JP2010173525A - Plated steel sheet for fuel tank of motorcycle, and fuel tank - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the fuel tank of a motorcycle having a corrosion resistance against fuel such as degraded gasoline and bio-gasoline, and having a long-term corrosion resistance even in an environment in which chlorine ions of snow-melting salt are concentrated, and the dry-wet condition is repeated. <P>SOLUTION: The plated steel sheet for the fuel tank of a motorcycle comprises a member having a plated layer of an alloy consisting of at least one of Zn or Zn and Fe, Ni, Co, Mg and Al on both sides or on an inner surface on the surface of ferritic stainless steel having the composition of, by mass, one or two kinds of 11.0-23.0% Cr, 0.015% or less C, 10% or less Si, 0.05-0.50% Ti or 0.10-0.50% Nb, and the balance Fe with inevitable impurities and with the mean crystalline grain size of 40 μm or less, and the fuel tank is formed of the plated steel sheet. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a plated steel sheet for a motorcycle fuel tank excellent in corrosion resistance and supplying gasoline, gasoline containing methanol, biofuel, and the like, and a fuel tank comprising the same.

Conventionally, as a material for a fuel tank for a motorcycle, a Zn—Ni plated steel plate having excellent corrosion resistance, workability, and weldability has been used. The Zn—Ni plated steel sheet is single-sided plating, and the inner surface of the tank is the plated surface, and the outer surface is coated with a top coat such as polyamide-based or polyurethane-based resin after being subjected to cationic electrodeposition coating.
Resin tanks are also used to reduce weight.
JP-A-10-181655

  Regarding the material of the fuel tank, there is a problem that a corrosion product is generated by corrosion of the inner surface of the Zn—Ni plated steel plate and clogs the fuel supply valve. In particular, biofuels that have recently been used in South America are more corrosive than conventional gasoline, and therefore need to improve the internal corrosion resistance.

From the viewpoint of corrosion resistance against internal corrosion, it can be said that it is preferable to use stainless steel as the material. However, since the fuel tank is exposed to the outside, rainwater infiltrates at the site constituting the gap and crevice corrosion occurs. There is a problem. In addition, in areas where snow melting salt is drowned on the road surface, salt enters the gaps, so that the environment becomes extremely severe due to dry concentration. In some cases, there is even perforation corrosion and even the function of the tank is impaired.
In addition, when exposed to direct sunlight in summer, the temperature of the tank surface may exceed 50 ° C, so when austenitic stainless steel is applied, the stress caused by the thermal stress generated during welding There is concern about corrosion cracking. On the other hand, in the case of a ferritic stainless steel in which the Cr content is increased or the corrosion resistance is improved by adding Mo, there is a problem that workability is lowered.

  Therefore, there has been a demand for the development of a fuel tank material for motorcycles that has internal corrosion resistance and workability, which is insufficient with conventional plated steel plates and solid stainless steel materials in terms of corrosion resistance.

  In order to solve these problems, in the present invention, as a motorcycle fuel tank material, Zn or an alloy composed of one or more of Zn and Fe, Ni, Co, Mg and Al is formed on both surfaces or one surface as an average. Ferritic stainless steel having a crystal grain size of 40 μm or less was applied.

Furthermore, the composition of the ferritic stainless steel constituting the tank is Cr: 11.0 to 23.0% by mass, C: 0.015% or less, Si: 1.0% by mass or less, Ti: 0.05 to 0.00. 50% by mass or Nb: 0.10 to 0.50% by mass or less of one or two types, with the balance being Fe and unavoidable impurities, sufficient corrosion resistance and workability in combination with the aforementioned plating It can be secured.
Further, the stainless steel further contains Mo: 3.0% by mass or less, Ni: 2.0% by mass, Cu: 2.0% by mass or less, and B: 0.0100% by mass or less. May be.

  In addition, processing into a fuel tank shape requires good material moldability, but in order to make the limit drawing ratio LDR, which is an index of deep drawing workability, 2.3 or more, plating What is necessary is just to make the average crystal grain diameter of stainless steel which is an original plate into 40 micrometers or less.

  According to the present invention, the fuel tank of a motorcycle has corrosion resistance against fuel such as deteriorated gasoline and biogasoline, and chlorine ions such as snow melting salt are concentrated against external surface corrosion, and long-term even in an environment where dry and wet are repeated. It has become possible to provide a material having excellent corrosion resistance. It can also handle complex drawing on motorcycles.

