Classifications

• • 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
  • 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
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/18—Hardening; Quenching with or without subsequent tempering
  • C21D1/25—Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
• • 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
• • 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
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/11—Making amorphous alloys
• • 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
• • 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
• • 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
• • 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
• • 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
  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/008—Martensite

Definitions

• the present invention relates to a hollow member made of an electric resistance welded steel pipe, which is suitable for a use such as a stabilizer.
• Such hollow products are usually made from seamless steel pipes made of electric-welded steel pipes in the cold and then formed into the desired shape, and then quenched or tempered. The product is subjected to tempering (quenching and tempering) and the like (thermal refining).
• tempering quenching and tempering
• thermal refining thermal refining
• electric resistance welded steel pipes are widely used as materials for hollow stabilizers because they are relatively inexpensive and have excellent accuracy of dimension.
• C 0.35% or less
• Si 0.25% or less
• Mn 0.30 to 1.20%
• Cr less than 0.50%
• N + O 0.
• JP-A-6-93339 proposes a method for producing a high-strength, high-ductility electric resistance welded steel pipe that can be used for a stabilizer or the like.
• the technology described in JP-A-6-93339 is as follows: C: 0.18 to 28%, Si: 0.10 to 50%, Mn: 0.60 to 1.80%, Ti: 0 020-0.050%, ⁇ : 0.0005-0.0050% included, Cr: 0.20-20.50%, Mo: 0.5% or less, Nb: 0.015-0.
• ERW pipes made of steel containing at least one of 050% or Ca: 0.0050% or less are subjected to normalizing treatment (850 to 95010) and then quenched.
• the electric heating in this patent is a heating method in which the average heating rate from room temperature to a maximum heating temperature of 900 or more is at least 2 seconds, and when it reaches 900 or more, the time required for the heating is within 1 minute. Disclosure of the invention
• the gist of the present invention is as follows.
• the steel sheet is, by mass%, C: 0.15 to 40%, Si: 0.05 to 0.50%, Mn: 0.30 to 2.00%, A1: 0.01 to 0.10%, Ti: 0.001 to 0 ⁇ 04%, ⁇ : 0.0005 to 0.0050%, ⁇ : 0.0010 to 0.0100%, and Ti and N satisfy (N / 14) ⁇ (Ti / 47.9), balance Fe and inevitable impure material strength
• the manufacturing method of the hollow member which is a steel plate which has a composition.
• a method for producing a hollow member comprising a composition containing one or more selected from the group consisting of 1.0% or less, Ni: 1.0% or less, and Cu: 1.0% or less.
• the composition further contains one or two selected in terms of mass% of Nb: 0.2% or less and V: 0.2% or less.
• a method for manufacturing a hollow member in (2) or (3), in addition to the above-mentioned composition, the composition further contains one or two selected in terms of mass% of Nb: 0.2% or less and V: 0.2% or less.
• composition further contains Ca: 0.0050% or less by mass%.
• the base metal part other than the ERW weld part is in mass%, C: 0.15-0.40%, Si: 0.05-0.50%, Mn: 0.30-2.00%, ⁇ 1: 0.01 ⁇ 0.10%, Ti: 0.001 ⁇ 0.04%, B: 0.0005 ⁇ 0.0050%, N: 0.0010 ⁇ 0.0100% included, and Ti and N satisfy (NZ14) ⁇ (Ti / 47.9), remaining Fe and inevitable A hollow member having a composition composed of mechanical impurities.
• Nb 0.2% or less
• V 0.2% or less
• Fig. 1 Hardening hardness HV0.5 of ERW weld, minimum C amount and E of base metal C It is a graph which shows a ratio with Ci Co, and a relationship.
• Figure 2 A graph schematically showing the heat cycle pattern of the quenching process.
• Fig. 3 is a diagram showing an example of measurement of the decarburized layer width.
• Fig. 4 is a graph showing the relationship between the reduction rolling reduction ratio during draw rolling and the bond width after reduction.
