JP5692148B2 - Al-plated steel sheet for hot pressing and its hot pressing method - Google Patents

Description

The present invention, main component to Rume Kki coated Al is applied, lubricity during hot pressing, Kki steel sheet for excellent corrosion resistance as a component, and a hot pressing method of the plated steel sheet.

  In recent years, in order to protect the environment and prevent global warming, there is an increasing demand for reducing consumption of chemical fuels, but this demand has an impact on various manufacturing industries. For example, an automobile that is indispensable for daily life and activities as a means of transportation is 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 not permitted in terms of product quality to simply reduce the weight of the vehicle body, and it is necessary to ensure appropriate safety.

  Most automobile structures are made of iron, particularly steel plates, and reducing the mass of these steel plates is important for reducing the weight of the vehicle body. However, as described above, it is not allowed to simply reduce the mass of the steel sheet, and it is required to ensure the mechanical strength of the steel sheet. Requests for such steel sheets are made not only in the automobile manufacturing industry but also in various manufacturing industries.

  Therefore, research and development have been conducted on steel plates that can maintain or increase mechanical strength even when they are thinner than the steel plates that have been used by increasing the mechanical strength of the steel plates.

  In general, a material having high mechanical strength has a low shape freezing property in a forming process such as a bending process. Therefore, when processing into a complicated shape, the process itself becomes difficult. As one of means for solving the problem concerning the formability, there is a so-called “hot pressing method (also called hot stamping method, hot pressing method, die quenching method)”.

  In the hot pressing method, a material to be molded is once heated to a high temperature, softened and pressed, and then cooled. According to this hot pressing method, since the material is once heated to a high temperature and softened, it can be easily pressed, and further, the mechanical strength of the material is increased by quenching by cooling after molding. Therefore, a hot-pressed product can be obtained that has both good shape freezing properties and high mechanical strength.

  However, when the hot pressing method is applied to a steel sheet, for example, heating is performed at a high temperature of 800 ° C. or higher, so that iron on the surface is oxidized to generate scale (oxide). Therefore, after the hot pressing, a process of removing scale (descaling process) is required, and productivity is lowered. Further, in the case of a member that requires corrosion resistance, it is necessary to subject the surface of the member to rust prevention treatment or metal coating after processing, which requires a surface cleaning step or a surface treatment step, which also reduces productivity.

  As a method for suppressing such a decrease in productivity, there is a method of coating a steel plate in advance. In general, various materials such as organic materials and inorganic materials are used as a coating material for a steel plate. In particular, zinc-based plated steel sheets that have a sacrificial anticorrosive action on steel sheets are widely used for automobile steel sheets and the like from the viewpoint of corrosion protection performance and production technology.

  However, the heating temperature (700 to 1000 ° C.) in the hot press is higher than the decomposition temperature of the organic material and the melting point of the metal material such as Zn, and when heated, the surface plating layer melts and evaporates. Properties may be significantly degraded.

  Therefore, as a steel plate to be hot pressed, for example, an organic material coating or a steel plate with an Al-based metal coating having a higher melting point than that of a Zn-based metal coating, a so-called Al-based plated steel plate may be used. desirable.

  When an Al-based metal coating is applied to the steel plate, scales can be prevented from being generated on the surface of the steel plate, and a process such as a descaling process becomes unnecessary, thereby improving productivity. Moreover, since the Al-based metal coating also has a rust prevention effect, the corrosion resistance after painting is also improved.

  Patent Document 1 discloses a method in which an Al-based plated steel sheet obtained by applying Al-based metal coating to steel having a predetermined component composition is applied to hot pressing.

  However, when an Al-based metal coating is applied to the steel sheet, depending on the heating conditions before hot pressing, the Al-based metal coating melts and forms Fe and Al-Fe compounds that diffuse from the steel sheet to form a steel sheet. In some cases, an Al—Fe compound (hereinafter also referred to as “Al—Fe alloy layer”) may be formed. Since the Al—Fe alloy layer is hard, it may come into contact with the mold during press working, and a processing flaw may be generated on the surface of the steel sheet.

  Originally, the Al—Fe alloy layer has a relatively difficult surface slip and poor lubricity. Furthermore, since the Al—Fe alloy layer is hard, it is relatively easy to crack, and the plating layer is cracked, and the plating layer may be powdered, thereby reducing the formability. Furthermore, when the peeled Al—Fe alloy layer adheres to the mold, or the surface of the Al—Fe alloy layer is strongly rubbed and adheres to the mold, the quality of the press-formed product is deteriorated.

  Therefore, it is necessary to remove the Al—Fe alloy powder adhered to the mold during repair, which contributes to a decrease in productivity and an increase in cost.

