening steel as a solid solution strengthening element. In order to effectively exhibit such an effect, the lower limit of the P amount is set to more than 0%. However, if added in excess, the workability, weldability and toughness may be deteriorated, so the upper limit is made 0.1% or less. The amount of P is preferably as small as possible, preferably 0.03% or less, more preferably 0.015% or less.
Sは、不可避的に含有する元素であり、MnSなどの硫化物を形成し、割れの起点なり、加工性を劣化させる虞がある。そのため、S量の上限を0.05%以下とする。S量は少ない方が良く、好ましくは0.01%以下、より好ましくは0.008%以下である。 S: more than 0% and 0.05% or less S is an element that is unavoidably contained, and forms sulfides such as MnS, which may cause cracks and deteriorate workability. Therefore, the upper limit of the S amount is set to 0.05% or less. The amount of S should be small, preferably 0.01% or less, more preferably 0.008% or less.
Alは、脱酸剤として作用する。またAlはNと結合してAlNとなり、オーステナイト粒径の微細化により加工性および耐遅れ破壊特性も向上する。このような作用を有効に発揮させるため、Al量の下限を0.005%以上とする。Al量の好ましい下限は0.01%以上であり、より好ましくは0.02%以上である。しかし、Alを過剰に添加すると、アルミナなどの介在物が増加して加工性が劣化するほか、靱性も劣化するようになる。そのため、Al量の上限を1%とする。Al量の好ましい上限は0.8%以下であり、より好ましくは0.6%以下である。 Al: 0.005 to 1%
Al acts as a deoxidizer. Further, Al combines with N to become AlN, and the workability and delayed fracture resistance are improved by making the austenite grain size finer. In order to effectively exhibit such an action, the lower limit of the Al amount is set to 0.005% or more. The minimum with the preferable amount of Al is 0.01% or more, More preferably, it is 0.02% or more. However, when Al is added excessively, inclusions such as alumina increase and workability deteriorates and toughness also deteriorates. Therefore, the upper limit of the Al amount is 1%. The upper limit with preferable Al amount is 0.8% or less, More preferably, it is 0.6% or less.
Nは、不可避的に含有する元素であるが、過剰に含まれると加工性が劣化する。また、鋼中にB(ホウ素)を添加した場合には、BN析出物が生成し、Bによる焼入れ性向上作用を阻害するため、Nはできるだけ低減する方が良い。そのため、N量の上限を0.01%以下とする。N量の好ましい上限は0.008%以下であり、より好ましくは0.005%以下である。 N: more than 0% and 0.01% or less N is an element inevitably contained, but if it is contained excessively, workability deteriorates. In addition, when B (boron) is added to the steel, BN precipitates are generated and inhibit the effect of improving the hardenability by B. Therefore, it is better to reduce N as much as possible. Therefore, the upper limit of the N amount is 0.01% or less. The upper limit with preferable N amount is 0.008% or less, More preferably, it is 0.005% or less.
これらの元素は、鋼板の強度上昇に有効な元素である。これらの元素は単独で添加しても良いし、二種以上を併用しても良い。 At least one selected from the group consisting of Cr: more than 0% and less than 1%, Mo: more than 0% and less than 1%, and B: more than 0% and less than 0.01%. These elements are effective in increasing the strength of the steel sheet. It is an element. These elements may be added alone or in combination of two or more.
これらの元素は、組織微細化による加工性および耐遅れ破壊特性向上に有効な元素である。これらの元素は単独で添加しても良いし、二種以上を併用しても良い。 At least one selected from the group consisting of Ti: more than 0% and not more than 0.2%, Nb: more than 0% and not more than 0.2%, and V: more than 0% and not more than 0.2%. It is an effective element for improving workability and delayed fracture resistance. These elements may be added alone or in combination of two or more.
CuおよびNiは、高強度化に有効な元素である。これらの元素は単独で添加しても良いし、併用しても良い。 At least one selected from the group consisting of Cu: more than 0% and not more than 1% and Ni: more than 0% and not more than 1% is an element effective for increasing the strength. These elements may be added alone or in combination.
