WO2018062341A1

WO2018062341A1 - Steel sheet for motorcycle fuel tank, and fuel tank member

Info

Publication number: WO2018062341A1
Application number: PCT/JP2017/035099
Authority: WO
Inventors: 鈴木　幸子; 安藤　聡; 千代子多田
Original assignee: Ｊｆｅスチール株式会社
Priority date: 2016-09-30
Filing date: 2017-09-28
Publication date: 2018-04-05
Also published as: CN109642330A; CN109642330B; JPWO2018062341A1; JP6354915B1; BR112019004095A2; WO2018061061A1

Abstract

The purpose of the present invention is to obtain: a steel sheet for a motorcycle fuel tank, the sheet being excellent in terms of press workability in a tank production process, seam weldability and corrosion resistance of the inner surface of a tank, and especially corrosion resistance (hereinafter abbreviated to moisture resistance) of gas phase parts on the inner surface of a tank, and being suitable for use in motorcycles having excellent global procurement potential in emerging markets; and a fuel tank member. This steel sheet for a motorcycle fuel tank comprises a one-side-plated steel sheet, has a zinc plating layer having a coating weight of 1-70 g/m² on a base steel sheet having an arithmetic-mean roughness Ra of 0.5-2.0 μm, with the zinc plating layer containing 5-1000 ppm by mass of Ni, and has a chromate coating film on the zinc plating layer, with the minimum film thickness of the chromate coating film being 10-100 nm.

Description

Steel plate and fuel tank member for motorcycle fuel tank

The present invention is an automatic machine that has excellent press workability in the tank manufacturing process, seam weldability, corrosion resistance on the inner surface of the tank when the tank is used, corrosion resistance, particularly moisture resistance, and global procurement in emerging markets. TECHNICAL FIELD The present invention relates to a motorcycle fuel tank steel plate and a fuel tank member that are optimal for motorcycles.

In recent years, with the growing demand for motorcycles in emerging countries, particularly in the Asian region, the production volume has increased significantly. In Asia, cold rolled steel plates (bare steel plates without plating) have been used as fuel tank steel plates for motorcycles, but in recent years, the trend of plating has been rapidly increasing. This is because the engine for motorcycles has become FI (Fuel Injection) as a result of compliance with EURO3 environmental regulations, so it is necessary to take measures against clogging of the FI device. In order to prevent red rust from clogging the FI device, The purpose is to improve corrosion resistance (red rust resistance) by using a plated steel sheet and to reduce red rust generated in the fuel tank.

As a plated steel plate for a fuel tank for a motorcycle, for example, a single-side plated steel plate with zinc (Zn) -nickel (Ni) alloy plating only on the inner surface side of a tank member, or Zn-Ni alloy plating in Japan. There is a single-sided plated steel sheet that is further chromated on the upper layer. As a technique for producing this fuel tank steel plate, for example, in Patent Document 1, an electric Zn—Ni alloy plating layer containing 5 to 30% by mass of Ni is provided on at least one side of the steel plate at 1 to 40 g / m ² per side. In the upper layer of the plating layer, chromic acid having a mass ratio (trivalent chromium) / (total chromium) of more than 0.5 and a mass ratio (phosphoric acid) / (total chromium) of 0.1 are formed on the upper layer of the plating layer. A method for producing a steel plate for a fuel tank heated by applying a chromate treatment solution containing phosphoric acid and an organic reducing agent of ˜5.0 is disclosed.

In addition, Patent Document 2 discloses that a steel plate for a fuel tank having excellent press formability even under severe press conditions in a fuel tank manufacturing process, containing 5 to 1000 ppm by mass of Ni on the inner surface of the tank. A pure galvanized layer having an adhesion amount of 1 to 150 g / m ² , and a chromic acid having a mass ratio (trivalent chromium) / (total chromium) of more than 0.5 on the pure galvanized layer; A fuel tank having a chromate film formed by applying a chromate treatment liquid containing phosphoric acid having a mass ratio (phosphoric acid) / (total chromium) of 0.1 to 5.0 and an organic reducing agent, followed by heating. A method for manufacturing a steel sheet is disclosed.

Japanese Patent No. 4654714 JP 2013-221206 A

When motorcycles are locally produced in emerging countries, especially in the Asian region, the number of materials procured locally is increasing rapidly. One example is steel plates for fuel tanks. Patent Documents 1 and 2 that disclose a method for manufacturing a steel plate for a fuel tank for a motorcycle do not cause a problem in Japan, but the following problem may occur when manufacturing in an emerging country.

The steel sheet for a fuel tank made of an electric Zn—Ni alloy plating material described in Patent Document 1 is excellent in press workability and seam weldability when manufactured into a tank, and excellent in corrosion resistance as a fuel tank. However, electric Zn-Ni alloy plating is expensive in chemicals, difficult to manage chemicals (concentration, replenishment method, etc.), and requires equipment for that purpose. Problems sometimes occurred from the viewpoint.