• Fig. 5 A graph showing the relationship between fatigue strength and the ratio of ERW weld hardness to base metal hardness.
• the present invention solves the above-mentioned problems of the prior art, and can suppress a decrease in the quenching hardness of the electric resistance welded portion even when a quenching process is performed in which rapid heating is performed for a short time and quenching is performed.
• An object of the present invention is to provide a method for producing a hollow member made of an electric resistance welded steel pipe, which is a member excellent in fatigue durability.
• the present inventors reduced the quenching hardness of the ERW welded part when the ERW welded steel pipe was subjected to quenching after rapid and short heating by means of current heating or the like.
• the ERW welded pipe has a layer with a reduced carbon content in the ERW weld as shown in the concentration distribution of C by EP A (Electron Probe Micro-Analysis) shown in Fig. 3.
• this decarburized layer is unavoidable in ERW welding and is formed as follows. (1) During ERW welding, the joint is heated to the solid-liquid phase coexisting zone, and C concentrates in the liquid phase and decreases in the solid phase.
• the present inventors have determined that the heating rate, the maximum temperature reached, the soaking time, and the primary cooling rate up to the quenching start temperature among the quenching treatment conditions are reduced in the decarburized layer of the ERW weld.
• the amount of C that can secure sufficient quenching hardness during the quenching process diffuses from the base metal part to the ERW welded part and is quenched. It has been found that the electric resistance welded portion hardness after the treatment can be set to a desired hardness and the fatigue durability of the member can be improved.
• the steel pipe material is formed into an open tube on a substantially cylindrical shape, and then the ends of the open tube are butted together and subjected to electric resistance welding by high-frequency resistance welding. Or, it was further drawn to form ERW welded steel pipes with various decarburized layer widths (2h : 7 to 54 m). Next, these ERW welded pipes were quenched to the maximum temperature (maximum heating temperature) T at the heating rate V h after the quenching process consisting of the thermal cycle shown in Fig. 2, and maintained for a soaking time k. Immediately after that, it was cooled to the quenching start temperature Tq at the primary cooling rate V c and subjected to secondary cooling (rapid cooling).
• the hardness was measured and the hardness was determined as it was quenched.
• Vickers hardness HV0.5 with a load of 500 g (test force: 4.9 N) was measured in the thickness direction of the base metal part and the ERW welded part, and the average value was measured for each part. Hardened and hardened.
• the heating rate V h , the ultimate temperature T, and the primary cooling rate V c were varied in various ways, and the cooling rate of secondary cooling (rapid cooling) was constant (80 / s).
• the width d is at the position of the distance da from the center in the width direction of the decarburized layer, and if there is an initial concentration of C, C is the base material part after time t.
• C is the base material part after time t.
• the C concentration in the decarburized layer formed during ERW welding is 0.09% C content from -h to + h in the width direction.
• a constant rectangular density was used. This is based on the fact that the C concentration of the decarburized layer formed during ERW welding is approximately 0.09 mass S % —regardless of the C concentration of the base metal and the welding conditions.
• Fig. 1 shows the relationship with the calculated ratio of the minimum C 'content of ERW welds to ( ⁇ ZC.) From Fig. 1, the hardness (hardening hardness) of ERW welds can be organized with It can be seen that a decrease in the quenching hardness can be prevented by adjusting C No C 0 to 0.83 or more
• Figure 5 shows the fatigue durability and the hardness and base metal part of the ERW weld after quenching and tempering.
• the fatigue strength is the fatigue strength at the number of repetitions of 10 6 obtained by the torsional fatigue test in accordance with JIS Z 2273. It can be seen that there is no significant decrease in fatigue strength if the seam weld hardness is 86% or more of the base metal hardness.
• ( ⁇ ZCQ can be adjusted to 0 ⁇ 83 or more to prevent deterioration of fatigue durability of ERW welds due to decrease in quenching hardness. No (: When 0 is less than 0.83 In some cases, quenching hardness is drastically reduced.
• the present invention has been completed with further studies based on the powerful findings.
• an ERW welded steel pipe made of a steel plate and having a reduced coal layer width of 2 h (m) is used.
