JP6084769B2 - Oil supply pipe and manufacturing method thereof - Google Patents

Description

  The present invention relates to an oil supply pipe for an automobile. In particular, the present invention relates to an oil supply pipe made of a material cheaper than the current SUS436L and having corrosion resistance equivalent to that of the current material.

  For oil supply pipes for automobiles, a 15-year or 150,000-mile life guarantee is obligated by US regulations, and oil supply pipes made of stainless steel (SUS436L: 17Cr-1.2Mo) have already been put into practical use. Has been.

  Since automobiles traveling in the North American region are exposed to the snow melting salt environment, excellent corrosion resistance is required for the materials used for the oil supply pipes. Conventionally, SUS436L has been applied. There is a demand for cost reduction. SUS436L contains about 1% of expensive Mo, and even if it is replaced with AISI 439 steel (17Cr) not containing Mo, a great cost reduction effect can be obtained.

  However, the reduction of alloy elements in the material causes deterioration of corrosion resistance. Therefore, it is necessary to compensate for the weakness caused by the lowering of the material by another method.

  The corrosion concern part in the oil supply pipe is a gap structure portion on the outer surface of the oil supply pipe that is exposed to a salt damage environment. Conventionally, cationic electrodeposition coating has been used as a means for improving the salt corrosion resistance of the gaps.

  For example, Patent Document 1 discloses a manufacturing method in which cationic electrodeposition coating is applied to an oil supply pipe that is assembled by using projection welding using a SUS436 pipe as a raw material. However, in this technique, SUS436 is used as a material, and according to the knowledge of the inventors, rust prevention is not complete even in SUS436. Therefore, when a lower material is used, it cannot be confirmed that this technique can provide a sufficient rust prevention effect.

  Patent Document 2 discloses a technique for preventing crevice corrosion by applying electrostatic coating to an oil supply pipe assembled from SUS436. Alternatively, Patent Document 3 discloses a technique for ensuring sufficient rust prevention even if chipping is applied to a stainless steel oil supply pipe and chipping is applied. However, these techniques are more costly than the electrodeposition coating. On the other hand, since it cannot be painted inside the gap, there is no guarantee that a sufficient rust prevention effect will be obtained.

  On the other hand, rust prevention methods other than painting are also presented. For example, Patent Document 4 discloses a technique for sacrificial corrosion prevention by disposing a zinc sacrificial anode in a part where a passive state film is damaged or a gap part by welding, brazing, plastic working, etc. in assembling a stainless steel oil supply pipe. Has been. However, it is cumbersome and troublesome to arrange zinc in all the corrosion-prone areas. Zinc is also an expensive metal. Furthermore, since zinc is easily consumed in a salt damage environment, there is a problem that a necessary amount increases. For these reasons, sacrificial anticorrosion is not a realistic technique in oil supply pipes.

Japanese Patent Laid-Open No. 2002-242779 JP 2004-210003 A JP 2006-231207 A Japanese Patent Laid-Open No. 2005-206064

  The present invention is based on the premise that a material lower than SUS436L is used, and an object thereof is to ensure salt corrosion resistance, which is a weak point of stainless steel, particularly corrosion resistance in a gap structure portion.

  The present inventors recalled that the cationic electrodeposition coating with a proven track record is the most suitable as an anticorrosion method for the purpose of being inexpensive, and devised the electrodeposition coating and its object. We thought that the anti-corrosion property could be improved and the effect could be returned to lowering the material. Therefore, first, the state of coating film formation in the gap of the SUS436L oil supply pipe subjected to electrodeposition coating was investigated, and the entire oil supply pipe was subjected to a salt corrosion test to observe the corrosion situation in detail. As a result, it was found that the corrosion of the portion where the coating film was not formed inside the gap was more severely corroded than the portion where the coating film was formed. It was also clarified that the corrosion problem does not occur if a coating film is formed in advance on the site forming the gap before forming the gap structure.