Hereinafter, the anticorrosion mechanism of the steel of the present invention will be described. In the present invention, since stainless steel is used as a base material for plating, the anticorrosive action of Zn that could not be obtained with a conventional galvanized steel sheet can be expected.
In the case of a steel plate in which conventional plain steel is galvanized, while the metallic zinc is present on the steel plate, the corrosion of the base metal is suppressed by the sacrificial dissolution of the zinc. Corrosion begins and leads to perforation.

The anticorrosive action against the corrosion product of zinc is the action of the zinc corrosion product adhering to the surface of the stainless steel plate to suppress the oxygen reduction reaction, which is a cathodic reaction in the corrosion process, and the pH buffering action due to the dissociation of zinc hydroxide. . This effect is manifested when stainless steel is used as the plating base steel, and is not observed when ordinary steel is used.
Moreover, the same anticorrosive action was recognized not only in the water environment but also in the air environment as long as the corrosion product was present. These anticorrosive effects are not limited to the case of zinc alone, but the same effect is observed when alloy plating of zinc and Fe, Ni, Co, Mg, and Al is used.

The anticorrosive action by the corrosion product of Zn is extremely effective for suppressing crevice corrosion of stainless steel. The corrosion product of Zn varies depending on the surrounding environment, but mainly consists of zinc oxide and zinc hydroxide. Zn is a metal that easily corrodes even in a neutral aqueous solution, and is particularly effective in a crevice environment because a corrosion product is easily generated in a crevice environment where Cl ⁻ is concentrated.
Therefore, applying the Zn-based plating to the outer surface is effective in preventing crevice corrosion caused by the snow melting agent that has jumped up and adhered in an area where the snow melting agent mainly composed of chloride is spread on the road.

On the other hand, the inside of the fuel tank is an environment where fuel such as gasoline exists. When gasoline deteriorates, a lower organic acid is generated, which is transferred to condensed water and a corrosive environment is formed. Even in this internal environment, galvanized stainless steel exhibits superior corrosion resistance to deteriorated gasoline than conventional plating materials due to the sacrificial anticorrosive action of Zn and the anticorrosive action of corrosion products.
In addition, since the material is stainless steel, even if the plating layer dissolves and a corrosion product is generated, the material does not progress in corrosion and the fuel injection valve is not clogged.

The plating method may be any method of electroplating, hot dipping, and vapor deposition. Since the fuel tank is manufactured by seam welding or spot welding, it is desirable that the corrosion protection action of the corrosion product on the weld gap when the Zn evaporates by welding has a plating layer of 5 g / m ² or more.

In galvanization, not only the single plating but also the case where the plating layer contains Fe, Ni, Co, Mg and Al are effective. Even when they are contained, there is no problem in the anticorrosive effect after the formation of the corrosion product because the corrosion product is mainly a hydroxide or oxide of zinc. Rather, the inclusion of these metal elements in the galvanized layer is effective because the corrosion resistance of the plated layer is improved.
In consideration of weldability, the melting point is higher than that of galvanized alone, so that the electrode life is improved.

  Although the two-wheeled automobile tank of the present invention is basically plated on both sides, the inner surface or the outer surface may be plated on one side depending on the assumed corrosive environment.

The stainless steel in the present invention is Cr: 11.0-23.0% by mass, C:
0.015% by mass or less, Si: 1.0% by mass or less, Ti: 0.05 to 0.50% by mass or Nb: 0.10 to 0.50% by mass alone or in combination, or Mo: 3. 0% by mass or less, N: 0.020% by mass or less, Ni: 2.0% by mass or less, Cu: 2.0% by mass or less, B: 0.0100% by mass or less, with the balance being substantially Fe Ferritic stainless steel having the following composition:
Further, Mo: 3.0% by mass or less, Ni: 2.0% by mass, Cu: 2.0% by mass or less, and B: 0.0100% by mass or less may be contained.

C: 0.015 mass% or less C forms carbides, which serve as recrystallization nuclei for randomization of recrystallized ferrite in the final annealing. However, C is an element that increases the strength after cold rolling annealing, and if it is too high, the ductility is lowered and disadvantageous for the processing of the fuel tank.

