Specification
Title of invention: Al-plated welded tube for quenching, Al-plated hollow member, and method for manufacturing the same
Technical field
[0001]
　TECHNICAL FIELD The present invention relates to an Al-plated welded tube for quenching, a method for manufacturing a hot-pressed Al-plated hollow member, and an Al-plated hollow member.
Background technology
[0002]
　In recent years, there has been an increasing demand for reducing the consumption of fossil fuels in order to protect the environment and suppress global warming, and this demand has affected various manufacturing industries. For example, automobiles, which are indispensable for daily life and activities as means of transportation, are no exception, and there is a demand for improvement in fuel consumption by reducing the weight of the vehicle body. However, in automobiles, it is necessary not only to simply reduce the weight of the vehicle body but also to secure required strength and appropriate safety.
[0003]
　Much of the structure of automobiles is made of steel, and reducing the mass of this steel is important for weight reduction of the vehicle body. In particular, since the steel pipe has a closed structure and high rigidity can be obtained, it has been increasingly used in recent years as a structural member for automobiles. As a method of processing a steel pipe into a member, a cold bending method or a hydroforming method has been conventionally used, but in recent years, after hot three-dimensional bending, immediately after water cooling, high strength is obtained. A method for processing the hollow member has been proposed.
[0004]
　In this hot bending method, the material to be molded is once heated to a high temperature (austenite region), the steel pipe softened by heating is bent and molded, and then cooled. According to this hot bending method, since the material is once heated to a high temperature to be softened, the material can be easily bent, and further, the mechanical strength of the material is improved by the quenching effect by cooling after forming. Can be increased. As a result, a molded product having both a complicated shape and high mechanical strength can be obtained.
[0005]
　When the hot bending method is applied to a steel pipe, by heating at a high temperature of 800° C. or higher, iron on the surface is oxidized and scales (oxides) are generated. Therefore, a step of removing the scale (descaling step) is required after performing the hot pressing, and the productivity is reduced. Further, in the case of a member requiring corrosion resistance, it is necessary to perform rust prevention treatment or metal coating on the surface of the member after processing, which requires a surface cleaning step and a surface treatment step, which also reduces productivity. In particular, in the case of a steel pipe shape, it is difficult to descale the inner surface side.
[0006]
　An example of a method for suppressing such a decrease in productivity is a method of coating steel. When a welded steel pipe is used, it is manufactured by forming a plated steel sheet and seam welding, so that the productivity of the plated steel sheet is affected. For example, a zinc-based plating coating having a sacrificial anticorrosion action is widely used from the viewpoint of its anticorrosion performance and steel plate production technology.
[0007]
　However, the heating temperature in hot working (800 to 1000° C.) is higher than the decomposition temperature of the organic material, the boiling point of Zn, etc., and when heated in hot working, the plating layer on the surface evaporates and the surface properties are May cause a significant deterioration of. Therefore, for a steel sheet that is hot-pressed to be heated to a high temperature, for example, a decomposition reaction unlike an organic material coating does not occur, and an Al-based metal having a higher boiling point than a Zn-based metal coating is used. It is desirable to use a steel sheet coated with (so-called Al-plated steel sheet).
[0008]
　By applying the Al-based metal coating, it is possible to prevent the scale from adhering to the steel surface, and as a result, the steps such as the descaling step are unnecessary, so that the productivity is improved. Further, since the Al-based metal coating also has a rust preventive effect, the corrosion resistance after coating is also improved.
[0009]
　Patent Document 1 describes a method in which an Al-plated steel sheet obtained by applying an Al-based metal coating to a steel having a predetermined steel component is used for hot press working.
[0010]
　Patent Document 2 discloses a technique for suppressing the generation of scale inside the plating layer in a hot-pressing steel sheet.
[0011]
　Patent Document 3 discloses a method of obtaining a high-strength member by forming an Al-plated steel sheet into a steel tube, heating and shaping a steel tube having a welded seam portion and quenching.
[0012]
　Patent Document 4 discloses a heat-treated steel material obtained by heat-treating a steel material coated with an Al-based plating layer. In the examples, an example is disclosed in which an Al-plated steel sheet is UO-formed into a steel pipe having an outer diameter of 31.8 mm and a wall thickness of 1.2 mm, and is bent.
Prior art documents
Patent literature
[0013]
Patent Document 1: Japanese Patent Laid-Open No. 2000-38640
Patent Document 2: Japanese Patent Laid-Open No. 2014-118628
Patent Document 3: Japanese Patent Laid-Open No. 2006-16674
Patent Document 4: Japanese Patent Laid-Open No. 2008-69398
Summary of the invention
Problems to be Solved by the Invention
[0014]
　As described above, as a structural member for automobiles, an Al-plated steel plate is used as a steel pipe and processed and used. Therefore, it is required to use an electric resistance welded steel pipe having high productivity. Further, from the viewpoint of the strength of the structural member, it is required to use a steel pipe having a large plate thickness. That is, when the plate thickness is t and the outer diameter of the steel pipe is D, it becomes necessary to process a steel pipe having a large t/D.
[0015]
　As an issue to be taken into consideration when forming an Al-plated steel plate into an electric resistance welded steel pipe and then performing hot working and quenching treatment, crack generation in the alloy layer during electric resistance welded steel pipe molding and the inside of the plating layer due to the crack And the generation of iron oxides (scales).
[0016]
　The cracks are generated in the Al—Fe—Si alloy layer at the interface between the strained steel plate and the Al plating layer when the Al plating steel plate is formed into a steel tube. Since the Al—Fe—Si alloy layer is extremely hard and brittle, when the steel sheet is formed into a steel pipe shape, the alloy layer is partially broken and cracks occur. Then, starting from the generated cracks, the oxygen in the atmosphere cannot be completely blocked by the plating layer during heating, and the steel sheet is oxidized, so that iron oxide (scale) is generated inside the plating layer.
[0017]
　In Patent Document 2, the alloy layer thickness and the plating layer thickness are specified in order to suppress the generation of iron oxide (scale). Patent Document 2 focuses on cracks in an Al-plated steel sheet for hot stamping, and discloses a technique for reducing cracks in the intermetallic compound layer in the C direction (direction perpendicular to the rolling direction).
[0018]
　However, in the case of an electric resistance welded steel pipe, its forming strain generally tends to be larger than that of a steel plate or a UO formed steel pipe. This is because, for example, bending back may be performed during pipe manufacturing, and there is a step of applying a compressive strain in the circumferential direction in the subsequent fin pass and squeeze steps. In addition, since the main strain in the process of forming the steel pipe is in the C direction, cracks propagate in the L direction (rolling direction). When t/D is large, the strain is further increased and cracks are likely to occur. That is, the problem that scales are generated at the time of heating from this crack as a starting point is more likely to occur as compared with thermal processing of a steel plate or UO steel pipe.
[0019]
　Furthermore, when performing electric resistance welding of an Al-plated steel sheet, the present inventors have found that, since the melting point of Al is low, electric resistance welding is more difficult than other steel sheets due to the influence of molten Al, and good electric resistance welding is possible. It was found that the weld can be the starting point of scale generation when the weld is not removed.