  Furthermore, the Al—Fe compound has poor reactivity with the phosphate treatment, and a film (phosphate film) is not generated in the chemical conversion treatment, which is a pretreatment for electrodeposition coating. Even if there is no chemical conversion treatment film, the Al-Fe alloy layer has good paint adhesion, and if a sufficient amount of Al-Fe alloy layer is formed, the corrosion resistance after coating will be good. If the adhesion amount of the Fe alloy layer is increased, the above-mentioned mold adhesion is caused.

  As described above, the adhesion includes adhesion of the peeled Al—Fe alloy layer and adhesion caused by strongly rubbing the surface of the Al—Fe alloy layer. Although the latter adhesion (scratch adhesion) is improved by improving the lubricity of the surface film, the improvement of the former adhesion (peeling adhesion) is relatively small. For improving the former adhesion, it is most effective to reduce the adhesion amount of the Al—Fe alloy layer. However, when the adhesion amount of the Al—Fe alloy layer is reduced, the corrosion resistance is lowered.

  On the other hand, in Patent Document 2, for the purpose of preventing the occurrence of processing flaws, an Al-based metal coating is applied on a steel plate having a predetermined component composition, and further, Si, Zr , Ti, or P contains an inorganic compound film, an organic compound film, or a composite compound film thereof.

In a steel sheet on which such a surface coating is formed, the surface coating remains even during the press working after heating, and the occurrence of processing flaws during the press working can be prevented. Also, Patent Document 2, since the surface film acts as a lubricant during pressing, but moldability is described to be improved, in fact, sufficient lubricity can be obtained, a new lubricating Agents and alternatives are needed.

  Patent Document 3 discloses a method for solving surface deterioration due to evaporation of a galvanized layer in hot pressing of a galvanized steel sheet. Specifically, a high melting point zinc oxide (ZnO) layer is formed as a barrier layer on the surface of the galvanized layer to prevent evaporation of the lower galvanized layer.

  However, the technique of Patent Document 3 is based on a galvanized layer. As for Al, the galvanized layer is allowed to contain up to 0.4%, but the Al concentration should be low, and this is a technology that does not substantially assume Al-based metal coating. Since the problem of the technique of Patent Document 3 is evaporation of Zn in the galvanized layer, it is a problem that cannot naturally occur with an Al-based metal coating having a high melting point.

Patent Document 4 discloses a technique for improving the hot lubricity and chemical conversion treatment by coating a surface of an Al-based plated steel sheet with a wurtzite type compound. This technique is effective in improving the lubricity and also improves the corrosion resistance after coating. However, in order to improve the lubricity, the coating amount of the film needs to be about 2 g / m ^{2 in} terms of Zn. The film thickness is about 1 μm at ² g / m ^2. With such a thickness, the film resistance becomes high and the spot weldability decreases, and as a result, the cross tensile strength decreases. Therefore, there is a need for a technique for improving lubricity with a smaller amount of coating.

JP 2000-38640 A JP 2004-21151 A JP 2003-129209 A International Publication WO2009 / 131233 Pamphlet

  As described above, high-melting point Al-based plated steel sheets (Al-based plated steel sheets) are considered promising as automotive steel sheets that require corrosion resistance, and are applied to hot pressing of Al-based plated steel sheets. Various proposals have been made. However, at the time of hot pressing, the Al-Fe alloy layer does not have good lubricity, and the press formability is poor. It is.

  Further, many automotive steel sheets are subjected to a coating treatment after forming, and Al-based plated steel sheets are also required to have chemical conversion treatment properties (paintability) after hot pressing and corrosion resistance after painting.

  Therefore, in view of the above problems, the present invention ensures the lubricity of the Al-based plating layer in the Al-based plated steel sheet, improves the formability and productivity during hot pressing, and further performs chemical conversion after hot pressing. The object is to improve the processability and the corrosion resistance after painting, and to provide a hot-pressed plated steel sheet and a hot pressing method for solving the problems.

The present inventors diligently studied a method for solving the above problems. As a result, ZnO is contained on the Al-based plating layer formed on one side or both sides of the steel plate, and Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Mo, W, La, It was found that when a surface film layer containing a compound such as Ce is formed, the lubricity during hot pressing is good even if the surface film layer has a small adhesion amount of about 1 g / m ² .

  The present invention has been made based on the above findings, and the gist thereof is as follows.