Therefore, as a fuel tank material for emerging countries, a galvanized steel sheet that is more advantageous than electric Zn-Ni alloy plating in terms of cost, chemical solution management, and current efficiency, and has excellent global procurement ability is a fuel tank. It is thought that it is suitable for materials for use.

On the other hand, when a galvanized steel sheet is used as the fuel tank material, the surface of the plating layer is easily damaged by press working. In the damaged portion, even if the plating layer disappears or the plating layer remains, the actual adhesion amount is remarkably reduced, so that the corrosion resistance is lowered.

As a material that has solved such a problem, a material by galvanization containing 5 to 1000 mass ppm of Ni described in Patent Document 2 has been proposed. Patent Document 2 is excellent in press workability, seam weldability, and inner surface corrosion resistance (deterioration gasoline resistance) as a fuel tank, as in Patent Document 1, as in Patent Document 1.

However, as a problem peculiar to the Asian region, rust in the gas phase that is not in contact with gasoline inside the fuel tank has occurred as a new problem. This is considered to occur when the gas phase inside the fuel tank has been under high humidity for a long time or when dew condensation has occurred for a long time. Often occurs.

The steel sheets for fuel tanks described in Patent Documents 1 and 2 are excellent in resistance to deterioration gasoline on the inner surface side of the fuel tank. However, the corrosion that occurs on the inner surface side is caused by the condensation water generated in the gas phase of the fuel tank falling and collecting at the bottom of the fuel tank, or by rainwater entering the fuel tank. A water layer is formed, and organic acid in deteriorated gasoline and poor gasoline is concentrated in this water layer and corrosion occurs. What is rust generated in the air layer newly generated in the Asian region? Is different.

The present invention has been made in view of such circumstances, and press workability in the tank manufacturing process, seam weldability, and corrosion resistance on the tank inner surface side, particularly corrosion resistance in the gas phase portion on the tank inner surface side (hereinafter referred to as moisture resistance). It is an object of the present invention to provide a steel plate and a fuel tank member for motorcycle fuel tanks that are optimal for motorcycles that are superior to each other, and that have excellent global procurement in emerging markets.

In order to examine measures to prevent damage to the plating layer during press working in the fuel tank member manufacturing process, first, test conditions that can simulate this press working were examined. As a result, it was found by the following sliding test that the damage of the plating layer that occurs in actual pressing can be reproduced.
<Test conditions>
-Contact area between mold and sample: 3mm x 10mm
・ Sliding distance: 100mm
・ Pressure: 200 MPa
・ Sliding speed: 1.0 m / min
Lubricant: Antirust oil As a result of various examinations under the above test conditions, in order to prevent damage to the plating layer, arithmetic average roughness Ra (JIS B 0601-2001) (hereinafter referred to as Ra) of the surface of the base steel plate ) Was found to be controlled to 0.5 μm or more.

Furthermore, when applying a galvanized steel sheet to the fuel tank material, it is necessary to consider the corrosion resistance on the inner surface of the tank (hereinafter sometimes referred to as corrosion resistance). Corrosion resistance is improved by having a galvanized layer on the surface, but when the fuel is left in the fuel tank for a long period of time, when poor fuel is used, or when dew condensation occurs due to a difference in temperature between day and night The corrosive environment in the tank becomes severe due to organic acids and moisture mixed in the fuel. Therefore, as a result of examining the anti-corrosion measures in the fuel tank, it is possible to perform further chromate treatment on the galvanized steel sheet in which the galvanized layer is formed on the Ra controlled steel sheet, and to control the minimum film thickness of the chromate layer. It was found that it is extremely effective in improving

The chromate solution was applied to steel sheets with different roughness so that the amount of Cr adhered per unit area was the same, and the cross section of the steel sheet after baking and drying was observed with a TEM. It has been found that the thickness distribution is different, which affects the internal corrosion resistance, moisture resistance, press workability, and seam weldability. Characteristic cross sections are classified into three, and a schematic diagram of each cross section is shown in FIG. FIG. 2A shows the case where Ra exceeds 2.0 μm, and the case where the film thickness of the chromate layer on the uneven portion of the base steel sheet roughness is less than 10 nm. FIG. 2B shows a case where Ra is 0.5 to 2.0 μm (in the scope of the present invention) and the thickness of the chromate layer of the convex portion is 10 nm or more. FIG. 2C shows the case where Ra is less than 0.5 μm, and the case where the film thickness of the chromate layer of the convex portion exceeds 100 nm. In addition, a base steel plate refers to the steel plate before plating. Further, the film thickness of the chromate layer of the convex part here refers to the film thickness (hereinafter referred to as the minimum film thickness of the chromate film) where the film thickness of the chromate layer is partially reduced in the convex part.

