JP4173990B2 - Zinc-based alloy-plated steel for welding and its ERW steel pipe - Google Patents

Description

【００６９】
［実施例２］
表２に示す成分を含有する母材鋼板に、目付量片面９０ｇ／ｍ²のＭｇ：３％、Ａｌ：１１％、Ｓｉ：０．３％、残部Ｚｎからなる亜鉛系合金めっきを施した引張強さ：４００ＭＰａ級の６ｍｍ厚の亜鉛系合金めっき鋼板を用いて、これを管状に成形後、その突合せ端部を溶接速度：３０ｍ／ｍｉｎ、高周波パワー：４５０ｋＷ、アプセット量：３ｍｍの条件で電縫溶接し、外径３５５ｍｍの電縫鋼管を製造した。電縫鋼管の溶接ＨＡＺ部の割れ長さ（板厚方向の割れの深さ）は断面観察により計測し、母材板厚に対する割れ深さの比で評価した。また、室温でのシャルピー試験によって鋼板の溶接ＨＡＺ部の靭性を計り、靭性の劣化率はＢ無添加（Ｂ量０％）の場合の溶接ＨＡＺ部の靭性値に対する各Ｂ量を添加した場合の溶接ＨＡＺ部の靭性値の比で評価した。なお、割れ深さ率および靭性劣化率は、各々５％以下、８０％以上を良好と判断した。
【００７０】
表２に母材鋼材中の主要な成分と割れおよび靱性の劣化率の結果を示す。記号１〜１１は本発明例である。記号１〜１１の発明例において溶接部の割れは実用上無視できる程度か、または皆無であった。また、いずれの発明例も溶接ＨＡＺ靭性の大幅な低下は見られなかった。
【００７１】
一方、記号１２〜２４は本発明の鋼材成分範囲から外れた比較例である。
【００７２】
記号１２から２０はＢ量が本発明で規定する範囲より少ないため液体金属脆化割れが生じた。
【００７３】
記号２１および２２は本発明で規定する範囲に比べＢが多いため、割れは皆無であったが、溶接ＨＡＺ部の靭性値の低下が激しかった。
【００７４】
記号２３および２４はＣ量およびＢ量が本発明で規定する範囲より多いために割れの程度大きくかつ溶接ＨＡＺ靭性の低下が激しかった。
【００７５】
【表２】

【００７６】
【発明の効果】
以上述べたように、本発明は、建築、自動車などの溶接構造部材として使用される亜鉛系合金めっき鋼材を種々の方法で溶接する際、さらには、亜鉛系合金めっき鋼材を用いて造管後、電縫溶接する際に、溶接熱影響部における液体金属脆化割れを抑制でき、溶接部品質に優れた亜鉛系合金めっき鋼材およびその電縫鋼管を提供することが可能となる。
【図面の簡単な説明】
【図１】ＣおよびＢ添加量とアーク溶接による溶接部の割れ深さの度合いを示す図。
【図２】ＣおよびＢ添加量とアーク溶接による溶接ＨＡＺ部の靱性劣化の度合いを示す図。
【図３】鋼管の電縫溶接における溶接部の割れ深さおよび溶接ＨＡＺ部の靭性劣化の度合いを示す図。
【図４】アーク溶接における液体金属脆化割れの評価方法を示す図。
【符号の説明】
１…厚手鋼板
２…めっき鋼板
３…嵌め込み溶接
４…丸鋼
５…円周溶接[0001]
BACKGROUND OF THE INVENTION
  The present invention is mainly used for welded structural members such as buildings and automobiles.Tensile strength of 400 MPa classRegarding zinc-based alloy-plated steel and its electric-welded steel pipe, in particular, when welding such zinc-based alloy-plated steel by various methods, further, after making pipes using zinc-based alloy-plated steel, electric resistance welding is performed. In particular, the present invention relates to a zinc-based alloy-plated steel material for welding capable of suppressing the occurrence of liquid metal embrittlement cracking (hereinafter sometimes referred to as galvanizing cracking) in a weld heat-affected zone, and an ERW steel pipe thereof.
[0002]
[Prior art]
Zn-plated steel materials are widely used from the viewpoint of improving the corrosion resistance of structural members of buildings and automobiles. Recently, Zn-Al-Mg-based alloy plating in which Al, Mg or Si is added during Zn plating, Zn-Al-Mg-- Patent Document 1 and Patent Document 2 disclose zinc-based alloy-plated steel materials having excellent corrosion resistance obtained by applying zinc-based alloy plating such as Si-based alloy plating to the steel material surface. These zinc-based alloy plated steel materials are often used as welded steel structures after being welded by various welding methods.
[0003]
In addition, steel pipes and square tubes are often used in which these galvanized alloy plated steel materials are formed into a tubular shape and then the butt ends are welded by high-frequency induction welding or high-frequency resistance welding (hereinafter referred to as electric resistance welding). .
[0004]
  However, when welding these zinc-based alloy-plated steel materials, the zinc-based alloy plating melted by the welding heat input remains in a molten state on the steel material surface in the heat affected zone of the steel material (hereinafter referred to as welded HAZ portion). It tends to remain, and the steel structure tends to be a structure in which crystal grains grow and become coarse. In this stateTensile stressIf this occurs, depending on the welded HAZ structure of the steel material, when the hot-dip plating penetrates into the crystal grain boundaries on the steel material surface and the grain boundaries become brittle, that is, an embrittled zone is formed and cracking occurs. There is. In particular, cracks may occur in the embrittled region of the welded HAZ portion during welding with the member to be welded being significantly constrained.
