WO2020189097A1 - 中空スタビライザー用電縫鋼管およびその製造方法 - Google Patents
中空スタビライザー用電縫鋼管およびその製造方法 Download PDFInfo
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- WO2020189097A1 WO2020189097A1 PCT/JP2020/005221 JP2020005221W WO2020189097A1 WO 2020189097 A1 WO2020189097 A1 WO 2020189097A1 JP 2020005221 W JP2020005221 W JP 2020005221W WO 2020189097 A1 WO2020189097 A1 WO 2020189097A1
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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
- C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B17/00—Tube-rolling by rollers of which the axes are arranged essentially perpendicular to the axis of the work, e.g. "axial" tube-rolling
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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
- 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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- 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
- 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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- 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
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/50—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for welded joints
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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
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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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
- C22C38/002—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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- 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
- C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
-
- 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
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
-
- 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
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- 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
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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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
- C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
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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
- C22C38/10—Ferrous alloys, e.g. steel alloys containing cobalt
- C22C38/105—Ferrous alloys, e.g. steel alloys containing cobalt containing Co and Ni
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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
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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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
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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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
- C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
Definitions
- the present invention relates to an electric-resistance-welded steel pipe or tube for hollow stabilizer, which does not contain Cr and has excellent quench crack resistance and corrosion fatigue resistance. It relates to an electric resistance sewn steel pipe for a hollow stabilizer that also has characteristics (corrosion fatigue resistance). The present invention also relates to a method for manufacturing the electric resistance welded steel pipe for a hollow stabilizer.
- Hollow stabilizers are usually manufactured by coldly forming a steel pipe as a raw material into a desired shape and then performing tempering treatment such as quenching and tempering.
- a steel pipe seamless steel pipe, electric resistance welded steel pipe (hereinafter referred to as electric resistance steel pipe) and the like are used.
- electric resistance steel pipe is widely used because it is relatively inexpensive and has excellent dimensional accuracy. ing.
- the electric resistance pipe (electric pipe for hollow stabilizer) used as a material for such a hollow stabilizer is required to have excellent strength (hardness) and fatigue resistance after quenching and tempering. Therefore, various techniques have been proposed in order to improve the strength and fatigue resistance of the electrosewn steel pipe for hollow stabilizer after quenching and tempering.
- Patent Document 1 after heat-treating an electro-sewn steel pipe, it is subjected to drawing rolling at a rolling temperature of 600 to 850 ° C. and a cumulative diameter reduction ratio of 40% or more to manufacture an electro-sewn steel pipe for a hollow stabilizer. Has been proposed.
- Patent Document 2 proposes a technique for controlling the contents of N and Ti so as to satisfy a specific relationship in an electrosewn steel pipe for a hollow stabilizer.
- Patent Document 3 proposes an electrosewn steel pipe for a hollow stabilizer in which the bond width of the electrosewn welded portion is 25 ⁇ m or less.
- Patent Document 4 proposes an electrosewn steel pipe for a hollow stabilizer in which the contents of N and Ti satisfy a specific relationship and the bond width of the electrosewn welded portion is 25 ⁇ m or less.
- Patent Document 5 proposes an electrosewn steel pipe for a hollow stabilizer having a predetermined component composition and having a structure in which the cleanliness of TiS particles and MnS particles is 0.1% or less.
- Patent Documents 1 to 5 it is possible to improve the strength (hardness) and fatigue resistance characteristics of the electrosewn steel pipe for hollow stabilizer after quenching and tempering.
- Patent Documents 1 to 4 can improve the fatigue resistance characteristics in the atmosphere, the fatigue resistance characteristics in a corrosive environment are not considered, and the corrosion fatigue resistance characteristics are sufficient. I could't say that.
- Patent Document 5 Cr is added in order to improve the corrosion resistance. Therefore, when the slab or the open pipe is heated in the process of manufacturing the electrosewn steel pipe, an Fe—Cr—O-based internal oxide layer is formed, and as a result, the descalability is lowered. If the descalability is low, the scale remaining on the surface is pushed in during the rolling process, and pushing flaws occur. As a result, the durability of the final stabilizer may be adversely affected.
- an object of the present invention is to solve the above-mentioned problems of the prior art and to provide an electrosewn steel pipe for a hollow stabilizer which does not contain Cr and has excellent shrinkage resistance and corrosion fatigue resistance. ..
- the fact that the electric resistance sewn steel pipe for a hollow stabilizer is excellent in corrosion fatigue resistance means that the electric resistance sewn steel pipe for a hollow stabilizer is excellent in fatigue resistance in a corrosive environment after being subjected to quenching and tempering treatment. Means that.
- the present inventors examined various factors affecting the corrosion fatigue resistance characteristics of the hollow stabilizer in order to achieve the above-mentioned object.
- the present invention has been made based on the above findings, and has the following gist.
- the component composition is further increased by mass%.
