WO2020230795A1 - 中空スタビライザー用電縫鋼管 - Google Patents
中空スタビライザー用電縫鋼管 Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
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- C22C38/008—Ferrous alloys, e.g. steel alloys containing tin
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
- B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
- B23K35/24—Selection of soldering or welding materials proper
- B23K35/30—Selection of soldering or welding materials proper with the principal constituent melting at less than 1550 degrees C
- B23K35/3053—Fe as the principal constituent
- B23K35/3073—Fe as the principal constituent with Mn as next major constituent
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D3/00—Diffusion processes for extraction of non-metals; Furnaces therefor
- C21D3/02—Extraction of non-metals
- C21D3/04—Decarburising
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/10—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies
- C21D8/105—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies of ferrous alloys
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/08—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes
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- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
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- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K2103/00—Materials to be soldered, welded or cut
- B23K2103/02—Iron or ferrous alloys
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/25—Process efficiency
Definitions
- the present invention relates to an electric-resistance-welded steel pipe or tube for hollow stabilizer, and in particular, even when heat treatment is performed in the air in the hollow stabilizer manufacturing process, only the ferrite decarburized layer is used.
- the present invention relates to an electric resistance welded steel pipe for a hollow stabilizer, which can suppress the formation of a total decarburized layer and can obtain a hollow stabilizer having excellent fatigue characteristics.
- General automobiles are equipped with stabilizers for the purpose of suppressing the rolling of the vehicle body during cornering and improving driving stability during high-speed driving.
- a solid stabilizer using steel bars has been used as the stabilizer, but in recent years, a hollow stabilizer using a steel pipe has been generally adopted in order to reduce the weight.
- a hollow stabilizer is usually manufactured by coldly forming a steel pipe as a material into a desired shape and then performing a tempering treatment such as quenching and tempering.
- a tempering treatment such as quenching and tempering.
- As the steel pipe seamless steel pipe, electric resistance welded steel pipe (hereinafter referred to as electric resistance steel pipe) and the like are used. Among them, electric resistance steel pipe is widely used because it is relatively inexpensive and has excellent dimensional accuracy. ing.
- the electro-sewn steel pipe used as a material for such a hollow stabilizer (electric-sewn steel pipe for a hollow stabilizer) is required to have excellent fatigue characteristics after being formed into a stabilizer and subjected to heat treatment such as quenching and tempering. Therefore, various studies have been conducted on the influence of the surface texture after the heat treatment on the fatigue characteristics.
- surface decarburization is considered to be an important factor in the surface properties. If surface decarburization occurs in the heating stage of quenching, the surface hardness cannot be improved even by quenching, and as a result, sufficient fatigue characteristics cannot be obtained.
- Patent Document 1 proposes a method for manufacturing an electrosewn steel pipe for a hollow stabilizer in which the thickness of the decarburized layer on the inner surface side of the pipe is suppressed to 120 ⁇ m or less.
- Patent Document 2 proposes an electro-sewn steel pipe in which the formation of a ferrite decarburized layer during quenching is suppressed by adding at least one of Cu and Sb. Specifically, the thickness of the ferrite decarburized layer formed when heated at 800 ° C. for 1 hour in the atmosphere is suppressed to less than 0.15 mm.
- the thickness of the decarburized layer on the inner surface side of the pipe is suppressed to 120 ⁇ m or less.
- the thickness of the decarburized layer which is the focus of Patent Document 1 is a value in the steel pipe before quenching, not a value after quenching.
- the stabilizer it is considered necessary to reduce the thickness of the decarburized layer after quenching, but the thickness of the decarburized layer after quenching is a condition of quenching. Therefore, it cannot always be said that the electrosewn steel pipe for a hollow stabilizer as proposed in Patent Document 1 can sufficiently suppress surface decarburization during quenching.
- the atmosphere at the time of quenching can be mentioned as one that has a particularly large effect on the thickness of the decarburized layer after quenching.
- heating at the time of quenching is performed in the atmosphere in consideration of productivity and the like.
- energization heating is used as a heating method having a short heating time and excellent productivity.
- heating is performed in the atmosphere by sandwiching both ends of the stabilizer with electrodes and passing electricity between the electrodes.
- surface decarburization occurs by heating in the atmosphere in this way.
- An object of the present invention is to solve the above problems, and it is possible to suppress the formation of not only the ferrite decarburized layer but also the entire decarburized layer even when heat treatment is performed in the air in the stabilizer manufacturing process. It is an object of the present invention to provide a heat-treated steel pipe for a hollow stabilizer capable of obtaining a hollow stabilizer capable of obtaining excellent fatigue characteristics.
- Patent Document 2 also proposes the addition of Sb to suppress decarburization.
- Sb has the effect of increasing the lattice constant of iron, but Sb liquefies during heating and erodes the austenite grain boundaries, thus reducing the toughness of the stabilizer after quenching and tempering. Therefore, it is necessary to keep the addition of Sb to the minimum necessary.
