JP3938052B2 - ERW steel pipe with excellent plating adhesion and workability and its manufacturing method - Google Patents

Description

【００８０】
【表２】

【００８１】
【発明の効果】
以上詳細に説明したように、本発明により、めっき付着性に優れ、かつ鋼管の加工性に優れた電縫鋼管を、高い生産性で製造することができる。
【００８２】
かかる効果を有する本発明の意義は、実際上からは、極めて著しい。
【図面の簡単な説明】
【図１】実施形態における電縫鋼管の製造工程の一例を模式的に示す説明図である。
【図２】本発明にかかる鋼管の表層の模式的拡大断面図である。
【符号の説明】
１、２：帯鋼
３：帯鋼加熱炉
４：成形および誘導加熱溶接装置
５：管再加熱装置
６：絞り圧延機
７：管切断装置
８：電縫鋼管[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric resistance welded steel pipe and a method for manufacturing the same, and more specifically, a welded steel pipe excellent in plating adhesion and excellent in formability and workability such as bending of a steel pipe, and manufactured at a lower cost. On how to do.
[0002]
[Prior art]
As is well known, forged steel pipes and ERW steel pipes are generally used as general pipe steel pipes, but in many cases they are used after hot dip galvanizing treatment for corrosion protection. When this hot-dip galvanized steel pipe (hereinafter simply referred to as “plated steel pipe”) is piped, processing such as bending or spreading to push the ends of the pipe is required.
[0003]
Forged steel pipes have a high base metal heating temperature, so it is difficult to completely remove the surface scale at the butt end face during solid-phase bonding, resulting in weld defects such as scale biting into the joint. The bonding strength is often inferior to that of the base material. For this reason, the forged steel pipe has a problem that the reliability of the pipe joint processing such as bending and spreading and the surface property of the pipe joint portion are inferior to those of the electric resistance welded pipe.
[0004]
Further, a general cold-worked electric resistance welded steel pipe has excellent surface properties. However, when a plated steel pipe is used, there is a problem that the surface plating is easily peeled off during processing. For this reason, in addition to the workability of the steel pipe itself at the time of pipe joint processing, an electric resistance steel pipe excellent in plating adhesion has been desired.
[0005]
[Problems to be solved by the invention]
In recent years, there has been an increasing number of cases where strong processing such as piping with a radius of 1 DR × 180 ° bending (for example, for refrigerant) and piping 90 ° widening at the end of the tube is performed. In contrast to such strong processing, conventional forged steel pipes have poor reliability in strong bending and joint processing due to scale biting into the welded portion and the like.
[0006]
Further, in the cold-worked ERW steel pipe, the steel pipe surface is smooth, and in the processing such as strong bending processing, plating peeling occurs, and it is necessary to strengthen the rust prevention after processing such as tape winding on the peeling portion.
[0007]
An object of the present invention is to provide a steel pipe that can solve the above-mentioned problems of the prior art and meet the needs of strong machining, and a method for manufacturing the steel pipe.
Moreover, the subject of this invention is providing the steel pipe which makes it possible to perform the plating which does not produce peeling also with respect to the above strong processes, and its manufacturing method.
[0008]
[Means for Solving the Problems]
As a result of repeated studies to solve the above-mentioned problems, the present inventors focused on the superiority of ERW steel pipes over forged steel pipes, and the steel pipe surface roughness, outermost surface crystal grain size, components, heat treatment conditions, By maintaining the plating conditions at the specified conditions, adhesion to galvanized steel pipes is ensured.For example, when the bending radius is 50 mm or less, 180 ° bending strength processing and pipe end surface 90 ° expansion processing cause plating peeling. Knowing that no hot dip galvanized steel pipe can be produced, the present invention has been completed.
[0009]
That is, the present inventors' knowledge is as follows.
(1) Continuously heating, forming, electric resistance welding, reheating and drawing rolling to the steel strip, and manufacturing the ERW steel pipe by hot finishing, depending on the material composition, Heating temperature of 1300 ℃ or less, Ae_ThreeMore than the transformation point, and the drawing rolling end temperature is Ae_ThreeMore than the transformation point or due to material composition limitation, (Ae_ThreeThe surface roughness Ra of the inner and outer surfaces of the ERW steel pipe is reduced to 0.5 to 5 μm by setting the cooling rate at the time of drawing rolling in the range of 3 ° C./second to 100 ° C./second. The average particle diameter of the outermost particle phase of the steel pipe surface layer can be kept at 20 μm or less, and the workability after plating can be improved.
[0010]
(2) Similarly, for ERW steel pipes made of alloy steel for special applications such as corrosion resistant environments, the heating temperature of the material is 1300 ° C or less, Ae_ThreeMore than the transformation point, and the drawing rolling end temperature is Ae_Three(Ae_Three(Transformation point −50 ° C.) In addition, the surface rate Ra of the inner and outer surfaces of the ERW steel pipe is reduced to 0.5 to 5 μm by adjusting the cooling rate during drawing rolling to the range of 3 ° C./second to 100 ° C./second. And the average particle diameter of the outermost particle phase of a steel pipe surface layer can be kept at 20 micrometers or less, and the workability after plating can be improved.