The content of the alloy element and the reason for limitation are as follows.
Si: 1.0% by mass or less Si is usually used for the purpose of deoxidation, but has a high solid solution strengthening ability, and if the content is too large, the material is hardened and the ductility is lowered. % Or less.
Mn: 2.0% by mass or less An austenite-forming element that has low solid solution strengthening ability and little adverse effect on the material. However, if the content is large, manufacturability decreases, such as Mn fume being generated during melting. Further, since S and MnS are produced in the steel and are likely to become a precious store for corrosion, the component range is desirably set to 2.0% or less.

Cr: 11.0-23.0 mass%
Cr is the most important element in the present invention. If Cr is 11% or more, the galvanizing anticorrosive action is recognized. However, an increase in the Cr content makes it difficult to process the fuel tank due to a decrease in workability, and the cost increases, so the upper limit is made 23.0%.

N: 0.020% by mass or less N forms a nitride, and like C, it acts as a recrystallization nucleus for randomizing the crystal orientation of the recrystallized ferrite in the final annealing. However, N is an element that increases the strength of the cold-rolled annealed material, and if it is too high, the ductility is lowered.

Al: 0.2% by mass or less Al is added at an upper limit of 0.2% for deoxidation of molten steel. If it exceeds 0.2%, nitride inclusions such as TiN form clusters and cause surface defects.
When the oxygen in the steel is controlled by Si, no addition is possible.

Ti: 0.05 to 0.50 mass%
Ti is an element that fixes C and N and improves workability and corrosion resistance, and the minimum Ti content at which the effect can be obtained is 0.05%. However, when Ti is added, the steel material cost increases, and surface defects caused by Ti inclusions become a problem. Therefore, the upper limit of the Ti content is set to 0.50%.

Nb: 0.10 to 0.50 mass%
Nb is an element that fixes C and N, improves impact resistance and secondary workability, and is an effective element for refining crystal grains. The minimum amount that produces these effects is 0.10%. However, when Nb is added too much, the material is cured and the workability is adversely affected. Further, since the recrystallization temperature is raised, the upper limit is made 0.5%.

B: 0.0005 to 0.0100 mass%
B is an alloy component that has the effect of fixing N and improving the corrosion resistance and workability, and is added as necessary. In order to exert the above action, it is desirable to add 0.0005% or more. However, if added excessively, the hot workability and weldability are reduced, so the upper limit was set to 0.0100%.

Mo: 3.0% by mass or less Mo is an element effective for improving the corrosion resistance. However, excessive addition causes a decrease in hot workability due to solid solution strengthening at high temperature and delay of dynamic recrystallization. Therefore, it was made 3.0% or less.

Ni: 2.0% by mass or less Ni may not be added. Ni is an austenite forming element, and addition exceeding 2.0% leads to hardening and cost increase. Therefore, when added for improving acid resistance, the upper limit is 2.0%.

Cu: 2.0 mass% or less Cu may not be added. Excessive addition reduces hot workability and corrosion resistance, so when added for softening, the content is made 2.0% or less.

P: 0.050 mass% or less
P is an element harmful to hot workability. In particular, when the content exceeds 0.050%, the influence becomes remarkable, so the content is desirably limited to 0.050% or less.

S: 0.020 mass%
S is an element that easily segregates at the crystal grain boundary and promotes a decrease in hot workability due to grain boundary embrittlement. If it exceeds 0.020%, the effect becomes remarkable, so it is preferably 0.020% or less.

V, Zr: 0.01-0.30 mass%
V and Zr improve workability due to the effect of precipitating solid solution C as carbides, and Zr is a useful element from the viewpoint of improving workability and toughness by capturing oxygen in steel as an oxide. However, if added in a large amount, the manufacturability is lowered, so the proper contents are V and Zr are 0.01 to 0.30%.

  In addition to these, Ca, Mg, Co, REM, and the like may be mixed from scraps and auxiliary materials as raw materials, but there is no effect on the shape freezing property of molded products unless they are contained in large amounts.

Further, in the stainless steel of the present invention, by making the crystal grain size after finish annealing 40 μm or less, it is possible to improve the drawing processability to the fuel tank and to obtain a good paint appearance.
In drawing into a tank shape, cracking and necking may occur due to ridging and rough skin. In order to suppress them, it is effective to make the crystal grains fine. This is due to the suppression of cracking at the most severely processed parts and the dispersion of strains due to the work hardening phenomenon due to fine graining. If the average crystal grain size is 40 μm or less, the effect is exhibited, and roughening of the processed steel sheet can be prevented, so that a smooth and glossy coating film can be obtained by painting.