[0020]
　That is, when an Al-plated steel sheet is electric resistance welded and hot-worked to manufacture a structural member, it is necessary to take specific measures in consideration of these.
[0021]
　The present invention has been made in view of the above problems, and for an electric resistance welded steel pipe obtained by forming an Al-plated steel sheet, while suppressing generation of scale inside the plating layer due to quenching treatment, hot working Provided are an Al-plated electric resistance welded pipe for quenching which can be subjected to press working, a method for producing a hot-worked Al-plated hollow member using the Al plated electric resistance welded pipe for quenching, and an Al-plated hollow member. The task is to do.
Means for solving the problem
[0022]
　As a result of intensive studies, the present inventors have found that, in addition to the thickness of the alloy layer and the thickness of the plating layer, the plate thickness and the outer diameter of the steel pipe play an important role in suppressing the generation of scale. In addition, it was found that the relationship between the thickness of the plating layer and the plate thickness is important for performing good electric resistance welding and suppressing the generation of scale.
[0023]
　The present invention has been completed based on the above findings, and its gist is as follows.
[0024]
　[1] An electric resistance welded pipe including a base material part made of a tubular steel plate and an electric resistance welded part provided at a butt part of the steel plate and extending in a longitudinal direction of the steel plate, wherein the base material part Is% by mass, C: 0.06 to 0.50%, Si: 0.01 to 0.80%, Mn: 0.60 to 3.00%, P: 0.050% or less, S:0 0.050% or less, Al: 0.10% or less, O: 0.006% or less, N: 0.020% or less, Ti: 0.01 to 0.10%, B: 0 to 0.1000%, Nb. : 0 to 0.10%, V: 0 to 0.30%, Cr: 0 to 0.50%, Mo: 0 to 0.50%, Ni: 0 to 0.50%, Cu: 0 to 0. 50%, Ca: 0. To 0.005% and REM: 0 to 0.005%, with the balance being Fe and impurities, the base metal portion is located on the surface of the steel sheet, and is an Al--Fe--Si based intermetallic material. An intermetallic compound layer containing a compound and an Al plating layer located on the surface of the intermetallic compound layer and containing Al and Si are further provided, and the thickness of the intermetallic compound layer is X (μm), and the Al plating is performed. When the layer thickness is Y (μm), the tube thickness of the steel pipe is t (mm), and the outer diameter of the steel pipe is D (mm), 70×X/D≦Y/t≦30 is satisfied. An Al-plated electric resistance welded pipe for quenching, which is characterized in that
[0025]
　[2] The Al-plated electric resistance welded tube for quenching according to [1] above, wherein X≦5.0 μm, Y≦32 μm, and 4.0≦Y/X≦6.0 are satisfied.
[0026]
　[3] A film containing ZnO as a main component is further provided on the surface of the Al plating layer, and the adhesion amount of the film is 0.1 to 1 g/m 2 in terms of Zn amount. ] Or [2] Al-plated electric resistance welded pipe for quenching.
[0027]
　[4] The Al-plated electric resistance welded pipe for quenching according to any one of [1] to [3], wherein the welded portion is covered with an alloy containing Al as a main component.
[0028]
　[5] The Al-plated electric resistance welded pipe for quenching according to [1] to [4], which satisfies 2%≦t/D≦10%.
[0029]
　[6] A base material portion made of a tubular steel plate, and an electric resistance welded portion provided at a butt portion of the steel sheet and extending in the longitudinal direction of the steel sheet. : 0.06 to 0.50%, Si: 0.01 to 0.80%, Mn: 0.60 to 3.00%, P: 0.050% or less, S: 0.050% or less, Al: 0.10% or less, O: 0.006% or less, N: 0.020% or less, Ti: 0.01 to 0.10%, B: 0 to 0.1000%, Nb: 0 to 0.10% , V: 0 to 0.30%, Cr: 0 to 0.50%, Mo: 0 to 0.50%, Ni: 0 to 0.50%, Cu: 0 to 0.50%, Ca: 0. To 0.005% and REM: 0 to 0.005%, with the balance being Fe and impurities, an electric resistance welded pipe, and an Al—Fe based alloy located on the surface of the electric resistance welded pipe, And an alloy layer containing at least one of Al—Fe—Si alloys, the generation rate of Fe oxide in the alloy layer is 5% or less, and the Vickers hardness Hv of the steel base of the electric resistance welded pipe is Hv. Is an Al-plated hollow member.
[0030]
　[7] The Al-plated hollow member according to the above [6], wherein unalloyed Al does not remain in the alloy layer.
[0031]
　[8] A film containing ZnO as a main component is further provided on the surface of the alloy layer, and the amount of the film adhered is 0.1 to 1 g/m 2 in terms of Zn amount. ] Or [7] Al plated hollow member.
[0032]
　[9] A base material part made of a tubular steel plate, and an electric resistance welded part provided in a butting part of the steel plate and extending in the longitudinal direction of the steel plate, wherein the base material part is C by mass% : 0.06 to 0.50%, Si: 0.01 to 0.80%, Mn: 0.60 to 3.00%, P: 0.050% or less, S: 0.050% or less, Al: 0.10% or less, O: 0.006% or less, N: 0.020% or less, Ti: 0.01 to 0.10%, B: 0 to 0.1000%, Nb: 0 to 0.10% , V:0 to 0.30%, Cr:0 to 0.50%, Mo:0 to 0.50%, Ni:0 to 0.50%, Cu:0 to 0.50%, Ca:0. To 0.005% and REM: 0 to 0.005%, the balance being Fe and impurities, the base metal part is located on the surface of the steel sheet, and is an Al--Fe--Si based intermetallic material. A heating temperature of 850° C. or higher for an Al-plated electric resistance welded tube for quenching, which further comprises an intermetallic compound layer containing a compound and an Al plated layer containing Al and Si, which is located on the surface of the intermetallic compound layer. The heating step of heating with a heating step, the forming step of forming the heated Al-plated electric resistance welded tube for quenching into a desired shape, and the Al-plated electric resistance welded welding tube for hardening with a desired shape are averaged. A quenching step of quenching at a cooling rate of 20° C./second or more, the thickness of the intermetallic compound layer is X (μm), the thickness of the Al plating layer is Y (μm), and the pipe thickness of the steel pipe is t( mm), the outer diameter of the steel pipe is D (mm), and the average heating rate from room temperature to the reached temperature of -50°C set during hot working is HR (°C/sec), A method for manufacturing an Al-plated hollow member, characterized in that the relationships represented by formulas (1) and (2) are satisfied.
[0033]
　　Y/X≧α×t/D (1)
　　α=168×HR −0.45　(2)
Effect of the invention
[0034]
　According to the present invention, a steel pipe obtained by forming an Al-plated steel sheet can be hot-pressed while quenching the steel pipe while suppressing generation of scale inside the plating layer. Therefore, it becomes possible to manufacture an Al-plated hollow member using an Al-plated steel pipe as a base material.
Brief description of the drawings
[0035]
FIG. 1 is a cross-sectional photograph of a scale in an alloy layer of an Al-plated hollow member that has been hot pressed.