(1) A plating layer formed on one or both sides of a steel sheet, containing 3 to 15% of Si and comprising the balance Al and unavoidable impurities, laminated on the plating layer, and ZnO on one side of the steel sheet, converted to Zn 0.3 to 7 g / m ² and further containing one or more compounds of Ti, Mn, Ni , Cu, and Zr , and the compound is any one of a sulfate compound, a fluorine compound, and a nitrate compound. , and the hot-press coated steel sheet, wherein the mass ratio of the total amount of ZnO in the compound has a 0.5 to 50% der Ru surface film layer.

( 2 ) The hot press according to (1 ) above, wherein a mass ratio of one or more of Ti, Mn, Ni , Cu, and Zr to ZnO is 1 to 40%. Plated steel sheet.

( 3 ) Hot-plated steel sheet for hot press, wherein the hot-pressed plated steel sheet according to any one of (1) to ( 2 ) is heated after blanking and then press-molded. Press method.

(4) In the heating before the press molding, according to (3), wherein the average heating rate up to peak metal temperature of from 10 ° C. lower temperature from 50 ° C. is 10 to 300 ° C. / sec Hot pressing method for plated steel sheet for hot pressing.

( 5 ) The hot pressing method for a plated steel sheet for hot pressing as described in ( 4 ) above, wherein the heating before the press forming is electric heating or induction heating.

According to the present invention, the lubricity of the plating layer containing 3 to 15% of Si and the balance Al and inevitable impurities is ensured, the formability and productivity in hot pressing are improved, and further after hot pressing The chemical conversion treatment property and the corrosion resistance after painting can be improved.

It is a figure which shows the aspect of the apparatus which evaluates the hot lubricity of Al type plated steel plate. It is a figure which shows the relationship between the coating amount (Zn conversion amount) of a surface film layer, and a film peeling rate. It is a figure which shows the relationship between the coating amount (Zn conversion amount) of a surface film layer, and hot lubricity (friction coefficient). It is a figure which shows the relationship between the coating amount (Zn conversion amount) of a surface membrane layer, and the intensity | strength of a spot joint.

The hot-pressed plated steel sheet of the present invention (hereinafter sometimes referred to as “the present steel sheet”) is formed on one or both sides of the steel sheet, contains 3 to 15% of Si, and consists of the balance Al and inevitable impurities. It is characterized by having a plating layer and a surface film layer laminated on the plating layer, containing ZnO, and further containing one or more compounds of Ti, Mn, Ni , Cu, and Zr. To do. Hereinafter, the patent requirements for the steel sheet of the present invention will be described.

<Plated steel plate>
The steel sheet of the present invention is characterized by having a film having at least a two-layer structure (a plating layer and a surface film layer containing 3 to 15% of Si and the balance Al and inevitable impurities) on one side or both sides of the steel plate. Specifically, on one or both sides of the steel sheet, a plating layer containing 3 to 15% of Si and the balance Al and unavoidable impurities is formed, and further, ZnO is contained on the plating layer, A surface film layer containing one or more compounds of Ti, Mn, Ni , Cu, and Zr is formed.

(steel sheet)
Steel sheets that form a two-layered film have the required mechanical properties (tensile strength, yield point, elongation, drawing, hardness, impact value, fatigue strength, creep strength, etc. A steel sheet having a characteristic) is desirable. The steel sheet is, for example, mass%, C: 0.1 to 0.4%, Si: 0.01 to 0.6%, Mn: 0.5 to 3%, Ti: 0.01 to 0.1. % And B: at least one of 0.0001 to 0.1%, and the balance Fe and unavoidable impurities.

  The said component composition is demonstrated. Hereinafter,% means mass%.

  C is an element that ensures the mechanical strength of the steel sheet. If it is less than 0.1%, sufficient mechanical strength cannot be obtained, and if C exceeds 0.4%, the hardness increases but melt cracking tends to occur. Therefore, C is preferably 0.1 to 0.4%.

  Si, like C, is an element that ensures the mechanical strength of the steel sheet. If it is less than 0.01%, the strength improving effect is not exhibited, and sufficient mechanical strength cannot be obtained. Since Si is also an easily oxidizable element, if it exceeds 0.6%, wettability is reduced during hot dip plating and non-plating occurs. Therefore, 0.01 to 0.6% of Si is desirable.

  Mn is an element that enhances hardenability and strengthens the steel sheet. Mn is an element that traps inevitable impurities S as MnS and prevents hot brittleness due to S. If it is less than 0.5%, the effect of addition does not appear, and if it exceeds 3%, the residual γ phase increases and the strength decreases. Therefore, Mn is desirably 0.5 to 3%.

  Ti is an element for improving the strength and is an element for improving the heat resistance of the Al-based plating layer. If it is less than 0.01%, the strength improvement effect and the heat resistance improvement effect cannot be obtained. If it exceeds 0.1%, carbides and nitrides are generated and the steel becomes soft, and the required mechanical strength cannot be obtained. Therefore, Ti is desirably 0.01 to 0.1%.