- Cu 1% or less
- Ni 1% or less
- Nb 0.05% or less
- W 0.05% or less
- a steel sheet having the above-mentioned composition is formed into a substantially cylindrical shape by cold forming to form an open tube.
- the widthwise ends of the open pipe are abutted against each other and welded by electric sewing to form an electric resistance steel pipe.
- the electric resistance steel pipe is heated to a heating temperature of 850 to 1000 ° C.
- an electrosewn steel pipe for a hollow stabilizer that does not contain Cr and has excellent shrinkage resistance and corrosion fatigue resistance.
- the electric resistance welded steel pipe for a hollow stabilizer of the present invention has an excellent shrinkage resistance because the C content is suppressed to less than 0.20% by mass. Therefore, the electrosewn steel pipe for a hollow stabilizer of the present invention can be hardened without causing cracks even if it is water-quenched. Further, the electrosewn steel pipe for a hollow stabilizer of the present invention is excellent in descalability because it does not contain Cr which causes a decrease in descalability.
- the electric resistance welded steel pipe for a hollow stabilizer of the present invention has excellent corrosion fatigue resistance even though it does not contain Cr.
- the electric resistance sewn steel pipe for a hollow stabilizer of the present invention it is possible to manufacture a hollow stabilizer having a Vickers hardness of 350 HV or more and excellent corrosion fatigue resistance. Further, even if the Vickers hardness is further increased to 450 HV or more, excellent performance is maintained without deteriorating the corrosion fatigue resistance. Therefore, according to the present invention, further thinning of the stabilizer can be achieved.
- the electrosewn steel pipe for a hollow stabilizer in one embodiment of the present invention has the above-mentioned component composition.
- component composition Hereinafter, the reasons for limiting the component composition will be described.
- “%" as a unit of element content shall represent “mass%”.
- C 0.15% or more and less than 0.20% C has the effect of promoting the formation of martensite and increasing the strength (hardness) of steel by solid solution through the improvement of hardenability.
- the C content In order for the hardness after quenching and tempering to be 350 HV or more in Vickers hardness, the C content needs to be 0.15% or more. Therefore, the C content is 0.15% or more, preferably 0.17% or more.
- the C content is less than 0.20%, preferably 0.19% or less.
- Si acts not only as a deoxidizer but also as a solid solution strengthening element. In order to obtain the above effect, the Si content needs to be 0.1% or more. Therefore, the Si content is set to 0.1% or more. On the other hand, if the Si content exceeds 1.0%, the electric sewing weldability is lowered. Therefore, the Si content is 1.0% or less, preferably 0.75% or less, more preferably 0.5% or less, still more preferably 0.20% 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 Mn content needs to be 0.1% or more.
- the Mn content is set to 0.1% or more, preferably 0.3% or more, and more preferably 0.5% or more.
- the Mn content exceeds 2.0%, the toughness is lowered and the risk of shrinkage is increased. Therefore, the Mn content is 2.0% or less, preferably 1.8% or less, and more preferably 1.5% or less.
- P 0.1% or less
- P is an element contained in steel as an impurity, and segregation at grain boundaries and the like adversely affects weld crackability and toughness. Therefore, the P content is set to 0.1% or less, preferably 0.05% or less.
- the lower the P content the better. Therefore, the lower limit of the P content is not limited and may be 0.
- the P content is preferably 0.001% or more, more preferably 0.005% or more, and further preferably 0.010% 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. Therefore, the S content is 0.01% or less, preferably 0.005% or less.
- the lower limit of the S content is not limited and may be 0.
- the S content is preferably 0.0001% or more, more preferably 0.0005% or more, and further preferably 0.001% or more.
- Al acts as a deoxidizer and has an effect of binding to N and securing an amount of solid solution B effective for improving hardenability.
- Al precipitates as AlN and has an action of preventing coarsening of austenite grains during quenching and heating.
- a content of 0.01% or more is required. Therefore, the Al content is 0.01% or more, preferably 0.02% or more.
- the Al content is 0.10% or less, preferably 0.05% or less.
- Ti More than 0.05%, 0.1% or less Ti has the effect of binding to N and securing the amount of solid solution B effective for improving hardenability.
- Ti precipitates as fine carbides, contributes to the refinement of austenite grains during heat treatment such as quenching, and contributes to the improvement of fatigue resistance (corrosion fatigue resistance) in a corrosive environment.
- the Ti content needs to be more than 0.05%.
- the Ti content is set to more than 0.05%, preferably 0.051% or more, and more preferably 0.052% or more.
- the Ti content exceeds 0.1%, coarse titanium sulfide (TiS), which is the starting point of the corrosion pit, is formed, and the corrosion resistance and the corrosion fatigue resistance are deteriorated. Therefore, the Ti content is 0.1% or less, preferably 0.091% or less, and more preferably 0.061% or less.
- B 0.0005-0.005%
- B is an element having an effect of improving the hardenability of steel in a small amount.
- B has the effect of strengthening the former austenite grain boundaries and suppressing grain boundary embrittlement due to P segregation, and as a result, suppressing the growth of fatigue cracks.