[0005]
On the other hand, conventionally, when a welded structure obtained by welding steel materials is plated in a high-temperature hot-dip zinc alloy plating bath, the welded portion of the welded structure, particularly the weld toe (weld bead (welded metal) ) And the steel material)) It was known that similar cracking occurs due to the residual tensile stress (hereinafter referred to as residual tensile stress) and thermal strain generated in the plating bath.
[0006]
As described above, when a certain liquid metal comes into contact with a certain solid metal surface at a high temperature and a certain amount of tensile stress acts on the solid metal surface, there is an embrittlement region on the solid metal surface. The phenomenon of formation and cracking is called liquid metal embrittlement cracking: LME (Liquid Metal Embrittlement), and is known, for example, in Non-Patent Document 1.
[0007]
Conventionally, as a method for suppressing liquid metal embrittlement cracking (LME) that occurs when plating a welded joint in a high-temperature hot-dipping bath, structural control based on the steel component definition has been attempted. The expression is standardized by JIS (for example, JIS G3219-1995 for steel materials and JIS G 3474-1995 for steel pipes).
[0008]
Moreover, in patent document 3, while limiting each component of steel materials with respect to the steel materials in which Zn-Al alloy plating is given, especially severe restrictions of 0.0002% or less are provided with respect to B.
[0009]
  However, the above LME carbon equivalent formula targets liquid metal embrittlement cracking (LME) when the welding joint is plated with a high temperature hot dip plating bath, and the temperature range where the crack occurs is the temperature of the plating bath: 450 ° C. ( The melting point of the plated metal), and when welding zinc-based alloy plated steelpeakTemperature: It targets liquid metal embrittlement cracking (LME) that occurs at very low temperature conditions compared to 1500 ° C. On the other hand, liquid metal embrittlement cracking (LME) that occurs when welding zinc-based alloy-plated steel materials is a wide temperature from the high temperature range where steel materials of about 1500 ° C. melt to the melting point of plated metals of about 450 ° C. Therefore, even if the conventional LME carbon equivalent formula is applied to a zinc-based alloy-plated steel material for welding, it has been difficult to sufficiently suppress liquid metal embrittlement cracking (LME) during welding.
[0010]
Conventionally, in the brazing of extremely low carbon IF (Interstitial Free) steel, which requires press formability, the occurrence of the above-mentioned liquid metal embrittlement crack due to solder brittleness is known. In Reference 4, 0.01 to 0.2% of Ti is added to the IF steel having a low C of 0.0005 to 0.03% to fix N, and B is 0.0002 to 0.03%. Addition of 003% prevents the molten metal from entering the grain boundaries and suppresses the generation of cracks.
[0011]
  This method is intended for low-strength, ultra-low carbon IF steels that require formability, and the temperature range where cracks occur is soldering.peakTemperature: It is assumed that the temperature is about 900 to 1000 ° C. (corresponding to the melting point of solder). On the other hand, a zinc-based alloy-plated steel material having a higher strength than IF steel (tensile strength: about 350 MPa or more) and high carbon steel (C: about 0.01 to 0.3%) as a base material,peakWhen welding is performed at a temperature of about 1500 ° C. (corresponding to the melting point of steel), liquid metal embrittlement cracking occurs even in a temperature range lower than 900 ° C. Therefore, the above method is applied to welding of high strength steel. However, it is difficult to sufficiently suppress the liquid metal embrittlement cracking.
[0012]
  In recent years, especially in the automotive field, as a zinc-based alloy-plated steel sheet, in consideration of the reduction in weight and fuel consumption of automobiles, and in consideration of the global environment, instead of conventional low-carbon IF steel sheets that emphasized formability,Tensile strengthZn-Al, Zn-Al-Mg, Zn-, which is high-strength steel with a high content of C and alloy elements and has higher corrosion resistance than the conventional Zn plating on the surface of the base material. Steel plates plated with zinc-based alloy plating such as Al-Mg-Si have come to be applied, and along with that, the occurrence of liquid metal embrittlement cracks during steel welding that was not a problem in the past becomes apparent It has become.
[0013]
Also, in the conventional automobile and construction fields, after welding ordinary steel materials, plating the welded structure in a high-temperature galvanizing bath was the mainstream, but in recent years the process has been omitted and manufacturing costs have been reduced. From the point of view, welding of pre-plated steel, which welds a plated steel or a molded member thereof, has been applied, and the industrial significance of technology for suppressing plating cracks that occur during welding has increased.
[0014]
In addition, as a method of manufacturing steel pipes with excellent corrosion resistance, from the viewpoint of improving productivity and reducing manufacturing costs, instead of using a conventional post-plating method for ERW steel pipe products, zinc-based alloy-plated steel sheets have recently been used. A method of electro-welding the butt end after forming into a tubular shape has also been put into practical use.
[0015]
However, during spring welding after pipe making, a large springback force (working reaction force), forming strain or heat shrinkage force acts, so Zn-Al-Mg alloy plating, Zn-Al-Mg-Si alloy Depending on the type of component system of zinc alloy plating such as plating, the molten zinc alloy plating remaining on the surface of the heat affected zone at temperatures below 900 ° C enters the grain boundary from the surface of the steel material and causes liquid metal embrittlement cracking. Will occur.
[0016]
  Conventionally, as a crack suppression technique at the time of electric-welding welding of such a zinc-based alloy-plated steel sheet, for example, in Patent Document 5, when a Zn-Al-Mg-based alloy-plated steel sheet is piped and its butt ends are welded By controlling the amount of upset, the shape of the weld toe becomes gentle.Tensile stressA technique for reducing the concentration of cracks and eliminating cracks is disclosed. However, with this upset amount controlTensile stressConditions that enable concentration reduction are limited to some steel pipe sizes and specific steel types, and it is difficult to exert stable effects over a wide range of conditions.
