JP2009221601A - Hot dip galvanized steel tube, and manufacturing method for hot dip galvanized material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for a hot dip galvanized material wherein non-plating is hardly caused even when using a molten zinc bath in which the Pb content and the Cd content are suppressed to be ≤0.1 mass% and ≤0.01 mass%, respectively, according to the RoHS (Restriction of Hazardous Substances) command, and a hot dip galvanized steel tube manufactured by this method. <P>SOLUTION: In the manufacturing method of the hot dip galvanized material, a flux-treated material to be plated is immersed in a heated molten zinc bath for the predetermined time, and cooled after pulling it up to form a hot dip galvanized film on a surface of the material to be plated. The molten zinc bath contains, by mass, 2.0-2.4% Sn and ≤0.1% Pb, respectively. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a hot dip galvanized steel pipe and a method for producing a hot dip galvanized material, and in particular, a Pb content within a range regulated by the RoHS directive, 0.1 mass% or less, and a Cd content. The present invention relates to a method for producing a hot dip galvanized material using a hot dip zinc bath of 0.01% by mass or less.

  Conventionally, after applying flux treatment to steel materials such as steel pipes and steel structures, the technology of enhancing the corrosion resistance of steel materials by immersing them in a molten zinc bath for a predetermined time, forming a galvanized film by cooling after pulling up is widely used. It is known and simple and widely used because it can process materials to be plated having various shapes and sizes on the same production line.

  However, for example, in JIS G3452 specified for carbon steel pipes for piping and JIS G3454 specified for carbon steel pipes for pressure piping, hot dip galvanized steel pipes are specified. It is recommended to use one kind of distilled zinc metal specified in JIS H2107. This one kind of distilled zinc ingot contains Pb of 1.3% by mass or less and Cd of 0.4% by mass or less. In practice, Pb is 1.2 to 1.3% by mass and Cd is 0. It is usual to contain about 0.09-0.1 mass%.

  In response to this, the European Union recently enforced the RoHS (Restriction of Hazardous Substances) Directive that restricts the use of specific hazardous substances to electrical and electronic equipment. This RoHS directive restricts the Pb content in the target product to 0.1 mass% or less and the Cd content to 0.01 mass% or less.

  Although the RoHS Directive is a foreign regulation, it has become necessary to respond to this and make it possible to supply better products to the environment, and the molten zinc bath containing Pb and Cd will not be used in the future. There is a tendency.

  However, as described above, many hot dip galvanized products are currently manufactured with hot dip galvanizing baths containing Pb and Cd in excess of the reference values regulated by the RoHS directive.

  The reason is that Pb has effects such as lowering the viscosity of the molten zinc bath and increasing fluidity. Thereby, for example, even if the surface of the steel material is not clean or there is an oxide, a plating film is easily formed.

  Therefore, when hot dip galvanizing is performed using a hot dip zinc bath having an extremely low Pb content using an electrolytic zinc ingot having a Pb content of 0.1% by mass or less within the regulations of the RoHS directive, After the immersion for a time, there is a possibility that a portion where a galvanized film is not formed may be generated when the galvanized film is pulled up from the molten zinc bath. This is a phenomenon that is commonly referred to as non-plating, and is an undesirable phenomenon that occurs remarkably when the Pb concentration in the molten zinc bath decreases.

  Regarding the above-described problems, for example, in hot dip galvanization of thin steel sheets used for automobiles and household appliance materials as disclosed in Patent Documents 1 and 2, it is usually sufficient by degreasing or heating at a high temperature. After the oil has been decomposed and removed, the surface of the steel sheet is continuously immersed in a bath in an inert or reducing atmosphere that is not easily oxidized. As a result, the surface of the molten zinc bath is immersed in the molten zinc bath in a very highly active and clean state.

  For this reason, the surface of the steel sheet is very reactive, and it is difficult for non-plating to occur compared to the batch-type hot dip galvanizing described later. Therefore, the concentration of Pb in the hot dip zinc bath is usually low. Not much of a problem with plating.

  In contrast, hot dip galvanizing performed in a batch process is performed by degreasing, pickling, and flux treatment of the material to be plated being immersed in a bath of degreasing solution, pickling solution, and flux treatment solution, respectively. For plating materials with complicated shapes and structures such as steel pipes and steel structures, the treatment is often inadequate, and after the pickling up to the flux treatment, the flux treatment Since the conveyance until it is immersed in a post-molten zinc bath is normally performed in the air, the steel material surface may be slightly oxidized.

