WO2018139671A1 - Steel pipe for underbody components of automobiles, and underbody component of automobiles - Google Patents
Steel pipe for underbody components of automobiles, and underbody component of automobiles Download PDFInfo
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- WO2018139671A1 WO2018139671A1 PCT/JP2018/002958 JP2018002958W WO2018139671A1 WO 2018139671 A1 WO2018139671 A1 WO 2018139671A1 JP 2018002958 W JP2018002958 W JP 2018002958W WO 2018139671 A1 WO2018139671 A1 WO 2018139671A1
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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
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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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- 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
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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
Definitions
- the present invention relates to a steel pipe for automobile underbody parts and an automobile underbody part using the same.
- Patent Document 1 discloses a seamless steel pipe that has excellent cold workability, hardenability, toughness, and torsional fatigue strength, and is optimal as a hollow shaft material for an integrally formed hollow drive shaft.
- Patent Document 2 discloses a steel material for automobile structural members that is excellent in delayed fracture resistance.
- Patent Document 3 discloses an electric-welded steel pipe excellent in workability and fatigue characteristics after quenching, suitable for materials such as automobile parts and machine structural parts.
- Patent Document 1 an ERW steel pipe having improved fatigue characteristics after quenching by controlling the form of Ca-based inclusions such as oxides and sulfides present in the base material and welds of the ERW steel pipe. Is obtained.
- materials for automobile undercarriage parts are required to have both excellent cold workability during production and high notch tensile strength during use.
- Patent Documents 1 to 3 do not consider notch tensile properties at all and leave room for improvement.
- the present invention solves the above-described problems, and provides a steel pipe for automobile underbody parts that is excellent in cold workability and has excellent notch tensile properties when used as a part, and an automobile underbody part using the same. For the purpose.
- the present invention has been made to solve the above problems, and the gist of the present invention is a steel pipe for automobile underbody parts and an automobile underbody part described below.
- each element symbol in the above formula represents the content of each element contained in the steel.
- the chemical composition is mass%, Ni: 0.1 to 1.0%, Cu: 0.1 to 1.0%, Cr: 0.3 to 1.5%, Nb: 0.02 to 0.2%, and V: 0.03-0.2%, Containing one or more selected from The steel pipe for automobile undercarriage parts according to the above (1).
- the chemical composition is mass%, Mg: 0.0001 to 0.02%, and REM: 0.001 to 0.02%, Containing one or more selected from The steel pipe for automobile undercarriage parts according to the above (1) or (2).
- a steel pipe excellent in cold workability can be obtained.
- the part manufactured using the steel pipe which concerns on this invention has high notch tensile strength. Therefore, the steel pipe is suitable for automobile undercarriage parts.
- C 0.10 to 0.60% Since C has an effect of improving the strength of steel, it is an element to be contained according to the required strength. In order to ensure the strength as an automobile underbody part, it is necessary to contain 0.10% or more of C. On the other hand, if the C content exceeds 0.60%, the toughness decreases. Therefore, the C content is set to 0.10 to 0.60%.
- the C content is preferably 0.20% or more, and preferably 0.50% or less.
- Si 0.25 to 1.0%
- Si is an element that has an effect on deoxidation of steel and enhances hardenability and strengthens steel. In order to acquire said effect, it is necessary to contain Si 0.25% or more. However, when the Si content exceeds 1.0%, coarse inclusions of Si are formed, and the notch tensile strength is reduced. Therefore, the Si content is set to 0.25 to 1.0%. In terms of notch tensile strength, the Si content is preferably low, and is preferably 0.50% or less.
- Mn 0.05 to 2.0% Mn, like Si, is effective in deoxidizing steel, and is an element that enhances hardenability and strengthens steel. In order to acquire said effect, it is necessary to contain Mn 0.05% or more. However, if the Mn content exceeds 2.0%, coarse MnS is formed, and the notch tensile strength is reduced. Therefore, the Mn content is set to 0.05 to 2.0%. In terms of notch tensile strength, the Mn content is preferably low, and is preferably 1.5% or less.
- P 0.1% or less P is contained as an impurity in the steel. P is an element that decreases the toughness by reducing the bonding force of the grain boundaries. Therefore, the P content is 0.1% or less. The P content is preferably 0.05% or less.
- S 0.03% or less S is contained as an impurity in the steel. If the S content exceeds 0.03%, the required notch tensile strength cannot be ensured. Therefore, the S content is 0.03% or less.
- the S content is preferably 0.01% or less.
- Al 0.005 to 0.1%
- Al is an element necessary for deoxidation of steel.
- Al combines with MnS to form composite inclusions, thereby detoxifying MnS and contributing to the improvement of notch tensile properties.
- it is necessary to contain Al 0.005% or more.
- the Al content is set to 0.005 to 0.1%.
- the Al content is preferably 0.01% or more, and preferably 0.05% or less.
- N 0.01% or less N is contained as an impurity in the steel. If the N content exceeds 0.01%, the toughness decreases. Therefore, the N content is 0.01% or less. The N content is preferably 0.005% or less.
- O 0.01% or less O (oxygen) is contained as an impurity in the steel. If the O content exceeds 0.01%, the toughness decreases. Therefore, the O content is 0.01% or less.
- the O content is preferably 0.005% or less.
- Ca 0.0005 to 0.005%
- Ca is an element that contributes to the improvement of notch tensile properties by detoxifying MnS by bonding with MnS to form composite inclusions.
- it is necessary to contain 0.0005% or more of Ca.
- the Ca content is set to 0.0005 to 0.005%.
- the Ca content is preferably 0.001% or more, and preferably 0.004% or less.
- Mo 0.20 to 1.5%
- Mo has the effect
- Mo it is necessary to contain Mo 0.20% or more.
- the Mo content exceeds 1.5%, the effect is saturated and the cost is increased. Therefore, the Mo content is 0.20 to 1.5%.
- the Mo content is preferably 0.25% or more, and preferably 0.50% or less.
- Ti 0.01 to 0.05% Ti has the effect of suppressing coarsening of crystal grains and improving toughness. Further, Ti binds to MnS to form composite inclusions, thereby detoxifying MnS and contributing to the improvement of notch tensile properties. In order to acquire said effect, it is necessary to contain Ti 0.01% or more. However, if the Ti content exceeds 0.05%, coarse inclusions are formed. Therefore, the Ti content is set to 0.01 to 0.05%. The Ti content is preferably 0.02% or more, and preferably 0.04% or less.
- B 0.0001 to 0.01% B is combined with Mo and thus has an effect of improving hardenability and improving the strength of steel. In order to acquire said effect, it is necessary to contain B 0.0001% or more. However, if the B content exceeds 0.01%, B precipitates and the effect of improving hardenability is reduced. Therefore, the B content is set to 0.0001 to 0.01%.
- the B content is preferably 0.0005% or more, and preferably 0.003% or less.
- Ni 0 to 1.0%
- Ni has an effect of improving the strength of the base material, and may be contained as necessary. However, if the Ni content exceeds 1.0%, the effect is saturated and the cost is increased. Therefore, the Ni content is 1.0% or less.
- the Ni content is preferably 0.5% or less. In order to obtain the above effect, the Ni content is preferably 0.1% or more.
- Cu 0 to 1.0% Since Cu has the effect of improving the strength of the base material, it may be contained as necessary. However, if the Cu content exceeds 1.0%, the effect is saturated and the cost is increased. Therefore, the Cu content is 1.0% or less. The Cu content is preferably 0.5% or less. In order to acquire said effect, it is preferable that Cu content is 0.1% or more.
- Cr 0 to 1.5% Since Cr has an effect of improving hardenability, it may be contained as necessary. However, if the Cr content exceeds 1.5%, the effect is saturated and the cost increases. Therefore, the Cr content is 1.5% or less.
- the Cr content is preferably 1.0% or less. In order to acquire said effect, it is preferable that Cr content is 0.3% or more.
- Nb 0 to 0.2% Since Nb has an effect of refining crystal grains and improving the strength of the base material, it may be contained as necessary. However, when the Nb content exceeds 0.2%, the effect is saturated and the cost is increased. Therefore, the Nb content is 0.2% or less. The Nb content is preferably 0.1% or less. In order to acquire said effect, it is preferable that Nb content is 0.02% or more.
- V 0 to 0.2%
- V has an effect of improving the strength of the base material, and may be contained as necessary. However, when the V content exceeds 0.2%, the effect is saturated and the cost is increased. Therefore, the V content is 0.2% or less.
- the V content is preferably 0.1% or less. In order to obtain the above effect, the V content is preferably 0.03% or more.
- Mg and REM both form oxides in the molten steel, have the effect of improving the cleanliness of the steel by deoxidation, and contribute to the improvement of notch tensile properties. Further, since it functions as a carbonitride formation nucleus, it has an effect of suppressing the formation of coarse carbonitride when appropriately finely dispersed. Therefore, you may contain 1 type, or 2 or more types of these elements as needed.
- the content of each element is as described above.
- the content of each element is preferably 0.01% or less, and more preferably 0.0050% or less.
- REM refers to a total of 17 elements of Sc, Y, and lanthanoid
- the content of REM refers to the total content of these elements.
- a lanthanoid it is industrially added in the form of misch metal.
- the balance is Fe and impurities.
- impurities are components that are mixed due to various factors of raw materials such as ores and scraps and manufacturing processes when steel is industrially manufactured, and are allowed within a range that does not adversely affect the present invention. Means something.
- each element symbol in the above formula represents the content of each element contained in the steel.
- Ca, Al, and Ti have the effect of detoxifying MnS by combining with MnS to form composite inclusions.
- the side value in the formula (i) is preferably 45.0 or less, and more preferably 30.0 or less.
- each element symbol in the above formula represents the content of each element contained in the steel.
- Si, Mo, and B are elements that enhance hardenability. Therefore, in order to increase the strength of the steel and improve the notch tensile properties, each element must satisfy the above formula (ii) in addition to satisfying the above range.
- 450 is practically the upper limit.
- the right side value of the formula (ii) is preferably 75.0 or less, and is preferably 50.0 or less. More preferably.
- the steel pipe according to the present invention has a metal structure in which the cementite area ratio is 5 to 70% and the cementite spheroidization ratio is 70% or more. If the area ratio of cementite is less than 5%, sufficient notch tensile strength may not be obtained. On the other hand, when the area ratio of cementite exceeds 70%, as will be described later, even if cementite is spheroidized, it is hard and processability deteriorates.
- the area ratio of cementite is preferably 10% or more, and more preferably 15% or more. Moreover, the area ratio of cementite is preferably 65% or less, and more preferably 60% or less. In the above metal structure, the balance is preferably ferrite.
- the spheroidization rate of cementite is preferably 75% or more.
- the “spheroidization rate of cementite” refers to the total area of all cementite when cementite particles having an aspect ratio of 3.0 or less are used as spheroidized cementite. , Means the ratio of the total area of spheroidized cementite.
- the area ratio and spheroidization ratio of cementite are calculated by the following methods, respectively.
- a specimen for observing the structure is cut out from the steel pipe sample so that the position of the thickness 1/4 of the cross section perpendicular to the longitudinal direction of the steel pipe becomes the observation surface.
- the above observation surface is mirror-polished, it undergoes nital corrosion to reveal a metal structure.
- the area ratio of cementite is calculated
- the area ratio of all cementite is obtained by observing the observation surface at a magnification of 2000 using a scanning electron microscope (SEM). Further, in the same field of view, the area ratio of spheroidized cementite having an aspect ratio of 3.0 or less is obtained. The aspect ratio is obtained by elliptically approximating cementite by image analysis and dividing the major axis length by the minor axis length. Then, the spheroidizing ratio of the cementite is calculated by dividing the area ratio of the spheroidized cementite by the area ratio of all the cementites obtained in the same field of view.
- the steel pipe according to the present invention includes, for example, a seamless steel pipe and an electric resistance steel pipe. There are no particular restrictions on the production conditions.
- the seamless steel pipe can be manufactured, for example, by the following method.
- ⁇ Melting and casting> For melting and casting, a method performed by a general steel pipe manufacturing method can be used, and the casting may be ingot casting or continuous casting. Moreover, you may cast in the shape of the round billet for pipe making by round CC.
- Hot working such as forging, drilling and rolling is performed.
- processes such as forging and partial rolling for forming the circular billet are not necessary.
- rolling is performed using a mandrel mill or a plug mill. Desirable conditions for hot working such as piercing and rolling are as follows.
- the billet may be heated to such an extent that hot piercing with a piercing and rolling mill is possible, but a desirable temperature range is 1000 to 1250 ° C.
- a desirable temperature range is 1000 to 1250 ° C.
- the finishing temperature should be 900 ° C or higher. Is desirable.
- the electric resistance welded steel pipe can be manufactured, for example, by the following method.