  B is an element that enhances hardenability and improves strength. If it is less than 0.0001%, the effect of improving the strength is not exhibited. If it exceeds 0.1%, inclusions are generated and the fatigue strength is lowered. Therefore, B is preferably 0.0001 to 0.1%.

  In addition, the steel plate may contain inevitable impurities mixed in the manufacturing process as long as the mechanical properties of the steel plate are not impaired.

  A steel sheet having the above composition increases in mechanical strength to about 1500 MPa or more by quenching in the hot pressing method. In the hot pressing method, the steel sheet is press-formed in a softened state, and thus forming is easy. Moreover, even if the said steel plate is thin for weight reduction, it maintains high mechanical strength.

(Al-based plating layer)
As described above, the plating layer containing 3 to 15% of Si of the steel sheet of the present invention and comprising the balance Al and inevitable impurities is formed on one or both surfaces of the steel sheet. The plating layer is, for example, formed by hot dipping method, a method of forming the above plating layer is not limited to the hot dipping.

The plating layer containing 3 to 15% Si and the balance Al and inevitable impurities contains Si for the following reason.

  Si is an element that suppresses the formation of the Fe—Al alloy layer during hot dipping. If it is less than 3%, the Fe—Al alloy layer grows thick at the time of hot dipping, and at the time of processing, cracking of the plating layer may be promoted and corrosion resistance may be impaired. If Si exceeds 15%, the workability and corrosion resistance of the Al-based plating layer deteriorate. Therefore, 3 to 15% of Si in the Al-based plating layer is desirable.

  The Al-based plating layer having the above component composition prevents corrosion of the steel sheet. Further, scale (iron oxide) is prevented from being formed on the surface of the steel plate during heating before hot pressing.

Therefore, it is possible to omit the scale removal step, the surface cleaning step, the surface treatment step, etc. by including a plating layer containing 3 to 15% Si and the balance Al and inevitable impurities on one side or both sides of the steel plate. And productivity is improved. Further, the plated layer is coated or an organic-based material, other metal-based material (e.g., Zn-based materials) because of its high melting point than the coating by, during hot pressing, it is possible to work at elevated temperatures.

A part of Al contained in the plating layer containing 3 to 15% Si and the balance Al and unavoidable impurities is alloyed with Fe in the steel sheet at the time of hot dipping or hot pressing. Therefore, the plating layer is not necessarily limited to component composition is formed by the constant single layer becomes partially intended to include alloyed layer (alloy layer).

(Surface film layer)
The surface coating layer of the steel sheet of the present invention is laminated on the surface of the plating layer containing 3 to 15% of Si and comprising the balance Al and inevitable impurities . The surface coating layer contains at least ZnO. The aqueous suspension of fine particles of ZnO, a roll coater or the like, applied to the surface of the plating layer to form a surface coating layer. The surface coating layer functions to improve the lubricity during hot pressing and the reactivity with the chemical conversion treatment liquid.

The surface coating layer contains one or more compounds of Ti, Mn, Ni , Cu, and Zr in order to improve lubricity during hot pressing. These elements are all transition metal elements (elements belonging to Group 3 to Group 11 in the periodic table).

  In particular, the effect of adding Ni, Ti, Zr, Mn, and Cu is remarkable. The compound of these elements is preferably an oxide, nitride, sulfide, phosphate or the like.

  The reason why the compound of the element contributes to the improvement of the lubricity during hot pressing is not clear, but the effect of improving the lubricity cannot be obtained with the compound of the element alone. It is considered to be an effect.

  It is ZnO that essentially bears the lubricity improvement effect, but with the addition of the compound of the element, during hot pressing, ZnO and the compound of the element react to form a composite oxide, and as a result, It is estimated that lubricity is improved.

The surface coating layer containing ZnO and one or more compounds of Ti, Mn, Ni , Cu, and Zr can be prepared by, for example, applying Si containing 3 by adding a paint containing these, baking and drying after application. It is formed on a plating layer containing -15% and the balance being Al and inevitable impurities.

As a coating method, for example, a suspension containing ZnO and one or more compounds of Ti, Mn, Ni , Cu, and Zr is mixed with an organic binder on the surface of the Al plating layer. A coating method or a coating method by powder coating can be used.

  Examples of the compound include Ni sulfate, Mn sulfate, Ti fluoride, Zr nitrate, Cu sulfate and the like, and organic binders include, for example, polyurethane resins, polyester resins, acrylic resins, and silane couplings. An agent or the like can be used.