[FIG. 2] A cross-sectional photograph of an Al-plated layer of an Al-plated steel pipe which is a material before heating.
MODE FOR CARRYING OUT THE INVENTION
[0036]
　Hereinafter, preferred embodiments of the present invention will be described in detail.
[0037]
　Prior to explaining an Al-plated electric resistance welded tube for quenching, an Al-plated hollow member manufacturing method, and a hot-pressed Al-plated hollow member according to an embodiment of the present invention, first, the inventors of the present invention described above. The contents of the study conducted to solve the problem will be explained.
[0038]
　The cracks when forming an electric resistance welded steel pipe depend on the strain at the time of forming. The strain at the time of molding can be almost arranged by paying attention to the parameter t/D representing the strain amount when the plate thickness is tmm and the outer diameter of the pipe is Dmm. When considering reducing the amount of cracks in the alloy layer when it receives this strain amount, even if cracks occur in the alloy layer, if the Al plating layer existing above the alloy layer is sufficiently thick, heating The crack is repaired in the process.
[0039]
　As a result of the study, the inventors of the present invention have taken a parameter Y/X representing the thickness ratio of each layer, where the Al plating layer thickness is Y (μm) and the alloy layer thickness (intermetallic compound layer thickness) is X (μm). The larger the value, the greater the resistance to scale generation due to cracks. Therefore, it has been found that the above problem can be solved by focusing on the relationship between the two parameters (t/D) and (Y/X).
[0040]
　Further, since the Al-plated steel sheet has a low melting point of Al, it is more difficult to perform electric resistance welding than other steel sheets due to the influence of molten Al. We have found that it is necessary to make the range appropriate.
[0041]
　Further, as a result of the study, the present inventors have found that the rate of temperature rise of the steel pipe during hot pressing also has a great influence on the scale generation, and the average temperature rise from room temperature to the reached temperature of −50° C. When the velocity is HR (° C./second), it is important to make the product of α and (t/D), which is a function of HR, larger than (Y/X). By satisfying this relationship, even if the Al-plated steel pipe is heated up to about 900° C., it becomes possible to suppress the scale generation inside the plating layer. The embodiment of the present invention has been completed based on the above findings.
[0042]
　The reason why the heating rate affects the scale inside the plating layer is considered as follows.
[0043]
　Due to the heating during the hot press working, the Al plating component and the steel pipe component mutually diffuse, and the alloy layer grows. When a crack occurs in the alloy layer, the growth of the alloy layer acts to repair the crack. However, when the generated crack is too large, the crack cannot be repaired. As a result, when the crack reaches the Al plating surface, the steel pipe is oxidized by oxygen in the atmosphere.
[0044]
　When the Al-plated steel pipe is rapidly heated, the Al-plated layer becomes a liquid phase at about 600° C., and the liquid phase enters the inside of the crack to accelerate the repair of the crack. Rapid heating is a treatment that facilitates the production of liquid phase Al, and it can be understood that rapid heating enhances the crack repairing action of liquid phase Al.
[0045]
　A value obtained by dividing (Y/X) by (t/D) is referred to as α in the following embodiment, and α=168×HR −0.68 is defined. This definition formula is calculated from an experiment by the present inventors.
[0046]
　Hereinafter, the Al-plated welded tube for quenching, the method for manufacturing the hot-pressed Al-plated hollow member, and the hot-pressed Al-plated hollow member according to the present embodiment will be described in detail. Hereinafter, “%” means “mass %”.
[0047]
　 The Al-plated welded tube for quenching according to the present embodiment is formed by forming an Al-plated steel sheet into an open pipe shape and forming a butt portion into a steel pipe shape by seam welding. As seam welding, electric resistance welding is preferable.
[0048]
　The Al-plated steel sheet used in this embodiment has an Al-plated layer containing Al formed on one side or both sides of the steel sheet. Further, a surface coating layer containing at least ZnO may be further laminated on the Al plating layer.
[0049]
　[About
　Steel Sheet ] As a steel sheet used for an Al-plated steel sheet, high mechanical strength (for example, tensile strength, yield point, elongation, drawing, hardness, impact value, fatigue strength, creep strength after hot press working is used. It is preferable to use a steel sheet designed to have mechanical deformation and fracture properties such as).
[0050]
　An example of the components of the steel sheet that achieves high mechanical strength that can be used in one embodiment of the present invention will be described below.
[0051]
　[C: 0.06 to 0.50%]
　C is an element to be contained in order to secure the desired mechanical strength. When the content of C is less than 0.06%, sufficient improvement in mechanical strength cannot be obtained, and the effect of containing C becomes poor. Further, the hardness cannot be set to Hv350 or higher by the quenching treatment after hot bending. If the C content exceeds 0.50%, the steel sheet can be further hardened, but melt cracking tends to occur. Therefore, the content of C is preferably 0.06% or more and 0.50% or less by mass %.
[0052]
　[Si: 0.01 to 0.80%]
　Si is an element used for deoxidation and is one of the strength improving elements for improving mechanical strength. Included in order to secure the mechanical strength. When the content of Si is less than 0.01%, deoxidation may not be sufficiently performed, the strength improving effect may not be easily exhibited, and sufficient mechanical strength may not be improved. On the other hand, Si is also an easily oxidizable element. Therefore, if the Si content exceeds 0.80%, the wettability may decrease during hot-dip Al plating, and non-plating may occur. Therefore, the Si content is preferably 0.01% or more and 0.80% or less in mass %.
[0053]
　[Mn: 0.60 to 3.00%]
　Mn is one of the strengthening elements for strengthening steel and one of the elements for improving hardenability. Further, Mn is an element effective for preventing hot embrittlement due to S which is one of impurities. When the Mn content is less than 0.60%, these effects cannot be obtained, and the above effects are exhibited at 0.60% or more. On the other hand, when the content of Mn exceeds 3.00%, the residual γ phase becomes too much and the strength may decrease. Therefore, the Mn content is preferably from 0.60% to 3.00% in mass %.
[0054]
　[P: 0.050% or less]
　P is an impurity and segregates at grain boundaries to embrittle the component. Therefore, the P content is preferably as small as possible and 0.050% or less. It is difficult to completely set the content to 0, and the practical lower limit is 0.001%.
[0055]
　[S: 0.050% or less]
　S is an impurity element that forms nonmetallic inclusions such as MnS. Since the non-metallic inclusions become the starting point of crack generation during cold working, the S content is preferably as small as possible, and is preferably 0.050% or less. The lower the S content, the better. However, if the S content is reduced to less than 0.001%, the refining cost increases significantly. Therefore, considering the refining cost, the S content may be 0.001% or more.
[0056]
　[Al: 0.10% or less]
　Al is an element used as a deoxidizing agent. Although it is not necessary to be contained in the deoxidized steel, 0.0003% or more of Al usually remains and is contained in the steel. When the content of Al exceeds 0.10%, a large amount of inclusions are generated and the workability is deteriorated, so 0.10% or less is preferable.
[0057]
　[O: 0.006% or less] When
　O is contained in a large amount, it forms a coarse oxide in the steel. The lower the O content, the better. However, if the O content is reduced to less than 0.001%, the refining cost increases significantly.