  Furthermore, since the surface of the molten zinc bath is exposed to the atmosphere, oxides such as zinc oxide are floating on the surface, and these oxides adhere to the surface of the material to be plated immersed in a batch. As a result of being immersed in a molten zinc bath, non-plating was likely to occur.

  Moreover, in an actual production line, steel pipes and steel structures, which are materials to be plated, are immersed one after another in the same flux liquid tank. The flux liquid is usually dirty, and according to the study by the present inventors, this has been one of the major causes of non-plating.

  According to the investigations of the present inventors, in a normal plating line, an object to be plated such as a steel pipe is immersed in a flux tank, but the flux liquid in a portion of the flux tank in which the object to be plated is immersed is collected. When analyzed, the hexane extract, which seems to be an oil component, was contained in an amount of about 0.001 to 0.03% by mass, and iron chloride was generally contained in an amount of 1% by mass or more.

  On the other hand, replacing the flux liquid with a new flux liquid is costly and is very complicated and obstructs the production, so it is actually not desirable to perform it.

  In Patent Document 3, Ni: 0.01 to 0.05 mass%, Al: 0.001 to 0.01 mass%, Bi: 0.01 to 0, even if a molten zinc bath containing substantially no Pb is used. Addition of 0.08% by mass to the molten zinc bath suppresses non-plating and forms a plating film. In particular, the addition of 0.01% by mass or more of Bi improves the fluidity of the bath. It is disclosed that sufficient fluidity can be obtained by adding 05 mass%.

  However, according to the study by the present inventors, in the hot dip galvanization in the state where the treatment in the inert atmosphere and the complete cleaning of the oil are difficult as described above, Bi is added in an amount of 0.3% by mass. However, non-plating could not be suppressed.

  In order to solve the above-described problems, the present inventors have performed non-plating even when a molten zinc bath having Pb of 0.1% by mass or less and Cd of 0.01% by mass or less is used. We studied to suppress it. It is very complicated to control the composition in the molten zinc bath, and from the viewpoint of production management or cost, it is better to add fewer elements to the molten zinc bath, and the elements to be added are inexpensive. It is preferable to use a new one.

JP-A-8-60329 JP 2006-348344 A JP 2006-307316 A

  The object of the present invention is to use a molten zinc bath that is within the limits of the RoHS Directive and has a Pb content of 0.1% by mass or less and a Cd content of 0.01% by mass or less. Another object of the present invention is to provide a method for producing a hot dip galvanized material with less unplating and a plated steel pipe produced by this method. In particular, in existing process lines, the material to be plated is in a state where it is difficult to treat in an inert atmosphere or completely clean the oil, that is, exposed to the atmosphere after pickling, and further contains oil and iron eluate. Hot-dip galvanization that can suppress the occurrence of non-plating even when it is immersed in a hot-dip zinc bath with impurities such as zinc oxide floating on the surface from the atmosphere after being treated with the flux liquid It is in providing the manufacturing method of a material, and the plated steel pipe manufactured by this method.

  In order to achieve the above object, the inventors conducted the following experiment. As shown in FIG. 1, when a pickled thin steel plate 1 is pressed down a predetermined depth from the bath surface of a molten zinc bath 2 containing Pb: 0.0012% by mass and Cd: less than 0.0002% by mass, the steel plate The upward force 3 acting on the was evaluated. If the wettability is bad, this force is large, and if the wettability is good, it is considered to be low. Therefore, this was evaluated as an index of wettability. This wettability index indicates that the larger the numerical value, the easier the wettability, and FIG. 2 shows the relationship with the added amount of Sn.

  As shown in FIG. 2, it can be seen that the addition of Sn improves the wettability of the bath. That is, in a molten zinc bath in which Pb is suppressed, if an appropriate amount of Sn is contained, the wettability with respect to the material to be plated is improved, and even if the Pb content is within the range of the RoHS directive, non-plating can be improved. I came up with it.