- the B content is 0.0005% or more, preferably 0.001% or more.
- the B content is 0.005% or less, preferably 0.003% or less.
- Ca 0.0001 to 0.0050%
- Ca is an element that controls the morphology of sulfide-based inclusions to form fine substantially spherical inclusions.
- the Ca content exceeds 0.0050%, the number of coarse CaS-based clusters becomes too large, which rather becomes the starting point of fatigue cracks and deteriorates the corrosion fatigue resistance. Therefore, the Ca content is 0.0050% or less, preferably 0.0030% or less.
- N 0.0050% or less
- N is an element inevitably contained as an impurity. N binds to the nitride-forming element in the steel and contributes to the suppression of coarsening of crystal grains and the increase in strength after tempering. However, if the N content exceeds 0.0050%, the toughness of the welded portion decreases. Therefore, the N content is 0.0050% or less, preferably 0.003% 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. In addition, 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 0.002% or more.
- the electrosewn steel pipe for a hollow stabilizer in one 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 electrosewn steel pipe for a hollow stabilizer according to an embodiment of the present invention can have a component composition consisting of each of the above elements, the balance Fe, and unavoidable impurities.
- the component composition of the electrosewn steel pipe for a hollow stabilizer in another embodiment of the present invention is further optionally selected from the group consisting of Cu, Ni, Nb, W, V, and REM (rare earth metal) 1 or 2.
- the above can be contained in the amounts described below.
- Cu 1% or less
- Cu is an element that further improves hardenability and corrosion resistance.
- the Cu content is set to 1% or less, preferably 0.50% or less, and more preferably 0.40% or less.
- the lower limit of the Cu content is not particularly limited.
- the Cu content is preferably 0.05% or more, preferably 0.10% or more, in order to enhance the effect of adding Cu.
- Ni 1% or less Ni, like Cu, is an element that further improves hardenability and corrosion resistance. However, since Ni is an expensive element, if the Ni content exceeds 1%, the material cost rises remarkably. Therefore, when Ni is added, the Ni content is set to 1% or less, preferably 0.50% or less, and more preferably 0.40% or less. On the other hand, the lower limit of the Ni content is not particularly limited. However, when Ni is added, the Ni content is preferably 0.05% or more, preferably 0.10% or more, in order to enhance the effect of adding Ni.
- Nb 0.05% or less
- Nb is an element that forms fine carbides and contributes to an increase in strength (hardness).
- the Nb content exceeds 0.05%, the effect of adding Nb is saturated, so that an effect commensurate with the content cannot be expected, which is economically disadvantageous. Therefore, when Nb is added, the Nb content is set to 0.05% or less, preferably 0.03% or less.
- the lower limit of the Nb content is not particularly limited. However, when Nb is added, the Nb content is preferably 0.001% or more, more preferably 0.005% or more, in order to enhance the effect of adding Nb.
- W 0.05% or less W is an element that forms fine carbides and contributes to an increase in strength (hardness), similar to Nb.
- the W content is set to 0.05% or less, preferably 0.03% or less.
- the lower limit of the W content is not particularly limited. However, when W is added, the W content is preferably 0.01% or more in order to enhance the effect of adding W.
- 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 exceeds 0.5%, the effect of adding V is saturated, so that an effect commensurate with the content cannot be expected, which is economically disadvantageous. Therefore, when V is added, the V content is set to 0.5% or less, preferably 0.3% or less.
- the lower limit of the V content is not particularly limited. However, when V is added, the V content is preferably 0.05% or more in order to enhance the effect of adding V.
- REM 0.02% or less REM is an element having an action of controlling the morphology of sulfide-based inclusions into fine substantially spherical inclusions, similarly to Ca.
- the REM content exceeds 0.02%, the amount of inclusions that are the starting points of fatigue cracks becomes too large, and the corrosion fatigue resistance characteristics are rather lowered. Therefore, when REM is added, the REM content is 0.02% or less, preferably 0.01% or less, and more preferably 0.008% or less.
- the lower limit of the REM content is not particularly limited, but from the viewpoint of enhancing the effect of adding REM, the REM content is preferably 0.001% or more.
- the electrosewn steel pipe for a hollow stabilizer C: 0.15% or more, less than 0.20%, Si: 0.1-1.0%, Mn: 0.1-2.0%, P: 0.1% or less, S: 0.01% or less, Al: 0.01 to 0.10%, Ti: Over 0.05%, 0.1% or less, B: 0.0005 to 0.005%, Ca: 0.0001 to 0.0050%, N: 0.0050% or less, Optionally, a group consisting of Cu: 1% or less, Ni: 1% or less, Nb: 0.05% or less, W: 0.05% or less, V: 0.5% or less, and REM: 0.02% or less. It can have a component composition consisting of one or more selected from the above, as well as the remaining Fe and unavoidable impurities.
- Cr is not included in the composition of the electric resistance welded steel pipe for the hollow stabilizer of the present invention.