- ⁇ Melting and casting> For melting and casting, a method performed by a general steel plate manufacturing method can be used. For example, a slab is formed by continuous casting.
- the obtained slab is hot-rolled, and further cold-rolled as necessary to produce a steel plate having a predetermined thickness.
- the rolled steel sheet may be wound in a coil shape.
- ⁇ Pipe making> The obtained steel sheet is roll-formed and subjected to high-frequency welding to produce an electric resistance welded steel pipe. You may heat-process with respect to a welding part as needed.
- the steel pipe obtained by the above method may be cold worked for the purpose of improving the dimensional accuracy as necessary.
- the cold working method is not particularly limited as long as it can uniformly process a steel pipe, for example, cold rolling called a so-called cold drawing machine or cold pilger mill using a perforated die and a plug. It is industrially advantageous to use a machine.
- spheroidizing annealing is performed on the steel pipe under the following conditions, for example.
- the steel pipe is heated to a temperature range of Ac 1 point to Ac 1 point + 20 ° C. and held for 30 minutes or less, and then slowly cooled at an average cooling rate of 1 ° C./s or less.
- a part of the layered cementite is re-dissolved to be divided and spheroidized.
- the heating temperature is less than 1 Ac, the spheroidization of cementite becomes insufficient, and it becomes difficult to obtain the effect of improving the cold workability.
- the heating temperature exceeds Ac 1 point + 20 ° C. or the heating time exceeds 30 min, not only may there be a re-dissolution of the cementite, but the austenite generation amount may be excessive. .
- the generated austenite is transformed into ferrite + pearlite by subsequent cooling, and the cold workability is deteriorated.
- spheroidized cementite grows by setting the average cooling rate after heating to 1 ° C./s or less.
- the average cooling rate exceeds 1 ° C./s, a part of the re-dissolved cementite may be deposited in a layer shape to form a pearlite structure.
- the steel pipe manufactured by the above method has the above-described metal structure, it is excellent in cold workability.
- the heating temperature at the time of quenching is not particularly limited, but it is desirable to set the temperature to Ac 3 points + 50 ° C. or higher. Also, the heating time is not particularly limited, but it is desirable that the soaking time is 5 minutes or more.
- the cooling rate during quenching if the average cooling rate at the central portion of the wall thickness is less than 10 ° C./s, sufficient strength cannot be obtained.
- the cooling method is not particularly limited as long as it is a method of performing accelerated cooling, but when cooling cracks occur after cooling depending on the shape of the component, it is preferable to perform oil cooling in order to reduce the cooling rate.
- the tempering temperature is not particularly limited, but is preferably 150 to 300 ° C.
- the area ratio of all cementite was determined by observing the observation surface at a magnification of 2000 times using SEM. Furthermore, in the same visual field, the area ratio of spheroidized cementite having an aspect ratio of 3.0 or less was determined. Then, the spheroidization rate of cementite was calculated by dividing the area ratio of spheroidized cementite by the area ratio of all cementite obtained in the same field of view.
- the hardness of each test material was measured for evaluation of cold workability. Specifically, the Vickers hardness was measured at the 1/4 thickness position using the above-mentioned specimen for observing the structure. The test force in the hardness measurement was 9.8N. In the present invention, when the hardness is 240 HV or less, it is determined that the cold workability is excellent.
- a notched tensile test piece having the shape shown in FIG. 1 was cut out from each test material after the tempering treatment, and a tensile test was performed using the test piece.
- the unit of the dimension shown in FIG. 1 is mm.
- the notch tensile strength was calculated
- the value of notch tensile strength becomes 1440 Mpa or more, it shall be excellent in a notch tensile characteristic.
- Test No. Reference numerals 1 to 10 are examples of the present invention that satisfy all the provisions of the present invention. As can be seen from Table 1, the hardness is 240 HV or less, excellent cold workability, and after quenching and tempering treatment, show notch tensile strength of 1470 MPa or more, resulting in excellent notch tensile properties. It was.
- test No. which is a comparative example. 11 and 12
- the chemical composition satisfied the provisions of the present invention, the spheroidizing annealing conditions were inadequate, so the spheroidizing rate of cementite was lowered and the cold workability was deteriorated. .
- test no. No. 15 has a high Mn content.
- No. 16 had a high S content, and in both cases, the median value in the formula (i) was less than the lower limit value, resulting in inferior notch tensile properties.
- test no. No. 19 although the content of each element satisfied the regulation, the notch tensile property was inferior because the median value in the formula (i) was less than the lower limit.
- test no. 17 since the Ca content was excessive and the median value in the formula (i) exceeded the upper limit value, coarse inclusions of CaO were formed, resulting in inferior notch tensile properties.
- a steel pipe excellent in cold workability can be obtained.
- the part manufactured using the steel pipe which concerns on this invention has high notch tensile strength. Therefore, the steel pipe is suitable for automobile undercarriage parts.
Abstract
A steel pipe for underbody components of automobiles, which has a chemical composition that contains, in mass%, 0.10-0.60% of C, 0.25-1.0% of Si, 0.05-2.0% of Mn, 0.1% or less of P, 0.03% or less of S, 0.005-0.1% of Al, 0.01% or less of N, 0.01% or less of O, 0.0005-0.005% of Ca, 0.20-1.5% of Mo, 0.01-0.05% of Ti, 0.0001-0.01% of B, 0-1.0% of Ni, 0-1.0% of Cu, 0-1.5% of Cr, 0-0.2% of Nb, 0-0.2% of V, 0-0.02% of Mg and 0-0.02% of REM, with the balance made up of Fe and impurities, while satisfying [5.0 ≤ (0.001 + Ca) × Al × Ti/(Mn × S) × 104 ≤ 60.0] and [2.0 ≤ 3 × Si × Mo × B × 104]. This steel pipe for underbody components of automobiles has a metal structure wherein the area ratio of cementite is 5-70% and the spheroidization rate of cementite is 70% or more.
Description
本発明は、自動車足回り部品用鋼管およびそれを用いた自動車足回り部品に関する。
The present invention relates to a steel pipe for automobile underbody parts and an automobile underbody part using the same.
自動車の燃費向上および安全性向上の観点から、自動車構造部材には高い強度が要求される。例えば、特許文献１には、優れた冷間加工性、焼き入れ性、靱性および捩り疲労強度を同時に備え、一体成形型の中空ドライブシャフト用の中空軸素材として最適なシームレス鋼管が開示されている。また、特許文献２には、耐遅れ破壊特性に優れる自動車構造部材用鋼材が開示されている。
From the viewpoint of improving fuel efficiency and safety of automobiles, automobile structural members are required to have high strength. For example, Patent Document 1 discloses a seamless steel pipe that has excellent cold workability, hardenability, toughness, and torsional fatigue strength, and is optimal as a hollow shaft material for an integrally formed hollow drive shaft. . Further, Patent Document 2 discloses a steel material for automobile structural members that is excellent in delayed fracture resistance.
さらに、特許文献３には、自動車用部品、機械構造用部品などの素材に好適な、加工性および焼入れ後の疲労特性に優れた電縫鋼管が開示されている。特許文献１によれば、電縫鋼管の母材および溶接部に存在する、酸化物および硫化物などのＣａ系介在物の形態を制御することによって、焼入れ後の疲労特性を高めた電縫鋼管が得られる。
Furthermore, Patent Document 3 discloses an electric-welded steel pipe excellent in workability and fatigue characteristics after quenching, suitable for materials such as automobile parts and machine structural parts. According to Patent Document 1, an ERW steel pipe having improved fatigue characteristics after quenching by controlling the form of Ca-based inclusions such as oxides and sulfides present in the base material and welds of the ERW steel pipe. Is obtained.
ところで、自動車構造部材のなかでも、自動車足回り部品は、複雑な部品形状に成形された上で使用される。成形には高い寸法精度が求められるため、一般的には部品は冷間加工によって製造される。そのため、部品の素材には優れた冷間加工性が要求される。
By the way, among automobile structural members, automobile undercarriage parts are used after being formed into a complicated part shape. Since high dimensional accuracy is required for molding, parts are generally manufactured by cold working. Therefore, excellent cold workability is required for the material of the parts.
加えて、自動車足回り部品には、走行時に様々な荷重が加えられる。そのため、使用時には、破壊に耐えうる強度が必要となる。ここで、部品が破壊する際は、最も弱い部分に応力集中し、破損するのが一般的である。本発明者らが検討を行ったところ、鋼材の切欠き引張強さを向上させることが、これらの部品の強度の向上に有効に繋がることを知見した。
In addition, various loads are applied to automobile underbody parts during driving. Therefore, it is necessary to have strength that can withstand destruction during use. Here, when a part breaks, it is common for stress to concentrate on the weakest part and to break. As a result of investigations by the present inventors, it has been found that improving the notch tensile strength of the steel material effectively leads to an improvement in the strength of these parts.
すなわち、自動車足回り部品の素材には、製造時における優れた冷間加工性と、使用時における高い切欠き引張強さとの両立が求められている。
In other words, materials for automobile undercarriage parts are required to have both excellent cold workability during production and high notch tensile strength during use.
しかしながら、特許文献１～３においては、切欠き引張特性について一切考慮されておらず、改善の余地が残されている。
However, Patent Documents 1 to 3 do not consider notch tensile properties at all and leave room for improvement.
本発明は、上記の課題を解決し、冷間加工性に優れ、かつ部品として使用する際には切欠き引張特性に優れる自動車足回り部品用鋼管およびそれを用いた自動車足回り部品を提供することを目的とする。
The present invention solves the above-described problems, and provides a steel pipe for automobile underbody parts that is excellent in cold workability and has excellent notch tensile properties when used as a part, and an automobile underbody part using the same. For the purpose.
本発明は、上記課題を解決するためになされたものであり、下記の自動車足回り部品用鋼管および自動車足回り部品を要旨とする。
DETAILED DESCRIPTION OF THE INVENTION The present invention has been made to solve the above problems, and the gist of the present invention is a steel pipe for automobile underbody parts and an automobile underbody part described below.
（１）質量％で、
Ｃ：０．１０～０．６０％、
Ｓｉ：０．２５～１．０％、
Ｍｎ：０．０５～２．０％、
Ｐ：０．１％以下、
Ｓ：０．０３％以下、
Ａｌ：０．００５～０．１％、
Ｎ：０．０１％以下、
Ｏ：０．０１％以下、
Ｃａ：０．０００５～０．００５％、
Ｍｏ：０．２０～１．５％、
Ｔｉ：０．０１～０．０５％、
Ｂ：０．０００１～０．０１％、
Ｎｉ：０～１．０％、
Ｃｕ：０～１．０％、
Ｃｒ：０～１．５％、
Ｎｂ：０～０．２％、
Ｖ：０～０．２％、
Ｍｇ：０～０．０２％、
ＲＥＭ：０～０．０２％、
残部：Ｆｅおよび不純物であり、
下記（ｉ）式および（ii）式を満足する化学組成を有し、
セメンタイトの面積率が５～７０％であり、かつ、前記セメンタイトの球状化率が７０％以上である金属組織を有する、
自動車足回り部品用鋼管。
５．０≦（０．００１＋Ｃａ）×Ａｌ×Ｔｉ／（Ｍｎ×Ｓ）×１０４≦６０．０ ・・・（ｉ）
２．０≦３×Ｓｉ×Ｍｏ×Ｂ×１０４ ・・・（ii）
但し、上記式中の各元素記号は鋼中に含まれる各元素の含有量を表す。 (1) In mass%,
C: 0.10 to 0.60%
Si: 0.25 to 1.0%,
Mn: 0.05 to 2.0%,
P: 0.1% or less,
S: 0.03% or less,
Al: 0.005 to 0.1%,
N: 0.01% or less,
O: 0.01% or less,
Ca: 0.0005 to 0.005%,
Mo: 0.20 to 1.5%,
Ti: 0.01 to 0.05%,
B: 0.0001 to 0.01%,
Ni: 0 to 1.0%,
Cu: 0 to 1.0%,
Cr: 0 to 1.5%,
Nb: 0 to 0.2%,
V: 0 to 0.2%,
Mg: 0 to 0.02%,
REM: 0 to 0.02%,
Balance: Fe and impurities,
Having a chemical composition satisfying the following formulas (i) and (ii):
Having a metal structure in which the area ratio of cementite is 5 to 70% and the spheroidization ratio of the cementite is 70% or more;
Steel pipe for automobile undercarriage parts.
5.0 ≦ (0.001 + Ca) × Al × Ti / (Mn × S) × 10 4 ≦ 60.0 (i)
2.0 ≦ 3 × Si × Mo × B × 10 4 ··· (ii)
However, each element symbol in the above formula represents the content of each element contained in the steel.
