WO2019131813A1 - 電縫溶接鋼管および電縫溶接鋼管の製造方法 - Google Patents
電縫溶接鋼管および電縫溶接鋼管の製造方法 Download PDFInfo
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Definitions
- the present invention relates to an electric resistance welded steel pipe, and more particularly to an electric resistance welded steel pipe which is excellent in fatigue durability after rapid rapid heating and quenching treatment and can be suitably used as a material for a hollow stabilizer or the like.
- the present invention also relates to a method of manufacturing the electric resistance welded steel pipe.
- the hollow parts including the above-mentioned hollow stabilizer are usually manufactured by cold-forming a steel pipe into a desired shape and then quenching or hardening-tempering to obtain the required strength.
- a steel pipe a seamless steel pipe, an electric resistance welded steel pipe, and a drawn steel pipe obtained by cold drawing them are mainly used.
- ERW welded steel pipes are widely used as materials for hollow parts because they are relatively inexpensive and are excellent in dimensional accuracy and surface quality without drawing processing (Patent Documents 1 to 3).
- One of the causes for the lack of fatigue durability is the lack of hardenability in the ERW welds.
- hollow parts are generally manufactured by cold-forming a steel pipe and then hardening it. Therefore, if the quenching in the ERW welded portion of the ERW welded steel pipe is insufficient, the hardness (quenched hardness) of the ERW welded portion after quenching is determined by the base metal portion (portion other than the ERW welded portion). It is lower than it.
- Such a lack of hardening hardness in the electric resistance welded portion is particularly caused when the electric resistance welded steel pipe is heated rapidly for a short time by electric heating and subjected to a hardening treatment (hereinafter referred to as "rapid short time heating hardening treatment”) Make it manifest.
- This "rapid short-time heat-quenching treatment" is widely used because it is effective to suppress decarburization at the time of heating in addition to high productivity.
- Patent Document 4 That is, among the quenching conditions, the heating rate, the maximum reaching temperature, the soaking time, and the primary cooling rate to the quenching start temperature are adjusted according to the bond width (corresponding to the decarburized layer width) of the electric resistance welded portion. It is a method.
- C carbon
- C (carbon) capable of securing sufficient hardening hardness diffuses from the base material to the electric resistance welded portion at the time of heating, and as a result, the hardness of the electric resistance welded portion after hardening increases.
- the fatigue resistance of the obtained member is improved.
- Patent Document 4 has a problem that it can be applied only to a steel pipe having a narrow bond width, such as a hot finish ERW welded steel pipe.
- a steel pipe having a narrow bond width such as a hot finish ERW welded steel pipe.
- a general as-welded welded steel pipe having a bond width of 40 ⁇ m or more there is no suitable short-term heating condition that can fully recarburize the welded joint.
- recarburization is possible by extending the heating time, but in that case, decarburization can not be prevented by increasing the heating time. Therefore, in the said method, in hardening of the member which has general bond width, there existed a problem that improvement of hardening hardness and prevention of decarburization in an electric resistance welding part can not be reconciled.
- the present invention has been made in view of the above-mentioned circumstances, and it is possible to achieve both improvement of the hardening hardness and prevention of decarburization in the electric resistance welded portion even if the bond width is 40 ⁇ 10 -6 m or more. It is an object of the present invention to provide an ERW welded steel pipe which is excellent in fatigue durability after rapid hardening treatment for a short time. Another object of the present invention is to provide a method of manufacturing the electric resistance welded steel pipe.
- rapid short-time heat-quenching treatment means that the maximum heating temperature is 900 ° C. or more, and the average heating rate between room temperature and the maximum heating temperature is 10 ° C./s or more, 900 ° C. or more It refers to a hardening treatment in which the time of residence in the temperature range of 1 min.
- heating time needs to be extended to perform sufficient recarburization to improve the quenching hardness in the ERW welds, Charcoal will be produced.
- heating may be performed in an atmosphere that does not cause decarburization, but as described above, since it is necessary to perform quenching in the heating step in the quenching process, an atmosphere that does not cause decarburization is used In order to do so, various measures are required.
- heat treatment prior to rapid rapid heating and quenching treatment, heat treatment (normalization) is performed under an appropriate condition according to the bond width in an atmosphere that does not cause decarburization, thereby preventing decarburization while performing electric resistance sewing. A sufficient amount of carbon can be diffused into the weld.
- the ERW welded steel pipe subjected to the above heat treatment has a high quenching hardness in the ERW welded portion after the rapid short-time heat-quenching treatment, and has excellent fatigue durability.
- the present invention has been completed based on the above findings, and the gist configuration is as follows.
- the component composition is, by mass%, Cr: 1.0% or less, Mo: 1.0% or less, W: 1.0% or less,
- the component composition is, by mass%, The resistance welded steel pipe according to the above 1 or 2, further containing one or both of Nb: 0.2% or less and V: 0.2% or less.
- the component composition is, by mass%, The electric resistance welded steel pipe according to any one of the above 1 to 3, which further contains Ca: 0.0050% or less.
- N N content in the above (1) (wt%)
- Ti is the Ti content (mass%), respectively
- C * 1 C 0 - ( C 0 -0.09) erf (h ') ...
- N N content in the above (1) (wt%)
- Ti is the Ti content (mass%), respectively
- C * 1 C 0 - ( C 0 -0.09) erf (h ') ...
- the component composition is, by mass%, Cr: 1.0% or less, Mo: 1.0% or less, W: 1.0% or less, 5.
- the component composition is, by mass%, The method for producing an electric resistance welded steel pipe according to any one of the above 5 to 7, further containing one or both of Nb: 0.2% or less and V: 0.2% or less.
- the component composition is, by mass%, The method for producing an ERW welded steel pipe according to any one of the above 5 to 8, further containing Ca: 0.0050% or less.
- the electric resistance welded steel pipe of the present invention can be extremely suitably used as a raw pipe for hollow parts such as a hollow stabilizer.
- the electric resistance welded steel pipe of the present invention is characterized in that a steel plate having the above-described composition is used as a base material.
- a steel plate having the above-described composition is used as a base material.
- “%” in description of the following component composition represents “mass%", unless it refuses.
- the component composition of the steel plate used as a raw material when manufacturing the electric resistance welded steel pipe can be the same as the component composition of the base material of the electric resistance welded steel pipe.
- C 0.15 to 0.40%
- C is a useful element which forms a solid solution to increase the strength of the steel and precipitates as one or both of carbide and carbonitride to enhance the strength after tempering.
- the C content is made 0.15% or more, preferably 0.20% or more.
- the toughness after the quenching treatment decreases. Therefore, the C content is 0.40% or less, preferably 0.35% or less.
- Si 0.05 to 0.50% Si is an element that acts as a deoxidizer. In order to obtain the effect, the content needs to be 0.05% or more. Therefore, the Si content is 0.05% or more, preferably 0.10% or more. On the other hand, even if it is contained in excess of 0.50%, the deoxidizing effect is saturated, so the effect corresponding to the content can not be expected, which is economically disadvantageous, and inclusions are likely to be generated during electric resistance welding. Adversely affect the integrity of the ERW welds. Therefore, the Si content is 0.50% or less, preferably 0.30% or less.
- Mn 0.30 to 2.00%
- Mn is an element which is solid-solved to increase the strength of the steel and to improve the hardenability of the steel.
- the Mn content is 0.30% or more.
- the Mn content is 2.00% or less, preferably 1.60% or less.
- Al 0.01 to 0.10%
- Al is an element that acts as a deoxidizing agent, has the effect of fixing N and securing the amount of solid solution B effective for improving the hardenability.
- the Al content is set to 0.01% or more, preferably 0.02% or more.
- the Al content is 0.10% or less, preferably 0.05% or less.
- Ti acts as an N fixing element, and has an effect of securing a solid solution B amount effective for improving the hardenability. Further, Ti precipitates as fine carbides, suppresses coarsening of crystal grains at the time of welding and heat treatment, and contributes to the improvement of toughness. In order to obtain the above effect, the Ti content is made 0.001% or more, preferably 0.02% or more. On the other hand, when the Ti content exceeds 0.04%, the formation of inclusions becomes remarkable and the toughness decreases. Therefore, the Ti content is 0.04% or less, preferably 0.03% or less.
- B 0.0005 to 0.0050%
- B is an effective element for improving the hardenability of steel.
- B also has the effect of strengthening grain boundaries and has the effect of preventing quenching and cracking.
- the B content is made 0.0005% or more, preferably 0.0010% or more.
- the B content exceeds 0.0050%, the above effect is saturated and it is economically disadvantageous.
- the B content exceeds 0.0050%, coarse B-containing precipitates are generated to lower the toughness. Therefore, the B content is made 0.0050% or less, preferably 0.0025% or less.
- N 0.0010 to 0.0100%
- N is an element which combines with alloy elements in steel to form nitrides and carbonitrides and contributes to securing the strength after tempering. In order to acquire the said effect, N content is made into 0.0010% or more. On the other hand, if the N content exceeds 0.0100%, the nitride becomes coarse, and the toughness and the fatigue life decrease. Therefore, the N content is made 0.0100% or less.
- the component composition of the steel plate in one embodiment of the present invention can consist of the above-mentioned elements, the balance of Fe and unavoidable impurities.
- content of an unavoidable impurity is not specifically limited, It is preferable to suppress content of P, S, and O each independently in the following range.
- P 0.020% or less
- P is an element that adversely affects weld cracking resistance and toughness. Therefore, it is preferable to suppress P content as an unavoidable impurity to 0.020% or less, and it is more preferable to suppress to 0.015% or less.