[0058]
　[N: 0.020% or less]
　N is an impurity and an element effective for improving strength. Since setting the N content to 0.001% requires a great deal of cost, it may be set to 0.001% or more. If the content of N increases, the ductility and toughness deteriorate, so the content is made 0.020% or less.
[0059]
　[Ti: 0.01 to 0.10%]
　Ti has the effects of improving the strength of steel, suppressing the surface defects of Al plating, and suppressing the deterioration of oxidation resistance when surface defects occur. In order to obtain this effect, the Ti content is 0.01% or more. If the content exceeds 0.10%, coarse Ti nitride is generated and the formability deteriorates, so the content is made 0.10% or less.
[0060]
　[B: 0.1000% or less]
　B is an element that acts at the time of quenching and has an effect of improving strength, and can be contained if necessary. In order to effectively obtain the strength improving effect, the B content is preferably 0.0003% or more. On the other hand, when the content of B exceeds 0.1000%, inclusions may be formed and embrittlement may occur, resulting in reduced fatigue strength. Therefore, the content should be 0.1000% or less and 0.0060% or less. Is desirable.
[0061]
　[Nb:0 to 0.10%]
　Nb raises the recrystallization temperature or forms carbonitrides to make the steel fine grain. In order to exert these effects, it is preferable to contain 0.01% or more. If the content exceeds 0.10%, the precipitation effect may impair the low temperature toughness, so the content is made 0.10% or less.
[0062]
　[V:0 to 0.30%]
　V is an element that forms a carbonitride and improves the strength, and can be contained if necessary. In order to effectively obtain the effect of improving strength, it is preferable to contain 0.01% or more. If the content exceeds 0.30%, the workability of the steel sheet deteriorates, so it is made 0.30% or less.
[0063]
　[Cr: 0 to 0.50%]
　Cr is an element having an effect on hardenability similar to Mn, and can be contained if necessary. In order to effectively obtain the effect of improving the hardenability, it is preferable to contain Cr in an amount of 0.01% or more. If the Cr content exceeds 0.50%, the carbide is stabilized during rapid heating, the dissolution of the carbide is delayed during quenching, and the required quenching strength may not be achieved, so the content is made 0.50% or less.
[0064]
　[Mo: 0 to 0.50%]
　Mo is an element that improves hardenability, and can be contained if necessary. In order to effectively obtain the effect of improving hardenability, it is preferable to contain 0.01% or more. If the content exceeds 0.50%, the heat resistance of the Al plating decreases, and it is set to 0.50% or less.
[0065]
　[Ni:0 to 0.50%]
　Ni is an element effective in improving the toughness, and can be contained if necessary. In order to effectively obtain the effect of addition, Ni is preferably 0.001% or more. If the Ni content exceeds 0.50%, the workability decreases, so Ni is made 0.50% or less.
[0066]
　[Cu: 0 to 0.50%]
　Cu is an element that improves the hardenability and contributes to the improvement of the strength, and can be contained if necessary. In order to effectively obtain the effect of addition, Cu is preferably 0.001% or more. If the Cu content exceeds 0.50%, defects may occur during hot rolling, so Cu is preferably 0.50% or less.
[0067]
　[Ca: 0. ~0.005%]
　Ca is an element capable of controlling the form of sulfide by addition in a trace amount, and can be contained if necessary. In order to effectively obtain the effect of addition, Ca is preferably 0.001% or more. When the content of Ca exceeds 0.005%, coarse Ca oxide is generated and becomes a starting point of crack generation during processing, so Ca is set to 0.005% or less.
[0068]
　[REM: 0 to 0.005%]
　REM is an element effective in improving moldability, and can be contained if necessary. In order to effectively obtain the effect of addition, the REM content is preferably 0.001% or more. If the content of REM is large, the ductility may be impaired, so the content is made 0.005% or less.
[0069]
　When forming an Al-plated steel sheet into a steel pipe, bending and welding are necessary, and the end of the bent Al-plated steel sheet may be removed to facilitate electric resistance welding. Furthermore, the weld beads generated by electric resistance welding are deleted. Therefore, there is no Al plating layer in the seam weld. Therefore, in order to prevent oxidation and decarburization from the welded portion and to avoid the possibility that the welded pipe is corroded during use, Al or the like may be sprayed. By applying a metal spray containing Al or the like, it becomes possible to suppress oxidation and decarburization from the welded portion to some extent.
[0070]
　P, N, and Al affect the adhesion between the sprayed metal and the weld bead. When spraying Al or the like, it is preferable that the contents of P, N, and Al in the steel sheet be lower than those described above, and P: 0.01% or less and N: 0.006% or less, respectively. Al: Particularly preferably 0.08% or less. When a steel sheet containing P, N, or Al in the above-mentioned content or more is used, the adhesion of the repaired sprayed part is deteriorated, and the sprayed part is peeled off due to a temperature rise during hot pressing in the subsequent process. It may happen.
[0071]
　The balance of the steel sheet is Fe and inevitable impurities. The unavoidable impurities are components contained in the raw materials or mixed in the manufacturing process, and are components not intentionally contained in the steel. Specific examples include P, S, O, N, Sb, Sn, W, Co, As, Mg, Pb, Bi, and H.
[0072]
　It is necessary to control the content of P, S, O and N within the above range. As for other elements, Sb, Sn, W, Co, and As are usually inevitable impurities of 0.1% or less, Mg, Pb and Bi of 0.005% or less, and H of 0.0005% or less. Mixing may occur, but within the normal range, no particular control is required.
[0073]
　A steel sheet formed with such a component is Al-plated, formed into a steel pipe shape, and then heated and processed by a hot pressing method or a hot bending method (hereinafter collectively referred to as “hot working”), and thereafter. , Heat removal by a press die, cooling with a medium such as water, steam, gas, etc. and quenching to obtain a mechanical strength of about 1500 MPa or more in tensile strength. Although the steel pipe has high mechanical strength as described above, if it is processed by the hot working method, it can be processed in a softened state by heating, so that it can be easily molded. Further, the steel pipe can realize high mechanical strength, and even if it is thinned for weight reduction, the mechanical strength can be maintained or improved.
[0074]
　[About Al Plating Layer] The
　Al plating layer is formed on one side or both sides of the steel sheet. The Al plating layer is formed on the surface of the steel sheet by, for example, the hot dipping method. The method for forming the Al plating layer according to the present embodiment is not limited to the hot dip plating method, and a known Al plating method such as an electroplating method can be used.
[0075]
　As a component of the Al plating layer, Al is preferably contained by 70% or more, more preferably 80% or more, and further Si is contained. That is, the Al plating layer according to this embodiment is a plating layer made of Al—Si.
[0076]
　When Si is contained in the Al plating layer, it is possible to control the alloy layer formed when the hot dip metal is coated. If the Si content is less than 3%, the Fe—Al alloy layer grows thick at the stage of Al plating, and cracks may occur during forming into a steel pipe, which may adversely affect corrosion resistance and the like. On the other hand, if the Si content exceeds 15%, the workability and corrosion resistance of the plated layer may be reduced. Therefore, the Si content is preferably 3% or more and 15% or less.