Ｃ：０．１０～０．６０％、
Ｓｉ：０．２５～１．０％、
Ｍｎ：０．０５～２．０％、
Ｐ：０．１％以下、
Ｓ：０．０３％以下、
Ａｌ：０．００５～０．１％、
Ｎ：０．０１％以下、
Ｏ：０．０１％以下、
Ｃａ：０．０００５～０．００５％、
Ｍｏ：０．２０～１．５％、
Ｔｉ：０．０１～０．０５％、
Ｂ：０．０００１～０．０１％、
Ｎｉ：０～１．０％、
Ｃｕ：０～１．０％、
Ｃｒ：０～１．５％、
Ｎｂ：０～０．２％、
Ｖ：０～０．２％、
Ｍｇ：０～０．０２％、
ＲＥＭ：０～０．０２％、
残部：Ｆｅおよび不純物であり、
下記（ｉ）式および（ii）式を満足する化学組成を有し、
セメンタイトの面積率が５～７０％であり、かつ、前記セメンタイトの球状化率が７０％以上である金属組織を有する、
自動車足回り部品用鋼管。
５．０≦（０．００１＋Ｃａ）×Ａｌ×Ｔｉ／（Ｍｎ×Ｓ）×１０４≦６０．０ ・・・（ｉ）
２．０≦３×Ｓｉ×Ｍｏ×Ｂ×１０４ ・・・（ii）
但し、上記式中の各元素記号は鋼中に含まれる各元素の含有量を表す。 (1) In mass%,
C: 0.10 to 0.60%
Si: 0.25 to 1.0%,
Mn: 0.05 to 2.0%,
P: 0.1% or less,
S: 0.03% or less,
Al: 0.005 to 0.1%,
N: 0.01% or less,
O: 0.01% or less,
Ca: 0.0005 to 0.005%,
Mo: 0.20 to 1.5%,
Ti: 0.01 to 0.05%,
B: 0.0001 to 0.01%,
Ni: 0 to 1.0%,
Cu: 0 to 1.0%,
Cr: 0 to 1.5%,
Nb: 0 to 0.2%,
V: 0 to 0.2%,
Mg: 0 to 0.02%,
REM: 0 to 0.02%,
Balance: Fe and impurities,
Having a chemical composition satisfying the following formulas (i) and (ii):
Having a metal structure in which the area ratio of cementite is 5 to 70% and the spheroidization ratio of the cementite is 70% or more;
Steel pipe for automobile undercarriage parts.
5.0 ≦ (0.001 + Ca) × Al × Ti / (Mn × S) × 10 4 ≦ 60.0 (i)
2.0 ≦ 3 × Si × Mo × B × 10 4 ··· (ii)
However, each element symbol in the above formula represents the content of each element contained in the steel.
（２）前記化学組成が、質量％で、
Ｎｉ：０．１～１．０％、
Ｃｕ：０．１～１．０％、
Ｃｒ：０．３～１．５％、
Ｎｂ：０．０２～０．２％、および、
Ｖ：０．０３～０．２％、
から選択される１種以上を含有する、
上記（１）に記載の自動車足回り部品用鋼管。 (2) The chemical composition is mass%,
Ni: 0.1 to 1.0%,
Cu: 0.1 to 1.0%,
Cr: 0.3 to 1.5%,
Nb: 0.02 to 0.2%, and
V: 0.03-0.2%,
Containing one or more selected from
The steel pipe for automobile undercarriage parts according to the above (1).
Ｎｉ：０．１～１．０％、
Ｃｕ：０．１～１．０％、
Ｃｒ：０．３～１．５％、
Ｎｂ：０．０２～０．２％、および、
Ｖ：０．０３～０．２％、
から選択される１種以上を含有する、
上記（１）に記載の自動車足回り部品用鋼管。 (2) The chemical composition is mass%,
Ni: 0.1 to 1.0%,
Cu: 0.1 to 1.0%,
Cr: 0.3 to 1.5%,
Nb: 0.02 to 0.2%, and
V: 0.03-0.2%,
Containing one or more selected from
The steel pipe for automobile undercarriage parts according to the above (1).
（３）前記化学組成が、質量％で、
Ｍｇ：０．０００１～０．０２％、および、
ＲＥＭ：０．００１～０．０２％、
から選択される１種以上を含有する、
上記（１）または（２）に記載の自動車足回り部品用鋼管。 (3) The chemical composition is mass%,
Mg: 0.0001 to 0.02%, and
REM: 0.001 to 0.02%,
Containing one or more selected from
The steel pipe for automobile undercarriage parts according to the above (1) or (2).
Ｍｇ：０．０００１～０．０２％、および、
ＲＥＭ：０．００１～０．０２％、
から選択される１種以上を含有する、
上記（１）または（２）に記載の自動車足回り部品用鋼管。 (3) The chemical composition is mass%,
Mg: 0.0001 to 0.02%, and
REM: 0.001 to 0.02%,
Containing one or more selected from
The steel pipe for automobile undercarriage parts according to the above (1) or (2).
（４）継目無鋼管である、
上記（１）から（３）までのいずれかに記載の自動車足回り部品用鋼管。 (4) Seamless steel pipe.
The steel pipe for automobile underbody parts according to any one of (1) to (3) above.
上記（１）から（３）までのいずれかに記載の自動車足回り部品用鋼管。 (4) Seamless steel pipe.
The steel pipe for automobile underbody parts according to any one of (1) to (3) above.
（５）上記（１）から（４）までのいずれかに記載の自動車足回り部品用鋼管を用いた、
自動車足回り部品。 (5) Using the steel pipe for automobile undercarriage parts according to any of (1) to (4) above,
Automobile undercarriage parts.
自動車足回り部品。 (5) Using the steel pipe for automobile undercarriage parts according to any of (1) to (4) above,
Automobile undercarriage parts.
本発明によれば、冷間加工性に優れる鋼管を得ることが可能になる。また、本発明に係る鋼管を用いて製造した部品は、高い切欠き引張強さを有する。したがって、上記鋼管は、自動車足回り部品用として好適である。
According to the present invention, a steel pipe excellent in cold workability can be obtained. Moreover, the part manufactured using the steel pipe which concerns on this invention has high notch tensile strength. Therefore, the steel pipe is suitable for automobile undercarriage parts.
以下、本発明の各要件について詳しく説明する。
Hereinafter, each requirement of the present invention will be described in detail.
（Ａ）化学組成
各元素の限定理由は下記のとおりである。なお、以下の説明において含有量についての「％」は、「質量％」を意味する。 (A) Chemical composition The reason for limitation of each element is as follows. In the following description, “%” for the content means “% by mass”.
各元素の限定理由は下記のとおりである。なお、以下の説明において含有量についての「％」は、「質量％」を意味する。 (A) Chemical composition The reason for limitation of each element is as follows. In the following description, “%” for the content means “% by mass”.
Ｃ：０．１０～０．６０％
Ｃは、鋼の強度を向上する効果を有するため、要求される強度に応じて含有させる元素である。自動車足回り部品としての強度を確保するためには、Ｃを０．１０％以上含有させる必要がある。一方、Ｃ含有量が０．６０％を超えると、靱性が低下する。そのため、Ｃ含有量は０．１０～０．６０％とする。Ｃ含有量は０．２０％以上であるのが好ましく、０．５０％以下であるのが好ましい。 C: 0.10 to 0.60%
Since C has an effect of improving the strength of steel, it is an element to be contained according to the required strength. In order to ensure the strength as an automobile underbody part, it is necessary to contain 0.10% or more of C. On the other hand, if the C content exceeds 0.60%, the toughness decreases. Therefore, the C content is set to 0.10 to 0.60%. The C content is preferably 0.20% or more, and preferably 0.50% or less.
Ｃは、鋼の強度を向上する効果を有するため、要求される強度に応じて含有させる元素である。自動車足回り部品としての強度を確保するためには、Ｃを０．１０％以上含有させる必要がある。一方、Ｃ含有量が０．６０％を超えると、靱性が低下する。そのため、Ｃ含有量は０．１０～０．６０％とする。Ｃ含有量は０．２０％以上であるのが好ましく、０．５０％以下であるのが好ましい。 C: 0.10 to 0.60%
Since C has an effect of improving the strength of steel, it is an element to be contained according to the required strength. In order to ensure the strength as an automobile underbody part, it is necessary to contain 0.10% or more of C. On the other hand, if the C content exceeds 0.60%, the toughness decreases. Therefore, the C content is set to 0.10 to 0.60%. The C content is preferably 0.20% or more, and preferably 0.50% or less.
Ｓｉ：０．２５～１．０％
Ｓｉは、鋼の脱酸に効果があり、また、焼入れ性を高めて、鋼を強化する元素である。上記の効果を得るためには、Ｓｉを０．２５％以上含有させる必要がある。しかしながら、Ｓｉ含有量が１．０％を超えると、Ｓｉの粗大な介在物が形成され、切欠き引張強さを低下させる。そのため、Ｓｉ含有量は０．２５～１．０％とする。なお、切欠き引張強さの面からは、Ｓｉ含有量は低い方が好ましく、０．５０％以下であるのが好ましい。 Si: 0.25 to 1.0%
Si is an element that has an effect on deoxidation of steel and enhances hardenability and strengthens steel. In order to acquire said effect, it is necessary to contain Si 0.25% or more. However, when the Si content exceeds 1.0%, coarse inclusions of Si are formed, and the notch tensile strength is reduced. Therefore, the Si content is set to 0.25 to 1.0%. In terms of notch tensile strength, the Si content is preferably low, and is preferably 0.50% or less.
Ｓｉは、鋼の脱酸に効果があり、また、焼入れ性を高めて、鋼を強化する元素である。上記の効果を得るためには、Ｓｉを０．２５％以上含有させる必要がある。しかしながら、Ｓｉ含有量が１．０％を超えると、Ｓｉの粗大な介在物が形成され、切欠き引張強さを低下させる。そのため、Ｓｉ含有量は０．２５～１．０％とする。なお、切欠き引張強さの面からは、Ｓｉ含有量は低い方が好ましく、０．５０％以下であるのが好ましい。 Si: 0.25 to 1.0%
Si is an element that has an effect on deoxidation of steel and enhances hardenability and strengthens steel. In order to acquire said effect, it is necessary to contain Si 0.25% or more. However, when the Si content exceeds 1.0%, coarse inclusions of Si are formed, and the notch tensile strength is reduced. Therefore, the Si content is set to 0.25 to 1.0%. In terms of notch tensile strength, the Si content is preferably low, and is preferably 0.50% or less.
Ｍｎ：０．０５～２．０％
ＭｎもＳｉと同様に、鋼の脱酸に効果があり、また、焼入れ性を高めて、鋼を強化する元素である。上記の効果を得るためには、Ｍｎを０．０５％以上含有させる必要がある。しかしながら、Ｍｎの含有量が２．０％を超えると、粗大なＭｎＳが形成され、切欠き引張強さを低下させる。そのため、Ｍｎ含有量は０．０５～２．０％とする。なお、切欠き引張強さの面からは、Ｍｎ含有量は低い方が好ましく、１．５％以下であるのが好ましい。 Mn: 0.05 to 2.0%
Mn, like Si, is effective in deoxidizing steel, and is an element that enhances hardenability and strengthens steel. In order to acquire said effect, it is necessary to contain Mn 0.05% or more. However, if the Mn content exceeds 2.0%, coarse MnS is formed, and the notch tensile strength is reduced. Therefore, the Mn content is set to 0.05 to 2.0%. In terms of notch tensile strength, the Mn content is preferably low, and is preferably 1.5% or less.
ＭｎもＳｉと同様に、鋼の脱酸に効果があり、また、焼入れ性を高めて、鋼を強化する元素である。上記の効果を得るためには、Ｍｎを０．０５％以上含有させる必要がある。しかしながら、Ｍｎの含有量が２．０％を超えると、粗大なＭｎＳが形成され、切欠き引張強さを低下させる。そのため、Ｍｎ含有量は０．０５～２．０％とする。なお、切欠き引張強さの面からは、Ｍｎ含有量は低い方が好ましく、１．５％以下であるのが好ましい。 Mn: 0.05 to 2.0%
Mn, like Si, is effective in deoxidizing steel, and is an element that enhances hardenability and strengthens steel. In order to acquire said effect, it is necessary to contain Mn 0.05% or more. However, if the Mn content exceeds 2.0%, coarse MnS is formed, and the notch tensile strength is reduced. Therefore, the Mn content is set to 0.05 to 2.0%. In terms of notch tensile strength, the Mn content is preferably low, and is preferably 1.5% or less.