In the case of FIG. 2 (a), the convex portion with a thin chromate layer works favorably as a conduction point and the seam weldability is good, but the convex portion is rusted because the effect of the chromate film on the convex portion is not sufficient. As a starting point, both internal corrosion resistance and moisture resistance decreased. In the case of FIG. 2B, the film thickness of the chromate layer was 10 nm or more, and the target level performance of the present invention was shown from the viewpoints of press workability, seam weldability, internal corrosion resistance, and moisture resistance. In the case of FIG.2 (c), since the film thickness of the chromate layer of a convex part exceeded 100 nm, although internal corrosion resistance and moisture resistance are favorable, the energizing point at the time of welding decreased and seam weldability fell extremely. .

As described above, in the past, the chromate adhesion amount was managed by the Cr adhesion amount per unit area. However, as in this time, the steel plate for motorcycle fuel tank and the fuel tank member using the same are not the Cr adhesion amount. It has been found that management by film thickness is extremely important in achieving various performances.

The present invention has been made based on the above findings, and the gist thereof is as follows.
[1] A steel plate for a fuel tank of a motorcycle made of a single-side plated steel plate,
A galvanized layer having an adhesion amount of 1 to 70 g / m ² on a base steel sheet having an arithmetic average roughness Ra of 0.5 to 2.0 μm;
The galvanized layer contains 5 to 1000 ppm by mass of Ni;
Having a chromate film on the galvanized layer,
A steel plate for a motorcycle fuel tank, wherein the chromate film has a minimum film thickness of 10 nm or more and 100 nm or less.
[2] A fuel tank steel plate for a motorcycle made of a single-side plated steel plate,
A galvanized layer having an adhesion amount of 1 to 70 g / m ² on a base steel sheet having an arithmetic average roughness Ra of 0.5 to 2.0 μm;
The galvanized layer contains 5 to 1000 ppm by mass of Ni;
Having a chromate film on the galvanized layer,
A steel plate for a motorcycle fuel tank, wherein the thickness of the chromate film on the uneven surface of the base steel plate roughness is 10 nm or more and 100 nm or less.
[3] A fuel tank member for a motorcycle made of a single-side plated steel plate,
The surface having a galvanized layer with an adhesion amount of 1 to 70 g / m ² on the base steel plate having an arithmetic average roughness Ra of 0.5 to 2.0 μm is the inner surface side of the fuel tank member,
The galvanized layer contains 5 to 1000 ppm by mass of Ni;
Having a chromate film on the galvanized layer,
A fuel tank member having a minimum film thickness of the chromate film of 10 nm or more and 100 nm or less.
[4] A fuel tank member for a motorcycle made of a single-side plated steel plate,
The surface having a galvanized layer with an adhesion amount of 1 to 70 g / m ² on the base steel plate having an arithmetic average roughness Ra of 0.5 to 2.0 μm is the inner surface side of the fuel tank member,
The galvanized layer contains 5 to 1000 ppm by mass of Ni;
Having a chromate film on the galvanized layer,
A fuel tank member, wherein a thickness of the chromate film on the convex and concave portions of the base steel plate roughness is 10 nm or more and 100 nm or less.

In the present invention, excellent seam weldability means that the sample is broken by a peel tensile test method (JIS Z 3141: test method for seam welded joint) as described in the seam weldability of Examples described later. Load is applied, the form of rupture is observed, the form of rupture is a base material rupture, and the welding current is sufficient when the nugget wrap is sufficient and the current is 3 kA or more.
In addition, as described in the inner surface corrosion resistance of the examples described later, and having excellent corrosion resistance on the tank inner surface side when using the tank, the cup obtained by cup drawing with the plating layer side as the punch surface is used as a test material. Degraded gasoline: 30 ml + 3 ml of organic acid aqueous solution (mixed with 100 ppm formic acid + 100 ppm acetic acid) is added to the cup, sealed with stainless steel through a Viton ring to prevent the gasoline from evaporating, and left inside at 40 ° C for 1 month, then generated inside The corrosion resistance is evaluated from the amount of red rust, and the case where no red rust is generated on the side wall of the cup inner surface in contact with the gasoline phase and the bottom of the cup inner surface in contact with the water phase. The side wall of the cup is a part that mainly comes in contact with gasoline, but the bottom of the cup is a part where water accumulates and the organic acid is concentrated. Tend to be low.
Moreover, it is excellent in moisture resistance, the sample which carried out cup squeezing on the same conditions as said inner surface corrosion resistance is set | placed on the conditions of 50 degreeC x 98% RHx360 hours, and the quantity of the rust which generate | occur | produced in the cup side wall part was evaluated, No white rust generation or white rust generation area: less than 5%.
Moreover, being excellent in press workability means that there is little surface damage in a slidability test.
Evaluation of surface damage in the slidability test is as follows. The contact area between the mold and the sample is 3 mm × 10 mm on the plating layer side of each sample, as described in the slidability test of the examples described later. : 100 mm, applied pressure: 200 MPa, sliding speed: 1.0 m / min, lubrication oil: slidability test was conducted under the test conditions of anti-rust oil, and surface damage caused by galling generated on the sample surface after the test The occurrence was observed by observing with a magnifier with a magnification of 10 times.