[0017]
[Patent Document 1]
Japanese Patent Laid-Open No. 10-226865
[Patent Document 2]
JP 2000-64061 A
[Patent Document 3]
JP 05-156406 A
[Patent Document 4]
JP 60-92453 A
[Patent Document 5]
JP 2002-115793 A
[Non-Patent Document 1]
Journal of Institute of Metals (1914) p.108. (A.K.Huntington)
[0018]
[Problems to be solved by the invention]
  The present invention is based on the problems of the prior art as described above, for example,Tensile strength of 400 MPa classWhen welding plated steel materials, in particular zinc alloy plated steel materials with Zn-Al-Mg alloy plating, Zn-Al-Mg-Si alloy plating, etc. by various methods, Can suppress the occurrence of liquid metal embrittlement cracking in the heat affected zone when welding by electro-sewing after pipe making using zinc-based alloy plated steel, and has excellent weld qualityTensile strength of 400 MPa classAn object is to provide a zinc-based alloy-plated steel material for welding and an ERW steel pipe thereof.
[0019]
[Means for Solving the Problems]
  The present invention has been made to solve the above problems, and the gist thereof is as follows.
(1) In the zinc-based alloy-plated steel material in which the zinc-based alloy plating layer is provided on the surface of the steel material, the steel material is in mass%,
C: 0.01 to 0.3%
Si: 0.01 to 2.0%
Mn:0.5~ 3.0%
S: 0.015% or less
Al: 0.001 to 0.5%
B:0.0003-0.004%
N: 0.0005 to 0.006%
And the balance consists of Fe and inevitable impuritiesTensile strength of 400 MPa classZinc-based alloy plated steel for welding. (2) In the above (1), the steel material further contains, by mass%, Ti: 0.001 to 0.5% and satisfies the condition given by the following formula (1): Zinc-based alloy-plated steel for welding as described.
[0020]
    0.5 ≧ [% Ti] + [% Al] ≧ 0.001 (1)
  However, [% X] indicates the content expressed by mass% of the alloy element X.
(3) The zinc content alloy-plated steel material for welding according to the above (1) or (2), wherein the S content in the steel material is 0.003% by mass or less.
(4) The welding zinc as set forth in any one of (1) to (3), wherein the steel material further contains P: 0.02 to 0.05% by mass. Alloy-plated steel.
(5) The zinc alloy plating is any one of Zn—Al alloy plating, Zn—Al—Mg alloy plating, and Zn—Al—Mg—Si alloy plating. The zinc-based alloy-plated steel material for welding according to any one of (1) to (4) above.
(6) The said Zn-Al type alloy plating contains Al: 0.18-5% by the mass%, Furthermore, Mg: 0.01-0.5%, La: 0.001-0.5 % And Ce: 0.001 to 0.5% of any one or two or more, the balance being Zn and unavoidable impurities as described in (5) above Zinc-based alloy plated steel for welding.
(7) The Zn—Al—Mg-based alloy plating contains, in mass%, Al: 2 to 19%, Mg: 0.5 to 10%, and the balance being Zn and inevitable impurities. The zinc-based alloy plated steel material for welding as described in (5) above.
(8) The Zn—Al—Mg—Si based alloy plating contains, in mass%, Al: 2 to 19%, Mg: 1 to 10%, Si: 0.01 to 2%, with the balance being Zn and The zinc-based alloy-plated steel material for welding as described in (5) above, which is an inevitable impurity.
(9) In mass%,
C: 0.01 to 0.15%
Si: 0.01 to 2.0%
Mn:0.5~ 3.0%
S: 0.015% or less
Al: 0.001 to 0.5%
B:0.0006-0.0015%
N: 0.0005 to 0.006%
A zinc-based alloy plating layer is provided on the surface of a steel plate containing the balance of Fe and inevitable impurities.Tensile strength of 400 MPa classA zinc-based alloy-plated electric-welded steel pipe, characterized in that a zinc-based alloy-plated steel sheet is formed into a tubular shape, and the butt end portion thereof is electro-welded.
(10) In the above (9), the steel sheet further contains, by mass%, Ti: 0.001 to 0.5%, and satisfies the condition given by the following formula (1): Zinc-based alloy plated ERW steel pipe.
[0021]
0.5 ≧ [% Ti] + [% Al] ≧ 0.001 (1)
However, [% X] indicates the content expressed by mass% of the alloy element X.
(11) The zinc-based alloy-plated electric-welded steel pipe according to (9) or (10) above, wherein the S content in the steel sheet is 0.003% or less by mass%.
(12) The zinc-based alloy according to any one of (9) to (11) above, wherein the steel sheet further contains P: 0.02 to 0.05% by mass. Plating ERW steel pipe.
(13) The zinc alloy plating is any one of Zn—Al alloy plating, Zn—Al—Mg alloy plating, and Zn—Al—Mg—Si alloy plating. The zinc alloy-plated ERW steel pipe according to any one of (9) to (12) above.
(14) The Zn—Al-based alloy plating contains, by mass%, Al: 0.18 to 5%, Mg: 0.01 to 0.5%, La: 0.001 to 0.5. % And Ce: 0.001 to 0.5% of any one or two or more types, and the balance is Zn and inevitable impurities as described in (13) above Zinc alloy plated ERW steel pipe.
(15) The Zn—Al—Mg-based alloy plating contains, by mass%, Al: 2 to 19%, Mg: 0.5 to 10%, and the balance being Zn and inevitable impurities. The zinc-based alloy plated ERW steel pipe according to (13) above.