- FIG. 1 is a graph showing an example between the phases of the Sn content and the total decarburized layer depth after quenching. Specifically, hot-rolled steel sheets (plate thickness: 4 mm) having various Sn contents were held in the air at 900 ° C. for 10 minutes, and then cooled at a cooling rate of about 20 ° C./s. Then, the total depth of the decarburized layer on the surface was measured. The composition of the hot-rolled steel sheet other than Sn was kept constant as follows.
- the present invention is based on the above findings, and its gist structure is as follows.
- the component composition is further increased by mass%.
- Sb The electrosewn steel pipe for a hollow stabilizer according to 1 above, which contains 0.020% or less.
- the component composition is further increased by mass%.
- the present invention it is possible to suppress the formation of not only the ferrite decarburized layer but also the entire decarburized layer even when the heat treatment is performed in the air in the hollow stabilizer manufacturing process. Therefore, by using the electrosewn steel pipe of the present invention as a material, a hollow stabilizer having excellent fatigue characteristics can be manufactured. Further, according to the present invention, surface decarburization can be suppressed not only in heat treatment in a high-cost non-oxidizing atmosphere but also in heat treatment in an atmosphere at low cost and excellent in productivity. Therefore, the electrosewn steel pipe for a hollow stabilizer of the present invention can be extremely suitably used as a material for manufacturing a hollow stabilizer.
- FIG. 1 is a graph showing the phase between the Sn content and the total decarburized layer depth after quenching.
- the electric resistance welded steel pipe for a hollow stabilizer of the present invention (hereinafter, may be simply referred to as an electric resistance welded steel pipe) has the above-mentioned composition.
- an electric resistance welded steel pipe has the above-mentioned composition.
- C 0.20 to 0.40%
- C is an element having an action of promoting the formation of martensite and increasing the strength (hardness) of steel by solid solution through the improvement of hardenability.
- the content of 0.20% or more is required. Therefore, the C content is 0.20% or more, preferably 0.21% or more.
- the C content is 0.40% or less, preferably 0.39% or less, and more preferably 0.38% or less.
- Si 0.1-1.0%
- Si is an element that acts not only as a deoxidizer but also as a solid solution strengthening element.
- a content of 0.1% or more is required. Therefore, the Si content is 0.1% or more, preferably 0.2% or more.
- the Si content is 1.0% or less, preferably 0.8% or less, more preferably 0.5% or less, still more preferably 0.41% or less.
- Mn 0.1-2.0%
- Mn is an element that dissolves in a solid solution and contributes to improving the strength of steel and also improves the hardenability of steel.
- the content of 0.1% or more is required. Therefore, the Mn content is 0.1% or more, preferably 0.5% or more.
- the Mn content is 2.0% or less, preferably 1.8% or less, and more preferably 1.7% or less.
- P 0.1% or less
- P is an element contained in steel as an impurity and segregates at grain boundaries and the like to reduce weld crackability and toughness. Therefore, in order to use it as a hollow stabilizer, it is necessary to reduce the P content to 0.1% or less. Therefore, the P content is 0.1% or less, preferably 0.05% or less, and more preferably 0.02% or less. On the other hand, from the viewpoint of weld crackability and toughness, the lower the P content, the better. Therefore, the lower limit of the P content is not limited and may be 0. However, excessive reduction of P content leads to an increase in manufacturing cost. Therefore, from the viewpoint of cost reduction, the P content is preferably 0.001% or more, more preferably 0.005% or more, and further preferably 0.008% or more.
- S 0.01% or less
- S is an element that exists as a sulfide-based inclusion in steel and lowers hot workability, toughness, and fatigue resistance. In order to use it as a hollow stabilizer, it is necessary to reduce the S content to 0.01% or less. Therefore, the S content is 0.01% or less, preferably 0.005% or less, and more preferably 0.003% or less. On the other hand, from the viewpoint of hot workability, toughness, and fatigue resistance, the lower the S content, the better. Therefore, the lower limit of the S content is not limited and may be 0. However, excessive reduction of S content leads to an increase in manufacturing cost. Therefore, from the viewpoint of cost reduction, the S content is preferably 0.0001% or more, more preferably 0.0005% or more, and further preferably 0.001% or more.
- Al 0.01 to 0.10%
- Al is an element that acts as an antacid and has the effect of binding to N and securing the amount of solid solution B effective for improving hardenability. Further, Al precipitates as AlN and has an effect of preventing coarsening of austenite grains during quenching and heating. In order to obtain the above effect, a content of 0.01% or more is required. Therefore, the Al content is set to 0.01% or more. On the other hand, if it is contained in a large amount exceeding 0.10%, the amount of oxide-based inclusions increases and the fatigue life decreases. Therefore, the Al content is 0.10% or less, preferably 0.07% or less, and more preferably 0.05% or less.
- Cr 0.01-0.50%
- Cr is an element having an effect of improving hardenability.
- the Cr content is 0.01% or more, preferably 0.05% or more.
- the Cr content is 0.50% or less, preferably 0.40% or less, and more preferably 0.30% or less.