[0011]
(3) Furthermore, the heating temperature of the steel strip is Ae_ThreeEven if it is less than the transformation point, the steel pipe before drawing rolling is reduced to 1300 ° C or less by reheating performed after ERW welding._ThreeHeat above the transformation point, and further set the end temperature of drawing rolling to Ae_Three(Ae)_ThreeThe surface roughness Ra of the inner and outer surfaces of the ERW steel pipe is reduced to 0.5 to 5 μm by setting the cooling rate at the time of drawing rolling in the range of 3 ° C./sec to 100 ° C./sec. And the average particle diameter of the outermost particle phase of a steel pipe surface layer can be kept at 20 micrometers or less, and the workability after plating can be improved.
[0012]
(4) The ERW steel pipes obtained in (1) to (3) above are pickled and fluxed, heated to below 80 to 100 ° C., and evaporated to remove moisture from the flux. By using and plating under the conditions of Al content of 0.001 to 0.05%, zinc plating bath temperature of 440 to 485 ° C and immersion time of 60 seconds or less, the deposited zinc film thickness was suppressed to 50 μm or less, and excellent workability was achieved. Plating can be applied.
[0013]
The pipe plating apparatus used in the present invention is, for example, a plating tank, a storage part that pivotally supports and rotates an ERW steel pipe inside the plating tank, and supplies the ERW steel pipe to the storage part. A pipe feeding mechanism, a transport mechanism for transporting the electric resistance steel pipe accommodated in the accommodating portion in an arc shape inside the plating tank, and the electric resistance steel pipe disposed inside the plating tank after the completion of plating. A pipe carry-out mechanism that adsorbs a roller and draws it out of the plating tank by the rotation of the roller.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of an electric resistance welded steel pipe and a method for manufacturing the same according to the present invention will be described in detail with reference to the accompanying drawings. Unless otherwise specified in this specification, “%” indicating a steel composition is indicated by “mass%”.
[0015]
  The steel composition in the present invention is as follows. In the case of such a steel composition, preferably the drawing rolling finish temperature is Ae._ThreeAbove the transformation point.
[0016]
  That is, in mass%,
C: 0.0002 to 0.50%, Si: 0.003 to0.28 %, Mn: 0.003 to0.58 %, Al: 0.002 ~0.031%, P: 0.15% or less, S: 0.03% or less, N: 0.01% or less, or further, including one or more of the following first to fourth groups ,
First group: B: 0.0002 to 0.01%,
Second group: 0.005 to 1.0% in total of one or more of Ti, Nb, V and Zr,
Third group: 0.005 to 3.0% in total of one or more of Cr, Mo, Cu and Ni,
Group 4: One or more of Ca: 0.0001 to 0.005% and REM (rare earth element): 0.0001 to 0.2%, with the balance being Fe and inevitable impurities.
[0017]
Here, the reason for limiting the above-described steel composition in the present invention will be described.
C: 0.0002 ~ 0.50 %
If C is less than 0.0002%, the crystal grains become extremely coarse, and high formability cannot be stably obtained, and cracks and surface roughness tend to occur during the formation of a steel pipe. Moreover, the plating adhesion is also reduced. Furthermore, in order to reduce the C content to less than 0.0002%, a special steelmaking technique is required, so the cost increases. If the content exceeds 0.50%, the strength will increase excessively, ductility and hot workability will decrease, defects will easily occur in the welded joints, the welding situation will become unstable, and the resistance of the ERW welded parts will be reduced. Deteriorates groove corrosivity. Therefore, in this embodiment, the C content is limited to 0.0002% or more and 0.50% or less, preferably 0.01% or more and 0.30% or less, and more preferably 0.03% or more and 0.25% or less. Furthermore, by setting it to 0.2% or less, preferably 0.03% or more and 0.2% or less, the finish temperature range of drawing rolling can be reduced to (Ae_Three−50 ° C) and above, it is possible to expand the appropriate rolling temperature range.
[0018]
Si: 0.003 ~0.28 %Less than
Si has an action of improving the strength of steel without impairing workability. Further, it has the effect of promoting the generation of ferrite and increasing the amount of ferrite. In order to exhibit such an effect, it is necessary to contain at least 0.003%.
[0019]
Moreover, although it acts as a deoxidation element by containing, there exists an effect of the alloy layer growth suppression of plating, and 3.0% or less is added. Preferably, 0.15% or more and 0.25% or less are effective.. Si: 0.01-0.28 %By limiting the lower limit of the finish rolling temperature of Ae to Ae₃ From point above (Ae₃−50 ° C.) It becomes possible to enlarge to the above. Hereinafter, it is simply referred to as the effect of expanding the rolling temperature.
[0020]
Mn: 0.003 to0.58 %
Mn has the effect of preventing hot brittleness of the steel due to S. Furthermore, it also has the effect of strengthening the solid solution. In order to exhibit such an effect, it is necessary to contain at least 0.003%. However, if the content exceeds 3.0%, the weldability and ductility are deteriorated, and the periphery of MnS, which is a nonmetallic inclusion, is easily dissolved. Grooved corrosiveness deteriorates.In the present invention, the upper limit is set to 0.58% in which the effect has been confirmed in the examples.From the viewpoint of harmonizing strength and elongation, the lower limit value of the Mn content is 0.05%.GoodMore preferably, 0.20% or moresois there. In addition, the effect of the above-mentioned rolling temperature expansion is seen by Mn: 0.01-3.0%.