• the electric welded steel pipe to be used is made of a steel plate, formed, preferably continuously formed into a substantially cylindrical open pipe, and then the ends of the open pipe are butted together by high frequency welding.
• the steel pipe has an ERW weld with a reduced coal layer width of 2h (m).
• the reduced carbon layer width is measured by EPMA (Electron Probe Micro-Analysis) C analysis and white layer width measurement by nital etching ( It can be measured by various methods such as the middle figure in Fig. 3.
• the quenching treatment conditions are adjusted so as to satisfy the formula (1), corresponding to the measured bond width (decarburized layer width) 2 h.
• the ERW welded steel pipe to be used is preferably subjected to a cold working to be processed into a desired member shape, and then subjected to a heat treatment comprising a quenching process or a tempering process to have a desired high strength.
• the “quenching process” in the present invention is a rapid and short-time heat treatment as shown in FIG. That is, the primary cooling rate V immediately after heating to the maximum temperature reached (maximum heating temperature) T at the heating rate V h and holding the soaking time k. This is a process of cooling to the quenching start temperature Tq and then secondary cooling (rapid cooling).
• the rapid and short-time heat treatment in this patent means that the average heating rate from room temperature to the maximum heating temperature of 900 ° C or higher is 10 ° C / second or more, and the time when the temperature is 900 ° C or higher is 1 It is a heating method within minutes.
• the specific heating method is preferably energization heating.
• the heating rate V h , the maximum heating temperature T, the soaking time k, and the primary cooling rate V c are adjusted so as to satisfy the following equation (1), and the quenching start temperature Tq is set to Ar: Temperature above 3 transformation points.
• the right side of equation (1) means that the specific force of the minimum C content ( ⁇ (0) of the ERW weld and the C content C 0 of the copper plate is 0.83 or more.
• Heating rate V h maximum heating temperature T, soaking time Primary cooling rate V.
• the soaking time k includes the case of Os (no retention).
• the quenching start temperature Tq in the quenching process is set to a temperature exceeding the Ar 3 transformation point of the ERW weld.
• the Ar 3 transformation point of the ERW weld is substituted with the value (Ac 3 transformation point) calculated using the following formula.
• the Ac 3 transformation point is a safe value because it shifts to a higher temperature side than the Ar 3 transformation point in determining the quenching start temperature Tq.
• Ac 3 transformation point (in) 910-203 (V ⁇ C)-15. 2Ni + 44. 7Si + 104V + 31. 5Mo + 13. 1W- (30Mn + l lCr + 20Cu- 700P-400A1-120As-400Ti (Where, C, Ni, Si, V, Mo, W, Mn, Cr, Cu, P, Al, As, Ti: Content of each element (mass%))
• secondary cooling depends on the composition of the steel sheet, which is a raw material as long as the cooling conditions can produce a 100% martensite structure.
• Secondary cooling is preferably water cooling or oil cooling from the viewpoint of productivity.
• the decarburized layer width 2h that satisfies the formula (1) under the set quenching conditions is obtained from the preset quenching conditions and the formula (1). It is preferable to adjust the electric resistance welding condition, particularly the heat input so that the width of the decarburized layer of the ERW weld is less than the calculated value. In this case, if the bond width of the ERW weld is too narrow, the additivity may be lowered. Therefore, a bending test etc.
• the workability of the ERW welded part decreases with ERW welding with a reduced carbonization layer width of 2h that satisfies equation (1), welding is performed so that the bond width is wider than the appropriate value during ERW welding.
• it is effective to continuously reduce the bond width by applying diameter reducing to the ERW welded steel pipe.
• drawing using a die or the like, punching, rolling using a perforated roll, or the like is suitable.
• the temperature of the diameter reduction may be cold, warm, or hot.
• Reduced diameter is especially reduced by using induction heating to 950 to 1000 ° C, 50 to 70% reduction of diameter and a finishing temperature of about 800 ° C. (Reducing rolling) is preferable.