本発明に係る第一の製造方法は、熱延工程と、酸洗、冷延工程と、連続溶融Znめっきライン[CGL(Continuous Galvanizing Line)]での酸化工程、還元工程、およびめっき工程とに大別される。そして本発明の特徴部分は、上記鋼中成分を満足する鋼板を、600℃以上の温度で巻取ることにより内部酸化層を形成した熱延鋼板を得る熱延工程と;内部酸化層の平均深さdが4μm以上残るように酸洗・冷間圧延する工程と;酸化帯にて、0.9~1.4の空気比で酸化する工程と;還元帯にて、(Ac1点+30℃)~Ac3点の範囲で保持して均熱する工程と;均熱後、冷却停止温度までの範囲を5℃/秒以上の平均冷却速度で冷却する工程と;を、この順序で含むところにある。 [First manufacturing method (no heat retention)]
The first manufacturing method according to the present invention includes a hot rolling process, a pickling process, a cold rolling process, an oxidation process, a reduction process, and a plating process in a continuous molten Zn plating line [CGL (Continuous Galvanizing Line)]. Broadly divided. And the characteristic part of this invention is the hot rolling process of obtaining the hot rolled steel plate which formed the internal oxide layer by winding the steel plate which satisfies the said steel component at the temperature of 600 degreeC or more; average depth of an internal oxide layer; Pickling and cold rolling so that the thickness d remains 4 μm or more; oxidizing in the oxidation zone at an air ratio of 0.9 to 1.4; and in the reduction zone (Ac 1 point + 30 ° C. And a step of soaking in the range of 3 to Ac; and a step of soaking and then cooling the range up to the cooling stop temperature at an average cooling rate of 5 ° C./second or more after soaking in this order. It is in.
Ac1(℃)=723-10.7×[Mn]-16.9×[Ni]+29.1×[Si]+16.9×[Cr]+290×[As]+6.38×[W]・・・(i) In the present invention, the Ac 1 point is calculated based on the following equation (i). In the formula, [] represents the content (% by mass) of each element. This equation is described in “Leslie Steel Material Science” (published by Maruzen Co., Ltd., William C. Leslie, p273).
Ac 1 (° C.) = 723-10.7 × [Mn] −16.9 × [Ni] + 29.1 × [Si] + 16.9 × [Cr] + 290 × [As] + 6.38 × [W] ·・ ・ (I)
Ac3(℃)=910-203×[C]1/2-15.2×[Ni]+44.7×[Si]+104×[V]+31.5×[Mo]+13.1×[W]-{30×[Mn]+11×[Cr]+20×[Cu]-700×[P]-400×[Al]-120×[As]-400×[Ti]}・・・(ii) In the present invention, the Ac 3 point is calculated based on the following equation (ii). In the formula, [] represents the content (% by mass) of each element. This equation is described in “Leslie Steel Material Science” (published by Maruzen Co., Ltd., William C. Leslie, p273).