- a Fe—Cr—O-based internal oxide layer is formed in the slab or pipe heating process (before diameter reduction rolling), which reduces the descaling property and causes scale indentation defects in the rolling process. , May adversely affect the durability of the final product, the stabilizer.
- the above component composition it is permissible for the above component composition to contain Cr as an unavoidable impurity.
- the Cr content as an unavoidable impurity is preferably less than 0.01%, more preferably 0.050% or less.
- TiS particles having a particle size of 10 ⁇ m or more and MnS particles having a particle size of 10 ⁇ m or more serve as starting points for corrosion pits and reduce corrosion resistance. Further, TiS particles having a particle size of 10 ⁇ m or more and MnS particles having a particle size of 10 ⁇ m or more promote the generation of fatigue cracks starting from the corrosion pits, thereby lowering the corrosion fatigue resistance characteristics. Specifically, when at least one of the cleanliness of TiS particles having a particle size of 10 ⁇ m or more and the cleanliness of MnS particles having a particle size of 10 ⁇ m or more exceeds 0.1%, the corrosion resistance and the corrosion fatigue resistance are lowered.
- the cleanliness of TiS particles having a particle size of 10 ⁇ m or more and the cleanliness of MnS particles having a particle size of 10 ⁇ m or more are set to 0.1% or less, respectively.
- the "particle size" refers to the maximum length of the particles.
- the cleanliness refers to a value at the center of the plate thickness of the steel pipe. The cleanliness can be measured by the method described in the examples.
- 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 7. % Or more is preferable.
- the t / D may be 10% or more, or 12% or more.
- t / D is preferably 35% or less.
- the t / D may be 30% or less, or 25% or less.
- the electric resistance welded steel pipe for a hollow stabilizer of the present invention can be manufactured by any method without particular limitation. Hereinafter, a preferred method for manufacturing the electric resistance welded steel pipe for the hollow stabilizer according to the embodiment of the present invention will be described.
- the electric resistance welded steel pipe for a hollow stabilizer of the present invention can be produced by sequentially performing the following steps (1) to (4) on a steel sheet having the above composition.
- (1) Cold forming (2) Electric stitch welding (3) Heating (4) Hot reduced diameter rolling
- a steel sheet having the above-mentioned composition is formed into a substantially cylindrical shape by cold forming to form an open tube.
- the cold forming method is not particularly limited, and for example, it may be performed according to a conventional method. Specifically, it is preferable to continuously cold-mold with a plurality of rolls.
- the widthwise ends of the open pipe are abutted against each other and electric sewing welded to obtain an electric resistance steel pipe.
- the abutting between the widthwise ends of the open pipe can be performed by any method, but usually, it can be performed by using a squeeze roll.
- the electric sewing welding is preferably performed by, for example, high frequency resistance welding or induction heating welding.
- the obtained electric resistance welded steel pipe is heated to a heating temperature of 850 to 1000 ° C. If the heating temperature is less than 850 ° C., the desired weld toughness may not be ensured. Therefore, the heating temperature is set to 850 ° C. or higher, preferably 860 ° C. or higher. On the other hand, when the heating temperature exceeds 1000 ° C., surface decarburization becomes remarkable and the surface texture may deteriorate. Therefore, the heating temperature is set to 1000 ° C. or lower, preferably 980 ° C. or lower.
- the hot reduced diameter rolling is performed on the heated electric resistance steel pipe under the conditions of a rolling temperature of 650 ° C. or higher and a cumulative diameter reduction ratio of 30 to 90%. 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.
- the upper limit of the rolling temperature is not particularly limited, but in practice, the rolling temperature is equal to or lower than the heating temperature.
- the cumulative diameter reduction ratio is 30 to 90%, it is possible to form a desired stabilizer shape without deteriorating the workability of the electrosewn steel pipe.
- the cumulative diameter reduction ratio is preferably 35% or more. Further, the cumulative diameter reduction ratio is preferably 80% or less.
- the electrosewn steel pipe for a hollow stabilizer of the present invention can be suitably used as a material for manufacturing a hollow stabilizer.
- the production of the hollow stabilizer is not particularly limited, and can be performed by any method.
- a hollow stabilizer can be obtained by forming the electric resistance welded steel pipe for a hollow stabilizer into a stabilizer shape and then performing a heat treatment.
- the electric resistance sewn steel pipe for the hollow stabilizer is formed into a stabilizer shape.
- the molding method any of the usual molding methods can be applied. From the viewpoint of suppressing surface decarburization, it is preferable that the molding is cold bending. Examples of the cold bending process include rotary pull bending, press bending, and the like.
- heat treatment is applied to the parts (hollow stabilizer) molded into the stabilizer shape.
- the heat treatment it is preferable to perform a quenching treatment or a quenching tempering treatment.
