JP2008297588A - High tensile strength steel pipe for high pressure piping of automobile - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high tension steel pipe for high pressure piping of automobile which has 800-1800 N/mm<SP>2</SP>tensile strength with a low alloy and excellent in repeated internal pressure fatigue resistant characteristic, and when injection pressure is by a direct injection type gasoline engine, can secure a welded steel pipe or an electroseamed steel pipe having the high strength of exceeding 12-20 MPa of injection pressure of the repeated inner pressure fatigue limit stress, and shows the sufficient corrosion-resistance to the repeated contact with corrosional fluid. <P>SOLUTION: This high tension steel pipe is the TRIP steel sheet (low alloy transformation induced plasticity steel sheet)-made electroseamed pipe or welded steel pipe composed of AM steel (annealing martensite steel: 0.1-0.6 wt.% C, 1.5 wt.% Si, 1.5 wt.% Mn, etc.) or BF steel (bainitic ferrite steel: 0.1-0.6 wt.% C, 1.5 wt.% Si, 1.5 wt.% Mn, etc.) and Ni-plating is applied on the inner peripheral surface. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention comprises an electric-welded steel pipe or a welded steel pipe for automobile high-pressure piping, which has excellent welding quality and can be suitably used as a high-pressure fluid pipe with high pressure fluctuation, such as automobile fuel pipes and brake pipes. More particularly, the present invention relates to a high-tensile steel pipe for automobile high-pressure piping that has the characteristics of a high-strength steel while being a low alloy steel and has excellent corrosion resistance.

High-strength steel pipes with a tensile strength of 490 N / mm class ^{2 to} 600 N / mm class ² and stainless steel double-wound steel pipes are generally used for fluid pipes that undergo severe pressure fluctuations at high pressures, such as automobile fuel pipes and brake pipes. (See, for example, Patent Documents 1 and 2). However, a material exhibiting high tensile strength is generally a tempered steel material made of high carbon and high alloy, so it has high hardness and poor workability. Therefore, it is extremely difficult to process the tube by roll forming or the like. In addition, it is difficult to obtain a tensile strength of 700 N / mm ² or more even if an austenitic material utilizing work hardening is used because it is a high alloy, and a pipe with high reliability due to poor weldability. It was also very difficult to obtain. In recent years, in addition to environmental measures for preventing global warming due to CO ₂ , as a part of fuel efficiency measures for energy saving, gasoline engines also have a high internal pressure (injection pressure) of 12 to 20 MPa or more for direct injection engines. ), And the conventional high-strength steel pipe described above cannot withstand internal pressure fatigue or vibration fatigue caused by high-pressure fluid in the gasoline engine as well as diesel engines that atomize fuel by high-pressure injection Is feared.

Furthermore, in the conventional general method for manufacturing steel pipes, in order to ensure good formability and weldability when manufacturing ERW steel pipes, it is advisable to use a soft material with a low carbon content. In particular, the tendency appears particularly in low frequency resistance welding, direct current resistance welding, etc., and excellent in high frequency induction welding, TIG welding, laser welding, plasma welding, etc. in other welded steel pipe or ERW steel pipe manufacturing methods. In order to ensure the welding quality characteristics, the upper limit of the carbon content in the steel plate material is about 0.6 wt%, and the carbon content is suppressed to 0.6 wt% or less, without hardening heat treatment, and 800%. ~1800N / mm ² in obtaining tensile strength is usually not possible, and be used work hardening characteristics of conventional austenitic material, its tensile strength is at most 700 N / mm ² Degree was the limit.
Therefore, the applicant of the present application first performs a specific solution treatment on the annealed martensitic steel (AM steel) or bainitec ferritic steel (BF steel) of a low alloy high strength steel prepared to a specific component ratio. after applying, more specific austempering alms were TRIP steels developed (low alloy variants induced plasticity type strength steel plates) ERW pipe or welded steel pipe, low alloy while also tensile strength 800~1800N / mm ² No. 2006-117298 (filed in 2006-4-20) as a high-strength steel pipe for automobile high-pressure piping that can secure the above-mentioned characteristics and can also ensure an internal pressure cyclic fatigue limit stress exceeding 12 to 20 MPa in a direct injection gasoline engine Has already proposed.