Ac 3 (° C.) = 910−203 × [C] 1/2 −15.2 × [Ni] + 44.7 × [Si] + 104 × [V] + 31.5 × [Mo] + 13.1 × [W] -{30 × [Mn] + 11 × [Cr] + 20 × [Cu] −700 × [P] −400 × [Al] −120 × [As] −400 × [Ti]} (ii)
本発明に係る第二の製造方法は、上記鋼中成分を満足する熱延鋼板を、500℃以上の温度で巻取る熱延工程と;500℃以上の温度で80分以上保温する工程と;内部酸化層の平均深さdが4μm以上残るように酸洗・冷間圧延する工程と;酸化帯にて、0.9~1.4の空気比で酸化する工程と;還元帯にて、(Ac1点+30℃)~Ac3点の範囲で保持して均熱する工程と;均熱後、冷却停止温度までの範囲を5℃/秒以上の平均冷却速度で冷却する工程と;を、この順序で含むところに特徴がある。前述した第一の製造方法と対比すると、上記第二の製造方法では、熱延後巻取温度の下限を500℃以上にしたこと、熱延工程の後に保温工程を設けたことの二点でのみ上記第一の製造方法と相違する。よって、以下では、当該相違点のみ説明する。上記第一の製造方法と一致する工程は、上記第一の製造方法を参照すればよい。 [Second manufacturing method (with heat retention)]
The second production method according to the present invention includes a hot rolling step of winding a hot-rolled steel sheet satisfying the above-mentioned components in the steel at a temperature of 500 ° C. or higher; a step of keeping the temperature at 500 ° C. or higher for 80 minutes or more; Pickling and cold rolling so that the average depth d of the internal oxide layer remains 4 μm or more; oxidizing in an oxidation zone at an air ratio of 0.9 to 1.4; (Ac 1 point + 30 ° C.) to Ac 3 point holding and soaking; and after soaking, cooling to the cooling stop temperature range at an average cooling rate of 5 ° C./second or more; In this order, there is a feature. In contrast to the first manufacturing method described above, in the second manufacturing method, the lower limit of the coiling temperature after hot rolling is set to 500 ° C. or more, and the heat retaining step is provided after the hot rolling step. Only the first manufacturing method is different. Therefore, only the difference will be described below. For the steps consistent with the first manufacturing method, the first manufacturing method may be referred to.
酸洗液:10%塩酸、温度:82℃、酸洗時間:表2のとおり。 Next, the hot-rolled steel sheet thus obtained was pickled under the following conditions and then cold-rolled at a cold rolling rate of 50%. The plate thickness after cold rolling is 1.2 mm.
Pickling solution: 10% hydrochloric acid, temperature: 82 ° C., pickling time: as shown in Table 2.
めっき鋼板の板幅をWとしたとき、W/4部からサイズ50mm×50mmの試験片を採取した後、グロー放電発光分析法[(GD-OES(Glow Discharge-Optical Emission Spectroscopy)]にて、めっき層表面からのO量、Fe量、およびZn量をそれぞれ分析し、定量した。詳細には、堀場製作所製GD-PROFILER2型GDA750のGD-OES装置を用いて、上記試験片の表面を、Arグロー放電領域内で高周波スパッタリングし、スパッタされるO、Fe、Znの各元素のArプラズマ内における発光線を連続的に分光することによって、素地鋼板の深さ方向における各元素量プロファイル測定した。スパッタ条件は以下のとおりであり、測定領域は、めっき層表面から深さ50μmまでとした。 (1) Measurement of the average depth d of the internal oxide layer in the plated steel sheet When the plate width of the plated steel sheet is W, a specimen having a size of 50 mm × 50 mm is taken from W / 4 part, and then the glow discharge emission analysis method [ (GD-OES (Glow Discharge-Optical Emission Spectroscopy)) was used to analyze and quantify the O amount, Fe amount, and Zn amount from the surface of the plating layer. Using the GD-OES apparatus, the surface of the test piece is subjected to high-frequency sputtering in an Ar glow discharge region, and emission lines in the Ar plasma of each of the O, Fe, and Zn elements to be sputtered are continuously dispersed. Each element amount profile in the depth direction of the base steel sheet was measured. The measurement area was as follows from the surface of the plating layer to a depth of 50 μm.
パルススパッタ周波数:50Hz
アノード径(分析面積):直径6mm
放電電力:30W
Arガス圧:2.5hPa (Sputtering conditions)
Pulse sputtering frequency: 50Hz
Anode diameter (analysis area): Diameter 6 mm
Discharge power: 30W
Ar gas pressure: 2.5 hPa
酸洗・冷間圧延後の素地鋼板を用いたこと以外は上記(1)と同様にして、内部酸化層の平均深さを算出した。 (2) Measurement of internal oxide layer depth after pickling and cold rolling (reference)
The average depth of the internal oxide layer was calculated in the same manner as in the above (1) except that the base steel sheet after pickling and cold rolling was used.