- Ti 0.010 to 0.050%
- Ti is an element having an action of fixing N in steel as TiN. However, if the Ti content is less than 0.010%, the above action is not sufficiently exhibited. Therefore, the Ti content is set to 0.010% or more. On the other hand, if the Ti content exceeds 0.050%, the workability and toughness of the steel deteriorate. Therefore, the Ti content is set to 0.050% or less, preferably 0.040% or less.
- B 0.0005 to 0.0050%
- B is an element that can improve the hardenability of steel by adding a small amount.
- B has an action of strengthening the grain boundaries and suppresses grain boundary embrittlement due to P segregation.
- a content of 0.0005% or more is required. Therefore, the B content is 0.0005% or more, preferably 0.0010% or more.
- the B content is 0.0050% or less, preferably 0.0030% or less.
- Ca 0.0001 to 0.0050%
- Ca is an element having an action of controlling the morphology of sulfide-based inclusions into fine substantially spherical inclusions.
- the Ca content is set to 0.0001% or more.
- the Ca content is 0.0050% or less, preferably 0.0030% or less, and more preferably 0.0015% or less.
- N 0.0050% or less
- N is an element that is inevitably contained as an impurity, and by combining with a nitride-forming element in steel, coarsening of crystal grains is suppressed, and further strength is increased after tempering. Contribute to.
- a content of more than 0.0050% reduces the toughness of the weld. Therefore, the N content is 0.0050% or less, preferably 0.0040% or less.
- the lower limit of the N content is not limited and may be 0, but the above effect can be obtained by adding a certain amount of N.
- excessive reduction of N content causes an increase in manufacturing cost. Therefore, from these viewpoints, the N content is preferably 0.001% or more, and more preferably 0.0015% or more.
- Sn 0.010 to 0.050%
- Sn is one of the most important elements in the present invention.
- the addition of Sn increases the lattice constant of iron, which suppresses the outward diffusion of carbon in the steel, thus suppressing the surface decarburization reaction.
- the Sn content is 0.050% or less, preferably 0.045% or less.
- the electrosewn steel pipe according to the embodiment of the present invention contains each of the above elements and has a component composition consisting of the balance Fe and unavoidable impurities.
- the above-mentioned component composition can further optionally contain Sb in the amounts described below.
- Sb 0.020% or less
- Sb is an element having an effect of increasing the lattice constant of iron and suppressing the outward diffusion of carbon in steel, similar to Sn. Therefore, by adding Sb in addition to Sn, surface decarburization can be further suppressed. However, Sb liquefies during heating and erodes the austenite grain boundaries, which lowers the toughness of the stabilizer after quenching and tempering. Therefore, it is necessary to keep the addition of Sb to the minimum necessary. Therefore, when Sb is added, the Sb content is 0.020% or less, preferably less than 0.010%, and more preferably 0.008% or less.
- the amount of the above-mentioned component composition further optionally one or two or more selected from the group consisting of Cu, Ni, Nb, W, V, Mo, and REM is described below. Can be included in.
- Cu 1.0% or less
- Cu is an element that has the effect of improving hardenability and corrosion resistance.
- the Cu content is 1.0% or less, preferably 0.50% or less.
- the lower limit of the Cu content is not particularly limited, but from the viewpoint of enhancing the effect of adding Cu, it is preferable that the Cu content is 0.05% or more when Cu is added.
- Ni 1.0% or less
- Ni is an element that has the effect of improving hardenability and corrosion resistance.
- the Ni content is 1.0% or less, preferably 0.50% or less.
- the lower limit of the Ni content is not particularly limited, but from the viewpoint of enhancing the effect of adding Ni, when Ni is added, the Ni content is preferably 0.05% or more.
- Nb 0.05% or less
- Nb is an element that forms fine carbides and contributes to an increase in strength (hardness).
- the Nb content is 0.05% or less, preferably 0.03% or less.
- the lower limit of the Nb content is not particularly limited, but from the viewpoint of enhancing the effect of adding Nb, when Nb is added, the Nb content is preferably 0.001% or more.
- W 0.5% or less W is an element that forms fine carbides and contributes to an increase in strength (hardness), similar to Nb. However, if the W content exceeds 0.5%, the addition effect is saturated and an effect commensurate with the content cannot be obtained, which is economically disadvantageous. Therefore, the W content is 0.5% or less, preferably 0.3% or less.
- the lower limit of the W content is not particularly limited, but from the viewpoint of enhancing the effect of adding W, when W is added, the W content is preferably 0.01% or more.
- V 0.5% or less
- V is an element that forms fine carbides and contributes to an increase in strength (hardness), like Nb and W.
- the V content is 0.5% or less, preferably 0.3% or less.
- the lower limit of the V content is not particularly limited, but from the viewpoint of enhancing the effect of adding V, when V is added, the V content is preferably 0.01% or more.