  The compound and organic binder are water soluble so that they can be mixed with the ZnO suspension. The coating solution thus obtained is applied to the surface of the Al-based plated steel sheet.

  The particle diameter of ZnO is not particularly limited, but a diameter of about 50 to 1000 nm is desirable. The particle size of ZnO is the particle size after the heat treatment. Specifically, the particle size after being held in a furnace at 900 ° C. for 5 to 6 minutes and rapidly cooled with a mold is determined by observing with SEM or the like.

The amount of one or more compounds of Ti, Mn, Ni , Cu and Zr in the surface coating layer is preferably 1 to 40% in terms of mass ratio with respect to ZnO. If it is less than 1%, there is no effect of improving the lubricity during hot pressing, and if it exceeds 40%, the adhesion of the film after heating is lowered.

  The content of an organic binder such as a resin component or a silane coupling agent is preferably 5 to 30% in terms of a mass ratio with respect to ZnO. If it is less than 5%, the binder effect is not sufficiently obtained, and the coating film before heating becomes easy to peel off. In order to stably obtain the binder effect, the organic binder is more preferably 10% or more by mass ratio. When the amount of the organic binder exceeds 30%, odor generation becomes remarkable during heating, which is not preferable.

  The present inventors can compare the present invention with an inorganic compound film, an organic compound film, or a composite compound film containing at least one of Si, Zr, Ti, or P described in Patent Document 2. It was confirmed that the surface coating layer of the steel sheet had high lubricity. Therefore, the surface coating layer of the steel sheet of the present invention can further improve the formability and productivity.

The adhesion amount of the surface coating layer containing ZnO and one or more compounds of Ti, Mn, Ni , Cu, and Zr is 0.3 to 7 g / m in terms of Zn in the surface coating layer on one side of the steel sheet. ² is preferred.

  The present inventors evaluated the lubricity of the surface film layer of the steel sheet of the present invention by the film peeling rate (= Zn amount of the peeled film / Zn amount of the film before the test), and the coating amount of the surface film layer ( The relationship between the Zn conversion amount) and the film peeling rate was investigated. The result is shown in FIG.

As shown in FIG. 2, when the Zn conversion amount is 0.3 to 7 g / m ² , the film peeling rate is 15% or less, and the lubricity of the surface film layer is good. When the Zn conversion amount exceeds 7 g / m ² , the surface film layer becomes thick, the film peeling rate increases rapidly, and the weldability and paint adhesion deteriorate.

Therefore, in the surface film layer on one side of the steel plate, ZnO is desirably 0.3 to 7 g / m ^{2 in} terms of Zn. 0.5 to ² g / m ² is more desirable, and in addition to lubricity during hot pressing, weldability and paint adhesion are improved.

  The baking / drying method after application may be, for example, a method using a hot air furnace, an induction heating furnace, a near infrared furnace, or a combination of these. Depending on the type of organic binder, a curing method using ultraviolet rays, electron beams, or the like may be employed instead of baking and drying after coating. In addition, the formation method of a surface film layer is not limited to the said method, Various film formation methods are employable.

  When an organic binder is not used, the adhesiveness with the Al-based plating layer before heating is slightly low, and when it is rubbed with a strong force, it is partially peeled off. Thus, since the surface coating layer of the steel sheet of the present invention exhibits good lubricity during hot pressing, the formability of the steel sheet of the present invention is improved, and the corrosion resistance of the steel sheet of the present invention after hot pressing is improved. improves.

  The surface coating layer of the steel sheet of the present invention suppresses adhesion of the steel sheet of the present invention to the mold. Even if the Al-based plating layer is powdered, the surface coating layer containing ZnO on the surface prevents powder (Al—Fe powder or the like) from adhering to the subsequent mold. Therefore, the process of removing the Al—Fe alloy powder adhered to the mold becomes unnecessary, and the productivity is improved.

  Since the surface coating layer also serves as a protective layer for preventing scratches and the like from being generated on the steel plate and / or the Al-based plating layer during hot pressing, the formability of the steel plate of the present invention is further improved. Furthermore, the surface coating layer does not deteriorate spot weldability, paint adhesion, and the like. By forming the chemical conversion treatment film, the corrosion resistance after painting is greatly improved, so that the amount of adhesion of the surface film layer can be reduced. As a result, the adhesion of the Al—Fe layer to the mold during rapid pressing is reduced, and the productivity is further improved.

<Processing by hot pressing method>
The steel sheet of the present invention can be processed and formed by various methods, but is suitable for forming by a hot press method. Therefore, the case where the steel sheet of the present invention is formed by a hot pressing method will be described.