- P is an impurity element, and the lower its content, the better, so the lower limit of the P content is not limited and may be 0. However, excessive reduction can lead to increased costs. Therefore, from the viewpoint of cost reduction, the P content is preferably 0.001% or more, and more preferably 0.005% or more.
- S 0.010% or less
- S is an element which is present as sulfide-based inclusions in steel and reduces the workability, toughness, and fatigue life of a steel pipe and increases the reheat cracking susceptibility. Therefore, it is preferable to suppress S content as an unavoidable impurity to 0.010% or less, and it is more preferable to suppress to 0.005% or less.
- S is an impurity element, and the lower its content, the better, so the lower limit of the S content is not limited and may be 0. However, excessive reduction can lead to increased costs. Therefore, from the viewpoint of cost reduction, the S content is preferably 0.0005% or more, and more preferably 0.0010% or more.
- O 0.005% or less
- O is an element which is mainly present as an oxide-based inclusion in steel and reduces the workability, toughness and fatigue life of a steel pipe. Therefore, it is preferable to suppress O content as an unavoidable impurity to 0.005% or less, and it is more preferable to suppress to 0.0021% or less.
- O is an impurity element, and the lower the content, the better, so the lower limit of the O content is not limited and may be 0. However, excessive reduction can lead to increased costs. Therefore, from the viewpoint of cost reduction, the O content is preferably 0.0005% or more, and more preferably 0.0010% or more.
- the above component composition may optionally contain one or more selected from the group consisting of Cr, Mo, W, Ni, and Cu, in the following contents: it can.
- Cr 1.0% or less
- Cr is an element having the function of forming fine carbides and increasing the strength in addition to the improvement of the hardenability.
- the Cr content exceeds 1.0%, the above-mentioned effect is saturated and it is economically disadvantageous, and inclusions are easily generated at the time of ERW welding, which adversely affects the soundness of the ERW welded portion. . Therefore, when adding Cr, the Cr content is made 1.0% or less, preferably 0.30% or less.
- the lower limit of the Cr content is not particularly limited, but from the viewpoint of sufficiently obtaining the addition effect of Cr, the Cr content is preferably 0.05% or more, preferably 0.10% or more. More preferable.
- Mo 1.0% or less
- Mo is an element having the function of forming fine carbides and increasing the strength in addition to the improvement of the hardenability.
- the Mo content exceeds 1.0%, the effect is saturated and economically disadvantageous, and coarse carbides are formed to lower the toughness. Therefore, when adding Mo, the Mo content is made 1.0% or less, preferably 0.30% or less.
- the lower limit of the Mo content is not particularly limited, but from the viewpoint of sufficiently obtaining the addition effect of Mo, the Mo content is preferably 0.05% or more, preferably 0.10% or more. More preferable.
- W 1.0% or less W is an element having the effect of improving the balance between hardness and toughness after temper treatment, in addition to the improvement of the hardenability.
- the W content exceeds 1.0%, the effect is saturated and it is economically disadvantageous. Therefore, when adding W, the W content is set to 1.0% or less, preferably 0.30% or less.
- the lower limit of the W content is not particularly limited, but from the viewpoint of sufficiently obtaining the addition effect of W, the W content is preferably 0.05% or more, preferably 0.10% or more. More preferable.
- Ni 1.0% or less
- Ni is an element which contributes to the improvement of toughness in addition to the improvement of hardenability.
- the Ni content exceeds 1.0%, the above-mentioned effect is saturated to be economically disadvantageous and the processability is lowered. Therefore, when adding Ni, the Ni content is made 1.0% or less, preferably 0.50% or less.
- the lower limit of the Ni content is not particularly limited, but from the viewpoint of sufficiently obtaining the addition effect of Ni, the Ni content is preferably 0.05% or more, preferably 0.10% or more. More preferable.
- Cu 1.0% or less
- Cu is an element effective in preventing delayed fracture in addition to the improvement of the hardenability.
- the Cu content exceeds 1.0%, the above effect is saturated, which is economically disadvantageous and the processability is lowered. Therefore, when adding Cu, the Cu content is 1.0% or less, preferably 0.30% or less.
- the lower limit of the Cu content is not particularly limited, but from the viewpoint of sufficiently obtaining the addition effect of Cu, the Cu content is preferably 0.05% or more, and 0.10% or more More preferable.
- the above component composition may further optionally contain one or both of Nb and V in the following content.
- Nb 0.2% or less
- Nb is an element that forms carbides and contributes to increase in strength, and can be selected and contained as necessary. However, if the Nb content exceeds 0.2%, the effect is saturated and it is economically disadvantageous. Therefore, when Nb is added, the Nb content is 0.2% or less.
- the lower limit of the Nb content is not particularly limited, but from the viewpoint of sufficiently obtaining the addition effect of Nb, the Nb content is preferably 0.01% or more.
- V 0.2% or less
- Nb is an element that forms carbides and contributes to increase in strength, and can be selected and contained as necessary. However, if the V content exceeds 0.2%, the effect is saturated and it is economically disadvantageous. Therefore, when adding V, the V content is 0.2% or less.
- the lower limit of the V content is not particularly limited, but it is preferable to set the V content to 0.01% or more from the viewpoint of sufficiently obtaining the addition effect of V.
- the above-mentioned component composition can further optionally contain Ca in the following content.
- Ca 0.0050% or less
- Ca is an element that controls the form of inclusions such as sulfides and improves the processability, and can be contained as necessary. However, if the Ca content exceeds 0.0050, the cleanliness of the steel decreases. Therefore, when adding Ca, the Ca content is made 0.0050% or less, preferably 0.0010% or less.
- the lower limit of the Ca content is not particularly limited, but from the viewpoint of sufficiently obtaining the addition effect of Ca, the Ca content is preferably made 0.0001% or more, preferably 0.0003% or more. More preferable.
- N in the above-mentioned formula (1) shows N content (mass%)
- Ti shows Ti content (mass%), respectively.
- B is an element having the effect of improving hardenability, but when it is combined with N and precipitated as BN, the hardenability improving effect is significantly reduced. If the Ti content and the N content do not satisfy the following expression (1), the fixation of N by Ti is insufficient, and the amount of solid solution B can not be secured at the time of quenching.
- C 0.15 to 0.40%, Si: 0.05 to 0.50%, Mn: 0.30 to 2.00%, Al: 0.01 to 0.10%, Ti: 0.001 to 0.04%, B: 0.0005 to 0.0050%, N: 0.0010-0.100%, Optionally selected from the group consisting of Cr: 1.0% or less, Mo: 1.0% or less, W: 1.0% or less, Ni: 1.0% or less, and Cu: 1.0% or less 1 or 2 or more, Optionally one or both of Nb: 0.2% or less and V: 0.2% or less, and Optionally, Ca: not more than 0.0050%,
- the balance consists of Fe and unavoidable impurities, and A steel plate having a component composition in which the Ti content and the N content satisfy the above equation (1) can be used.
- the electric resistance welded steel pipe of the present invention is characterized in that the bond width and the C content of the electric resistance welded portion satisfy the following conditions.
- the ERW welded steel pipe is manufactured by forming a steel plate as a raw material to form a substantially cylindrical open pipe, and then abutting end portions of the open pipe to perform electric seam welding.
- a carbon reduction layer having a C content lower than that of the base metal is formed. The width of the reduced carbon layer and the C content in the reduced carbon layer greatly affect the properties of the ERW welded steel pipe.
- the width of the decarburized layer is observed by analyzing the amount of C with an EPMA (Electron Probe Micro Analyzer) as shown in the upper drawing of FIG. 1 or by nital etching of the welded portion as shown in the middle part of FIG. It is possible to measure by various methods, such as a method of measuring the width of the white layer. However, if the amount of C is less than 0.30%, and if it is an ERW welded steel pipe which has been subjected to only heat treatment at a temperature of less than 800 ° C., the metal flow etching shown in the lower part of FIG. By doing this, the width of the bond, which is a region where no segregation line is observed, can be measured relatively easily and clearly.
- EPMA Electro Probe Micro Analyzer
- the width (bond width) of this bond portion matches well with the width of the decarburized layer measured by the above-mentioned method.
- the width of the reduced carbon layer measured by EPMA or the width of the white layer observed by nital etching is used as the bond width.
- the bond width 40 ⁇ 10 ⁇ 6 m or more, 120 ⁇ 10 ⁇ 6 m or less
- the bond width is preferably narrow. Therefore, the bond width is set to 120 ⁇ 10 ⁇ 6 m or less.
- the bond width is set to 40 ⁇ 10 ⁇ 6 m or more.
- the bond width may be measured by the method described above, and specifically, can be measured by the method described in the examples.
- Patent Document 4 The technique described in Patent Document 4 can be applied only to a steel pipe having a narrow bond width in order to enable sufficient recarburization in rapid rapid heating and quenching treatment. Therefore, in Patent Document 4, processing such as diameter reduction rolling is performed on the steel pipe to narrow the bond width. Even if a general steel pipe having a bond width of 40 ⁇ 10 -6 m or more is subjected to the quenching treatment described in Patent Document 4 without processing such as diameter reduction rolling, the conditions of the present invention are satisfied. Steel pipes can not be manufactured.
- [C content] C 0 -C 1 0.05 mass% or less
- the minimum C content of the ERW weld C 1 (mass%)
- the C content of the steel plate which is the base material The difference from C 0 (% by mass), C 0 -C 1 is 0.05% by mass or less, preferably 0.04% by mass or less.
- the lower limit of C 0 -C 1 is not particularly limited because C 0 -C 1 is preferably as low as possible from the viewpoint of securing the hardening hardness of the electric resistance welded portion. However, usually, since C 0> is C 1, C 0 -C 1 may be greater than 0 wt%. Further, from the viewpoint of easiness of production, C 0 -C 1 is preferably 0.01% by mass or more, and more preferably 0.02% by mass or more.