[0021]
Al: 0.002 to0.031%
Al also acts as a deoxidizing element by containing 0.002% or more, but if the Al content exceeds 2.00%, the amount of inclusions increases and the cleanliness of the steel decreases and the corrosion resistance decreases. Invite.In the present invention, the upper limit is set to 0.031% in which the effect is confirmed in the examples.. Preferably, 0.015% or lessAboveYes, more preferably 0.015% or moresois there. The effect of extending the rolling temperature is seen at Al: 0.01 to 2.00%.
[0022]
P: 0.15 %Less than
P is an unavoidable impurity, and segregates at the grain boundaries to deteriorate both toughness and groove-like corrosion resistance. However, since extreme reduction of P is accompanied by a corresponding increase in cost, the P content is set to 0.15% or less in the present embodiment. Preferably it is 0.04% or less, More preferably, it is 0.02% or less. P: The effect of expanding the rolling temperature is seen at 0.1% or less.
[0023]
S: 0.03 %Less than
S is an unavoidable impurity, and since it produces sulfides and degrades both the cleanliness and the groove-like corrosion resistance of steel, it is desirable that its content be small. However, since extreme reduction of S is accompanied by a corresponding increase in cost, in this embodiment, the upper limit value of the S content is preferably 0.03%, more preferably 0.01% or less.
[0024]
N: 0.01 %Less than
N is a steel strengthening element and is an unavoidable impurity. Although the amount usually contained as an impurity is about 0.005%, the content up to 0.01% is allowed without any harmful effects. Therefore, in the present embodiment, the N content is preferably limited to 0.01% or less, more preferably 0.004% or less.
[0025]
These elements are the basic components of the electric resistance welded steel pipe according to the present embodiment. By adding at least one of the elements described below as an optional additive element to this basic component, even more excellent groove-like corrosion resistance It is possible to obtain an electric resistance welded steel pipe having both properties and other characteristics. Therefore, these optional additive elements will be described below.
[0026]
In the present invention, the steel composition may further include one or more of the following first group to fourth group.
First group: B: 0.0002 to 0.01%,
Second group: 0.005 to 1.0% in total of one or more of Ti, Nb, V and Zr,
Group 3: One or more of Cr, Mo, Cu and Ni in total 0.005 to 3.0%,
Group 4: Any one or more elements of Ca: 0.0001 to 0.005% and REM (rare earth element): 0.0001 to 0.2%.
[0027]
B: 0.0002 ~ 0.010 %
Since B has the effect of enhancing the hardenability of the steel, it may be utilized when controlling the crystal grain size of the ferrite phase during the cooling process. If the B content is less than 0.0002%, it is difficult to obtain the effect. However, if the B content exceeds 0.010%, both weldability and toughness deteriorate. Therefore, when B is added, its content is preferably limited to 0.010% or less.
[0028]
Ti , Nb , V and Zr One or more of them in total 0.005 ~ 1 .0 %
Ti, Nb, V, and Zr have the effect of fixing the solid solution C, solid solution N, and solid solution S contained in the steel as precipitates, making them harmless, and without particularly reducing the ductility and deep drawability. Has the effect of increasing the strength of steel. Therefore, in order to improve the deep drawability of the steel, one or more of Ti Nb, V and Zr may be contained. However, if the total content is less than 0.005%, it is difficult to obtain such an effect. When the total exceeds 1.0%, the above effects are saturated and, on the contrary, ductility and deep drawability are lowered. Therefore, when adding one or more of Nb, V, Zr and Ti, it is desirable to limit the total content to 1.0% or less. The lower limit is not particularly defined, but it is preferably at least one or more and a total of 0.005% or more.
[0029]
Cr , Mo , Cu and Ni In total one or more of 0.005 ~ 3.0 %
Since Cr, Mo, Cu and Ni have an effect of improving hardenability, it becomes easy to control the crystal grain size and area ratio of ferrite and the remaining phase in the cooling process. In addition to enhancing the hardenability, Cu also has the effect of enhancing corrosion resistance.
[0030]
As described above, one or more of Cr, Mo, Cu, and Ni may be contained in a total amount of 0.005 to 3.0%. When these contents exceed 3.0% in total, the above effect is saturated and the ductility is reduced. Therefore, when adding one or more of Cr, Mo, Cu and Ni, it is desirable to limit the total content to 3.0% or less.
[0031]
The lower limit is not particularly defined, but if the content of at least one of these is less than 0.005% in total, it is difficult to obtain the quenching effect. Therefore, the lower limit is preferably 0.005% in total.
[0032]
Ca: 0.0001 ~ 0.005 %,and REM ( Rare earth elements ): 0.0001 ~ 0.2 %
Ca and REM (rare earth elements) are elements of 0.0001% or more, respectively, and have the effect of improving the workability by controlling the form of inclusions, and improve the resistance to groove corrosion of the ERW weld. However, if the Ca content exceeds 0.005% or REM exceeds 0.2%, the cleanliness of the steel decreases and the ductility deteriorates. Therefore, when Ca and / or REM is added, its content is desirably limited to 0.005% or less and 0.2% or less, respectively.