- Mo 0.2% or less Mo is an element having an effect of improving hardenability. However, since Mo is a very expensive element, excessive addition leads to an increase in material cost. Therefore, the Mo content is 0.2% or less, preferably 0.15% or less. On the other hand, the lower limit of the Mo content is not particularly limited, but from the viewpoint of enhancing the effect of adding Mo, the Mo content is preferably 0.01% or more, and more preferably 0.05% or more. ..
- REM 0.02% or less REM (rare earth metal) is an element having an action of controlling the morphology of sulfide-based inclusions into fine substantially spherical inclusions, like Ca. REM can optionally be added to complement the action of Ca. However, if the REM content exceeds 0.02%, the amount of inclusions that are the starting points of fatigue cracks becomes excessive, so that the corrosion fatigue resistance characteristics are rather deteriorated. Therefore, the REM content is 0.02% or less, preferably 0.01% or less. On the other hand, the lower limit of the REM content is not particularly limited, but from the viewpoint of enhancing the effect of adding REM, when REM is added, the REM content is preferably 0.001% or more.
- Total decarburized layer depth 100 ⁇ m or less
- both the total decarburized layer depth on the inner surface and the total decarburized layer depth on the outer surface are 100 ⁇ m or less.
- the total decarburized layer depth referred to here refers to the total decarburized layer depth in a hollow stabilizer electrosewn steel pipe (bare pipe) as a material before being used in the stabilizer manufacturing process.
- the total decarburized layer depth is the total decarburized layer depth before heat treatment such as quenching.
- the total decarburized layer depth can be measured by the method described in Examples.
- the total decarburized layer depth exceeds 100 ⁇ m, the total decarburized layer depth further increases in the heat treatment in the subsequent stabilizer manufacturing process, and as a result, the fatigue strength required for the stabilizer cannot be secured.
- This increase in the depth of the total decarburized layer is remarkable especially when the heat treatment is performed in the atmosphere. Therefore, in order to obtain a hollow stabilizer having excellent fatigue characteristics even when heat treatment is performed in the air in the stabilizer manufacturing process, the total decarburized layer depth on the inner and outer surfaces of the electric resistance sewn steel pipe for the hollow stabilizer is obtained.
- Each must be 100 ⁇ m or less.
- the total depth of the decarburized layer is preferably 50 ⁇ m or less, and more preferably 20 ⁇ m or less.
- the lower limit is not particularly limited and may be, for example, 0 ⁇ m.
- the total depth of the decarburized layer on the inner and outer surfaces should be 1 ⁇ m or more from the viewpoint of ease of manufacturing. It is preferably 5 ⁇ m or more, and more preferably 5 ⁇ m or more.
- the depth of the ferrite decarburized layer on the inner surface and the outer surface is 100 ⁇ m or less.
- the dimensions of the electrosewn steel pipe for the hollow stabilizer can be any size without particular limitation, but the ratio of the wall thickness t (mm) to the outer diameter D (mm) of the steel pipe, t / D, is 10. It is preferably about 30%.
- the electric resistance welded steel pipe for a hollow stabilizer of the present invention can be manufactured by any method without particular limitation. That is, it is possible to use a steel material having the above-mentioned composition and manufacture according to a conventional method. Hereinafter, a suitable manufacturing method of the electric resistance welded steel pipe for the hollow stabilizer according to the embodiment of the present invention will be described.
- the electric resistance sewn steel pipe for a hollow stabilizer can be manufactured by subjecting a steel plate to an electric sewn pipe to form an electric sewn steel pipe, reheating the electric resistance sewn steel pipe, and then performing hot reduction rolling.
- the steel sheet any steel sheet having the above-mentioned composition can be used.
- the steel sheet is preferably a hot-rolled steel sheet.
- the electric sewing tube can be performed by any method without particular limitation.
- the steel plate is continuously cold-formed by a plurality of rolls to form a substantially cylindrical open pipe, and then the widthwise ends of the open pipes are abutted with each other by a squeeze roll and welded by electric stitching. It can be a sewn steel pipe.
- the electric sewing welding can be performed by, for example, high frequency resistance welding, induction heating, or the like.
- the progress of surface decarburization becomes particularly remarkable at high temperatures exceeding 1000 ° C.
- heating to such a high temperature is usually performed only in a reheating step after the electrosewn pipe and before hot reduction rolling. Therefore, conditions such as the heating temperature and time in the reheating step may be adjusted so that the total decarburized layer depth of the finally obtained electric resistance welded steel pipe for the stabilizer satisfies the above conditions.
- the heating temperature (reheating temperature) at the time of the reheating is preferably 850 to 1000 ° C. If the reheating temperature is less than 850 ° C., the desired weld toughness may not be ensured. On the other hand, when the reheating temperature exceeds 1000 ° C., surface decarburization becomes remarkable.
- the rolling temperature in the hot reduced diameter rolling is preferably 650 ° C. or higher. If the rolling temperature is less than 650 ° C., the workability may be lowered and it may be difficult to form a desired stabilizer shape. Further, the cumulative diameter reduction ratio in the hot reduction diameter rolling is preferably 30 to 90%. When the cumulative diameter reduction ratio is 30 to 90%, an electrosewn steel pipe for a hollow stabilizer having excellent workability can be obtained.