The gist configuration of the present invention obtained from the above knowledge is as follows.
(1) Melting by forming a hot dip galvanized film on the surface of the material to be plated by immersing the material to be plated, which has been flux-treated, in a hot-melted molten zinc bath for a predetermined period of time and then cooling it. In the manufacturing method of a galvanized material, the said hot dip zinc bath contains Sn: 2.0-2.4 mass% and Pb: 0.1 mass% or less, The manufacturing method of the hot dip galvanized material characterized by the above-mentioned.

  (2) The method for producing a hot dip galvanized material according to 1, wherein the hot dip galvanizing bath contains Al: 0.02% by mass or less.

  (3) The manufacturing method of the hot dip galvanized material as described in said (1) or (2) whose Pb content in the said hot dip zinc bath is 0.002 mass% or less.

  (4) The method for producing a hot dip galvanized material according to the above (1), (2) or (3), wherein the temperature of the hot dip zinc bath is 435 to 475 ° C.

  (5) The said galvanized material is a manufacturing method of the hot dip galvanized material of any one of said (1)-(4) which is a steel pipe.

  (6) The method for producing a hot-dip galvanized material according to (5), wherein the steel pipe is a carbon steel pipe having an outer diameter of 10 to 700 mm.

  (7) A hot-dip galvanized steel pipe manufactured by the method described in (5) or (6) above.

  According to the present invention, the material to be plated subjected to the flux treatment is immersed in a hot-melted molten zinc bath for a predetermined time, pulled up, and then cooled to form a hot-dip galvanized film on the surface of the material to be plated. In the method for producing a hot dip galvanized material, Sn is 2. even if the Pb content in the hot dip zinc bath is 0.1 mass% or less and the Cd content is 0.01 mass% or less. By containing 0-2.4 mass%, the manufacturing method of the hot dip galvanized material which can suppress non-plating generation | occurrence | production and the plated steel pipe manufactured by this method can be provided.

It is a schematic diagram at the time of evaluating wettability. It is a graph which shows the relationship between Sn addition amount and the wettability parameter | index.

Next, an embodiment of the present invention will be described.
In the present invention, a plated material subjected to flux treatment is immersed in a hot-melted molten zinc bath for a predetermined time, pulled up, and then cooled to form a hot-dip galvanized film on the surface of the plated material. In the method for producing a hot dip galvanized material, the hot dip galvanizing bath contains Sn: 2.0 to 2.4 mass% and Pb: 0.1 mass% or less.

  Examples of the material to be plated include steel, and steel pipes used for gas pipes, water pipes, air conditioning pipes, and the like can be used. For example, SGP steel pipes defined in JIS G3452 and JIS G3454. STPG steel pipes and the like specified in the above are mentioned, and each pipe may be piped by a forging method or piped by an electric sewing method. Moreover, it is preferable that the said steel pipe is a carbon steel pipe whose outer diameter is 10-700 mm from a viewpoint of ensuring the pipe space and the flow volume of a sent object.

  As the plating process, for example, the usual 1. Pickling, 2. 2. flux treatment; Dry, 4 A method of performing immersion in the order of molten zinc bath can be used. In each step, degreasing and washing can be appropriately combined.

  As the pickling treatment, a known standard method used as a pickling treatment of steel materials can be used. For example, a method such as immersing in an aqueous hydrochloric acid solution to which an inhibitor has been added until the scale of the steel material surface is visually reduced is used. be able to.

  As for the flux treatment, the steel material is dipped in a usual flux treatment solution containing ammonium chloride, zinc chloride and the like as main components, and then pulled up and dried as necessary.

  In addition, the bath used in the above-described process is contaminated with oil or iron eluate while processing a plurality of materials to be plated, but may contain those impurities.

  The molten zinc bath contains Sn: 2.0 to 2.4 mass% and Pb: 0.1 mass% or less.

  The use of Sn as an element containing element is preferable in terms of production control because of its relatively low cost and few types of elements. If the Sn content is less than 2.0% by mass, non-plating may occur, and if it exceeds 2.4% by mass, the effect will not change so much that it may be economically disadvantageous. .

