WO2017017905A1

WO2017017905A1 - Method for producing hot-pressed member

Info

Publication number: WO2017017905A1
Application number: PCT/JP2016/003196
Authority: WO
Inventors: 中島　清次; 安藤　聡
Original assignee: Ｊｆｅスチール株式会社
Priority date: 2015-07-29
Filing date: 2016-07-05
Publication date: 2017-02-02
Also published as: CN107921509A; KR20180021125A; JPWO2017017905A1; KR102050175B1; EP3330016A1; MX2018001125A; EP3330016A4; JP6409878B2; US20180216219A1; EP3330016B1

Abstract

Provided is a method for producing a hot-pressed member having excellent surface appearance, which enables stable production of a hot-pressed member that has a uniform and good surface appearance without causing a significant increase of the cost. In a method for producing a hot-pressed member wherein hot pressing and cooling are performed after heating a galvanized steel sheet within a temperature range from the Ac3 transformation point to 1,000°C, the galvanized steel sheet is subjected to a surface purification treatment before the heating. In a method for producing a hot-pressed member wherein a galvanized steel sheet is heated within a temperature range from the Ac3 transformation point to 1,000°C and cooled after cold pressing the galvanized steel sheet, the galvanized steel sheet is subjected to a surface purification treatment before the heating. The galvanized steel sheet is preferably a Zn-Ni alloy plated steel sheet which contains 10-25% by mass of Ni with the balance made up of Zn and unavoidable impurities, while having a plating layer on one surface or both surfaces, with the adhesion amount per one surface being 10-90 g/m².

Description

Manufacturing method of hot press member

The present invention relates to a method for manufacturing a hot press member suitable for application to an undercarriage member or a vehicle body structural member of an automobile.

Conventionally, many undercarriage members and body structural members of automobiles are manufactured by pressing a steel plate having a predetermined strength. In recent years, from the viewpoint of the preservation of the global environment, there has been a strong desire to reduce the weight of automobile bodies, and efforts have been made to increase the strength of steel sheets to be used and to reduce their thickness. However, since press workability decreases with increasing strength of the steel sheet, it is often difficult to process the steel sheet into a desired member shape.

In response to the above, Patent Document 1 discloses a hot press that enables both easy processing and high strength by simultaneously processing a heated steel sheet using a die and a punch and simultaneously quenching. Has been proposed. However, in this hot press, the steel plate is heated to a high temperature of around 950 ° C. before hot pressing, so scale (iron oxide) is generated on the surface of the steel plate and the scale peels off during hot pressing. There is a problem that the mold is damaged or the surface of the member after hot pressing is damaged. In addition, the scale remaining on the surface of the member also causes poor appearance and poor paint adhesion. For this reason, the scale on the surface of the member is usually removed by processing such as pickling or shot blasting. However, this complicates the manufacturing process and reduces productivity.

Furthermore, excellent corrosion resistance is required for automobile suspension members and body structure members. However, since the hot press member manufactured by the process as described above is not provided with a rust preventive film such as a plating layer, the corrosion resistance is very insufficient.

In view of the above, there is a demand for hot pressing technology that can suppress the formation of scale during heating before hot pressing and improve the corrosion resistance of members after hot pressing, and a coating such as a plating layer on the surface. Steel plates provided with a hot pressing method using the same have been proposed.

For example, Patent Document 2 discloses a hot pressed member excellent in corrosion resistance in which a steel sheet coated with Zn or a Zn base alloy is hot pressed and a Zn—Fe base compound or a Zn—Fe—Al base compound is provided on the surface. A manufacturing method is disclosed.

Patent Document 3 describes a hot pressed member excellent in scale resistance, coating adhesion, post-coating corrosion resistance, and hydrogen penetration resistance, corresponding to the Ni diffusion region on the surface layer of the steel sheet and the γ phase of Zn—Ni alloy. A hot press member having an intermetallic compound layer and a ZnO layer is disclosed.