- C 1 is the C content in the electric resistance welded portion from the outer surface of the steel pipe at a position of 200 ⁇ m (depth 200 ⁇ m) in the thickness direction along the pipe circumferential direction It can be determined by measuring with EPMA.
- Total decarburization depth 50 ⁇ 10 ⁇ 6 m or less
- the depths of all the decarburized layers in the inner surface layer and the outer surface layer of the electric resistance welded steel pipe are respectively 50 ⁇ 10 ⁇ 6 m or less, preferably 30 ⁇ 10 ⁇ 6 m or less.
- the lower limit of the total decarburization depth is not limited.
- the depth of all decarburized layers in the inner surface layer and the outer surface layer is preferably 6 ⁇ 10 ⁇ 6 m or more, and 12 ⁇ 10 ⁇ 6 m or more. More preferable.
- the depth of the entire decarburized layer is affected by the heat treatment conditions, decarburization can be prevented and the total decarburized layer depth can be made within the above range by performing the normalization under the conditions described later.
- the decarburized layer depth is also affected by the decarburized layer depth of the steel strip used as the material of the ERW welded steel pipe. Therefore, for example, when using a heat-rolled steel plate as a material, it is preferable to lower the winding temperature at the time of manufacturing the heat-rolled steel plate or to perform high-pressure descaling to reduce the scale thickness.
- the depth of the total decarburized layer can be measured according to the “measuring method by a microscope” defined in JIS G 0558 “Depcarburized layer depth measuring method of steel”. Specific measurement can be performed by the method described in the examples.
- the outer diameter (D) of the electric resistance welded steel pipe of the present invention is not particularly limited and can be set to any value.
- the outer diameter is preferably 20 mm or more. Moreover, it is preferable that the said outer diameter shall be 40 mm or less.
- the thickness (t) of the electric resistance welded steel pipe of the present invention is not particularly limited, and can be set to any value.
- the thickness is preferably 2 mm or more, and the thickness is preferably 8 mm or less.
- the ratio (t / D) of the wall thickness t to the outer diameter D is preferably 0.14 or more.
- the ratio (t / D) is preferably 0.28 or less.
- the electric resistance welded steel pipe of the present invention can be obtained by performing electric resistance welding on a steel plate as a material to form an electric resistance welded steel pipe, and standardizing the electric resistance welded steel pipe under specific conditions. Each step will be specifically described below.
- steel sheet As a steel plate as a raw material, if it is a steel plate which has the said component composition, although a hot rolled steel plate and a cold-rolled steel plate arbitrary ones can be used, it is preferable to use a hot rolled steel plate.
- the term "steel plate” as used herein also includes "steel strip”.
- ERW welding The steel sheet is subjected to ERW welding to form an ERW welded steel pipe.
- the method of ERW welding is not particularly limited, generally, after the steel plate is roll-formed to form a substantially cylindrical open pipe, ends of the open pipe are butted and ERW welded.
- the butt surfaces are generally formed from as-sheared surfaces, but it is also preferable to finish by cutting from the viewpoint of preventing welding defects.
- the electric resistance welding is preferably performed by high frequency resistance welding, but from the viewpoint of preventing surface flaws, induction heating is preferred rather than the contact electrode type.
- the convex portion does not remain.
- the descaling can be performed by any method such as pickling.
- the bond width of the ERW welded steel pipe shall be 40 ⁇ 10 ⁇ 6 m or more and 120 ⁇ 10 ⁇ 6 m or less.
- the depth of all decarburized layers in both the inner surface layer and the outer surface layer of the electric resistance welded steel pipe shall be 50 ⁇ 10 ⁇ 6 m or less.
- the equation (2) is an equation for calculating the C content at the center position of the bond width after normalizing based on the diffusion of C during the normalizing. Therefore, the minimum C content (C * 1 ) in the electric resistance welded portion after normalizing can be estimated by using the above-mentioned equation (2). Therefore, by selecting the heating condition according to the bond width so that C 0 -C * 1 is 0.05% by mass or less, the actual minimum value of the electric resistance welded portion in the electric resistance welded steel pipe after normalizing C content: A difference between C 1 (mass%) and C content of the steel plate: C 0 (mass%), C 0 -C 1 can be made 0.05 mass% or less.
- the normalizing can be performed by any method as long as the above conditions are satisfied.
- the steel pipe may be heated to the maximum heating temperature: T, held at the maximum heating temperature (soaking), and then cooled.
- the conditions for the cooling are not particularly limited, and may be determined according to the composition of the steel pipe and the heating temperature.
- the average cooling rate from the start of cooling to 650 ° C. is preferably 10 ° C./s or less. If the average cooling rate from the start of cooling to 650 ° C. is 10 ° C./s or less, it is possible to obtain a structure which is composed of one or both of ferrite and pearlite and does not contain a hard phase.
- cooling from the viewpoint of preventing decarburization, it is preferable to perform cooling in a first atmosphere or a second atmosphere described later until reaching at least 650 ° C., and until reaching at least 450 ° C. It is more preferable to perform cooling in a first atmosphere or a second atmosphere described later during the period.
- the normalizing can be performed using any equipment as long as the above atmosphere can be used, but it is preferable to use a continuous heat treatment furnace (continuous furnace) from the viewpoint of productivity. From the viewpoint of atmosphere control, it is preferable to use a bright annealing furnace generally used for bright annealing as the heat treatment.
- the normalizing needs to be performed in an atmosphere that does not cause decarburization. If the atmosphere is not appropriate, decarburization of the base material portion, which is a supply source of carbon for recarburizing to the electric resistance welded portion, proceeds, and recarburization to the electric resistance welded portion does not proceed.
- the following two atmospheres can be mentioned as an atmosphere which does not produce the above-mentioned decarburization.
- the above-mentioned normalizing is composed of CO, CO 2 , H 2 , H 2 O, and a gas neutral to C and Fe, and the following equations (3) and (4) It can be done in a filling atmosphere.
- P CO P CO2 ⁇ K ⁇ a ⁇ C ...
- G c ⁇ is the free energy of C in the austenite phase
- G c gr is the free energy of C in the graphite
- ⁇ FeC ⁇ is an interaction coefficient between C and Fe in the austenite phase
- W MC ⁇ is an interaction coefficient between C and the element A in the austenite phase.
- the reason why the parameters in the austenite phase are used is that, when a steel pipe made of a steel plate having the above-described composition is subjected to normalizing, the microstructure of the steel becomes a microstructure substantially consisting of austenite single phase. is there.
- the mole fractions of C, Si, Mn, and Cr in the austenite phase are equal to the mole fractions of each element in the steel. Therefore, in the calculation of the equations (3) and (4), the value of the mole fraction in the steel can be used as the mole fraction in the austenite phase.
- the austenite single phase structure is formed by the normalizing, the microstructure of the steel before the normalizing can be an arbitrary structure.
- the atmosphere can be prepared by any method without particular limitation, but in general, it can be prepared by removing CO 2 and H 2 O from a gas obtained by incomplete combustion of methane, propane or the like. it can.
- the aforementioned "neutral gas to C and Fe" for example, can be used one or both of N 2 and Ar.
- the sintered semi, the mole fraction in the atmosphere, H 2: 0 ⁇ 10% , O 2: 80ppm comprises less, and the balance of H 2 O and N 2, and, It can carry out in the atmosphere whose dew point is 0 ° C or less.
- H 2 is a component that can be optionally added, and the molar fraction thereof may be zero.
- H 2 is a component having an effect of suppressing oxidation and decarburization of a steel pipe, it is preferable to add it.
- the mole fraction of H 2 is preferably 1% or more, and more preferably 2% or more.
- the mole fraction of H 2 is 10% or less, preferably 7% or less, and more preferably 5% or less.
- O 2 and H 2 O are components that cause decarburization. Furthermore, O 2 and H 2 O oxidize iron to form an oxide scale, and in the case of significant oxidation, it leads to a decrease in surface properties such as an increase in surface roughness. Therefore, it is desirable that the amounts of O 2 and H 2 O in the atmosphere be small. Specifically, when the mole fraction of O 2 exceeds 80 ppm, the above-mentioned adverse effect becomes remarkable, so the mole fraction of O 2 is 80 ppm or less, preferably 40 ppm or less, more preferably 20 ppm or less. With respect to H 2 O, the above-mentioned adverse effect becomes significant when the dew point exceeds 0 ° C.
- the dew point is made 0 ° C. or less, preferably ⁇ 20 ° C. or less, more preferably ⁇ 40 ° C. or less.
- the dew point is preferably ⁇ 60 ° C. or higher, and more preferably ⁇ 50 ° C. or higher, from the viewpoint of easiness of adjusting the atmosphere.
- the electric resistance welded steel pipe of the present invention can be manufactured by the above procedure.
- the electric resistance welded steel pipe obtained in this manner is excellent in fatigue durability after rapid rapid heating and quenching and can be suitably used as a material for a hollow stabilizer or the like.
- the electric resistance welded steel pipe manufactured as described above can be used for any application. As an example, it can be used as a material of hollow parts such as the hollow stabilizer as described above.
- the electric resistance welded steel pipe be subjected to processing for processing into a desired member shape, and then subjected to rapid short time heating and quenching treatment.
- processing for processing into a desired member shape, and then subjected to rapid short time heating and quenching treatment.
- rapid short time heating and quenching treatment Although arbitrary processing can be used as said processing, it is preferable to use cold processing.
- the above-mentioned rapid short-time heat-quenching treatment is the time during which the maximum heating temperature is 900 ° C. or more and the average heating rate between room temperature and the maximum heating temperature is 10 ° C./s or more and 900 ° C. or more. Perform on condition of less than 1 min.