めっき鋼板の板幅W方向に対して垂直な断面であるW/4部を露出させ、サイズ20mm×20mmの試験片を採取した後、樹脂に埋め込み、めっき層と素地鋼板の界面から素地鋼板の板厚t内部に向かってビッカース硬さを測定した。測定はビッカース硬度計を用い、荷重3gfにて行った。詳細には図3に示すように、めっき層1と素地鋼板2の界面から板厚内部深さ10μmの測定位置から、板厚内部に向かって5μmピッチごとに測定を行い、深さ100μmまでビッカース硬さを測定した。測定点同士の間隔;すなわち図3中、×と×の距離は、最低でも15μm以上とした。各深さでn=1ずつビッカース硬さを測定し、板厚内部方向の硬さ分布を調査した。更に、素地鋼板のt/4部におけるビッカース硬さを、ビッカース硬度計を用いて荷重1kgfにて測定した(n=1)。素地鋼板のt/4部と比較してビッカース硬さが90%以下の領域を軟質層とし、その深さを計算した。同様の処理を、同じ試験片で10箇所実施し、その平均を軟質層の平均深さDとした。 (3) Measurement of average depth D of soft layer After exposing W / 4 part which is a cross section perpendicular to the plate width W direction of the plated steel sheet, a test piece having a size of 20 mm × 20 mm was collected and embedded in resin. The Vickers hardness was measured from the interface between the plating layer and the base steel plate toward the inside of the thickness t of the base steel plate. The measurement was performed using a Vickers hardness meter at a load of 3 gf. Specifically, as shown in FIG. 3, the measurement is performed at a pitch of 10 μm from the interface between the
めっき鋼板の板幅W方向に対して垂直な断面であるW/4部を露出させ、この断面を研磨し、更に電解研磨した後、ナイタールで腐食させたものをSEM(Scanning Electron Microscope)観察した。観察位置は素地鋼板の板厚をtとしたときt/4位置とし、観察倍率は2000倍、観察領域は40μm×40μmとした。SEMで撮影した金属組織写真を画像解析し、マルテンサイトとベイナイト(両者は区別せず)、およびフェライトの面積率を夫々測定した。表3中、α=フェライト、(B+M)=(ベイナイト+マルテンサイト)を意味する。また、表3中、「その他」の組織の面積分率は、100面積%から、マルテンサイトとベイナイト、およびフェライトの各面積率を引いて算出した。観察は任意に3視野について行い、平均値を算出した。 (4) Method for measuring the fraction of the structure of the plated steel sheet The W / 4 part, which is a section perpendicular to the width W direction of the plated steel sheet, is exposed, this section is polished, further electropolished, and then corroded with nital. What was made to observe was observed by SEM (Scanning Electron Microscope). The observation position was a t / 4 position where the thickness of the base steel sheet was t, the observation magnification was 2000 times, and the observation area was 40 μm × 40 μm. Image analysis of the metal structure photograph taken by SEM was performed, and martensite, bainite (not distinguished from each other), and the area ratio of ferrite were measured. In Table 3, α = ferrite, (B + M) = (bainite + martensite). In Table 3, the area fraction of the “other” structure was calculated by subtracting each area ratio of martensite, bainite, and ferrite from 100 area%. Observation was arbitrarily performed for three visual fields, and an average value was calculated.
めっき鋼板の圧延方向に垂直な方向と試験片の長手方向が平行になるようにJIS 13号B引張試験片を採取し、JIS Z2241に従ってC方向の引張強度(TS)、降伏応力(YS)、および伸び(EL)を測定した。TSおよびYSより、降伏比YR(YS/TS)を算出した。 (5) Measurement method of tensile test JIS No. 13B tensile test specimen was sampled so that the direction perpendicular to the rolling direction of the plated steel sheet and the longitudinal direction of the specimen were parallel, and the tensile strength in the C direction (TS according to JIS Z2241) ), Yield stress (YS), and elongation (EL). Yield ratio YR (YS / TS) was calculated from TS and YS.