[0077]
　When the Al plating layer is formed by the hot dipping method, 2 to 4% of Fe eluted from the equipment or steel strip in the bath may be contained as an element other than Si. Further, in addition to such Fe, at least any one of Mg, Ca, Sr, and Li may be contained in the Al plating bath in an amount of about 0.01 to 1%.
[0078]
　[About Intermetallic Compound Layer] When the
　Al plating layer as described above is formed on the surface of the steel plate as described above, the components of the steel plate and the components of the Al plating layer interdiffuse between the steel plate and the Al plating layer. As a result, an intermetallic compound layer containing an intermetallic compound made of an Al—Fe—Si alloy is formed. The thickness of the intermetallic compound layer is determined depending on the bath temperature at the time of Al plating, the plate passing speed, the steel composition, etc., but is in the range of, for example, 3 μm to 8 μm.
[0079]
　The components of the intermetallic compound layer usually contain, by mass%, Al: 35 to 65% and Si: 3 to 15%, and the balance is Fe and impurities.
[0080]
　[Measuring Method of Thickness of Al Plating Layer and Intermetallic Compound Layer]
　The thicknesses of the Al plating layer and the intermetallic compound layer as described above can be measured by various known measuring methods. For example, it can be measured by observing the cross section of the Al-plated steel sheet before forming the steel pipe or the Al-plated welded pipe with an optical microscope or a scanning electron microscope.
[0081]
　Specifically, the cross section of the Al-plated steel plate or the Al-plated welded pipe is observed in a plurality of visual fields at an appropriate magnification, and the thicknesses of the Al-plated layer and the intermetallic compound layer in each visual field are measured. Then, the thickness of the Al plating layer and the intermetallic compound layer can be obtained by averaging the measured values ​​obtained between the measured visual fields.
[0082]
　[Regarding Surface Coating Layer] A
　surface coating layer may be further laminated on the surface of the Al plated steel sheet. The surface coating layer preferably contains at least ZnO. A surface coating layer can be formed by using a liquid prepared by suspending fine particles of ZnO in an aqueous solution and applying and drying the suspension with a roll coater or the like. The surface coating layer has an effect of improving lubricity in hot working and reactivity with a chemical conversion treatment liquid.
[0083]
　The surface coating layer may contain, for example, an organic binder component as a component other than ZnO. Examples of the organic binder include water-soluble resins such as polyurethane resins, polyester resins, acrylic resins, and silane coupling agents. Further, the surface coating layer may contain an oxide other than ZnO (for example, SiO 2 , TiO 2 , Al 2 O 3 or the like).
[0084]
　Examples of the method for forming the surface coating layer containing the binder component as described above include, for example, a method of mixing a ZnO-containing suspension with a predetermined organic binder and applying the mixture on the surface of the Al plating layer, or a powder. A coating method by painting and the like can be mentioned.
[0085]
　The amount of the ZnO-containing surface coating layer attached is preferably 0.1 to 1 g/m 2 in terms of Zn amount per one side of the steel sheet . When the ZnO content is 0.1 g/m 2 or more in terms of Zn content, the effect of improving coating film adhesion and the effect of improving lubrication can be effectively exhibited. On the other hand, when the content of ZnO exceeds 1 g/m 2 as Zn , the economical rationality is lacking because the film is applied more than necessary. In high-strength steel pipe parts used in automobiles, etc., the inner surface of the steel pipe parts is less likely to be exposed to the corrosive environment, so it is possible to apply a surface coating layer containing ZnO only to the outer surface of the steel pipe parts. Is.
[0086]
　The method for forming the surface coating layer is not limited to the above example, and various known methods can be used.
[0087]
　When an Al-plated steel sheet having a surface coating layer is formed into a steel pipe, the surface coating layer may be partially peeled or removed during the forming. In order to avoid this, the surface coating layer may be applied after forming the steel pipe. The surface coating layer after forming the steel pipe can be applied by a method of immersing the steel pipe in the suspension, or applying the suspension by spraying.
[0088]
　 In the
　present embodiment, an Al-plated steel plate is processed into an open pipe shape, and both ends are heated and pressed to perform electric resistance welding to produce a pipe, which is an Al-plated welded pipe. High frequency welding is often used as the electric resistance welding. Generally, it is preferable to remove the plating layer at the portion to be the weld bead portion by grinding in advance and then perform welding. Further, it is preferable to use cutting work or the like in order to flatten the weld bead portion after welding.
[0089]
　Further, since the weld bead portion is not coated with plating, surface oxidation during subsequent hot working, decarburization from the surface layer due to it, and corrosion during use may occur. To avoid this, a metal containing Al may be sprayed onto the weld bead portion to form a sprayed coating on the weld bead portion. Here, examples of the metal containing Al include pure Al, Al-Zn, Al-Si, and Al-Mg. Since Al is excellent in heat resistance, it is excellent in protection during hot working. At this time, the thickness of the sprayed coating is preferably, for example, 5 to 100 μm. Thermal spraying is performed on the outer surface of the steel pipe.
[0090]
　The diameter of the steel pipe is usually about 20 to 70 mm, but it is not particularly limited. Since the Al-plated hollow member of the present embodiment is obtained after hot working of the Al-plated welded pipe, it is difficult to obtain an accurate steel pipe diameter and plate thickness in the steel pipe state from the Al-plated hollow member. Therefore, in this embodiment, the state before hot working is defined.
[0091]
　[Regarding Relation between Thickness and Strain Amount of Al Plating Layer and Intermetallic Compound Layer]
　The Al plating layer formed of the above components can suppress oxidation of the steel base when the steel sheet is heated, Moreover, the corrosion resistance is also improved. Furthermore, as described above, the resistance to scale generation due to cracks can be improved by appropriately setting the two parameters (t/D) and (Y/X). Specifically, by satisfying 70×t/D≦Y/X (1), excellent resistance to scale generation due to cracks can be obtained. Here, X is an intermetallic compound layer (alloy layer) thickness (μm), Y is an Al plating layer thickness (μm), t is a plate thickness (mm), and D is a steel pipe outer diameter (mm). Further, the “Al plating layer” means a plating layer containing Al or Al and Si containing no alloy layer.
[0092]
　Further, as described above, (Y/t) needs to be in an appropriate range in order to perform good electric resistance welding. Specifically, by satisfying Y/t≦30 (2), good electric resistance welding can be performed. As a result, it is possible to suppress the generation of scale starting from the weld.
[0093]
　The above equations (1) and (2) can be summarized as 70×X/D≦Y/t≦30.
[0094]
　As described above, the larger Y/X, the greater the resistance to scale generation due to cracks. However, as described above, when the thickness Y of the Al plating layer increases, electric resistance welding becomes difficult. Considering this point, it is preferable that X≦5.0 (μm), Y≦32 (μm), and 4.0≦Y/X≦6.0.