According to the present invention, each of press workability in the fuel tank manufacturing process, seam weldability, corrosion resistance on the inner surface of the tank when the tank is used, corrosion resistance, particularly moisture resistance, and global procurement in emerging markets. An excellent steel plate and fuel tank member for a motorcycle fuel tank that is excellent for a motorcycle can be obtained.

FIG. 1 is a schematic view of a seam welding apparatus used for a seam weldability test and a cross-sectional view of an electrode (Example). Figures 2 (a) to 2 (c) show the cross-section of a steel sheet after applying a chromate solution to steel sheets of different roughness so that the amount of Cr deposited per unit area is the same and baking and observing them with a TEM. It is the schematic of the cross section explaining the result.

Hereinafter, embodiments of the present invention will be described. In addition, this invention is not limited to the following embodiment.

(Fuel tank member)
A fuel tank member is a product formed into a fuel tank product shape, and usually a plurality of fuel tank members are joined and painted to form a fuel tank product. The fuel tank member of the present invention is a fuel tank member formed by press-forming the steel plate of the present invention.

Further, the surface of the fuel tank member of the present invention has a galvanized layer with a coating amount of 1 to 70 g / m ² and a chromate film on one surface, and the outer surface of the fuel tank member is a steel plate surface. is there. The fuel tank member of the present invention is obtained by pressing a steel plate having a galvanized layer and a chromate film on only one side of the present invention so that the galvanized layer side is the inner surface side of the fuel tank.

(Steel plate roughness)
In the present invention, on the inner surface side of the fuel tank member, the amount of zinc deposited on one side is 1 to 70 g / m ² on a steel plate having a Ra of the steel plate (base steel plate) surface of 0.5 to 2.0 μm. It has a galvanized layer and a chromate film on the galvanized layer.

If Ra is less than 0.5 μm, press formability is insufficient, shoulder galling is likely to occur between the mold and the steel plate during press processing, and press processing cannot be performed. On the other hand, when Ra exceeds 2.0 μm, as described above, the thickness of the chromate layer on the uneven portion of the base steel plate roughness becomes less than 10 nm, and the inner surface corrosion resistance and moisture resistance decrease. Therefore, the steel sheet roughness (Ra) is preferably 0.5 to 2.0 μm.

Ra may be adjusted only on the inner surface of the fuel tank member, but from the viewpoint of press formability, Ra on both surfaces of the steel plate is preferably 0.5 μm or more.

Although the method for controlling the surface roughness of the steel sheet is not particularly specified, it is mainly controlled by changing the roll surface roughness, rolling load and tension at the time of pressure rolling. Examples of the roll processing method include shot dull, laser dull, and electric discharge dull processing.

(Zinc plating layer)
The fuel tank member of the present invention has a galvanized layer on the inner surface side thereof. Since the galvanized layer shows a lower potential than the steel substrate (non-plated (bare) steel plate), even if this plated layer is damaged, the occurrence of red rust (iron rust) can be suppressed by the sacrificial anticorrosive action of zinc. And exhibits excellent corrosion resistance.

The zinc adhesion amount per side of the galvanized layer is 1 to 70 g / m ² . This is because when the zinc adhesion amount is less than 1 g / m ² , there is no effect of improving the corrosion resistance, and when it exceeds 70 g / m ² , seam welding becomes difficult. From the viewpoint of corrosion resistance, 1 g / m ² or more is preferable. From the viewpoint of seam weldability, 50 g / m ² or less is preferable.

Further, in the present invention, 5 to 1000 ppm by mass of Ni is added to the galvanized layer for the purpose of further improving the press workability. It was found that when a galvanized layer containing 5 to 1000 ppm by mass of Ni was used as the plating composition, the initial friction coefficient of press working was low and the occurrence of plating surface damage was small. The galvanizing treatment is performed by a normal method. The galvanized layer of the present invention may contain inevitable impurity elements contained in a normal galvanized layer in addition to the Ni.

(Chromate film)
In the present invention, a chromate film is formed on the aforementioned galvanized layer as a countermeasure against corrosion occurring in a severe corrosive environment on the inner surface side of the fuel tank member and as a countermeasure for improving press formability. By forming a chromate film, it is possible to achieve further improvement in corrosion resistance when in contact with an organic acid or moisture, and it is effective in measures against clogging of FI due to generation of corrosion products. Further, the hard chromate layer has an effect of reducing metal touch between the mold and the galvanized layer, and the press formability is further improved.