Recently, however, there has been a further increase in the demand for environmental protection in the field, and CO (carbon monoxide), CO ₂ (carbon dioxide), HC (hydrocarbon), NOx (nitrogen oxide) contained in exhaust gas. ), In order to reduce the concentration of PM (particulate matter) etc., to ensure high combustion efficiency regardless of gasoline engine and diesel engine, and to reduce the amount of these components generated as much as possible, the fuel itself The so-called biomass fuel such as low-grade gasoline, sour gasoline, alcohol and alcohol blended fuel is mixed and used, and the water contained in these fuels, the organic acid produced by gasoline oxidation and alcohol decomposition High pressure piping such as fuel piping and brake piping subject to repeated severe pressure fluctuations due to high pressure fluid Corrosion has emerged as a new problem, and there is a need for high-tensile steel pipes for high-pressure pipes with high tensile strength and excellent pressure resistance, as well as excellent corrosion resistance. For example, many proposals have already been made for high-pressure fuel pipes with high corrosion resistance. Has been made.
As an example, a first plating layer made of Ni, Co, and an alloy based on these is formed on one surface of a strip steel plate, and a second plating made of a metal having a lower melting point than the first plating layer is formed on the first plating layer. After forming the layer, a highly corrosion-resistant welded pipe (for example, refer to Patent Document 3) in which the obtained plated layer is formed on the inner side, and an inner peripheral surface including a bead portion of the welded pipe in advance with Sn, Sn- A first plating layer made of one of Zn, Sn-Ni, Ni-P, and Ni-B is applied, and one of Ni, Co, and their base alloys is formed on the first plating layer that does not include the bead portion. As a corrosion resistant steel plate for steel plate parts including a fuel pipe, a highly corrosion resistant welded pipe formed as a second plating layer (for example, see Patent Document 4), Ni, Co and alloys based on these are used on the inner surface. 1 type of thickness A first plating layer having a thickness of 0.5 to 10 μm made of a metal having a melting point lower than that of the first plating layer is formed on the first plating layer. The first plating layer is formed by heat-treating a steel plate having a total thickness of 1 to 15 μm and further having the first plating layer and the second plating layer at 600 to 1200 ° C. for 5 seconds to 15 minutes. A steel plate in which a diffusion layer is formed between the first plating layer and the second plating layer, a method for manufacturing the steel plate (for example, see Patent Document 5), and the like are disclosed.
JP 2000-5813 A JP 2000-5814 A Japanese Patent No. 3176399 Japanese Patent No. 3176405 Japanese Patent No. 3200164

In each of the prior arts described above, the problem of repeated fatigue limit stress corresponding to the high internal pressure of 180 MPa or more remaining in Patent Document 1 and Patent Document 2 is disclosed in Japanese Patent Application No. 2006-2006 related to the prior application of the present applicant. The corrosion resistance of high-pressure pipes for fluids such as high-strength steel pipes for automobile high-pressure pipes provided by 117298, such as fuel pipes produced by mixing biomass fuel and brake pipes where repeated severe pressure fluctuations occur at high pressure With regard to, there were still issues that needed further improvement.
That is, “Corrosion-resistant welded pipe and method for manufacturing the same” disclosed in Patent Documents 3 and 4, and “Panel for manufacturing a steel plate part having a contact portion with fuel” and the manufacture of the steel plate proposed in Patent Document 5 According to the “Method”, a first plating layer made of Ni, Co, Sn and an alloy based on these is applied to one side of a strip-shaped steel sheet that is a material for pipe making, and the first plating layer is made of metals having different melting points. After forming the second plating layer, the tube is formed into a tubular body or a desired shape by roll forming, overhanging, etc. so that the plating layer is inside, that is, a portion in contact with the fuel, and is subjected to electric resistance welding or seam welding. Thereafter, heat treatment is performed at a predetermined temperature to produce parts such as fuel pipes and fuel tanks. This heat treatment causes a metal having a low melting point or a diffusion layer between the first and second plating layers. The exposed parts of steel base, cracks, pinholes due to welding, pooling, peeling, etc. are covered, and excellent corrosion resistance is secured, and at the same time, welded pipes and various parts with excellent bending and terminal formability can be obtained. Excellent effects have been confirmed. However, since the plating layer applied according to Patent Documents 3 to 5 is an essential requirement to apply at least two plating layers with metals having different melting points, the number of steps in forming the plating layer increases and the cost increases. There was an inconvenience. In addition, the part covered by the heat treatment performed after the formation of the fuel pipe and the brake pipe becomes a metal layer having a low melting point, and therefore, by repeated contact with a high-temperature fuel or a fluid with high pressure and severe pressure fluctuation, There was also a fear that the sound plating layer might be damaged, and there were new issues that were urgently desired to be solved. A high-pressure pipe for fuel with an inner pipe made of stainless steel pipe inside the outer pipe made of carbon steel pipe is also known, but when performing heat treatment to prevent oxidation of the stainless steel that becomes the inner pipe The use of a hydrogen furnace is an essential requirement, and there is a negative factor that it is expensive on the equipment. In the case of a simple non-oxidation furnace that does not use a hydrogen furnace or a vacuum furnace or a reduction furnace with a high dew point, the inner tube It is feared that oxides are generated in the inner surface of the tube, the fitting gap between the inner tube and the outer tube, and that internal pressure fluctuation causes internal pressure fatigue damage due to fluctuations in the internal pressure.

  The present invention has been made in order to solve such a problem remaining in the prior art, and is excellent in repeated internal pressure fatigue resistance characteristics, and it is possible to secure an internal pressure repeated fatigue limit stress in which the injection pressure exceeds 180 MPa. In addition, when biomass fuel or a mixture of these fuels is used, moisture and alcohol contained in the alcohol, alcohol mixed fuel, gasoline oxidation, corrosive components such as organic acids generated by alcohol decomposition, etc. Comparison of high-strength steel pipes for high-pressure automobiles that have high tensile strength and excellent corrosion resistance as well as high-pressure fuel pipes with sufficient corrosion resistance and brake pipes that are subject to repeated severe pressure fluctuations due to high-pressure fluid It is intended to be offered at a low price.