Furthermore, Patent Document 4 discloses a steel sheet for hot pressing in which a ZnO layer that suppresses evaporation of zinc is formed in advance on the surface layer of a zinc-based plating layer. By using this steel sheet, the appearance of a pressed product is disclosed. It has been shown that a hot press-molded article having good coating film adhesion and excellent corrosion resistance after coating can be obtained.

British Patent No. 1490535 Japanese Patent No. 3663145 Japanese Patent No. 4849186 Japanese Patent No. 3582511

As disclosed in the above prior art, the use of a galvanized steel sheet as a steel sheet for hot pressing is effective in improving corrosion resistance. However, since the melting point of zinc is 419 ° C. and the boiling point is 907 ° C., both of them are low, so in the heating process before hot pressing, the zinc in the plating layer melts and the zinc evaporates from the plating layer. It has been difficult to stably produce a hot press member having a surface appearance.

For example, a hot-pressed member manufactured by the method described in Patent Document 2 uses a galvanized steel sheet or a galvanized aluminum-plated steel sheet having a low melting point. Therefore, in the heating step before hot pressing, the plating layer is melted or zinc is evaporated. Occurs violently. As a result, a hot press member having a uniform and good surface appearance, such as a hot-pressed member finally obtained having a patchy non-uniform appearance or many white or black spot-like defects, is obtained. Was difficult. In addition, in the spot-like defect part, not only the surface appearance problem but also the paint adhesion is poor, so a technique for preventing the spot-like defect has been eagerly desired, but no effective countermeasure has been proposed so far. It was.

Since the hot press member described in Patent Document 3 is manufactured using a steel plate having a Zn—Ni alloy plating layer having a melting point higher than that of zinc, the hot press member is hotter than when using a galvanized steel plate or a galvanized aluminum plated steel plate. Although the surface appearance of the pressed member is improved, it has not been able to completely prevent the occurrence of local point defects.

When the steel sheet for hot pressing described in Patent Document 4 was used, the surface appearance of the hot pressing member was improved to some extent by the action of the ZnO layer formed on the surface layer. However, there is still a problem that a local point defect is generated at a portion where the formation process of the ZnO layer is not uniform. In addition, the ZnO layer forming process needs to be performed by a method such as an oxidation process by heat, a contact process with a solution, an electrolytic process in an aqueous solution, and a coating and drying process of a solution, resulting in a significant increase in cost. there were.

The present invention has been made for the purpose of solving the problems of the prior art as described above, and can stably produce a hot press member having a uniform and good surface appearance without incurring a significant cost increase. It aims at providing the manufacturing method of the hot press member excellent in the surface external appearance which enables manufacture.

In order to solve the above-mentioned problems, the present inventors diligently studied a method for manufacturing a hot press member having an excellent surface appearance. First, the state of occurrence of point defects generated on the surface of a hot press member was examined. As a result, even when the same type of galvanized steel sheet is heated under the same conditions, it has been found that point defects do not occur at a certain position and may occur more or less frequently. did. In addition, a hot-pressed steel sheet having a Zn—Ni alloy plating layer with a higher melting point than a zinc-based steel sheet with a relatively low melting point, such as a hot-dip galvanized steel sheet or an alloyed hot-dip galvanized steel sheet, is used. However, it was found that the point defects cannot be completely prevented even in the case of a Zn—Ni alloy-plated steel sheet.

From these facts, the occurrence of point defects was not determined only by the type of plating and heating conditions, but the surface was soiled or cleaned based on the hypothesis that other factors such as surface contamination were involved. Later, a verification experiment was conducted in which the galvanized steel sheet was heated. As a result, it was found that the point defects generated on the surface of the hot press member were caused by dirt such as dust, dust, fingerprints, etc. adhering to the surface of the plating layer. That is, in the heating step before hot pressing, the deposits derived from these dirt components burn and cause a local temperature rise, thereby destroying the ZnO layer covering the surface of the zinc-based plating layer. Thus, it became clear that the evaporation of zinc was promoted and the scale was generated in this part. And it discovered newly that generation | occurrence | production of a point defect could be suppressed remarkably by performing the surface cleaning process before a heating process in order to remove these stain | pollution | contamination components. Furthermore, the effect of suppressing the point defects by the surface cleaning treatment prior to heating is not only effective in the process of hot pressing and cooling after heating the zinc-based plated steel sheet, After the press working, it was found that it has an effect even in the process of heating and cooling, and the present invention has been completed.