  In the hot pressing method for the steel sheet of the present invention (hereinafter sometimes referred to as “the method of the present invention”), the steel sheet of the present invention is first heated and softened. The softened steel sheet of the present invention is press-formed into a required shape and then cooled. Since the steel sheet of the present invention is once softened, subsequent press forming can be easily performed. The steel sheet of the present invention is quenched by heating and cooling and has a high mechanical strength of 1500 MPa or more.

  For the heating of the method of the present invention, heating by a normal electric furnace, a radiant tube furnace, or other heating such as infrared heating can be employed. When an Al-based plated steel sheet is heated to a temperature equal to or higher than the melting point of Al, the Al plating is melted, Al and Fe are diffused to each other, and an Al—Fe alloy layer or an Al—Fe—Si alloy layer is generated. The Al—Fe alloy layer and the Al—Fe—Si alloy layer have a high melting point and about 1150 ° C.

  There are a plurality of compounds forming the Al—Fe alloy layer and the Al—Fe—Si layer, and the compound changes to a compound having a high Fe concentration by high-temperature heating or long-time heating. A desirable surface state as a final product of the steel sheet of the present invention is a state in which the surface is alloyed and the Fe concentration in the alloy layer is not high.

  If unalloyed Al remains, only this portion is rapidly corroded, and the coating film swells easily after coating. On the other hand, even if the Fe concentration in the Al—Fe alloy layer becomes too high, the corrosion resistance of the Al—Fe alloy layer itself is lowered, and the coating film swells easily after coating. This is because the corrosion resistance of the Al—Fe alloy layer depends on the Al concentration in the alloy layer.

  Therefore, there is a desirable alloying state in securing the corrosion resistance after painting, and this alloying state is determined by the amount of plating adhesion and heating conditions.

  In the method of the present invention, the average rate of temperature increase from 50 ° C. to a temperature 10 ° C. lower than the maximum attainable plate temperature can be set to 10 to 300 ° C./second. The average rate of temperature rise affects the productivity of the steel sheet of the present invention, but the general average rate of temperature rise is about 5 ° C./second at high temperature in the case of atmospheric heating. An average temperature increase rate of 100 ° C./second or more can be achieved by energization heating or high frequency induction heating.

  When the high average heating rate is realized, productivity is improved. In addition, the average heating rate is an important factor for controlling the quality of the product because it affects the composition and thickness of the Al—Fe alloy layer. In the case of the steel sheet of the present invention, the rate of temperature increase can be increased to 300 ° C./second, so that productivity is improved and the quality of the product can be controlled in a wider range.

  The heating before hot pressing needs to be performed in the austenite region based on the principle of hot pressing. The maximum temperature reached by heating (maximum temperature reached) is usually 900 to 950 ° C. In the method of the present invention, the maximum temperature reached is not particularly limited, but if it is less than 850 ° C., it is not preferable because sufficient hardness cannot be obtained. In addition, the Al-based plating layer needs to be changed to an Al—Fe alloy layer. From this point of view, it is not preferable that the temperature is lower than 850 ° C.

  When heating temperature exceeds 1000 degreeC, alloying will advance too much and the Fe density | concentration in an Al-Fe alloy layer will rise and the corrosion resistance after coating will fall. Corrosion resistance after painting depends on the rate of temperature rise and the amount of Al-based plating layer deposited, so it cannot be said unconditionally. However, in consideration of economy, heating at a temperature exceeding 1000 ° C. is not desirable. .

<Examples of effects of Al-based plated steel sheet and hot press method>
The steel sheet according to the present invention includes ZnO and a surface coating layer containing one or more compounds of Ti, Mn, Ni , Cu, and Zr, so that, as described above, Si during hot pressing is 3 to 3 The lubricity of the plating layer containing 15% of the balance Al and inevitable impurities is improved, and the chemical conversion treatment of the Al-based plating layer after hot pressing is improved.

  The reason why the adhesion of the chemical conversion coating is improved by ZnO is not clear, but the chemical conversion reaction is a reaction that proceeds with an etching reaction to the material by acid, and ZnO itself is an amphoteric compound and dissolves in acid. It is thought that it reacts with the chemical conversion treatment liquid.

  Next, examples of the present invention will be described. The conditions in the examples are one example of conditions used for confirming the feasibility and effects of the present invention, and the present invention is based on this one example of conditions. It is not limited. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

<Example 1>
Al-based plating was applied to cold-rolled steel sheets (thickness 1.4 mm) having the composition shown in Table 1 by the Sendzimer method. The annealing temperature was about 800 ° C., and the Al-based plating bath contained Si: 9%, and also contained Fe eluted from the steel plate.