- the heating in the said hardening can be performed by arbitrary methods, for example, high frequency heating and conduction heating can be used.
- the quenching start temperature Tq in the rapid short time heating and quenching treatment is a temperature higher than the Ar3 transformation point of the electric resistance welded portion. If Tq is below the Ar3 transformation point of the ERW weld, ferrite transformation or bainite transformation occurs before the start of quenching (quenching), and the ERW weld can not be made to have a 100% martensite structure. . And as a result, desired hardening hardness can not be ensured but fatigue durability falls.
- the Ar3 transformation point of the electric resistance welded portion is a value calculated using the following equation (5). This value is shifted to a higher temperature side than the actual Ar3 transformation point, so it is a value on the safe side in determining the quenching initiation temperature.
- the above equation for calculating the Ac3 transformation point is cited from Leslie Iron and Steel Science (translated by Koda, 1985: Maruzen, p. 273).
- the cooling rate at the time of hardening should just be the cooling conditions which can produce 100% martensitic structure.
- the cooling conditions under which a 100% martensitic structure can be obtained depend on the component composition of the steel sheet which is the material, but in the present invention, from the quenching initiation temperature: Tq, the average cooling rate: 30 ° C./s or more, preferably 80 ° C. It is preferable to cool to room temperature by 1 / s or more.
- a cooling medium obtained by adding a polymer to water or water for quenching (secondary cooling) in the quenching treatment.
- oil cooling may be employed in order to suppress the generation of quenching cracks, deformation at the time of quenching, and residual stress.
- a tempering treatment may be optionally performed to improve the toughness.
- the heating temperature (tempering temperature) in the tempering treatment is preferably 150 to 450 ° C. If the heating temperature is less than 150 ° C., desired toughness may not be secured. On the other hand, if the heating temperature exceeds 450 ° C., the hardness may be reduced, and the desired durability may not be ensured.
- an electric resistance welded steel pipe was manufactured in the following procedure. First, the hot rolled steel sheet was pickled to remove scale. Then, the hot-rolled steel plate was cold-rolled continuously to form a substantially cylindrical open pipe. Then, the end portions of the open pipe were butted and welded by high frequency resistance welding to form a seam welded steel pipe. The outer diameter of the obtained electric resistance welded steel pipe was 25.4 mm, and the thickness was 4.5 mm.
- the bond width of the electric resistance welded portion was adjusted to the values shown in Tables 2 and 3 by changing the welding conditions.
- collected the test piece for structure
- the test piece for structure observation was cut out so that a cross section perpendicular to the longitudinal (pipe axis) direction of the electric resistance welded steel pipe would be an observation surface. The cross section of the cut-out test piece was polished.
- each of the obtained electric resistance welded steel pipes (before normalizing) is subjected to the inner surface layer and the outer surface according to the “measurement method with a microscope” defined in JIS G 0558 “Method for measuring depth of decarburized layer of steel”.
- the depth of all decarburized layers in both of the surface was measured.
- the measurement cut the electric resistance welded steel pipe at the longitudinal center, and adopted the maximum value of the decarburized layer depth in the cross section.
- the depth of the ferrite decarburized layer was also measured by the same method. The measurement results are shown in Tables 2 and 3.
- the normalizing comprises the following steps (1) to (3). (1) From room temperature to the maximum heating temperature: T (° C.), heating at an average heating rate: 5 (° C./s). (2) The maximum heating temperature: maintained at a predetermined soaking time at T (° C.). (3) Cooling to room temperature, average cooling rate: 3 (° C./s).
- the time t (s) defined as the time during which the steel pipe is held in the temperature range between (T-50K) and T during the steps (1) to (3) is shown in Tables 2 and 3. I did it. In Tables 2 and 3, the maximum heating temperature T is shown not in terms of absolute temperature (K) but in degrees Celsius (° C.) for the sake of simplicity.
- the atmosphere in Table 4 corresponds to the first atmosphere described above, and consists of CO, CO 2 , H 2 , H 2 O, and N 2 .
- N 2 is a gas neutral to C and Fe.
- the atmosphere in Table 5 corresponds to the second atmosphere described above, and includes H 2 , O 2 , H 2 O, and the balance N 2 .
- the amount of H 2 O is shown as the dew point.
- the minimum C content of the ERW welded portion was measured.
- the measurement method was as follows. In addition, the said measurement was implemented before the hardening process mentioned later.
- the C content in the electric resistance welded portion of the obtained electric resistance welded steel pipe was determined based on the result of the EPMA measurement.
- the measurement position was a position of 200 ⁇ m (depth 200 ⁇ m) in the thickness direction from the outer surface in a cross section including the electric seam welded portion perpendicular to the longitudinal direction of the steel pipe.
- the said measurement was performed in the following procedures. First, a sample was cut out from the ERW steel pipe so that the cross section perpendicular to the longitudinal direction was at the measurement position.
- an EPMA measurement was performed in a line having a bond width of +200 ⁇ m in the circumferential direction around the bond portion, and the X-ray intensity derived from C was measured.
- an average value A of X-ray intensities in a range of ⁇ bond width ⁇ 0.4 was obtained with the bond portion at the center.
- the average value B of the X-ray intensities in the range from the position separated 20 ⁇ m from the end of the bond portion to the position separated 80 ⁇ m among the lines was determined.
- the measurement position of the average strength B corresponds to the base material portion.
- the above measurement was performed on three cross sections, and the average value of A and the average value of B in the three cross sections were determined.
- the minimum C content of the electric resistance welded portion: C 1 was calculated as the C content of the steel plate: C 0 ⁇ (average value of A) / (average value of B).
- Tables 6 and 7 show values of C 0 -C 1 which is the difference between the minimum C content of the electric resistance welded portion obtained: C 1 and the C content of the steel plate: C 0 .
- the C content of the steel sheet: as C 0 used the value of C content shown in Table 1.
- the actual measured values of C 0 -C 1 in Tables 6 and 7 agree well with the calculated values of C 0 -C * 1 in Tables 2 and 3. From this, it is understood that when the normalizing atmosphere is within the range of the present invention, the minimum C content of the electric resistance welded portion after normalizing can be estimated using the equation (2).
- the Vickers hardness in the base material portion: Hv 0 and the Vickers hardness in the electric resistance welded portion: Hv 1 were measured for each of the electric resistance welded steel pipes after the quenching treatment.
- the measurement results are shown in Tables 6 and 7.
- the measurement method was as follows.
- a test piece for measuring hardness is obtained from the obtained ERW welded steel pipe, and the Vickers hardness (HV 0.5) is measured with a Vickers hardness meter (load: 4.9 N) in the thickness direction for the ERW welded part and the base material part.
- the measurement was carried out at a pitch of 0.2 mm from the outer surface and the inner surface to 1 mm, respectively, and the obtained values were arithmetically averaged to determine the hardness of the electric resistance welded portion and base material of each steel pipe.
- Test fatigue test A test material for fatigue test (length in the axial direction of the pipe: 250 mm) was taken from the electric resistance welded steel pipe after tempering and subjected to torsional fatigue test of both swings in accordance with JIS Z 2273. The stress .tau. For steel pipes using A, B, E, F, G, I, and J, 380 MPa, steel plate no. In a steel pipe using C, D, and H, it was 470 MPa. The fracture condition was observed after the torsion fatigue test, and the case where an abnormal crack was shown along the electric resistance welded portion was evaluated as x, and the case where other cracks were shown was evaluated as ⁇ . Tables 6 and 7 show the evaluation results and the number of repetitions until breakage: Nf.
- FIG. 3 shows the difference between the minimum C content of the electric resistance welded portion: C 1 (% by mass) and the C content of the steel plate: C 0 (% by mass), C 0 -C 1 and the electric resistance after tempering welds of Vickers hardness: Vickers hardness Hv 1 and the base material part: the difference between Hv 0, is a graph showing a relationship between Hv 0 -Hv 1.
- Each point in FIG. 3 is a white circle when an abnormal crack is shown along the ERW weld in the above-mentioned torsion fatigue test, and a black circle is drawn when no abnormal crack is shown along the ERW weld. did.
- FIG. 4 is a calculated value of the minimum C content of the electric resistance welded portion obtained by the equation (2): C * 1 (mass%) and the C content of the steel sheet: C 0 (mass%) the difference, the C 0 -C * 1 the horizontal axis is a plot of the C 0 -C 1 is a measured value as the vertical axis.
- the minimum C content of the ERW welds calculated using equation (2): ERW welding measured by C * 1 It can be seen that it is in good agreement with the lowest C content of part: C 1 .