• the bond width (reduced coal layer width) 2h is narrowed by increasing the rolling reduction ratio during reduction rolling. can do.
• the bond width 2h was measured as the decarburized layer width.
• the decarbonized layer width 2h of the present invention is considered to be 900 or less within 1 minute at the longest after heating to 1000 in order to prevent decarburization in the conventional heating method. To 25 ⁇ or less, more preferably 16 / ⁇ m or less.
• the width of the decarburized layer in ERW welding is preferably ⁇ ⁇ ⁇ ⁇ ⁇ or more, and more than 30 / xm.
• the width of the decarburized layer in ERW welding is preferably ⁇ ⁇ ⁇ ⁇ ⁇ or more, and more than 30 / xm.
• a tempering treatment may be performed as necessary to improve toughness.
• the heating temperature in the tempering treatment is preferably a temperature in the range of 150 to 450 ° C. If the tempering heating temperature is less than 150 ° C, the desired toughness cannot be secured. On the other hand, if it exceeds 450, the hardness decreases and the desired fatigue durability cannot be ensured.
• Suitable steel as a material of the conductive sewing welded steel pipe in the present invention in mass%, C:. 0. 15 ⁇ 0 40 %, Si: 0. 0 5 ⁇ 0. 50%, Mn: 0. 30 ⁇ 2. 00%, A1: 0.01 to 0.1%, Ti: 0.001 to 04%, ⁇ : 0.0005 to 0.0050%, ⁇ : 0.0010 to 0.0100%, and Ti and ⁇ satisfies (NZ14) and (TiZ47.9), or Cr: 1.0% or less, Mo: 1.0% or less, W: 1.0% or less, Ni: 1.0% 1 or 2 types selected from Cur l.
• / or Ca a copper plate, preferably a hot-rolled steel plate, containing not more than 0.0005% and having the balance Fe and inevitable impurities.
• the “copper plate” mentioned here includes steel strips.
• C is a useful element that increases the strength of steel by solid solution and precipitates as carbide and / or carbonitride and increases the strength after tempering. is there.
• the content of 0.15% or more is required in order to ensure the desired strength of the steel pipe and the strength after the desired quenching treatment as a member for a hollow stabilizer or the like.
• the toughness after the quenching process decreases.
• C is limited to the range of 0.15-0.40%.
• Si 0.05-0.50%
• Si is an element that acts as a deoxidizing agent. In order to obtain such an effect, it is necessary to contain 0.05% or more. On the other hand, even if the content exceeds 0.50%, the deoxidation effect is saturated, so the effect commensurate with the content cannot be expected, which is economically disadvantageous, and inclusions are likely to occur during ERW welding. It adversely affects the soundness of ERW welds. For this reason, Si was limited to the range of 0.05 to 0.50%. In addition, Preferably it is 0.10 to 0.30%.
• Mn is an element that solidifies to increase the strength of copper and improve the hardenability of copper. In the present invention, it is necessary to contain 0.30% or more in order to secure a desired strength. . On the other hand, if it exceeds 2.00%, retained austenite ( ⁇ ) is generated and the toughness after tempering is lowered. For this reason, Mn was limited to the range of 0.30 to 2.00%. Preferably, it is 0 ⁇ 30 to 1.60%.
• A1 is an element that acts as a deoxidizer and has the effect of fixing the soot and ensuring the amount of solid solution effective in improving hardenability. In order to obtain such an effect, a content of 0.01% or more is required. On the other hand, if the content exceeds 0.10%, inclusions are often generated and the fatigue life may be reduced. For this reason, A1 is limited to the range of 0.0% -0.10%. Preferably, it is 0 ⁇ 02 to 0.05%.
• B is an effective element that improves the hardenability of steel, and B has the effect of strengthening the grain boundaries and the effect of preventing quenching cracks.
• a content of 0.0005% or more is required.
• the content exceeds 0.0005%, the above effect is saturated, which is economically disadvantageous.
• the content exceeds 0.0050%, coarse B-containing precipitates may be produced and the toughness may be lowered. Therefore, B is limited to the range of 0.0005% to 0.0050%. In addition, Preferably it is 0.0010 to 0.0025%.