- a hot-rolled steel sheet (plate thickness: 4.5 mm) having the component composition shown in Table 1 was continuously formed by a plurality of rolls in a cold state to obtain a substantially cylindrical open tube.
- the circumferential ends of the open pipe were abutted and pressure-welded, and electric resistance welding was used to obtain an electric resistance steel pipe (outer diameter 89.1 mm ⁇ x wall thickness 4.5 mm). ..
- the obtained electric resistance sewn steel pipe was heated to 980 ° C. by induction heating and then subjected to diameter reduction rolling to obtain an electric sewn steel pipe for a hollow stabilizer.
- the conditions for the reduced diameter rolling were a rolling temperature of 800 ° C. and a cumulative diameter reduction ratio of 71%.
- the rolling temperature is a temperature measured by a radiation thermometer on the outlet side of the final rolling stand.
- the dimensions of the obtained electrosewn steel pipe for the hollow stabilizer were an outer diameter of 25.4 mm ⁇ ⁇ a wall thickness of 4.0 mm.
- the obtained electric resistance welded steel pipe for the hollow stabilizer was heat-treated. Specifically, first, the hollow stabilizer electric resistance sewn steel pipe was heated in an atmospheric furnace, held at 900 ° C. for 10 minutes, and then cooled at a cooling rate of 80 ⁇ 10 ° C./s to perform quenching. Next, the tempering treatment was performed in an atmospheric furnace under the conditions of a tempering temperature of 350 ° C. and a holding time of 20 minutes.
- a test piece for structure observation was taken from the heat-treated hollow stabilizer electrosewn steel pipe so that the cross section perpendicular to the pipe axis direction became the observation surface, and the ferrite decarburization depth and the ferrite decarburization depth were determined according to the method of JIS G 0558.
- the total decarburization depth was measured.
- the temperature of the steel pipe during the heat treatment was measured using a K thermocouple attached to the steel pipe.
- a torsional fatigue test was carried out in the atmosphere using the above-mentioned hardened and tempered tubular test piece, and the number of repetitions (fatigue life) until cracking occurred was determined.
- the conditions of the torsional fatigue test were load stress: ⁇ 400 MPa (both swings) and load cycle: 1 Hz.
- Step 2 the electric resistance welded steel pipe for the hollow stabilizer manufactured under the same conditions is heat-treated under the same conditions as in step 1 above, except that the heating during quenching is performed in a non-oxidizing atmosphere furnace (bright heat treatment furnace). , A reference sample without surface decarburization was prepared. Using the reference sample, a torsional fatigue test was performed under the same conditions as in step 1 above to determine the average fatigue life of 10 samples.