  The high-strength steel pipe for automobile high-pressure piping according to the present invention for solving the above-mentioned problems is a low alloy high-strength steel AM steel (annealed martensite steel: C 0.1 to 0.1) that has been subjected to austempering after solution treatment. 0.6 wt%, Si 1.5 wt%, Mn 1.5 wt%, etc.) or BF steel (Bainitec ferrite steel: C 0.1-0.6 wt%, Si 1.5 wt%, Mn 1.5 wt% Etc.), an electric-welded steel pipe or a welded steel pipe made of a TRIP steel plate (low alloy transformation-induced plastic-type strength steel plate), characterized in that its inner peripheral surface is plated with Ni, The main point is high-tensile steel pipes for high-pressure piping.

  In the present invention, the AM steel is annealed martensitic steel containing C 0.1-0.6 wt%, Si 1.5 wt%, Mn 1.5 wt%), and the BF steel is C 0.1-0. It is a bainiteitic ferritic steel containing 6 wt%, Si 1.5 wt%, and Mn 1.5 wt%.

  Furthermore, the present invention is characterized in that the Ni plating is any one of pure Ni plating, Ni / P plating, and Ni alloy plating.

  In the present invention, the Ni plating is Ni / P plating or Ni / B chemical Ni plating.

  The high-tensile steel pipe for automobile high-pressure piping according to the present invention is further characterized in that the film thickness of the Ni plating is 1 to 10 μm.

  In the high-strength steel pipe for automobile high-pressure piping according to the present invention, the solution treatment for the AM steel is a heat treatment that is rapidly cooled after being heated and held at 950 ° C., and the solution treatment for the BF steel is heated and held at 950 ° C. Each is characterized by being a heat treatment that rapidly cools to an austempering treatment temperature.

  Moreover, in the high-tensile steel pipe for automobile high-pressure piping according to the present invention, the austempering treatment for the AM steel is held at 780 ° C. for 60-3000 seconds, then rapidly cooled to 325-475 ° C., and then in this temperature range for 60-3000 seconds. It is a heat treatment to hold, and the austempering treatment for the BF steel is a heat treatment to heat and hold in a temperature range of 325 to 475 ° C., respectively.

  Furthermore, in the above-described high-tensile steel pipe for automobile high-pressure piping according to the present invention, the TRIP steel plate (low-alloy transformation-induced plastic type strength steel plate) made of AM steel or BF steel of the low alloy high strength steel is in a rolled state or a normal state. The steel sheet is subjected to a softening heat treatment and has a retained austenite content of 5 to 25 wt%.

The high-strength steel pipe for automobile high-pressure piping according to the present invention also has a thickness of 2.5 mm or less, an outer diameter of 12.7 mm or less, and a retained austenite of 5 to 25 wt. %, And tensile strength is 800 to 1800 N / mm ² .

  The high-strength steel pipe for automobile high-pressure piping according to the present invention is further characterized in that the above-mentioned TRIP steel electric-welded steel pipe or welded steel pipe is formed by forming a tubular body by molding, and the joint end thereof is high-frequency induction welding, high-frequency resistance welding. , Low frequency resistance welding, DC resistance welding, TIG welding, plasma welding, and laser welding are used.

  The high-tensile steel pipe for automobile high-pressure piping, which is made of TRIP steel ERW steel pipe or welded steel pipe with an Ni plating layer on the inner peripheral surface according to the present invention, has a high plastic deformability and is machine-induced martensite by plastic working. Direct-injection gasoline engine that can improve the internal pressure fatigue resistance by preventing the progress of cracks occurring at the notch tip originating from internal flaws or non-metallic inclusions caused by internal pressure or external force. In the high-pressure fuel pipe, the steel pipe exposed to repeated contact with a high-pressure fluid in addition to the inherent high tensile property of withstanding internal pressure repeated fatigue of 12 to 20 MPa or more, vibration fatigue accompanying vibration of the engine or vehicle body, and the like The inner peripheral surface is protected in a healthy state by the Ni plating layer applied according to the present invention. Further, the high-tensile steel pipe for automobile high-pressure piping according to the present invention has an excellent effect in corrosion resistance against biomass fuel and the like even when it is adopted as a pipe for high-pressure fluid such as automobile fuel pipe and brake pipe. Can do.

In recent years, TRIP steel that has been subjected to austempering treatment after solution treatment and used as high-tensile steel pipe for high-pressure automobiles, that is, low alloy transformation-induced plastic-type strength steel, has recently been reduced in weight of undercarriage press-formed parts of passenger cars. Ferrite (α _f ) + bainite (α _b ) + γ _R composite structure steel that has been developed for the purpose of the above, and has significantly improved press formability using strain-induced transformation (TRIP) of retained austenite (γ _R ) [TRIP type dual-phase steel, TDP steel] and _bainitech ferrite (α _bf ) + γ _R steel [TRIP type bainite steel, TB steel]. Here, the transformation-induced plasticity is a large elongation accompanying the transformation of an austenite (γ) layer that exists in a scientifically unstable state into martensite by the addition of mechanical energy. That is, the TRIP steel is a steel obtained by performing a specific heat treatment on a steel having a limited composition to obtain a metal structure in which retained austenite and bainite structure are mixed around the grain boundary of the α layer. The characteristics of TRIP steel having such a metal structure include high plastic deformability and high strength and hardness because it becomes a martensite structure by processing.