Ｐ：０．１％以下
Ｐは鋼中に不純物として含有される。Ｐは粒界の結合力を小さくして、靱性を低下させる元素である。そのため、Ｐ含有量は０．１％以下とする。Ｐ含有量は０．０５％以下であるのが好ましい。 P: 0.1% or less P is contained as an impurity in the steel. P is an element that decreases the toughness by reducing the bonding force of the grain boundaries. Therefore, the P content is 0.1% or less. The P content is preferably 0.05% or less.
Ｐは鋼中に不純物として含有される。Ｐは粒界の結合力を小さくして、靱性を低下させる元素である。そのため、Ｐ含有量は０．１％以下とする。Ｐ含有量は０．０５％以下であるのが好ましい。 P: 0.1% or less P is contained as an impurity in the steel. P is an element that decreases the toughness by reducing the bonding force of the grain boundaries. Therefore, the P content is 0.1% or less. The P content is preferably 0.05% or less.
Ｓ：０．０３％以下
Ｓは鋼中に不純物として含有される。Ｓ含有量が０．０３％を超えると、必要な切欠き引張強さを確保することができない。したがって、Ｓ含有量は０．０３％以下とする。Ｓ含有量は０．０１％以下であるのが好ましい。 S: 0.03% or less S is contained as an impurity in the steel. If the S content exceeds 0.03%, the required notch tensile strength cannot be ensured. Therefore, the S content is 0.03% or less. The S content is preferably 0.01% or less.
Ｓは鋼中に不純物として含有される。Ｓ含有量が０．０３％を超えると、必要な切欠き引張強さを確保することができない。したがって、Ｓ含有量は０．０３％以下とする。Ｓ含有量は０．０１％以下であるのが好ましい。 S: 0.03% or less S is contained as an impurity in the steel. If the S content exceeds 0.03%, the required notch tensile strength cannot be ensured. Therefore, the S content is 0.03% or less. The S content is preferably 0.01% or less.
Ａｌ：０．００５～０．１％
Ａｌは、鋼の脱酸に必要な元素である。また、Ａｌは、ＭｎＳと結合して複合介在物を形成することにより、ＭｎＳを無害化して切欠き引張特性の向上に寄与する。上記の効果を得るためには、Ａｌを０．００５％以上含有させる必要がある。一方、Ａｌ含有量が０．１％を超えると、クラスター状の非金属介在物が生成して靱性が低下する。そのため、Ａｌ含有量は０．００５～０．１％とする。Ａｌ含有量は０．０１％以上であるのが好ましく、０．０５％以下であるのが好ましい。 Al: 0.005 to 0.1%
Al is an element necessary for deoxidation of steel. In addition, Al combines with MnS to form composite inclusions, thereby detoxifying MnS and contributing to the improvement of notch tensile properties. In order to acquire said effect, it is necessary to contain Al 0.005% or more. On the other hand, if the Al content exceeds 0.1%, cluster-like non-metallic inclusions are generated and the toughness is lowered. Therefore, the Al content is set to 0.005 to 0.1%. The Al content is preferably 0.01% or more, and preferably 0.05% or less.
Ａｌは、鋼の脱酸に必要な元素である。また、Ａｌは、ＭｎＳと結合して複合介在物を形成することにより、ＭｎＳを無害化して切欠き引張特性の向上に寄与する。上記の効果を得るためには、Ａｌを０．００５％以上含有させる必要がある。一方、Ａｌ含有量が０．１％を超えると、クラスター状の非金属介在物が生成して靱性が低下する。そのため、Ａｌ含有量は０．００５～０．１％とする。Ａｌ含有量は０．０１％以上であるのが好ましく、０．０５％以下であるのが好ましい。 Al: 0.005 to 0.1%
Al is an element necessary for deoxidation of steel. In addition, Al combines with MnS to form composite inclusions, thereby detoxifying MnS and contributing to the improvement of notch tensile properties. In order to acquire said effect, it is necessary to contain Al 0.005% or more. On the other hand, if the Al content exceeds 0.1%, cluster-like non-metallic inclusions are generated and the toughness is lowered. Therefore, the Al content is set to 0.005 to 0.1%. The Al content is preferably 0.01% or more, and preferably 0.05% or less.
Ｎ：０．０１％以下
Ｎは鋼中に不純物として含有される。Ｎ含有量が０．０１％を超えると靱性が低下する。そのため、Ｎ含有量は０．０１％以下とする。Ｎ含有量は０．００５％以下であるのが好ましい。 N: 0.01% or less N is contained as an impurity in the steel. If the N content exceeds 0.01%, the toughness decreases. Therefore, the N content is 0.01% or less. The N content is preferably 0.005% or less.
Ｎは鋼中に不純物として含有される。Ｎ含有量が０．０１％を超えると靱性が低下する。そのため、Ｎ含有量は０．０１％以下とする。Ｎ含有量は０．００５％以下であるのが好ましい。 N: 0.01% or less N is contained as an impurity in the steel. If the N content exceeds 0.01%, the toughness decreases. Therefore, the N content is 0.01% or less. The N content is preferably 0.005% or less.
Ｏ：０．０１％以下
Ｏ（酸素）は鋼中に不純物として含有される。Ｏの含有量が０．０１％を超えると靱性が低下する。そのため、Ｏ含有量は０．０１％以下とする。Ｏ含有量は０．００５％以下であるのが好ましい。 O: 0.01% or less O (oxygen) is contained as an impurity in the steel. If the O content exceeds 0.01%, the toughness decreases. Therefore, the O content is 0.01% or less. The O content is preferably 0.005% or less.
Ｏ（酸素）は鋼中に不純物として含有される。Ｏの含有量が０．０１％を超えると靱性が低下する。そのため、Ｏ含有量は０．０１％以下とする。Ｏ含有量は０．００５％以下であるのが好ましい。 O: 0.01% or less O (oxygen) is contained as an impurity in the steel. If the O content exceeds 0.01%, the toughness decreases. Therefore, the O content is 0.01% or less. The O content is preferably 0.005% or less.
Ｃａ：０．０００５～０．００５％
Ｃａは、ＭｎＳと結合して複合介在物を形成することにより、ＭｎＳを無害化して切欠き引張特性の向上に寄与する元素である。上記の効果を得るためには、Ｃａを０．０００５％以上含有させる必要がある。しかしながら、Ｃａ含有量が０．００５％を超えると、Ｃａ自体が粗大な介在物となり、切欠き引張強さの低下および靭性の低下を招く。そのため、Ｃａ含有量は０．０００５～０．００５％とする。Ｃａ含有量は０．００１％以上であるのが好ましく、０．００４％以下であるのが好ましい。 Ca: 0.0005 to 0.005%
Ca is an element that contributes to the improvement of notch tensile properties by detoxifying MnS by bonding with MnS to form composite inclusions. In order to acquire said effect, it is necessary to contain 0.0005% or more of Ca. However, if the Ca content exceeds 0.005%, Ca itself becomes coarse inclusions, leading to a decrease in notch tensile strength and a decrease in toughness. Therefore, the Ca content is set to 0.0005 to 0.005%. The Ca content is preferably 0.001% or more, and preferably 0.004% or less.
Ｃａは、ＭｎＳと結合して複合介在物を形成することにより、ＭｎＳを無害化して切欠き引張特性の向上に寄与する元素である。上記の効果を得るためには、Ｃａを０．０００５％以上含有させる必要がある。しかしながら、Ｃａ含有量が０．００５％を超えると、Ｃａ自体が粗大な介在物となり、切欠き引張強さの低下および靭性の低下を招く。そのため、Ｃａ含有量は０．０００５～０．００５％とする。Ｃａ含有量は０．００１％以上であるのが好ましく、０．００４％以下であるのが好ましい。 Ca: 0.0005 to 0.005%
Ca is an element that contributes to the improvement of notch tensile properties by detoxifying MnS by bonding with MnS to form composite inclusions. In order to acquire said effect, it is necessary to contain 0.0005% or more of Ca. However, if the Ca content exceeds 0.005%, Ca itself becomes coarse inclusions, leading to a decrease in notch tensile strength and a decrease in toughness. Therefore, the Ca content is set to 0.0005 to 0.005%. The Ca content is preferably 0.001% or more, and preferably 0.004% or less.
Ｍｏ：０．２０～１．５％
Ｍｏは、焼入れ性を高め、鋼の強度を向上させる作用を有する。上記の効果を得るためには、Ｍｏを０．２０％以上含有させる必要がある。しかしながら、Ｍｏ含有量が１．５％を超えると、効果が飽和してコストの上昇を招く。そのため、Ｍｏ含有量は０．２０～１．５％とする。Ｍｏ含有量は０．２５％以上であるのが好ましく、０．５０％以下であるのが好ましい。 Mo: 0.20 to 1.5%
Mo has the effect | action which raises hardenability and improves the intensity | strength of steel. In order to acquire said effect, it is necessary to contain Mo 0.20% or more. However, if the Mo content exceeds 1.5%, the effect is saturated and the cost is increased. Therefore, the Mo content is 0.20 to 1.5%. The Mo content is preferably 0.25% or more, and preferably 0.50% or less.
Ｍｏは、焼入れ性を高め、鋼の強度を向上させる作用を有する。上記の効果を得るためには、Ｍｏを０．２０％以上含有させる必要がある。しかしながら、Ｍｏ含有量が１．５％を超えると、効果が飽和してコストの上昇を招く。そのため、Ｍｏ含有量は０．２０～１．５％とする。Ｍｏ含有量は０．２５％以上であるのが好ましく、０．５０％以下であるのが好ましい。 Mo: 0.20 to 1.5%
Mo has the effect | action which raises hardenability and improves the intensity | strength of steel. In order to acquire said effect, it is necessary to contain Mo 0.20% or more. However, if the Mo content exceeds 1.5%, the effect is saturated and the cost is increased. Therefore, the Mo content is 0.20 to 1.5%. The Mo content is preferably 0.25% or more, and preferably 0.50% or less.
Ｔｉ：０．０１～０．０５％
Ｔｉは、結晶粒の粗粒化を抑制し、靱性を向上させる作用を有する。また、Ｔｉは、ＭｎＳと結合して複合介在物を形成することにより、ＭｎＳを無害化して切欠き引張特性の向上に寄与する。上記の効果を得るためには、Ｔｉを０．０１％以上含有させる必要がある。しかしながら、Ｔｉ含有量が０．０５％を超えると、粗大な介在物が形成される。そのため、Ｔｉ含有量は０．０１～０．０５％とする。Ｔｉ含有量は０．０２％以上であるのが好ましく、０．０４％以下であるのが好ましい。 Ti: 0.01 to 0.05%
Ti has the effect of suppressing coarsening of crystal grains and improving toughness. Further, Ti binds to MnS to form composite inclusions, thereby detoxifying MnS and contributing to the improvement of notch tensile properties. In order to acquire said effect, it is necessary to contain Ti 0.01% or more. However, if the Ti content exceeds 0.05%, coarse inclusions are formed. Therefore, the Ti content is set to 0.01 to 0.05%. The Ti content is preferably 0.02% or more, and preferably 0.04% or less.
Ｔｉは、結晶粒の粗粒化を抑制し、靱性を向上させる作用を有する。また、Ｔｉは、ＭｎＳと結合して複合介在物を形成することにより、ＭｎＳを無害化して切欠き引張特性の向上に寄与する。上記の効果を得るためには、Ｔｉを０．０１％以上含有させる必要がある。しかしながら、Ｔｉ含有量が０．０５％を超えると、粗大な介在物が形成される。そのため、Ｔｉ含有量は０．０１～０．０５％とする。Ｔｉ含有量は０．０２％以上であるのが好ましく、０．０４％以下であるのが好ましい。 Ti: 0.01 to 0.05%
Ti has the effect of suppressing coarsening of crystal grains and improving toughness. Further, Ti binds to MnS to form composite inclusions, thereby detoxifying MnS and contributing to the improvement of notch tensile properties. In order to acquire said effect, it is necessary to contain Ti 0.01% or more. However, if the Ti content exceeds 0.05%, coarse inclusions are formed. Therefore, the Ti content is set to 0.01 to 0.05%. The Ti content is preferably 0.02% or more, and preferably 0.04% or less.
Ｂ：０．０００１～０．０１％
Ｂは、Ｍｏと複合的に含有させることで、焼入れ性を高め、鋼の強度を向上させる作用を有する。上記の効果を得るためには、Ｂを０．０００１％以上含有させる必要がある。しかしながら、Ｂ含有量が０．０１％を超えると、Ｂが析出してしまい焼入れ性向上効果が却って低減してしまう。そのため、Ｂ含有量は０．０００１～０．０１％とする。Ｂ含有量は０．０００５％以上であるのが好ましく、０．００３％以下であるのが好ましい。 B: 0.0001 to 0.01%
B is combined with Mo and thus has an effect of improving hardenability and improving the strength of steel. In order to acquire said effect, it is necessary to contain B 0.0001% or more. However, if the B content exceeds 0.01%, B precipitates and the effect of improving hardenability is reduced. Therefore, the B content is set to 0.0001 to 0.01%. The B content is preferably 0.0005% or more, and preferably 0.003% or less.