- a hollow stabilizer electrosewn steel pipe satisfying the conditions of the present invention has both a ferrite decarburized layer depth and a total decarburized layer depth on the inner and outer surfaces even after being heat-treated at 900 ° C. for 10 minutes in the atmosphere. was 70 ⁇ m or less.
- all of the electric resistance welded steel pipes for hollow stabilizers satisfying the conditions of the present invention had a reduction rate of fatigue strength of less than 10% when heat-treated in the atmosphere.
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Abstract
Description
C :0.35%、
Si:0.20%、
Mn:1.22%、
P :0.018%、
S :0.0015%、
Al:0.035%、
Cr:0.15%、
Ti:0.035%、
B :0.0020%、
Ca:0.0015%、
N :0.0022%、および
残部Feおよび不可避不純物。
C :0.20~0.40%、
Si:0.1~1.0%、
Mn:0.1~2.0%、
P :0.1%以下、
S :0.01%以下、
Al:0.01~0.10%、
Cr:0.01~0.50%、
Ti:0.010~0.050%、
B :0.0005~0.0050%、
Ca:0.0001~0.0050%、
N :0.0050%以下、および
Sn:0.010~0.050%、を含み、
残部Feおよび不可避的不純物からなる成分組成を有し、
内表面および外表面における全脱炭層深さが100μm以下である、中空スタビライザー用電縫鋼管。
Sb:0.020%以下を含む、上記1に記載の中空スタビライザー用電縫鋼管。
Cu:1.0%以下、
Ni:1.0%以下、
Nb:0.05%以下、
W :0.5%以下、
V :0.5%以下、
Mo:0.2%以下、および
REM:0.02%以下、からなる群より選択される1または2以上を含む、上記1または2に記載の中空スタビライザー用電縫鋼管。
本発明の中空スタビライザー用電縫鋼管(以下、単に電縫鋼管という場合がある)は、上述した成分組成を有する。以下、各成分の含有量の限定理由について説明する。なお、特に断らない限り、「%」は「質量%」を指すものとする。
Cは、焼入れ性の向上を介して、マルテンサイトの生成を促進するとともに、固溶して鋼の強度(硬さ)を増加させる作用を有する元素である。中空スタビライザーに求められる強度(硬さ)を確保するためには、0.20%以上の含有を必要とする。そのため、C含有量は0.20%以上、好ましくは0.21%以上とする。一方、C含有量が0.40%を超えると、焼割れの危険性が高くなることに加え、焼入れ後の靭性が低下する。そのため、C含有量は0.40%以下、好ましくは0.39%以下、より好ましくは0.38%以下とする。
Siは、脱酸剤として作用するとともに、固溶強化元素としても作用する元素である。前記効果を得るためには0.1%以上の含有を必要とする。そのため、Si含有量は0.1%以上、好ましくは0.2%以上とする。一方、1.0%を超えて含有すると、電縫溶接性が低下する。そのため、Si含有量は1.0%以下、好ましくは0.8%以下、より好ましくは0.5%以下、さらに好ましくは0.41%以下とする。
Mnは、固溶して鋼の強度向上に寄与するとともに、鋼の焼入れ性を向上させる元素である。中空スタビライザーに求められる強度(硬さ)を確保するためには、0.1%以上の含有を必要とする。そのため、Mn含有量は0.1%以上、好ましくは0.5%以上とする。一方、2.0%を超えて含有すると、靭性が低下することに加え、焼割れの危険が増大する。そのため、Mn含有量は2.0%以下、好ましくは1.8%以下、より好ましくは1.7%以下とする。
Pは、不純物として鋼中に含まれる元素であり、粒界等に偏析し、溶接割れ性および靭性を低下させる。そのため、中空スタビライザーとして用いるためにはP含有量を0.1%以下に低減する必要がある。そのため、P含有量は0.1%以下、好ましくは0.05%以下、より好ましくは0.02%以下とする。一方、溶接割れ性および靭性の観点からは、P含有量は低ければ低いほど良いため、P含有量の下限は限定されず、0であってよい。しかし、過度のP含有量の低減は製造コストの増加を招く。そのため、コスト低減という観点からは、P含有量を0.001%以上とすることが好ましく、0.005%以上とすることがより好ましく、0.008%以上とすることがさらに好ましい。
Sは、鋼中では硫化物系介在物として存在し、熱間加工性、靭性、耐疲労特性を低下させる元素である。中空スタビライザーとして用いるためにはS含有量を0.01%以下に低減する必要がある。そのため、S含有量は0.01%以下、好ましくは0.005%以下、より好ましくは0.003%以下とする。一方、熱間加工性、靭性、および耐疲労特性の観点からは、S含有量は低ければ低いほど良いため、S含有量の下限は限定されず、0であってよい。しかし、過度のS含有量の低減は製造コストの増加を招く。そのため、コスト低減という観点からは、S含有量を0.0001%以上とすることが好ましく、0.0005%以上とすることがより好ましく、0.001%以上とすることがさらに好ましい。