(16) The Zn—Al—Mg—Si based alloy plating contains, in mass%, Al: 2 to 19%, Mg: 1 to 10%, Si: 0.01 to 2%, with the balance being Zn and The zinc-based alloy-plated ERW steel pipe according to (13) above, which is an inevitable impurity.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
  In general, the welded part after welding the steel material heat shrinks in the cooling process to room temperature after the molten weld metal solidifies, so the weld metal and base metal of the welded part are not affected by any external force applied to the welded part. Heat-affected zone is accompanied by heat shrinkageTensile stressWill occur. Liquid metal embrittlement cracks that occur when welding steel materials plated with zinc-based alloy plating of specific components such as Zn-Al, Zn-Al-Mg, and Zn-Al-Mg-Si Hot-dip zinc-based alloy plating that remained on the surface of the weld heat affected zone without evaporating occurred with the heat shrinkage of the weld heat affected zoneTensile stressThis is considered to occur by entering the crystal grain boundary with
[0023]
  Occurs with thermal shrinkage after weldingTensile stressVaries depending on the high-temperature strength of the steel around the weld, which changes according to the temperature. For example, the tensile stress generated in the weld at a high temperature of about 900 ° C. is relatively small, whereas the melting point of zinc-based alloy plating In the corresponding low temperature range of about 400 to 500 ° C., it is large due to the recovery of the high temperature strength around the weld and the increase in the amount of heat shrinkage.Tensile stressWork. In addition, the high temperature strength of steel usually depends on its cold strength.Tensile strengthThe higher the value, the greater the heat shrinkageTensile stressWill grow. Also accompanying the heat shrinkageTensile stressThe size of the weld also changes depending on the restraint state of the welded part during welding. When welding with the welded part being mechanically restrained by a jig or the like to suppress welding deformation, When welding with a joint shape that has a large processing reaction force such as end butt welding after molding, it is accompanied by thermal shrinkage.Tensile stressWill increase.
[0024]
  In the case of brazing of conventional ultra-low carbon IF steel, cracking occurred only in the high temperature range of about 900 ° C or higher, which is the melting point of solder, whereas in welding of zinc-based alloy plated steel , Cracks occur in a wide temperature range from a temperature lower than 900 ° C. to a low temperature range of about 400 ° C. corresponding to the melting point of plating, and the cracks are large due to thermal contraction of the weld zone.Tensile stressThis is different from the embrittlement cracking of brazing of conventional IF steel materials in that it is generated by the action of.
[0025]
  In the welding construction of the zinc-based alloy plated steel material, in order to suppress plating cracks that frequently occur not only in a high temperature range of 900 ° C. or higher but also in a range from a lower temperature to a low temperature range of about 400 ° C., Of welding heat-affected zone during welding (hereinafter referred to as welded HAZ zone)Tensile stressThe technical idea is to improve the proof stress, that is, the grain boundary strength.
[0026]
  The present invention is based on this technical idea.Tensile strengthIs about 350MPa or more and about 800MPa or less, steel material with higher strength than IF steel, zinc-based alloy plated steel material with zinc-based alloy plating on its surface, liquid metal embrittlement cracking at the time of welding As a result of examining the prevention measures in detail, the toughness of the welded portion is ensured by adding 0.0003 to 0.004% B to a steel material containing 0.01 to 0.3% by mass C as a base material component. However, the inventors have obtained a new knowledge that liquid metal embrittlement cracking during welding can be prevented, and the present invention has been made based on this.
[0027]
The present invention is described in detail below.
[0028]
First, as a result of verifying the prevention of cracking in a relatively low temperature region where a large tensile stress is generated in the welding process, it was found that the improvement of the hardenability by C is effective. Although the reason is not clear, it is considered that the plastic strain accompanying the tensile stress was effectively reduced by increasing the strength of the welded HAZ portion of the steel material in which the molten zinc-based alloy plating remained.
[0029]
  However, in the case of welding restrained with a jig in advance for the purpose of preventing welding deformation, etc.,Tensile stressTherefore, there remains a problem that cracking still occurs in welding under extremely severe welding conditions in such a restrained state. In particular, in the process of manufacturing a steel pipe with excellent corrosion resistance, after forming a zinc-based alloy-plated steel sheet into a tubular shape and then subjecting the butt end to electro-welding, the welded portion is combined with the heat shrinkage force to form the steel. As a result, a large springback force (working reaction force) acts, so that hot dip zinc alloy plating cracks are likely to occur.
[0030]
  Under such severe welding conditions, even in a high temperature range where the tensile stress of the welded HAZ portion is considered to be relatively mild, a predetermined value is required.Tensile stressIs considered to lead to liquid metal embrittlement cracking, so it is not sufficient to control the C content alone.
[0031]
Then, the influence of B in the steel material containing predetermined C amount was examined.
[0032]
Conventionally, as a technique for preventing solder embrittlement cracking, low melting point molten metal grains are segregated and concentrated by grain boundary segregation / concentration of B in the austenite temperature range of about 900 ° C. or higher by addition of B when brazing ultra-low carbon IF steel materials. It is known that there is an effect of suppressing the intrusion of the field. Since the present invention is directed to weld cracking under welding conditions where the welding peak temperature is 1500 ° C. (corresponding to the melting point of the steel material) or higher compared to soldering, it is possible to suppress embrittlement cracking at high temperatures. It is considered that the effect of suppressing the penetration of the zinc-based alloy plating in the molten state into the grain boundaries by the grain boundary segregation / concentration of B is obtained similarly. This grain boundary segregation of B occurs at a temperature higher than the austenite-ferrite two-phase region, and B enters the vacancies / defects of the grain boundary to lower the interfacial energy, so that the molten plating component penetrates and diffuses into the grain boundary. The grain boundary segregation of B becomes difficult to occur as the temperature decreases.