[0033]
In another aspect of the present invention, in order to obtain the effect of expanding the rolling temperature, the steel composition of the steel strip is further limited as follows, in mass%,
C: 0.2% or less, Si: 0.01 to0.28 %,Mn: 0.01 ~0.58 %, Al: 0.01-0.031%, P: 0.1% or less, S: 0.03% or less, N: 0.01% or less, or
In addition, one or more of the following first to fourth groups,
First group: B: 0.01% or less,
Second group: 1.0% or less in total of at least one of Ti, Nb, V and Zr,
Third group: one or more of Cr, Mo, Cu and Ni in a total of 3.0% or less,
Group 4: Ca: 0.005% or less, and REM (rare earth element): containing one or more of 0.2% or less,
The balance is Fe and inevitable impurities.
[0034]
In this embodiment, the finishing temperature in the drawing rolling is (Ae_Three(Transformation point −50 ° C.)
Next, the manufacturing method of the ERW steel pipe concerning this invention is demonstrated.
[0035]
Drawing 1 is an explanatory view showing typically an example of manufacturing process 9 of ERW steel pipe 8 in this embodiment.
In the present embodiment, the ERW steel pipe 8 is manufactured by hot finishing or warm finishing by continuously heating, forming, ERW welding, reheating, drawing rolling, cutting, and the like on the steel strip 2. The Hereinafter, the manufacturing process 9 of this embodiment will be described with reference to FIG.
[0036]
(Heating process)
The band steel 2 is a pipe making material of the electric resistance welded steel pipe 8, and the composition thereof may be set as appropriate according to the performance required for the electric resistance welded steel pipe 8, and is not limited to a specific composition. .
[0037]
In FIG. 1, prior to forming the steel strip 2, the steel strip 2 discharged from the uncoiler 1 is charged into the steel strip heating furnace 3 to heat the steel strip 2.
The heating of the steel strip 2 suppresses as much as possible the temperature difference that is inevitably generated between the welding edge and the base material portion in the vicinity thereof during the electric welding performed by the forming and induction heating welding device 4 later. This is done to homogenize the structure by preventing the generation of heat-affected hardened structures.
[0038]
The heating of the steel strip 2 may be performed using the steel strip heating furnace 3 as in the present embodiment, but is not limited to this, for example, heating using an induction coil or resistance due to energization Heating using heating may be used.
[0039]
If the heating temperature of the steel strip 2 by the steel strip heating furnace 3 is less than 400 ° C, the deformation resistance during the forming of the steel strip 2 increases, and roll scratches due to biting from the corner of the forming roll occur on the surface of the steel pipe. It becomes easier and undesirable.
[0040]
The heating temperature of the steel strip 2 is Ae_ThreeIf the temperature is less than the transformation point, the structure of the steel strip 2 after heating does not become uniform austenite grains, local phase transformation occurs during the subsequent drawing rolling, and the grain size of the final product is uneven. Become. For this reason, remarkable unevenness of the structure particle size tends to occur particularly in the heat affected zone in the vicinity of the ERW weld. In this case, the welding speed is reduced and the time for the reheating treatment to be performed later is lengthened._ThreeBy raising the temperature above the transformation point, it is possible to prevent the structure non-uniformity, but the productivity is lowered.
[0041]
Therefore, in the present embodiment, it is desirable that the steel strip 2 is heated to 400 ° C. or higher. In order to suppress the decrease in productivity, Ae_ThreeIt is more desirable to heat above the transformation point.
On the other hand, if the heating temperature of the steel strip 2 exceeds 1300 ° C., the austenite grains become coarse, and even if strong processing is performed by the subsequent drawing rolling, the crystal grains of the final product become coarse and sufficient strength cannot be obtained. Scale of the surface of the steel strip 2 is likely to occur, and the surface properties of the steel pipe after the drawing rolling are deteriorated.
[0042]
Therefore, in this embodiment, the heating of the steel strip 2 is Ae._ThreePerform in the temperature range from the transformation point to 1300 ° C.
(Molding process)
In FIG. 1, the steel strip 2 heated to the above temperature range by the steel strip heating furnace 3 is continuously formed into an open pipe by a plurality of forming rolls (not shown) provided in the forming and induction heating welding device 4. Molded.
[0043]
Since these forming rolls are well-known and commonly used, the arrangement, roll schedule, and the like may be appropriately diverted / remodeled for normal hot-water-welded steel pipes and the like, so further explanation will be omitted. .
[0044]
(Electronic welding process)
The open tube is locally heated to the melting point with both edge portions as targets by an induction heating coil (not shown) provided in the forming and induction heating welding device 4.
[0045]
It is desirable that the induction heating of both edge portions be performed in a state where the entire cross section of the open tube is equal to or lower than the steel strip heating temperature and (Curie point −50 ° C.) or higher. If the steel strip temperature during ERW welding is less than (Curie point –50 ° C), the efficiency of induction heating for ERW welding will be greatly reduced, and it will be necessary to reduce the welding speed, hindering productivity. It is because there is a possibility of doing.