The chromate film according to the present invention is a trivalent chromium chromate film that does not contain hexavalent chromium. By forming a chromate film with trivalent chromium, hexavalent chromium is not eluted even when the fuel tank member of the present invention is immersed in boiling water or an alkaline solution. Therefore, even when rainwater or condensed water enters the fuel tank of the fuel tank member of the present invention, hexavalent chromium does not elute therein.

In order to form such a chromate film, chromic acid having a mass ratio of trivalent chromium to total chromium of more than 0.5, phosphoric acid having a mass ratio of 0.1 to 5.0 with respect to total chromium, and an organic reducing agent A chromate treatment solution containing is used. After this chromate treatment solution is applied to the surface of the galvanized layer, the chromate film can be formed by heating so that the steel plate temperature is 120 ° C. or higher.

The chromate treatment liquid is in a state where hexavalent chromium and trivalent chromium are mixed. Among these, hexavalent chromium is reduced to trivalent chromium by reaction with an organic reducing agent during heating after coating. Of these total chromium amounts of hexavalent chromium and trivalent chromium, if the amount of hexavalent chromium is excessive, hexavalent chromium may remain in the chromate film after heating. The mass ratio of the valent chromium is more than 0.5. The mass ratio of phosphoric acid is 0.1 to 5.0 with respect to the total chromium. When the mass ratio of phosphoric acid is less than 0.1, trivalent chromium is polymerized to form a gel-like precipitate. For this reason, the property as a chromate treatment liquid cannot be maintained, and it cannot be applied to the steel sheet. On the other hand, when this ratio exceeds 5.0, phosphoric acid remains excessively in the chromate film, and this phosphoric acid elutes in a wet environment, causing pitting corrosion and blackening of plating.

In the present invention, the chromate treatment solution contains an organic reducing agent in addition to the chromic acid and phosphoric acid. As the organic reducing agent to be contained in the chromate treatment solution, it is preferable to use at least one selected from diols and saccharides. For example, ethylene glycol, saccharose, sucrose and the like are advantageously suitable. This organic reducing agent is preferably contained in the chromate treatment solution so that the mass ratio with respect to the total chromium is 0.1 to 0.4. If it is 0.1 or more, a sufficient reduction effect is obtained, and there is no possibility that hexavalent chromium remains in the chromate film. On the other hand, if it is 0.4 or less, the stability of the chromate treatment liquid cannot be maintained. In addition, it is preferable to add an organic reducing agent to a chromate processing liquid just before apply | coating a chromate processing liquid to a zinc plating layer from a viewpoint of improving the stability of a chromate processing liquid.

Further, the chromate treatment liquid may contain an inorganic inhibitor as necessary for the purpose of improving the corrosion resistance. For example, an inorganic colloid such as silica, ZrO ₂ , TiO ₂ or the like is added as an inorganic inhibitor in a mass ratio of less than 0.05 with respect to the total chromium.

(Minimum film thickness of chromate film)
In the present invention, in order to further improve the corrosion resistance, the cross section of the chromate film was observed with a transmission electron microscope. As a result, the roughness of the surface of the galvanized layer was partially thin and the chromate layer was thin. It was observed that the thickness of the chromate layer was increased in the recesses with a roughness of. Furthermore, as a result of observing the cross section of the chromate film at the initial stage of corrosion, it was found that the portion where corrosion occurred was a convex portion where the chromate film was thin. Therefore, as a result of various analyzes on the film thickness of the chromate film at the initial stage of corrosion, the film thickness where the film thickness of the chromate layer is partially thin at the above-described convex portion, that is, the minimum value of the minimum film thickness of the chromate film. It was found that the corrosion resistance is remarkably improved when the thickness is 10 nm. Therefore, in this invention, the minimum film thickness of a chromate film shall be 10 nm or more. As for the upper limit of the minimum film thickness of the chromate film, thicker is more advantageous for the corrosion resistance. Does not exceed 100 nm.

In order to secure such a minimum chromate film thickness, the Ra of the steel sheet is set to 0.5 to 2.0 μm, and it is achieved by appropriately adjusting the concentration of the chromate treatment liquid and the squeezing pressure of the roll. be able to.

The minimum film thickness of the chromate film can be measured by observing the cross section of the film with a transmission electron microscope and measuring the film thickness on the screen. A sample for observation of the steel sheet on which the chromate film is formed is prepared by the FIB method or the like, and the cross section of the chromate film is observed. Since the steel plate protrusion is the thinnest portion of the chromate film, the thickness of the chromate film at this location is read from the magnification at the time of observation. For example, a 500 mm square sample for measurement is prepared, 10 fields of view are observed, and the minimum film thickness of each chromate film is measured.

(Steel plate for fuel tank)
Next, the steel plate for a fuel tank of the present invention will be described.