- the stabilizer manufactured by using the electrosewn steel pipe for hollow stabilizer of the present invention has the above-mentioned composition and TiS particles having a particle size of 10 ⁇ m or more and MnS particles having a particle size of 10 ⁇ m or more, respectively, in accordance with JIS G0555. It has a structure with a cleanliness of 0 to 0.1% or less determined by the point calculation method, the average particle size of the old austenite particles is 50 ⁇ m or less, and the hardness is Vickers hardness of 400 HV or more and less than 550 HV. That is, the composition and cleanliness of the electric resistance welded steel pipe for the hollow stabilizer are maintained even in the hollow stabilizer after the quenching and tempering treatment.
- Example 1 An electrosewn steel pipe for a hollow stabilizer was prepared by the following procedure.
- a steel slab was manufactured by a continuous casting method using molten steel having the component compositions shown in Table 1.
- the steel slab was hot-rolled to obtain a hot-rolled steel sheet having a plate thickness of 4.5 mm.
- the cleanliness of steel is affected not only by the composition of the components but also by the steelmaking conditions. Therefore, in the production of the steel slab by the continuous casting method, the molten steel temperature and the casting speed are kept constant.
- the hot-rolled steel sheet was cold and continuously formed using a plurality of rolls 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 welded steel pipe was heated to a heating temperature of 980 ° C. by induction heating.
- the heated electric resistance welded steel pipe was hot-reduced and rolled to obtain an electric resistance welded steel pipe for a hollow stabilizer.
- the hot reduced diameter rolling was carried out under the conditions of a reduced diameter rolling temperature: 800 ° C. and a diameter reduction ratio: 71%.
- the reduced diameter rolling temperature was measured with a radiation thermometer on the exit side of the final rolling stand.
- the dimensions of the final electrosewn steel pipe for the hollow stabilizer were an outer diameter of 21.7 to 54 mm ⁇ ⁇ a wall thickness of 4.0 mm.
- a test piece for tissue observation was taken so that the observation surface had a cross section parallel to the pipe axis direction.
- the surface of the tissue observation test piece at the center of the plate thickness was observed using a scanning electron microscope (magnification: 500 to 2000 times), and the type, size, and number of inclusion particles present were measured. ..
- the type (composition) of the inclusion particles was identified by analyzing the elements constituting the inclusion particles with an energy dispersive X-ray analyzer (EDX type analyzer) attached to the scanning electron microscope. Further, the maximum length of the particles in the cross section (observation surface) was defined as the particle size of the particles.
- the number of particles having a particle size of 10 ⁇ m or more was measured for each of the TiS particles and the MnS particles. From the number of particles obtained, the area ratio (%) of inclusions was calculated by a point calculation method in accordance with JIS G0555, and the average value in 60 fields of view was taken as the cleanliness.
- the electric resistance sewn steel pipe for the hollow stabilizer was heated by energization heating until the surface temperature reached 950 ° C.
- the energization heating was carried out by sandwiching both ends of the electrosewn steel pipe in the longitudinal direction with electrodes and energizing between the electrodes. The surface temperature was measured with a radiation thermometer. Then, after holding the steel pipe at 950 ° C. for 3 seconds, the hollow stabilizer electrosewn steel pipe was put into a quenching tank (water) and rapidly cooled at a cooling rate of 80 ⁇ 10 ° C./s to perform quenching treatment.
- a tempering process was performed in which the tempering temperature was kept at 350 ° C. for 20 minutes.
- the tempering temperature was measured by attaching a thermocouple to the steel pipe.
- the electrosewn steel pipe was hardened and tempered without being cold-worked.
- Vickers hardness In order to evaluate the strength after the quenching and tempering treatment, a test piece was taken from the electrosewn steel pipe after the quenching and tempering treatment, and the Vickers hardness in the cross section (C cross section) perpendicular to the pipe axis direction of the steel pipe was calculated as the Vickers hardness. It was measured using a meter. In the measurement, the Vickers hardness was measured at a pitch of 0.1 mm over the entire thickness of the cross section from the outer surface of the pipe to the inner surface of the pipe, and the average value was obtained. The measurement condition of Vickers hardness was a load: 500 gf (4.9 N).
- a test piece was collected from the electrosewn steel pipe after the above quenching and tempering treatment so that the cross section orthogonal to the pipe axis direction became the observation surface. After polishing the cross section, it was corroded with a corrosive solution (picric acid aqueous solution) to reveal the former austenite grain boundaries. Then, the cross section was observed with an optical microscope (magnification: 100 times) and imaged with 10 or more fields of view. The obtained tissue photograph was image-analyzed to calculate the average particle size of the old austenite grains.
- a corrosive solution (picric acid aqueous solution)
- a test piece of a predetermined length was sampled from an electrosewn steel pipe for a hollow stabilizer before the above quenching and tempering treatment, and processed into a test piece for a corrosion fatigue test.
- a parallel portion having an outer diameter of 24.4 mm ⁇ was formed in the central portion of the test piece.
- the test piece was subjected to quenching and tempering treatment.