  The outer surface of the tank may be made of solid stainless steel, but if corrosion resistance or design from the outside of the tank is required, it is coated with a polyamide or polyurethane resin after the cationic electrodeposition coating.

  Hereinafter, the present invention will be described specifically by way of examples.

Stainless steel was melted by vacuum melting. Test pieces with a plate thickness of 1 mm were produced by forging, hot rolling, cold rolling, annealing, and pickling. Table 1 shows the details of the test materials used. Then, 10g / m ² of Zn plating, Zn-Ni plating, Zn-Fe plating, Zn-Co plating (more electroplating), Zn-Mg plating and Zn-Al plating (more molten) by electroplating or hot dipping. The sample was plated.
As pretreatment of plating, sulfuric acid reduction electrolysis was performed in the case of electroplating, and iron flash plating was performed in the case of hot dipping. Sn-Zn plated steel plate and SUS304 2B finish were used as comparative materials. For the test piece, the gap between the tank mounting part and the test piece in which the weld gap was formed by seam welding the two test pieces in consideration of the welding operation of the tank, and the rubber gasket was formed. Two types of test pieces were used.

  The corrosion resistance test on the outer surface was carried out by a combined salt / wet cycle test. One cycle of the test is salt spray (5% NaCl, 15 minutes) → drying (60 ° C., 35% RH, 60 minutes) → wet (50 ° C., 95% RH, 180 minutes), crevice corrosion after 300 cycles The corrosion resistance was evaluated from the erosion depth of the part. In the corrosion test on the inner surface, the steel plate was immersed at 40 ° C. for one month in a test solution in which commercially available gasoline was diluted to 70% with water and 10 ppm formic acid was added. Table 2 shows the test results for evaluating the corrosion resistance based on the erosion depth after the test.

In the Sn—Zn plated steel plate as a comparative example, no corrosion of the substrate was particularly observed with respect to the outer surface corrosion resistance, but deep corrosion was observed with respect to the inner surface corrosion resistance. On the other hand, although SUS304 did not cause internal corrosion, deep crevice corrosion was observed in the external corrosion test, and stress corrosion cracking due to stress during welding was observed in the seam weld specimen. On the other hand, No. which is steel of the present invention. 1-No. No crevice corrosion was observed on the steel plate in which the invention 6 was plated, and no internal corrosion was observed. However, no. Although internal corrosion was not observed in the steel sheets plated with 7-9 steel, crevice corrosion was observed on the outer surface.
From the above results, it can be seen that the steel of the present invention has excellent corrosion resistance against salt damage environments even when it has a gap structure. Moreover, crevice corrosion and internal corrosion were not recognized in the test piece which gave Zn-Ni plating, Zn-Fe plating, Zn-Co plating, Zn-Mg plating, and Zn-Al plating, but anticorrosive action was recognized.

  In order to evaluate the processability to the fuel tank, the materials shown in Table 1 were further cold-rolled to 0.5 mm, and the samples were changed in particle size by adjusting the annealing temperature in the range of 900-1000 ° C. The deep drawing test was conducted. For the processability, an LDR test was performed. LDR was evaluated with punch = φ40R4 and die: φ41.92R3. The measurement results of LDR are shown in Table 3. No. which is steel of the present invention. 1-No. Three steels showed LDR 2.3 or higher. However, no. The 8 and 9 steels had a lower LDR. It was found that good drawability can be obtained when the particle diameter is 40 μm or less.

Claims (3)

Composition: Cr: 11.0 to 23.0 mass%, C: 0.015% or less, Si: 1.0 mass% or less, Ti: 0.05 to 0.50 mass%, or Nb: 0.10 to 0 Zn or Zn and Fe, Ni, Co, Mg, and Al on the surface of ferritic stainless steel containing one or two of 50 mass% or less, the balance Fe and the inevitable impurities being an average crystal grain size of 40 μm or less A plated steel sheet for a motorcycle fuel tank, characterized by comprising a member having a plated layer of an alloy composed of one or more of these on both sides or one side. The stainless steel further contains Mo: 3.0% by mass or less, Ni: 2.0% by mass, Cu: 2.0% by mass or less, B0.0100% by mass or less, or one or more of them. A plated steel sheet for a motorcycle fuel tank according to claim 1. A motorcycle fuel tank comprising the plated steel sheet according to claim 1.