The fuel tank steel plate according to the present invention has a galvanized layer with an adhesion amount of 1 to 70 g / m ² on a base steel plate having an arithmetic average roughness Ra of 0.5 to 2.0 μm, as described above for the fuel tank member. The galvanized layer is a steel plate containing 5 to 1000 ppm by mass of Ni, having a chromate film on the galvanized layer, and having a minimum film thickness of 10 nm or more and 100 nm or less.

As the base steel plate, for example, in mass%, C: 0.0007 to 0.0050%, Si: 0.5% or less, Mn: 2.0% or less, P: 0.1% or less, S: 0.00. 015% or less, Al: 0.01 to 0.20%, N: 0.01% or less, or Ti: 0.005 to 0.08%, B: 0.001 to 0.01%, Nb: 0 A cold-rolled steel sheet containing at least one of .0005 to 0.0050% or more and the balance being Fe and inevitable impurities is preferable.

Hereinafter, the reasons for limitation of each component will be described. In the following description, the unit of the content of each element of the steel component composition is “mass%”, and hereinafter, it is simply indicated by “%” unless otherwise specified.

C: 0.0007 to 0.0050%
Since C adversely affects deep drawability, the content is preferably 0.0050% or less. Moreover, if content is 0.0007% or more, the improvement of deep drawability will be recognized, without causing the cost increase of a decarburization process. Therefore, the C content is preferably 0.0007 to 0.0050%.

Si: 0.5% or less Si has an action of increasing the strength of steel, and can be added according to a desired strength. However, if the amount is 0.5% or less, the deep drawability does not deteriorate. Therefore, the Si amount is preferably 0.5% or less.

Mn: 2.0% or less Mn, like Si, has the effect of increasing the strength of steel, so it can be added according to the desired strength. However, if the amount is 2.0% or less, the deep drawability does not deteriorate. Accordingly, the Mn content is preferably 2.0% or less.

P: 0.1% or less P segregates at the grain boundary to strengthen the grain boundary, suppresses cracking of the welded portion, and has an effect of strengthening the steel. However, if the amount is 0.1% or less, the deep drawability does not deteriorate. Therefore, the P content is preferably 0.1% or less. In order to more reliably suppress cracking in the welded portion, it is more preferable that the P content is 0.01 to 0.05%. When the P content is less than 0.01%, the effect of suppressing cracks in the welded portion is not significant. Further, when the P content exceeds 0.05%, the deep drawability tends to decrease.

S: 0.015% or less S adversely affects deep drawability. However, if the amount is 0.015% or less, no adverse effect is observed. Therefore, the S content is preferably 0.015% or less.

Al: 0.01-0.20%
Al is added for deoxidizing steel and improving the yield of carbonitride-forming elements such as Ti. If the amount is 0.01% or more and 0.20% or less, the effect of addition can be obtained, and even if the amount exceeds 0.20%, a greater effect cannot be obtained. Accordingly, the Al content is preferably 0.01 to 0.20%.

N: 0.01% or less N adversely affects deep drawability. However, if the amount is 0.01% or less, no adverse effect is observed. Therefore, the N content is preferably 0.01% or less.

The balance is Fe and inevitable impurities. Here, the amount of inevitable impurities should just be in a normal range, for example, O is 0.010% or less.

In addition to the above components, at least one of Ti: 0.005 to 0.08%, B: 0.001 to 0.01%, Nb: 0.0005 to 0.0050% or more may be added. Good. Addition of at least one of Ti, B, and Nb is suitable for improving deep drawability.

Ti: 0.005 to 0.08%
Ti has the effect of improving deep drawability by forming precipitates with C and N in steel to reduce solid solution C and N. However, if the amount is 0.005% or more and 0.08% or less, the effect can be obtained, and even if the amount exceeds 0.08%, a greater effect cannot be obtained. Therefore, the Ti content is preferably 0.005 to 0.08%.

B: 0.001 to 0.01%
B, like P, has the effect of suppressing cracks in the weld. If the amount is 0.001% or more, the effect is obtained, while if it is 0.01% or less, the deep drawability does not deteriorate. Accordingly, the B content is preferably 0.001 to 0.01%, and more preferably 0.001 to 0.004%.

The reason why B and P suppress cracks in the weld is considered as follows. In other words, the weld crack is presumed to be due to liquid metal embrittlement in which copper (Cu), which is the main component of the electrode, and zinc of the plating component become liquid during welding and enter the steel grain boundaries and embrittle the grain boundaries. . In this respect, since B and P are easily segregated at the grain boundary, the grain boundary is strengthened to suppress such weld cracking.

The other component composition is not particularly limited, but in the case where the crystal grains of the hot-rolled sheet are refined and the deep drawability after cold rolling-annealing is improved, in addition to the above components, Nb: It is preferable to add in the range of 0.0005 to 0.0050%.