The manufacturing method of the hot press member of the present invention has been made based on such knowledge, and the gist thereof is as follows.
[1] A method for manufacturing a hot pressed member in which a zinc-based plated steel sheet is heated to a temperature range of Ac3 transformation point to 1000 ° C., and then hot-pressed and cooled. A method for producing a hot-pressed member excellent in surface appearance for performing surface cleaning treatment.
[2] A method for producing a hot pressed member in which a zinc-based plated steel sheet is cold-pressed and then heated to a temperature range of Ac3 transformation point to 1000 ° C. and cooled.
Prior to the heating, a method for producing a hot pressed member having an excellent surface appearance that performs a surface cleaning process on a zinc-based plated steel sheet.
[3] The galvanized steel sheet contains 10 to 25% by mass of Ni, the balance is made of Zn and unavoidable impurities, and a coating layer having an adhesion amount per side of 10 to 90 g / m ² is provided on one side or both sides. The manufacturing method of the hot press member as described in [1] or [2] which is a Zn-Ni alloy plating steel plate which has.
In addition, in this specification,% which shows the component of steel, and% which shows the component of plating are all the mass%.

According to the present invention, it is possible to stably manufacture a hot press member having a uniform and good surface appearance without incurring a significant cost increase. The hot press member manufactured according to the present invention is suitable for an automobile suspension member and a vehicle body structural member.

FIG. 1 is a view showing a typical appearance of a hot-pressed member, and is an appearance photograph of (a) a good appearance product and (b) a point defect generation product, respectively. FIG. 2 is a view showing a typical appearance of a point defect, and is an enlarged photograph of (a) a white defect and (b) a black defect, respectively.

1) Zinc-based plated steel sheet The method for producing a hot-pressed member of the present invention uses a zinc-based plated steel sheet having a zinc-based plated layer on one or both surfaces of the steel sheet surface. Examples of zinc-based plating include hot dip galvanizing, alloyed hot dip galvanizing, hot dip zinc-aluminum alloy plating, hot dip zinc-aluminum-magnesium alloy plating, electrogalvanizing, and electrogalvanizing-nickel alloy plating. The known zinc-based plating containing zinc is applicable.

The coating amount on the surface of these galvanized steel sheets is preferably 10 to 90 g / m ² per side. If the amount of adhesion per side (hereinafter sometimes simply referred to as the amount of adhesion) is 10 g / m ² or more, the corrosion resistance will not be insufficient. On the other hand, if the adhesion amount is 90 g / m ² or less, the cost is not increased. A more preferable adhesion amount is 20 to 80 g / m ² . The adhesion amount can be obtained by a wet analysis method. Specifically, for example, the entire plating layer of a test piece with a known adhesion area is dissolved in an aqueous solution obtained by adding 1 g / L of hexamethylenetetramine as an inhibitor to a 6% by mass hydrochloric acid aqueous solution. What is necessary is just to obtain | require the adhesion amount.