The present invention is configured based on the above findings, and the gist thereof is as follows.
(1) By mass%, C: ≦ 0.015%, Si: 0.01 to 0.50%, Mn: 0.01 to 0.50%, P ≦ 0.050%, S: ≦ 0.010 %, N: ≦ 0.015%, Al: 0.010-0.100%, Cr: 13.0-18.0%, Ti: 0.03-0.30% and Nb : A steel pipe member formed from a steel pipe made of ferritic stainless steel containing 0.03 to 0.30% of one or two types, the balance being Fe and inevitable impurities, and non-welded to the steel pipe member An oil supply pipe comprising a bundling part attached by means having a gap structure part on a surface exposed to a salt damage environment between the bundling part attached to the steel pipe member and the steel pipe member, and the gap structure part Both internal bundling parts and steel pipe members, or steel if the bundling member is non-metallic Oil supply pipe, characterized in that the cationic electrodeposition coating film is formed with respect to the total area of the member only.
(2 ) The gap structure portion has a cationic electrodeposition coating film on each surface of the steel pipe member and the binding component, and the cationic electrodeposition coating films are in contact with each other in the gap structure portion. The oil supply pipe according to (1 ) .
( 3 ) The oil supply pipe according to (1) or (2) , wherein the binding component is fastened to a steel pipe member by a bolt and nut.
( 4 ) The fastening method of the bundling part to the steel pipe member is mechanical fastening with bolts and nuts. In advance, separately from the bundling part and the steel pipe member, or when the bundling member is nonmetal, The method for producing an oil supply pipe according to the above (1) or (3) , wherein the fastening is performed after applying the coating.

  According to the present invention, an inexpensive oil supply pipe can be provided while stably securing the salt corrosion resistance, so that the industrial effect is great.

It is a figure which shows the state by which the binding component was fastened by the oil supply pipe main body with the volt | bolt nut. It is a figure which shows a crevice sample, (a) is a top view, (b) (c) is an AA arrow partial sectional view, (b) is an example painted before crevice formation, (c) is a crevice. It is a comparative example painted after formation. It is a figure which shows the example of the clearance gap structure which exists in the conventional oil supply pipe | tube.

  Hereinafter, the present invention will be described in detail.

  The conventional oil supply pipe includes a gap structure as illustrated in FIG. FIG. 3 shows a state in which a bundling part (metal part) for bundling a main pipe, which is a steel pipe member, and a breather tube and fixing it to a vehicle body is attached by welding. A mode that the clearance gap is formed in the welding part vicinity of a pipe or a breather tube is shown. It is usually difficult to form an electrodeposition coating within such a gap. This is because the gap opening amount is too small, so that the electrodeposition coating liquid cannot penetrate into the gap. In the present invention, as the binding component, either a metal material or a non-metal material may be used as will be described later. When a metal material is used as the binding part, the binding part is also referred to as a metal part.

  In the present invention, the binding parts (metal parts) for binding the steel pipe members are not attached by welding. As illustrated in FIG. 1, the gap structure portion 3 has a cation electrodeposition coating on the surfaces of the steel pipe member 1 and the binding component (metal fitting part) 2, and the cation electrodeposition coating on the gap structure portion 3. This problem was solved by adopting a structure in which they are in contact with each other. When the binding part is made of a non-metallic material, only the steel pipe member has the cationic electrodeposition coating film in the gap constituting part, and the cationic electrodeposition coating film need not be formed on the binding part. Before joining the steel pipe member 1 and the binding part (metal part) 2 to form the gap structure, cationic electrodeposition coating is performed on the surface of each of the steel pipe member 1 and the binding part (metal part) 2 or only the steel pipe member 1. A film is formed. In particular, a cationic electrodeposition coating film is formed on the surface of the steel pipe member 1 and the bundling component (metal component) 2 that forms the gap structure portion 3. Thereafter, the steel pipe member 1 and the binding part (metal part) 2 are joined to form the gap structure part 3, so that the total area of both the binding part and the steel pipe member inside the gap structure part 3 or only the steel pipe member is obtained. Thus, a cationic electrodeposition coating film is formed. After forming the cationic electrodeposition coating on the surface of both the steel pipe member 1 and the binding part (metal part) 2 and forming the gap structure part 3, the steel pipe member 1 and the binding part (metal part) 2 are combined. By forming the gap structure portion 3, the gap structure portion 3 has a cationic electrodeposition coating film on each surface of the steel pipe member 1 and the binding component 2, and the cationic electrodeposition coating films are formed in the gap structure portion 3. It will be in contact. Further, in the oil supply pipe of the present invention, as shown in FIG. 1, the binding part (metal part) 2 is preferably fastened by a bolt and nut 4.