[0033]
  As a result of the study by the present inventors, in addition to the effect of B described above, as a new finding, B has a relatively high cooling rate as in the welded HAZ part even in a temperature range lower than the austenite-ferrite two-phase region. In the region, B acts as a strengthening element of the prior austenite grain boundary, and is generated in the welded HAZ portion by heat shrinkage.Tensile stressIt has been found that it is effective in improving the grain boundary strength against hot dip, and thus preventing hot-dip cracking at low temperatures.
[0034]
Fig. 1 shows the crack depth of the weld and Fig. 2 shows the experimental results when arc welding was performed on a zinc-based alloy-plated steel material with zinc-based alloy plating applied to the surface of the steel material with varying amounts of C and B. Indicates the rate of deterioration of the toughness of the weld. The crack depth in FIG. 1 is expressed by the ratio of the crack depth to the base metal plate thickness, and the toughness deterioration rate in FIG. 2 is the respective B amount relative to the HAZ toughness value of the B-free steel material (B amount 0%). It was expressed as a ratio of HAZ toughness values of the added steel materials. Further, a zinc-based alloy plated steel material having a plate thickness of 6 mm and an 11% Al + 3% Mg + 0.2% Si + Zn plating layer applied thereto was used.
[0035]
As shown in FIGS. 4 (a) and 4 (b), as a method for evaluating cracks in the welded portion, a plated steel material 2 to be evaluated is fitted into the thick steel material 1 and welded 3, and further round steel is applied on the plated steel material 2. The depth of the crack which generate | occur | produces in the crater part (terminal part) of the weld bead of circumferential welding 5 was measured and evaluated by carrying out circumferential welding 5 of 4. By welding the plated steel material 2 to the thick steel material 1, the restraint conditions when the plated steel material 2 was circumferentially welded 5 were tightened.
[0036]
In addition, the crack depth of the welded portion was obtained by observing a cross section of the welded portion and measuring the length in the thickness direction in which the crack extends from the steel surface.
[0037]
  From FIG. 1, although the crack of the welded portion tends to decrease with an increase in the B content regardless of the C content in the steel material, the medium C material (C: 0.005%) compared to the low C material (C: 0.005%). 0.01%) and high C material (C: 0.15%)0.0003%And even with a relatively small amount, cracks in the welded portion are drastically reduced, and the B amount is reduced.0.0005%From the above, it can be seen that the occurrence of cracks in the welded portion is almost eliminated. On the other hand, even in the case of low C material (C: 0.005%) or medium C material (C: 0.01%), the amount of B is0.0020%Or more0.0040%When added in a large amount as described above, cracks in the welded portion become relatively small, but the toughness value of the welded portion decreases as shown in FIG. 2, and it is understood that the target toughness (80% or more) cannot be obtained. This is thought to be due to the fact that the grain size of the low C and medium C materials is likely to be coarser than that of the high C material, so that the decrease in toughness due to segregation of B grain boundaries increases with the increase in the amount of B. 1 and 2 C: When arc welding a zinc-based alloy-plated steel material having a medium C material and a high C material of 0.01% or more as a base material, melting while ensuring the target toughness of the welded portion B content in steel to prevent zinc alloy plating cracking is0.0003-0.004%It is necessary to.
[0038]
Further, a steel pipe in which the zinc content is plated on the surface of the steel material in which the C content and the B content are changed is formed into a tubular shape, and then the butt end portion is electro-welded and welded to the steel pipe FIG. 3 shows the crack depth and the toughness deterioration rate of the welded portion as the experimental results when manufacturing the steel. In addition, the crack depth of the welded portion was obtained by observing a cross section of the welded portion and measuring the length in the thickness direction in which the crack extends from the steel surface. The crack depth and toughness deterioration rate of the weld were determined by the same method as in FIGS. The zinc-based alloy-plated steel sheet used was a plate thickness of 6 mm and was provided with an 11% Al + 3% Mg + 0.3% Si + Zn plating layer.
[0039]
  From FIG. 3, about the hot galvanized alloy plating crack at the time of electric resistance welding of a steel pipe, C content is 0.15% or less of medium C material,Low C materialIn B, the increase in the amount of B added effectively reduces the cracking, and the amount of B added0.0006%Although cracking of the weld zone is almost eliminated as described above, the effect of reducing cracking due to the addition of B is hardly obtained with a high C material having a C content of about 0.35%. On the other hand, medium C material with a C content of 0.15% or less,Low C materialAs the amount of B added increases, the toughness value of the weld decreases. B content in steel to prevent hot-dip zinc alloy plating cracking during electric resistance welding of steel pipe while ensuring target toughness (80% or more)0.0006-0.0015%It is necessary to.
[0040]
  The above knowledgeTheIn light of the above, the base material components of the zinc-based alloy-plated steel material for welding of the present invention and the ranges of the contents thereof are as follows. In addition, the following% shall show the mass% unless there is particular description.
[0041]
  C: In the present invention, C is necessary for securing a tensile strength of 350 MPa or more, and is caused by thermal shrinkage during welding as described above.Tensile stressOn the other hand, it is an essential element for improving the quenching of the welded HAZ part, that is, for preventing cracking by reducing the plastic strain in the stress concentrated part. From the above FIG. 1 and FIG. 2, the lower limit was set to 0.01% as the C content that can sufficiently prevent the occurrence of cracking in the welded portion and ensure good toughness by combination with addition of B. Excessive addition of C not only hardens the welded HAZ and leads to bending performance degradation and delayed cracking, but also facilitates the formation of Fe-C-B precipitates and reduces the effect of suppressing the embrittlement of B plating. Therefore, the upper limit of the C content is set to 0.3%.
[0042]
In addition, as shown in FIG. 3, when welding with a steel pipe, or when welding around the welded portion with a high restraining force, cracking of the welded HAZ portion is likely to occur, so the upper limit of the C content is limited. 0.15% is preferable.