めっき鋼板の圧延方向に垂直な方向と試験片の長手方向が平行になるようにめっき鋼板から切り出した20mm×70mmの試験片を用意し、曲げ稜線が長手方向となるように90°V曲げ試験を行った。曲げ半径Rを適宜変化させて試験を実施し、試験片に割れが発生することなく曲げ加工できる最小曲げ半径Rminを求めた。 (6) Bending test A test piece of 20 mm × 70 mm cut out from the plated steel sheet is prepared so that the direction perpendicular to the rolling direction of the plated steel sheet and the longitudinal direction of the test specimen are parallel, and the bending ridge line is in the longitudinal direction. A 90 ° V bending test was conducted. The test was carried out by appropriately changing the bending radius R, and the minimum bending radius Rmin that could be bent without cracking the test piece was determined.
TSが980MPa以上、1080MPa未満の場合、Rmin/t<2.0を合格
TSが1080MPa以上、1180MPa未満の場合、Rmin/t<3.0を合格
TSが1180MPa以上の場合、Rmin/t<3.7を合格 The bendability was evaluated for each tensile strength TS based on Rmin / t obtained by dividing Rmin by the plate thickness t of the base steel sheet. Details are as follows. In addition, the evaluation of bendability was not performed for TS not satisfying the acceptable standard of 980 MPa or more (indicated as “−” in Table 3).
When TS is 980 MPa or more and less than 1080 MPa, Rmin / t <2.0 is satisfied, and when TS is 1080 MPa or more and less than 1180 MPa, Rmin / t <3.0 is satisfied, and when TS is 1180 MPa or more, Rmin / t <3 .7 passed
めっき鋼板の板幅W方向に対して垂直な断面であるW/4部を露出させ、150mm(W)×30mm(L)の試験片を切り出し、最小曲げ半径にてU曲げ加工を行った後、ボルトで締め付け、U曲げ加工試験片の外側表面に1000MPaの引張応力を負荷した。引張応力の測定は、U曲げ加工試験片の外側に歪ゲージを貼り付け、歪を引張応力に換算して行った。その後、U曲げ加工試験片のエッジ部をマスキングし、電気化学的に水素をチャージさせた。水素チャージは、試験片を、0.1M-H2SO4(pH=3)と0.01M-KSCNの混合溶液中に浸漬し、室温且つ100μA/mm2の定電流の条件で行なった。 (7) Delayed fracture resistance test Exposing the W / 4 part, which is a cross section perpendicular to the plate width W direction of the plated steel sheet, cutting out a test piece of 150 mm (W) × 30 mm (L) to the minimum bending radius After the U-bending was performed, the bolt was tightened and a tensile stress of 1000 MPa was applied to the outer surface of the U-bending test piece. The tensile stress was measured by attaching a strain gauge on the outside of the U-bending test piece and converting the strain into tensile stress. Then, the edge part of the U bending process test piece was masked, and hydrogen was charged electrochemically. The hydrogen charging was performed by immersing the test piece in a mixed solution of 0.1M-H 2 SO 4 (pH = 3) and 0.01M-KSCN under the conditions of room temperature and a constant current of 100 μA / mm 2 .
日本鉄鋼連盟規格JFST1001に準じて穴拡げ試験を実施し、λを測定した。詳細には、めっき鋼板に直径10mmの穴を打ち抜いた後、周囲を拘束した状態で60°円錐のポンチを穴に押し込み、亀裂発生限界における穴の直径を測定した。下記式から限界穴拡げ率λ(%)を求めた。
限界穴拡げ率λ(%)={(Df-D0)/D0}×100
式中、Dfは亀裂発生限界における穴の直径(mm)、D0は初期穴の直径(mm) (8) Hole expansion test A hole expansion test was performed in accordance with Japan Iron and Steel Federation standard JFST1001, and λ was measured. Specifically, after punching a hole with a diameter of 10 mm in a plated steel sheet, a punch having a 60 ° cone was pushed into the hole in a state where the periphery was constrained, and the hole diameter at the crack initiation limit was measured. The critical hole expansion ratio λ (%) was obtained from the following formula.