[0095]
　The t/D of the Al-plated electric resistance welded tube for quenching of the present invention is not particularly limited. However, when t/D is large, the strain at the time of electric resistance welding becomes large, and the generation of scale during hot working is more likely to be a problem. %, t/D≧4% is particularly effective for the electric resistance welded pipe. Further, as described above, since the molding strain increases as t/D increases, t/D is preferably 10% or less.
[0096]
　
　Next, a case where an Al-plated steel pipe (Al-plated welded pipe) is processed by the hot working method will be described. The working method by hot working of the steel pipe described below is basically the same as that when hot working a steel sheet.
[0097]
　In the hot working method according to the present embodiment, first, the Al-plated steel pipe (Al-plated welded pipe) is heated to a high temperature to be softened. Subsequently, the softened plated steel sheet is formed by pressing or bending, and then the formed plated steel tube is rapidly cooled by heat removal from a press die or a cooling medium such as water, steam, or gas. By thus softening the steel sheet once, it is possible to easily perform press working and bending. Further, the Al-plated steel pipe having the above-mentioned components is quenched by being heated and cooled, and a high mechanical strength of about 1500 MPa or more in tensile strength is realized.
[0098]
　Here, in heating during hot working of the Al-plated steel pipe (Al-plated welded pipe) according to the present embodiment, a method of heating by passing the Al-plated steel pipe through a furnace maintained at a high temperature such as an electric furnace Can be used. In this case, since the surface emissivity of Al plating is relatively low, the temperature rising rate is often 4 to 5° C./second. On the other hand, for example, by applying a near infrared heating furnace, high frequency heating, or electric heating, rapid heating of 15° C./second or more can be achieved. Considering oxidation and decarburization of the sprayed portion, rapid heating is preferably performed.
[0099]
　The oxidation of the steel base is greatly affected by the thickness of the alloy layer and the thickness of the Al plating layer as an upper layer thereof, and also depends on the forming dimensions of the steel pipe and the heating rate during heating. Therefore, in the present embodiment, as described above, (Y/X) is set to be α times or more of (t/D). α is 168×HR −0.45 . HR is an average heating rate (°C/sec) from room temperature to (achieved temperature-50)°C, which is set during hot working. That is, the temperature rising rate is set so as to satisfy the following expressions (101) and (103).
[0100]
[Number 1]

[0101]
　If the Al-plated welded pipe satisfies the relations represented by the above formulas (101) and (103), the cracks generated in the intermetallic compound layer during the hot working performed in the subsequent stage are appropriately repaired, and the plating is performed. It is possible to hot work the Al-plated welded pipe while suppressing the generation of scale in the layer. On the other hand, when the Al-plated welded pipe does not satisfy the relationships represented by the above formulas (101) and (103), the cracks generated in the intermetallic compound layer during the hot working performed in the subsequent stage cannot be repaired. It may not catch up and may generate scale due to cracks.
[0102]
　When a steel pipe is hot-worked, since the object to be worked is a tubular body, heat is removed from one side unlike the plate material, and it is difficult to increase the cooling rate. Therefore, it is preferable to introduce gas (fluid having a small heat capacity) into the inside. Since it is difficult to spray the inner surface of the steel pipe, the gas introduced into the inner surface is preferably non-oxidizing (for example, nitrogen gas).
[0103]
　After hot working, the obtained molded product is rapidly cooled. Cooling is usually performed by removing heat from a mold and a cooling medium such as water, steam or gas. The cooling rate (average cooling rate) is 20° C./second or more in order to obtain a high strength member by quenching. The upper limit of the cooling rate is not particularly specified, but it is practically difficult to set it to 300° C./sec or more. More preferably, the cooling rate of the quenching by the mold is 30° C./sec or more and 300° C./sec or less.
[0104]
　
　The Al-plated layer in the Al-plated steel pipe (Al-plated welded pipe) melts at a temperature equal to or higher than the melting point when the Al-plated steel pipe is heated, and at the same time, due to mutual diffusion with Fe, Al-Fe It changes to the centered alloy layer. The Al—Fe alloy layer has a high melting point, which is about 1150° C. There are a plurality of Al-Fe or Si-containing Al-Fe-Si compounds, and when heated at high temperature or for a long time, they are transformed into compounds having a higher Fe concentration.
[0105]
　The surface condition of the hot-pressed Al-plated hollow member that is the final product is such that the surface of the Al-plated layer in the Al-plated steel pipe (Al-plated welded pipe) that is the material is alloyed and The Fe oxide (scale) generation rate in the resulting plated layer is preferably 5% or less. Further, a more preferable surface state as the hot-worked Al-plated hollow member which is the final product is a state in which the surface of the Al-plated layer in the Al-plated steel pipe (Al-plated welded pipe) which is the material is alloyed, and This is a state in which no Fe oxide is generated in the plating layer formed as a result of alloying.
[0106]
　If unalloyed Al remains in the alloy layer of the hollow member, only the portion where the unalloyed Al remains remains is rapidly corroded, and the coating film swelling is extremely likely to occur in the corrosion resistance after coating, which is not preferable. If 5% or more of scale is present inside the alloy layer, a decarburized layer is present on the surface of the steel pipe, which may deteriorate the fatigue properties. Moreover, since the portion corresponding to the decarburized layer has no plating, the corrosion resistance is also reduced.
[0107]
　When a surface coating layer mainly composed of ZnO is formed on the surface of the Al-plated layer of the Al-plated steel pipe (Al-plated welded pipe) used as the material, even on the alloy layer of the final-product Al-plated hollow member, There is a surface coating layer mainly composed of ZnO. In addition, after an Al-plated hollow member is manufactured by a hot working method using an Al-plated steel pipe (Al-plated welded pipe) mainly composed of ZnO and not having a surface coating layer formed thereon, the surface of the manufactured Al-plated hollow member In addition, a surface coating layer composed mainly of ZnO as described above may be provided.
[0108]
　The scale generation rate in the alloy layer is defined as follows. The cross section of the steel pipe part is embedded and polished, and the 0.5 mm range in the circumferential direction is observed by an optical microscope or SEM to measure the proportion of the entire structure in which scale is generated. Since the scale inside the alloy layer is relatively coarse (for example, 5 to 20 μm width), it can be easily measured by optical microscope observation as shown in FIG. 1, for example. For example, when a 0.5 mm (500 μm) range is observed under an optical microscope and five scales with a width of 10 μm are present in the range, it is determined that the scale occurrence rate is (10 μm×5)/500 μm=10%. For comparison, FIG. 2 shows a cross-sectional photograph of the Al-plated layer of the Al-plated steel pipe, which is the material before heating.
[0109]
　The hardness of the steel base portion of the quenched part is about 350 to 800 in Vickers hardness (Hv). The hardness value almost corresponds to the amount of C in the steel. When the amount of C is 0.06%, the Hv is about 350 at the maximum, and when the amount of C is 0.5%, the Hv is about 800. Hv can be measured according to JIS Z2244, and when measuring Hv, a load of 5 kgf (1 kgf is about 9.8 N) is measured in the vicinity of the center of the thickness of the steel sheet. And
Example
[0110]
　Hereinafter, the Al-plated welded tube for quenching, the method for manufacturing the hot-bent Al-plated hollow member, and the Al-plated hollow member according to the present invention will be specifically described with reference to experimental examples. The experimental examples described below are merely examples of the Al-plated welded tube for quenching, the method for producing a hot-worked Al-plated hollow member, and the Al-plated hollow member according to the present invention, and the examples for quenching according to the present invention The Al-plated welded pipe, the method of manufacturing the hot-worked Al-plated hollow member, and the Al-plated hollow member are not limited to the following examples. In particular, hot working can be applied to bending, diameter reduction, pipe expansion, crushing, and the like.