- the quenching and tempering treatment first, the test piece is heated to a surface temperature of 950 ° C. by induction heating, held for 3 seconds, and sprayed with a water spray to perform the quenching treatment at a cooling rate of 80 ° C./s. gave. After the quenching treatment, a tempering treatment was performed under the condition of holding at 350 ° C. for 20 minutes.
- cotton wool containing a 5% NaCl aqueous solution is wrapped around the central parallel portion of the test piece to carry out a fatigue test in a wet state, and the number of repetitions until cracking occurs is determined to determine the corrosion fatigue resistance. evaluated.
- the test conditions were a load stress of ⁇ 400 MPa (both swings) and a load cycle of 1 Hz.
- the fatigue life obtained in this way can be regarded as an index of corrosion fatigue resistance characteristics.
- the electrosewn steel pipe for a hollow stabilizer satisfying the conditions of the present invention has a smaller grain size of the old austenite after the quenching and tempering treatment and is also excellent in corrosion fatigue resistance after the quenching and tempering treatment.
- the grain size of the old austenite is small, the grain boundaries increase, and the grain boundaries can block the propagation of cracks. Further, if the old austenite grains are refined, the influence of hydrogen embrittlement on the corrosion fatigue resistance can be suppressed and the corrosion fatigue resistance can be improved. Therefore, the stabilizer obtained by using the electric resistance welded steel pipe for the hollow stabilizer of the present invention has excellent crack propagation resistance and therefore has high fatigue strength.
- Example 2 Using hot-rolled steel sheets having the component compositions shown in Table 1 as steel types A, B, and C, electrosewn steel pipes for hollow stabilizers were prepared under the conditions shown in Table 3. Other conditions were the same as in Example 1 above.
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Abstract
Description
C :0.15%以上、0.20%未満、
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%、
Ti:0.05%超、0.1%以下、
B :0.0005~0.005%、
Ca:0.0001~0.0050%、および
N :0.0050%以下を含み、
残部Feおよび不可避的不純物からなる成分組成と、
粒径:10μm以上のTiS粒子および粒径:10μm以上のMnS粒子のそれぞれについて、JIS G 0555に準拠して点算法で求めた清浄度が0~0.1%である組織と、を有する中空スタビライザー用電縫鋼管。
Cu:1%以下、
Ni:1%以下、
Nb:0.05%以下、
W :0.05%以下、
V :0.5%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以上を含有する、上記1に記載の中空スタビライザー用電縫鋼管。
前記成分組成を有する鋼板を、冷間成形により略円筒状に成形してオープン管とし、
前記オープン管の幅方向端部同士を衝合し、電縫溶接して電縫鋼管とし、
前記電縫鋼管を、850~1000℃の加熱温度に加熱し、
前記加熱後の電縫鋼管に、圧延温度:650℃以上、累積縮径率:30~90%の条件で熱間縮径圧延を施す、中空スタビライザー用電縫鋼管の製造方法。
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は、上述した成分組成を有する。以下、前記成分組成の限定理由について説明する。なお、本願明細書においては、特に断らないかぎり、元素の含有量の単位としての「%」は「質量%」を表すものとする。