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Abstract
Description
C :0.15~0.40%、
Si:0.05~0.50%、
Mn:0.30~2.00%、
Al:0.01~0.10%、
Ti:0.001~0.04%、
B :0.0005~0.0050%、および
N :0.0010~0.0100%、を含み、
残部がFeおよび不可避的不純物からなり、かつ、
Ti含有量とN含有量とが下記(1)式を満足する成分組成を有する鋼板を母材とし、
ボンド幅が40×10-6m以上、120×10-6m以下である電縫溶接部を有する電縫溶接鋼管であって、
前記電縫溶接部の最低C含有量:C1(質量%)と前記鋼板のC含有量:C0(質量%)との差、C0-C1が0.05質量%以下であり、かつ、
前記電縫溶接鋼管の内側表層と外側表層における全脱炭層の深さが、それぞれ50×10-6m以下である、電縫溶接鋼管。
(N/14)<(Ti/47.9)…(1)
ここで、上記(1)式におけるNはN含有量(質量%)、TiはTi含有量(質量%)を、それぞれ示す
Cr:1.0%以下、
Mo:1.0%以下、
W :1.0%以下、
Ni:1.0%以下、および
Cu:1.0%以下からなる群より選択される1または2以上をさらに含有する、上記1に記載の電縫溶接鋼管。
Nb:0.2%以下、および
V :0.2%以下の一方または両方をさらに含有する、上記1または2に記載の電縫溶接鋼管。
Ca:0.0050%以下をさらに含有する、上記1~3のいずれか一項に記載の電縫溶接鋼管。
C :0.15~0.40%、
Si:0.05~0.50%、
Mn:0.30~2.00%、
Al:0.01~0.10%、
Ti:0.001~0.04%、
B :0.0005~0.0050%、および
N :0.0010~0.0100%、を含み、
残部がFeおよび不可避的不純物からなり、かつ、
Ti含有量とN含有量とが下記(1)式を満足する成分組成を有する鋼板を電縫溶接して、ボンド幅が40×10-6m以上、120×10-6m以下である電縫溶接部を有し、内側表層と外側表層における全脱炭層の深さが、それぞれ50×10-6m以下である電縫溶接鋼管とし、
次いで、下記(2)式で求められる前記電縫溶接部の最低C含有量の計算値:C* 1(質量%)と前記鋼板のC含有量:C0(質量%)との差、C0-C* 1が0.05質量%以下となる条件で、かつ、
CO、CO2、H2、H2O、ならびにCおよびFeに対して中性なガスからなり、下記(3)および(4)式を満たす雰囲気で焼準する、電縫溶接鋼管の製造方法。
(N/14)<(Ti/47.9)…(1)
ここで、上記(1)式におけるNはN含有量(質量%)、TiはTi含有量(質量%)を、それぞれ示す
C* 1=C0-(C0-0.09)erf(h’)…(2)
ここで、
C0:鋼板のC含有量(質量%)
h’=h/(Dt)1/2
h(m):ボンド幅/2
D(m2/s)=D0 exp(-Q/RT)
D0=4.7×10-5 m2/s
Q=155 kJ/mol・K
R=8.31 J/mol・K、
T:前記焼準における最高加熱温度(K)
t(s):前記焼準において(T-50K)からTの間の温度域に保持されている時間
(PCO)2/PCO2≧K・aγ C…(3)
PH2・PCO/PH2O≧K’・aγ C…(4)
ここで、
log(K)=-9460/T-1.26log(T)+13.52
K’=exp[-(131300-134.3T)/RT]
aC γ=xC γ・exp[(GC γ+ΩFeC γ-GC gr)・RT]・exp[(-2ΩFeC γ・xC γ+ΣWMC γ・xM γ)/RT]
GC γ-GC gr=73744J/mol
2ΩFeC γ=-51956J/mol
WMnC γ=-41900J/mol
WSiC γ=+125700J/mol
WCrC γ=-104750/mol
PCO(atm):炉内雰囲気中のCOの分圧
PCO2(atm):炉内雰囲気中のCO2の分圧
PH2(atm):炉内雰囲気中のH2の分圧
PH2O(atm):炉内雰囲気中のH2Oの分圧
R=8.31 J/mol・K
T:前記焼準における最高加熱温度(K)
aC γ:オーステナイト相中におけるCの活量
xC γ:オーステナイト相中のCのモル分率
xSi γ:オーステナイト相中のSiのモル分率
xMn γ:オーステナイト相中のMnのモル分率
xCr γ:オーステナイト相中のCrのモル分率
GC γ:オーステナイト相中におけるCの自由エネルギー
GC gr:グラファイト中におけるCの自由エネルギー
C :0.15~0.40%、
Si:0.05~0.50%、
Mn:0.30~2.00%、
Al:0.01~0.10%、
Ti:0.001~0.04%、
B :0.0005~0.0050%、および
N :0.0010~0.0100%、を含み、
残部がFeおよび不可避的不純物からなり、かつ、
Ti含有量とN含有量とが下記(1)式を満足する成分組成を有する鋼板を電縫溶接して、ボンド幅が40×10-6m以上、120×10-6m以下である電縫溶接部を有し、内側表層と外側表層における全脱炭層の深さが、それぞれ50×10-6m以下である電縫溶接鋼管とし、
次いで、下記(2)式で求められる前記電縫溶接部の最低C含有量の計算値:C* 1(質量%)と前記鋼板のC含有量:C0(質量%)との差、C0-C* 1が0.05質量%以下となる条件で、かつ、
炉内雰囲気中のモル分率でH2:10%以下、O2:80ppm以下、ならびに残部のH2OおよびN2からなり、露点が0℃以下である雰囲気で焼準する、電縫溶接鋼管の製造方法。
(N/14)<(Ti/47.9)…(1)
ここで、上記(1)式におけるNはN含有量(質量%)、TiはTi含有量(質量%)を、それぞれ示す
C* 1=C0-(C0-0.09)erf(h’)…(2)
ここで、
C0:鋼板のC含有量(質量%)
h’=h/(Dt)1/2
h(m):ボンド幅/2
D(m2/s)=D0 exp(-Q/RT)
D0=4.7×10-5 m2/s
Q=155 kJ/mol・K
R=8.31 J/mol・K、
T:前記焼準における最高加熱温度(K)
t(s):前記焼準において(T-50K)からTの間の温度域に保持されている時間
Cr:1.0%以下、
Mo:1.0%以下、
W :1.0%以下、
Ni:1.0%以下、および
Cu:1.0%以下からなる群より選択される1または2以上をさらに含有する、上記5または6に記載の電縫溶接鋼管の製造方法。
Nb:0.2%以下、および
V :0.2%以下の一方または両方をさらに含有する、上記5~7のいずれか一項に記載の電縫溶接鋼管の製造方法。
Ca:0.0050%以下をさらに含有する、上記5~8のいずれか一項に記載の電縫溶接鋼管の製造方法。
本発明の電縫溶接鋼管は、上述した成分組成を有する鋼板を母材とすることを特徴の一つとする。以下、成分組成を上記範囲に限定する理由を説明する。なお、以下の成分組成の説明における「%」は、特に断らない限り「質量%」を表す。また、前記電縫溶接鋼管を製造する際に素材として用いる鋼板の成分組成も、上記電縫溶接鋼管の母材の成分組成と同様とすることができる。
Cは、固溶して鋼の強度を増加させるとともに、炭化物および炭窒化物の一方または両方として析出し、焼戻後の強度を高める有用な元素である。所望の鋼管の強度および焼入れ後の強度を確保するために、C含有量を0.15%以上、好ましくは0.20%以上とする。一方、C含有量が0.40%を超えると、焼入れ処理後の靭性が低下する。そのため、C含有量は0.40%以下、好ましくは0.35%以下とする。
Siは、脱酸剤として作用する元素である。その効果を得るためには、0.05%以上の含有を必要とする。そのため、Si含有量は0.05%以上、好ましくは0.10%以上とする。一方、0.50%を超えて含有しても、脱酸の効果が飽和するため、含有量に見合う効果を期待できず、経済的に不利となるうえ、電縫溶接時に介在物が生じやすくなり、電縫溶接部の健全性に悪影響を及ぼす。そのため、Si含有量は0.50%以下、好ましくは0.30%以下とする。
Mnは、固溶して鋼の強度を高めるとともに、鋼の焼入れ性を向上させる元素である。所望の強度を確保するために、Mn含有量は0.30%以上とする。一方、Mn含有量が2.00%を超えると、残留オーステナイトが生成し、焼戻後の靭性が低下する。そのため、Mn含有量は2.00%以下、好ましくは1.60%以下とする。
Alは、脱酸剤として作用するとともに、Nを固定し、焼入れ性向上に有効な固溶B量を確保する効果を有する元素である。前記効果を得るために、Al含有量を0.01%以上、好ましくは0.02%以上とする。一方、Al含有量が0.10%を超えると、介在物の生成が多くなり、疲労寿命が低下する。そのため、Al含有量は0.10%以下、好ましくは0.05%以下とする。
Tiは、N固定化元素として作用し、焼入れ性向上に有効な固溶B量を確保する効果を有する。また、Tiは、微細な炭化物として析出し、溶接時や熱処理時の結晶粒の粗大化を抑制し、靭性の向上に寄与する。前記効果を得るために、Ti含有量を0.001%以上、好ましくは0.02%以上とする。一方、Ti含有量が0.04%を超えると、介在物の形成が著しくなり靭性が低下する。そのため、Ti含有量を0.04%以下、好ましくは0.03%以下とする。
Bは、鋼の焼入れ性を向上させる有効な元素である。また、Bは粒界を強化する作用を有し、焼割れを防止する効果を有する。前記効果を得るために、B含有量を0.0005%以上、好ましくは0.0010%以上とする。一方、B含有量が0.0050%を超えると、上記効果が飽和し経済的に不利となる。また、B含有量が0.0050%を超えると、粗大なB含有析出物が生じ靭性が低下する。そのため、B含有量を0.0050%以下、好ましくは0.0025%以下とする。