Limit hole expansion rate λ (%) = {(Df−D0) / D0} × 100
Where Df is the diameter of the hole at the crack initiation limit (mm), D0 is the diameter of the initial hole (mm)
めっき鋼板の外観を目視で観察し、不めっきの発生の有無に基づいてめっき性を評価した。 (9) Plating appearance The appearance of the plated steel sheet was visually observed, and the plating property was evaluated based on whether or not non-plating occurred.
2 素地鋼板
3 内部酸化層
4 軟質層
5 硬質層 DESCRIPTION OF
Claims (6)
- 素地鋼板の表面に、溶融亜鉛めっき層または合金化溶融亜鉛めっき層を有するめっき鋼板であって、
(1)前記素地鋼板は、質量%で、
C :0.08~0.30%、
Si:0.25~3%、
Mn:1.5~4%、
P :0%超0.1%以下、
S :0%超0.05%以下、
Al:0.005~1%、および
N :0%超0.01%以下を含有し、
残部が鉄および不可避不純物からなり、
(2)前記素地鋼板と前記めっき層との界面から素地鋼板側に向って順に、
SiおよびMnよりなる群から選択される少なくとも一種の酸化物を含む内部酸化層と、
前記内部酸化層を含む層であって、且つ、前記素地鋼板の板厚をtとしたとき、ビッカース硬さが、前記素地鋼板のt/4部におけるビッカース硬さの90%以下を満足する軟質層と、
マルテンサイトおよびベイナイト:20面積%以上60面積%未満と、ポリゴナルフェライト:40面積%超80面積%以下と、を含む硬質層と、
を有し、且つ、
前記軟質層の平均深さDが20μm以上、および
前記内部酸化層の平均深さdが4μm以上、前記D未満
を満足し、引張強度が980MPa以上である高強度めっき鋼板。 A plated steel sheet having a hot-dip galvanized layer or an alloyed hot-dip galvanized layer on the surface of the base steel sheet,
(1) The base steel sheet is mass%,
C: 0.08 to 0.30%,
Si: 0.25 to 3%,
Mn: 1.5 to 4%
P: more than 0% and 0.1% or less,
S: more than 0% and 0.05% or less,
Al: 0.005 to 1%, and N: more than 0% and 0.01% or less,
The balance consists of iron and inevitable impurities,
(2) In order from the interface between the base steel plate and the plating layer toward the base steel plate side,
An internal oxide layer comprising at least one oxide selected from the group consisting of Si and Mn;
A soft layer satisfying 90% or less of the Vickers hardness at t / 4 part of the base steel sheet when the thickness of the base steel sheet is t, the layer including the internal oxide layer. Layers,
A hard layer containing martensite and bainite: 20 area% or more and less than 60 area%, and polygonal ferrite: more than 40 area% and 80 area% or less,
And
A high-strength plated steel sheet in which the average depth D of the soft layer is 20 μm or more, and the average depth d of the internal oxide layer is 4 μm or more, less than D, and the tensile strength is 980 MPa or more. - 前記素地鋼板は、更に、質量%で、以下の(a)~(c)の少なくとも1つを含有する請求項1に記載の高強度めっき鋼板。
(a)Cr:0%超1%以下、Mo:0%超1%以下、およびB:0%超0.01%以下よりなる群から選択される少なくとも一種
(b)Ti:0%超0.2%以下、Nb:0%超0.2%以下、およびV:0%超0.2%以下よりなる群から選択される少なくとも一種
(c)Cu:0%超1%以下、およびNi:0%超1%以下よりなる群から選択される少なくとも一種 The high-strength plated steel sheet according to claim 1, wherein the base steel sheet further contains at least one of the following (a) to (c) by mass%.