  The high-tensile steel pipe for automobile high-pressure piping according to the present invention is made of a low alloy transformation-induced plastic type strength steel having 5 to 25 wt% of retained austenite having such characteristics, so that the workability is in the middle of pipe making. The inner surface of the flow path is a tube having a depth of 20 μm or less. Further, when the tube is drawn, the reduction can be made large, so that the number of times of drawing can be reduced, and further, if the same reduction is performed, the processing can be performed with a small drawing machine with a small die and a small drawing force. Also, since the austenite (γ) structure is improved in hardness and tensile strength due to the precipitation of work-induced martensite, internal pressure fatigue resistance, sheet surface scratch resistance, and bending shape stability Excellent vibration fatigue resistance. Furthermore, the low alloy transformation induced plasticity strength steel has the property (TRIP phenomenon) that the austenite in the locally deformed part transforms into hard martensite and strengthens that part (TRIP phenomenon). In the case of high-strength piping made of mold strength steel, even if vibration fatigue or internal pressure fatigue progresses, the fatigue portion is strengthened by the above characteristics and a resistance force is generated to prevent the tube from being broken. Therefore, the conventional STKM material of JIS G 3445 Compared with STS material of JIS G 3455, SUS material of JIS G 3459, etc., a long life is guaranteed. In the present invention, the retained austenite of the low alloy transformation-induced plastic-type strength steel is limited to 5 to 25 wt% because the transformation amount from retained austenite to martensite is less than 5 wt% when exposed to high stress. This is because the strength cannot be increased sufficiently, and when it exceeds 25 wt%, it is difficult to secure a desired strength.

When manufacturing high-strength steel pipes for automobile high-pressure pipes made of TRIP steel electric-welded steel pipes or welded steel pipes according to the present invention, AM steel (annealing) is selected from coil materials made of thin steel strips with a wall thickness of 2.5 mm or less. When martensitic steel: C 0.1-0.6 wt%, Si 1.5 wt%, Mn 1.5 wt%, etc., hereinafter simply referred to as “AM steel”) is used, it is heated to 950 ° C. The solution is preferably held for 1200 seconds, and then subjected to a solid solution treatment by rapid cooling, and then heated to 780 ° C. and held at that temperature range for 60 to 3000 seconds, preferably 1000 seconds, and then rapidly cooled to 325 to 475 ° C. Then, the austempering treatment is performed by maintaining the temperature in the temperature range for 60 to 3000 seconds, preferably 1000 seconds. On the other hand, BF steel (Bainitec ferritic steel: C 0.1-0.6 wt%, Si 1.5 wt%, Mn 1.5 wt%, etc., among the coil materials made of thin steel strips having the same wall thickness, hereinafter simply In the case of adopting “BF steel”), the solution is heated to 950 ° C., preferably held for 1200 seconds, and then rapidly cooled to the austempering temperature, that is, 325 to 475 ° C. Then, the austempering treatment is performed by holding in the temperature range, that is, the temperature range of 325 to 475 ° C. for 60 to 3000 seconds, preferably 1000 seconds. As the austempering treatment conditions in the heat treatment of the present invention, the treatment temperature was set to 325 to 475 ° C. The amount of retained austenite was insufficient when the temperature was lower than 325 ° C., whereas the amount of residual austenite was precipitated when the temperature exceeded 475 ° C. This is because there is a shortage. Further, the reason why the austempering time is set to 60 to 3000 seconds is that when the amount is less than 60 seconds, the amount of retained austenite is insufficient, and when it exceeds 3000 seconds, the retained austenite decomposes and decreases.
The TRIP steel (AM steel or BF steel) includes those disclosed in, for example, Japanese Patent No. 3253068, Japanese Patent Application Laid-Open No. 2002-302734, Japanese Patent Application Laid-Open No. 2006-207021, and the like. Absent.

  The solution treatment and austempering treatment by the above heat treatment for the TRIP steel sheet is any of high frequency induction welding, high frequency resistance welding, low frequency resistance welding, DC resistance welding, TIG welding, plasma welding, and laser welding. After adopting the method, after forming a desired ERW steel pipe or welded steel pipe, or after cutting a coil material made of a strip steel plate made of TRIP steel into a predetermined dimension, the above heat treatment is applied to the steel plate Any one of the methods of forming a desired ERW steel pipe or welded steel pipe can be arbitrarily employed, but in the present invention, the inner peripheral surface of the obtained ERW steel pipe or welded steel pipe, that is, various fuels It is an indispensable requirement to form a Ni plating layer at a site where high-pressure fluid such as the same repeatedly contacts. As a means for forming the Ni plating layer, any of pure Ni plating, Ni / P plating, Ni alloy plating, etc., electric Ni plating, chemical Ni / P plating, and chemical Ni / B plating may be used alone or in combination. Moreover, it is desirable that the thickness of the Ni plating layer to be formed is in the range of 1 to 10 μm. If the Ni plating film thickness is less than 1 μm, sufficient corrosion resistance cannot be ensured against repeated contact with high-pressure fluid. If the film thickness exceeds 10 μm, the plating layer is cured and plastic such as bending There is concern about the occurrence of cracks and peeling due to deformation.