Nは、鋼中の合金元素と結合し窒化物、炭窒化物を形成し、焼戻後の強度確保に寄与する元素である。前記効果を得るために、N含有量を0.0010%以上とする。一方、N含有量が0.0100%を超えると、窒化物が粗大化し、靭性や疲労寿命が低下する。そのため、N含有量を0.0100%以下とする。
Pは、溶接割れ性、靭性に悪影響を及ぼす元素である。そのため、不可避不純物としてのP含有量は、0.020%以下に抑制することが好ましく、0.015%以下に抑制することがより好ましい。一方、Pは不純物元素であって、その含有量は低ければ低いほど良いため、P含有量の下限は限定されず、0であってよい。しかし、過度の低減はコストの増加を招く場合がある。そのため、コスト低減という観点からはP含有量を0.001%以上とすることが好ましく、0.005%以上とすることがより好ましい。
Sは、鋼中では硫化物系介在物として存在し、鋼管の加工性、靭性、疲労寿命を低下させるとともに、再熱割れ感受性を増大する元素である。そのため、不可避的不純物としてのS含有量は、0.010%以下に抑制することが好ましく、0.005%以下に抑制することがより好ましい。一方、Sは不純物元素であって、その含有量は低ければ低いほど良いため、S含有量の下限は限定されず、0であってよい。しかし、過度の低減はコストの増加を招く場合がある。そのため、コスト低減という観点からはS含有量を0.0005%以上とすることが好ましく、0.0010%以上とすることがより好ましい。
Oは、鋼中では主として酸化物系介在物として存在し、鋼管の加工性、靭性、疲労寿命を低下させる元素である。そのため、不可避的不純物としてのO含有量を0.005%以下に抑制することが好ましく、0.0021%以下に抑制することがより好ましい。一方、Oは不純物元素であって、その含有量は低ければ低いほど良いため、O含有量の下限は限定されず、0であってよい。しかし、過度の低減はコストの増加を招く場合がある。そのため、コスト低減という観点からはO含有量を0.0005%以上とすることが好ましく、0.0010%以上とすることがより好ましい。
Crは、焼入れ性向上に加えて、微細な炭化物を形成し強度を上昇させる作用を有する元素である。しかし、Cr含有量が1.0%を超えると、前記効果が飽和して経済的に不利となるとともに、電縫溶接時に介在物を生じ易くなり、電縫溶接部の健全性に悪影響を及ぼす。そのため、Crを添加する場合、Cr含有量を1.0%以下、好ましくは0.30%以下とする。一方、Cr含有量の下限は特に限定されないが、Crの添加効果を十分に得るという観点からは、Cr含有量を0.05%以上とすることが好ましく、0.10%以上とすることがより好ましい。
Moは、焼入れ性向上に加えて、微細な炭化物を形成し強度を上昇させる作用を有する元素である。しかし、Mo含有量が1.0%を超えると、前記効果が飽和して経済的に不利となるとともに、粗大な炭化物を生成し、靭性が低下する。そのため、Moを添加する場合、Mo含有量を1.0%以下、好ましくは0.30%以下とする。一方、Mo含有量の下限は特に限定されないが、Moの添加効果を十分に得るという観点からは、Mo含有量を0.05%以上とすることが好ましく、0.10%以上とすることがより好ましい。
Wは、焼入れ性向上に加えて、調質処理後の硬さと靭性のバランスを良好にする作用を有する元素である。しかし、W含有量が1.0%を超えると、前記効果が飽和して経済的に不利となる。そのため、Wを添加する場合、W含有量を1.0%以下、好ましくは0.30%以下とする。一方、W含有量の下限は特に限定されないが、Wの添加効果を十分に得るという観点からは、W含有量を0.05%以上とすることが好ましく、0.10%以上とすることがより好ましい。
Niは、焼入れ性向上に加えて、靭性向上にも寄与する元素である。しかし、Ni含有量が1.0%を超えると、前記効果が飽和して経済的に不利となるうえ、加工性が低下する。そのため、Niを添加する場合、Ni含有量を1.0%以下、好ましくは0.50%以下とする。一方、Ni含有量の下限は特に限定されないが、Niの添加効果を十分に得るという観点からは、Ni含有量を0.05%以上とすることが好ましく、0.10%以上とすることがより好ましい。
Cuは、焼入れ性向上に加えて、遅れ破壊防止に効果のある元素である。しかし、Cu含有量が1.0%を超えると、前記効果が飽和して経済的に不利となるうえ、加工性が低下する。そのため、Cuを添加する場合、Cu含有量を1.0%以下、好ましくは0.30%以下とする。一方、Cu含有量の下限は特に限定されないが、Cuの添加効果を十分に得るという観点からは、Cu含有量を0.05%以上とすることが好ましく、0.10%以上とすることがより好ましい。
Nbは、炭化物を形成して強度増加に寄与する元素であり、必要に応じて選択して含有できる。しかし、Nb含有量が0.2%を超えると、前記効果が飽和して経済的に不利となる。そのため、Nbを添加する場合、Nb含有量は0.2%以下とする。一方、Nb含有量の下限は特に限定されないが、Nbの添加効果を十分に得るという観点からは、Nb含有量を0.01%以上とすることが好ましい。
Vは、Nbと同様に、炭化物を形成して強度増加に寄与する元素であり、必要に応じて選択して含有できる。しかし、V含有量が0.2%を超えると、前記効果が飽和して経済的に不利となる。そのため、Vを添加する場合、V含有量は0.2%以下とする。一方、V含有量の下限は特に限定されないが、Vの添加効果を十分に得るという観点からは、V含有量を0.01%以上とすることが好ましい。
Caは、硫化物等の介在物の形態を制御し、加工性を向上させる元素であり、必要に応じて含有できる。しかし、Ca含有量が0.0050%を超えると鋼の清浄度が低下する。そのため、Caを添加する場合、Ca含有量を0.0050%以下、好ましくは0.0010%以下とする。一方、Ca含有量の下限は特に限定されないが、Caの添加効果を十分に得るという観点からは、Ca含有量を0.0001%以上とすることが好ましく、0.0003%以上とすることがより好ましい。
本発明においては、上記鋼板の成分組成におけるTi含有量とN含有量が下記(1)式を満足する必要がある。
(N/14)<(Ti/47.9)…(1)
ここで、上記(1)式におけるNはN含有量(質量%)、TiはTi含有量(質量%)を、それぞれ示す。
R=(N/14)/(Ti/47.9)…(a)
C :0.15~0.40%、
Si:0.05~0.50%、
Mn:0.30~2.00%、
Al:0.01~0.10%、
Ti:0.001~0.04%、
B :0.0005~0.0050%、
N :0.0010~0.0100%、
任意に、Cr:1.0%以下、Mo:1.0%以下、W:1.0%以下、Ni:1.0%以下、およびCu:1.0%以下からなる群より選択される1または2以上、
任意に、Nb:0.2%以下、およびV:0.2%以下の一方または両方、ならびに、
任意に、Ca:0.0050%以下を含み、
残部がFeおよび不可避的不純物からなり、かつ、
Ti含有量とN含有量とが上記(1)式を満足する成分組成を有する鋼板を用いることができる。
本発明の電縫溶接鋼管は、ボンド幅および電縫溶接部のC含有量が以下の条件を満たすことを特徴とする。
電縫溶接鋼管は、素材としての鋼板を成形して略円筒状のオープン管としたのち、該オープン管の端部同士を突き合わせて電縫溶接することによって製造される。このようにして得られる電縫溶接鋼管の電縫溶接部には、C含有量が母材よりも低くなっている減炭層が形成される。この減炭層の幅や、減炭層におけるC含有量は、電縫溶接鋼管の特性に大きく影響する。
電縫溶接部の焼入れ硬さの観点からは、ボンド幅が狭い方が好ましい。そのため、ボンド幅を120×10-6m以下とする。一方、ボンド幅が狭くなりすぎると、加工性や電縫溶接時のロバスト性が低下する。そのため、ボンド幅を40×10-6m以上とする。前記ボンド幅は、上述した方法で測定すればよく、具体的には、実施例に記載する方法によって測定することができる。
C0-C1:0.05質量%以下
電縫溶接部におけるC含有量が低いと、焼入れ性が不足し、焼入れ後における電縫溶接部の硬さが不十分となる。そこで、電縫溶接部の焼入れ硬さを確保し、疲労強度を向上させるために、電縫溶接部の最低C含有量:C1(質量%)と、母材である鋼板のC含有量:C0(質量%)との差、C0-C1を0.05質量%以下、好ましくは0.04質量%以下とする。一方、電縫溶接部の焼入れ硬さを確保するという観点からは、C0-C1は低ければ低いほどよいため、C0-C1の下限はとくに限定されない。しかし、通常、C0>C1であるため、C0-C1は0質量%超であってよい。また、製造の容易さという観点からは、C0-C1を0.01質量%以上とすることが好ましく、0.02質量%以上とすることが好ましい。なお、電縫溶接部の最低C含有量:C1は、電縫溶接部におけるC含有量を、鋼管の外表面から厚み方向に200μm(深さ200μm)の位置で、管周方向に沿ってEPMAで測定することによって求めることができる。
全脱炭深さ:50×10-6m以下
全脱炭層深さが大きいと、焼入れ後の硬さが低下して疲労強度が確保できなくなる。そのため、電縫溶接鋼管の内側表層と外側表層における全脱炭層の深さを、それぞれ50×10-6m以下、好ましくは30×10-6m以下とする。一方、前記全脱炭深さの下限については限定されない。しかし、製造の容易さという観点からは、内側表層と外側表層における全脱炭層の深さを、それぞれ6×10-6m以上とすることが好ましく、12×10-6m以上とすることがより好ましい。