Ｂは、Ｍｏと複合的に含有させることで、焼入れ性を高め、鋼の強度を向上させる作用を有する。上記の効果を得るためには、Ｂを０．０００１％以上含有させる必要がある。しかしながら、Ｂ含有量が０．０１％を超えると、Ｂが析出してしまい焼入れ性向上効果が却って低減してしまう。そのため、Ｂ含有量は０．０００１～０．０１％とする。Ｂ含有量は０．０００５％以上であるのが好ましく、０．００３％以下であるのが好ましい。 B: 0.0001 to 0.01%
B is combined with Mo and thus has an effect of improving hardenability and improving the strength of steel. In order to acquire said effect, it is necessary to contain B 0.0001% or more. However, if the B content exceeds 0.01%, B precipitates and the effect of improving hardenability is reduced. Therefore, the B content is set to 0.0001 to 0.01%. The B content is preferably 0.0005% or more, and preferably 0.003% or less.
Ｎｉ：０～１．０％
Ｎｉは、母材の強度を向上させる効果を有するため、必要に応じて含有させてもよい。しかしながら、Ｎｉ含有量が１．０％を超えると、効果は飽和しコストの上昇を招く。そのため、Ｎｉ含有量は１．０％以下とする。Ｎｉ含有量は０．５％以下であるのが好ましい。上記の効果を得るためには、Ｎｉ含有量は０．１％以上であるのが好ましい。 Ni: 0 to 1.0%
Ni has an effect of improving the strength of the base material, and may be contained as necessary. However, if the Ni content exceeds 1.0%, the effect is saturated and the cost is increased. Therefore, the Ni content is 1.0% or less. The Ni content is preferably 0.5% or less. In order to obtain the above effect, the Ni content is preferably 0.1% or more.
Ｎｉは、母材の強度を向上させる効果を有するため、必要に応じて含有させてもよい。しかしながら、Ｎｉ含有量が１．０％を超えると、効果は飽和しコストの上昇を招く。そのため、Ｎｉ含有量は１．０％以下とする。Ｎｉ含有量は０．５％以下であるのが好ましい。上記の効果を得るためには、Ｎｉ含有量は０．１％以上であるのが好ましい。 Ni: 0 to 1.0%
Ni has an effect of improving the strength of the base material, and may be contained as necessary. However, if the Ni content exceeds 1.0%, the effect is saturated and the cost is increased. Therefore, the Ni content is 1.0% or less. The Ni content is preferably 0.5% or less. In order to obtain the above effect, the Ni content is preferably 0.1% or more.
Ｃｕ：０～１．０％
Ｃｕは、母材の強度を向上させる効果を有するため、必要に応じて含有させてもよい。しかしながら、Ｃｕ含有量が１．０％を超えると、効果は飽和しコストの上昇を招く。そのため、Ｃｕ含有量は１．０％以下とする。Ｃｕ含有量は０．５％以下であるのが好ましい。上記の効果を得るためには、Ｃｕ含有量は０．１％以上であるのが好ましい。 Cu: 0 to 1.0%
Since Cu has the effect of improving the strength of the base material, it may be contained as necessary. However, if the Cu content exceeds 1.0%, the effect is saturated and the cost is increased. Therefore, the Cu content is 1.0% or less. The Cu content is preferably 0.5% or less. In order to acquire said effect, it is preferable that Cu content is 0.1% or more.
Ｃｕは、母材の強度を向上させる効果を有するため、必要に応じて含有させてもよい。しかしながら、Ｃｕ含有量が１．０％を超えると、効果は飽和しコストの上昇を招く。そのため、Ｃｕ含有量は１．０％以下とする。Ｃｕ含有量は０．５％以下であるのが好ましい。上記の効果を得るためには、Ｃｕ含有量は０．１％以上であるのが好ましい。 Cu: 0 to 1.0%
Since Cu has the effect of improving the strength of the base material, it may be contained as necessary. However, if the Cu content exceeds 1.0%, the effect is saturated and the cost is increased. Therefore, the Cu content is 1.0% or less. The Cu content is preferably 0.5% or less. In order to acquire said effect, it is preferable that Cu content is 0.1% or more.
Ｃｒ：０～１．５％
Ｃｒは、焼入れ性を向上させる効果を有するため、必要に応じて含有させてもよい。しかしながら、Ｃｒ含有量が１．５％を超えると、効果は飽和しコストの上昇を招く。そのため、Ｃｒ含有量は１．５％以下とする。Ｃｒ含有量は１．０％以下であるのが好ましい。上記の効果を得るためには、Ｃｒ含有量は０．３％以上であるのが好ましい。 Cr: 0 to 1.5%
Since Cr has an effect of improving hardenability, it may be contained as necessary. However, if the Cr content exceeds 1.5%, the effect is saturated and the cost increases. Therefore, the Cr content is 1.5% or less. The Cr content is preferably 1.0% or less. In order to acquire said effect, it is preferable that Cr content is 0.3% or more.
Ｃｒは、焼入れ性を向上させる効果を有するため、必要に応じて含有させてもよい。しかしながら、Ｃｒ含有量が１．５％を超えると、効果は飽和しコストの上昇を招く。そのため、Ｃｒ含有量は１．５％以下とする。Ｃｒ含有量は１．０％以下であるのが好ましい。上記の効果を得るためには、Ｃｒ含有量は０．３％以上であるのが好ましい。 Cr: 0 to 1.5%
Since Cr has an effect of improving hardenability, it may be contained as necessary. However, if the Cr content exceeds 1.5%, the effect is saturated and the cost increases. Therefore, the Cr content is 1.5% or less. The Cr content is preferably 1.0% or less. In order to acquire said effect, it is preferable that Cr content is 0.3% or more.
Ｎｂ：０～０．２％
Ｎｂは、結晶粒を微細化し母材の強度を向上させる効果を有するため、必要に応じて含有させてもよい。しかしながら、Ｎｂ含有量が０．２％を超えると、効果は飽和しコストの上昇を招く。そのため、Ｎｂ含有量は０．２％以下とする。Ｎｂ含有量は０．１％以下であるのが好ましい。上記の効果を得るためには、Ｎｂ含有量は０．０２％以上であるのが好ましい。 Nb: 0 to 0.2%
Since Nb has an effect of refining crystal grains and improving the strength of the base material, it may be contained as necessary. However, when the Nb content exceeds 0.2%, the effect is saturated and the cost is increased. Therefore, the Nb content is 0.2% or less. The Nb content is preferably 0.1% or less. In order to acquire said effect, it is preferable that Nb content is 0.02% or more.
Ｎｂは、結晶粒を微細化し母材の強度を向上させる効果を有するため、必要に応じて含有させてもよい。しかしながら、Ｎｂ含有量が０．２％を超えると、効果は飽和しコストの上昇を招く。そのため、Ｎｂ含有量は０．２％以下とする。Ｎｂ含有量は０．１％以下であるのが好ましい。上記の効果を得るためには、Ｎｂ含有量は０．０２％以上であるのが好ましい。 Nb: 0 to 0.2%
Since Nb has an effect of refining crystal grains and improving the strength of the base material, it may be contained as necessary. However, when the Nb content exceeds 0.2%, the effect is saturated and the cost is increased. Therefore, the Nb content is 0.2% or less. The Nb content is preferably 0.1% or less. In order to acquire said effect, it is preferable that Nb content is 0.02% or more.
Ｖ：０～０．２％
Ｖは、母材の強度を向上させる効果を有するため、必要に応じて含有させてもよい。しかしながら、Ｖ含有量が０．２％を超えると、効果は飽和しコストの上昇を招く。そのため、Ｖ含有量は０．２％以下とする。Ｖ含有量は０．１％以下であるのが好ましい。上記の効果を得るためには、Ｖ含有量は０．０３％以上であるのが好ましい。 V: 0 to 0.2%
V has an effect of improving the strength of the base material, and may be contained as necessary. However, when the V content exceeds 0.2%, the effect is saturated and the cost is increased. Therefore, the V content is 0.2% or less. The V content is preferably 0.1% or less. In order to obtain the above effect, the V content is preferably 0.03% or more.
Ｖは、母材の強度を向上させる効果を有するため、必要に応じて含有させてもよい。しかしながら、Ｖ含有量が０．２％を超えると、効果は飽和しコストの上昇を招く。そのため、Ｖ含有量は０．２％以下とする。Ｖ含有量は０．１％以下であるのが好ましい。上記の効果を得るためには、Ｖ含有量は０．０３％以上であるのが好ましい。 V: 0 to 0.2%
V has an effect of improving the strength of the base material, and may be contained as necessary. However, when the V content exceeds 0.2%, the effect is saturated and the cost is increased. Therefore, the V content is 0.2% or less. The V content is preferably 0.1% or less. In order to obtain the above effect, the V content is preferably 0.03% or more.
Ｍｇ：０～０．０２％
ＲＥＭ：０～０．０２％
ＭｇおよびＲＥＭは、いずれも溶鋼中で酸化物を形成し、脱酸作用により鋼の清浄度を向上させる作用を有し、切欠き引張特性改善に寄与する。また、炭窒化物の形成核として作用するため、適切に微細分散化すると、粗大な炭窒化物の形成を抑制する作用も有する。したがって、必要に応じてこれらの元素の１種または２種以上を含有させてもよい。 Mg: 0 to 0.02%
REM: 0 to 0.02%
Mg and REM both form oxides in the molten steel, have the effect of improving the cleanliness of the steel by deoxidation, and contribute to the improvement of notch tensile properties. Further, since it functions as a carbonitride formation nucleus, it has an effect of suppressing the formation of coarse carbonitride when appropriately finely dispersed. Therefore, you may contain 1 type, or 2 or more types of these elements as needed.
ＲＥＭ：０～０．０２％
ＭｇおよびＲＥＭは、いずれも溶鋼中で酸化物を形成し、脱酸作用により鋼の清浄度を向上させる作用を有し、切欠き引張特性改善に寄与する。また、炭窒化物の形成核として作用するため、適切に微細分散化すると、粗大な炭窒化物の形成を抑制する作用も有する。したがって、必要に応じてこれらの元素の１種または２種以上を含有させてもよい。 Mg: 0 to 0.02%
REM: 0 to 0.02%
Mg and REM both form oxides in the molten steel, have the effect of improving the cleanliness of the steel by deoxidation, and contribute to the improvement of notch tensile properties. Further, since it functions as a carbonitride formation nucleus, it has an effect of suppressing the formation of coarse carbonitride when appropriately finely dispersed. Therefore, you may contain 1 type, or 2 or more types of these elements as needed.
しかし、いずれの元素も０.０２％を超えて含有させると、粗大な酸化物を形成し、却って鋼の清浄度を低下させ、切欠き引張強さが低下する。したがって、各元素の含有量は上記のとおりとする。各元素の含有量は、いずれも０.０１％以下とすることが好ましく、０.００５０％以下とすることがより好ましい。上記の効果を得るためには、Ｍｇ：０．０００１％およびＲＥＭ：０．００１％以上から選択される１種以上を含有させることが好ましい。
However, if any element exceeds 0.02%, a coarse oxide is formed, and on the contrary, the cleanliness of the steel is lowered and the notch tensile strength is lowered. Accordingly, the content of each element is as described above. The content of each element is preferably 0.01% or less, and more preferably 0.0050% or less. In order to acquire said effect, it is preferable to contain 1 or more types selected from Mg: 0.0001% and REM: 0.001% or more.
ここで、ＲＥＭは、Ｓｃ、Ｙおよびランタノイドの合計１７元素を指し、上記ＲＥＭの含有量は、これらの元素の合計含有量を指す。ランタノイドの場合、工業的にはミッシュメタルの形で添加される。
Here, REM refers to a total of 17 elements of Sc, Y, and lanthanoid, and the content of REM refers to the total content of these elements. In the case of a lanthanoid, it is industrially added in the form of misch metal.
本発明に係る鋼管の化学組成において、残部はＦｅおよび不純物である。ここで「不純物」とは、鋼を工業的に製造する際に、鉱石、スクラップ等の原料、製造工程の種々の要因によって混入する成分であって、本発明に悪影響を与えない範囲で許容されるものを意味する。
In the chemical composition of the steel pipe according to the present invention, the balance is Fe and impurities. Here, “impurities” are components that are mixed due to various factors of raw materials such as ores and scraps and manufacturing processes when steel is industrially manufactured, and are allowed within a range that does not adversely affect the present invention. Means something.