[0111]

　Cold-rolled steel sheets (sheet thickness: 1.2 to 2.0 mm) having the steel components shown in Table 1 below were used to perform Al plating by the hot dip coating method. The annealing temperature at the time of Al plating was about 800° C., and the Al plating bath contained Si: 9%, and additionally contained about 2% Fe eluted from the steel strip. The amount of plating adhered after plating was adjusted to 20 to 100 g/m 2 per side by the gas wiping method .
[0112]
　After cooling, some cold-rolled steel sheets were coated with a roll coater on a suspension containing ZnO having an average particle diameter of about 50 nm to contain a 20% acrylic binder in the ZnO content, It was baked at about 80°C. The amount of adhesion was the amount of Zn and was 0.1 to 1.5 g/m 2 per side .
[0113]
[table 1]

[0114]
　An Al-plated steel pipe (Al-plated welded pipe) was manufactured using the manufactured Al-plated steel plate. The electric resistance welding was high frequency welding, the frequency during welding was 300 kHz, and the welding speed was 5 m/sec. The weld bead portion was cut, that is, bead-cut, and an Al sprayed coating of 50 μm was applied to the outer surface portion of a part of the steel pipe. Steel pipes with various plate thicknesses and outer diameters were manufactured and their characteristics were evaluated. The evaluation method is shown below.
[0115]
　(1) Cross-sectional structure and plating thickness
　The cross-section of the steel pipe is mirror-polished, etched with a 2 volume% nital solution, and then observed under an optical microscope to measure the thickness of the alloy layer (intermetallic compound layer) and the thickness of the Al plating layer, respectively. did. Three samples were taken in the circumferential direction of the steel pipe, and one optical micrograph of the outer surface of each sample was taken, and the average value of the alloy layer thickness and the average value of the Al plating layer thickness at the total of 6 sites were calculated. Regarding the sprayed sample, similarly, three spray coating thicknesses were sampled in the longitudinal direction, and the average value of the three sites was calculated.
[0116]
　(2) Example of Hot Pressing
　A metal mold for forming was arranged in a hydraulic press machine, and a steel pipe and a heating device for the steel pipe were arranged therein. Both ends of a steel pipe having a length of 800 mm were sealed via flanges, and nitrogen gas was introduced into the inner surface. In that state, the steel pipe was heated to 900° C. by using high frequency heating. The high frequency heating was performed by moving the induction coil from one side of the steel pipe to the opposite side, and after heating, the coil was conveyed to the outside of the mold and then molded by a pressing machine. The atmosphere during heating was atmospheric air. By controlling the conveyance speed of the induction coil, the heating rate of the steel pipe (average heating rate) was changed.
[0117]
　The shape of the steel pipe was simply reduced to 1/2 the thickness (diameter in the vertical direction) and quenched with a mold. At this time, the weld bead portion was arranged so as to come to the upper surface. After that, a sample was taken from the molded product, and the structure of the steel and the plated layer was revealed by cross-section polishing and 2% by volume of nital etching. At this time, there was a sample in which a scale composed mainly of FeO was present inside the Al—Fe layer, and the scale generation rate was observed and evaluated according to the above method. Moreover, the thickness of the decarburized layer was also measured for the sample in which the decarburized layer was formed. The evaluation criteria are as follows. Further, Hv: Vickers hardness was measured from a cross section of each sample according to the method specified in JIS Z2244 under a load of 5 kgf.
[0118]
　　G: No scale generation rate (0%)
　　F: Scale generation rate 1 to 5%
　　P: Scale generation rate is over 5% and decarburized layer is 3 μm or more
[0119]
(3) Adhesion of Sprayed Material
　After spraying Al, the adhesion of the sprayed portion was evaluated. The evaluation was performed using taping, and the following criteria were used for evaluation. Specifically, a commercially available cellophane tape was attached to each sample, and when the attached cellophane tape was peeled off, it was evaluated whether or not peeling occurred in the sprayed portion.
[0120]
　　G: No peeling
　　F: Peeling within 1 mm diameter
　　P: Peeling over 1 mm
[0121]
(4) Adhesion of coating film From
　a steel pipe test piece after hot pressing, a portion including a weld bead portion was cut out and the adhesion of coating film was evaluated. For chemical conversion treatment, a chemical conversion treatment liquid (PB-SX35) manufactured by Nippon Parkerizing Co., Ltd. was used, and for electrodeposition coating, an electrodeposition coating (Powernics 110) manufactured by Nippon Paint Co., Ltd. was applied with a target of 15 μm, and 170 Baked at °C.
[0122]
　As a coating film adhesion evaluation, it was immersed in 5% salt water at 50° C. for 480 hours, taken out, and then a 1 mm cross-cut was applied with a cutter, followed by taping. The peeling condition at this time was evaluated according to the following criteria.
[0123]
　　G: No peeling
　　F: Peeling 3 squares or less
　　P: Peeling 4 squares or more or peeling regardless of square
[0124]
(5) Adhesion to salt hot water The
　samples that have been subjected to the above chemical conversion treatment and electrodeposition coating are immersed in 5% salt water at 50°C for 2 weeks without scratches on the coating film, and within 1 hour after immersion. After applying a 1 mm cross pattern, taping was performed to evaluate coating film adhesion. This evaluation is much stricter than the adhesiveness shown in (4). Normally, such severe coating film adhesion is not required, but it is a characteristic required when used in a particularly severe corrosive environment.
[0125]
　　G: No peeling
　　F: Peeling 3 squares or less
　　P: Peeling 4 squares or more or peeling regardless of square
[0126]
　The evaluated levels and the evaluation results at that time are summarized in Table 2 below.
[0127]
[Table 2]

[0128]
　As is clear from Table 2 above, when observing the state of scale generation from the cross section after hot pressing, 70×X/D≦Y/t≦30 is satisfied, and Y/X is α times t/D or more. In the case of, the generation of scale was slight or not observed at all. It was revealed that the scale generation situation also depends on the heating rate, and that the scale generation tends to be reduced by increasing the heating rate. Further, it has been clarified that, by applying a ZnO-containing coating on the Al-plated surface, the coating adhesion is particularly improved by a salt hot water test. Further, as is clear from Table 2, the hardness (Hv) of the steel substrate of the sample corresponding to the example of the present invention showed a value between 450 and 530 in all cases.
[0129]
　Experimental Example 2
　A steel plate having a steel composition shown in Table 3 below and a thickness of 1.4 mm was plated with Al under the same conditions as in Example 1. The Al plating layer had a thickness of 24 μm, and the alloy layer had a thickness of 5 μm. This steel plate was formed into a steel pipe having an outer diameter of 32 mm, and the welded portion was sprayed with Al having a thickness of about 30 μm. Then, the thermal spray material adhesion evaluation shown in Example 1 was performed.