[0046]
Since these induction heating coils may use well-known and conventional ones, description regarding the induction heating coils is omitted.
The open pipe whose both edge portions are locally heated to the melting point is abutted and welded by a squeeze roll (not shown) provided in the forming and induction heating welding apparatus 4 and becomes a mother pipe for subsequent drawing rolling. Made of steel pipe.
[0047]
Moreover, the melt bead discharged | emitted in the case of abutting welding has generate | occur | produced in the inner and outer surface of the steel pipe welded by the squeeze roll. For this reason, it is desirable to remove the generated molten bead at this stage.
[0048]
The method for removing the molten bead is not a specific means. For example, the use of a well-known and commonly used cutting removal method is exemplified. This cutting and removal method is a fixed cutting tool method used for ordinary ERW steel pipes or a rotating cutting tool method to prevent hot tool wear, and the cutting tool pressing force can be adjusted with the built-in hydraulic cylinder. Thus, it is possible to use a well-known and commonly used cutting removal method such as a method capable of automatically responding to a change in the thickness of the electric resistance welded steel pipe.
[0049]
(Reheating process, drawing rolling process)
The steel pipe from which the molten bead generated on the inner and outer surfaces has been removed is used for the purpose of equalizing the temperature difference between the welded part and the surrounding base metal part and adjusting the rolling temperature in the subsequent drawing rolling. Heating temperature rise or soaking is performed by the heating device 5.
[0050]
The reheating method is not limited to a specific heating means as long as it is a heating means capable of soaking the tube. For example, any of a gas combustion type continuous heating furnace, an induction heating apparatus for pipes, an electric heating system, or a combination thereof can be used.
[0051]
The mother pipe that has been heat-treated so that the temperature distribution in the circumferential direction of the pipe becomes substantially uniform by the pipe reheating device 5 is drawn to a predetermined outer diameter by the drawing mill 6 to obtain a final product.
[0052]
In the present embodiment, the rolling temperature of the drawing by the drawing mill 6 is the rolling end temperature Ae._ThreeBy setting the temperature above the transformation point or limiting the material composition (Ae_Three(Transformation point −50 ° C.) or higher, preferably, the starting temperature of drawing rolling is set to 1300 ° C. or lower.
[0053]
Thereby, it becomes possible to finish a rolling process in an austenite area | region, and can make the steel pipe whole cross section including a welding part into a substantially uniform structure | tissue.
That is, the rolling end temperature is Ae_ThreeLess than the transformation point or by limiting the material composition (Ae_ThreeIf the temperature is lower than the transformation point −50 ° C., transformation from austenite occurs during drawing rolling, so the crystal grains between the microstructure transformed after undergoing processing in the austenite region and the microstructure subjected to processing after transformation. A difference in diameter is produced. For this reason, the structure of the final product is a mixed grain structure of coarse grains and fine grains. When the structure on the surface of the steel pipe becomes coarse, the crystal grain interface area becomes small, and when plating is performed, the unevenness becomes small, so that plating peeling tends to occur during processing. In addition, when the underground piping or the like is in a wet environment or a corrosive environment, a local battery is generated due to this structural difference, and the groove-like corrosion resistance is deteriorated.
[0054]
In particular, since the ERW weld is once heated to the melting temperature (1400-1500 ° C.) during welding, austenite grains around the weld become coarse. For this reason, when this portion passes through the transformation point without undergoing rolling, it becomes coarse crystal grains, and the difference in structure with the base material portion is further increased.
[0055]
Therefore, in this embodiment, the end temperature of the drawing rolling, that is, the finishing temperature is Ae._ThreeBy exceeding the transformation point or limiting the material composition (Ae_Three(Transformation point −50 ° C.)
[0056]
By limiting the material composition, the drawing rolling end temperature, that is, the finishing temperature is set to (Ae_Three(Transformation point −50 ° C.) This is because the temperature range in the two-phase region is wide when the amount of C is small._ThreeEven when the temperature drops to the transformation point (-50 ° C), the volume ratio of transformation from austenite to ferrite is low, and even if this is processed, the volume ratio of processed ferrite is small, and most ferrite has austenite. This is because the material is transformed after being processed. Conversely, when the amount of C is large, the temperature range in the two-phase region is narrow, so (Ae_ThreeWhen the temperature drops to the transformation point −50 ° C.), the volume fraction transformed from austenite to ferrite at that time becomes considerably large, and when this is processed, the volume fraction of the processed ferrite increases, and from the processed austenite Since the volume fraction of polygonal ferrite produced by transformation is reduced, the structure of the final product becomes a mixed grain structure of coarse grains and fine grains, and the workability and the like are lowered.
[0057]
Therefore, when the material composition is limited to the components shown in claim 6, the drawing rolling end temperature is set to (Ae_Three(Transformation point -50 ℃)
Moreover, when the finish temperature of drawing rolling exceeds 1000 degreeC, the crystal grain refinement effect by drawing processing will reduce and the crystal grain of a final product will coarsen. When the structure on the surface of the steel pipe becomes coarse, the crystal grain interface area becomes small, and when plating is performed, the unevenness becomes small, so that plating peeling tends to occur during processing. In addition, when the crystal grains become coarse, sufficient strength cannot be obtained, so that the finish temperature of the drawing rolling is desirably 1000 ° C. or less.