Further, the thickness of the steel plate is preferably 0.6 to 2.0 mm. If it is 0.6 mm or more, the strength as a tank can be secured, and if it is 2.0 mm or less, the degree of molding freedom can be secured.

Hereinafter, the present invention will be specifically described by way of examples. The present invention is not limited to these examples.

The steel plate used for the fuel tank member is a cold-rolled steel plate having a thickness of 0.8 mm (mass%, C: 0.0015%, Si: 0.01%, Mn: 0.08%, P: 0.011% , S: 0.008%, Al: 0.05%, N: 0.0019%, Ti: 0.035%, Nb: 0.0030% and B: 0.004%, the balance being Fe and Cold-rolled steel sheet having an inevitable impurity composition). Table 1 shows the results of measuring Ra by adjusting the roughness of the steel sheet by changing the roll surface roughness during rolling. Electrogalvanizing treatment was performed on one surface of this steel sheet to form a galvanized layer having a coating adhesion amount per one surface shown in Table 1 to obtain a galvanized steel sheet.

Some of the obtained galvanized steel sheets were chromated on the surface of the galvanized layer. Specifically, a chromate treatment solution having the composition shown in Table 1 was applied by a roll coater, and then heated so that the maximum reached steel plate temperature was 150 ° C. to form a chromate film. The treatment was carried out by adjusting the concentration of the chromate treatment solution according to the target chromate film thickness. The minimum film thickness of the chromate film is as shown in Table 1.

A fuel tank member can be manufactured by pressing the steel plate for a fuel tank obtained as described above.

Each sample of the obtained fuel tank steel plate was evaluated for chromium elution resistance, slidability, seam weldability, internal corrosion resistance and moisture resistance after forming, and global procurement. Each evaluation method is as follows.

Table 1 shows a conventional example (No. 41) that has a Zn—Ni alloy plating only on the inner surface side of the tank member and a chromate film on the upper layer.

(1) Resistance to chromium elution As a chromium elution resistance evaluation, elution of hexavalent chromium was evaluated for the sample on which the chromate layer was formed.
Based on the boiling water immersion method (JIS K 5400-1990), the chromium adhesion amount of each sample was measured by fluorescent X-rays, and the change rate of the chromium adhesion amount before and after immersion was determined by the following formula. In view of the measurement error when measuring the chromium adhesion amount, it was determined that no hexavalent chromium remained in the chromate film if the change rate of the chromium adhesion amount was within 2.0%.
Change rate (%) = (Amount of chromium before immersion−Amount of chromium after immersion) / Amount of chromium attached before immersion × 100
About change rate (%) obtained by the said measurement, it determined as follows using symbol (circle) (excellent) and symbol x (inferior).
○: Change rate within 2.0% ×: Change rate over 2.0% (2) Slidability test As a press workability evaluation, a slidability test was performed on the plating layer side of each sample. The occurrence of surface damage due to galling that occurred on the surface of the sample after the test was observed and evaluated with a magnifier of 10 times magnification.
<Test conditions>
-Contact area between mold and sample: 3mm x 10mm
・ Sliding distance: 100mm
・ Pressure: 200 MPa
・ Sliding speed: 1.0 m / min
・ Lubricant: Antirust oil ・ Criteria 4: No surface damage
3: Surface damage occurred (less than 5% of sliding part)
2: Surface damage occurred (5% or more and less than 20% of sliding part)
1: Surface damage occurs (more than 20% of sliding parts)
(3) Internal Corrosion Resistance For evaluation of internal corrosion resistance, the corrosion resistance against deteriorated gasoline was evaluated using a cup obtained by cup drawing with the plating layer side of each sample as a punch surface.
For cup drawing, a sample with a blank diameter of φ100 mm coated with rust preventive oil was processed into a cup shape with a height of 30 mm using a punch with φ50 mm and a shoulder R of 2.75 mm. The following deteriorated gasoline was added into the cup and sealed with stainless steel through a Viton ring so that the gasoline would not evaporate. After leaving at 40 ° C. for one month, the corrosion resistance was evaluated from the amount of red rust generated inside. The side wall part of the cup inner surface in contact with the gasoline phase and the bottom part of the cup inner surface in contact with the aqueous phase were evaluated.
<Test conditions>
・ 40 ℃ × 1 month ・ Degraded gasoline composition Regular gasoline 30ml + Organic acid aqueous solution 3ml (mixed with 100ppm formic acid + 100ppm acetic acid)
・ Criteria 4: No red rust generated 3: Red rust generated (Red rust generated area less than 5%)
2: Red rust generated (Red rust generated area 5% or more and less than 20%)
1: Red rust generated (Red rust generated area 20% or more)
(4) As an evaluation of the rust generated in the gas phase part inside the moisture-resistant tank, the sample of the cup squeezed under the same conditions as in (4) is placed under the following conditions, and the moisture resistance is determined from the amount of rust generated on the cup side wall. Evaluated.
<Test conditions>
・ 50 ℃ × 98% RH × 360 hours ・ Criteria 4: No white rust generation 3: White rust generation (white rust generation area less than 5%)
2: White rust generated (white rust generated area 5% or more and less than 20%)
1: White rust is generated (white rust generated area is 20% or more)
(5) Seam weldability As an evaluation of seam weldability, the lap seam welding was performed by combining the plating layer sides of each sample, and an appropriate current range was evaluated.
The plating layer side of the sample having a size of 500 mm × 300 mm was put together (the electrode contact surface was plated and no chromate film), and welding was performed by lap seam welding (see FIG. 1). The welding conditions are as follows.
Electrode: Chrome-copper alloy electrode shape Electrode diameter 230mmφ, electrode thickness 8.0mm, end 4mmR
Center tip 15mmR (4.5mm width)
・ Welding method: 2 pieces, lap seam welding ・ Pressure: 2.942kN (300kgf)
Energizing time: 2/50 sec energization on, 1/50 sec energization off
・ Cooling: Internal water cooling ・ Welding speed: 2.5 m / min
・ Welding current: Vary.
A load was applied to the sample after lap seam welding by a peel tensile test method (JIS Z 3141: test method for seam welded joint) until the sample broke, and the form of fracture was observed. The appropriate current range was determined by setting the welding current (kA), in which the form of the fracture was a base metal fracture and the nugget lap was sufficient, as the appropriate current, and was evaluated according to the following criteria.
3: 4 kA or more 2: 3 kA or more and less than 4 kA 1: less than 3 kA (6) Global procurement property Global procurement property was evaluated by the following criteria using symbol ○ (excellent) and symbol x (inferior).
○: Easy to procure materials outside of Japan.
×: Difficult to procure materials outside Japan