[0130]
[Table 3]

[0131]
　As a result, with respect to the symbols B to D, peeling of the thermal spray material was recognized. From this result, it was clarified that it is preferable to reduce P, Al, and N as components in the steel. No peeling of the thermal spray material was observed under any other conditions.
[0132]
　Further, these steel pipes were hot-pressed under the same conditions as in Example 1 (heating rate was 10° C./sec), and evaluated in the same manner as in Example 1. As a result, after hot pressing, the evaluation results equivalent to "G" were obtained for both the cross-sectional structure and the coating film adhesion.
[0133]
　Although the preferred embodiment of the present invention has been described in detail above, the present invention is not limited to this example. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.
Industrial availability
[0134]
　If the Al-plated welded tube for quenching of the present invention is used, it is possible to manufacture a high-strength member by hot working, and it is possible to obtain a part that is lighter than conventional parts. This contributes to further weight reduction in the final application such as an automobile.
The scope of the claims
[Claim 1]
　A base material part made of a tubular steel plate, and an electric resistance welded pipe provided at the abutting part of the steel plate and comprising an electric resistance welded part extending in the longitudinal direction of the steel plate,
　wherein the base material part is a mass. %,
　　C: 0.06 to 0.50%,
　　Si: 0.01 to 0.80%,
　　Mn: 0.60 to 3.00%,
　　P: 0.050% or less,
　　S: 0.050% Hereinafter,
　　Al: 0.10% or less,
　　O: 0.006% or less,
　　N: 0.020% or less,
　　Ti: 0.01 to 0.10%,
　　B: 0 to 0.1000%,
　　Nb: 0 to 0.10%,
　　V: 0 to 0.30%,
　　Cr: 0 to 0.50%,
　　Mo: 0 to 0.50%,
　　Ni: 0 to 0.50%,
　　Cu: 0 to 0.50%,
　　Ca: 0. To 0.005% and
　　REM: 0 to 0.005%
, the balance being Fe and impurities, the
　base metal part is located on the surface of the steel sheet, and is an Al--Fe--Si based intermetallic material. An intermetallic compound layer containing a compound,
　An Al plating layer,
which is located on the surface of the intermetallic compound layer and contains Al and Si, is further provided, the
　thickness of the intermetallic compound layer is X (μm), and the thickness of the Al plating layer is Y (μm). When the thickness of the steel pipe is t (mm) and the outer diameter of the steel pipe is D (mm),
　　70×X/D≦Y/t≦30
is satisfied. Plated ERW welded pipe.
[Claim 2]
　The Al-plated ERW pipe for quenching according to claim 1, wherein X≦5.0, Y≦32, and 4.0≦Y/X≦6.0 are satisfied.
[Claim 3]
　The coating of ZnO as a main component is further provided on the surface of the Al plating layer, and the deposition amount of the coating is 0.1 to 1 g/m 2 in terms of Zn amount. Al-plated electric resistance welded pipe for quenching described.
[Claim 4]
　The Al-plated electric resistance welded tube for quenching according to any one of claims 1 to 3, wherein the welded portion is coated with an alloy containing Al as a main component.
[Claim 5]
　The Al-plated ERW pipe for quenching according to any one of claims 1 to 4, wherein 2% ≤ t/D ≤ 10% is satisfied.
[Claim 6]
　It is composed of a base metal part made of a tubular steel plate and an electric resistance welded part provided at the abutting part of the steel plate and extending in the longitudinal direction of the steel plate. The base metal part is
　　C: 0. 06 to 0.50%,
　　Si: 0.01 to 0.80%,
　　Mn: 0.60 to 3.00%,
　　P: 0.050% or less,
　　S: 0.050% or less,
　　Al: 0.10. %
　　Or less, O: 0.006% or less,
　　N: 0.020% or less,
　　Ti: 0.01 to 0.10%,
　　B: 0 to 0.1000%,
　　Nb: 0 to 0.10%,
　　V: 0 to 0.30%,
　　Cr: 0 to 0.50%,
　　Mo: 0 to 0.50%,
　　Ni: 0 to 0.50%,
　　Cu: 0 to 0.50%,
　　Ca: 0. To 0.005%, and
　　REM: 0 to 0.005%
, the balance being Fe and impurities, the electric resistance welded pipe, and
　the Al-Fe alloy, which is located on the surface of the electric resistance welded pipe. And an alloy layer containing at least one of Al—Fe—Si alloys
,
An Al-plated hollow member 　,
　wherein the Fe oxide generation rate in the alloy layer is 5% or less, and the Vickers hardness Hv of the steel base of the electric resistance welded pipe is 350 to 800
.
[Claim 7]
　The Al-plated hollow member according to claim 6, wherein unalloyed Al does not remain in the alloy layer.
[Claim 8]
　8. The surface of the alloy layer is further provided with a film containing ZnO as a main component, and the
　amount of the film deposited is 0.1 to 1 g/m 2 in terms of Zn amount. The Al-plated hollow member described.
[Claim 9]
　It is composed of a base metal part made of a tubular steel plate and an electric resistance welded part provided at the abutting part of the steel plate and extending in the longitudinal direction of the steel plate. The base metal part is
　　C: 0. 06 to 0.50%,
　　Si: 0.01 to 0.80%,
　　Mn: 0.60 to 3.00%,
　　P: 0.050% or less,
　　S: 0.050% or less,
　　Al: 0.10. %
　　Or less, O: 0.006% or less,
　　N: 0.020% or less,
　　Ti: 0.01 to 0.10%,
　　B: 0 to 0.1000%,
　　Nb: 0 to 0.10%,
　　V: 0 to 0.30%,
　　Cr: 0 to 0.50%,
　　Mo: 0 to 0.50%,
　　Ni: 0 to 0.50%,
　　Cu: 0 to 0.50%,
　　Ca: 0. To 0.005% and
　　REM: 0 to 0.005%
, the balance being Fe and impurities, the
　base metal part is located on the surface of the steel sheet, and is an Al--Fe--Si based intermetallic material. An intermetallic compound layer containing a compound,
　Located on the surface of the intermetallic compound layer, Al coating layer and containing Al and Si
and a heating process of heating further including quenching for Al plating electric resistance welding pipe 850 ° C. or more heating temperature,
　heated A forming step of forming the
　Al-plated electric resistance welded pipe for quenching into a desired shape, and quenching the Al-plated electric resistance welded pipe for quenching formed into a desired shape at an average cooling rate of 20° C./sec or more. a quenching step of
including a
　thickness of the intermetallic compound layer as X ([mu] m), the thickness of the Al plating layer and Y ([mu] m), the wall thickness of the steel pipe and t (mm), outer diameter of the steel pipe Is D (mm), and HR (°C/sec) is the average rate of temperature increase from room temperature to the reached temperature of -50°C set during hot working, the following equations (1) and (2) The manufacturing method of the Al plating hollow member characterized by satisfying the relation represented by.