[0043]
  Si: Si is necessary for deoxidation of the base material, and the lower limit of its content was set to 0.01%. Si is solid solution strengtheningUseYes Used to adjust the base material strength together with the following Mn. In addition, since excessive Si addition leads to an increase in oxide scale during hot rolling and a decrease in ductility, the upper limit of the content was set to 2.0%.
[0044]
Further, there is no problem when plating on a hot-rolled steel sheet, but when plating on a cold-rolled steel sheet, the plating adhesion deteriorates, so the Si amount is more preferably 0.1% or less.
[0045]
  Mn: Since Mn is made harmless by fixing S as an inevitable impurity in steel which causes hot brittleness of steel as MnS, the lower limit of the content is 0.1%.Therefore, 0.5% (preferable lower limit value) based on the Mn amount of “Symbol 4” in Table 1 of Example 1 and the Mn amount of “Symbols 8 to 11” in Table 2 of Example 2It was. On the other hand, excessive addition of Mn hardens the welded HAZ part and leads to bending performance degradation and delayed cracking, so the upper limit of its content was made 3.0%.
[0046]
S: Since S is an element which reduces the hot workability of steel materials, the smaller the amount, the better. The upper limit is set to 0.015%.
[0047]
In addition, from the viewpoint of suppressing plating embrittlement cracking during welding, S has an effect of suppressing embrittlement by lowering S, so the upper limit of its content is preferably made 0.003%.
[0048]
Al: Al is a deoxidizing element of steel and has an action of fixing N in the steel, so that B is prevented from precipitating as a nitride and suppresses liquid metal embrittlement cracking in hot dip zinc alloy plating. There is also an effect. In order to obtain these effects, it is necessary to add 0.001% or more. On the other hand, if Al is added excessively, coarse non-metallic inclusions are formed and the performance such as toughness of the steel material is lowered, so the upper limit value was set to 0.5%.
[0049]
  B: As described above, B is segregated / concentrated at the grain boundary or penetrated into pores / defects at the grain boundary at the temperature of the austenite region or the austenite-ferrite two-phase region at the time of welding to lower the interfacial energy. It has the effect of suppressing the penetration and diffusion of the molten zinc-based alloy plating into the grain boundaries. Further, in the cooling process of the weld zone, B is an element for improving hardenability, promotes the formation of bainite or martensite structure, and refines the structure and causes heat shrinkage.Tensile stressOn the other hand, the effect of reducing stress and plastic strain can be obtained by strengthening the grain boundary in the welded HAZ part. As the B content that can sufficiently prevent the occurrence of cracks in the welded portion under a predetermined C amount from FIG.0.0003%On the other hand, from FIG. 2 above, the upper limit of the B content is to suppress the deterioration of the toughness of the weld.0.0040%And
[0050]
  Also, as shown in FIG. 3, when welding with steel pipes or when welding around the welded part with a high restraining force, cracking of the welded HAZ part tends to occur, so the lower limit of the B content is set.0.0006%And the upper limit of B content to suppress toughness deterioration of the weld zone.0.0015%Is preferable.
[0051]
While N: N increases the strength of the steel material, the addition of a large amount of N decreases the toughness of the steel material and precipitates B as a nitride such as BN, which also impairs the effect of suppressing the embrittlement of B. Therefore, the upper limit is set to 0.006%. N is preferably as small as possible, but if it is 0.0005% or less, the cost is increased, so the lower limit is set to 0.0005%.
[0052]
In the present invention, in addition to the above components, the following component addition amounts are further defined for the following reasons.
[0053]
Ti: Ti has the effect of fixing N in steel as a nitride and preventing B from precipitating as a nitride such as BN, thereby further suppressing liquid metal embrittlement cracking in hot dip zinc alloy plating. Is preferably added in an amount of 0.001% or more. On the other hand, even if Ti is added in excess of 0.5%, the effect of suppressing cracking is saturated, and the alloy addition cost only increases unnecessarily, so the upper limit of its content was set to 0.5%.
[0054]
  In addition, the Ti content is the same as that of Ti with the content of Al having the function of fixing N.With quantityIt is preferable to adjust so that the total amount of is 0.001% or more and 0.5% or less.
[0055]
  P: P is generally desirable to reduce from the viewpoint of improving weldability, such as hot cracking, but because of the effect of reducing cracks due to P grain boundary segregation against plating embrittlement cracking during welding, It is preferable to add 0.02% or more. On the other hand, excessive addition causes hot cracking.ForThe upper limit of the content is preferably 0.05%.
[0056]
Further, in the present invention, the zinc-based alloy plating applied to the surface of the steel material containing the above components is described in Zn-Al-Mg system as described in Patent Document 1 and Patent Document 2. Such Zn-Al-Mg-Si-based or Zn-Al-based zinc-based alloy plating is used. Incidentally, the Zn—Al-based alloy plating contains Al: 0.18 to 5%, Mg: 0.01 to 0.5%, La: 0.001 to 0.5%, and Ce: It contains any one or more of 0.001 to 0.5%, and the balance is made of Zn. In Zn—Al—Mg alloy plating, Al: 2 to 19%, Mg: 0.00. It consists of 5-10% and the remaining Zn plating. In Zn-Al-Mg-Si alloy plating, Al: 2-19%, Mg: 0.5-10%, Si: 0.01-2%, It consists of plating which consists of remainder Zn. The present invention exhibits the above-described remarkable effects when welding a zinc-based alloy-plated steel material that has been plated with any one of these zinc-based alloy platings to form a welded structure.