本発明の電縫溶接鋼管の外径(D)は、特に限定されることなく任意の値とすることができる。前記外径は20mm以上とすることが好ましい。また、前記外径は40mm以下とすることが好ましい。また、本発明の電縫溶接鋼管の肉厚(t)は、特に限定されることなく任意の値とすることができる。前記肉厚は2mm以上とすることが好ましい、また、前記肉厚は8mm以下とすることが好ましい。外径Dに対する肉厚tの比(t/D)は、0.14以上とすることが好ましい。また、前記比(t/D)は0.28以下とすることが好ましい。
次に、本発明の一実施形態における電縫溶接鋼管の製造方法を説明する。本発明の電縫溶接鋼管は、素材としての鋼板を電縫溶接して電縫溶接鋼管とし、前記電縫溶接鋼管を特定の条件で焼準することによって得ることができる。以下、各工程について具体的に説明する。
素材としての鋼板としては、上記成分組成を有する鋼板であれば、熱延鋼板、冷延鋼板を問わず任意のものを用いることができるが、熱延鋼板を用いることが好ましい。なお、ここでいう「鋼板」には「鋼帯」をも含むものとする。
前記鋼板を、電縫溶接して電縫溶接鋼管とする。電縫溶接の方法は特に限定されないが、一般的には、鋼板をロール成形して略円筒状のオープン管としたのち、該オープン管の端部同士を突き合わせて電縫溶接する。突合せ面は一般には剪断したままの面から成形されるが、溶接欠陥を防止する観点からは切断で仕上げることも好ましい。電縫溶接は、高周波抵抗溶接で行うことが好ましいが、特に表面疵の防止の観点からは接触電極式ではなく誘導加熱が好ましい。また、電縫溶接部の耐久性の不安定要因となりうるため、電縫溶接後に外面だけでなく内面もビードカットを行って凸部が残らないようにすることが好ましい。なお、電縫溶接鋼管への加工に先立って、素材鋼板に対してデスケーリングを施すことが好ましい。前記デスケーリングは、酸洗など、任意の方法で行うことができる。
次いで、得られた電縫溶接鋼管に対して焼準(焼入れ前熱処理)を施す。本発明においては、前記焼準の際の加熱条件と雰囲気の両者を以下に述べるように制御することが重要である。
下記(2)式で求められる前記電縫溶接部の最低C含有量の計算値:C* 1(質量%)と前記鋼板のC含有量:C0(質量%)との差、C0-C* 1が0.05質量%以下となる条件で前記焼準を行う。
C* 1=C0-(C0-0.09)erf(h’)…(2)
ここで、
C0:鋼板のC含有量(質量%)
h’=h/(Dt)1/2
h(m):ボンド幅/2
D(m2/s)=D0 exp(-Q/RT)
D0=4.7×10-5 m2/s
Q=155 kJ/mol・K
R=8.31 J/mol・K、
T:前記焼準における最高加熱温度(K)
t(s):前記焼準において(T-50K)からTの間の温度域に保持されている時間
上記焼準は、脱炭を生じさせない雰囲気で行う必要がある。雰囲気が適切でないと、電縫溶接部へ復炭する炭素の供給源である母材部の脱炭が進んで電縫溶接部への復炭が進まない。前記脱炭を生じさせない雰囲気としては、次の2つの雰囲気を挙げることができる。
本発明の一実施形態においては、上記焼準を、CO、CO2、H2、H2O、ならびにCおよびFeに対して中性なガスからなり、下記(3)および(4)式を満たす雰囲気で行うことができる。
(PCO)2/PCO2≧K・aγ C…(3)
PH2・PCO/PH2O≧K’・aγ C…(4)
ここで、
log(K)=-9460/T-1.26log(T)+13.52
K’=exp[-(131300-134.3T)/RT]
aC γ=xC γ・exp[(GC γ+ΩFeC γ-GC gr)・RT]・exp[(-2ΩFeC γ・xC γ+ΣWMC γ・xM γ)/RT]
GC γ-GC gr=73744J/mol
2ΩFeC γ=-51956J/mol
WMnC γ=-41900J/mol
WSiC γ=+125700J/mol
WCrC γ=-104750/mol
PCO(atm):炉内雰囲気中のCOの分圧
PCO2(atm):炉内雰囲気中のCO2の分圧
PH2(atm):炉内雰囲気中のH2の分圧
PH2O(atm):炉内雰囲気中のH2Oの分圧
R=8.31 J/mol・K
T:前記焼準における最高加熱温度(K)
aC γ:オーステナイト相中におけるCの活量
xC γ:オーステナイト相中のCのモル分率
xSi γ:オーステナイト相中のSiのモル分率
xMn γ:オーステナイト相中のMnのモル分率
xCr γ:オーステナイト相中のCrのモル分率
GC γ:オーステナイト相中におけるCの自由エネルギー
GC gr:グラファイト中におけるCの自由エネルギー
本発明の一実施形態においては、上記焼準を、雰囲気中のモル分率で、H2:0~10%、O2:80ppm以下含み、残部がH2OおよびN2からなり、かつ、露点が0℃以下である雰囲気で行うことができる。
鋼管の酸化や脱炭を抑制する効果を有する成分であるため、添加することが好ましい。具体的には、H2のモル分率を1%以上とすることが好ましく、2%以上とすることがより好ましい。一方、H2を過剰に添加しても、その添加効果は飽和し、さらに、爆発が生じやすくなる。そのため、H2のモル分率は、10%以下、好ましくは7%以下、より好ましくは5%以下とする。
上記のようにして製造された電縫溶接鋼管は、任意の用途に用いることができる。一例としては、上述したような中空スタビライザーなどの中空部品の素材として用いることができる。
上記急速短時間加熱焼入れ処理は、最高加熱温度が900℃以上、室温から前記最高加熱温度の間における平均加熱速度が10℃/s以上、かつ900℃以上の温度域に滞留している時間が1min以内の条件で行う。前記条件で焼入れを行うことにより、脱炭を防止しつつ、所望の強度を有する部品を得ることができる。前記焼入れにおける加熱は、任意の方法で行うことができるが、例えば、高周波加熱や通電加熱を用いることができる。
Ac3変態点(℃)=910-203(C1/2)-15.2Ni+44.7Si+104V+31.5Mo+13.1W-(30Mn+11Cr+20Cu-700P-400Al-120As-400Ti)…(5)
(上記(5)式における元素記号は、各元素の含有量(質量%)であり、当該元素が含まれていない場合にはゼロとする)
上記急速短時間加熱焼入れ後、任意に、靭性を向上させるための焼戻処理を施しても良い。焼戻処理における加熱温度(焼戻し温度)は、150~450℃とすることが好ましい。前記加熱温度が150℃未満では、所望の靭性を確保できなくなる場合がある。一方、前記加熱温度が450℃を超えると、硬さが低下し、所望の耐久性が確保できなくなる場合がある。
上記電縫溶接においては、溶接条件を変更することにより、電縫溶接部のボンド幅を表2、3に示す値に調整した。なお、ボンド幅は、得られた電縫溶接鋼管から電縫溶接部を含む組織観察用試験片を採取し、組織観察を行って求めた。前記組織観察用試験片は、電縫溶接鋼管の長手(管軸)方向に垂直な断面が観察面となるように切り出した。切り出された試験片の断面を研磨した。
研磨後の試験片の表面を、メタルフローエッチング液(5%ピクリン酸+界面活性剤)を用いて腐食した。その後、光学顕微鏡(倍率:400倍)を用いて、断面組織を観察した。該断面組織における偏析線が観察されない領域(層)の最大幅を測定し、ボンド幅とした。
研磨後の試験片の表面を、ナイタールエッチング液(5%硝酸アルコール)を用いて腐食した。その後、光学顕微鏡(倍率:400倍)を用いて、断面組織を観察した。該断面組織における明るく観察される領域(白色層)の最大幅を測定し、ボンド幅とした。
また、得られた電縫溶接鋼管(焼準前)のそれぞれについて、JIS G 0558「鋼の脱炭層深さ測定方法」に規定されている「顕微鏡による測定方法」に準じて、内側表層と外側表層の両者における全脱炭層の深さ測定した。測定は、電縫溶接鋼管を長手方向中心で切断し、その断面における脱炭層深さの最大値を採用した。また、前記測定においては、同様の方法でフェライト脱炭層の深さも測定した。測定結果を表2、3に示した。
次に、前記電縫溶接後の電縫溶接鋼管(電縫溶接まま)に対し、表2、3に示した条件で焼準を施した。前記焼準は、次の(1)~(3)の工程からなる。
(1)室温から最高加熱温度:T(℃)まで、平均加熱速度:5(℃/s)で加熱。
(2)前記最高加熱温度:T(℃)で所定の均熱時間、保持。
(3)室温まで、平均冷却速度:3(℃/s)で冷却。
得られた電縫溶接鋼管の電縫溶接部におけるC含有量を、EPMA測定の結果に基づいて求めた。測定位置は、鋼管の長手方向に垂直な、電縫溶接部を含む断面における、外表面から厚み方向に200μm(深さ200μm)の位置とした。前記測定は、以下の手順で行った。まず、電縫鋼管から長手方向に垂直な断面が測定位置となるように試料を切り出した。次いで、前記断面において、ボンド部を中心にして、円周方向にボンド幅+200μmの長さのラインでEPMA測定を行い、Cに由来するX線強度を測定した。次に、前記ラインのうち、ボンド部を中心に±ボンド幅×0.4の範囲におけるX線強度の平均値Aを求めた。さらに、前記ラインのうち、ボンド部の端から20μm離れた位置から80μm離れた位置までの範囲におけるX線強度の平均値Bを求めた。前記平均強度Bの測定位置は母材部にあたる。
また、得られた電縫溶接鋼管(焼準後、焼入れ前)のそれぞれについて、内側表層と外側表層の両者における全脱炭層深さおよびフェライト脱炭層深さを測定した。前記測定は、焼準前の脱炭層深さの測定と同様の方法で実施した。測定結果を表6、7に併記する。この結果より、本発明の条件を満たす方法で製造された電縫溶接鋼管においては、著しい脱炭は生じておらず、全脱炭層深さおよびフェライト脱炭層深さが低減できていることが分かる。