Among the zinc-based plated steel sheets, a Zn-Ni alloy-plated steel sheet having a plating layer containing 10 to 25% by mass of Ni and the balance of Zn and inevitable impurities on one side or both sides is preferable. When the Ni content in the plating layer is 10 to 25% by mass, the phase structure of the plating layer becomes a γ phase, and since this γ phase has a high melting point of 881 ° C., the effect of suppressing the occurrence of point defects Becomes more prominent. Note that the γ phase has a crystal structure of Ni ₂ Zn ₁₁ , NiZn ₃ , or Ni ₅ Zn ₂₁ and can be confirmed by an X-ray diffraction method. Here, a base plating layer such as a plating layer mainly composed of Ni may be provided below the plating layer.
2) Underlying steel plate In order to obtain the hot-pressed member of the present invention, as the underlying steel plate of the zinc-based plating layer, for example, C: 0.15-0.50%, Si: 0.05-2. 00%, Mn: 0.5 to 3.0%, P: 0.10% or less, S: 0.05% or less, Al: 0.10% or less, N: 0.010% or less, the balance Can be used a hot-rolled steel sheet or a cold-rolled steel sheet having a composition composed of Fe and inevitable impurities. When a hot-rolled steel sheet or a cold-rolled steel sheet having such a component composition is used as the base steel sheet, a hot-pressed member that can obtain the required high strength such as having a strength of 980 MPa or more can be obtained.
The reason for limitation of each component composition is demonstrated below.

C: 0.15-0.50%
C is an element that improves the strength of steel. In order to increase the tensile strength of the hot-pressed member (hereinafter sometimes referred to as TS) to 980 MPa or more, the amount needs to be 0.15% or more. is there. On the other hand, if the amount of C exceeds 0.50%, the blanking workability of the raw steel plate is significantly lowered. Accordingly, the C content is preferably 0.15 to 0.50%.

Si: 0.05-2.00%
Si, like C, is an element that improves the strength of steel. To increase the TS of the hot-pressed member to 980 MPa or more, the amount needs to be 0.05% or more. On the other hand, when the amount of Si exceeds 2.00%, the occurrence of surface defects called red scale during hot rolling is remarkably increased, the rolling load is increased, and the ductility of the hot rolled steel sheet is deteriorated. Further, if the Si content exceeds 2.00%, the plating processability may be adversely affected when a plating process for forming a plating film mainly composed of Zn or Al on the steel sheet surface is performed. Accordingly, the Si content is preferably 0.05 to 2.00%.

Mn: 0.5 to 3.0%
Mn is an element effective for suppressing the ferrite transformation and improving the hardenability, and also reduces the Ac ₃ transformation point, so that it is an effective element for lowering the heating temperature before hot pressing. is there. In order to exhibit such an effect, the amount needs to be 0.5% or more. On the other hand, when the amount of Mn exceeds 3.0%, it segregates and the uniformity of the characteristics of the raw steel plate and hot pressed member is lowered. Therefore, the amount of Mn is preferably 0.5 to 3.0%.

P: 0.10% or less When the amount of P exceeds 0.10%, the properties of the steel plate and the hot press member as materials are segregated and the uniformity is deteriorated, and the toughness is also significantly reduced. Therefore, the P content is preferably 0.10% or less.

S: 0.05% or less When the amount of S exceeds 0.05%, the toughness of the hot pressed member is lowered. Therefore, the amount of S is preferably 0.05% or less.

Al: 0.10% or less When the Al content exceeds 0.10%, blanking workability and hardenability of the steel plate as a raw material are lowered. Therefore, the Al content is preferably 0.10% or less.

N: 0.010% or less When the N content exceeds 0.010%, nitride of AlN is formed during hot rolling or heating before hot pressing, and blanking workability and hardenability of the raw steel sheet. Reduce. Accordingly, the N content is preferably 0.010% or less.

The balance is Fe and inevitable impurities. Further, in addition to the above component composition, it was selected from Cr: 0.01 to 1.0%, Ti: 0.01 to 0.20%, and B: 0.0005 to 0.0800% for the following reasons. It is preferable that at least one kind or Sb: 0.003 to 0.030% is contained individually or simultaneously.

Cr: 0.01 to 1.0%
Cr is an element effective for strengthening steel and improving hardenability. In order to exhibit such an effect, the Cr content is preferably 0.01% or more. On the other hand, if the Cr content exceeds 1.0%, the cost is significantly increased, so the upper limit is preferably set to 1.0%.