After hot-plating the steel sheet, the amount of plating was adjusted to 160 g / m ² on both sides by gas wiping. After cooling, the film treatment liquid shown in Table 2 and Table 3 (continuation of Table 2) was applied with a roll coater and baked at about 80 ° C. Each of the film treatment solutions shown in Tables 2 and 3 is a suspension or an aqueous solution in which a reagent and distilled water are mixed.

  The characteristics of the Al-based plating layer and the surface coating layer formed on the steel plate were evaluated by the following methods.

(1) Hot lubricity Hot lubricity was evaluated using the apparatus shown in FIG. The test piece 1 of 150 × 200 mm is placed on the test piece base 4 of the furnace body 3 provided with the heater 2 at the top, heated to 900 ° C., and then loaded on the test piece 1 at about 700 ° C. with the load load device 5. P (pressing load) was applied, and the furnace body 3 was driven along the ball way 7 by the furnace body driving device 6 to measure the pulling load.

  The pull-out load was measured with the load cell 8 connected to the load application device 5. The pulling load / pressing load was defined as the dynamic friction coefficient.

(2) Film adhesion after heating The test piece was placed in an atmospheric furnace, heated at 900 ° C. for 6 minutes, taken out, and immediately cooled by being sandwiched between stainless steel molds. The temperature rising rate was about 5 ° C./second, and the cooling rate was about 150 ° C./second. Next, the test piece was cut into 50 mm × 50 mm and subjected to a rubbing test. The gauze to which a load of 1.5 kgf was applied was reciprocated 10 times with a width of 30 mm, the Zn adhesion amount before and after the test was measured, and the weight loss ratio (%) was calculated.

(3) Strength of Spot Welded Joint The test piece was placed in an atmospheric furnace, heated at 900 ° C. for 6 minutes, taken out, and immediately cooled by being sandwiched between stainless steel molds. The temperature rising rate was about 5 ° C./second, and the cooling rate was about 150 ° C./second. Next, the cross tensile strength was measured according to JIS Z3137. The welding conditions at this time are as follows. The test was performed at N = 3, and the average value of joint strength was calculated.

Electrode: Chrome copper, DR (tip 8mmφ is 40R)
Pressurization: 880kgf
Energizing time: Upslope 3 cycles-Energizing 22 cycles (60 Hz)
Welding current: 9.5 kA
(4) Corrosion resistance after painting The test piece was placed in an atmospheric furnace, heated at 900 ° C. for 6 minutes, taken out, and immediately cooled by being sandwiched between stainless steel molds.

  The temperature rising rate was about 5 ° C./second, and the cooling rate was about 150 ° C./second. Next, it cut | disconnects to 70 mm x 150 mm, and after chemical conversion treatment with a chemical conversion treatment liquid (PB-SX35) manufactured by Nippon Parkerizing Co., Ltd., an electrodeposition paint (Powernics 110) manufactured by Nippon Paint Co., Ltd. is 20 μm. Painted with aim and baked at 170 ° C.

Evaluation of corrosion resistance after painting was carried out by the method specified in JASO M609 established by the Automotive Engineering Association. The coating film was previously cross-cut with a cutter, and the width (maximum value on one side) of the coating film swelling from the cross-cut after 180 cycles (60 days) of the corrosion test was measured. As a comparative example, a single-sided 45 g / m ² alloyed hot-dip galvanized steel sheet was evaluated. The swollen width was 7 mm.

  The evaluation results are summarized in Table 2 and Table 3 (continuation of Table 2). Moreover, it evaluated similarly, without providing a surface film layer for the comparison. The results are shown in Table 4.

  The hot lubricity indicates the measured dynamic friction coefficient, the film adhesion indicates the Zn peeling rate before and after the test, the spot joint strength indicates the cross tensile strength, and the corrosion resistance after painting is the maximum on one side from the cross cut. The swollen width is shown. Inventive examples (Nos. 1 to 23 in Tables 2 and 3) having a surface coating layer containing ZnO have hot lubricity compared to comparative examples having no surface coat layer (Nos. 24 to 29 in Table 3). Has improved.

  However, sufficient hot lubricity cannot be obtained unless the adhesion amount of the surface coating layer is relatively increased. When the adhesion amount of the surface coating layer is increased, the strength of the spot joint, particularly the cross tensile strength is lowered. A decrease in the strength of the spot joint and a decrease in the cross tensile strength are undesirable for the quality stability of the automobile. Although the reason is not clear, there is a possibility that oxide remains in the weld nugget and stress is concentrated at the site during tension.