  The range of the Sn content exhibits remarkable effects such as improvement of fluidity, particularly in a molten zinc bath on the assumption that the Pb content is 0.1% by mass or less. In addition, even if the Cd content is 0.01% by mass or less, the above effect is not hindered in the range of the Sn content. The range of the Pb content and the Cd content is within the range defined in the RoHS directive from the viewpoint of the environment. From a further environmental viewpoint, if the Pb content in the zinc bath is 0.002 mass% or less and / or the Cd content is 0.0002 mass% or less, a more preferable bath composition is obtained.

Since non-plating tends to be suppressed by increasing the plating temperature and lengthening the plating time, it is a plating condition that satisfies other requirements such as manufacturing efficiency and performance of plated products, and suppresses non-plating. Other elements other than the above components may be contained in the bath as long as the plating conditions can be used.
As other specific contained elements, even if Fe is contained at a saturation concentration or less at the bath temperature, the above effect is not hindered in the range of the Sn content. Although the non-plating tends to be improved as the Fe content is high, even if the Fe content is below the detection limit, the non-plating can be effectively suppressed if Sn is contained in an amount of 2.0% by mass or more. .
The balance other than the above components is preferably composed of Zn and inevitable impurities.
The composition of the molten zinc bath contains Sn: 2.0 to 2.4% by mass, Pb: 0.1% by mass or less, and Cd: 0.01% by mass or less, with the balance being Zn and inevitable impurities. It is preferable to have the following composition. Furthermore, in this case, it is more preferable from the viewpoint of the environment if the Pb content in the molten zinc bath is 0.002 mass% or less and / or the Cd content is 0.0002 mass% or less.

  The surface of the molten zinc bath into which the material to be plated is immersed need not be in an inert atmosphere, and may be exposed to the atmosphere, and impurities such as zinc oxide may float on the surface.

Further, in order to clean the plating surface, a predetermined amount of Al can be contained in the molten zinc bath. It is known that by containing a predetermined amount of Al, it is possible to reduce zinc oxide and the like adhering to the plating surface when pulling up the object to be plated from the molten zinc bath, and to make the surface gloss more beautiful. . However, non-plating tends to occur by containing Al. Based on the above-mentioned knowledge, the present inventors are able to produce a material having a very clean glossiness by suppressing both non-plating and batch-type plating as described above by containing both Sn and Al. I found.
Specifically, in the above-described batch-type hot dip galvanizing, a hot dip galvanizing bath containing Sn: 2.0 to 2.4 mass%, Al: 0.02 mass% or less, and Pb: 0.1 mass% or less. Is preferably used. Also in this case, even if the Cd content is 0.01% by mass or less, the above effects are not hindered in the range of the Sn and Al contents. The range of the Pb content and the Cd content is within the range defined in the RoHS directive from the viewpoint of the environment. From a further environmental viewpoint, if the Pb content in the molten zinc bath is 0.002 mass% or less and / or the Cd content is 0.0002 mass% or less, a more preferable bath composition is obtained. Furthermore, as other specific contained elements, even if Fe is contained in a range not exceeding the saturation concentration at the bath temperature, the above effects are not hindered in the range of the Sn and Al contents.
The balance other than the above components is preferably composed of Zn and inevitable impurities.
The composition of the molten zinc bath is Sn: 2.0% by mass or more and 2.4% by mass or less, Al: 0.02% by mass or less, Pb: 0.1% by mass or less, and Cd: 0.01% by mass or less. It is preferable that the remainder has a composition composed of Zn and inevitable impurities. Furthermore, in this case, it is more preferable from the viewpoint of the environment if the Pb content in the molten zinc bath is 0.002 mass% or less and / or the Cd content is 0.0002 mass% or less.

  For the temperature and immersion time of the hot dip zinc bath, normal hot dip galvanizing conditions can be used. For example, a bath temperature of 435 ° C. or higher and 475 ° C. or lower is recommended. The lower the bath temperature, the better the economy, and the formation of alloy layers that adversely affect workability can be suppressed. It will be disadvantageous. According to the present invention, since the bath temperature used in the above-described normal hot dip galvanizing can be used, the bath temperature and the immersion time can be adjusted in accordance with the desired plating adhesion amount and alloy layer generation amount.

  Considering these matters, the temperature of the molten zinc bath is more preferably 450 ° C. or higher and 465 ° C. or lower.

  Further, when the material to be plated is pulled up from the bath or after being pulled out of the bath, the surface of the material to be plated, in particular, the outer surface and the inner surface of the steel pipe may be sprayed with air or steam to adjust the amount of plating adhesion. .