Ti: 0.01-0.20%
Ti is an element effective for strengthening steel and improving toughness by refining. Further, it is also an element effective for forming a nitride in preference to B described below and exhibiting the effect of improving hardenability by solid solution B. Therefore, the Ti amount is preferably 0.01% or more. However, if the amount of Ti exceeds 0.20%, the rolling load during hot rolling increases extremely, and the toughness of the hot pressed member decreases, so the upper limit may be 0.20%. preferable.

B: 0.0005 to 0.0800%
B is an element effective for improving the hardenability during hot pressing and toughness after hot pressing. In order to achieve such effects, the B content is preferably 0.0005% or more. On the other hand, if the amount of B exceeds 0.0800%, the rolling load at the time of hot rolling is extremely increased, and a martensite phase and a bainite phase are generated after hot rolling to cause cracking of the steel sheet. The upper limit is preferably 0.0800%.

Sb: 0.003 to 0.030%
Sb has an effect of suppressing a decarburized layer generated in the surface layer portion of the steel sheet between the time when the galvanized steel sheet is heated and before hot pressing and cooling. In order to exhibit such an effect, the amount needs to be 0.003% or more. On the other hand, if the amount of Sb exceeds 0.030%, the rolling load increases and the productivity is lowered. Therefore, the Sb content is preferably 0.003 to 0.030%.
3) Hot press process In the manufacturing method of the hot press member of this invention, a hot press member is manufactured by using the process of either of the following two aspects as a hot press process.

The first aspect is a method of manufacturing a hot press member in which a zinc-based plated steel sheet is heated to a temperature range of Ac 3 to 1000 ° C., and then hot pressed and cooled. In a hot press process called a direct process, is there. When the heating temperature is less than the Ac3 transformation point, the steel sheet is not sufficiently quenched, and the desired strength may not be obtained. Further, when the heating temperature exceeds 1000 ° C., not only is it uneconomical in energy, but also the occurrence of point defects becomes significant, making it difficult to produce a hot pressed member having a uniform and good surface appearance. Become. The cooling after hot pressing may be performed using a mold simultaneously with the hot pressing, or may be performed using a coolant such as water at the same time as or immediately after the hot pressing.

The second aspect is a method for producing a hot pressed member in which a zinc-based plated steel sheet is cold-pressed and then heated to a temperature range of Ac3 transformation point to 1000 ° C. and then cooled, which is called an indirect process. This is a hot pressing process. In this step, cold pressing is first performed before heating the galvanized steel sheet. Next, the cold-pressed member is heated and then cooled. The heating temperature is in the temperature range of Ac3 transformation point to 1000 ° C. for the same reason as described above. Cooling may be performed using a mold for cooling the member, or may be performed using a coolant such as water. Moreover, you may perform the additional process by a hot press, when cooling using a metal mold | die.

In addition, the heating temperature here means the highest temperature reached of the steel sheet. Examples of the heating method include heating by an electric furnace or a gas furnace, flame heating, energization heating, high frequency heating, induction heating, and the like.
4) Surface cleaning treatment In the method for producing a hot-pressed member of the present invention, zinc is coated for the purpose of removing dirt, dust, fingerprints and the like adhering to the surface of the plating layer before heating the zinc-based plated steel sheet. The surface-cleaning treatment of the galvanized steel sheet is performed. This surface cleaning treatment is an important requirement in the present invention. When this surface cleaning treatment is not performed, point defects are generated as shown in FIG. However, when the surface cleaning treatment is performed, a product having a good appearance can be produced as shown in FIG. As shown in FIG. 2 (a), the point defects include white defects which are traces of destruction of the ZnO layer covering the surface of the zinc-based plating layer and intense zinc evaporation, or FIG. 2 (b). As shown in Fig. 2, there is a black defect, etc., in which the scale of the underlying steel plate is further oxidized in the white defect part, and any point-like defect not only impairs the surface appearance but also deteriorates the coating adhesion, so the surface is cleaned. It is necessary to suppress point defects as much as possible by performing the treatment. As described above, in the present invention, the surface cleaning process is a process for removing a point-like defect.