  Further, in the method of manufacturing the oil supply pipe of the present invention, when the binding part (metal part) 2 is mechanically fastened to the steel pipe member 1 of the oil supply pipe body using a bolt and nut 4 as illustrated in FIG. The entire area inside the gap structure part 3 (all parts forming the inside of the gap structure part 3) by adopting a method of fastening the bundled part (metal fitting part) 2 and the steel pipe member 1 separately or after coating only the steel pipe member in advance. ), The cationic electrodeposition coating film can be reliably formed, and the oil supply pipe of the present invention can be obtained. When the binding component is made of a metal material, the binding component and the steel pipe member are separately subjected to cationic electrodeposition coating and then bonded. When the binding member is made of a non-metallic material, the binding may be performed after the cationic electrodeposition coating is applied only to the steel pipe member.

  Next, the material of the steel pipe member will be described. The steel pipe member here means a main pipe and a breather tube filled with fuel gas.

  In the present invention, the alloy element content is lower than that of SUS436L. Of course, Mo does not contain an element for improving corrosion resistance such as Ni and Cu, and is characterized by being an inexpensive material. Specifically, ferritic stainless steel having the following composition is used as a raw material.

  C, N: C and N are elements that cause intergranular corrosion in the weld heat affected zone, and deteriorate the corrosion resistance. Moreover, cold workability is deteriorated. For this reason, the C and N contents should be limited to the lowest possible level. The upper limit of C and N is preferably 0.015%, and more preferably 0.010%. In addition, although a lower limit is not prescribed | regulated in particular, considering refinement cost, it is good to set it as C: 0.0010% and N: 0.0050%.

  Si: Si is useful as a deoxidizing element in the refining process and contains 0.01% or more. However, in order to deteriorate the workability, it should not be contained in a large amount, and the upper limit should be limited to 0.50%. . A preferable range is 0.10 to 0.30%.

  Mn: Mn also contains 0.01% or more as a deoxidizing element and S-fixing element, but Mn should not be contained in a large amount in order to deteriorate workability, and the upper limit should be limited to 0.50%. A preferable range is 0.10 to 0.30%.

  P: P is an element that significantly deteriorates workability. For this reason, the P content is desirably as low as possible. The upper limit of the allowable content is 0.050%. A desirable upper limit of P is 0.030%.

  S: Since S is an element that degrades corrosion resistance, the content of S is preferably as low as possible. The upper limit of the allowable content is 0.010%. A desirable upper limit of the S content is 0.0050%.

  Cr: Cr is a basic element that ensures corrosion resistance, and an appropriate amount is essential, and the lower limit of the Cr content needs to be 13.0%. On the other hand, the upper limit content is preferably set to 18.0% from the viewpoints of being an element that deteriorates workability and suppressing alloy costs. A preferable range of the Cr content is 15.0% to 17.5%, and more preferably 16.5% to 17.5%.

  Al: Al is useful as a deoxidizing element and contains 0.010% as the minimum amount necessary for deoxidation. However, in order to deteriorate the workability, the upper limit should be limited to 0.100%. It is good to do. Preferably, the upper limit of the content is 0.070%.

  In this invention, 1 type or 2 types of Ti and Nb are contained.