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し、中空スタビライザーの強度(硬さ)確保のために重要な元素である。焼入れ焼戻処理後の硬さをビッカース硬さで350HV以上とするためには、C含有量を0.15%以上とする必要がある。そのため、C含有量は0.15%以上、好ましくは0.17%以上とする。一方、C含有量が0.20%以上であると、焼割れの危険性が高くなることに加え、焼入れ処理後の靭性が低下する。そのため、C含有量は0.20%未満、好ましくは0.19%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。前記効果を得るためには、Si含有量が0.1%以上である必要がある。そのため、Si含有量を0.1%以上とする。一方、Si含有量が1.0%を超え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0.75%以下、より好ましくは0.5%以下、さらに好ましくは0.20%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。所望の強度を確保するためには、Mn含有量を0.1%以上とする必要がある。また、Mn含有量が0.1%未満であると、鋼中のSがTiと結合しやすくなり、TiSが粗大化する。そのため、Mn含有量を0.1%以上、好ましくは0.3%以上、より好ましくは0.5%以上とする。一方、Mn含有量が2.0%を超えると、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1.5%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、粒界等に偏析することによって溶接割れ性、靭性に悪影響を及ぼす。そのため、P含有量を0.1%以下、好ましくは0.05%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、0.010%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。そのため、S含有量は0.01%以下、好ましくは0.005%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。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含有量を0.01%以上、好ましくは0.02%以上とする。一方、Al含有量が0.10%を超えると、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0.05%以下とする。
Tiは、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。また、Tiは、微細な炭化物として析出し、焼入れ等の熱処理時にオーステナイト粒の微細化に寄与し、腐食環境における耐疲労特性(耐腐食疲労特性)の向上に寄与する。前記効果を得るために、Ti含有量を0.05%超とする必要がある。また、Ti含有量が0.05%以下であると、鋼中のSがMnと結合しやすくなり、相対的にMnSの粗大化につながる。そのため、Ti含有量は0.05%超、好ましくは0.051%以上、より好ましくは0.052%以上とする。一方、Ti含有量が0.1%を超えると、腐食ピットの起点となる粗大な硫化チタン(TiS)が形成され、耐食性および耐腐食疲労特性が低下する。そのため、Ti含有量は0.1%以下、好ましくは0.091%以下、より好ましくは0.061%以下とする。
Bは、微量で鋼の焼入れ性を向上させる効果を有する元素である。また、Bは、旧オーステナイト粒界を強化するとともに、P偏析による粒界脆化を抑制し、その結果、疲労き裂の進展を抑制する効果を有する。前記効果を得るために、B含有量を0.0005%以上、好ましくは0.001%以上とする。一方、0.005%を超えてBを添加しても、効果が飽和し、経済的に不利となる。このため、B含有量は0.005%以下、好ましくは0.003%以下とする。
Caは、硫化物系介在物の形態を制御して、微細な略球形の介在物とする作用を有する元素である。本発明では、腐食ピットの起点となる粒径:10μm以上のMnS粒子および粒径:10μm以上のTiS粒子の数を低減するために、0.0001%以上のCaを添加する必要がある。そのため、Ca含有量は0.0001%以上、好ましくは0.001%以上とする。一方、Ca含有量が0.0050%を超えると、粗大なCaS系のクラスターが多くなりすぎて、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る。Nは、鋼中の窒化物形成元素と結合し、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、N含有量が0.0050%を超えると、溶接部の靭性が低下する。そのため、N含有量は0.0050%以下、好ましくは0.003%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、0.002%以上とすることがより好ましい。
Cuは、焼入れ性をさらに向上させるとともに、耐食性をさらに向上させる元素である。しかし、Cuは高価な元素であるため、Cu含有量が1%を越えると材料コストの高騰が顕著となる。そのため、Cuを添加する場合、Cu含有量を1%以下、好ましくは0.50%以下、より好ましくは0.40%以下とする。一方、Cu含有量の下限は特に限定されない。しかし、Cuを添加する場合、Cuの添加効果を高めるためには、Cu含有量を0.05%以上、好ましくは0.10%以上とすることが好ましい。
Niは、Cuと同様、焼入れ性をさらに向上させるとともに、耐食性をさらに向上させる元素である。しかし、Niは高価な元素であるため、Ni含有量が1%を越えると材料コストの高騰が顕著となる。そのため、Niを添加する場合、Ni含有量を1%以下、好ましくは0.50%以下、より好ましくは0.40%以下とする。一方、Ni含有量の下限は特に限定されない。しかし、Niを添加する場合、Niの添加効果を高めるためには、Ni含有量を0.05%以上、好ましくは0.10%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Nbの添加効果が飽和するため、含有量に見合う効果が期待できず、経済的に不利となる。そのため、Nbを添加する場合、Nb含有量を0.05%以下、好ましくは0.03%以下とする。一方、Nb含有量の下限は特に限定されない。しかし、Nbを添加する場合、Nbの添加効果を高めるためには、Nb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い。
Wは、Nbと同様、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0.05%を超えるとWの添加効果が飽和するため、含有量に見合う効果が期待できず、経済的に不利となる。そのため、Wを添加する場合、W含有量を0.05%以下、好ましくは0.03%以下とする。一方、W含有量の下限は特に限定されない。しかし、Wを添加する場合、Wの添加効果を高めるためには、W含有量を0.01%以上とすることが好ましい。
Vは、Nb、Wと同様、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Vの添加効果が飽和するため、含有量に見合う効果が期待できず、経済的に不利となる。そのため、Vを添加する場合、V含有量を0.5%以下、好ましくは0.3%以下とする。一方、V含有量の下限は特に限定されない。しかし、Vを添加する場合、Vの添加効果を高めるためには、V含有量を0.05%以上とすることが好ましい。