  The high-tensile steel pipe for automobile high-pressure piping obtained as described above is made of TRIP steel such as AM steel and BF steel, and has a wall thickness of 2.5 mm or less and an outer diameter of 12.7 mm or less. Since it is an electric-welded steel pipe or a welded steel pipe, it can be provided at a relatively low cost as a high-pressure pipe for fluid that fluctuates violently at high pressure, such as a fuel pipe for automobiles, a brake pipe, a power steering pipe, and an injection pipe for a direct injection gasoline engine. In addition, the coil material of thin steel strip such as AM steel and BF steel selected for thin-walled electric-welded steel pipe or welded steel pipe has a very smooth surface due to the transfer of the rolling roll finished as the original characteristics of the coil material. In addition to the original advantages, the surface layer structure becomes dense due to surface reduction and rapid cooling during rolling, and defects such as non-metallic inclusions and wrinkles are extremely small compared to seamless steel pipes. High-strength steel pipes made of thin TRIP steel that are welded or electro-welded with very few surface defects are intense at high pressures such as automotive fuel pipes, brake pipes, power steering pipes, and direct-injection gasoline engine injection pipes. When used as a piping for fluids with variable pressure, the bending process of the pipe adds processing strain to the inside and outside of the bent part, so that processing-induced martensite is achieved regardless of compression or tension. Reinforced by the hardened occur, it is possible to improve the 耐繰 barbs pressure fatigue strength.

  Further, when the high-tensile steel pipe for high-pressure automobile piping according to the present invention is used as a fuel injection pipe having an injection pressure of 12 to 20 MPa or more in a direct injection gasoline engine, processing-induced martensite is generated on the entire inner surface of the pipe, thereby improving internal pressure fatigue strength. Needless to say, even though it is a welded steel pipe or an ERW steel pipe made from a coil material of a thin steel strip with very few surface defects, it should have a non-metallic inclusion or notch on the inner surface. Even when the tensile stress due to the repeated internal pressure exceeding 12 to 20 MPa is concentrated at the tip of the notch of the defect and the crack is about to proceed, the processing-induced martens that are intensively generated at the tip of the crack. Properties that can harden the site and prevent the progress of cracks, and work-hardening martensite due to the bending strain described above, resulting in compressive stress on the inner surface Become effective and - together, can provide a high-tensile steel pipe for automotive high-pressure pipe having a high resistance to internal pressure fatigue limit stress. In addition, the high-tensile steel pipe for automobile high-pressure piping according to the present invention is formed on the inner peripheral surface of the pipe where the high-pressure fluid is repeatedly contacted with a strong Ni plating layer having excellent corrosion resistance. A healthy state can be maintained over a long period of time even against repeated contact with a corrosive fluid of high temperature and pressure.

Using a TRIP steel plate (steel plate strength 460 MPa) having a plate thickness of 0.6 mm and a coil width of 41.2 mm made of AM steel (annealed martensite steel: C 0.20 wt%, Si 1.5 wt%, Mn 1.5 wt%), A plurality of ERW steel pipes with a pipe diameter of 8 mm at a pipe making speed of 60 m / min with a DC characteristic low frequency resistance welder, and then according to the heat pattern of AM steel solution treatment and austemper treatment shown in FIG. These electric resistance welded steel pipes were held at 950 ° C. for 1000 seconds and subjected to a solution treatment, then rapidly cooled by an oil quench process, then held at 780 ° C. for 1000 seconds and reheated to 400 ° C. The steel wire is made of TRIP steel with a strength of 1150 MPa and an austenite volume ratio of 21%. To obtain a number.
One was taken out from the obtained ERW steel pipe, and the exposed part except the inner peripheral part was masked, and then the inner peripheral surface of the ERW steel pipe was subjected to Ni plating by electroplating. At this time, the composition of the plating solution used is as follows: nickel sulfate: 250 g / L, nickel chloride: 40 g / L, boric acid: 40 g / L, top Leona NL1 (Okuno Pharmaceutical): 15 g / L, top Leona NL2 (Okuno) Pharmaceutical): 0.75 g / L, nickel carrier (Okuno Pharmaceutical): 3.0 g / L, plating solution temperature: 55 ° C., plating solution pH: 4.3, current density: 3 A / dm ² , electrode As a result, electric Ni plating was performed using a Pt wire for a processing time of 5 minutes to obtain a high-tensile steel pipe for automobile high-pressure piping according to the present invention.
It was confirmed that an Ni plating layer having a film thickness of 3 μm was formed in a uniform state on the inner peripheral surface of the obtained high-tensile steel pipe. Note that it is also possible to use an insoluble electrode such as Ni, Ta, Ti, Ti—Pt in place of the Pt line used as the electrode.