  Ti: Ti has the action of fixing C and N as carbonitrides and suppressing intergranular corrosion. For this reason, 0.03% is contained as the lower limit, but even if it is contained excessively, the effect is saturated and the workability is impaired, so the upper limit of the content is made 0.30%. In addition, the proper content of Ti is preferably 5 times or more and 30 times or less the total content of C and N. Ti is preferably contained in the range of 10 to 25 times the total amount of C and N.

  Nb: Nb, like Ti, Nb fixes C and N as carbonitrides and suppresses intergranular corrosion, so 0.03% is included as the lower limit. Therefore, the upper limit of the content is made 0.30%. The appropriate content of Nb is preferably 5 times or more and 30 times or less the total content of C and N. Nb is preferably contained in the range of 10 to 20 times the total amount of C and N.

  B: B is an element useful for preventing secondary work embrittlement and hot workability deterioration, and is an element that does not affect corrosion resistance. Therefore, if necessary, 0.0002% is contained as the lower limit. However, if it exceeds 0.0050%, hot workability deteriorates, so the upper limit is preferably made 0.0050%. Preferably, the upper limit of the B content is 0.0020%.

  Sn: Sn is an element useful for improving the corrosion resistance with a small amount of inclusion, and is contained in a range that does not impair the inexpensiveness as required. If the content is less than 0.01%, the effect of improving the corrosion resistance is not expressed. If the content exceeds 0.50%, the increase in cost becomes obvious and the workability also decreases. And Preferably it is 0.05 to 0.40%.

  Ni, Cu, Mo, V, Co: These elements are elements that improve weather resistance and are not contained in the present invention. However, it can be contained in a range that does not impair the inexpensiveness as required. The effect becomes more remarkable due to the synergistic effect with Sn. When Ni, Cu, and Mo are contained, the effect is 0.05% or more. A preferable range of Ni and Cu is 0.1 to 0.4%, and a preferable range of Mo is 0.1 to 0.3%. When V and Co are contained, they are each made 0.01% or more at which the effect is manifested. However, excessive addition leads to an increase in alloy costs and a decrease in manufacturability, so the upper limit is made 0.5%.

  Mg: Mg forms Mg oxide together with Al in molten steel and acts as a deoxidizer, and also acts as a crystallization nucleus of TiN. TiN becomes a solidification nucleus of the ferrite phase in the solidification process, and by facilitating crystallization of TiN, the ferrite phase can be finely formed during solidification. By reducing the solidification structure, surface defects caused by coarse solidification structures such as product ridging and roping can be prevented, and workability can be improved. Can be contained. When it contains, it is made 0.0001% which expresses these effects. However, if it exceeds 0.005%, manufacturability deteriorates, so the upper limit is made 0.005%. Preferably, considering the manufacturability, the content is made 0.0003 to 0.002%.

  Ca: Ca is an element that improves the hot workability and the cleanliness of the steel, and can be contained in a range that does not impair the inexpensiveness as required. When it contains, it is made into 0.0003% or more which expresses these effects. However, excessive addition leads to a decrease in manufacturability and a decrease in weather resistance due to water-soluble inclusions such as CaS, so the upper limit is made 0.005%. Preferably, considering the manufacturability and weather resistance, the content is made 0.0003 to 0.0015%.

  Zr, La, Y, Hf, REM: These elements have the effect of improving hot workability and cleanliness of steel, and significantly improving oxidation resistance and hot workability. It can contain in the range which does not impair. When it contains, it makes it 0.001% or more in which the effect expresses, respectively. However, excessive addition leads to an increase in alloy cost and a decrease in manufacturability, so the upper limit is made 0.1%. Preferably, considering the effect, economic efficiency, and manufacturability, one or two or more is 0.001 to 0.05%.

  Remaining Fe and inevitable impurities: Fe and inevitable impurities other than the elements described above.