From the results of Table 1, all of the examples of the present invention are excellent in press workability, seam weldability and global procurement required for the production of fuel tank members. In addition, all of the examples of the present invention are particularly excellent in moisture resistance among chromium elution resistance, corrosion resistance on the inner surface side of the tank, and corrosion resistance required when used as a fuel tank member. It can be seen that the formation of a chromate film has excellent moisture resistance among press workability, corrosion resistance on the inner surface side, and corrosion resistance. Furthermore, it can be seen that the moisture resistance is further improved by setting the minimum film thickness of the chromate film to 10 nm or more.

On the other hand, a comparative example outside the scope of the present invention does not satisfy any of press workability, seam weldability, inner surface corrosion resistance, moisture resistance, and global procurement.

The motorcycle fuel tank steel plate and the fuel tank member using the steel plate of the present invention can be used particularly as a fuel tank steel plate and a fuel tank member of a motorcycle.

Claims

A steel plate for a fuel tank of a motorcycle made of a single-side plated steel plate,
A galvanized layer having an adhesion amount of 1 to 70 g / m 2 on a base steel sheet having an arithmetic average roughness Ra of 0.5 to 2.0 μm;
The galvanized layer contains 5 to 1000 ppm by mass of Ni;
Having a chromate film on the galvanized layer,
A steel plate for a motorcycle fuel tank, wherein the chromate film has a minimum film thickness of 10 nm or more and 100 nm or less.
A steel plate for a fuel tank of a motorcycle made of a single-side plated steel plate,
A galvanized layer having an adhesion amount of 1 to 70 g / m 2 on a base steel sheet having an arithmetic average roughness Ra of 0.5 to 2.0 μm;
The galvanized layer contains 5 to 1000 ppm by mass of Ni;
Having a chromate film on the galvanized layer,
A steel plate for a motorcycle fuel tank, wherein the thickness of the chromate film on the uneven surface of the base steel plate roughness is 10 nm or more and 100 nm or less.
A fuel tank member for a motorcycle made of a single-side plated steel plate,
The surface having a galvanized layer with an adhesion amount of 1 to 70 g / m 2 on the base steel plate having an arithmetic average roughness Ra of 0.5 to 2.0 μm is the inner surface side of the fuel tank member,
The galvanized layer contains 5 to 1000 ppm by mass of Ni;
Having a chromate film on the galvanized layer,
A fuel tank member having a minimum film thickness of the chromate film of 10 nm or more and 100 nm or less.
A fuel tank member for a motorcycle made of a single-side plated steel plate,
The surface having a galvanized layer with an adhesion amount of 1 to 70 g / m 2 on the base steel plate having an arithmetic average roughness Ra of 0.5 to 2.0 μm is the inner surface side of the fuel tank member,
The galvanized layer contains 5 to 1000 ppm by mass of Ni;
Having a chromate film on the galvanized layer,
A fuel tank member, wherein a thickness of the chromate film on the convex and concave portions of the base steel plate roughness is 10 nm or more and 100 nm or less.