[0057]
Moreover, the zinc-based alloy-plated electric resistance welded steel pipe in the present invention uses these zinc-based alloy-plated steel sheets, and after forming the steel sheet into a tubular shape, the butt end portion is subjected to electric-resistance welding such as high-frequency induction welding or high-frequency resistance welding. It is an electric resistance welded steel pipe manufactured by performing
[0058]
The zinc-based alloy-plated ERW steel pipe of the present invention is a steel pipe excellent in quality without weld cracking manufactured by electro-welding a zinc-based alloy-plated steel sheet, and a method for post-plating a conventional ERW steel pipe product Compared with the zinc-based alloy-plated electric resistance welded steel pipe manufactured by the above, it is possible to improve the productivity and reduce the manufacturing cost while maintaining a good quality of the welded portion.
[0059]
  In the above description of the embodiment of the present invention, the welding method has been described only with respect to arc welding or electric welding of steel pipes, but is not limited to these welding methods. For example, laser welding, spot welding, and projection welding are subjected to the same thermal cycle as arc welding,Tensile stressCan cause liquid metal embrittlement cracks in welds,The present inventionSimilarly, the effect of preventing plating cracking during welding can be obtained.
[0060]
【Example】
[Example 1]
  The base material steel containing the components shown in Table 1 has a basis weight of 90 g / m per side.²Zinc-based alloy plating composed of Mg: 3%, Al: 11%, Si: 0.3%, and the balance Zn was applied.Tensile strength: A 400 MPa class 6 mm-thick zinc-based alloy-plated steel material was arc-welded and cracks and toughness of the welded portion were evaluated in the same manner as in the evaluation method. In addition, it is known that the said Zn-Al-Mg-Si alloy plating shows the extremely superior corrosion resistance compared with the conventional simple Zn plating.
[0061]
  Welding was performed by pulse MAG arc welding with a welding current of 200 A, a welding voltage of 23 V, a welding speed of 30 cm / min, and YGW-12 was used as the welding wire. In addition, as shown in FIGS. 4 (a) and 4 (b), the crack of the welded portion is inspected by observing a cross section at the weld end portion that is likely to occur in the weld bead of the circumferential weld 5 (Table 1 shows the base metal). (Determined by the ratio of crack depth to plate thickness). Moreover, the deterioration rate of toughness was evaluated by the ratio of the toughness value of the welded HAZ part when each B content was added to the toughness value of the welded HAZ part when B was not added (B content 0%). In addition, crack depth rate and toughnessdeteriorationThe rates were determined to be good at 5% or less and 80% or more, respectively.
[0062]
  Table 1 shows the main components, cracks and toughness in the base steel.deteriorationRate results are shown. Symbols 1 to 10 are examples of the present invention. In the invention examples of symbols 1 to 10, when the amount of C was relatively small as 0.03 (symbol 1), a slight crack occurred, but it was practically negligible, and in other cases, there was no crack. Moreover, in any of the inventive examples, no significant reduction in welded HAZ toughness was observed.
[0063]
On the other hand, the symbols 11 to 14 are comparative examples deviating from the steel component range of the present invention.
[0064]
Symbols 11 and 12 had liquid metal embrittlement cracks because the amount of B was less than the range specified in the present invention.
[0065]
Since the symbol 13 has a C amount less than the range defined in the present invention, the weld HAZ toughness was severely lowered.
[0066]
Since symbol 14 has more B than the range defined in the present invention, the cracks generated were extremely small, but the toughness value of the welded HAZ part was severely lowered.
[0067]
In the above examples, arc welding was used as the welding method. Similarly, in tests using laser welding, spot welding, and projection welding, liquid metal embrittlement cracking of the welded portion can be suppressed, and the toughness of the welded HAZ portion can be suppressed. Was good.
[0068]
[Table 1]

[0069]
[Example 2]
  A base material steel plate containing the components shown in Table 2 has a basis weight of 90 g / m per side.²Zinc-based alloy plating composed of Mg: 3%, Al: 11%, Si: 0.3%, and the balance Zn was applied.Tensile strength: 400MPa class 6mm-thick zinc-based alloy plated steel sheet was formed into a tubular shape, and its butt end was welded under conditions of welding speed: 30m / min, high-frequency power: 450kW, upset amount: 3mm Thus, an electric resistance steel pipe having an outer diameter of 355 mm was manufactured. The crack length (depth of crack in the plate thickness direction) of the welded HAZ portion of the ERW steel pipe was measured by cross-sectional observation and evaluated by the ratio of the crack depth to the base metal plate thickness. In addition, the toughness of the welded HAZ part of the steel sheet is measured by a Charpy test at room temperature, and the deterioration rate of toughness is obtained when each B amount is added to the toughness value of the welded HAZ part when B is not added (B amount is 0%). It evaluated by the ratio of the toughness value of the welding HAZ part. In addition, crack depth rate and toughnessdeteriorationThe rates were determined to be good at 5% or less and 80% or more, respectively.
[0070]
  Table 2 shows the main components, cracks and toughness in the base steel.deteriorationRate results are shown. Symbols 1 to 11 are examples of the present invention. In the inventive examples 1 to 11, cracks in the welded portion were negligible in practical use or none at all. Moreover, in any of the inventive examples, no significant reduction in welded HAZ toughness was observed.
[0071]
On the other hand, symbols 12 to 24 are comparative examples that deviate from the steel component range of the present invention.
[0072]
Symbols 12 to 20 caused liquid metal embrittlement cracking because the amount of B was less than the range specified in the present invention.
[0073]
Symbols 21 and 22 had more B than the range defined in the present invention, so there were no cracks, but the toughness value of the welded HAZ part was severely reduced.
[0074]
Symbols 23 and 24 had a larger amount of C and B than the ranges specified in the present invention, so the degree of cracking was large and the weld HAZ toughness was severely degraded.