  Stainless steel having the above composition is manufactured by a normal stainless steel sheet manufacturing method in which a steel piece melted and refined in a converter or electric furnace is subjected to hot rolling, pickling, cold rolling, annealing, finish pickling, and the like. It is manufactured as a steel plate, and is further manufactured as a welded pipe by a normal stainless steel pipe manufacturing method such as electric resistance welding, TIG welding, or laser welding using this steel plate as a raw material.

  This stainless steel pipe is usually used for cold plastic working such as bending, pipe expansion, drawing, spot welding, projection welding, MIG welding, TIG welding, brazing, or mounting various metal fittings with bolts and nuts. After being molded and assembled, it is molded into an oil supply pipe.

  Bundling parts include metal parts made of ferrous metal materials such as carbon steel, low alloy steel, and stainless steel, and nonferrous metal materials such as aluminum, aluminum alloy, titanium, titanium alloy, copper alloy, and magnesium alloy. In addition, a molded part using FRP reinforced with resin such as epoxy and polycarbonate, glass fiber, carbon fiber, or the like may be used as a binding part composed of a non-metallic material other than the metal fitting.

  When using metal fittings for the binding parts, it is desirable that the material is the same material as the steel pipe member. It is often thought that the fuel inside the oil supply pipe does not leak even if the metal fitting is corroded, but the corrosion of the metal fitting parts makes the environment inside the gap severe, and as a result induces crevice corrosion on the steel pipe member side. This is because it will accelerate.

  The invention is explained in more detail on the basis of examples.

  Ferritic stainless steel having the composition shown in Table 1 is melted in a 150 kg vacuum melting furnace, cast into a 50 kg steel ingot, and then subjected to hot rolling, hot rolled sheet annealing, pickling, cold rolling, annealing, and finish pickling. A steel plate having a thickness of 0.8 mm was produced.

<Preparation of gap sample>
From the steel plate material, a large plate of t0.8 × 70 × 70 size and a small plate of t0.8 × 40 × 40 size were collected (a large plate was a steel pipe member, and a small plate was a binding component (metal fitting)). ). A hole for fastening a bolt and nut with a diameter of 5 mm was formed in the center of these two sheets, and cationic electrodeposition was applied to each of the large plate and the small plate. The paint used was PN-110 manufactured by Nippon Paint Co., Ltd., energized at a bath temperature of 28 ° C. and a coating voltage of 170 V, and the conditions were selected so that the coating thickness would be 20 to 25 μm in the general part. The baking conditions were 170 ° C. × 20 minutes. Thereafter, the large plate 11 and the small plate 12 were fastened using a bolt 14 and a nut 15 made of polycarbonate having a diameter of 4 mm, and gap samples as shown in FIGS. 2A and 2B were produced (Examples 20 to 55 of the present invention). Comparative Examples 102 and 103). The gap structure portion 3 between the large plate 11 and the small plate 12 is in contact with both coating films 13. Moreover, about the comparative example 101, before performing the electrodeposition coating to the large board 11 and the small board 12, two sheets were fastened using the volt | bolt 14 and the nut 15, and the cationic electrodeposition coating was performed after that. As a result, as shown in FIGS. 2A and 2C, a slight gap is formed in the gap structure portion 3, and the large plate 11 and the small plate 12 that do not have a coating film face each other with respect to the gap structure portion 3. It became. In FIG. 2C, a gap larger than the actual gap is drawn for the gap structure portion 3 in order to clarify the difference.

  In preparing some of the gap samples, ferritic stainless steel having the composition E01 shown in Table 1 was used for the large plate, and the small plate was made of a non-metallic material (polycarbonate resin). Invention Example No. In No. 56, only the large plate was subjected to cationic electrodeposition coating, and thereafter, the large plate and the small plate were fastened using a φ4 mm polycarbonate bolt and nut to prepare a gap sample. Comparative Example No. For 104, before applying the cationic electrodeposition coating, two plates, a large plate and a child plate, were fastened using bolts and nuts, and then the cationic electrodeposition coating was applied.