５．０≦（０．００１＋Ｃａ）×Ａｌ×Ｔｉ／（Ｍｎ×Ｓ）×１０４≦６０．０ ・・・（ｉ）
但し、上記式中の各元素記号は鋼中に含まれる各元素の含有量を表す。
鋼の切欠き引張特性を向上させるためには、鋼中に析出するＭｎＳの量を低減するとともに、析出したＭｎＳを無害化する必要がある。そのため、ＭｎＳの析出量を低減する観点からＭｎおよびＳの含有量を低くする必要がある。また、上述のように、Ｃａ、ＡｌおよびＴｉはＭｎＳと結合して複合介在物を形成することにより、ＭｎＳを無害化する効果を有する。 5.0 ≦ (0.001 + Ca) × Al × Ti / (Mn × S) × 10 4 ≦ 60.0 (i)
However, each element symbol in the above formula represents the content of each element contained in the steel.
In order to improve the notch tensile properties of steel, it is necessary to reduce the amount of MnS precipitated in the steel and to render the precipitated MnS harmless. Therefore, it is necessary to reduce the contents of Mn and S from the viewpoint of reducing the amount of MnS deposited. Further, as described above, Ca, Al, and Ti have the effect of detoxifying MnS by combining with MnS to form composite inclusions.
但し、上記式中の各元素記号は鋼中に含まれる各元素の含有量を表す。
鋼の切欠き引張特性を向上させるためには、鋼中に析出するＭｎＳの量を低減するとともに、析出したＭｎＳを無害化する必要がある。そのため、ＭｎＳの析出量を低減する観点からＭｎおよびＳの含有量を低くする必要がある。また、上述のように、Ｃａ、ＡｌおよびＴｉはＭｎＳと結合して複合介在物を形成することにより、ＭｎＳを無害化する効果を有する。 5.0 ≦ (0.001 + Ca) × Al × Ti / (Mn × S) × 10 4 ≦ 60.0 (i)
However, each element symbol in the above formula represents the content of each element contained in the steel.
In order to improve the notch tensile properties of steel, it is necessary to reduce the amount of MnS precipitated in the steel and to render the precipitated MnS harmless. Therefore, it is necessary to reduce the contents of Mn and S from the viewpoint of reducing the amount of MnS deposited. Further, as described above, Ca, Al, and Ti have the effect of detoxifying MnS by combining with MnS to form composite inclusions.
そのため、Ｃａ、Ａｌ、Ｔｉ、ＭｎおよびＳの含有量は、上記（ｉ）式中辺値が５．０以上になるよう制御する必要がある。一方、ＭｎＳの析出量に比べて、Ｃａ、ＡｌおよびＴｉの含有量が過剰になり、上記（ｉ）式中辺値が６０．０を超えると、これらの元素自体が酸素または窒素と結びつき粗大な介在物を形成し、切欠き引張強さの低下を招く。したがって、本発明においては、上記（ｉ）式を満足する必要がある。上記（ｉ）式中辺値は、４５．０以下であるのが好ましく、３０．０以下であるのがより好ましい。
Therefore, it is necessary to control the contents of Ca, Al, Ti, Mn, and S so that the side value in the formula (i) is 5.0 or more. On the other hand, when the content of Ca, Al, and Ti becomes excessive compared to the amount of MnS deposited and the median value of the above formula (i) exceeds 60.0, these elements themselves are combined with oxygen or nitrogen and are coarse. Forming the inclusions, leading to a decrease in the notch tensile strength. Therefore, in the present invention, it is necessary to satisfy the above formula (i). The side value in the formula (i) is preferably 45.0 or less, and more preferably 30.0 or less.
２．０≦３×Ｓｉ×Ｍｏ×Ｂ×１０４ ・・・（ii）
但し、上記式中の各元素記号は鋼中に含まれる各元素の含有量を表す。
Ｓｉ、ＭｏおよびＢは、焼入れ性を高める元素である。そのため、鋼の強度を高め、切欠き引張特性を向上させるためには、各元素が上述の範囲を満足することに加えて、上記（ii）式を満足する必要がある。上記（ii）式右辺値に上限を定める必要はないが、実質的には４５０が上限となる。なお、焼入れ性向上の観点からは高ければ高い方が好ましいが、製造コストを重視する場合には、上記（ii）式右辺値は、７５．０以下であるのが好ましく、５０．０以下であるのがより好ましい。 2.0 ≦ 3 × Si × Mo × B × 10 4 (ii)
However, each element symbol in the above formula represents the content of each element contained in the steel.
Si, Mo, and B are elements that enhance hardenability. Therefore, in order to increase the strength of the steel and improve the notch tensile properties, each element must satisfy the above formula (ii) in addition to satisfying the above range. Although it is not necessary to set an upper limit to the right side value of the above equation (ii), 450 is practically the upper limit. In addition, from the viewpoint of improving hardenability, a higher value is preferable. However, in the case where manufacturing cost is important, the right side value of the formula (ii) is preferably 75.0 or less, and is preferably 50.0 or less. More preferably.
但し、上記式中の各元素記号は鋼中に含まれる各元素の含有量を表す。
Ｓｉ、ＭｏおよびＢは、焼入れ性を高める元素である。そのため、鋼の強度を高め、切欠き引張特性を向上させるためには、各元素が上述の範囲を満足することに加えて、上記（ii）式を満足する必要がある。上記（ii）式右辺値に上限を定める必要はないが、実質的には４５０が上限となる。なお、焼入れ性向上の観点からは高ければ高い方が好ましいが、製造コストを重視する場合には、上記（ii）式右辺値は、７５．０以下であるのが好ましく、５０．０以下であるのがより好ましい。 2.0 ≦ 3 × Si × Mo × B × 10 4 (ii)
However, each element symbol in the above formula represents the content of each element contained in the steel.
Si, Mo, and B are elements that enhance hardenability. Therefore, in order to increase the strength of the steel and improve the notch tensile properties, each element must satisfy the above formula (ii) in addition to satisfying the above range. Although it is not necessary to set an upper limit to the right side value of the above equation (ii), 450 is practically the upper limit. In addition, from the viewpoint of improving hardenability, a higher value is preferable. However, in the case where manufacturing cost is important, the right side value of the formula (ii) is preferably 75.0 or less, and is preferably 50.0 or less. More preferably.
（Ｂ）金属組織
本発明に係る鋼管は、セメンタイトの面積率が５～７０％であり、かつ、セメンタイトの球状化率が７０％以上である金属組織を有する。セメンタイトの面積率が５％未満では、十分な切欠き引張強さが得られない場合がある。一方、セメンタイトの面積率が７０％を超えると、後述するようにセメンタイトを球状化しても硬く、加工性が劣化する。 (B) Metal Structure The steel pipe according to the present invention has a metal structure in which the cementite area ratio is 5 to 70% and the cementite spheroidization ratio is 70% or more. If the area ratio of cementite is less than 5%, sufficient notch tensile strength may not be obtained. On the other hand, when the area ratio of cementite exceeds 70%, as will be described later, even if cementite is spheroidized, it is hard and processability deteriorates.
本発明に係る鋼管は、セメンタイトの面積率が５～７０％であり、かつ、セメンタイトの球状化率が７０％以上である金属組織を有する。セメンタイトの面積率が５％未満では、十分な切欠き引張強さが得られない場合がある。一方、セメンタイトの面積率が７０％を超えると、後述するようにセメンタイトを球状化しても硬く、加工性が劣化する。 (B) Metal Structure The steel pipe according to the present invention has a metal structure in which the cementite area ratio is 5 to 70% and the cementite spheroidization ratio is 70% or more. If the area ratio of cementite is less than 5%, sufficient notch tensile strength may not be obtained. On the other hand, when the area ratio of cementite exceeds 70%, as will be described later, even if cementite is spheroidized, it is hard and processability deteriorates.
セメンタイトの面積率は１０％以上であるのが好ましく、１５％以上であるのがより好ましい。また、セメンタイトの面積率は６５％以下であるのが好ましく、６０％以下であるのがより好ましい。なお、上記金属組織において、残部はフェライトであることが好ましい。
The area ratio of cementite is preferably 10% or more, and more preferably 15% or more. Moreover, the area ratio of cementite is preferably 65% or less, and more preferably 60% or less. In the above metal structure, the balance is preferably ferrite.
また、変形能に有害な層状のセメンタイトの割合を低減し、セメンタイトの球状化率を７０％以上にすることによって、優れた冷間加工性が得られるようになる。セメンタイトの球状化率は７５％以上であるのが好ましい。
Further, by reducing the ratio of layered cementite harmful to the deformability and making the cementite spheroidization ratio 70% or more, excellent cold workability can be obtained. The spheroidization rate of cementite is preferably 75% or more.
なお、本発明において「セメンタイトの球状化率」とは、金属組織中に含まれるセメンタイト粒子のうち、アスペクト比が３．０以下であるものを球状化セメンタイトとした時に、全セメンタイトの総面積に対する、球状化セメンタイトの総面積の割合を意味する。
In the present invention, the “spheroidization rate of cementite” refers to the total area of all cementite when cementite particles having an aspect ratio of 3.0 or less are used as spheroidized cementite. , Means the ratio of the total area of spheroidized cementite.
具体的には、セメンタイトの面積率および球状化率は、それぞれ以下の方法により算出する。まず、鋼管試料から、鋼管の長手方向に垂直な断面の肉厚１／４位置が観察面となるように、組織観察用の試験片を切り出す。続いて、上記の観察面を鏡面研磨した後、ナイタール腐食して金属組織を現出させる。その後、光学顕微鏡を用いて、５００倍の倍率で観察面を観察することによって、セメンタイトの面積率を求める。
Specifically, the area ratio and spheroidization ratio of cementite are calculated by the following methods, respectively. First, a specimen for observing the structure is cut out from the steel pipe sample so that the position of the thickness 1/4 of the cross section perpendicular to the longitudinal direction of the steel pipe becomes the observation surface. Subsequently, after the above observation surface is mirror-polished, it undergoes nital corrosion to reveal a metal structure. Then, the area ratio of cementite is calculated | required by observing an observation surface with 500-times multiplication factor using an optical microscope.
同様にして、走査電子顕微鏡（ＳＥＭ）を用いて２０００倍の倍率で観察面を観察することによって、全セメンタイトの面積率を求める。さらに同じ視野において、アスペクト比が３．０以下である球状化セメンタイトの面積率を求める。なお、アスペクト比は、セメンタイトを画像解析により楕円近似し、長軸長さを短軸長さで割ることによって求めるものとする。そして、球状化セメンタイトの面積率を同じ視野において求めた全セメンタイトの面積率で割ることによって、セメンタイトの球状化率を算出する。
Similarly, the area ratio of all cementite is obtained by observing the observation surface at a magnification of 2000 using a scanning electron microscope (SEM). Further, in the same field of view, the area ratio of spheroidized cementite having an aspect ratio of 3.0 or less is obtained. The aspect ratio is obtained by elliptically approximating cementite by image analysis and dividing the major axis length by the minor axis length. Then, the spheroidizing ratio of the cementite is calculated by dividing the area ratio of the spheroidized cementite by the area ratio of all the cementites obtained in the same field of view.
（Ｃ）鋼管の製造方法
本発明に係る鋼管には、例えば、継目無鋼管および電縫鋼管が含まれる。それらの製造条件について特に制限はない。 (C) Steel pipe manufacturing method The steel pipe according to the present invention includes, for example, a seamless steel pipe and an electric resistance steel pipe. There are no particular restrictions on the production conditions.
本発明に係る鋼管には、例えば、継目無鋼管および電縫鋼管が含まれる。それらの製造条件について特に制限はない。 (C) Steel pipe manufacturing method The steel pipe according to the present invention includes, for example, a seamless steel pipe and an electric resistance steel pipe. There are no particular restrictions on the production conditions.
継目無鋼管は、例えば、以下に示す方法により、製造することができる。
The seamless steel pipe can be manufactured, for example, by the following method.
＜溶解および鋳造＞
溶解および鋳造については一般的な鋼管の製造方法で行われる方法を用いることができ、鋳造はインゴット鋳造でも連続鋳造でもよい。また、ラウンドＣＣにより、製管用ラウンドビレットの形状に鋳造してもよい。 <Melting and casting>
For melting and casting, a method performed by a general steel pipe manufacturing method can be used, and the casting may be ingot casting or continuous casting. Moreover, you may cast in the shape of the round billet for pipe making by round CC.
溶解および鋳造については一般的な鋼管の製造方法で行われる方法を用いることができ、鋳造はインゴット鋳造でも連続鋳造でもよい。また、ラウンドＣＣにより、製管用ラウンドビレットの形状に鋳造してもよい。 <Melting and casting>
For melting and casting, a method performed by a general steel pipe manufacturing method can be used, and the casting may be ingot casting or continuous casting. Moreover, you may cast in the shape of the round billet for pipe making by round CC.