[0058]
On the other hand, if the start temperature of drawing rolling is not higher than the end temperature by 50 ° C or more, the end temperature is Ae_ThreeA transformation point or higher or material composition limitation (Ae_Three(Transformation point -50 ° C) Even in the above case, the structure difference between the welded part once austenite grains coarsened by electro-welding and the surrounding base metal part is not completely eliminated. A difference is produced, and the structure of the final product becomes a mixed grain structure of coarse grains and fine grains. When the structure on the surface of the steel pipe becomes coarse, the crystal grain interface area becomes small, and when plating is performed, the unevenness becomes small, so that plating peeling tends to occur during processing. Moreover, due to the mixed grain structure, the groove-like corrosion resistance deteriorates.
[0059]
Therefore, in this embodiment, the end temperature of the drawing rolling is Ae_ThreeA transformation point or higher or material composition limitation (Ae_Three(Transformation point −50 ° C.) or higher, and the starting temperature of drawing rolling is higher by 50 ° C. than the end temperature.
[0060]
Moreover, it is preferable that the upper limit value of the starting temperature of the drawing rolling is 1300 ° C. or less. Similar to the heating of the strip steel, the austenite grains become coarse when the starting temperature exceeds 1300 ° C., and the crystal grains of the final product become coarse even if strong processing is performed by drawing. When the structure on the surface of the steel pipe becomes coarse, the crystal grain interface area becomes small, and when plating is performed, the unevenness becomes small, so that plating peeling tends to occur during processing. Further, when the crystal grains become coarse, sufficient strength cannot be obtained, and the surface scale of the steel pipe is liable to be generated, and the normal surface of the steel pipe after drawing rolling may be deteriorated.
[0061]
Furthermore, the heating temperature of the steel strip before ERW welding is Ae_ThreeBelow the transformation point, more preferably 400 ° C or higher Ae_ThreeIf the temperature is below the transformation point, the heating temperature is 1300 ° C or less in the reheating process of the steel pipe, Ae_ThreeAbove the transformation point.
[0062]
The processing rate k in the drawing rolling is exemplified to be 20% or more and 90% or less from the viewpoint of crystal grain refinement by introducing processing strain. The processing rate k is the outer diameter of the steel pipe before drawing rolling.₁, Wall thickness₁And the outer diameter of the final product is D₂, Wall thickness₂Then, K = {1-t₂(D₂−t₂) / T₁(D₁−t₁)} × 100 (%).
[0063]
When the cooling rate during drawing rolling is lower than 3 ° C./second, scale generation during drawing becomes remarkable, Ra ≧ 5 μm, the amount of plating increases, and local cracks are likely to occur during processing. Become. On the other hand, when the cooling rate is 100 ° C./second or more, the structure of the welded portion becomes non-uniform, and the workability as a steel pipe deteriorates. Therefore, the cooling rate at the time of drawing rolling shall be 3-100 degrees C / sec.
[0064]
(Cutting process)
The steel pipe that has been subjected to the drawing and rolling by the drawing mill 6 is cut into a predetermined length by the pipe cutting device 7 to form an electric-welded steel pipe 8.
[0065]
The electric resistance welded steel pipe 8 manufactured in this way is further transported to a cooling bed (not shown) after that and allowed to cool until the transformation is completely completed. And you may water-cool to the temperature (room temperature) suitable for handling.
[0066]
(Electric welded steel pipe 8 obtained)
In the present embodiment, the electric resistance welded steel pipe 8 is manufactured in this way.
In the electric resistance welded steel pipe 8 according to the present invention, the surface roughness of the inner and outer surfaces of the steel pipe is 0.5 to 5.00 μm in Ra, and the outermost particle layer on the surface of the steel pipe, that is, from the outermost surface of the steel pipe to the second layer. The average crystal grain (not including the second layer) is 20 μm or less.
[0067]
Here, the surface roughness of the inner and outer surfaces of the steel pipe is measured according to JIS B0601 by measuring Ra at five appropriate locations on the inner and outer surfaces of the steel pipe (manufacturer: Mitutoyo, product number: SURF TEST SV-600) and taking the average. It is a thing.
[0068]
Further, “average particle diameter of the outermost particle phase of the steel pipe surface layer”, that is, the average grain size of the outermost surface of the steel pipe from the first layer to the second layer (not including the second layer) as shown in FIG. That is, the average value of the crystal particle diameters measured in the cross section.
[0069]
Specifically, the crystal grain size at this time is the cross-section perpendicular to the longitudinal direction of the steel pipe using an optical microscope (manufacturer: Nikon, product number: OPTI PHOTO). And the average diameter was determined.
[0070]
According to the present invention, the surface roughness of the inner and outer surfaces of the steel pipe measured in this way is Ra: 0.5 to 5.00 μm, and the average particle diameter of the outermost particle layer of the steel pipe surface layer is 20 μm or less. That is, an alloy layer development area increases and a plating layer stronger in workability can be obtained due to the unevenness effect. When only one of the inner and outer surfaces satisfies the above-described surface roughness, a plated layer with higher workability can be obtained on the satisfied surface.