On the other hand, the surface film layer (refer to the numbers 7 to 13 in Table 2) containing one or more compounds of Ti, Mn, Ni , Cu and Zr is excellent in the region where the amount of adhesion is small. In addition, the strength of the spot joint was not lowered as long as it had hot lubricity and was 2 g / m ² or less in terms of Zn.

  Regarding the corrosion resistance after painting, the influence of the above compounds is not clear, but all show excellent corrosion resistance after painting as compared with those without a surface film layer. This is considered to be due to the improved chemical conversion processability.

  The effect of the surface coating layer on the properties was investigated. Table 2 numbers 7 to 13 (invention example), Table 3 numbers 24 to 29 (comparative example), and the film peeling rate when there is no surface film layer of Table 4, hot lubricity (friction coefficient), and FIG. 2, FIG. 3, and FIG. 4 show the strength of the spot joint, respectively.

It can be seen that the system containing these compounds has a lower adhesion amount and improved hot lubricity than the system not containing one or more compounds of Ti, Mn, Ni , Cu, and Zr. .

When the adhesion amount of the surface coating layer increases, the strength of the spot welded joint and the coating adhesion deteriorate. In order to increase the strength of the spot welded joint, it is preferable that the adhesion amount of the surface coating layer is 2 g / m ² or less (see FIG. 3), and in order to increase the adhesion of the coating, the adhesion amount is 7 g / m ² . It can be seen that m ² or less is preferable (see FIG. 2).

<Example 2>
The test piece of No. 1 in Example 1 was rapidly heated with near infrared rays. The heating rate was 21 ° C./second. Quenching was performed in the same manner as in Example 1, and the subsequent evaluation was performed in the same manner as in Example 1. The evaluation results are shown in Table 5. Although the corrosion resistance after painting was improved, the other characteristics were unchanged. From this, it can be expected that the characteristics are further improved by rapid heating.

<Example 3>
Based on an aqueous solution in which 20% urethane resin was added to ZnO, 10% sodium vanadate, sodium dichromate, iron sulfate, cobalt chloride, sodium molybdate, sodium tungstate, and cerium nitrate were added thereto. .

Using the treatment liquid thus prepared, 1 g / m ^{2 in} terms of Zn was applied to the Al-based plated steel sheet used in Example 1, and the hot lubricity was measured by the method described in Example 1. As a result, numerical values in the range of 0.60 to 0.65 were obtained by all methods. From this, it is understood that any of the above compounds contributes to the improvement of hot lubricity.

According to the present invention, in the hot pressing of the plated steel sheet with a plating layer composed of the remainder Al and unavoidable impurities contained Si 3 to 15%, to ensure the lubrication of the plating layer, moldability in the hot press Further, productivity can be improved, and further, chemical conversion treatment property after hot pressing and corrosion resistance after painting can be improved. Therefore, this invention expands the application range to the hot press of the plated steel plate which contains 3-15% of Si, and comprises the plating layer which consists of remainder Al and an unavoidable impurity, and is applied to the automobile and industrial machine which are end uses. Since the applicability of the Al-plated steel sheet is enhanced, the industrial applicability is high.

DESCRIPTION OF SYMBOLS 1 Test piece 2 Heater 3 Furnace body 4 Test piece stand 5 Load loading apparatus 6 Furnace body drive apparatus 7 Ballway 8 Load cell

Claims (5)

Formed on one or both surfaces of the steel sheet, 3 to 15% of Si, the remaining Al and unavoidable impurities are deposited on the plated layer, and ZnO is deposited on the one surface of the steel sheet in a Zn conversion of 0. Containing 3 to 7 g / m ² , and further containing one or more compounds of Ti, Mn, Ni , Cu, and Zr , the compound being any one of a sulfate compound, a fluorine compound, and a nitrate compound, for hot pressing plated steel sheet, wherein the mass ratio of the total amount of ZnO in the compound has a 0.5 to 50 percent der Ru surface film layer. The plated steel sheet for hot pressing according to claim 1, wherein a mass ratio of one or more compounds of Ti, Mn, Ni , Cu, and Zr to ZnO is 1 to 40%. A hot pressing method for a hot-pressed plated steel sheet, wherein the hot-pressed plated steel sheet according to any one of claims 1 to 2 is heated after blanking and then press-molded. 4. The hot press according to claim 3 , wherein an average rate of temperature increase from 50 ° C. to a temperature 10 ° C. lower than a maximum attained plate temperature is 10 to 300 ° C./second in the heating before the press forming. Hot pressing method for plated steel sheet. The method of hot pressing a plated steel sheet for hot pressing according to claim 4 , wherein the heating before press forming is energization heating or induction heating.

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