  For these gap samples, after sealing the back end face of the large plate, a cycle corrosion test stipulated by JASO-M609-91 simulating a salt damage environment (salt water spray: 5% NaCl spray 35 ° C. × 2 Hr, dry: relative humidity 20% , 60 ° C. × 4 Hr, wet: relative humidity 90%, 50 ° C. × 2 Hr repeated). The test period was 300 cycles. After 300 cycles, the bolts and nuts were removed and immersed in a coating film release agent to peel the coating film, and then the corrosion depth inside the gap was measured by a microscope focal depth method. Ten points were measured and the maximum value was taken as the representative value of the sample. The maximum corrosion depth of 400 μm or less was considered good.

  Table 2 shows the sample history, evaluation method, and evaluation results.

  This invention No. In Nos. 20 to 55, a coating film equivalent to the general portion outside the gap is reliably formed over the entire area inside the gap. In No. 56, polycarbonate resin was used for the small plate, and a coating film equivalent to the general portion outside the gap was reliably formed on the large plate side of the gap, so extremely excellent corrosion resistance was obtained.

  Comparative Example No. For 101 and 104, the material satisfies the conditions of the present invention, but satisfactory gap corrosion resistance was not obtained because electrodeposition coating was performed after the gap was formed. Comparative Example No. Reference numeral 102 denotes a test result when the current material X01 (SUS436L) is used. Since SUS436L was used, the crevice corrosion resistance was good, but the cost reduction effect could not be obtained because the material was expensive. Comparative Example No. 103 is a result of 11Cr steel whose material is outside the scope of the present invention. Even if electrodeposition coating is performed before forming the gap portion to form a coating film, the corrosion resistance of the material is insufficient, and corrosion under the coating film progresses, leading to severe crevice corrosion. Invention Example No. 24 (material E05) and Comparative Example No. Comparing 103, it can be seen that when a coating film is formed in the gap, the corrosion resistance rapidly changes between 11% and 13% of Cr.

DESCRIPTION OF SYMBOLS 1 Steel pipe member 1a Main pipe 1b Breather tube 2 Bundling parts 3 Gap structure part 4 Bolt nut 5 Bolt hole 6 Brazing 11 Large plate 12 Small plate 13 Coating film 14 Bolt 15 Nut

Claims (4)

  In mass%, C: ≦ 0.015%, Si: 0.01 to 0.50%, Mn: 0.01 to 0.50%, P ≦ 0.050%, S: ≦ 0.010%, N : ≦ 0.015%, Al: 0.010 to 0.100%, Cr: 13.0 to 18.0%, Ti: 0.03 to 0.30%, and Nb: 0.0. A steel pipe member molded from a steel pipe made of ferritic stainless steel containing 03 or 0.30% of one or two types, the balance being Fe and inevitable impurities, and attached to the steel pipe member by non-welding means An oil supply pipe composed of a bundled part having a gap structure part on a surface exposed to a salt damage environment between the bundle part attached to the steel pipe member and the steel pipe member, and the bundle inside the gap structure part Both parts and steel pipe members, or steel pipe members if the bundling member is non-metallic See, filler tube, characterized in that the cationic electrodeposition coating film is formed with respect to the total area of. In the gap structure, according to claim 1, characterized in that a cationic electrodeposition coating film on each surface of the binding component and the steel pipe member, is the cationic electrodeposition coating together in the gap structure is in contact Refueling pipe as described in 4. The oil supply pipe according to claim 1 or 2 , wherein the binding part is fastened to the steel pipe member by a bolt and a nut. The method of attaching the bundled part to the steel pipe member is mechanical fastening with bolts and nuts. Cationic electrodeposition coating is applied separately to the bundled part and the steel pipe member in advance, or only to the steel pipe member if the binding member is non-metallic. The method for manufacturing an oil supply pipe according to claim 1 , wherein the oil supply pipe is fastened after being applied.

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