• Ti acts as an N-fixing element and has the effect of securing a solid solution B amount effective for improving hardenability. Ti also precipitates as fine carbides, which suppresses the coarsening of crystal grains during welding and heat treatment and contributes to improved toughness. In order to obtain such an effect, it is necessary to contain 0.001% or more. On the other hand, when the content exceeds 0.04%, inclusions are remarkably formed and the toughness is lowered. For this reason, Ti is limited to the range of 0.001 to 0.04%. In addition, Preferably it is 0.02 to 0.03%.
• ⁇ is an element that combines with alloy elements in steel to form nitrides and carbonitrides and contributes to securing the strength after tempering. It needs to contain 0010% or more. on the other hand, If the content exceeds 0.0100%, the nitride becomes coarse, and the toughness and the fatigue life are reduced. For this reason, N is limited to the range of 0.0010 to 0.0100%.
• the present invention may further contain one or more of group A, group B and group C shown below. Good.
• Group A Cr: 1.0% or less, Mo: 1.0% or less, W: 1.0% or less, Ni: 1.0% or less, Cu: 1.0% or less Or two or more, and Z or
• Group B Nb: less than 0.2%, V: less than 0.2% power 1 or 2 selected, and / "or"
• Group C Ca: 0.005% or less
• Group A Cr: 1.0% or less, Mo: 1.0% or less, W: 1.0% or less, Ni: 1.0% or less, Cu: 1.0% or less 1 Seeds or more
• Cr, Mo, W, Cu, and Ni are all elements that have the effect of improving the hardenability of the steel, and can be selected according to need and contained in one or more.
• Cr In addition to improving hardenability, Cr also has the effect of forming fine carbides and increasing strength, contributing to securing the desired strength. In order to obtain such an effect, it is desirable to contain 0.05% or more, but if it exceeds 1.0%, the above effect will be saturated and economically disadvantageous, and at the time of ERW welding. Inclusions are likely to occur, adversely affecting the soundness of the ERW weld. Therefore, Cr is preferably limited to 1.0% or less. More preferably, it is 0.10 to 0.30%.
• Mo In addition to improving hardenability, Mo also has the effect of forming fine carbides and increasing strength, contributing to securing the desired strength. In order to obtain such an effect, it is desirable to contain 0.05% or more. However, if it exceeds 1.0%, the above effect is saturated, which is economically disadvantageous, and coarse carbides are added. May be produced and the toughness may be reduced. For this reason, it is preferable to limit Mo. to 10% or less. More preferably, it is from 0.10 to 0.30%.
• W is an element that has the effect of improving the balance between hardness and toughness after tempering (thermal refining). In order to obtain such an effect, it is desirable to contain 0.05% or more. On the other hand, if the content exceeds 1.0%, the effect is saturated and it is economically disadvantageous. For this reason, W is preferably limited to 1.0% or less. More preferably, it is 0.10 to 0.30%.
• Ni is an element that contributes to improving toughness in addition to improving hardenability. To obtain these effects, Ni is preferably contained in an amount of 0.05% or more. However, the effects described above are saturated and disadvantageous economically, and the workability is reduced. Therefore, it is desirable to limit Ni to 1.0% or less. More preferably, it is 0.10 to 0.50%.
• Cu is an element that has an effect of preventing delayed fracture in addition to improving hardenability.
• Cu is desirably contained in an amount of 0.5% or more.
• the content exceeds 1.0%, the above effect is saturated and disadvantageous economically, and the workability decreases.
• Cu is preferably limited to 1.0% or less. More preferably, it is 0.10 to 0.30%.
• Group B Nb: 0. 2% or less, V: 0.2% or less of power 1 or 2 types selected
• Nb and V are elements that form carbides and contribute to an increase in strength, and can be selected and contained as necessary. In order to obtain such effects, it is desirable to contain Nb : 0.01% or more and V: 0.01% or more, but Nb : 0.2% and V: contain more than 0.2%, respectively. However, the effect is saturated and the economy is unsatisfactory. Therefore, it is preferable to limit to Nb: 0.2% or less and V: 0.2% or less, respectively.