[0075]
[Table 2]

[0076]
【The invention's effect】
As described above, the present invention is suitable for welding zinc-based alloy-plated steel materials used as welded structural members for buildings, automobiles, etc. by various methods. When carrying out electric resistance welding, it is possible to suppress the liquid metal embrittlement cracking in the heat affected zone, and to provide a zinc-based alloy plated steel material having excellent weld quality and its electric resistance welded pipe.
[Brief description of the drawings]
FIG. 1 is a diagram showing the amount of addition of C and B and the degree of crack depth of a welded part by arc welding.
FIG. 2 is a view showing the amount of addition of C and B and the degree of toughness deterioration of a welded HAZ portion by arc welding.
FIG. 3 is a diagram showing a crack depth of a welded portion and a degree of toughness deterioration of a welded HAZ portion in electric resistance welding of a steel pipe.
FIG. 4 is a view showing a method for evaluating liquid metal embrittlement cracking in arc welding.
[Explanation of symbols]
1. Thick steel plate
2 ... Plated steel sheet
3 ... Fitting welding
4. Round steel
5. Circumferential welding

Claims (16)

In the zinc-based alloy plated steel material provided with a zinc-based alloy plating layer on the steel material surface, the steel material is in mass%,
C: 0.01 to 0.3%
Si: 0.01 to 2.0%
Mn: 0.5 to 3.0%
S: 0.015% or less Al: 0.001-0.5%
B: 0.0003 to 0.004%
N: 0.0005 to 0.006%
A zinc-based alloy-plated steel material for welding having a tensile strength of 400 MPa , characterized in that the balance is made of Fe and inevitable impurities. 2. The welding material according to claim 1, wherein the steel material further contains, in mass%, Ti: 0.001 to 0.5% and satisfies a condition given by the following expression (1): Zinc-based alloy plated steel.
0.5 ≧ [% Ti] + [% Al] ≧ 0.001 (1)
However, [% X] indicates the content expressed by mass% of the alloy element X.   3. The zinc-based alloy-plated steel material for welding according to claim 1, wherein an S content in the steel material is 0.003% by mass or less.   4. The zinc-based alloy-plated steel material for welding according to claim 1, wherein the steel material further contains P: 0.02 to 0.05% by mass.   The zinc-based alloy plating is any one of Zn-Al-based alloy plating, Zn-Al-Mg-based alloy plating, and Zn-Al-Mg-Si-based alloy plating. Item 5. A zinc-based alloy plated steel material for welding according to any one of Items 1 to 4.   The Zn—Al-based alloy plating contains, by mass%, Al: 0.18 to 5%, Mg: 0.01 to 0.5%, La: 0.001 to 0.5%, and Ce: Any one or more of 0.001 to 0.5% is contained, and the balance is Zn and unavoidable impurities, The zinc system for welding according to claim 5 Alloy plated steel.   The Zn-Al-Mg-based alloy plating contains, in mass%, Al: 2 to 19%, Mg: 0.5 to 10%, and the balance being Zn and inevitable impurities. 5. A zinc-based alloy-plated steel material for welding according to 5.   The Zn—Al—Mg—Si based alloy plating contains, in mass%, Al: 2 to 19%, Mg: 1 to 10%, Si: 0.01 to 2%, the balance being Zn and inevitable impurities The zinc-based alloy-plated steel material for welding according to claim 5, wherein: % By mass
C: 0.01 to 0.15%
Si: 0.01 to 2.0%
Mn: 0.5 to 3.0%
S: 0.015% or less Al: 0.001-0.5%
B: 0.0006 to 0.0015%
N: 0.0005 to 0.006%
After forming a 400 MPa-grade zinc-based alloy-plated steel sheet with a zinc-based alloy plating layer on the surface of a steel sheet that contains Fe and inevitable impurities, the butt end of the butt end is electro-welded A zinc-based alloy-plated ERW steel pipe. The zinc-based steel according to claim 9, wherein the steel sheet further contains, by mass%, Ti: 0.001 to 0.5% and satisfies a condition given by the following formula (1). Alloy-plated ERW steel pipe.
0.5 ≧ [% Ti] + [% Al] ≧ 0.001 (1)
However, [% X] indicates the content expressed by mass% of the alloy element X.   11. The zinc-based alloy-plated electric-welded steel pipe according to claim 9, wherein the S content in the steel sheet is 0.003% by mass or less.   The zinc-based alloy plated electric-welded steel pipe according to any one of claims 9 to 11, wherein the steel sheet further contains P: 0.02 to 0.05% in terms of mass%.   The zinc-based alloy plating is any one of Zn-Al-based alloy plating, Zn-Al-Mg-based alloy plating, and Zn-Al-Mg-Si-based alloy plating. Item 13. A zinc-based alloy plated electric-welded steel pipe according to any one of Items 9 to 12.   The Zn—Al-based alloy plating contains, by mass%, Al: 0.18 to 5%, Mg: 0.01 to 0.5%, La: 0.001 to 0.5%, and The zinc-based alloy plating according to claim 13, characterized in that any one or more of Ce: 0.001 to 0.5% is contained, and the balance is Zn and inevitable impurities. ERW steel pipe.   The Zn-Al-Mg-based alloy plating contains, in mass%, Al: 2 to 19%, Mg: 0.5 to 10%, and the balance being Zn and inevitable impurities. 13. Zinc-based alloy-plated ERW steel pipe.   The Zn—Al—Mg—Si based alloy plating contains, in mass%, Al: 2 to 19%, Mg: 1 to 10%, Si: 0.01 to 2%, the balance being Zn and inevitable impurities The zinc-based alloy plated electric-welded steel pipe according to claim 13, wherein

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