REM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。本発明では、Caの作用を補完する観点からREMを添加することが好ましい。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量が多くなりすぎて、かえって耐腐食疲労特性が低下する。そのため、REMを添加する場合、REM含有量を0.02%以下、好ましくは0.01%以下、より好ましくは0.008%以下とする。一方、REM含有量の下限は特に限定されないが、REMの添加効果を高めるという観点からは、REM含有量を0.001%以上とすることが好ましい。
C :0.15%以上、0.20%未満、
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%、
Ti:0.05%超、0.1%以下、
B :0.0005~0.005%、
Ca:0.0001~0.0050%、
N :0.0050%以下、
任意に、Cu:1%以下、Ni:1%以下、Nb:0.05%以下、W:0.05%以下、V:0.5%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、並びに
残部のFeおよび不可避的不純物からなる成分組成を有することができる。
本発明の中空スタビライザー用電縫鋼管は、さらに、粒径:10μm以上のTiS粒子および粒径:10μm以上のMnS粒子のそれぞれについて、JIS G 0555に準拠して点算法で求めた清浄度が0~0.1%である組織を有する。以下、前記組織の限定理由について説明する。
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7%以上とすることが好ましい。t/Dは、10%以上であってもよく、12%以上であってもよい。一方、t/Dは35%以下であることが好ましい。t/Dは、30%以下であってもよく、25%以下であってもよい。
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。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。
(1)冷間成形
(2)電縫溶接
(3)加熱
(4)熱間縮径圧延
まず、上記成分組成を有する鋼板を、冷間成形により略円筒状に成形してオープン管とする。前記冷間成形の方法はとくに限定されず、例えば、常法にしたがって行えばよい。具体的には、複数のロールにより連続して冷間成形することが好ましい。
次いで、前記オープン管の幅方向端部同士を衝合し、電縫溶接して電縫鋼管とする。前記オープン管の幅方向端部同士の衝合は、任意の方法で行うことができるが、通常は、スクイズロールを用いて行うことができる。また、前記電縫溶接は、例えば、高周波抵抗溶接または誘導加熱溶接によって行うことが好ましい。
次いで、得られた電縫鋼管を、850~1000℃の加熱温度に加熱する。前記加熱温度が850℃未満であると、所望の溶接部靭性を確保できない場合がある。そのため、前記加熱温度を850℃以上、好ましくは860℃以上とする。一方、前記加熱温度が1000℃を超える場合、表面脱炭が著しくなり、表面性状が低下する場合がある。そのため、前記加熱温度を1000℃以下、好ましくは980℃以下とする。
さらに、前記加熱後の電縫鋼管に、圧延温度:650℃以上、累積縮径率:30~90%の条件で熱間縮径圧延を施す。前記圧延温度が650℃未満であると、加工性が低下し、所望のスタビライザー形状への成形が難しくなる場合がある。前記圧延温度の上限はとくに限定されないが、実際的には、前記圧延温度は前記加熱温度以下である。また、前記累積縮径率が30~90%であれば、電縫鋼管の加工性が劣化することなく、所望のスタビライザー形状への成形が可能である。前記累積縮径率は35%以上とすることが好ましい。また、前記累積縮径率は80%以下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、中空スタビライザーを製造するための素材として好適に使用することができる。中空スタビライザーの製造は特に限定されることなく、任意の方法で行うことができる。一般的には、上記中空スタビライザー用電縫鋼管をスタビライザー形状に成形した後、熱処理を施すことによって中空スタビライザーとすることができる。
以下の手順で中空スタビライザー用電縫鋼管を作成した。
次いで、得られた中空スタビライザー用電縫鋼管のそれぞれについて、以下の手順で組織を観察し、JIS G 0555に準拠して点算法により清浄度を求めた。
次に、焼入れ焼戻し後の特性を評価するために、得られた中空スタビライザー用電縫鋼管のそれぞれに、以下の条件で焼入れ焼戻し処理を施した。
焼入れ焼戻し処理後の強度を評価するために、上記焼入れ焼戻処理後の電縫鋼管から試験片を採取し、鋼管の管軸方向に垂直な断面(C断面)におけるビッカース硬さを、ビッカース硬度計を用いて測定した。前記測定においては、前記断面の、管外表面から管内表面までの全厚にわたって、0.1mmピッチでビッカース硬さを測定し、その平均値を求めた。なお、ビッカース硬さの測定条件は、荷重:500gf(4.9N)とした。
上記焼入れ焼戻処理後の電縫鋼管における旧オーステナイト粒径(旧γ粒径)を、以下の手順で測定した。
上記焼入れ焼戻処理後の電縫鋼管の耐腐食疲労特性を評価するために、以下の手順で疲労試験を行って、疲労寿命を求めた。
表1に鋼種A、B、Cとして示した成分組成を有する熱延鋼板を用いて、表3に示した条件で中空スタビライザー用電縫鋼管を作成した。その他の条件は、上記実施例1と同様とした。
Claims (3)
- 質量%で、
C :0.15%以上、0.20%未満、
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%、
Ti:0.05%超、0.1%以下、
B :0.0005~0.005%、
Ca:0.0001~0.0050%、および
N :0.0050%以下を含み、
残部Feおよび不可避的不純物からなる成分組成と、
粒径:10μm以上のTiS粒子および粒径:10μm以上のMnS粒子のそれぞれについて、JIS G 0555に準拠して点算法で求めた清浄度が0~0.1%である組織と、を有す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、
Cu:1%以下、
Ni:1%以下、
Nb:0.05%以下、
W :0.05%以下、
V :0.5%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以上を含有する、請求項1に記載の中空スタビライザー用電縫鋼管。 - 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の製造方法であって、
前記成分組成を有する鋼板を、冷間成形により略円筒状に成形してオープン管とし、
前記オープン管の幅方向端部同士を衝合し、電縫溶接して電縫鋼管とし、
前記電縫鋼管を、850~1000℃の加熱温度に加熱し、
前記加熱後の電縫鋼管に、圧延温度:650℃以上、累積縮径率:30~90%の条件で熱間縮径圧延を施す、中空スタビライザー用電縫鋼管の製造方法。
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