[0071]
(Plating process)
Regarding the plating conditions, the ERW steel pipe obtained by the above-described manufacturing method is subjected to pickling and flux treatment, heated to 80 ° C. or more and less than 100 ° C., and the moisture in the flux is evaporated. A pipe supply mechanism for supplying an electric resistance welded steel pipe to a tank and a receiving part that rotates and is pivotally supported inside the plating tank, and after being conveyed in an arc shape inside the plating tank after being accommodated in the accommodating part By using a pipe plating apparatus equipped with a pipe carry-out mechanism that attracts a roller to each of the ERW steel pipes placed inside the tank and draws it out of the plating tank by rotation of the roller, an Al content of 0.001 to By plating under the conditions of 0.05%, zinc plating bath temperature of 440 to 485 ° C., and immersion time of 60 seconds or less, the adhered zinc can be suppressed to 50 μm or less and plating with excellent workability can be performed. In addition, as a tube plating apparatus used in such a preferred embodiment, for example, an apparatus disclosed in JP-A-11-92907 can be used.
[0072]
In the plating bath, Al contained in the Zn bath is generally effective in suppressing the development of the alloy layer, but if it is less than 0.001%, the fluidity of the zinc phase cannot be ensured and the frequency of defective zinc sagging increases. However, if it exceeds 0.05%, the occurrence frequency of non-plating increases, both of which are unfavorable for operation. Therefore, the Al content is controlled at 0.001 to 0.05%.
[0073]
The temperature of the galvanizing bath affects the development of the alloy layer, and a lower temperature is preferable for suppressing the development of the alloy layer. . On the other hand, if it exceeds 485 ° C, the development of the alloy layer becomes excessive, which adversely affects bending workability. Therefore, the temperature range of the temperature of the galvanizing bath is set to 440 to 485 ° C.
[0074]
The dipping time affects the development of the alloy layer, and the alloy layer develops excessively for a long time. For the purpose of plating with excellent workability, the immersion time is 60 seconds or less.
Thus, according to the present invention, an ERW steel pipe excellent in plating adhesion can be obtained. Here, “plating adhesion” in the present invention is the presence or absence of peeling of the plating film when 1D bending is performed. It is that evaluated, and the workability is that evaluated by the presence or absence of cracks during such bending.
[0075]
【Example】
Next, the effects of the present invention will be described more specifically with reference to examples.
Using the manufacturing process shown in FIG. 1 and using the steel strip 2 having the steel composition shown in Table 1 as a raw material, the heating temperature, drawing rolling temperature (drawing rolling start temperature and drawing rolling end temperature), and drawing rolling speed are shown in Table 2. The electric resistance welded steel pipe 8 was manufactured as shown in FIG.
[0076]
That is, a steel strip 2 having a width of 365 mm and a thickness of 3.7 mm is heated by a steel strip heating furnace 3, formed and electro-welded by a forming and induction heating welding device 4, and an electric resistance steel pipe having an outer diameter of 114.3 mm. The ERW steel pipe was continuously reheated by the pipe reheating device 5, then subjected to drawing rolling by a 3-roll type stretch reducer (drawing rolling mill) 6, and further to a predetermined pipe length by the pipe cutting device 7. By cutting, an ERW steel pipe 8 having an outer diameter of 48.6 mm and a wall thickness of 3.31 mm was obtained.
[0077]
Then, these ERW steel pipes were galvanized, and the relationship between the plating performance, the surface roughness of the inner and outer surfaces, and the crystal grain size of the outermost surface of the steel pipe was investigated.
The plating performance was evaluated by setting various bending radii and bending angles.
[0078]
These results are summarized in Table 2.
In this example, the surface roughness (Ra) was measured at five locations on the inner and outer surfaces of the ERW steel pipe according to the method described above, and the average value was taken. Further, the outermost crystal grain size (average of the welded portion) was also measured at five locations for the first layer and the second layer at arbitrary locations on the ERW steel pipe according to the method described above, and the average value was obtained. .
[0079]
[Table 1]

[0080]
[Table 2]

[0081]
【The invention's effect】
As described in detail above, according to the present invention, an electric resistance welded steel pipe having excellent plating adhesion and excellent workability of the steel pipe can be manufactured with high productivity.
[0082]
The significance of the present invention having such an effect is extremely remarkable in practice.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is an explanatory view schematically showing an example of a process for producing an ERW steel pipe in an embodiment.
FIG. 2 is a schematic enlarged sectional view of a surface layer of a steel pipe according to the present invention.
[Explanation of symbols]
1: Steel strip
3: Steel strip heating furnace
4: Forming and induction heating welding equipment
5: Tube reheating device
6: Drawing mill
7: Pipe cutting device
8: ERW steel pipe

Claims (6)

A forming process having the following steel composition, forming a heated steel strip into an open tube, and performing an electric resistance welding by locally heating the edge portion of the open tube with an induction heating device to obtain an electric resistance steel tube ERW welding process, reheating process to reheat the resulting ERW steel pipe to make the circumferential temperature distribution of the ERW steel pipe substantially uniform, drawing rolling process to draw-roll the reheated ERW steel pipe , And a method for producing an ERW steel pipe comprising a plating step of subjecting the obtained ERW steel pipe to hot dip galvanization using a pipe plating apparatus , wherein the heating temperature of the steel strip in the forming step is 1300 ° C. or lower, Ae ₃ A transformation point or higher, the end temperature of the reducing rolling in the reducing rolling step, along with the (Ae ₃ transformation point -50 ° C.) or higher, in the range of the cooling rate at the time of reducing rolling 3 ° C. / sec to 100 ° C. / sec A method for producing an ERW steel pipe.