  The present invention further provides a plated steel pipe manufactured by the method described above.

  The above description is merely an example of the embodiment of the present invention, and various modifications can be made within the scope of the claims.

Although the manufacturing method of the hot dip galvanized material of this invention and a plated steel pipe are demonstrated based on an Example below, this invention is not limited only to the following Examples.
In addition, the pickling solution and flux solution used in the process were reproduced in the state of being soiled by the plating of the steel pipe, so that the pickling tank and the flux tank of the actual steel pipe plating line were plated, respectively. What was collected from the part where the steel pipe, which is a product, was immersed, and what was simulated in the laboratory in the presence of a pseudo-impurity with the result of the analysis were used.

[Group 1]
Sample No. 1-1 to 8 used steel pipes A or B cut out to a length of 20 cm with a nominal diameter of 50A shown in Table 1 as test materials. These steel pipes were immersed in pickling solution B shown in Table 2 and allowed to stand until the scale of the surface was visually observed. Thereafter, it was washed with water, immersed in the flux liquid shown in Table 3, pulled up, and dried in a hot air oven at 100 ° C. These steel pipes were dipped in a molten zinc bath having a predetermined bath temperature and bath composition for a predetermined time and pulled up. At the time of pulling up, the outer surface of the steel pipe was blown circumferentially with air, left in the air for 30 seconds after being pulled up, and then cooled with water to obtain a sample for evaluation.
The zinc used in preparing the molten zinc bath is an electrolytic zinc ingot, Pb: 0.0012% by mass and Cd: less than 0.0002% by mass.

  Sample No. 1-9 and 1-10, except that zinc ingot used in preparing the molten zinc bath is distilled zinc containing Pb: 1.2% by mass and Cd: 0.09% by mass, and does not contain Sn Sample No. The same treatment as 1-1 and 1-2 was performed.

[Group 2]
Sample No. In 2-1 to 2-8, steel pipes A or B cut out to a length of 20 cm with a nominal diameter of 50A shown in Table 1 were used as test materials. These steel pipes were immersed in pickling solution A shown in Table 2 and allowed to stand until the scale of the surface dropped visually. Thereafter, it was washed with water, immersed in a flux solution C shown in Table 3, pulled up, and dried in a 100 ° C. hot air oven. These steel pipes were dipped in a molten zinc bath having a predetermined bath temperature and bath composition for a predetermined time and pulled up. At the time of pulling up, the outer surface of the steel pipe was blown circumferentially with air, left in the air for 30 seconds after being pulled up, and then cooled with water to obtain a sample for evaluation.
The zinc used in preparing the molten zinc bath is an electrolytic zinc ingot, Pb: 0.0012% by mass and Cd: less than 0.0002% by mass.

  Sample No. 2-9 and 2-10, except that zinc ingot used in preparing the molten zinc bath is distilled zinc containing Pb: 1.2% by mass, Cd: 0.09% by mass, and not containing Sn Sample No. The same treatment as 2-9 and 2-10 was performed.

The evaluation was performed on the outer surface of the steel pipe, and the range of 1 cm from both ends was excluded from the evaluation target.
The parts that were not plated, that is, not plated, were evaluated by visual observation. “◎” indicates that there are no unplated parts, “◯” indicates that there are 3 or less unplated parts with a diameter of 1 mm or less, which are finally recognized by the naked eye, and 4 or more unplated parts with a diameter of 1 mm or more than 1 mm in diameter. The case where the number of non-plating of 2 mm or less was 8 or less was “Δ”, and the case where there was non-plating worse than the above Δ was “x”.
Moreover, based on the method prescribed | regulated to JISH0401, the plating adhesion amount was measured from the mass difference before and behind melt | dissolving a plating part with hydrochloric acid, and the amount of fabric weight was computed.

  Tables 4 and 5 show sample Nos. 1-1 to 1-10 and Sample No. Evaluation of 2-1 to 2-10 is shown. In addition, the composition of the molten zinc bath in Table 4 and Table 5 shows only the contained elements, and the balance shows Zn and inevitable impurities.