  The high-tensile steel pipe for automobile high-pressure piping according to the present embodiment thus obtained was added to ethanol mixed gasoline (E30) as a base fuel, formic acid: 0.15% as an additive, and distilled water: 2 As a result of being subjected to a corrosion resistance test immersed in a test fuel heated to 40 ° C. for 1000 hours, no red rust or the like was found on the inner peripheral surface of the high-strength steel pipe, It was confirmed that the Ni plating layer was maintained in a healthy state. On the other hand, a 180-degree bending test was performed on the high-tensile steel pipe with a grooved roll at a radius of 20 mm. The occurrence of was not seen. In addition, as a result of conducting a spreading test and a bending test according to JASO M 101 “Regulation of metal pipes for automobile piping” on ERW steel pipes that were not subjected to Ni plating after the above heat treatment, 1.4D (1.2D or more) was shown, and in the bending test, no adhesion abnormality was confirmed in the welded portion. That is, in this example, the TRIP steel sheet was piped without being subjected to austempering, and austempering was performed after pipe making, but the sheet thickness (thickness) was as thin as 0.6 mm so that it was in a complete state. It was also confirmed that the austempering treatment was performed and processing-induced martensite was generated.

Using the electric resistance welded steel pipe obtained in Example 1, the composition of the plating solution used was nickel sulfate: 250 g / L, nickel chloride: 40 g / L, boric acid: 40 g / L, BLS-MU (manufactured by Ebara Eugene ): 10 g / L, BLS-L (manufactured by Ebara Eugene): 1.5 g / L, plating solution temperature: 55 ° C., plating solution pH: 4.3, current density: 3 A / dm ² , Pt wire as electrode Was used, and the electric Ni plating was performed in the same manner as in Example 1 except that the treatment time was set to 13 minutes. Thus, a high-tensile steel pipe for automobile high-pressure piping according to this example was obtained.
It was confirmed that an Ni plating layer having a film thickness of 8 μm was formed in a uniform state on the inner peripheral surface of the obtained high-tensile steel pipe. The obtained high-tensile steel pipe was subjected to a corrosion resistance test and a bending test under the same conditions as in Example 1. As a result, the same excellent results as in Example 1 were confirmed.

As a plating solution to be used, Sumer S-780 (manufactured by Kanigen): 200 g / L was used, a plating solution temperature: 92 ° C., a plating solution pH: 4.4, and a treatment time: 10 minutes of chemical Ni / P plating was applied. Except for the above, a high-tensile steel pipe for automobile high-pressure piping was obtained in the same manner as in Example 1 above.
It was confirmed that a Ni / P plating layer having a thickness of 3 μm was formed in a uniform state on the inner peripheral surface of the obtained high-tensile steel pipe. In addition, as a result of subjecting the high-tensile steel pipe for automobile high-pressure piping according to the present example to the corrosion resistance test and the bending test under the same conditions as in Example 1, the same excellent results as in Example 1 were confirmed.

  A high-strength steel pipe for automobile high-pressure piping was obtained in the same manner as in Example 3 except that the plating solution used was Nimden 5X (manufactured by Uemura Kogyo): 200 g / L and the treatment time was 20 minutes. It was confirmed that a 6 μm thick Ni / P plating layer was formed in a uniform state on the inner peripheral surface of the obtained high-tensile steel pipe. In addition, as a result of subjecting the high-tensile steel pipe for automobile high-pressure piping according to the present example to the corrosion resistance test and the bending test under the same conditions as in Example 1, the same excellent results as in Example 1 were confirmed.

  The plating solution to be used is a top chemialloy B-1 (Okuno Pharmaceutical Co., Ltd.) stock solution, the plating solution temperature: 65 ° C., the plating solution pH: 6.7, and the treatment time: 15 minutes, except for chemical Ni / B plating. Obtained a high-tensile steel pipe for automobile high-pressure piping in the same manner as in Example 3 above. It was confirmed that a Ni / B plating layer having a thickness of 1.5 μm was formed in a uniform state on the inner peripheral surface of the obtained high-tensile steel pipe. In addition, as a result of subjecting the high-tensile steel pipe for automobile high-pressure piping according to the present example to the corrosion resistance test and the bending test under the same conditions as in Example 1, the same excellent results as in Example 1 were confirmed.

  A high-tensile steel pipe for automobile high-pressure piping was obtained in the same manner as in Example 5 except that the treatment time for chemical Ni / B plating was changed to 30 minutes. It was confirmed that a Ni / B plating layer having a thickness of 3 μm was formed in a uniform state on the inner peripheral surface of the obtained high-tensile steel pipe. In addition, as a result of subjecting the high-tensile steel pipe for automobile high-pressure piping according to the present example to the corrosion resistance test and the bending test under the same conditions as in Example 1, the same excellent results as in Example 1 were confirmed.

The above Example 5 except that the plating solution used was BEL801 (manufactured by Uemura Kogyo Co., Ltd.), the plating solution temperature was 62 ° C., the plating solution pH was 6.3, and the treatment time was 20 minutes. In the same manner, a high-tensile steel pipe for automobile high-pressure piping was obtained. On the inner peripheral surface of the obtained high strength steel pipe, it was confirmed that a Ni / B plating layer having a thickness of 2 μm was formed in a uniform state. As a result of being subjected to a corrosion resistance test and a bending test under the same conditions, excellent results similar to those of Example 1 were confirmed.
[Comparative Example 1]

Using the ERW steel pipe obtained by Example 1 and not plated with Ni on its inner peripheral surface, it was subjected to a corrosion resistance test under the same conditions as in Example 1. As a result, the inner circumference of the steel pipe after 1000 hours passed. On the surface, scattered red rust was observed, and it was confirmed that the weight after the test was reduced by 0.13%.
[Comparative Example 2]