Since the surface cleaning treatment needs to be performed prior to the heating step, in the first embodiment (the hot press working after heating the zinc-based plated steel sheet to the temperature range of Ac3 transformation point to 1000 ° C.), the steel sheet coil It is necessary to carry out the surface cleaning treatment in the state of the above, or in the state of the steel plate sheet or steel plate blank cut out from the steel plate coil. In the second aspect (after the zinc-plated steel sheet is cold-pressed and heated to a temperature range of Ac3 transformation point to 1000 ° C.), the state of the steel sheet coil, the steel sheet sheet cut from the steel sheet coil or the steel sheet blank The surface cleaning process can be performed in the state of the above, or the surface cleaning process can be performed in the state of the member after the cold pressing. In both the first aspect and the second aspect, it is preferable to perform the surface cleaning treatment as much as possible immediately before heating. Further, since the treatment is easy and the surface cleaning effect is high, it is preferable to perform the surface cleaning treatment in the state of the steel plate blank.

The method of the surface cleaning treatment is not limited as long as it is a method capable of removing dirt, dust, fingerprints and the like adhering to the surface of the plating layer. For example, a method of wiping the steel sheet surface with a cloth cloth, a method of brushing the steel sheet surface using a brush such as nylon, a method of brushing the surface after applying a liquid that does not harm the steel sheet such as cleaning oil to the steel sheet surface, Examples include alkali degreasing and solvent degreasing. Cleaning methods such as cleaning oil brushing and brushing, alkali degreasing, solvent degreasing, etc., bringing the liquid into contact with the steel plate surface is more effective than physical methods such as wiping or brushing with cloth cloth. Therefore, a method of bringing a liquid into contact with the steel plate surface is preferable from the viewpoint of completely cleaning the steel plate surface. However, when alkaline degreasing is performed as a surface cleaning treatment, if the pH of the alkaline degreasing solution is 12.5 or more, the action of dissolving the zinc-based plating layer itself is too strong. The generation is promoted, and the amount of plating is reduced to deteriorate the corrosion resistance. Therefore, when alkali degreasing is performed as the surface cleaning treatment, the pH of the alkaline degreasing solution is less than 12.5. Furthermore, the cost required for the surface cleaning process is preferably low. If you have a combination of cleaning oil coating and brushing as equipment for cold pressing, this equipment can be used for hot pressing and can be processed at low cost and with a high cleaning effect. Therefore, it is preferable.

As a base steel plate, in mass%, C: 0.23%, Si: 0.25%, Mn: 1.2%, P: 0.01%, S: 0.01%, Al: 0.03%, A component composition containing N: 0.005%, Cr: 0.2%, Ti: 0.02%, B: 0.0022%, Sb: 0.008%, with the balance being Fe and inevitable impurities. A cold rolled steel sheet having an Ac3 transformation point of 820 ° C. and a thickness of 1.6 mm was used. On the surface of this cold-rolled steel sheet, hot dip Zn plating, hot dip Zn—Al alloy plating (Al content: 55% by mass), alloyed hot dip Zn plating (Fe content: 10% by weight), electric Zn plating, electric Zn— One of Ni alloy plating (Ni content: 12% by mass) was applied and sheared to a size of 200 mm × 300 mm to obtain a test material.

The surface specimen was subjected to surface cleaning treatment. As the surface cleaning treatment, one of A: cloth wiping, B: brushing, C: combined use of cleaning oil coating and brushing, D: alkaline degreasing (pH is 12.0), E: solvent degreasing was performed. . As comparative examples, F: a test material that had been subjected to strong alkali degreasing (pH was 13.0) and a test material that was not subjected to surface cleaning treatment were also prepared.

Cloth wiping was performed by manually wiping the surface of the test material twice with a cloth waste (cleaning white knitted cloth (cotton), manufactured by Nippon Wes Co., Ltd.).