[Group 3]
Sample No. 3-1 to 3-6 were steel pipes A or B cut out to a length of 20 cm with a nominal diameter of 50 A shown in Table 1 as test materials. These steel pipes were immersed in pickling solution A shown in Table 2 and allowed to stand until the scale of the surface dropped visually. Thereafter, it was washed with water, immersed in a flux solution C shown in Table 3, pulled up, and dried in a 100 ° C. hot air oven. These steel pipes were dipped in a molten zinc bath having a predetermined bath temperature and bath composition for a predetermined time and pulled up. At the time of pulling up, the outer surface of the steel pipe was blown circumferentially with air, left in the air for 30 seconds after being pulled up, and then cooled with water to obtain a sample for evaluation.
The zinc used in preparing the molten zinc bath is an electrolytic zinc ingot, Pb: 0.0012% by mass and Cd: less than 0.0002% by mass.

The evaluation was performed on the outer surface of the steel pipe, and the range of 1 cm from both ends was excluded from the evaluation target.
The parts that were not plated, that is, not plated, were evaluated by visual observation. “◎” indicates that there are no unplated parts, “◯” indicates that there are 3 or less unplated parts with a diameter of 1 mm or less, which are finally recognized by the naked eye, and 4 or more unplated parts with a diameter of 1 mm or more than 1 mm in diameter. The case where the number of non-plating of 2 mm or less was 8 or less was “Δ”, and the case where there was non-plating worse than the above Δ was “x”. Furthermore, the color and glossiness of the outer plating portion were visually evaluated. With respect to the glossiness, “の も の” was given for the shiny one, “◯” for the slightly inferior one, “△” for the slightly dull one, and “×” for the one having no glossiness.
Moreover, based on the method prescribed | regulated to JISH0401, the plating adhesion amount was measured from the mass difference before and behind melt | dissolving a plating part with hydrochloric acid, and the amount of fabric weight was computed.

  In Table 6, Sample No. 3-1 to 3-6 and Sample No. Evaluation of 2-4 is shown. The composition of the molten zinc bath in Table 6 shows only the contained elements, and the balance shows Zn and inevitable impurities.

As mentioned above, it turns out that the example which contained 2.0-2.4 mass% of Sn in both group 1 and group 2 has very good plating property.
Moreover, as seen in Group 3, in the bath containing 0.005 to 0.02% by mass of Al, non-plating is suppressed by containing 2.0% by mass or more of Sn, and the surface is silver white. It can be seen that a very bright and beautiful plating can be obtained.

  The present invention does not require treatment in an inert atmosphere or complete cleaning of oil, and is usually performed in a method used in hot dip galvanization of many steel pipes and steel structures, that is, in a pretreatment process for plating. The RoHS regulation also applies to a method in which the plating material is exposed to the atmosphere and further treated with a flux containing oil and then immersed in a molten zinc bath in which impurities such as zinc oxide are suspended from the atmosphere. A good galvanized steel product with suppressed non-plating can be provided by using a hot dip galvanizing bath substantially free of Pb that matches.

1 Thin steel plate that has been pickled 2 Molten zinc bath 3 Upward force acting on steel plate

Claims (7)

A hot-dip galvanized material formed by immersing a hot-melted material to be plated for a predetermined time in a hot-melted hot-dip zinc bath, pulling up, and cooling to form a hot-dip galvanized film on the surface of the material to be plated In the manufacturing method of
The method for producing a hot dip galvanized material, wherein the hot dip galvanizing bath contains Sn: 2.0 to 2.4 mass% and Pb: 0.1 mass% or less.   The method for producing a hot dip galvanized material according to claim 1, wherein the hot dip galvanizing bath contains Al: 0.02 mass% or less.   The method for producing a hot dip galvanized material according to claim 1 or 2, wherein the Pb content in the hot dip zinc bath is 0.002 mass% or less.   The method for producing a hot dip galvanized material according to claim 1, 2 or 3, wherein the temperature of the hot dip zinc bath is 435 to 475 ° C.   The method for producing a hot dip galvanized material according to any one of claims 1 to 4, wherein the material to be plated is a steel pipe.   The method for producing a hot-dip galvanized material according to claim 5, wherein the steel pipe is a carbon steel pipe having an outer diameter of 10 to 700 mm.   A hot-dip galvanized steel pipe manufactured by the method according to claim 5 or 6.

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