次に、上記焼準後の電縫溶接鋼管に、図2に示すヒートパターンで急速短時間加熱焼入れ処理を施した。すなわち、下記(1)~(3)の工程を順次実施した。
(1)室温から990℃まで、平均加熱速度:20℃/sで加熱。
(2)990℃から980℃まで、平均冷却速度:5℃/sで冷却(一次冷却)。
(3)980℃から室温まで、平均冷却速度:80℃/sで水冷(二次冷却)。
上記焼入れ処理後の電縫溶接鋼管のそれぞれについて、母材部におけるビッカース硬さ:Hv0、電縫溶接部におけるビッカース硬さ:Hv1を測定した。測定結果を表6、7に示した。測定法は、以下のとおりとした。
さらに、上記焼入れ後の電縫溶接鋼管に対し、表6、7に示した焼戻し温度で、20分間の焼戻しを施した。焼戻し後の電縫溶接鋼管についても、焼入れ後の電縫溶接鋼管と同様の方法で、電縫溶接部におけるビッカース硬さ:Hv0、および電縫溶接部におけるビッカース硬さ:Hv1を測定した。測定結果を表6、7に示す。
上記焼戻し後の電縫溶接鋼管から疲労試験用試験材(管軸方向長さ:250mm)を採取し、JISZ 2273に準拠した両振りのねじり疲労試験を行った。ねじり疲労試験の応力τは、鋼板No.A、B、E、F、G、I、およびJを用いた鋼管では380MPa、鋼板No.C、D、およびHを用いた鋼管では470MPaとした。ねじり疲労試験後に破断状況を観察し、電縫溶接部に沿った異常な割れ方を示した場合を×、それ以外の割れ方を示した場合を○として評価した。評価結果と、破断するまでの繰返し数:Nfを表6、7に示す。
Claims (9)
- 質量%で、
C :0.15~0.40%、
Si:0.05~0.50%、
Mn:0.30~2.00%、
Al:0.01~0.10%、
Ti:0.001~0.04%、
B :0.0005~0.0050%、および
N :0.0010~0.0100%、を含み、
残部がFeおよび不可避的不純物からなり、かつ、
Ti含有量とN含有量とが下記(1)式を満足する成分組成を有する鋼板を母材とし、
ボンド幅が40×10-6m以上、120×10-6m以下である電縫溶接部を有する電縫溶接鋼管であって、
前記電縫溶接部の最低C含有量:C1(質量%)と前記鋼板のC含有量:C0(質量%)との差、C0-C1が0.05質量%以下であり、かつ、
前記電縫溶接鋼管の内側表層と外側表層における全脱炭層の深さが、それぞれ50×10-6m以下である、電縫溶接鋼管。
(N/14)<(Ti/47.9)…(1)
ここで、上記(1)式におけるNはN含有量(質量%)、TiはTi含有量(質量%)を、それぞれ示す - 前記成分組成が、質量%で、
Cr:1.0%以下、
Mo:1.0%以下、
W :1.0%以下、
Ni:1.0%以下、および
Cu:1.0%以下からなる群より選択される1または2以上をさらに含有する、請求項1に記載の電縫溶接鋼管。 - 前記成分組成が、質量%で、
Nb:0.2%以下、および
V :0.2%以下の一方または両方をさらに含有する、請求項1または2に記載の電縫溶接鋼管。 - 前記成分組成が、質量%で、
Ca:0.0050%以下をさらに含有する、請求項1~3のいずれか一項に記載の電縫溶接鋼管。 - 質量%で、
C :0.15~0.40%、
Si:0.05~0.50%、
Mn:0.30~2.00%、
Al:0.01~0.10%、
Ti:0.001~0.04%、
B :0.0005~0.0050%、および
N :0.0010~0.0100%、を含み、
残部がFeおよび不可避的不純物からなり、かつ、
Ti含有量とN含有量とが下記(1)式を満足する成分組成を有する鋼板を電縫溶接して、ボンド幅が40×10-6m以上、120×10-6m以下である電縫溶接部を有し、内側表層と外側表層における全脱炭層の深さが、それぞれ50×10-6m以下である電縫溶接鋼管とし、
次いで、下記(2)式で求められる前記電縫溶接部の最低C含有量の計算値:C* 1(質量%)と前記鋼板のC含有量:C0(質量%)との差、C0-C* 1が0.05質量%以下となる条件で、かつ、
CO、CO2、H2、H2O、ならびにCおよびFeに対して中性なガスからなり、下記(3)および(4)式を満たす雰囲気で焼準する、電縫溶接鋼管の製造方法。
(N/14)<(Ti/47.9)…(1)
ここで、上記(1)式におけるNはN含有量(質量%)、TiはTi含有量(質量%)を、それぞれ示す
C* 1=C0-(C0-0.09)erf(h’)…(2)
ここで、
C0:鋼板のC含有量(質量%)
h’=h/(Dt)1/2
h(m):ボンド幅/2
D(m2/s)=D0 exp(-Q/RT)
D0=4.7×10-5 m2/s
Q=155 kJ/mol・K
R=8.31 J/mol・K、
T:前記焼準における最高加熱温度(K)
t(s):前記焼準において(T-50K)からTの間の温度域に保持されている時間
(PCO)2/PCO2≧K・aγ C…(3)
PH2・PCO/PH2O≧K’・aγ C…(4)
ここで、
log(K)=-9460/T-1.26log(T)+13.52
K’=exp[-(131300-134.3T)/RT]
aC γ=xC γ・exp[(GC γ+ΩFeC γ-GC gr)・RT]・exp[(-2ΩFeC γ・xC γ+ΣWMC γ・xM γ)/RT]
GC γ-GC gr=73744J/mol
2ΩFeC γ=-51956J/mol
WMnC γ=-41900J/mol
WSiC γ=+125700J/mol
WCrC γ=-104750/mol
PCO(atm):炉内雰囲気中のCOの分圧
PCO2(atm):炉内雰囲気中のCO2の分圧
PH2(atm):炉内雰囲気中のH2の分圧
PH2O(atm):炉内雰囲気中のH2Oの分圧
R=8.31 J/mol・K
T:前記焼準における最高加熱温度(K)
aC γ:オーステナイト相中におけるCの活量
xC γ:オーステナイト相中のCのモル分率
xSi γ:オーステナイト相中のSiのモル分率
xMn γ:オーステナイト相中のMnのモル分率
xCr γ:オーステナイト相中のCrのモル分率
GC γ:オーステナイト相中におけるCの自由エネルギー
GC gr:グラファイト中におけるCの自由エネルギー - 質量%で、
C :0.15~0.40%、
Si:0.05~0.50%、
Mn:0.30~2.00%、
Al:0.01~0.10%、
Ti:0.001~0.04%、
B :0.0005~0.0050%、および
N :0.0010~0.0100%、を含み、
残部がFeおよび不可避的不純物からなり、かつ、
Ti含有量とN含有量とが下記(1)式を満足する成分組成を有する鋼板を電縫溶接して、ボンド幅が40×10-6m以上、120×10-6m以下である電縫溶接部を有し、内側表層と外側表層における全脱炭層の深さが、それぞれ50×10-6m以下である電縫溶接鋼管とし、
次いで、下記(2)式で求められる前記電縫溶接部の最低C含有量の計算値:C* 1(質量%)と前記鋼板のC含有量:C0(質量%)との差、C0-C* 1が0.05質量%以下となる条件で、かつ、
炉内雰囲気中のモル分率でH2:0~10%、O2:80ppm以下ならびに残部のH2OおよびN2からなり、露点が0℃以下である雰囲気で焼準する、電縫溶接鋼管の製造方法。
(N/14)<(Ti/47.9)…(1)
ここで、上記(1)式におけるNはN含有量(質量%)、TiはTi含有量(質量%)を、それぞれ示す
C* 1=C0-(C0-0.09)erf(h’)…(2)
ここで、
C0:鋼板のC含有量(質量%)
h’=h/(Dt)1/2
h(m):ボンド幅/2
D(m2/s)=D0 exp(-Q/RT)
D0=4.7×10-5 m2/s
Q=155 kJ/mol・K
R=8.31 J/mol・K、
T:前記焼準における最高加熱温度(K)
t(s):前記焼準において(T-50K)からTの間の温度域に保持されている時間 - 前記成分組成が、質量%で、
Cr:1.0%以下、
Mo:1.0%以下、
W :1.0%以下、
Ni:1.0%以下、および
Cu:1.0%以下からなる群より選択される1または2以上をさらに含有する、請求項5または6に記載の電縫溶接鋼管の製造方法。 - 前記成分組成が、質量%で、
Nb:0.2%以下、および
V :0.2%以下の一方または両方をさらに含有する、請求項5~7のいずれか一項に記載の電縫溶接鋼管の製造方法。 - 前記成分組成が、質量%で、
Ca:0.0050%以下をさらに含有する、請求項5~8のいずれか一項に記載の電縫溶接鋼管の製造方法。
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WO2020129337A1 (ja) * | 2018-12-19 | 2020-06-25 | Jfeスチール株式会社 | 電縫鋼管 |
TWI697563B (zh) * | 2019-09-26 | 2020-07-01 | 中國鋼鐵股份有限公司 | 鋼胚加熱爐及抑制鋼胚表面脫碳層之厚度增加的方法 |
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WO2022065223A1 (ja) * | 2020-09-24 | 2022-03-31 | Ntn株式会社 | ころ軸受用溶接保持器、保持器付きころ、溶融接合部の判別方法、およびころ軸受用溶接保持器の品質確認方法 |
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JP7472826B2 (ja) | 2021-03-03 | 2024-04-23 | Jfeスチール株式会社 | 電縫溶接鋼管およびその製造方法 |
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