The brushing was performed by manually wiping the surface of the specimen twice twice using a nylon fiber-implanted brush (SK linear brush, Showa Kogyo Co., Ltd.).

The combination of cleaning oil coating and brushing is performed by applying a cleaning rust preventive oil (Preton R352L, manufactured by Sugimura Chemical Co., Ltd.) to the surface of the test material so that the amount of coating is 2.0 g / m ² . Brushing was performed as described above.

Alkaline degreasing was performed by spraying an alkali degreasing solution (CL-N364S, 20 g / L, 60 ° C., manufactured by Nihon Parkerizing Co., Ltd.) for 10 seconds on the test material, and then washing and drying. The pH of the alkaline degreasing solution at this time was 12.0.

Solvent degreasing was performed by immersing the test material in a 1: 1 mixed solvent of toluene and ethanol, performing ultrasonic cleaning for 1 minute, and then drying.

The strong alkaline degreasing performed as a comparative example was performed by immersing the test material in a strong alkaline degreasing solution (NaOH aqueous solution, pH adjusted to 13.0, 50 ° C.) for 5 seconds, followed by washing with water and drying.

Next, it is heated in an electric furnace with a furnace temperature of 950 ° C. and heated so that the in-furnace time is 8 minutes, and immediately after the heating is completed, it is taken out from the electric furnace and sandwiched between Al flat molds (cooling rate) 50 ° C./s).

The surface appearance was evaluated by the following method for the test material (zinc-based plated steel sheet) obtained as described above.

In order to improve the accuracy of determining the surface appearance, 10 samples were produced under the same conditions. The state of the point-like defect of the sample was visually observed, the surface appearance was judged according to the following judgment criteria, and ◎ or ○ was judged as acceptable. In this example, the effect of the present invention was evaluated by evaluating the surface appearance after heating and cooling the flat plate as described above, without performing actual press molding by the direct process or the indirect process. However, since the surface appearance after heating and cooling is determined by the presence or absence of dirt components on the surface and its removal effect, this evaluation result is the same as the evaluation result of the surface appearance after actual press molding by both processes. It is.
A: 10 out of 10 samples in which no point defects occurred ○: 8-9 in 10 samples in which no point defects occurred Δ: 10 samples in which no point defects occurred Medium 5 to 7 sheets ×: Samples in which no point defects were generated 0 to 4 out of 10 Table 1 shows the evaluation results of the surface appearance together with the manufacturing conditions.

It can be seen that all of the zinc-based plated steel sheets (invention examples) manufactured by performing the surface cleaning treatment by the manufacturing method of the present invention are excellent in surface appearance. In particular, it can be seen that the surface appearance is most excellent when an electric Zn—Ni alloy plated steel sheet is used. On the other hand, the zinc-based plated steel sheet (comparative example) that has been subjected to strong alkaline degreasing with a pH of 12.5 or higher and the zinc-based plated steel sheet (comparative example) that has not been subjected to surface cleaning treatment are both poor in surface appearance. ing.

Claims

A method for producing a hot pressed member in which a zinc-based plated steel sheet is heated to a temperature range of Ac3 transformation point to 1000 ° C., followed by hot pressing and cooling.
Prior to the heating, a method for producing a hot pressed member having an excellent surface appearance that performs a surface cleaning process on a zinc-based plated steel sheet.
A method for producing a hot-pressed member in which a zinc-based plated steel sheet is cold-pressed, heated to a temperature range of Ac3 transformation point to 1000 ° C., and cooled.
Prior to the heating, a method for producing a hot pressed member having an excellent surface appearance that performs a surface cleaning process on a zinc-based plated steel sheet.
The zinc-based plated steel sheet contains 10 to 25% by mass of Ni, the remainder is made of Zn and inevitable impurities, and has a plating layer on one side or both sides with a coating amount of 10 to 90 g / m 2 per side. It is a Ni alloy plating steel plate, The manufacturing method of the hot press member of Claim 1 or 2.