(A) At least one selected from the group consisting of Cr: more than 0% and 1% or less, Mo: more than 0% and 1% and B: more than 0% and 0.01% or less (b) Ti: more than 0% and 0 .2% or less, Nb: more than 0% and 0.2% or less, and V: at least one selected from the group consisting of more than 0% and 0.2% or less (c) Cu: more than 0% and 1% or less, and Ni : At least one selected from the group consisting of more than 0% and 1% or less - 前記内部酸化層の平均深さdと前記軟質層の平均深さDは、D>2dの関係を満足する請求項1に記載の高強度めっき鋼板。 The high-strength plated steel sheet according to claim 1, wherein an average depth d of the internal oxide layer and an average depth D of the soft layer satisfy a relationship of D> 2d.
- 前記内部酸化層の平均深さdと前記軟質層の平均深さDは、D>2dの関係を満足する請求項2に記載の高強度めっき鋼板。 The high-strength plated steel sheet according to claim 2, wherein the average depth d of the internal oxide layer and the average depth D of the soft layer satisfy a relationship of D> 2d.
- 請求項1~4のいずれかに記載の高強度めっき鋼板を製造する方法であって、
前記素地鋼板の鋼中成分を満足する鋼板を、600℃以上の温度で巻取る熱延工程と、
内部酸化層の平均深さdが4μm以上残るように酸洗・冷間圧延する工程と、
酸化帯にて、0.9~1.4の空気比で酸化する工程と、
還元帯にて、(Ac1点+30℃)~Ac3点の範囲で保持して均熱する工程と、
均熱後、冷却停止温度までの範囲を5℃/秒以上の平均冷却速度で冷却する工程と、を、この順序で含む高強度めっき鋼板の製造方法。 A method for producing the high-strength plated steel sheet according to any one of claims 1 to 4,
A hot rolling step of winding a steel plate satisfying the steel components of the base steel plate at a temperature of 600 ° C. or higher;
Pickling and cold rolling so that the average depth d of the internal oxide layer remains 4 μm or more;
Oxidizing in an oxidation zone at an air ratio of 0.9 to 1.4;
In the reduction zone, holding in the range of (Ac 1 point + 30 ° C.) to Ac 3 point and soaking,
A method for producing a high-strength plated steel sheet comprising, in this order, a step of cooling the range up to the cooling stop temperature after soaking at an average cooling rate of 5 ° C./second or more. - 請求項1~4のいずれかに記載の高強度めっき鋼板を製造する方法であって、
前記素地鋼板の鋼中成分を満足する鋼板を、500℃以上の温度で巻取る熱延工程と、
500℃以上の温度で80分以上保温する工程と、
内部酸化層の平均深さdが4μm以上残るように酸洗・冷間圧延する工程と、
酸化帯にて、0.9~1.4の空気比で酸化する工程と、
還元帯にて、(Ac1点+30℃)~Ac3点の範囲で保持して均熱する工程と、
均熱後、冷却停止温度までの範囲を5℃/秒以上の平均冷却速度で冷却する工程と、
を、この順序で含む高強度めっき鋼板の製造方法。 A method for producing the high-strength plated steel sheet according to any one of claims 1 to 4,
A hot rolling step of winding a steel plate satisfying the steel components of the base steel plate at a temperature of 500 ° C. or higher;
Maintaining the temperature at 500 ° C. or higher for 80 minutes or more;
Pickling and cold rolling so that the average depth d of the internal oxide layer remains 4 μm or more;
Oxidizing in an oxidation zone at an air ratio of 0.9 to 1.4;
In the reduction zone, holding in the range of (Ac 1 point + 30 ° C.) to Ac 3 point and soaking,
After soaking, cooling the range up to the cooling stop temperature at an average cooling rate of 5 ° C./second or more;
A method for producing a high-strength galvanized steel sheet.
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