• Group C Ca: 0.005% or less
• Ca is an element that controls the form of inclusions such as sulfides and improves processability, and can be contained as needed.
• the content is preferably 0.0001% or more.
• the content exceeding 0.0005% lowers the cleanness of the steel.
• Ca is preferably limited to 0.0050% or less. More preferably, it is 0.0003% to 0.0010%.
• the balance other than the above components is composed of Fe and inevitable impurities.
• Inevitable impurities include P: 0.020% or less, S: 0.010% or less, and 0: 0.005% or less.
• P is an element that adversely affects weld cracking resistance and toughness, and is preferably adjusted to 0.020% or less. Further, it is more preferably 0.015% or less.
• S exists as a sulfide inclusion in steel, and is an element that decreases the workability, toughness and fatigue life of steel pipes and increases the reheat crack sensitivity.
• a hollow stabilizer it is preferable to adjust to not more than 0.001%. Further, it is more preferably 0.005% or less.
• the hollow member obtained by the manufacturing method described above is formed by subjecting at least a quenching treatment to an ERW welded steel pipe having an ERW welded portion made of a steel plate and having a reduced carbon layer width of 2 h (m), preferably
• the base material portion (steel plate) other than the ERW weld portion is a hollow member that satisfies the above-described composition.
• the hollow member according to the present invention has a ratio between the minimum C content of the ERW weld and the C content C 0 of the base material (steel plate). Is a member with excellent durability, characterized by having a value of 0.83 or more.
• the values obtained by EPMA in the pipe circumferential direction or C analysis by chemical analysis shall be used.
• the present invention will be further described based on examples.
• a hot rolled steel sheet having the composition shown in Table 1 was used as a material. These materials are continuously cold formed to form a substantially cylindrical open pipe, the ends of the open pipe are butted together, and high-frequency resistance welding is performed. As a result of ERW welding, ERW welded steel pipe (outer diameter 30 mm ⁇ X wall thickness 6) was used.
• CC was calculated, and after tempering the quenched steel pipe at 350 "C for 20 min, torsion fatigue test (torsion fatigue, In the test, the presence or absence of abnormal cracks along the ERW welds was investigated, X was indicated for cracks along the ERW welds, and ⁇ was indicated for other cracks.
• the test method was as follows.
• a specimen for hardness measurement was taken from the obtained ERW welded pipe, and the Vickers hardness meter (load): 4 ⁇ Vickers hardness HV0.5 was measured in 9).
• a test material for fatigue test (length in the axial direction: 250 mm) was taken from an ERW welded steel pipe with an outer diameter of 30 mm and an X wall thickness of 6 nm, and subjected to a torsional fatigue test in accordance with JIS Z 2273.
• Is 0.83 or more of the present invention are the A marked decrease in the quenching hardness occurred, and in the torsional fatigue test, abnormal cracking was observed along the ERW weld (indicated in Table 2 and Table 3 as X).
• Comparative Example Component E Material No. 36 which does not satisfy (NZ14) and (Ti / 47.9), which are the component ranges of the present invention, is the appropriate range for the reduced coal width 2 h and heat treatment conditions of the present invention. Even if the equation is satisfied (C Co is 0.83 or more), the hardness of the base metal part and the ERW welded part are significantly reduced compared to the A material with the same C content.

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• 2009
  • 2009-01-16 JP JP2009007203A patent/JP5353256B2/ja active Active
  • 2009-01-20 CN CN2009801027494A patent/CN101925678B/zh not_active Expired - Fee Related
  • 2009-01-20 WO PCT/JP2009/051148 patent/WO2009093728A1/ja active Application Filing
  • 2009-01-20 EP EP09703762.6A patent/EP2239343B1/de not_active Not-in-force
  • 2009-01-20 KR KR1020107017004A patent/KR101321681B1/ko active IP Right Grant

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