＜熱間加工（鍛造、穿孔、圧延）＞
鋳造後は、鍛造、穿孔、圧延等の熱間加工が施される。なお、上述のラウンドＣＣによって円形ビレットを鋳造した場合、円形ビレットに成形するための鍛造、分塊圧延等の工程は必要ない。上記の穿孔工程の後、マンドレルミルまたはプラグミルを使用して圧延が行われる。穿孔、圧延等の熱間加工の望ましい条件は、以下のとおりである。 <Hot processing (forging, drilling, rolling)>
After casting, hot working such as forging, drilling and rolling is performed. In addition, when a circular billet is cast by the above-described round CC, processes such as forging and partial rolling for forming the circular billet are not necessary. After the above piercing step, rolling is performed using a mandrel mill or a plug mill. Desirable conditions for hot working such as piercing and rolling are as follows.
鋳造後は、鍛造、穿孔、圧延等の熱間加工が施される。なお、上述のラウンドＣＣによって円形ビレットを鋳造した場合、円形ビレットに成形するための鍛造、分塊圧延等の工程は必要ない。上記の穿孔工程の後、マンドレルミルまたはプラグミルを使用して圧延が行われる。穿孔、圧延等の熱間加工の望ましい条件は、以下のとおりである。 <Hot processing (forging, drilling, rolling)>
After casting, hot working such as forging, drilling and rolling is performed. In addition, when a circular billet is cast by the above-described round CC, processes such as forging and partial rolling for forming the circular billet are not necessary. After the above piercing step, rolling is performed using a mandrel mill or a plug mill. Desirable conditions for hot working such as piercing and rolling are as follows.
ビレットの加熱は、穿孔圧延機での熱間穿孔が可能な程度に行えばよいが、望ましい温度範囲は１０００～１２５０℃である。穿孔圧延およびマンドレルミル、プラグミル等のその他の圧延機による圧延に関しても特別の制約はないが、熱間加工性の上から、具体的には表面疵の防止のために、仕上げ温度を９００℃以上とするのが望ましい。仕上げ温度の上限にも特に制約はないが、１１００℃までに留めるのがよい。
The billet may be heated to such an extent that hot piercing with a piercing and rolling mill is possible, but a desirable temperature range is 1000 to 1250 ° C. There are no particular restrictions on piercing rolling and rolling by other rolling mills such as mandrel mills, plug mills, etc. However, in terms of hot workability, in order to prevent surface flaws, the finishing temperature should be 900 ° C or higher. Is desirable. Although there is no restriction | limiting in particular also in the upper limit of finishing temperature, it is good to keep it to 1100 degreeC.
また、電縫鋼管は、例えば、以下に示す方法により、製造することができる。
Moreover, the electric resistance welded steel pipe can be manufactured, for example, by the following method.
＜溶解および鋳造＞
溶解および鋳造については一般的な鋼板の製造方法で行われる方法を用いることができ、例えば、連続鋳造によりスラブとする。 <Melting and casting>
For melting and casting, a method performed by a general steel plate manufacturing method can be used. For example, a slab is formed by continuous casting.
溶解および鋳造については一般的な鋼板の製造方法で行われる方法を用いることができ、例えば、連続鋳造によりスラブとする。 <Melting and casting>
For melting and casting, a method performed by a general steel plate manufacturing method can be used. For example, a slab is formed by continuous casting.
＜熱間圧延および冷間圧延＞
得られたスラブを熱間圧延し、さらに必要に応じて冷間圧延することにより、所定の厚さの鋼板を製造する。圧延後の鋼板は、コイル状に巻き取ってもよい。 <Hot rolling and cold rolling>
The obtained slab is hot-rolled, and further cold-rolled as necessary to produce a steel plate having a predetermined thickness. The rolled steel sheet may be wound in a coil shape.
得られたスラブを熱間圧延し、さらに必要に応じて冷間圧延することにより、所定の厚さの鋼板を製造する。圧延後の鋼板は、コイル状に巻き取ってもよい。 <Hot rolling and cold rolling>
The obtained slab is hot-rolled, and further cold-rolled as necessary to produce a steel plate having a predetermined thickness. The rolled steel sheet may be wound in a coil shape.
＜製管＞
得られた鋼板に対して、ロール成形し、高周波溶接することにより、電縫鋼管を製造する。溶接部に対して、必要に応じて熱処理を施してもよい。 <Pipe making>
The obtained steel sheet is roll-formed and subjected to high-frequency welding to produce an electric resistance welded steel pipe. You may heat-process with respect to a welding part as needed.
得られた鋼板に対して、ロール成形し、高周波溶接することにより、電縫鋼管を製造する。溶接部に対して、必要に応じて熱処理を施してもよい。 <Pipe making>
The obtained steel sheet is roll-formed and subjected to high-frequency welding to produce an electric resistance welded steel pipe. You may heat-process with respect to a welding part as needed.
以上の方法により、継目無鋼管または電縫鋼管を製造することができる。
By the above method, seamless steel pipes or ERW steel pipes can be manufactured.
＜冷間加工＞
上記の方法によって得られた鋼管には、必要に応じて寸法精度の向上を目的として、冷間加工を施してもよい。冷間加工方法としては、鋼管を均一に加工できる方法であれば、特に制限されなく、例えば、孔明きダイスとプラグとを用いるいわゆる冷間抽伸機またはコールドピルガーミルと称される冷間圧延機等を用いるのが工業的に有利である。 <Cold processing>
The steel pipe obtained by the above method may be cold worked for the purpose of improving the dimensional accuracy as necessary. The cold working method is not particularly limited as long as it can uniformly process a steel pipe, for example, cold rolling called a so-called cold drawing machine or cold pilger mill using a perforated die and a plug. It is industrially advantageous to use a machine.
上記の方法によって得られた鋼管には、必要に応じて寸法精度の向上を目的として、冷間加工を施してもよい。冷間加工方法としては、鋼管を均一に加工できる方法であれば、特に制限されなく、例えば、孔明きダイスとプラグとを用いるいわゆる冷間抽伸機またはコールドピルガーミルと称される冷間圧延機等を用いるのが工業的に有利である。 <Cold processing>
The steel pipe obtained by the above method may be cold worked for the purpose of improving the dimensional accuracy as necessary. The cold working method is not particularly limited as long as it can uniformly process a steel pipe, for example, cold rolling called a so-called cold drawing machine or cold pilger mill using a perforated die and a plug. It is industrially advantageous to use a machine.
＜球状化焼鈍＞
その後、鋼管に対して、セメンタイトの球状化を目的として、例えば、以下の条件により球状化焼鈍を施す。 <Spheroidizing annealing>
Thereafter, for the purpose of spheroidizing cementite, spheroidizing annealing is performed on the steel pipe under the following conditions, for example.
その後、鋼管に対して、セメンタイトの球状化を目的として、例えば、以下の条件により球状化焼鈍を施す。 <Spheroidizing annealing>
Thereafter, for the purpose of spheroidizing cementite, spheroidizing annealing is performed on the steel pipe under the following conditions, for example.
鋼管をＡｃ１点～Ａｃ１点＋２０℃の温度範囲まで加熱して３０ｍｉｎ以下保持した後、１℃／ｓ以下の平均冷却速度で徐冷する。上記温度範囲まで加熱することにより、層状のセメンタイトの一部を再固溶させることで分断し、球状化することが可能となる。
The steel pipe is heated to a temperature range of Ac 1 point to Ac 1 point + 20 ° C. and held for 30 minutes or less, and then slowly cooled at an average cooling rate of 1 ° C./s or less. By heating to the above temperature range, a part of the layered cementite is re-dissolved to be divided and spheroidized.
加熱温度がＡｃ１点未満では、セメンタイトの球状化が不十分となり、冷間加工性の向上効果が得られにくくなる。一方、加熱温度がＡｃ１点＋２０℃を超えるか、または加熱時間が３０ｍｉｎを超えると、セメンタイトを全て再固溶してしまうおそれがあるだけでなく、オーステナイトの生成量が過剰となるおそれがある。生成したオーステナイトは、その後の冷却によりフェライト＋パーライトに変態し、冷間加工性を劣化させる。
When the heating temperature is less than 1 Ac, the spheroidization of cementite becomes insufficient, and it becomes difficult to obtain the effect of improving the cold workability. On the other hand, when the heating temperature exceeds Ac 1 point + 20 ° C. or the heating time exceeds 30 min, not only may there be a re-dissolution of the cementite, but the austenite generation amount may be excessive. . The generated austenite is transformed into ferrite + pearlite by subsequent cooling, and the cold workability is deteriorated.
さらに、加熱後の平均冷却速度を１℃／ｓ以下にすることによって、球状化したセメンタイトが成長する。平均冷却速度が１℃／ｓを超える場合には、再固溶したセメンタイトの一部が層状に析出し、パーライト組織となるおそれがある。
Furthermore, spheroidized cementite grows by setting the average cooling rate after heating to 1 ° C./s or less. When the average cooling rate exceeds 1 ° C./s, a part of the re-dissolved cementite may be deposited in a layer shape to form a pearlite structure.
以上の方法によって製造された鋼管は、上述した金属組織を有するため、冷間加工性に優れる。
Since the steel pipe manufactured by the above method has the above-described metal structure, it is excellent in cold workability.
（Ｄ）自動車足回り部品の製造方法
本発明に係る鋼管に対して、冷間加工を施し所定形状に成形した後、例えば、以下に示す条件で焼入れおよび焼戻しの処理を施すことにより、切欠き引張特性に優れた自動車足回り部品を製造することができる。 (D) Manufacturing method of automobile underbody parts After the steel pipe according to the present invention is cold-worked and formed into a predetermined shape, for example, by performing quenching and tempering treatment under the conditions shown below, An automobile undercarriage component having excellent tensile properties can be manufactured.
本発明に係る鋼管に対して、冷間加工を施し所定形状に成形した後、例えば、以下に示す条件で焼入れおよび焼戻しの処理を施すことにより、切欠き引張特性に優れた自動車足回り部品を製造することができる。 (D) Manufacturing method of automobile underbody parts After the steel pipe according to the present invention is cold-worked and formed into a predetermined shape, for example, by performing quenching and tempering treatment under the conditions shown below, An automobile undercarriage component having excellent tensile properties can be manufactured.
＜焼入れ処理＞
焼入れ時の加熱温度については特に制限は設けないが、Ａｃ３点＋５０℃以上の温度とするのが望ましい。また、加熱時間についても特に制限は設けないが、均熱時間を５ｍｉｎ以上とするのが望ましい。 <Hardening treatment>
The heating temperature at the time of quenching is not particularly limited, but it is desirable to set the temperature to Ac 3 points + 50 ° C. or higher. Also, the heating time is not particularly limited, but it is desirable that the soaking time is 5 minutes or more.
焼入れ時の加熱温度については特に制限は設けないが、Ａｃ３点＋５０℃以上の温度とするのが望ましい。また、加熱時間についても特に制限は設けないが、均熱時間を５ｍｉｎ以上とするのが望ましい。 <Hardening treatment>
The heating temperature at the time of quenching is not particularly limited, but it is desirable to set the temperature to Ac 3 points + 50 ° C. or higher. Also, the heating time is not particularly limited, but it is desirable that the soaking time is 5 minutes or more.
焼入れ時の冷却速度については、肉厚中央部における平均冷却速度が１０℃／ｓ未満であると十分な強度が得られなくなるため、１０℃／ｓ以上の加速冷却を行うのが望ましい。また、冷却方法について、加速冷却を行う方法であれば特に制限はないが、部品の形状によって冷却後に焼き割れを起こす場合には、冷却速度を緩めるために油冷を行うのが好ましい。
Regarding the cooling rate during quenching, if the average cooling rate at the central portion of the wall thickness is less than 10 ° C./s, sufficient strength cannot be obtained. Further, the cooling method is not particularly limited as long as it is a method of performing accelerated cooling, but when cooling cracks occur after cooling depending on the shape of the component, it is preferable to perform oil cooling in order to reduce the cooling rate.
＜焼戻し処理＞
焼入れ処理後には、脱水素を目的として、低温焼戻し処理を行うのが望ましい。焼戻し温度については特に制限は設けないが、１５０～３００℃とするのが望ましい。 <Tempering treatment>
After the quenching treatment, it is desirable to perform a low temperature tempering treatment for the purpose of dehydrogenation. The tempering temperature is not particularly limited, but is preferably 150 to 300 ° C.
焼入れ処理後には、脱水素を目的として、低温焼戻し処理を行うのが望ましい。焼戻し温度については特に制限は設けないが、１５０～３００℃とするのが望ましい。 <Tempering treatment>
After the quenching treatment, it is desirable to perform a low temperature tempering treatment for the purpose of dehydrogenation. The tempering temperature is not particularly limited, but is preferably 150 to 300 ° C.