% By mass, C: 0.0002 -0.50%, Si: 0.003 ~ 0.28 %, Mn: 0.003 ~ 0.58 %, Al: 0.002 -0.031%, P: 0.15% or less, S: 0.03% or less, N: 0.01% or less, or
Furthermore, it has a composition containing one or more of the following first to fourth groups in the above composition,
First group: B: 0.0002 ~ 0.01 %,
Second group: 0.005 in total of one or more of Ti, Nb, V and Zr ~ 1.0%,
Group 3: One or more of Cr, Mo, Cu and Ni in total 0.005 ~ 3.0 % ,
Group 4: Ca: 0.0001-0.005 %, And REM (rare earth element): 0.0001 to 0.2 Containing one or more of
The balance is Fe and inevitable impurities. The heating temperature of the steel strip in the forming step is Ae ₃ Be less than transformation point, in the reheating step, by reheating performed in an electric resistance welded steel pipe, 1300 ° C. The electric resistance welded steel pipe in the previous reducing rolling below, Ae ₃ 2. The method of manufacturing an electric resistance welded steel pipe according to claim 1, wherein the heating is performed at a temperature higher than the transformation point. In the plating step, Al content 0.001 to 0.05%, galvanizing bath temperature 440 ~485 ℃, and facilities galvanizing with the following conditions: immersion time 60 seconds, said tube plating apparatus, the plating tank A housing part that pivots around and supports an ERW steel pipe inside the plating tank, a pipe supply mechanism that supplies the ERW steel pipe to the housing part, and a housing that is housed in the housing part. A transport mechanism that transports the ERW steel pipe in an arc shape, and after plating is completed, the ERW steel pipe disposed inside the plating tank is made to adsorb a roller, and is drawn out of the plating tank by the rotation of the roller. A method for manufacturing an electric resistance welded steel pipe according to claim 1, comprising a pipe carry-out mechanism. % By mass
C: 0.0002 to 0.50%, Si: 0.003 to 0.28 % , Mn: 0.003 to 0.58 % , Al: 0.002 to 0.031% , P: 0.15% or less, S: 0.03% or less, N: 0.01% or less. The composition comprises one or more of the following first to fourth groups,
First group: B: 0.0002 to 0.01%,
Second group: 0.005 to 1.0% in total of one or more of Ti, Nb, V and Zr,
Third group: 0.005 to 3.0% in total of one or more of Cr, Mo, Cu and Ni,
Group 4: Ca: 0.0001 to 0.005%, and REM (rare earth element): 0.0001 to 0.2% of one or more of containing,
The balance has a steel composition composed of Fe and inevitable impurities, the surface roughness of the inner and outer surfaces of the steel pipe is Ra: 0.5 to 5.00 (μm), and the average of the outermost particle phase of the steel pipe surface layer The electric resistance welded steel pipe manufactured according to any one of claims 1 to 3, wherein the particle diameter is 20 µm or less. The chemical composition of the steel strip is mass%,
C: 0.0002 to 0.50%, Si: 0.003 to 0.28 % , Mn: 0.003 to 0.58 % , Al: 0.002 to 0.031% , P: 0.15% or less, S: 0.03% or less, N: 0.01% or less, or further, the following first to fourth groups Including one or more of a group,
First group: B: 0.0002 to 0.01%,
Second group: 0.005 to 1.0% in total of one or more of Ti, Nb, V and Zr,
Third group: 0.005 to 3.0% in total of one or more of Cr, Mo, Cu and Ni,
Group 4: Ca: 0.0001 to 0.005%, and REM (rare earth element): 0.0001 to 0.2% of any one or more elements,
The balance is Fe and inevitable impurities, and the finishing temperature of the drawing rolling is Ae ₃ The method for producing an electric resistance welded steel pipe according to any one of claims 1 to 3, wherein the method is at least the transformation point. The steel composition of the steel strip is mass%,
C: 0.2% or less, Si: 0.01 to 0.28 % , Mn: 0.01 to 0.58 % , Al: 0.01-0.031 % ,
P: 0.1% or less, S: 0.03% or less, N: 0.01% or less, or further includes one or more of the following first group to fourth group,
First group: B: 0.01% or less,
Second group: 1.0% or less in total of at least one of Ti, Nb, V and Zr,
Third group: one or more of Cr, Mo, Cu and Ni in a total of 3.0% or less,
Group 4: Ca: 0.005% or less, and REM (rare earth element): containing any one or more elements of 0.2% or less,
Balance being Fe and unavoidable impurities, diaphragm manufacturing method of ERW steel pipe according to any one of the finishing temperature of rolling is claims 1 is (Ae ₃ transformation point -50 ° C.) or higher 3.

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