Alは、脱酸剤として作用するとともに、Nと結合し、焼入れ性向上に有効な固溶B量を確保する効果を有する元素である。また、Alは、AlNとして析出し、焼入れ加熱時のオーステナイト粒の粗大化を防止する作用を有する。前記効果を得るためには、0.01%以上の含有を必要とする。そのため、Al含有量は0.01%以上とする。一方、0.10%を超えて多量に含有すると、酸化物系介在物量が増加し、疲労寿命が低下する。そのため、Al含有量は0.10%以下、好ましくは0.07%以下、より好ましくは0.05%以下とする。
Crは焼入れ性を向上させる効果を有する元素である。前記効果を得るために、Cr含有量を0.01%以上、好ましくは0.05%以上とする。一方、Cr含有量が0.50%を超えると、酸化物が形成されやすくなり、電縫溶接部にCr酸化物が残存して電縫溶接品質が低下する。そのため、Cr含有量は0.50%以下、好ましくは0.40%以下、より好ましくは0.30%以下とする。
Tiは、鋼中のNをTiNとして固定する作用を有する元素である。しかし、Ti含有量が0.010%未満では前記作用が十分に発揮されない。そのため、Ti含有量は0.010%以上とする。一方、Ti含有量が0.050%を超えると鋼の加工性および靭性が低下する。そのため、Ti含有量は0.050%以下、好ましくは0.040%以下とする。
Bは、微量の添加で鋼の焼入れ性を向上させることができる元素である。また、Bは、粒界を強化する作用を有し、P偏析による粒界脆化を抑制する。前記効果を得るためには、0.0005%以上の含有を必要とする。そのため、B含有量は0.0005%以上、好ましくは0.0010%以上とする。一方、0.0050%を超えて含有しても、効果が飽和し経済的に不利となる。そのため、B含有量は0.0050%以下、好ましくは0.0030%以下とする。
Caは、硫化物系介在物の形態を微細な略球形の介在物に制御する作用を有する元素である。Caを添加することにより、腐食ピットの起点となる粒径:10μm以上の粗大なMnS粒子および粒径:10μm以上の粗大なTiS粒子の数を低減することができる。前記効果を得るために、Ca含有量を0.0001%以上とする。一方、0.0050%を超えて多量に含有すると、粗大なCaS系のクラスターが多くなりすぎ、かえって疲労き裂の起点となり、耐腐食疲労特性が低下する。そのため、Ca含有量は0.0050%以下、好ましくは0.0030%以下、より好ましくは0.0015%以下とする。
Nは、不純物として不可避的に含有される元素であり、鋼中の窒化物形成元素と結合することによって結晶粒の粗大化の抑制、さらには焼戻後の強度増加に寄与する。しかし、0.0050%を超える含有は、溶接部の靭性を低下させる。そのため、N含有量は0.0050%以下、好ましくは0.0040%以下とする。一方、N含有量の下限は限定されず、0であってよいが、ある程度の量のNを添加することにより前記効果を得ることもできる。また、過度のN含有量の低減は製造コストの増加を招く。そのため、これらの観点からは、N含有量を0.001%以上とすることが好ましく、0.0015%以上とすることがより好ましい。
Snは本発明において、もっとも重要な元素のひとつである。Snの添加により、鉄の格子定数が増大し、これにより鋼中の炭素の外方拡散が抑制されるために、表面脱炭反応が抑制される。前記効果を得るには、0.010%以上の添加が必要である。そのため、Sn含有量は0.010%以上、好ましくは0.020%以上とする。一方、0.050%を超えて添加しても、その効果は飽和する。したがって、Sn含有量は0.050%以下、好ましくは0.045%以下とする。
Sbは、Snと同様、鉄の格子定数が増大させ、鋼中の炭素の外方拡散を抑制する作用を有する元素である。したがって、Snに加えてSbを添加することにより、さらに表面脱炭を抑制することができる。しかし、Sbは、加熱時に液状化してオーステナイト粒界に侵食するため、焼入れ焼き戻し後のスタビライザーの靭性を低下させる。よって、Sbの添加は必要最小限にとどめる必要がある。そのため、Sbを添加する場合、Sb含有量は0.020%以下、好ましくは0.010%未満、より好ましくは0.008%以下とする。
Cuは、焼入れ性を向上させるとともに、耐食性を向上させる作用を有する元素である。しかし、Cuは高価な合金元素であるため、Cu含有量が1.0%を超えると材料コストの高騰を招く。そのため、Cu含有量は1.0%以下、好ましくは0.50%以下とする。なお、Cu含有量の下限はとくに限定されないが、Cuの添加効果を高めるという観点からは、Cuを添加する場合、Cu含有量を0.05%以上とすることが好ましい。
Niは、Cuと同様、焼入れ性を向上させるとともに、耐食性を向上させる作用を有する元素である。しかし、Niは高価な合金元素であるため、Ni含有量が1.0%を超えると材料コストの高騰を招く。そのため、Ni含有量は1.0%以下、好ましくは0.50%以下とする。一方、Ni含有量の下限はとくに限定されないが、Niの添加効果を高めるという観点からは、Niを添加する場合、Ni含有量を0.05%以上とすることが好ましい。
Nbは、微細な炭化物を形成して強度(硬さ)の増加に寄与する元素である。しかし、Nb含有量が0.05%を超えると、添加効果が飽和して含有量に見合う効果が得られないため、経済的に不利となる。そのため、Nb含有量は0.05%以下、好ましくは0.03%以下とする。一方、Nb含有量の下限はとくに限定されないが、Nbの添加効果を高めるという観点からは、Nbを添加する場合、Nb含有量を0.001%以上とすることが好ましい。
Wは、Nbと同様に、微細な炭化物を形成して強度(硬さ)の増加に寄与する元素である。しかし、W含有量が0.5%を超えると、添加効果が飽和して含有量に見合う効果が得られないため、経済的に不利となる。そのため、W含有量は0.5%以下、好ましくは0.3%以下とする。一方、W含有量の下限はとくに限定されないが、Wの添加効果を高めるという観点からは、Wを添加する場合、W含有量を0.01%以上とすることが好ましい。