A high-tensile steel pipe for automobile high-pressure piping was obtained in the same manner as in Example 1 except that when the electric Ni plating was applied to the inner peripheral surface of the ERW steel pipe after the heat treatment, the treatment time was 1 minute. Under the present circumstances, the film thickness of the Ni plating layer produced | generated on the internal peripheral surface of the said high-tensile steel pipe for motor vehicle high-pressure piping was 0.5 micrometer. As a result of subjecting the obtained high-tensile steel pipe for automobile high-pressure piping to a corrosion resistance test under the same conditions as in Example 1, generation of red rust scattered on the inner peripheral surface of the inner pipe 2 after 1000 hours. It was confirmed that the weight after the test was reduced by 0.1%.
[Comparative Example 3]

  A high-tensile steel pipe for automobile high-pressure piping was obtained in the same manner as in Example 4 except that chemical Ni / P was applied in which the treatment time was changed to 45 minutes. On the inner peripheral surface of the obtained high-tensile steel pipe, it was recognized that a Ni / P plating layer having a film thickness of 13 μm was generated in a uniform state, and the obtained high-tensile steel pipe for automobile high-pressure piping was As a result of being subjected to a corrosion resistance test and a bending test under the same conditions as in Example 1, no occurrence of rust was observed on the inner peripheral surface of the high-strength steel pipe, and no abnormality such as a decrease in weight was observed. In the test, the occurrence of cracks was observed in the plating film.

A TRIP steel plate made of BF steel (Bainitec ferrite steel: C 0.35 wt%, Si 1.5 wt%, Mn 1.5 wt%) having a plate thickness of 1.0 mm and a coil width of 39.1 mm is fixed to the BF steel shown in FIG. Based on the heat pattern of the solution treatment and austempering treatment, it is held at 950 ° C. for 1200 seconds for solid solution treatment, then rapidly cooled to about 400 ° C. and held at the temperature range for 500 seconds to perform austempering treatment. Further, after performing an oil quench treatment to room temperature, the obtained austempered steel plate (steel plate strength 1120 MPa) was used to make a pipe with a TIG welder at a pipe making speed of 4.2 m / min, and a strength of 1010 MPa, A plurality of welded steel pipes made of TRIP steel having a volume fraction of retained austenite of 21% and a pipe diameter of 12.7 mm were obtained. This example is obtained by taking out one of the obtained welded pipes and masking the exposed portion excluding the inner peripheral surface, and then performing an electric Ni plating process under the same conditions as in Example 1 above. A high-tensile steel pipe for automobile high-pressure piping was obtained.
It was confirmed that a Ni plating layer having a thickness of 3 μm was formed in a uniform state on the inner peripheral surface of the obtained high-strength steel pipe as in Example 1. The obtained high strength steel pipe was subjected to a corrosion resistance test and a bending test under the same conditions as in Example 1. As a result, the Ni plating layer formed on the inner peripheral surface of the high strength steel pipe was in a healthy state. The same excellent results as those of Example 1 were confirmed.
On the other hand, as a result of subjecting the welded steel pipe that was piped after the above heat treatment and had not yet been subjected to Ni plating to the pipe expansion test and the bending test as in Example 1, the pipe expansion test showed 1.4D (1.2D or more). In the bending test, as in Example 1, no special adhesion abnormality was observed in the welded portion.
Further, in this example, the heat treatment was performed in the state of a steel plate, and since the austempering treatment was not performed after the pipe forming, a slight disappearance of retained austenite was seen in the part affected by the bonding heat, but the reheating treatment was performed. As a result, it was easily compensated by application, and a result comparable to that of Example 1 was confirmed.

  A high-tensile steel pipe for automobile high-pressure piping according to this example was used in the same manner as in Example 3 except that a welded steel pipe made of BF steel piped according to Example 8 was used instead of the ERW electric steel pipe. Obtained. It was confirmed that a Ni / P plating layer having a thickness of 3 μm was formed in a uniform state on the inner peripheral surface of the obtained high-tensile steel pipe. In addition, as a result of subjecting the high-tensile steel pipe for automobile high-pressure piping according to the present example to the corrosion resistance test and the bending test under the same conditions as in Example 1, the same excellent results as in Example 1 were confirmed.

  A high-tensile steel pipe for automobile high-pressure piping according to this example was used in the same manner as in Example 5 except that a welded steel pipe made of BF steel produced in Example 8 was used instead of the ERW steel pipe made of AM steel. Obtained. It was confirmed that a Ni / B plating layer having a thickness of 1.5 μm was formed in a uniform state on the inner peripheral surface of the obtained high-tensile steel pipe. In addition, as a result of subjecting the high-tensile steel pipe for automobile high-pressure piping according to the present example to the corrosion resistance test and the bending test under the same conditions as in Example 1, the same excellent results as in Example 1 were confirmed.