以下、実施例によって本発明をより具体的に説明するが、本発明はこれらの実施例に限定されるものではない。
Hereinafter, the present invention will be described more specifically by way of examples. However, the present invention is not limited to these examples.
表１に示す化学組成を有する鋼を真空炉で溶製した後、熱間鍛造、熱間圧延および冷間圧延を行って厚さが１６ｍｍの板材を作製した。その後、上記の板材に対して、表２に示す条件で球状化焼鈍を施し、試験材を得た。なお、本実施例においては、板状の試料を用いているが、本発明において評価する特性は形状には影響を受けないため、管状にした場合でも同様の効果が得られる。
After melting the steel having the chemical composition shown in Table 1 in a vacuum furnace, hot forging, hot rolling and cold rolling were performed to produce a plate material having a thickness of 16 mm. Thereafter, the plate material was subjected to spheroidizing annealing under the conditions shown in Table 2 to obtain a test material. In this embodiment, a plate-like sample is used. However, since the characteristics evaluated in the present invention are not affected by the shape, the same effect can be obtained even in the case of a tubular shape.
次に、得られた試験材から、圧延方向に垂直な断面の肉厚１／４位置が観察面となるように、組織観察用の試験片を切り出した。続いて、上記の観察面を鏡面研磨した後、ナイタール腐食して金属組織を現出させた。その後、光学顕微鏡を用いて、５００倍の倍率で観察面を観察することによって、セメンタイトの面積率を求めた。
Next, a specimen for observing the structure was cut out from the obtained test material so that the position of the thickness 1/4 of the cross section perpendicular to the rolling direction was the observation surface. Subsequently, the above observation surface was mirror-polished and then subjected to nital corrosion to reveal a metal structure. Then, the area ratio of cementite was calculated | required by observing an observation surface with 500-times multiplication factor using an optical microscope.
また、ＳＥＭを用いて２０００倍の倍率で観察面を観察することによって、全セメンタイトの面積率を求めた。さらに同じ視野において、アスペクト比が３．０以下である球状化セメンタイトの面積率を求めた。そして、球状化セメンタイトの面積率を同じ視野において求めた全セメンタイトの面積率で割ることによって、セメンタイトの球状化率を算出した。
Also, the area ratio of all cementite was determined by observing the observation surface at a magnification of 2000 times using SEM. Furthermore, in the same visual field, the area ratio of spheroidized cementite having an aspect ratio of 3.0 or less was determined. Then, the spheroidization rate of cementite was calculated by dividing the area ratio of spheroidized cementite by the area ratio of all cementite obtained in the same field of view.
続いて、冷間加工性の評価のために、各試験材の硬さの測定を行った。具体的には、上記の組織観察用の試験片を用い、肉厚１／４位置において、ビッカース硬さの測定を行った。硬さ測定における試験力は、９．８Ｎとした。本発明においては、硬さが２４０ＨＶ以下である場合に、冷間加工性に優れると判断することとした。
Subsequently, the hardness of each test material was measured for evaluation of cold workability. Specifically, the Vickers hardness was measured at the 1/4 thickness position using the above-mentioned specimen for observing the structure. The test force in the hardness measurement was 9.8N. In the present invention, when the hardness is 240 HV or less, it is determined that the cold workability is excellent.
その後、上記試験材を９２０℃で３０分保持した後、水冷する焼入れ処理を行い、続いて、２００℃で２時間保持する焼戻し処理を行った。
Then, after holding the said test material at 920 degreeC for 30 minutes, the quenching process which water-cools was performed, and the tempering process hold | maintained at 200 degreeC for 2 hours was then performed.
そして、焼戻し処理後の各試験材から、図１に示す形状を有する切欠き付き引張試験片を切り出し、当該試験片を用いて引張試験を行った。なお、図１中に示す寸法の単位はｍｍである。そして、上記引張試験によって得られた最大荷重を、切欠き部の断面積で除することで切欠き引張強さを求めた。なお、本発明においては、切欠き引張強さの値が１４４０ＭＰａ以上となる場合に、切欠き引張特性に優れるものとする。
Then, a notched tensile test piece having the shape shown in FIG. 1 was cut out from each test material after the tempering treatment, and a tensile test was performed using the test piece. In addition, the unit of the dimension shown in FIG. 1 is mm. And the notch tensile strength was calculated | required by remove | dividing the maximum load obtained by the said tension test by the cross-sectional area of a notch part. In addition, in this invention, when the value of notch tensile strength becomes 1440 Mpa or more, it shall be excellent in a notch tensile characteristic.
それらの結果を表２に併せて示す。
The results are also shown in Table 2.
試験Ｎｏ．１～１０は、本発明の規定を全て満足する本発明例である。表１から分かるように、硬さが２４０ＨＶ以下であり、冷間加工性に優れるとともに、焼入れおよび焼戻し処理後には、１４７０ＭＰａ以上の切欠き引張強さを示し、切欠き引張特性に優れる結果となった。
Test No. Reference numerals 1 to 10 are examples of the present invention that satisfy all the provisions of the present invention. As can be seen from Table 1, the hardness is 240 HV or less, excellent cold workability, and after quenching and tempering treatment, show notch tensile strength of 1470 MPa or more, resulting in excellent notch tensile properties. It was.
これらに対して、比較例である試験Ｎｏ．１１および１２は、化学組成は本発明の規定を満足しているものの、球状化焼鈍条件が不適切であったため、セメンタイトの球状化率が低くなり、冷間加工性が劣化する結果となった。
In contrast, test No. which is a comparative example. 11 and 12, although the chemical composition satisfied the provisions of the present invention, the spheroidizing annealing conditions were inadequate, so the spheroidizing rate of cementite was lowered and the cold workability was deteriorated. .
また、試験Ｎｏ．１３～２０は、全て切欠き引張強さが１４４０ＭＰａ未満となった。具体的には、試験Ｎｏ．１３は、Ｃ含有量が規定範囲より低いため、必要な強度が得られなかった。試験Ｎｏ．１４はＳｉ含有量が低く、また試験Ｎｏ．１８はＭｏ含有量が低く、双方とも（ii）式を満足しなかったため、焼入れ性が不十分となり必要な強度が得られなかった。同様に、試験Ｎｏ．２０は各元素の含有量は規定を満足するものの、（ii）式を満足しなかったため、焼入れ性が不十分となり必要な強度が得られなかった。
Also, test no. In all of Nos. 13 to 20, the notch tensile strength was less than 1440 MPa. Specifically, Test No. In No. 13, since the C content was lower than the specified range, the required strength could not be obtained. Test No. No. 14 has a low Si content. No. 18 had a low Mo content, and both did not satisfy the formula (ii), so the hardenability was insufficient and the required strength could not be obtained. Similarly, test no. In No. 20, the content of each element satisfied the regulation, but did not satisfy the formula (ii), so the hardenability was insufficient and the required strength could not be obtained.
さらに、試験Ｎｏ．１５はＭｎ含有量が高く、試験Ｎｏ．１６はＳ含有量が高く、双方とも（ｉ）式中辺値が下限値未満となったため、切欠き引張特性が劣る結果となった。同様に、試験Ｎｏ．１９は各元素の含有量は規定を満足するものの、（ｉ）式中辺値が下限値未満となったため、切欠き引張特性が劣る結果となった。そして、試験Ｎｏ．１７は、Ｃａ含有量が過剰であり、（ｉ）式中辺値が上限値を超えたため、ＣａＯの粗大な介在物が形成し、切欠き引張特性が劣る結果となった。
Furthermore, test no. No. 15 has a high Mn content. No. 16 had a high S content, and in both cases, the median value in the formula (i) was less than the lower limit value, resulting in inferior notch tensile properties. Similarly, test no. No. 19, although the content of each element satisfied the regulation, the notch tensile property was inferior because the median value in the formula (i) was less than the lower limit. And test no. In No. 17, since the Ca content was excessive and the median value in the formula (i) exceeded the upper limit value, coarse inclusions of CaO were formed, resulting in inferior notch tensile properties.
本発明によれば、冷間加工性に優れる鋼管を得ることが可能になる。また、本発明に係る鋼管を用いて製造した部品は、高い切欠き引張強さを有する。したがって、上記鋼管は、自動車足回り部品用として好適である。
According to the present invention, a steel pipe excellent in cold workability can be obtained. Moreover, the part manufactured using the steel pipe which concerns on this invention has high notch tensile strength. Therefore, the steel pipe is suitable for automobile undercarriage parts.
Claims (5)
- 質量％で、
Ｃ：０．１０～０．６０％、
Ｓｉ：０．２５～１．０％、
Ｍｎ：０．０５～２．０％、
Ｐ：０．１％以下、
Ｓ：０．０３％以下、
Ａｌ：０．００５～０．１％、
Ｎ：０．０１％以下、
Ｏ：０．０１％以下、
Ｃａ：０．０００５～０．００５％、
Ｍｏ：０．２０～１．５％、
Ｔｉ：０．０１～０．０５％、
Ｂ：０．０００１～０．０１％、
Ｎｉ：０～１．０％、
Ｃｕ：０～１．０％、
Ｃｒ：０～１．５％、
Ｎｂ：０～０．２％、
Ｖ：０～０．２％、
Ｍｇ：０～０．０２％、
ＲＥＭ：０～０．０２％、
残部：Ｆｅおよび不純物であり、
下記（ｉ）式および（ii）式を満足する化学組成を有し、
セメンタイトの面積率が５～７０％であり、かつ、前記セメンタイトの球状化率が７０％以上である金属組織を有する、
自動車足回り部品用鋼管。
５．０≦（０．００１＋Ｃａ）×Ａｌ×Ｔｉ／（Ｍｎ×Ｓ）×１０４≦６０．０ ・・・（ｉ）
２．０≦３×Ｓｉ×Ｍｏ×Ｂ×１０４ ・・・（ii）
但し、上記式中の各元素記号は鋼中に含まれる各元素の含有量を表す。 % By mass
C: 0.10 to 0.60%
Si: 0.25 to 1.0%,
Mn: 0.05 to 2.0%,
P: 0.1% or less,
S: 0.03% or less,
Al: 0.005 to 0.1%,
N: 0.01% or less,
O: 0.01% or less,
Ca: 0.0005 to 0.005%,
Mo: 0.20 to 1.5%,
Ti: 0.01 to 0.05%,
B: 0.0001 to 0.01%,
Ni: 0 to 1.0%,
Cu: 0 to 1.0%,
Cr: 0 to 1.5%,
Nb: 0 to 0.2%,
V: 0 to 0.2%,
Mg: 0 to 0.02%,
REM: 0 to 0.02%,
Balance: Fe and impurities,
Having a chemical composition satisfying the following formulas (i) and (ii):
Having a metal structure in which the area ratio of cementite is 5 to 70% and the spheroidization ratio of the cementite is 70% or more;
Steel pipe for automobile undercarriage parts.
5.0 ≦ (0.001 + Ca) × Al × Ti / (Mn × S) × 10 4 ≦ 60.0 (i)
2.0 ≦ 3 × Si × Mo × B × 10 4 (ii)
However, each element symbol in the above formula represents the content of each element contained in the steel. - 前記化学組成が、質量％で、
Ｎｉ：０．１～１．０％、
Ｃｕ：０．１～１．０％、
Ｃｒ：０．３～１．５％、
Ｎｂ：０．０２～０．２％、および、
Ｖ：０．０３～０．２％、
から選択される１種以上を含有する、
請求項１に記載の自動車足回り部品用鋼管。 The chemical composition is mass%,
Ni: 0.1 to 1.0%,
Cu: 0.1 to 1.0%,
Cr: 0.3 to 1.5%,
Nb: 0.02 to 0.2%, and
V: 0.03-0.2%,
Containing one or more selected from
The steel pipe for automobile underbody parts according to claim 1. - 前記化学組成が、質量％で、
Ｍｇ：０．０００１～０．０２％、および、
ＲＥＭ：０．００１～０．０２％、
から選択される１種以上を含有する、
請求項１または請求項２に記載の自動車足回り部品用鋼管。 The chemical composition is mass%,
Mg: 0.0001 to 0.02%, and
REM: 0.001 to 0.02%,
Containing one or more selected from
The steel pipe for automobile underbody parts according to claim 1 or 2. - 継目無鋼管である、
請求項１から請求項３までのいずれかに記載の自動車足回り部品用鋼管。 Seamless steel pipe,
The steel pipe for automobile underbody parts according to any one of claims 1 to 3. - 請求項１から請求項４までのいずれかに記載の自動車足回り部品用鋼管を用いた、
自動車足回り部品。
Using the steel pipe for automobile undercarriage parts according to any one of claims 1 to 4,
Automobile undercarriage parts.
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