Vは、NbおよびWと同様に、微細な炭化物を形成して強度(硬さ)の増加に寄与する元素である。しかし、V含有量が0.5%を超えると、添加効果が飽和して含有量に見合う効果が得られないため、経済的に不利となる。そのため、V含有量は0.5%以下、好ましくは0.3%以下とする。一方、V含有量の下限はとくに限定されないが、Vの添加効果を高めるという観点からは、Vを添加する場合、V含有量を0.01%以上とすることが好ましい。
Moは焼入れ性を向上させる効果を有する元素である。しかし、Moは非常に高価な元素であるため過剰な添加は素材コストの上昇につながる。そのため、Mo含有量は0.2%以下、好ましくは0.15%以下とする。一方、Mo含有量の下限はとくに限定されないが、Moの添加効果を高めるという観点からは、Mo含有量を0.01%以上とすることが好ましく、0.05%以上とすることがより好ましい。
REM(希土類金属)は、Caと同様に、硫化物系介在物の形態を微細な略球形の介在物に制御する作用を有する元素である。Caの作用を補完するために、任意にREMを添加することができる。しかし、REM含有量が0.02%を超えると、疲労き裂の起点となる介在物の量が過剰となるため、かえって耐腐食疲労特性が低下する。そのため、REM含有量は0.02%以下、好ましくは0.01%以下とする。一方、REM含有量の下限はとくに限定されないが、REMの添加効果を高めるという観点からは、REMを添加する場合、REM含有量を0.001%以上とすることが好ましい。
全脱炭層深さ:100μm以下
本発明の中空スタビライザー用電縫鋼管は、内表面における全脱炭層深さおよび外表面における全脱炭層深さの両者が100μm以下である。ここでいう全脱炭層深さは、スタビライザーの製造工程に供される前の素材としての中空スタビライザー用電縫鋼管(素管)における全脱炭層深さを指す。言い換えると、上記全脱炭層深さは、焼入れなどの熱処理を行う前の全脱炭層深さである。なお、前記全脱炭層深さは、実施例に記載する方法で測定することが出来る。
上記中空スタビライザー用電縫鋼管の寸法は、とくに限定されることなく任意の寸法とすることができるが、鋼管の外径D(mm)に対する肉厚t(mm)の比、t/Dを10~30%とすることが好ましい。
本発明の中空スタビライザー用電縫鋼管は、特に限定されることなく、任意の方法で製造することができる。すなわち、上述した成分組成を有する鋼素材を使用し、常法に従って製造することが可能である。以下、本発明の一実施形態における中空スタビライザー用電縫鋼管の好適な製造方法について説明する。
得られた中空スタビライザー用電縫鋼管から、観察面が管軸方向に平行な断面となるように組織観察用試験片を採取し、JIS G 0558に定められた方法に従って内表面および外表面におけるフェライト脱炭層深さおよび全脱炭層深さを測定した。
次いで、熱処理を施した後の脱炭層深さを評価するために、得られた中空スタビライザー用電縫鋼管に熱処理を施した。具体的には、まず、中空スタビライザー用電縫鋼管を大気炉中で加熱し、900℃で10分保持した後、冷却速度80±10℃/sで冷却することにより焼入れを行った。次いで、大気中炉中で、焼戻温度350℃、保持時間20分の条件で焼戻処理を施した。その後、前記熱処理後の中空スタビライザー用電縫鋼管から、管軸方向に垂直な断面が観察面となるように組織観察用試験片を採取し、JIS G 0558の方法にしたがいフェライト脱炭深さおよび全脱炭深さを測定した。なお、上記熱処理中の鋼管の温度は、該鋼管に取り付けたK熱電対を用いて測定した。
次に、本発明の効果を確認するために、大気中で熱処理を行った場合の疲労強度の低下を以下の手順で評価した。
まず、以下の手順で、大気中で熱処理を行った場合の疲労強度を評価した。得られた中空スタビライザー用電縫鋼管から長さ400mmの管状試験片を採取し、該管状試験片に焼入れ焼戻しを施した。前記焼入れは、前記管状試験片を大気炉で900℃、10分保持した後、焼入れ槽(水)に投入し、冷却速度80±10℃/sで急冷することによって行った。前記焼戻しは、焼戻し温度350℃で、保持時間20分の条件で行った。前記焼戻し温度は、試験片に取り付けた熱電対によって測定した。
次に、同じ条件で製造された中空スタビライザー用電縫鋼管に対し、焼入れ時の加熱を非酸化雰囲気炉(光輝熱処理炉)で行った点以外は上記手順1と同一条件で熱処理を行うことにより、表面脱炭のない基準サンプルを作成した。前記基準サンプル用いて、上記手順1と同条件でねじり疲労試験を行い、10サンプルでの平均疲労寿命を求めた。
上記手順2で求めた基準サンプルの平均疲労寿命に対する、上記手順1で求めた平均疲労寿命の低下率を算出し、疲労強度低下率とした。前記疲労強度低下率が10%未満のものを良好な結果と判定した。
Claims (3)
- 質量%で、
C :0.20~0.40%、
Si:0.1~1.0%、
Mn:0.1~2.0%、
P :0.1%以下、
S :0.01%以下、
Al:0.01~0.10%、
Cr:0.01~0.50%、
Ti:0.010~0.050%、
B :0.0005~0.0050%、
Ca:0.0001~0.0050%、
N :0.0050%以下、および
Sn:0.010~0.050%、を含み、
残部Feおよび不可避的不純物からなる成分組成を有し、
内表面および外表面における全脱炭層深さが100μm以下である、中空スタビライザー用電縫鋼管。 - 前記成分組成が、さらに、質量%で、
Sb:0.020%以下を含む、請求項1に記載の中空スタビライザー用電縫鋼管。 - 前記成分組成が、さらに、質量%で、
Cu:1.0%以下、
Ni:1.0%以下、
Nb:0.05%以下、
W :0.5%以下、
V :0.5%以下、
Mo:0.2%以下、および
REM:0.02%以下、からなる群より選択される1または2以上を含む、請求項1または2に記載の中空スタビライザー用電縫鋼管。
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EP3971307A4 (en) | 2022-03-30 |
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