  The high-strength steel pipe for automobile high-pressure piping according to the present invention has extremely excellent pressure strength as described above, and at the same time, has a film thickness of 1 to 10 μm on the inner peripheral surface of the pipe that directly contacts various fluids including biomass fuel. By applying the Ni plating layer, the corrosion resistance is remarkably improved, and not only the moisture contained in the biomass fuel but also the high pressure fuel containing corrosive factors such as the organic acid generated by the oxidation of gasoline and the decomposition of alcohol It has been confirmed that it can sufficiently withstand repeated contact, and when forming the Ni plating layer, any of Ni electroplating, chemical Ni / P plating, and chemical Ni / B plating can be used. Since only a single plating layer is applied by a simple operation, it can greatly contribute to simplification of operations and cost reduction. The plating in the present invention may be multilayer plating by combining electroplating and chemical plating.

The high-strength steel pipe for automobile high-pressure piping made of the TRIP steel welded steel pipe or ERW steel pipe of the present invention has high plastic deformability and becomes a work-induced martensite structure by plastic working, and the internal flaw generated by internal pressure or external force. Because it is possible to effectively prevent the progress of cracks and the like originating from the notch tip due to non-metallic inclusions, etc., the internal pressure fatigue resistance can be improved, so automobile fuel piping, brake piping, power steering piping In the case of an injection pipe for a direct-injection gasoline engine, an excellent effect of being able to withstand a high injection pressure of 12 to 20 MPa or more can be obtained, and in addition, the high-tensile steel pipe for automobile high-pressure piping according to the present invention is The Ni plating layer applied to the peripheral surface exhibits an excellent anticorrosive action against high-temperature and high-pressure corrosive fluids, including, for example, various alcohol components. In the case of using the biomass fuel, etc., it is possible to maintain the fuel pipe in a healthy state, global warming in environmental by CO ₂ in recent years, further fuel efficiency measures like for laborsaving It is expected to contribute greatly.

It is a figure which shows an example of the heat pattern of the solution treatment and the austemper process of AM steel in this invention. It is a figure which similarly shows an example of the heat pattern of the solution treatment of BF steel, and an austemper process.

Claims (10)

  Low alloy high strength steel AM steel (annealed martensite steel: C 0.1 to 0.6 wt%, Si 1.5 wt%, Mn 1.5 wt%, etc.) that has undergone austempering treatment after solution treatment, or ERW made of TRIP steel plate (low alloy transformation induced plastic strength steel plate) made of BF steel (Bainitec ferrite steel: C 0.1 to 0.6 wt%, Si 1.5 wt%, Mn 1.5 wt%, etc.) A high-strength steel pipe for automobile high-pressure piping, which is a steel pipe or a welded steel pipe and has an inner peripheral surface plated with Ni.   The AM steel is annealed martensitic steel containing C 0.1-0.6 wt%, Si 1.5 wt%, Mn 1.5 wt%), and the BF steel is C 0.1-0.6 wt%, Si 1 The high-tensile steel pipe for automobile high-pressure piping according to claim 1, wherein the high-tensile steel pipe is a bainiteitic ferritic steel containing 0.5 wt% and Mn 1.5 wt%.   The high-strength steel pipe for high-pressure automobile piping according to claim 1 or 2, wherein the Ni plating is an electric Ni plating of pure Ni plating, Ni / P plating, or Ni alloy plating.   The high-tensile steel pipe for automobile high-pressure piping according to claim 1 or 2, wherein the Ni plating is Ni / P plating or chemical Ni plating of Ni / B.   The high-tensile steel pipe for automobile high-pressure piping according to any one of claims 1 to 4, wherein the Ni plating has a thickness of 1 to 10 µm.   The solution treatment for the AM steel is a heat treatment which is rapidly cooled after being heated to 950 ° C., and the solution treatment for the BF steel is a heat treatment for rapidly cooling to the austempering temperature after being heated to 950 ° C. The high-tensile steel pipe for high-pressure automobile piping according to any one of claims 1 to 5.   The austempering treatment for the AM steel is a heat treatment that is held at 780 ° C. for 60 to 3000 seconds and then rapidly cooled to 325 to 475 ° C. and then held in the temperature range for 60 to 3000 seconds, and the austempering treatment for the BF steel is The high-tensile steel pipe for automobile high-pressure piping according to any one of claims 1 to 5, wherein the high-tensile steel pipe is used for heat-holding in a temperature range of 325 to 475 ° C.   The TRIP steel plate (low alloy transformation-induced plastic type strength steel plate) made of AM steel or BF steel of the low alloy high strength steel is a steel plate that has been rolled or subjected to normal softening heat treatment, and has retained austenite. The high-tensile steel pipe for automobile high-pressure piping according to any one of claims 1 to 7, wherein the high-tensile steel pipe is held in an amount of 5 to 25 wt%. The thickness of the ERW or welded steel pipe made of TRIP steel is 2.5 mm or less, the outer diameter is 12.7 mm or less, the retained austenite is 5 to 25 wt%, and the tensile strength is 800 to 1800 N / mm ^2. The high-tensile steel pipe for high-pressure automobile piping according to any one of claims 1 to 8.   The above-mentioned TRIP steel ERW steel pipe or welded steel pipe is formed by forming a tubular body, and the joint ends thereof are high frequency induction welding, high frequency resistance welding, low frequency resistance welding, DC resistance welding, TIG welding, plasma. The high-tensile steel pipe for automobile high-pressure piping according to any one of claims 1 to 9, wherein the high-tensile steel pipe is joined by welding or laser welding.

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